The document provides an introduction to the Abu Dhabi Roadside Design Guide. It discusses the background and purpose of developing uniform roadside design standards and guidelines for Abu Dhabi. It outlines the key approaches taken in the guide, including using a performance-based rather than prescriptive approach, emphasizing proprietary rather than non-proprietary systems, adopting American testing standards over European ones, and using a single testing standard. The scope of the guide is also summarized, covering topics like the risk mitigation process, clear zone concepts and calculations, hazard identification, passively safe design, and descriptions of different barrier types.

1. ROADSIDE DESIGN GUIDE
PAGE 1
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
1 INTRODUCTION
1.1 Overview
In 2010, the Abu Dhabi Department of Municipal Affairs and Transport commenced with the “Unifying and
Standardizing of Road Engineering Practices” Project. The objective of the project was to enhance the
management, planning, design, construction, maintenance and operation of all roads and related
infrastructures in the Emirate and ensure a safe and uniform operational and structural capacity throughout
the road network.
To achieve this objective a set of standards, specifications, guidelines and manuals were developed in
consultation with all relevant authorities in the Abu Dhabi Emirate, including the Department of Municipal Affairs
(DMA) and Urban Planning Council (UPC). In future, all authorities or agencies involved in roads and road
infrastructures in the Emirate shall exercise their functions and responsibilities in accordance with these
documents. The purpose, scope and applicability of each document are clearly indicated in each document.
It is recognized that there are already published documents with similar objectives and contents prepared by
other authorities. Such related publications are mentioned in each new document and are being superseded
by the publication of the new document, except in cases where previously published documents are recognized
and referenced in the new document.
1.2 Purpose and scope
The guidance supplied in this document, the Abu Dhabi Roadside Design Guide (ADRSDG), is based on
established international practices. This especially includes the American Association of State Highway and
Transportation Officials (AASHTO) Roadside Design Guide [1] and is supplemented by recent research and
documents prepared by the CEDR funded ‘SAVERS’ [2] project, the United Kingdom, Austroads [3] and Dubai
[4].
This Guide has been prepared to provide uniform practices for government transport agencies within the Abu
Dhabi Emirate and consultant personnel preparing studies, reports and contract road plans for these agencies.
The designer should use this document to develop roadside designs that meet the operational and safety
requirements while preserving the aesthetic, historic, and cultural resources of an area. This Guide will be
updated regularly as new data and experience with best practices become available.
Roadside design is defined as the design of the area between the outside shoulder edge and the right-of-way
limits. The Abu Dhabi Emirate is reducing the number of fatalities year on year, however, roadside crashes
account for a significant portion of the total fatal highway crashes. Approximately 25 percent are the result of
a single vehicle run-off-the-road crash. This emphasizes the importance of providing as safe a roadside design
as practical.
1.3 The application of the Abu Dhabi Roadside Design Guide
The guidance presented in this document is intended for the roadside design of new construction and major
reconstruction of roads and streets located within the Abu Dhabi road network. Local municipalities are
encouraged to adopt these guidelines to ensure uniformity of roadside designs

2. ROADSIDE DESIGN GUIDE
PAGE 2
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
within the Emirate. Design guidance is provided, and is considered applicable, for all facility types in both urban
and rural locations.
The designer should attempt to meet all criteria and practices presented in this Guide; however, it should not
be considered a standard that must be met regardless of cost and impacts. Designers must exercise good
judgment on individual projects and, frequently, they must be innovative in their approach to roadside design.
Designers should review the listed references to gain an understanding of the basis for the selected roadside
design criteria. The guidance provided in this document should not be a substitute for good engineering
knowledge, experience, or sound judgment. The concepts, designs and philosophies presented in this Guide
may not be applicable to every project. Each project is unique and offers an individual opportunity to enhance
that particular roadside environment.
The amount of monetary resources available for all roadside safety enhancements is limited. The objective of
designers is to maximize roadside safety on a system-wide basis with the given funds. Accomplishing this
objective means addressing those specific roadside features that can contribute the most to the safety
enhancement of that individual project. Given that objects and slope changes must be introduced at varying
points off the pavement edge, the enhancement of roadside safety involves selecting the “best” choice among
several acceptable design alternatives. This document is intended to represent the spectrum of commonly
available roadside design alternatives.
1.3.1 Background to Some of the Key Approaches Adopted
One of the main aims of this Guide is to provide guidance on roadside design based on international best
practice which fits best to reflect the local conditions, requirements and applications. To help achieve this, a
team of internationally recognised, independent road safety specialists have carried out site visits around the
Abu Dhabi Road Network, reviewed the existing processes and assessed the local conditions in collaboration
with the Abu Dhabi Department of Municipal Affairs and Transport. A summary of these assessments were
presented in the “Abu Dhabi Roadside Design Guide – Inception Report” (See Appendix B).
An important outcome of the Inception Report was recommendations for some key approaches, which helped
form the basis of this Guide. An overview of these key approaches is presented in the following sections. For
more detail, please refer to Appendix B.
1.3.2 A Performance Based Approach Rather Than a Prescriptive One
During the development of Vehicle Restraint Systems (VRS), the number and type of systems available to the
roadside designer/engineer were limited. The limited number of designs would have distinct performance
characteristics and therefore the designer/engineer could prescriptively refer to these systems. For example a
designer/engineer could expect a concrete or a cable barrier to perform at a certain performance level. As
alternative systems were developed, the available types of different systems increased substantially, and now
there are many different systems available on the market together with variants of the same original design,
all with slightly different performance characteristics. As the number of the alternative designs increased, the
gaps between the performance levels of the original VRS designs were filled by new products. Therefore it is
no longer valid to use a product-specific prescriptive approach, where reference is only made to a number of
specific designs.

3. ROADSIDE DESIGN GUIDE
PAGE 3
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
A prescriptive approach, which focuses on the use of a limited number and type of systems, is not necessarily
the best one. The lack of choice can force a designer/engineer to use systems which may not be the optimal
solution for a specific site in terms of performance and cost. This sort of prescriptive approach not only limits
the ability of the designer to use engineering judgment but it also makes it difficult for new systems to enter
the market. It furthermore leads to less of an understanding from the engineer, which may lead to inappropriate
systems and arrangements being used in certain locations.
In order to overcome these issues, current international best practice is to identify the performance
requirements and physical constraints of a site under consideration and then let the engineer/designer chose
the most appropriate solution based on proven properties of impact tested and approved systems. Therefore,
this version of the manual is based on the required performance specifications, rather than prescriptive
descriptions of certain products. In order to achieve this, rather than listing the design details of certain products
available on the market, the proposed layout of the roadside design guide was organised to explain, for each
VRS type, in basic terms:
• The main types of systems available on the worldwide market;
• The performance classifications of the products based on impact testing;
• The selection criteria based on the performance classifications of the product.
1.3.3 The Use of Proprietary over Non-Proprietary Systems
The term ‘proprietary’ means that the system has been independently designed and successfully tested by a
VRS manufacturer, who is ultimately responsible for the design of the system. Conversely, non-proprietary
systems have often been developed by National Road Authorities and/or Universities, who have subsequently
published the drawings of the system and, as such, these can be manufactured by anyone.
Whilst many of the non-proprietary systems have historically performed well, many of these systems were
developed a number of years ago, and were tested to older versions of the testing standards. Due to budgetary
constraints within the original developers of the systems, these systems are often not updated, nor are they
supported in terms of future development and product refinement.
This is not the case in the commercial domain of the proprietary systems, where development of systems
continues on a frequent basis, with product designers keen to develop more effective products than their rivals,
testing and certifying products to the latest standards. This competition and the continuous development have
led to proprietary products which perform better (higher containment levels with less deflection and lower
acceleration severity) than their non-proprietary predecessors.
For these reasons, it is now common practice for many countries to install proprietary systems, with a number
of countries, such as the UK, USA (FHWA) and Ireland maintaining a list of ‘accepted’ vehicle restraint systems
products. Therefore the use of proprietary systems is recommended over non-proprietary ones.

4. ROADSIDE DESIGN GUIDE
PAGE 4
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
1.3.4 Use of a Single Testing Standard
In the past, barriers successfully tested to the requirements of USA NCHRP350 [5]/MASH [6], European
EN1317 [7], and non-proprietary systems were permitted for use on the Abu Dhabi road Network, and in many
other countries. However, the testing parameters for these two types of international systems are very different.
As a result, no comparison or equivalence can be assumed between systems tested to the different standards.
This can lead to, for example, inappropriate transitions between systems, and unknown levels of performance
where the performance of one system depends on that of another (for example where the performance of a
safety barrier relies on the performance of a terminal). For this reason it is recommended that systems which
are tested only to a single standard are permitted for future use on the Abu Dhabi road network.
1.3.5 The Use of NCHRP350 and MASH Tested Products Instead of
EN1317
The road network and the vehicle fleet in Abu Dhabi are more similar to an American one rather than a
European one. The adoption of the American testing standards NCHRP350 and MASH are felt to be more
suitable for the Abu Dhabi road network, over the European test standard EN1317 for the reasons explained
in the following sub-sections. However, it is felt that the knowledge of the European test standard EN1317 [7]
can still be useful to designers/engineers, especially when comparing VRS products tested to different
standards. The Appendix A provides a brief overview of the EN1317. The information provided includes the
test types and performance classes and test criteria for barriers, bridge parapets, terminals, transitions and
crash cushions.
1.3.5.1 Weight of Vehicles used in NCHRP350, MASH & EN1317
Vehicles used in NCHRP350 and more recently MASH, represent larger and heavier vehicles, such as pickup
trucks, which are more common in the USA; whilst EN1317 uses smaller and lighter vehicles which are more
common in Europe. This can be seen by comparing Test Level-3 of MASH and NCHRP350 to containment
level N2 of EN1317 as these are the most commonly used base performance criteria for America and Europe,
respectively.
In MASH, a product should perform satisfactorily during impact testing to achieve the basic test level TL-3
using a 1,100 kg passenger car and a 2,270kg pickup truck. While in EN1317 to achieve an N2 containment
level, a barrier should perform satisfactorily using a 900kg passenger car and a 1,500kg passenger car (see
Appendix A). There is currently no vehicle type in EN1317 which represents an SUV or a pickup truck, which
are common in the Abu Dhabi vehicle fleet.
As a result, it can be said that American testing standards MASH and NCHRP350, offer a better representation
of the vehicle fleet, more specifically enabling vehicle restraint systems to prove their ability to safely contain
and redirect (under standard testing conditions) the high percentage of SUVs in Abu Dhabi; while the vehicle
classes in EN1317 do not represent the SUVs and therefore are not guaranteed to work on impact with these
types of vehicles.
1.3.5.2 Height of Vehicles used in NCHRP350, MASH & EN1317
The weight of the vehicles used in NCHRP350 and MASH are a better representation of the SUVs which
represent a high percentage of the vehicles used in Abu Dhabi. However, it is not only the

5. ROADSIDE DESIGN GUIDE
PAGE 5
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
weight of the vehicles that make American standards a better fit for Abu Dhabi, but it is also the height, more
specifically the height of the centre of mass, required for the test vehicles.
Vehicle rollover is one of the more common types of incidents observed in Abu Dhabi. Vehicles with a higher
centre of mass, such as SUVs are more likely to roll over. The minima required centre of mass locations for a
pickup truck for testing to the basic TL-3 containment levels in MASH & NCHRP350 are 710mm and
700±50mm, respectively. In EN1317 the highest vehicle used to test a N2 normal containment level, requires
to have a centre of mass location 530mm above the ground. As can be seen from these numbers, EN1317
test vehicles are far from representing the higher centre of mass seen with SUVs, which are common in Abu
Dhabi. Therefore, there is no guarantee that an SUV, which is likely to have a centre of mass higher than
530mm, will be contained by an N2 containment level barrier.
1.3.5.3 Impact Angles used in NCHRP350, MASH & EN1317
Another important difference between the American and European testing standards is the angle of impact.
A good comparison can be made between the base performance levels of TL-3 for MASH/NCHRP350 and N2
for EN1317. MASH uses an impact angle of 25˚ for car and pickup truck impacts, to demonstrate a successful
TL-3 classification. EN1317 on the other hand, uses an impact angle of 20˚ for TB11 and TB32 tests, which
are required to demonstrate a successful classification of N2.
The roads in Abu Dhabi, in general, appear to be wider than the European ones, with expressways regularly
featuring up to 4 lanes in each direction with generous shoulder areas provided on each side of the road.
Research shows that in similar conditions, impacts with roadside barriers are more likely to occur with higher
angles of incidence on wider carriageways. For this reason it is believed that the larger impact angles used in
MASH and NCHRP350 may provide a better representation of the actual impacts that are likely to occur on
the Abu Dhabi road network.
1.4 Scope of the ADRSDG
1.4.1 Overview
This Guide has been developed to enable practitioners to follow a step-by-step risk-based process to
understand and mitigate the risks posed by hazards, integrating International best practice.
This has been achieved by first introducing the user of the Guide to the Risk Mitigation Approach, explaining
the concept of the clear zone, and assisting users in the identification of hazards. The following chapters
provide information on experience-based advice and internationally recognised practices, to assist Engineers
in dealing with the hazards present. This includes details of the various product types available on the market
to mitigate road user risk. An overview of the ways in which these solutions can be assessed on an economic
basis is then presented. The final chapter of this Guide deals exclusively with the risks existing within the urban
environment, and ways in which such risks should be assessed. An overview of the content of each chapter
is presented below:
1.4.2 Chapter 2 “Risk Mitigation Approach”
This chapter discusses the hazard mitigation process and the forgiving roadside approach to road safety. The
Chapter also introduces the clear roadside concept and its application to roadside design.

6. ROADSIDE DESIGN GUIDE
PAGE 6
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
1.4.3 Chapter 3 “Concept and Calculation of Clear Zone”
This chapter gives further details of the clear zone concept, providing advice on how the clear zone distance
should be calculated for straight sections, foreslopes, backslopes and for curved sections of road.
Consideration is also given for determining the clear zone for medians and high risk hazards. To aid
understanding, examples of clear zone calculations are also detailed.
1.4.4 Chapter 4 “Identification of Roadside Hazards”
Once the user of this Guide has followed the procedures within Chapter 3 to determine the clear zone for a
particular road scheme, location or hazard, Chapter 4 assists the designer in determining whether objects
and/or features within the clear zone are hazards. This includes the identification of risks to third parties.
1.4.5 Chapter 5 “Passively Safe Support Structure and Traversable
Objects”
This chapter investigates ways in which hazards can be made passively safe or traversable (i.e. less
hazardous to road users in the event of an impact). Advice is given on the types of commercially available
systems and technologies which exist, and how these should be selected and applied.
1.4.6 Chapter 6 “Description of Roadside, Median and Bridge Barriers”
If a hazard cannot be made passively safe or traversable, one of the most common road safety devices is the
barrier. However, there are many different types available and this chapter gives an overview of the three
different types available (flexible, semi-rigid and rigid). Details of the testing procedures for barrier systems are
then explained.
1.4.7 Chapter 7 “Selection and Application of Roadside, Median, and
Bridge Barriers”
This chapter firstly gives an overview of the way in which roadside, median and bridge barriers should be
specified, in terms of their containment level, deflection characteristics, impact severity level and both
maintenance and inspection requirements.
Secondly, the chapter provides guidance on how the barrier systems should be used on the roadside in terms
of the length required and where this should be sited, how to place the barrier laterally at the side of the road,
and how to flare back the end of the barrier to reduce road user risk. Guidance on barrier foundations, such
as compaction requirements, push-and-pull test and common foundation mistakes to avoid, are also given.
Specific guidance is also presented for roadside barriers (in terms of barriers which are installed on sharp
horizontal curves), median barriers (in terms of emergency and maintenance crossings and glare screens),
and bridge barriers (in terms of minimum height requirements and fixation to bridge decks).
1.4.8 Chapter 8 “Motorcyclist Protection Systems”
This chapter gives details of the different types of motorcyclist protection systems (MPS) available (continuous
and discontinuous), and gives details of the impact testing requirements for such systems. An explanation of
the performance classifications resulting from this testing is also given, together with a description of how to
use the performance classifications for the application of the

7. ROADSIDE DESIGN GUIDE
PAGE 7
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
products. Specific guidance is given with regard to locations where a positive cost/benefit could result from the
application of an MPS.
1.4.9 Chapter 9 “Terminals”
This chapter gives details of the different types of terminals available (ramped down end, full height, flared and
buried), and gives details of the impact testing requirements for such systems. An explanation of the
performance classifications resulting from this testing (for example gating and non-gating terminals) is also
given, together with an explanation of how to use the performance classifications for the application of the
products. Specific guidance is provided with regard to the site grading for terminals.
1.4.10 Chapter 10 “Crash Cushions”
This chapter gives details of the different types of crash cushions available (redirective/ non- redirective,
sacrificial/reusable and both low maintenance and self-restoring crash cushions). The chapter gives details of
the impact testing requirements for such systems, and an explanation of the performance classifications
resulting from this testing (for example gating and non-gating terminals). An explanation of how to use the
performance classifications for the application of the products is also outlined. Specific guidance is provided
with regard to the site grading for crash cushions.
1.4.11 Chapter 11 “Transitions”
This chapter gives details of the different types of terminals available and gives details of the impact testing
requirements for such systems. An explanation of the performance classifications resulting from this testing is
also provided, together with an explanation of how to use the performance classifications for the application of
the products. Specific guidance is provided with regard to the design of terminals, and examples of good and
bad practice are outlined.
1.4.12 Chapter 12 “Economic Assessment”
The chapter discusses the use of economic analysis to make roadside safety decisions, and provides an
overview of the economic assessment process which should be undertaken. The first part of the chapter
focuses on the assessment of economic feasibility for alternative roadside treatment options. A step by step
guide into benefit/cost ratio (BCR) analysis is presented. Guidance is provided into the prediction of expected
number of crashes at a site, prediction of decrease in the number of crashes due to a safety treatment and the
estimation of monetary benefits associated with roadside crashes prevented. Example calculations are
included for each step of the BCR analysis. A wide range of crash modification factors is provided to help
designer/engineers estimate the reduction in the number and/or severity of crashes due to specific roadside
safety treatments.
The second part of the chapter focuses on treatment prioritization methods. Guidance is given on treatment
assessment and ranking based on cost-effectiveness, risk reduction and non-monetary considerations.
1.4.13 Chapter 13 “Urban Roadside Design”
This final chapter of this Guide identifies risk relating to the specific case of urban areas, and provides
overarching guidance as to how the risks in these areas differ and, hence, which additional measures should
be considered when mitigating risk to road users, and to vulnerable users of the road corridor (such as
pedestrians).

8. ROADSIDE DESIGN GUIDE
PAGE 8
01 INTRODUCTION FIRST EDITION -DECEMBER 2016
Guidance is provided on the lateral offset required between the roadway and the roadside hazards, for different
road configurations, such as curves, merge locations and junctions. Information is also provided on the specific
applications for pedestrian and bicyclist facilities. Finally, specific guidance is provided into the application of
common urban roadside features, such as curbs, pedestrian barriers, street furniture, etc.
1.5 References
[1]AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of State Highway
and Transportation Officials, 2011.
[2]CEDR, “SAVERS (Selection of Appropriate Vehicle Restraint Systems) - WP1: Defining the Different
Parameters which can Influence the Need and Selection of VRS (Unpublished Report),” Conference of
European Directors of Roads, 2014.
[3]Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney, NSW: Austroads,
2010.
[4]Roads & Transport Authority, Roadside Design Guide for Dubai, First Edition, Dubai: RTA, 2008.
[5]NCHRP, “NCHRP Report 350, Recommended Procedures for the Safety Performance Evaluation of
Highway Features,” Transportation Research Board, National Research Council, Washington DC, 1993.
[6]AASHTO, “Manual for Assessing Safety Hardware,” Ammerican Association of State Highway and
Transportation Officials, Washington DC, 2009.
[7]CEN , “EN 1317 Road Restraint Systems - Part 2: Performance classes, impact test
acceptance criteria and test methods for safety barriers including vehicle parapets,” CEN (European
Committee for Standardization), Brussels, 2010.

9. ROADSIDE DESIGN GUIDE
PAGE 9
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
2 ROADSIDE RISK MITIGATION
2.1 Introduction
There are many reasons why vehicles may leave the road and potentially encroach on the roadside. These
include:
• Driver fatigue or inattention;
• Excessive speed;
• Crash avoidance;
• Roadway conditions (e.g. pavement deterioration);
• Vehicle component failure;
• Poor visibility; and
• Driver impairment.
When a vehicle runs off the road, it may reach a hazard, collide or overturn; all of which may result in injuries
or even fatalities. These casualties may be reduced by making every roadside flat, traversable and free of
obstacles; therefore giving enough space to errant vehicles to regain control and return to the road with a
reduced likelihood of injury. However, in reality this is not always possible due to physical and economic
constraints. Engineers and designers often have to find an optimal solution; one that finds a balance between
the maximum amount of safety and economic feasibility.
A good way of achieving this is to evaluate each roadside on a case by case basis with a risk based approach.
Not every road has the same probability of a vehicle running off the road, nor does every roadside hazard
have the same level of consequences, if reached by an errant vehicle. It is important to identify and prioritise
the sites with a higher level of risk and apply the necessary countermeasures to keep the risk to a reasonable
level.
This approach forms the basis for the roadside design guides and standards of many countries around the
world [1]. In the UK the decision for roadside treatments is based on The Road Restraint Risk Assessment
Process (RRRAP); a software based tool which aims to decrease the level of risk for the evaluated area to “As
Low as Reasonably Practicable” [2]. In Germany, the decision on whether to implement a roadside barrier is
based on the probability of a vehicle running off the road and the level of risk posed by different type of hazards
[3]. In the United States, a recommended practice is the evaluation of different roadside treatment options with
Roadside Safety Analysis Program (RSAP); a risk based benefit/cost analysis tool [4].
Following International best practice, the Abu Dhabi Roadside Design Guide is structured as an easy to use
and understand roadside risk mitigation tool.
This chapter presents an explanation of the concept of risk from a roadside safety perspective and the
recommended risk mitigation approach of this Guide.

10. ROADSIDE DESIGN GUIDE
PAGE 10
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
2.2 Definition of Risk from a Roadside Safety Perspective
There are many definitions of hazard and risk, but for the purpose of roadside safety design a hazard can be
described as a roadside feature or object that can cause physical, economic, time- based or strategic harm or
loss. Risk is the chance, high or low, that somebody or something will be harmed by the roadside hazard.
Risk, as shown in Figure 2.1, is directly related to the likelihood of the hazard being reached by a vehicle and
the resulting consequences if the hazard is reached.
Figure 2.1 - Risk from a roadside safety perspective
As shown in Figure 2.1, the likelihood of a roadside accident depends on the probability of a vehicle running
off the road and the probability of the errant vehicle subsequently reaching the hazard if it does leave the
carriageway. Run-off-the road probability is related to parameters such as traffic volume and horizontal curve
radius; while the probability of an errant vehicle reaching a hazard depends on factors such as the distance of
the hazard from the edge of the travelled way, speed of the errant vehicle and roadside topography.
When a vehicle reaches a hazard, the most obvious consequences are the ones to the occupants of the
vehicle, in the form of physical harm and economic loss. But some hazards, if reached by errant vehicles can
have consequences for third parties as well. For example, an errant vehicle reaching the opposite side of a
dual carriageway can cause serious harm to the people travelling on the other side. An errant vehicle entering
a water reservoir may contaminate the drinking water needed by many others.
Engineers and designers can mitigate the level of risk by controlling either or both likelihood and/or
consequences of a roadside accident. The following sections present the methodology to achieve this.
2.3 Abu Dhabi Roadside Design Guide Risk Mitigation Approach
2.3.1 Outline of the Risk Mitigation Approach
Figure 2.2 presents the risk mitigation approach adopted for this Design Guide. As can be seen from the figure,
the corresponding chapter/s for each step is also presented.

11. ROADSIDE DESIGN GUIDE
PAGE 11
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Figure 2.2 – Abu Dhabi Roadside Design Guide risk mitigation approach
The following sections present further explanation on each step of the hazard mitigation approach.
2.3.2 Step 1 - Understand the Area under Evaluation
The first action the designer/engineer needs to take is to gather information and understand the conditions at
the site being evaluated. The area under evaluation may be a section of roadside / median, or it may even be
a specific hazard with a known history of accidents. As defined in Section 1.3.1, the area of evaluation may be
a part of the design of a new construction or a major reconstruction of an existing road.
Information gathered at this stage will not only be necessary in the following steps of the risk mitigation process,
but it will also enable the designer/engineer to establish an overall
Design the Optimal
roadside treatment
Step 7
Choose the Optimal
treatment option
Step 6
Chapter 12
Assess & Rank
treatment options
Step 5
Shield Delineate
Safe
Roadside
Provide Recoverable Make Passively
Relocate
Remove
Chapters 5 to 11
Identify applicable
treatment options
Step 4
Identify the hazards
within clear zone
Step 3
Calculate the
clear zone
Step 2
Chapter 4
Understand the area
under evaluation
Step 1

12. ROADSIDE DESIGN GUIDE
PAGE 12
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
understanding of the site and hence will enable them to make more informed decisions in each of the following
steps of the risk mitigation process.
The following are some example questions which can guide a designer/engineer into a better understanding
of the area:
• What are the traffic characteristics? Traffic information such as volume and speed are not
only necessary for the clear zone calculations (See Section 2.2.3), but they are also useful
during the assessment of treatment options (See Section 2.2.5). For example the
designer/engineer may consider a motorcyclist protection system (MPS) installation
depending on the volume of motorcyclist traffic; subject to engineering judgment. However,
depending on the traffic speed, they may not always be able to gain the full benefits from
these systems, as they are designed to work up to certain impact speeds. (See Chapter 8).
• What are the physical characteristics of the road and the roadside? Geometric
characteristics such as horizontal curve radius and the gradient of the side slope are not only
necessary information for the calculation of the clear zone (See Section 2.2.3), but they may
also become physical boundary conditions; limiting the type of countermeasures, which may
be applicable to the site. For example, relocating a hazard (See Section 2.2.5.2) may not be
a possible option if there isn’t enough physical space for this, and all mitigation measures,
such as crash cushions and terminals have a defined road space requirement, both for their
installation, and their operation.
• What is the history of accidents on the site? This document is designed to give guidance
to designers/engineers on the mitigation of most common roadside risks, based on
international best practice. However, every site is different and should be evaluated
individually. Studying the accident history can reveal local problems, which would help in a
more focused risk mitigation approach.
• What and why are the potential hazards located on the roadside? Identifying the
potential hazards on the roadside is one of the required steps of the risk mitigation approach
(see Section 2.2.4). But understanding the nature and reasons why they are located on the
roadside is also important for identifying applicable countermeasures. For example, a
roadside sign may need to be within a certain distance to the roadside, and therefore
relocating it beyond the clear zone may not even be an applicable countermeasure.
Figure 2.3 introduces an example of a typical roadside hazard in Abu Dhabi. Examination of this example case
will be followed through in the subsequent step-based analysis. The figure represents some of the information
that needs to be gathered at Step 1.
2.3.3 Step 2 – Calculate the Clear Zone
The second step of the hazard mitigation process is the calculation of the clear zone. The clear zone is the
area beside the road, along which the majority of the errant vehicles are expected to regain control. This is the
area which should ideally be kept clear of any hazards; hence leading to the title “Clear Zone”.

13. ROADSIDE DESIGN GUIDE
PAGE 13
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Figure 2.3 – Understanding the area under evaluation
Clear Zone effectively represents the “likelihood” element of the risk formula shown in Figure 2.1, as it is a
measure of how far errant vehicles are likely to travel along the roadside. It therefore gives an idea of the
likelihood of a hazard being reached, depending on parameters such as traffic volume, design speed,
horizontal curve radius, gradient of side slope and the distance of the hazard from the edge of the travelled
way. By controlling one or more of these parameters, the designer/engineer may be able to decrease the
likelihood of a hazard being reached; hence decreasing the risk posed by the hazard.
Figure 2.4 shows the required clear zone area for the example roadside and it can be seen that the sign post
lies within it. Hazards lying within the clear zone are more likely to be reached by errant vehicles than the
hazards lying beyond it.
Chapter 3 presents a detailed explanation of the concept and the calculation of recommended clear zones.

14. ROADSIDE DESIGN GUIDE
PAGE 14
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Figure 2.4 – Clear zone area
2.3.4 Step 3 – Identify Hazards within Clear Zone
Step 3 in hazard mitigation process involves the identification of all roadside hazards within the clear zone and
consideration of high-risk hazards beyond the clear zone, for example a railway line. The road designer should
identify all roadside hazards within the area of interest (based on clear zone widths). However, it is not always
straightforward to understand if and when a roadside feature becomes a hazard. For example, a roadside ditch
may be considered a hazard or a traversable roadside feature, depending on its geometry. A tree may be
considered a hazard or not, depending on the diameter of its trunk. A shallow pool of water may become a
hazard with floods following seasonal rain.
To help the designer/engineer with identifying hazards within the clear zone, Chapter 4 presents a detailed
explanation of the types and properties of the most common types of roadside hazards. The following types of
hazards are explained in detail within Chapter 4:
• Foreslopes (Embankments);
• Backslopes(Cutting Slopes);
• Ditches;
• Transverse Slopes;
• Trees;
• Overhead Gantries and Cantilevers;
• Other Sign Supports;
• CCTV Masts and Luminaire Supports;

15. ROADSIDE DESIGN GUIDE
PAGE 15
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
• Concrete Foundations Protruding from the Ground;
• Bridge Piers, Abutments and Portals;
• Bridge Railing Ends & Ends of Concrete Barriers;
• Above Ground Equipment;
• Culverts, Pipes, Headwalls;
• Pedestrian Fences and Walls;
• Retaining Walls;
• Noise Barriers;
• Bodies of Water;
• Adjacent Roads and Carriageways;
• Storage of Hazardous Material;
• Places of Frequent Pedestrian Activity / Places of Public Gathering;
• Cycle Lanes;
• Structures at Risk of Collapse;
• Rail Lines
• Speed cameras.
Hazard identification effectively relates to the “consequences” element of the risk formula shown in Figure 2.1,
as it is a measure of how severe the consequences would be if an errant vehicle reaches a hazard. Hazards
that lie within the clear zone, as previously shown in Figure 2.4, pose a risk to road users and this risk should
be mitigated through one of the treatment options explained in the following step.
2.3.5 Step 4 – Identify Applicable Treatment Options
Where hazards exist within the clear zone (or outside the clear zone in the case of high- consequence
hazards), potential treatment options should be identified so that their effectiveness in reducing the risk
associated with the hazard can be assessed.
The following are the basic treatment options that should be considered:
• Remove the hazard;
• Relocate the hazard;
• Make the hazard passively safe or traversable;
• Shield the hazard with a longitudinal barrier or crash cushion;
• Delineate the hazard;
• Design roadside safety (refer Austroads Sections 4.4 bullet point no: 3).
These options are listed in an order of decreasing desirability from a safety perspective; i.e. it is more desirable
to completely remove a hazard than shielding it with a barrier, if costs and physical attributes are not
constraints. Details of each of these approaches are given in the subsequent sections.

16. ROADSIDE DESIGN GUIDE
PAGE 16
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
2.3.5.1 Remove the hazard
The first approach in decreasing roadside risk is to remove the hazard. This is the most desirable treatment
option from a safety perspective as it completely eliminates the risk of a roadside accident through eliminating
the consequences if a vehicle were to run-off-the road.
This option, although desirable from a safety perspective, may not always be physically possible, as the hazard
may be an item of essential roadside infrastructure, or it may not be cost effective, as the costs of completely
removing the hazard may not be justified by the benefits. See Chapter 12 for more information on Economic
Assessment. Figure 2.5 follows the previous example and shows the hazard removed from the clear zone,
therefore eliminating the risk.
Figure 2.5 – Hazard removed from the area
2.3.5.2 Relocate the hazard
If removing a hazard is not physically possible or cost effective, the second option to be considered is the
relocation of the hazard beyond the clear zone, where it is less likely to be reached by an errant vehicle.
Relocating a hazard may not always be physically possible due to right-of-way or other physical constraints.
For example a roadside sign may have to be within a certain distance from the travelled way, so that it is clearly
visible by all travelling vehicles. Relocating some of the roadside features may be too expensive to justify the
benefits. Figure 2.6 follows the previous example and shows it with the hazard relocated beyond the clear
zone.

17. ROADSIDE DESIGN GUIDE
PAGE 17
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Figure 2.6 – Hazard relocated beyond the clear zone
2.3.5.3 Provide recoverable roadside
This treatment option refers to the provision of a recoverable roadside between the road and the hazard, which
would assist the driver to regain the control of the vehicle once it has left the road, before reaching the hazard.
This type of treatment is related to the likelihood part of the risk model, more specifically to the probability of
an errant vehicle reaching the hazard, once it runs off the road. An example to this kind of treatment is flattening
of a foreslope between the edge of the travelled way and a hazard. Errant vehicles travel further on steeper
foreslopes and therefore a wider clear zone is required. By flattening the foreslope, designer/engineer may
decrease the required clear zone to a point where the hazard is left outside. Therefore the risk of a vehicle
reaching the hazard would be considerably less. Section 3.3.3 provides further guidance on the effects of
roadside topography on the required clear zone.
2.3.5.4 Make the hazard passively safe or traversable
Another treatment option is to make the hazard either passively safe or traversable. For example, it may be
possible to replace a fixed sign post with a crash tested passively safe alternative, such as slip-base system
(see Figure 5.1 in Chapter 5). A cross-drainage culvert may be made traversable by installing an appropriate
grate to cover the opening (see Section 4.3.2.9).
Unfortunately, not every roadside hazard can be made passively safe or traversable; therefore this alternative
may not always be applicable. Chapter 5 provides guidance on the use of available passively safe roadside
hardware and the ways of making roadside features traversable.
Figure 2.7 shows the example roadside with the sign post still within the clear zone, but with the post made
passively safe through the use of a slip base system.

18. ROADSIDE DESIGN GUIDE
PAGE 18
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Figure 2.7 – Hazard made passively safe
2.3.5.5 Shield the hazard with a longitudinal barrier or crash cushion
If none of the previous alternatives is physically possible or cost effective, the alternative of shielding the hazard
with an appropriate VRS (or a longitudinal barrier or crash cushion) should be considered. At this point the
designer should remember that vehicle restraint systems, although designed to provide controlled impact, are
a hazard themselves and they should ideally be used only if the consequences of hitting the VRS is likely to
be less than the consequences of reaching and/or impacting the hazard behind.
VRS systems have their own physical requirements, which they need in order to perform as designed, such
as enough clear space behind, minimum length of installation, etc. The roadside under consideration may not
always have the required physical space or it may not always be cost effective to install VRS for hazards that
are less likely to be reached.
Chapters 6 to 11 provide comprehensive information on vehicle restraint systems; i.e. roadside and median
barriers, parapets, terminals, transitions and crash cushions. Information on the general principals of these
systems, testing requirements and detailed design properties are also provided.
Figure 2.8 shows the example roadside with the sign post being shielded by a roadside barrier.

19. ROADSIDE DESIGN GUIDE
PAGE 19
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Figure 2.8 – Hazard shielded with a roadside barrier
2.3.5.6 Delineate the hazard
The final treatment option is to delineate the hazard; i.e. make it more visible to the motorists and make them
aware of the danger. This may be achieved by using reflective material, as shown in Figure 2.9, and/or by
warning signs. This treatment option does not provide any physical protection but it may still be better than
doing nothing, where other options are either physically impossible or not cost effective.
Figure 2.9 – Hazard delineated

20. ROADSIDE DESIGN GUIDE
PAGE 20
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
2.3.6 Step 5 – Assessment & Ranking of Treatment Options
2.3.6.1 Overview of Treatment Assessment & Ranking Process
Once the potential treatment options are identified, each option should be assessed from a perspective of
physical applicability and economic feasibility. The options which are both physically applicable and
economically feasible should then be ranked based on the amount of risk reduction they provide, their benefit
cost ratio and other non-monetary considerations should be determined for a final decision. An overview of the
treatment assessment and ranking process is shown in Figure 2.10. Further detail on each individual step of
the process is presented in the following sections.
Figure 2.10 – Overview of treatment assessment & ranking process

21. ROADSIDE DESIGN GUIDE
PAGE 21
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
2.3.6.2 Assess Physical Practicability
After a hazard and the possible safety treatments are identified, an initial evaluation to the physical
practicability of the treatment should be carried out. A treatment option may not be reasonably practicable for
reasons such as:
• Constructability of the treatment;
• Right of Way Limitations;
• Insufficient physical space for the treatment to function as intended;
• Intended function of the hazardous object.
Some of the more obvious of the physically impracticable or extremely difficult to apply treatment options may
be related to the removal of a hazard. For example for coastal roads, the sea may be considered as a
continuous hazard, if the water is located within the clear zone distance, removal of such a hazard would be
considered extremely difficult, if not entirely impossible.
Some treatment options may not be possible due to the right of way limitations. For example a hazard may not
be able to be relocated beyond the clear zone, if the end of the clear zone area lies outside the right-of-way
boundaries.
Some treatment options may not be practicable due to restrictions in physical space available. For example
“shielding a hazard with a barrier” is only possible if the distance between the back face of the barrier and the
hazard is less than the deflection distance of the barrier (eee Section 7.3.5). If not, the impacting vehicle would
still reach the object behind as the barrier deflects. If the hazard is simply too close to the travelled way,
designer/engineer may not be able use certain types of barriers, due to physical limitations of the product and
the physical space available on the site.
Sometimes the intended function of a roadside hazard may be a reason for a treatment to be impracticable.
For example “relocation of the hazard beyond clear zone” may not be possible for a road sign as the sign
should be within a certain distance from the road to fulfil its intended function. Similarly “removal of the hazard”
may also not be an option for the same hazard.
For some treatment options, assessing the physical practicability is relatively straightforward. Treatment
options, which are either extremely difficult to apply or simply impracticable may be discarded from the risk
mitigation process, or the treatment may be modified and reassessed again.
Treatment options which are physically practicable should be carried over to the next phase of the process.
2.3.6.3 Assess Economic Feasibility
Once the physically impracticable treatment options are eliminated, the remaining should be assessed for their
economic feasibility. The expected benefits of a treatment (i.e. the anticipated reduction in the frequency and
severity of injuries, reduction in economic loss, reduction in losses due to traffic disruptions, etc.) should be
more than the associated costs (i.e. construction costs, maintenance costs, etc.) for its application. In other
words, the Benefit/Cost Ratio (BCR) of any safety treatment should be more than 1 (see Chapter 12 for
Economic Analysis).

22. ROADSIDE DESIGN GUIDE
PAGE 22
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Any treatment option with a BCR less than or equal to 1.0 should be discarded from the risk assessment
process and the following phase should continue for options with a BCR greater than 1.0.
2.3.6.4 Rank Treatment Options
After economically feasible treatment options are identified, they should be compared and ranked from a risk
reduction and an economic perspective. Ranking is useful to identify the optimal treatment option.
Rank by Risk Reduction:
Different safety treatments provide different levels of reduction in overall risk. For example, as explained in
Section 0.1, removing a hazard usually provides a higher risk reduction than shielding the hazard with a VRS.
For this reason, alternative treatment options should be ranked by the amount of risk reduction they are
expected to provide. The amount of risk reduction can be quantified in terms of the expected reduction in crash
frequency, injuries and property damage. Example methods of carrying out such a ranking are presented in
Chapter 12. At this point the road authority or the designer/engineer may choose to set a certain level of risk
reduction as a minimum and eliminate any treatment options which do not provide the minimum desired level
of risk reduction.
Once the treatment options are ranked in risk reduction order, options that provide a higher level of risk
reduction should be given greater consideration. However the amount of risk reduction is not the only factor to
be used to determine the optimal solution. The treatment which provides the highest level of risk reduction
may also be the most expensive. In such a case, a second alternative may provide an acceptable level of risk
reduction for a better economic value. For this reason, the treatment options should also be assessed from an
economic perspective:
Rank by Benefit Cost Ratio
As explained above, the amount of risk reduction is not the only important factor when deciding upon the
optimal safety treatment. Treatment options which provide an acceptable level of risk reduction should also be
evaluated and ranked from a cost effectiveness perspective. BCR is a good indicator of project value. However,
simply comparing the BCR of different treatment options to each other may be misleading. This is because
BCR is a ratio of the benefits of a specific treatment to its costs and it does not necessarily provide a meaningful
comparison between the benefits of different treatment options.
For example, “delineation of a hazard” is often the cheapest treatment option and due to its low cost compared
to its potential benefits, it is usually the option with the highest BCR. However, this high BCR does not
necessarily mean that the benefits gained from delineation is more than the benefits gained from a more
expensive option, for example shielding the hazard with a barrier. A barrier would cost more, but its benefits
would also be greater than for delineation. Therefore, a solution can provide higher benefits, but with a lower
BCR.
In such a case an incremental BCR analysis may be applied to rank the treatment options economically. For
incremental BCR and more on Economic Analysis, see Chapter 12.

23. ROADSIDE DESIGN GUIDE
PAGE 23
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
The economic ranking of treatment options is essential, but is not the only consideration for deciding upon an
optimal solution. The decision should also be based on the assessment of non- monetary considerations.
2.3.6.5 Assess Non-Monetary Considerations
In most cases, the main benefits of applying a roadside safety treatment can be quantified in monetary terms;
i.e. the monetary gains expected due to a reduction in crash frequency, severity, and the associated repair
costs.
However, there are some factors which may be influential in the decision about which safety treatment to adopt
which cannot be quantified in monetary terms. Examples of these considerations include:
• Aesthetics;
• Public demands and perception of road safety improvements;
• Air quality, noise, visual intrusion or other environmental considerations;
• Road user needs.
As these considerations cannot be quantified, their effect in the final decision should be evaluated on a case
by case basis through engineering judgment. For example, aesthetics may be of a significant importance in
the selection of a certain type of treatment over the other alternatives around areas of natural beauty, land
marks, major tourist attractions, etc. while it may not be an important factor in a remote rural area of no special
importance.
Environmental concerns may be of significant importance in areas such as natural reserves, natural protection
areas such as source of drinking water, in conservation areas for a certain species of animal, etc.
In some cases the designer/engineer may choose to apply a certain treatment option to satisfy the public
demand, although it may not be the best option from an economic perspective. For example, one may choose
to install a motorcyclist protection system on a certain location to satisfy the demands of a motorcyclist action
group.
Non-monetary considerations can be of significant importance in the final decision; however the
designer/engineer should always ensure that an adequate level of safety is provided.
2.3.7 Step 6 – Choose the Optimal Treatment Option
Once the risk reduction and BCR ranking, and the non-monetary assessment of treatment options are
complete, the designer/engineer should rank the preferred treatment options based upon the risk reduction,
cost effectiveness and non-monetary considerations. As each site is different, engineering judgment should
be used to find the optimal solution that fits the needs of the particular site, as shown in Figure 2.11.
2.3.8 Step 7 – Design the Optimal Roadside Treatment
The final step in the risk mitigation process is the detailed design of the appropriate (optimal) roadside
treatment. This step may include the design of just a single treatment or the whole safety improvement scheme
along a section of road which addresses different types of hazards in one

24. ROADSIDE DESIGN GUIDE
PAGE 24
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
go. In some cases Abu Dhabi DoT Standard Drawings will provide the necessary detail, whereas the road
design layout will show the location of the treatment as well as information not covered by the standard
drawings. Necessary guidance for the design of individual roadside safety treatments is provided between
Chapters 3 to 11 of this Guide.
Figure 2.11 – Selection of optimal treatment option through engineering judgment
The designer/engineer of a specific treatment should consider that the final design of the roadside treatment
can affect the other responsible bodies which provide roadside infrastructure items, such as signage and
lighting. Lateral extensions of the clear zone or hazard corridor should be shown on the final plans so the other
responsible bodies can assess the final design from their own perspective.
The final design should include, but not be limited to the following information:
• All hazards for which a treatment warrant has been identified;
• The treatment options chosen for those hazards;
• The priority of the treatment options.

25. ROADSIDE DESIGN GUIDE
PAGE 25
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
2.4 Abu Dhabi DoT Product Approval Process
Prior to the use of any proprietary vehicle restraint system on the Abu Dhabi road network, the system must
have been accepted for use by the Abu Dhabi Department of Municipal Affairs and Transport, or their
representatives. This is to ensure that the product has been successfully tested to appropriate standards
(NCHRP350 and MASH), and that sufficient consideration has been given to the local conditions and demands
of the Abu Dhabi road environment. Whilst a large number of systems currently exist on the market, these
have often been developed with the local requirements of the USA, Australasia and (in some cases) European
road conditions in mind, not necessarily those of Abu Dhabi. A list of those products deemed to be acceptable
for use on such roads is available.
In order for a product to be listed, an application must first be filed with the Abu Dhabi Department of Municipal
Affairs and Transport, or its representatives. The Department will then issue a proforma detailing questions
regarding the suitability of product for the local conditions in Abu Dhabi. This must be completed in a
satisfactory way, supported by evidence where possible.
For each product, the manufacturer will also be required to supply a set of full (i.e. not summary) impact test
reports and videos of their system to the Department of Municipal Affairs and Transport, or its representatives,
for assessment against the relevant testing standard (either NCHRP350 or MASH). This should be
accompanied by any other relevant supporting evidence which may include:
• Inspection, maintenance and repair requirements;
• Installation manual;
• Restrictions on the use of the product, and compatibility with other products;
• Details of any modifications made to the product since it was tested, and any supporting
evidence/independent approval of the modifications made;
• Details of agreements with local distributors;
• Drawings and specifications for the system;
• Details of any in-service performance evaluation (including impacts with higher and faster
vehicles than specified in the testing standards);
• Details of any durability/environmental testing;
• Promotional literature;
• Any other information supporting the application.
Note that whilst the acceptance of a product in another territory (e.g. by Federal Highways in the USA or by
the award of a CE mark within Europe) may be considered as part of the approval process, this will be no
guarantee of acceptance for use by the Abu Dhabi Department of Municipal Affairs and Transport due to its
local needs and road conditions.
2.5 Summary and Conclusions
This chapter explains the recommended risk mitigation approach for Abu Dhabi. It also provides an overview
of how the manual should be used in general, by referencing the related chapters of the manual for each step
of the risk mitigation procedure.

26. ROADSIDE DESIGN GUIDE
PAGE 26
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
Risk, from a roadside safety perspective, is defined as the probability, high or low, that somebody or something
will be harmed by a roadside hazard. Roadside risk is directly related to both the likelihood of a roadside
accident and the consequences of it. Designers/engineers can mitigate the risk by controlling either or both
the likelihood or consequences of a run-off-the road accident, through the recommended treatment options.
The recommended risk mitigation approach consists of the following stages:
1. Understand the area under evaluation;
2. Calculate the clear zone;
3. Identify the hazards located within the clear zone;
4. Identify applicable treatment options to mitigate risks from the hazards located within the
clear zone. Recommended treatment options include:
o Remove the hazard;
o Relocate the hazard;
o Provide recoverable roadside;
o Replace the hazard with a passively safe system;
o Shield the hazard with a VRS;
o Delineate the hazard;
5. Assess and rank applicable treatment options:
o Assess physical applicability;
o Assess economic feasibility;
o Rank treatment options economically;
o Assess non-monetary considerations;
6. Choose the optimal treatment option through engineering judgment;
7. Design the appropriate (optimal) roadside treatment.
An overview of the DoT product approval process is also given in this chapter. Prior to the use of any
proprietary vehicle restraint system on the Abu Dhabi road network, the system must have been accepted for
use by the Abu Dhabi Department of Municipal Affairs and Transport, or its representatives.
2.6 References
[1]CEDR, “SAVERS (Selection of Appropriate Vehicle Restraint Systems) - WP1: Defining the Different
Parameters which can Influence the Need and Selection of VRS (Unpublished Report),” Conference of
European Directors of Roads, 2014.
[2]TD19/06 Design Manual for Roads and Bridges, Volume2 Highway Structures: Design, Section
2 Special Structures, Part 8, The Highways Agency, Transport Scotland, Welsh Assembly Government,
The Department for Regional Development Norther Ireland, 2006.
[3]FGSV, Traffic Management Work Group, “Guidlines for passive protection on roads by vehicle

27. ROADSIDE DESIGN GUIDE
PAGE 27
02 ROADSIDE RISK MITIGATION FIRST EDITION -DECEMBER 2016
restraint systems,” FGSV Verlag GmbH, Koln, 2009.
[4] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of State
Highway and Transportation Officials, 2011.

28. ROADSIDE DESIGN GUIDE
PAGE 28
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
3 CONCEPT AND CALCULATION OF CLEAR ZONE
3.1 Introduction
The “Clear Zone Concept” is a key part of this Guide’s risk mitigation process, as it provides engineers and
designers an easy to use tool for the assessment of risk of a roadside accident for selected road environments.
The chapter starts with a brief look at the concept of clear zone, its origins and its evolution over time. This is
followed by a look at the factors which may affect the required clear zone distance for different roads.
The Clear Zone Calculation Model for this Guide is presented in detail and followed by examples on clear zone
distance calculations.
3.2 The Clear Zone Concept
“The clear zone is the unobstructed, traversable area provided beyond the edge of the through travelled way
for the recovery of errant vehicles”. [1]
In an ideal world, providing unlimited, flat and obstacle-free areas along every road would completely eliminate
the problem of roadside accidents. However, in reality this is neither economically viable, nor physically
possible. For this reason, engineers and designers should assess the level of risk along each roadside and
find an optimal design solution; one which provides a balance between the amount of forgiving roadside
provided and the economic feasibility of the selected application.
Accordingly, AASHTO became the first organization to promote the idea of providing clear recovery areas
along highways. In 1974, the AASHTO document known as the “Yellow Book” stated that, “for adequate safety,
it is desirable to provide an unencumbered roadside recovery area that is as wide as practical on a specific
highway section. Studies have indicated that on high- speed highways, a width of 9 m or more from the edge
of the through travelled way permits about 80 percent of the errant vehicles leaving the roadway to recover.”
[2]. The idea of providing 9m wide clear zones was trialled by several highways agencies, and it was
understood that a constant width of recovery space is not always the optimal solution for roads with different
characteristics. Errant vehicles travel further along the roadside with increased traffic speeds, sharper
horizontal curves and steeper side slopes. Therefore 9m clear zone was not always enough for errant vehicles
to recover safely. On the other hand it was understood that 9m is too wide and economically not viable for
roads with lower speeds and traffic volumes.
For these reasons, in 1977 AASHTO modified its earlier clear zone concept by introducing variable clear-zone
distances based on traffic volumes, speeds and roadside geometry [3]. This new approach was well received
and became widespread. Many countries around the world today either use the exact AASHTO variable clear
zone model or modified versions of it to fit the specific needs of their road networks. [4]
The clear zone distances recommended by AASHTO Roadside Design Guide [1] are based on empirical
research data, which was later extrapolated to fill in the gaps of the database. Therefore, they are intended as
reference points rather than definitive values. It should be noted that these

29. ROADSIDE DESIGN GUIDE
PAGE 29
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
clear zone values, although considered sufficient for majority of errant vehicles to safely regain control, are not
enough to stop all 100% of errant vehicles. For example, the recommended clear zone widths may not be
enough for an over-speeding errant vehicle to safely regain control. A clear zone, where even the over-
speeding errant vehicles would regain control before reaching the end, would require a considerably wider
space. However, considering the low probability of such incidents, providing this extra space is not always
economically viable. However, The Abu Dhabi DoT lately extended the speed range of AASHTO Table, shown
in Table 3.2, up to 140 km/h. The values given were only extracted by interpolating the trend of previous speed
ranges given by AASHTO.
The relationship between the distance from the edge of the travelled way to a hazard and the proportion of
errant vehicles that will be able to reach the hazard has been the subject of several researches. One of the
most comprehensive datasets of run-off-road accidents was collected during late 1970s in Canada by P.
Cooper [5]. Cooper’s research involved weekly observations of wheel tracks on grass-covered roadsides of
rural highways of various functional classes, where he looked at the distance travelled by errant vehicles.
Cooper’s encroachment data was later re-analysed for development of the RSAP [6], and the relationship
shown in Figure 3.1 was derived. Figure 3.1 shows the proportion of errant vehicles which are expected to
travel over a certain distance from the edge of the travelled way during a run-off-road accident. The relationship
is presented for two-lane undivided roads, multi-lane divided roads and for the combination of both undivided
and divided roads. It can be seen from the figure that, as the distance from the edge of the travelled way
increases, the proportion of errant vehicles which are likely to reach the distance decreases.
Figure 3.1 shows that clear zone distances recommended by AASHTO are likely to allow enough space for
approximately 85% of the errant vehicles to stop or regain control. In other words, roughly 15% of errant
vehicles could still reach a hazard beyond these distances. A considerably wider space is required to ensure
that more than 85% of the errant vehicles will stop within the clear zone. For example for divided road,
increasing the proportion of vehicles which would stop within the clear zone from 85% to 95%, would require
the clear zone distance to increase from roughly around 12m to 20m. To take the same ratio from around 85%
to around 100%, the clear zone distance should almost be tripled from 12m to 30m. The considerable increase
in the required clear zone to cater for every single possible incident may not always be justified due to
economic reasons. Therefore, the designer should always use engineering judgment on a site-by- site basis
when deciding the acceptable clear zone distance.
However, some hazards, especially the ones where third parties may be affected, would yield more severe
consequences if reached by an errant vehicle. Examples of these are chemical plants, school playgrounds,
areas of public gathering, source of drinking water, etc. The consequences of a vehicle reaching these hazards
would be so high, that even a low likelihood of a vehicle reaching them would pose a significant risk (see
Section 2.2). For such high consequence hazards, the extra width required to increase the 85% mark to 95-
100% may be justified.
This approach of providing wider clear zones for higher consequence hazards is adopted by several countries
around the world. For example, the Norwegian VRS Manual [7] recommends up to doubling the clear zone
distance for higher risk hazards, while the German guidelines [8] recommend 8, 4 and 3m of extra clear zone
space for high risk hazards located close to highways of 100, 80 and 60km/h posted speed limit, respectively.
This approach forms the basis of the clear zone calculation model for the ADRSDG.

30. ROADSIDE DESIGN GUIDE
PAGE 30
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Distance from the edge of travelled way (m)
Figure 3.1 – Distance from the edge of travelled way vs proportion of errant vehicles which may
reach it by highway type [6]
3.3 Factors Affecting the Clear Zone Distance
The required clear zone distance along a particular road is related to several factors. These factors are
explained briefly to provide an insight into how the clear zone calculation model works.
3.3.1 Traffic Volume
Traffic Volume is an important factor which affects the required clear zone distance, as it is directly related to
the exposure level of a roadside. Probability of a vehicle running off the road increases as the number of
vehicles passing through the area increases.
Traffic volume does not directly affect the distance travelled by an errant vehicle. However, there is an indirect
effect, as the probability of a faster vehicle running off the road increases with increased traffic volume. For
this reason, the required clear zone distance goes up with increased volume of traffic.
3.3.2 Design Speed
Design speed is another important factor, which affects the required clear zone distance. Design speed
determines the distance up to which an errant vehicle will travel and therefore the likelihood of the vehicle
reaching a hazard within a certain distance. For this reason, the required clear zone distance goes up with
increased design speed.
er
c
e
nt
of
v
e
hi
cl
e
s
e
x
c
e
e
di
10

31. ROADSIDE DESIGN GUIDE
PAGE 31
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
3.3.3 Roadside Topography
Roadside topography has an important effect on how far an errant vehicle would travel; i.e. the probability of
an errant vehicle reaching a hazard within a certain distance. Due to the change in its potential energy, an
errant vehicle is likely to travel further distance along steeper downhill slopes,
i.e. foreslopes, and is likely to travel less distance along steeper uphill slopes, i.e. backslopes.
3.3.3.1 Foreslopes
According to their gradient, foreslopes are usually divided into three categories:
Recoverable Slopes:
Recoverable slopes are those on which a motorist can retain or regain control of a vehicle. Slopes equal to or
flatter than 1V:4H, as shown in Figure 3.2, are considered recoverable. Smooth, compact slopes with no
significant discontinuities and no protruding fixed objects are required from a safety standpoint. Slope should
be rounded so that an encroaching vehicle remains in contact with the ground. Also the toe of the slope should
be rounded to improve reversibility by an errant vehicle.
Figure 3.2 – Recoverable slope
Non-recoverable Slopes:
A non-recoverable foreslope is defined as one that is traversable but from which most vehicles will not be able
to stop or return to the roadway easily. A foreslope with gradient between 1V:4H and 1V:3H, as shown in
Figure 3.3, is considered as non-recoverable, as long as it has firm compacted surface or if it is treated with
concrete, rip-rap, etc. Conversely if it has a loose sandy surface which may cause a vehicle to overturn, a
foreslope with gradient between 1V:4H and 1V:3H should be considered as a hazard rather than a non-
recoverable slope. See Chapter 4 for more information on hazard assessment of foreslopes.
An errant vehicle reaching a non-recoverable slope would continue at least until it reaches the end of it. For
this reason, fixed obstacles along such slopes should be avoided and a clear runout area should be provided
at the base. This is also why, for the calculations, the total width of a non- recoverable slope is added to the
clear zone distance.

32. ROADSIDE DESIGN GUIDE
PAGE 32
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Figure 3.3 – Non-recoverable slope
Critical Slopes:
A foreslope with gradient steeper than 1V:3H, as shown in Figure 3.4, is considered as a critical slope; one on
which an errant vehicle has a higher probability to overturn. For this reason a foreslope is considered as a
hazard by itself. Critical slopes which are located within the clear zone should ideally be flattened. If this is not
possible, or economically viable, a barrier is typically used.
3.3.3.2 Backslopes
Figure 3.4 – Critical slope
A backslope in a cut section may be traversable depending on its relative smoothness and the presence of
fixed obstacles. It may not be a significant obstacle if the front slope between the roadway and the base of the
backslope is traversable (1V:3H or flatter) and the backslope is obstacle-free. However, a steep, rough-sided
rock cut normally should begin outside the clear zone or be shielded. A rock cut normally is considered to be
rough-sided when the face will cause excessive vehicle snagging rather than provide relatively smooth
redirection.
3.3.4 High Risk Hazards
The type of a hazard does not affect the probability of an errant vehicle reaching it. However, it is still an
important factor for the determination of the required clear zone distance as it affects the overall risk. As
explained in Section 3.2, some hazards yield higher consequences than others in case of an errant vehicle
reaching them. Since risk is a product of likelihood and consequences (see Chapter 2), these high
consequence hazards can still pose a considerable risk for even low

33. ROADSIDE DESIGN GUIDE
PAGE 33
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
probability of a vehicle reaching them. Therefore, high risk hazards affect the required clear zone distance,
as they can economically justify the provision of wider clear zones.
3.4 Calculation of Clear Zone Distance
3.4.1 Clear Zone Model
The clear zone is calculated by using the following formula, as detailed in Table 3.1:
Where:
Table 3.1 – Calculation of clear zone distance, Cz
Calculation of Clear Zone Distance, Cz
Cz=(Bcw x Mc)
Bcw, Base Clear Zone Width See Table 3.2
Mc, Modification Factor for
Outside of Horizontal Curves
Straight Sections & Inside of Curves Mc=1.0
Outside of Curves See Table 3.3
3.4.2 Base Clear Zone Width
The base clear zone width is the recommended clear zone width from the edge of the travelled way for straight
road sections, and it is determined on the basis of ADT, Design Speed and Side Slope, by using Table 3.2.
The clear zone distances presented in Table 3.2 are based on the clear zone distances suggested by AASHTO
Roadside Design Guide [1]. To cater for the needs of the Abu Dhabi Road Network the AASHTO clear zone
values are extrapolated for design speeds up to 140km/h.
The clear zone values presented in Table 3.2 are based on empirical research data, which was later
extrapolated to fill in the gaps of the database. Therefore, they are intended as guidance values rather than
definitive values. It should be remembered that, as explained in Section 3.2, some vehicles can still travel
further than these recommended clear zone distances. Therefore, designer/engineer should assess the risk
for each site on a case-by-case basis, using engineering judgment.
In Table 3.2, a two-way ADT should be used for single carriageways and one-way ADT should be used per
direction of dual carriageways. The traffic volumes should be based on a 20-year projection from the
anticipated date of construction. For recommended clear zone widths over 15m, an additional assessment
should be carried out to justify the required empty space, as these are likely to cross the right-of-way limitations.

34. ROADSIDE DESIGN GUIDE
PAGE 34
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Table 3.2 - Recommended base clear zone width, Bcw (in metres)
Design Year ADT
Design
Speed
(km/h)
Under 750 750-1500 1500-6000 Over 6000
Foreslopes
60 2.0 - 3.0 3.0 - 3.5 3.5 - 4.5 4.5 - 5.0
80 3.0 - 3.5 4.5 - 5.0 5.0 - 5.5 6.0 - 6.5
1V:6H 90 3.5 - 4.5 5.0 - 5.5 6.0 - 6.5 6.5 - 7.5
100 5.0 - 5.5 6.0 - 7.5 8.0 - 9.0 9.0 - 10.0
or
flatter
110 5.5 - 6.0 7.5 - 8.0 8.5 - 10.0 9.0 - 10.5
120 6.5 - 7.0 8.5 - 10.0 10.5 - 11.5 11.0 - 12.5
140 9.5 - 10.5 12.5 - 14.0 15.5* - 16.5* 16.0* - 17.5*
60 2.0 - 3.0 3.5 - 4.5 4.5 - 5.0 5.0 - 5.5
Steeper 80 3.5 - 4.5 5.0 - 6.0 6 - 8.0 7.5 - 8.5
90 4.5 - 5.5 6.0 - 7.5 7.5 - 9.0 8.0 - 10.0
than
1V:6H to
100 6.0 - 7.5 8.0 - 10.0 10.0 - 12.0 11.0 - 13.5
Flatter
110 6.0 - 8.0 8.5 - 11.0 10.5 - 13.0 11.5 - 14.0
than
1V:3H
120 8.5 - 10.5 10.5 - 13.5 13.0 - 16.5* 14.5 - 18.0*
140 13.5 - 15.5* 15.5* - 20.0* 19.0* - 25.0* 20.0* - 27.0*
Backslopes
60 2.0 - 3.0 3.0 - 3.5 3.5 - 4.5 4.5 - 5.0
80 2.5 - 3.0 3.0- 3.5 3.5 - 4.5 4.5 - 5.0
1V:3H 90 2.5 - 3.0 3.0 - 3.5 4.5 - 5.0 5.0 - 5.5
100 3.0 - 3.5 3.5 - 4.5 4.5 - 5.5 6.0 - 6.5
or
steeper
110 3.0 - 3.5 3.5 - 5.0 5.0 - 6.0 6.5 - 7.5
120 3.5 - 3.5 3.5 - 5.0 5.5 - 6.0 6.5 - 7.5
140 4.0 - 4.5 4.0 - 6.0 6.0 - 7.0 8.0 - 9.0
60 2.0 - 3.0 3.0 - 3.5 3.5 - 4.5 4.5 - 5.0
Steeper 80 2.5 - 3.0 3.5 - 4.5 4.5 - 5.0 5.5 - 6.0
90 3.0 - 3.5 4.5 - 5.0 5.0 - 5.5 6.0 - 6.5
than
1V:6H
100 3.5 - 4.5 5.0 - 5.5 5.5 - 6.5 7.5 - 8.0
Flatter
110 4.5 - 5.0 5.5 - 6.0 6.5 - 7.5 8.0 - 9.0
than
1V:3H 120 5.0 - 5.5 6.5 - 7.0 7.0 - 8.0 9.0 - 10.0
140 6.5 - 7.0 8.0 - 8.5 9.0 - 10.0 11.5 - 12.5
60 2.0 - 3.0 3.0 - 3.5 3.5 - 4.5 4.5 - 5.0
80 3.0 - 3.5 4.5 - 5.0 5.0 - 5.5 6.0 - 6.5
1V:6H 90 3.0 - 3.5 5.0 - 5.5 6.0 - 6.5 6.5 - 7.5
100 4.5 - 5.0 6.0 - 6.5 7.5 - 8.0 8.0 - 8.5
or
flatter
110 4.5 - 5.0 6.0 - 6.5 8.0 - 8.5 8.5 - 9.0
120 5.5 - 5.5 7.5 - 8.0 9.0 - 10.0 10.0 - 10.5
140 7.0 - 8.0 10.0 - 10.5 11.5 - 13.0 13.0 - 13.5
* Clear Zone distances over 15m should be evaluated on a site-by-site basis to justify the extra space

35. ROADSIDE DESIGN GUIDE
PAGE 35
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
3.4.3 Modification for the Outside of Curves
The base clear zone width (Bcw) values in Section 3.4.2 assume a tangent alignment. However, horizontal
curves may increase the angle of departure from the roadway and thus increase the distance the vehicle will
need to recover. The designer should adjust the tangent values to provide wider clear zones on the outside of
horizontal curves. Table 3.3 provides recommended modification factors for the outside of curves (Mc). A value
of Mc=1.0 should be used for straight sections and insides of curves, as a modification is not necessary for
these.
3.4.4 Clear Zone on Combination of Slopes
3.4.4.1 Variable Slopes
Sometimes a combination of two different side slopes may be used on a roadside, as shown in Figure 3.5. A
common application is a relatively flat recovery area immediately adjacent to the roadway followed by a steeper
foreslope. This type of application, often called as ‘barn roof’, can provide the flat recovery area by using less
material and space than a single continuous slope would require.
Figure 3.5 – Variable Slope
If the clear zone width required for the first slope does not reach the second one, no extra consideration is
necessary, as an errant vehicle would stop before reaching the second slope. If the clear zone width required
for the first slope extends beyond the first and overlaps into the second slope, the clear zone width for the
steeper slope should be used.
Table 3.3 – Modification factor for the outside of curves, Mc [1]
Radius (m)
Design Speed km/h
60 70 80 90 100 110 120
900 1.1 1.1 1.1 1.2 1.2 1.2 1.3
700 1.1 1.1 1.2 1.2 1.2 1.3 -
600 1.1 1.2 1.2 1.2 1.3 1.4 -
500 1.1 1.2 1.2 1.3 1.3 1.4 -
400 1.2 1.2 1.3 1.3 1.4 - -
300 1.2 1.3 1.4 1.5 1.5 - -
200 1.3 1.4 1.5 - - - -
100 1.5 - - - - - -

36. ROADSIDE DESIGN GUIDE
PAGE 36
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
3.4.4.2 Drainage Channels
Drainage channels are typically variable slopes with at least one foreslope and one backslope, as shown in
Figure 3.6. Drainage channels, depending on their geometry, can become hazards by themselves. This can
be checked from Figure 4.8 and Figure 4.9 in Chapter 4.
Drainage channels, which are not considered to be hazards, should be treated as variable slopes, and the
clear zone should be calculated accordingly, as explained in Section 3.4.4.1.
3.4.5 High Risk Hazards
Figure 3.6 – Drainage channel
High risk hazards are the ones where people other than the vehicle occupants (third parties) may be harmed
if reached by an errant vehicle. Chapter 4, Section 4.4 presents more detail into the identification of some of
the more common high risk hazards. Following are some of the examples to high risk hazards where 3rd
parties
may be harmed:
• Adjacent roads and carriageways (Section 4.4.1)
• Storage of hazardous material (Section 4.4.2)
• Places of frequent pedestrian activity / places of public gathering (Section 4.4.3)
• Cycle Lanes (Section 4.4.4)
• Structures at Risk of Collapse (Section 4.4.5)
• Rail Lines (Section 4.4.6)
As explained in Sections 3.2 & 3.3.4, the recommended clear zone distances in Table 3.2 are expected to
provide enough space for approximately %85 of the errant vehicles to stop or regain control. However, roughly
%15 of errant vehicles may still travel further than the recommended clear zone distance. It is possible to
ensure a safe stop for a higher percentage of errant vehicles by providing even wider clear zones. However,
for regular roadside hazards, the costs of providing the extra space may not always be justified by the benefits
gained.
However, in the case of 3rd
party hazards, the consequences can be so high, that even a 15% probability of
an errant vehicle reaching the hazard may result in an unacceptable level of risk. Therefore, if a high risk
hazard is located in the vicinity of the travelled way, the designer/engineer should check for distances which
are even further than the clear zone width recommended in Table 3.2. Based on the information presented in
Figure 3.1, it is recommended that the risk posed by any 3rd
party hazard located up to 30m to the travelled
way should be assessed using engineering judgment. If the assessment suggests that the likelihood of a
vehicle reaching the 3rd
party hazard is too high, then the hazard should be removed, relocated to a further
distance or

37. ROADSIDE DESIGN GUIDE
PAGE 37
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
shielded by an appropriate barrier. Considering the high consequences of the hazard, a high containment level
barrier should be used (see Chapter 7).
3.4.6 Other Considerations
3.4.6.1 The Use of Engineering Judgement
As explained in the previous sections, the recommended clear zone widths presented in this chapter are based
on empirical research data, which was later extrapolated to fill in the gaps in the database. Therefore, the clear
zone distances recommended in this chapter should only be taken as guidance, rather than definitive values.
The designer/engineer should assess each site on a case-by-case basis applying engineering judgment and
a justification should be provided for the final decision.
3.4.6.2 Departures from Standards
A Departure or Departure from Standard can be described as a non-compliance with a Mandatory Requirement
of a Declared Standard. The clear zone distances presented in this chapter are given as reference points
rather than definitive values. However, the designer/engineer should aim to provide at least the minimum
recommended clear zone width for each site. Where special circumstances arise and the straightforward
application of the technical requirements cannot be achieved or justified for some reason, such as the
environmental impact, exceptional layout situations or cost, users are encouraged to come forward with
Departures or to propose additional criteria (for aspects not covered by existing documents) based on a
reasoned assessment.
Full justification for the grounds of the proposed departure must be forwarded to Abu Dhabi Department of
Municipal Affairs and Transport at an early stage in design. The departure must demonstrate that the risk level
of the proposed solution is as low as reasonably practicable. Formal approval of the proposed Departure must
be received before incorporation into the design and the commencement of construction. Departures from
Standard are determined on an individual basis and a decision regarding a Departure for one location must
not be assumed to apply to any other site, even for similar situations.
3.5 Example Clear Zone Distance Calculations
3.5.1 Example 1 – Simple Recoverable Side Slope
Calculate the clear zone and evaluate the location of the electrical box.
Road Type: Multilane Divided ADT:
10,000 per direction Design Speed:
120km/h Horizontal Alignment: Straight

38. ROADSIDE DESIGN GUIDE
PAGE 38
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Solution:
Step 1 - Determine Base Clear Zone Width (Bcw)
Using Table 3.2 for:
• A foreslope of 1V:10H (i.e. 1V:6H or flatter)
• Design Speed: 120km/h
• ADT: 10,000 (i.e. over 6,000)
Bcw = 11.0 to 12.5m
Step 2 – Modifier for Outside of Curves
• This is a straight section of road; a curve modification is not necessary. Mc = 1.0
Step 3 – Calculate the Clear Zone Distance (Cz)
Cz = Bcw x Mc
Cz = 11.0 to 12.5m
Step 4 – Comment on the location of the electrical box
As shown in the figure below, the electrical box lies within the minimum recommended clear zone distance of
11.0m from the edge of the travelled way.
The following treatment options should be evaluated:
• Remove the electrical box
• Relocate the electrical box beyond the 11.0 to 12.5m clear zone
• Use a passively safe electrical box
• Shield the electrical box with a barrier
• Delineate the electrical box, for example with reflective material.

39. ROADSIDE DESIGN GUIDE
PAGE 39
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
3.5.2 Example 2 – Side Slope on the Outside of a Curve
Calculate the clear zone and evaluate the location of the tree.
Road Type: Two Lane Undivided ADT:
5,000 for both directions Design Speed:
60km/h
Radius of Horizontal Curvature: 900m
Solution:
Step 1 - Determine Base Clear Zone Width (Bcw)
Using Table 3.2 for:
• A foreslope of 1V:4H.(1V:6H to 1V:4H)
• Design speed: 60km/h
• ADT: 5,000 (1,500 – 6,000)
Bcw = 4.5 to 5.0m
Step 2 – Determine Modifier for Outside of Curves (Mc)
Using Table 3.3 for:
• Radius: 900m
• Design speed: 60 km/h,
Mc = 1.1
Step 3– Calculate the Clear Zone Distance (Cz)
Cz = Bcw x Mc
Cz = (4.5 x 1.1) to (5.0 x 1.1)
Cz = 4.95m to 5.5m

40. ROADSIDE DESIGN GUIDE
PAGE 40
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Step 4 – Comment on the location of the tree
• As shown in the figure below, the tree lies outside both minimum and maximum
recommended clear zone distance. Therefore no action is required.
3.5.3 Example 3 – Variable Side Slope
Calculate the clear zone for the variable side slope.
Road Type: Multilane Divided ADT:
8,000 per direction Design Speed:
100km/h Horizontal Alignment: Straight
Surface Condition of the Side Slope: Firm Compacted Soil
Solution:
Step 1 - Determine if the Non-Recoverable Side Slope (1V:3.5H) is a Hazard by Itself:
The surface of the side slope is firm and compacted, therefore, it should be considered as a non-
recoverable slope rather than a hazard by itself (see Section 3.3.3.1)
Step 2 - Determine Base Clear Zone Width (Bcw) for each side slope
Using Table 3.2 for both side slopes:
• For foreslope 1V:10H Bcw = 9.0 to 10.0m
• For foreslope 1V:8H, Bcw = 9.0 to 10.0m
• Foreslope 1V:3.5H is a non-recoverable slope. An errant vehicle would continue until the
bottom of the slope.

41. ROADSIDE DESIGN GUIDE
PAGE 41
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Step 3 – Modifier for Outside of Curves
• This is a straight section of road; a curve modification is not necessary. Mc = 1.0
Step 4 – Calculate the Clear Zone Distance (Cz)
• For side slope 1V:10H, Cz = (9.0 x 1.0) to (10.0 x 1.0) = 9.0 to 10.0m
• For side slope 1V:8H, Cz = (9.0 x 1.0) to (10.0 x 1.0) = 9.0 to 10.0m
• Because foreslopes 1V:10H & 1V:8H both require the same clear zone width of 9.0 to 10.0m,
there is no need to prioritise one distance over the other. If different clear zone distances
were required for the two side slopes, the one with the longest width should have been
selected as the deciding distance.
• The non-recoverable foreslope 1V:3.5H falls within the recommended clear zone distance of
the 1V:10H foreslope. Because an errant vehicle would continue travelling until it reaches
the bottom, the clear zone distance cannot logically end on a non-recoverable slope. In such
cases, an additional clear zone space is needed at the bottom of the non- recoverable slope.
This additional clear zone is referred to as the Clear Runout Area. The width of the Clear
Runout Area should be equal to that portion of the clear zone distance that is located on the
non-recoverable slope. In this example, the clear zone distance based on the recoverable
slope (9.0 to 10.0 meters) overlaps on to the non-recoverable slope by
2.0 to 3.0 meters. Therefore, a Clear Runout Area of 2 to 3m is added from the bottom of the non-recoverable
slope, as shown in the figure below.
• Alternatively, the full width of the non-recoverable slope (3.0m) can be added to the
suggested clear zone distance based on recoverable slope (9.0 to 10.0m). Therefore, for the
combination of all three slopes;
Cz = 9.0+3.0 = 12.0m to 10.0+3.0 = 13.0m.
As shown in the figure below, this would give the same result, as the previous method.

42. ROADSIDE DESIGN GUIDE
PAGE 42
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
3.5.4 Example 4 – High Risk Hazard
Calculate the clear zone and evaluate the location of the high speed railway.
Road Type: Multilane Divided Design
ADT: 25,000 per direction Design Speed:
120km/h Horizontal Alignment: Straight
Solution:
Step 1 - Determine Base Clear Zone Width (Bcw)
Using Table 3.2 for:
• A foreslope of 1V:8H.(1V:6H or flatter)
• Design speed: 120km/h
• ADT: 25,000 (Over 6,000)
Bcw = 11.0 to 12.5m
Step 2 – Modifier for Outside of Curves
This is a straight section of road; a curve modification is not necessary. Mc = 1.0
Step 3 – Calculate the Clear Zone Distance (Cz)
Cz = Bcw x Mc
Cz = (11.0 x 1.0) to (12.5 x 1.0)

43. ROADSIDE DESIGN GUIDE
PAGE 43
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
Cz = 11.0 to 12.5m
Step 4 – Check for High Risk Hazards
• There is a railway line located 3.0m further away from the minimum recommended clear
zone and 1.5m further away from the maximum recommended clear zone.
Step 5 – Comment on the location of the railway line
As shown in the figure above, the railway line does not lie within the normally recommended clear zone
distances. However, as explained in Section 3.2, a small percentage of errant vehicles may still travel further
than the recommended clear zone distance. Considering the high consequences of an errant vehicle reaching
a high-speed railway line, and the relatively close distance of the railway line to the minimum required clear
zone width (3.0m), it can be said that the level of risk posed by the current layout is unacceptable.
Designer/ Engineer should evaluate the following treatment options:
• Remove the railway line
• Relocate the railway line further away from the road
• Shield the railway line with an appropriate roadside barrier
3.6 References
[1] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of State
Highway and Transportation Officials, 2011.
[2] J. Graham and D. Hardwood, “NCHRP Report 247: Effectiveness of Clear Recovery Zones,” NCHRP,
Transportation Research Board, Washington D.C., 1982.
[3] AASHTO, Guide for Selecting, Locating and Designing Traffic Barriers., Washington D.C.: American
Association of State Highway and Transportation Officials, 1977.
[4] CEDR, “SAVERS (Selection of Appropriate Vehicle Restraint Systems) - WP1: Defining the Different
Parameters which can Influence the Need and Selection of VRS (Unpublished Report),” Conference of
European Directors of Roads, 2014.
[5] P. Cooper, “Analysis of Roadside Encroachments - Single Vehicle Run-off-road Accident Data Analysis
for Five Provinces,” B.C. Research, Vancouver, British Columbia, Canada,

44. ROADSIDE DESIGN GUIDE
PAGE 44
03 CONCEPT AND CALCULATION OF CLEAR ZONE FIRST EDITION -DECEMBER 2016
March 1980.
[6] M. King and D. Sicking, “NCHRP 492 - Roadside Safety Analysis Program Engineer's
Manual,” Transportation Research Board, Washington, D.C., 2003.
[7] Norwegian Public Roads Administration, “Manual 231E, Vehicle Restraint Systems and
Roadside Areas,” Norwegian Directorate of Public Roads, Oslo, 2011.
[8] FGSV, Traffic Management Work Group, “Guidlines for passive protection on roads by vehicle
restraint systems,” FGSV Verlag GmbH, Koln, 2009.

45. ROADSIDE DESIGN GUIDE
PAGE 45
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4 IDENTIFICATION OF HAZARDS
4.1 Introduction
A hazard is a roadside feature or object that can cause physical, economic, time-based or strategic harm or
loss, if reached by an errant vehicle (see Section 2.1).
Identification of roadside hazards is an integral part of the risk mitigation process. Hazards that lie within the
recommended clear zone area (see Chapter 3) are under the risk of being reached by errant vehicles, which
may lead to injury or even fatal accidents. Therefore, it is very important to identify and evaluate all hazards
within the clear zone, so that suitable countermeasures can be applied.
However, it may not always be clear to the engineer/designer, whether a specific roadside feature should be
considered a hazard. For example, a roadside ditch may be considered a hazard or a traversable roadside
feature, depending on its geometry. A tree may be considered a hazard, depending on the diameter of its
trunk.
This chapter provides guidance to designer/engineers in the identification of roadside hazards. The chapter
presents a general overview of the types and properties of roadside features that may be considered as
hazards. Each type of feature is presented with local photos and physical properties to help designers
determine if the feature should be considered a hazard.
Information presented in this chapter does not cover every single possible roadside hazard and therefore
should be taken as a general guidance, rather than a definitive check-list. Engineering judgment should be
used to assess possible hazards on a case by case basis, prior to a final decision.
4.2 Overview of Roadside Hazards
Table 4.1 presents an overview of the common roadside features that may be considered as a hazard. As can
be seen from the table, roadside hazards can be grouped into two main categories:
• Hazards with consequences to vehicle occupants;
• Hazards with consequences to vehicle occupants and third parties.
The first group of hazards are the roadside objects and terrain features, which may cause harm or loss to the
occupants of the errant vehicles.
The second group of hazards are the roadside features and areas, which may also have consequences for
third parties. The term “third parties” refers to a group or collection of people in a public space, such as school,
hospital or railway that might be injured in numbers by an errant vehicle or by a hazard that is hit by an errant
vehicle or a high value asset or facility that might be adversely affected by such an event. These hazards are
often referred to as “high risk hazards”. A more detailed description for each of the hazards is presented in the
following sections.

46. ROADSIDE DESIGN GUIDE
PAGE 46
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Table 4.1 – Guidance towards potential roadside hazards [1]
Type of Hazard Examples of Parameters to Evaluate
A - Hazards with Consequences to Vehicle Occupants
Roadside
Topography
Foreslopes (Embankments)
Backslopes (Cutting Slopes)
Gradient
Height
Compaction
Surface Condition
Ditches
Ditch Type
Gradient of Foreslope
Gradient of Backslope
Bottom Width
Compaction
Surface Condition
Transverse Slopes
Gradient Road
Type Design
Speed
Compaction
Surface Condition
Edges of Bridges & Retaining Walls Drop Height
Non-deformable
Single
Objects
Trees
Trunk Diameter
Stump Height
Overhead Gantries and Cantilevers Passively Safe or Not
Roadside Sign Supports
Support Structure
Diameter & Thickness of Support Posts
Passively Safe or Not
CCTV Masts and Luminaire Supports Passively Safe or Not
Concrete Foundations Protruding from the Ground Height from the Ground
Bridge Piers, abutments, tunnel portals Always considered as a hazard
Bridge Railing Ends & Ends of Concrete Barriers Always considered as a hazard
Above Ground Equipment Passively Safe or Not
Drainage Pipes & Culverts
Level with Ground Profile?
Pipe Diameter
Traversable or not?
Non-deformable
Continuous
Objects
Non-deformable extensive obstacles parallel to direction of
travel
Passively Safe or Not
Retaining walls Surface Roughness
Noise barriers Barrier Incorporated or not?
Fencing (Stone wall, wooden fence, concrete wall, etc.) Passively Safe or Not
Roadside Barriers Is it Necessary or not?
Permanent bodies or streams of water
Water Depth
Flooding Expected or not?
B - Hazards with Consequences to 3rd Parties
Adjacent Roads / Opposite Side of Dual Carriageways
Volume of Adjacent Road
Speed of Adjacent Road
Locations of Hazardous Material Storage such as Chemical Plants Always considered as a hazard
Structures at risk of collapse, support and load bearing Always considered as a hazard
Places of public gathering and heavy pedestrian activity
Average Number of People
Volume of Pedestrian Traffic
Average Time People are Exposed
Heavily used bicycle paths Volume of Bicycle Traffic
Structures at risk of collapse Always considered as a hazard
Adjacent Rail lines
Number of Trains per day
Average Speed of Trains
Area of environmental concern such as source of drinking water Always considered as a hazard

47. ROADSIDE DESIGN GUIDE
PAGE 47
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3 Hazards with Risk to Vehicle Occupants
4.3.1 Roadside Topography
4.3.1.1 Fill Slopes / Embankments
Fill slopes / embankments are the front slopes extending outward and downward from the shoulder or verge
hinge point to intersect with the natural ground line. Consequences of reaching a fill slope for an errant vehicle
may be more serious depending on height, gradient, surface condition and compactness of the slope. A steep
embankment with a very high drop, such as the one shown in Figure 4.1, is an obvious hazard for errant
motorists. However, for embankments with less steep side slopes and lower drops, it may not always be
obvious if a foreslope should be considered as a hazard.
Figure 4.1 – A hazardous embankment
A foreslope of 1V:3H or steeper, such as the one shown in Figure 4.2, is considered as critical (see Section
3.3.3.1) and a hazard by many countries around the world (such as US [2], UK [3], Germany [4], etc.). This is
because experience shows that the likelihood of a rollover increases significantly when the slope is steeper
than the 1V:3H level.
Figure 4.2 – Critical side slope by an interchange ramp

48. ROADSIDE DESIGN GUIDE
PAGE 48
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Foreslopes which have a gradient between 1V:3H and 1V:4H are generally considered as non- recoverable
by many countries around the world (such as US [2], UK [3], Australia [5], etc.). A vehicle entering a non-
recoverable slope is generally not expected to overturn, but it is expected to continue to the bottom of the slope
as it cannot generally regain control and return to the road. As long as they are free of obstacles and have a
traversable smooth surface, these slopes are not usually considered as hazards. However, the sandy roadside
environment of Abu Dhabi introduces an additional level of risk, as local experience indicates that vehicles are
more likely to overturn on areas of loose sand; even on side slopes flatter than 1V:3H. Unfortunately the
available research on the effect of loose sand on rollover incidents is not sufficient to provide a quantifiable
relationship. For this reason, engineering judgment should be used when evaluating fill sections with side
slopes from 1V:3H to 1V:4H and the height of the embankment and the compactness of the soil should also
be part of the evaluation process.
If the side slope has a loose sandy surface, which may cause vehicle snagging, the designer/engineer may
consider foreslopes up to 1V:4H as non-traversable and therefore a hazardous slope. Conversely, if the
foreslope has a firm compacted surface, or if it is treated with a concrete surface, as shown in Figure 4.3, it
may not be considered as a hazard for gradients between 1V:3H and 1V:4H, subject to engineering judgment.
Figure 4.3 – Concrete covered foreslope
Fill slopes which are 1V:4H or flatter are considered as traversable and therefore generally not considered a
hazard. However 1V:6H is the recommended gradient for fill sections in new roadsby the Abu Dhabi Road
Geometric Design Manual [6]. Therefore, ideally, the designer/engineer should aim for foreslopes of 1V:6H
or flatter. In addition to increased roadside safety, such flat foreslopes are also ideal for maintenance
operations and erosion control.
Figure 4.4 summarizes the recommended approach on evaluating if a fill slope should be considered as a
hazard or not. This is based on the AASHTO Roadside Design Guide [2] approach and modified for the
requirements of the Abu Dhabi road network.
A fill section should ideally have a smooth surface, be free of rocks and any other obstacles. Fill sections with
non-smooth surfaces may be considered as hazards, subject to engineering judgment.

49. ROADSIDE DESIGN GUIDE
PAGE 49
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.4 – Hazard assessment for fill slopes
The following countermeasures should be considered, for hazardous fill slopes that lie within the clear zone:
• Flatten the side slope
• Provide adequate compaction for loose soil
• Provide a smooth surface of the slope
• Stabilise the top soil with cement (as shown in Figure 4.3)
• Shield the slope with a barrier
EMBANKMENT IS CONSIDERED
TRAVERSABLE AND THEREFORE
IT IS NOT A HAZARD
DECISION BASED ON ENGINEERING
JUDGMENT AND SURFACE CONDITION
EMBANKMENT IS NOT
CONSIDERED TRAVERSABLE
AND THEREFORE IT IS A HAZARD

50. ROADSIDE DESIGN GUIDE
PAGE 50
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3.1.2 Backslopes / Rock Cuts
A backslope in a cut section may be traversable and therefore not a hazard depending on its relative
smoothness and the presence of fixed obstacles. It may not be a significant obstacle if the front slope between
the roadway and the base of the backslope is traversable (1V:6H or flatter) and the backslope is obstacle-free.
However, a steep, rough-sided rock cut, as shown in Figure 4.5, is normally considered as a hazard and should
begin outside the clear zone or be shielded. A rock cut is considered to be rough-sided when the face is likely
to cause excessive vehicle snagging, rather than provide relatively smooth redirection.
Figure 4.5 – A hazardous rock cut, shielded by barrier
A common hazard associated with rock cuts is the rocks and boulders which may fall onto the road. These
rocks and boulders pose a significant danger to vehicles. To counter this problem, roadside ditches that are
wide enough to capture the falling rock, as shown in Figure 4.6, are one solution provided alongside rock cuts.
Other solutions which may be used include providing nets and stabilising surface with spray concrete.
The bottom flat section of the ditches for capturing falling rocks should also be considered as hazards and
therefore should not be located within the clear zone. If the ditch and the cut face have to be within the clear
zone, they should be shielded by an appropriate roadside barrier.
Figure 4.6 – Typical rock cut section [6]

51. ROADSIDE DESIGN GUIDE
PAGE 51
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3.1.3 Roadside Ditches
On facilities without curbs, roadside ditches may be provided adjacent to embankment locations and in cut
sections to control drainage, as shown in Figure 4.7. A smooth and relatively flat ditch, with rounded corners
can be safely traversable and not considered a hazard. These traversable ditches should be considered as
variable slopes, for clear zone calculation purposes (see Section 3.4.5.1). Conversely a ditch with steeper
slopes and non-smooth toe transitions may not be safely traversable and could therefore pose the risk of
overturning or even launching an errant vehicle into the air. These non-traversable ditches should be
considered a hazard, and ideally should not be located within the clear zone.
Figure 4.7 – Typical roadway ditch section [6]
Figure 4.8 and Figure 4.9 give guidance on the assessment of basic ditch configurations, from a hazard
perspective, based on the profile, foreslope and back slope. In the figures, light grey areas represent
traversable geometry combinations as recommended by the AASHTO Roadside Design Guide [2]. Ditches
with these properties are not considered hazards. White areas are considered as non-traversable and a hazard
and therefore should be redesigned to be located within the traversable area.

52. ROADSIDE DESIGN GUIDE
PAGE 52
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Ditch sections which are considered a hazard should be redesigned to a traversable cross section to eliminate
the risk, if practical,. However, if a redesign is not practical, a roadside barrier may be warranted.
Note: This chart is applicable to flat bottom ditches with bottom widths equal to or greater than 1.2 m.
Figure 4.8 – Assessment of cross sections for flat bottomed ditches [2]
HAZARDOUS AND
NON-TRAVERSABLE
DITCH
(NON-PREFERABLE
CROSS SECTION)
NON-HAZARDOUS AND
TRAVERSABLE DITCH
(PREFERABLE
CROSS SECTION)

53. ROADSIDE DESIGN GUIDE
PAGE 53
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Note: This chart is applicable to all V-ditches and flat-bottom ditches with bottom
widths less than 1.2 m.
Figure 4.9 – Assessment of cross sections for V-profile ditches [2]
In addition to the geometry, the ditch should be smooth, well graded and should have well compacted firm
ground. Roadside hardware such as road signs, luminaire supports, electrical cabinets, etc. should not be
located in or near ditch bottoms, as shown in Figure 4.10, even if they are designed to be passively safe. This
is because an errant vehicle reaching the ditch is likely to be funnelled into the bottom of the ditch. Therefore,
any hazardous object located at or near the ditch bottom would be more likely to get hit. Furthermore, due to
the geometry of the ditch, an errant vehicle may hit the roadside hardware while sliding sideways or even go
airborne. In such an impact the passively safe system may not function as intended. For these reasons
roadside hardware should be moved beyond the ditch and outside of clear zone.
HAZARDOUS AND
NON-TRAVERSABLE
DITCH
(NON-PREFERABLE
CROSS SECTION)
NON-HAZARDOUS AND
TRAVERSABLE DITCH
(PREFERABLE
CROSS SECTION)

54. ROADSIDE DESIGN GUIDE
PAGE 54
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.10 – Incorrect and correct placement of roadside hardware around ditches
4.3.1.4 Transverse/Intersecting Slopes
Transverse slopes are slopes that are created by intersecting roadways, median crossovers, berms or
driveways. A transverse slope is actually the foreslope located at the side of the intersecting road, as
shown in
Figure 4.11. However, from the perspective of vehicles using the main road, these are slopes which increase
in height in the direction of traffic. As an errant vehicle may engage them almost head-on, depending on the
gradient of the slope, these may act as a ramp and launch an errant vehicle in the air, or may even act as a
rigid object and result in a head-on impact. For this reason the gradient of the transverse slope is of importance
when assessing whether it should be considered a hazard or not.
Roadside hardware located at the bottom of the
ditch
✓
Roadside Hardware
located beyond the
ditch; outside of the
clear-zone
F
or
e
sl
o
Foreslope
Transverse Slope
Direction of
Travel
Transverse Slope

55. ROADSIDE DESIGN GUIDE
PAGE 55
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.11 – Example of a transverse slope at an intersecting road
Transverse slopes located in the vicinity of freeways and expressways should be considered as hazards.
However, ideally there should not be any transverse slopes located at the sides of freeways and expressways
as these should be access-controlled via ramps, and perpendicular access at grade intersections should not
permitted. Transverse slopes may exist in the median of freeways and expressways at the areas of emergency
access; however, these areas should already be shielded by barriers under DoT’s policy to stop illegal U-
Turns.
For other road types, transverse slopes should be as flat as possible to eliminate any risk of ramping. A
transverse slope of gradient 1V:10H or flatter is considered desirable and therefore not a hazard. The
designer/engineer should ideally aim for transverse slopes of 1V:10H or flatter. However, transverse slopes
this flat may not always be applicable due to right of way and drainage restrictions. If this is the case a
transverse slope of gradient 1V:6H or flatter may be considered acceptable, if the speed is considered low
enough to not pose a significant risk. Speeds under 80kph are generally considered low speed. Transverse
slopes which are steeper than 1V:6H pose the risk of ramping and therefore should always be considered a
hazard.
Once a transverse slope is identified as a hazard, the designer/engineer should assess the option of flattening
the slope to an acceptable level. If the slope cannot be flattened it should be shielded by a roadside barrier.
Transverse slopes should be free of roadside hardware such as road signs, luminaire supports, electrical
cabinets, because an errant vehicle may get launched into these hazards head on. Passively safe systems
located on a transverse slope may not always function as intended either. This is because hitting the slope
head on would cause the front suspensions of the errant vehicle to get compressed and this would alter the
vehicle dynamics and impact height with the passively safe system.
The evaluation of a transverse slope application at a specific site should depend upon many factors, including:
• Height of transverse embankment,
• Traffic volumes,
• Presence of culverts and practicality of treating the culvert end,
• Construction costs, and
• Right-of-way and environmental impacts.
4.3.1.5 Edges of Bridges & Edges of Retaining Walls
A vehicle falling off the edge of a bridge or the edge of a retaining wall may lead to severe injury. A vehicle
falling off the edge of the bridge shown in Figure 4.12 is highly likely to cause severe or fatal injury. The edge
of such a bridge should be considered a hazard. However for bridges spanning a much smaller and lower gap,
it may not be obvious if the edge of the bridge should be considered a hazard or not.
In Abu Dhabi, edges of bridges and retaining walls which have a drop height over 1m, as shown in Figure
4.13, should be considered a hazard, and an appropriate bridge parapet should be provided.

56. ROADSIDE DESIGN GUIDE
PAGE 56
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
For more details on the selection and application of bridge parapets, refer to Chapter 7.
Figure 4.12 – Example of bridge edge with a very high drop
Figure 4.13 – Bridge drop height
4.3.2 Non-deformable Single Objects
4.3.2.1 Trees
Trees with a trunk diameter over 100mm at maturity, measured from 400mm above ground level should be
considered a hazard. Groups of small trees with trunk diameter less than 100mm may also be considered a
hazard, if located close to each other. Tree stumps which protrude more than 150mm from the ground should
also be considered a hazard.

57. ROADSIDE DESIGN GUIDE
PAGE 57
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.14 – Trees located in a median
Designers and engineers should remember that the removal of trees is a sensitive issue within Abu Dhabi and
therefore may not be acceptable. It is for this reason that designer and engineers should asses the position
of trees and landscaping carefully for new road projects; with a special focus on possible future expansion of
the road.
4.3.2.2 Overhead Gantries & Cantilever Sign Supports
In Abu Dhabi, roadside signs are required to carry both Arabic and English languages. The dual language
requirement leads to larger and heavier road signs. Overhead gantries and cantilever supports are often
required to support these large signs, as shown in Figure 4.15.
Figure 4.15 – A cantilever sign support

58. ROADSIDE DESIGN GUIDE
PAGE 58
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Overhead gantries and cantilever sign supports should always be considered hazards. These structures, due
to their size and weight, are not designed to yield or breakaway during impact and pose a risk to the occupants
of errant vehicles. They also pose a risk of collapse on other road users during an impact by a vehicle. For
these reasons, the option of using a passively safe system is generally not available. Also, it is usually not
possible to relocate them too far off the road, as they should be clearly visible to road users.
Due to these limitations, roadside barriers are often the only treatment option available to reduce the risk posed
by these systems when they are located within the clear zone.
4.3.2.3 Roadside Sign Supports
Roadside sign supports may be considered crashworthy or a hazard, depending on their structure. Any support
structure which would not yield and cause the impacting vehicle to stop abruptly should be considered a
hazard.
Unlike gantries and cantilevers, large and small roadside sign supports can be designed to yield, break away
or absorb the energy during an impact. Signs with an area greater than 5m2
may be defined “large” and those
with an area smaller or equal to 5m2
may be defined “small” [2], as shown in Figure 4.16. These passively safe
sign supports are not considered hazards if their impact performances are proven in accordance with an impact
test standard acceptable by Abu Dhabi DoT, i.e. NCHRP350, MASH or EN12767. See Chapter 5 for more
information on the passively safe support structures and their testing.
Figure 4.16 – Small (left) and large (right) roadside sign supports
In addition to the impact worthy systems mentioned above, supports which are below certain physical
properties may also be accepted as passively safe and therefore not a hazard. These include:
• Steel posts that do not exceed the equivalent section properties of a tubular steel post
having an external diameter of 89 mm or less and a wall thickness of 3.2 mm or less [7]
• Wood posts with dimensions of 100 mm x 100 mm or less [2]
Once a hazardous sign support is identified within the clear zone, the designer/engineer should first consider
removing or relocating the sign, as this would eliminate the risk of impact. Removal or relocation is not always
practical as signs should remain near the travelled way to serve their

59. ROADSIDE DESIGN GUIDE
PAGE 59
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
intended purpose, therefore passively safe systems or shielding with a vehicle restraint system should be
considered.
Another important factor to consider is the spacing of consecutive sign posts. Ideally, individual sign posts
should be as far away from each other as possible. This is firstly because consecutive signs in a small
area would catch the attention of drivers for a longer time and may cause confusion, which in turn may
lead to accidents. The second reason is that the probability of an errant vehicle hitting a pole increases as
the pole spacing decreases, as shown in Figure 4.17 – Effect of pole spacing
4.3.2.4 CCTV Masts and Luminaire Supports
Similar to sign supports, luminaire supports and CCTV masts are also considered as hazards if not designed
to be passively safe. Currently, luminaire supports which are up to a height of 18,5m & a mass of 450kg may
be designed to be passively safe [2]. However, passively safe designs are not generally possible for high-level
lighting supports and CCTV masts, which are fixed-base support systems. For more information on the
assessment of passive safety of luminaire supports please refer to Chapter 5.

60. ROADSIDE DESIGN GUIDE
PAGE 60
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.17 – Effect of pole spacing
Figure 4.18 – Examples of large luminaire support (left) and CCTV mast (right)

61. ROADSIDE DESIGN GUIDE
PAGE 61
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Once a hazardous luminaire support is identified with the clear zone, the designer/engineer should first
consider removing or relocating the poles, as these would eliminate the risk of impact completely. However,
removal or relocation is not always practical as illumination and the CCTV mast may need to remain close to
the travelled way to serve their intended purpose. Therefore, passively safe systems or shielding with a vehicle
restraint system should be considered.
Additionally, similar to the sign posts, spacing of the illumination and CCTV masts is an important factor to
consider. As shown in Figure 4.17-Effect of pole spacing, the probability of a vehicle hitting a hazard goes
up as the spacing between the poles goes down. Therefore the designer/engineer should aim to minimise
the number and frequency of poles as reasonably possible.
4.3.2.5 Concrete Foundations Protruding from the Ground
Concrete foundations of roadside furniture such as luminaire supports, control boxes, etc. are rigid objects,
and can cause significant harm if impacted by errant vehicles.
Ideally, concrete foundations should be level with the ground. However, soils in Abu Dhabi are generally
extremely corrosive. One of the applied methods to tackle corrosion in Abu Dhabi is to elevate the roadside
furniture above the ground level with concrete foundations protruding from the ground, as shown in Figure
4.19. This way the contact of metal with soil is partly prevented.
However, breakaway systems such as luminaire and sign supports, would not work as intended if the concrete
foundations which they are installed on are protruding high above the ground. Concrete foundations which
protrude more than 150mm from the ground level should be considered as individual roadside hazards,
regardless of the system installed above them.
Proper compaction of the soil around concrete foundations is also of extreme importance. Wind may blow
loose sand off and expose the sides of an originally level concrete foundation. This may transform the
foundation into a hazard.
Figure 4.19 – Examples of concrete foundations protruding from the ground
4.3.2.6 Bridge Piers and Abutments
Bridge piers and abutments, as shown in Figure 4.20, are rigid load bearing structures which pose a significant
risk to the occupants of errant vehicles in the event of an impact. These structures are also at risk of collapse
if not protected properly and suffer a high energy impact by a heavy vehicle. For these reasons, bridge piers
and abutments should always be considered hazards.

62. ROADSIDE DESIGN GUIDE
PAGE 62
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
It is often not possible to remove or relocate these structural elements. Shielding with an appropriate vehicle
restraint system is often the only available option to mitigate the risk associated with these hazards.
Figure 4.20 – A bridge pier (left) & a bridge abutment (right)
4.3.2.7 Bridge Railing Ends & Ends of Concrete Barriers
Ends of bridge railings and concrete barriers, as shown in Figure 4.21, are rigid obstacles that are at risk of
head-on impacts if left unprotected. They should always be considered hazards, and therefore, any restraint
system should be properly connected to it to eliminate the hazard.
Figure 4.21 – Examples of unprotected bridge railing and concrete barrier ends
Due to their intended function, these systems are more likely to be within the clear zone and therefore should
be protected with one of the following options:
• Shield with a crash cushion,
• Connect to a crashworthy terminal, via proper transition,
• Connect to an adjacent barrier system via proper transition.
Treatment is always necessary for the approach ends in both dual and single carriageway roads. On single
carriageways the departure ends should also be treated as these may be reached by vehicles travelling on
the opposite direction.
For more information on crashworthy terminals, see Chapter 9. For more information on crash cushions see
Chapter 10. For more information on transitions see Chapter 11.

63. ROADSIDE DESIGN GUIDE
PAGE 63
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3.2.8Other Roadside Furniture, including Control Cabinets,
Electricity Cabinets, Speed Cameras, etc.
In addition to the specific examples given in the previous sections, there may be other items of roadside
furniture located within the clear zone, such as control cabinets, electricity cabinets, and speed cameras, as
shown in Figure 4.22.
In general, these objects should be considered hazards if they are expected to cause vehicle snagging and
an abrupt stop to an impacting errant vehicle. Conversely, if they are not expected to cause vehicle snagging,
they may not be considered hazards. One way of achieving this is the use of passively safe systems. For more
information on passive safety, refer to Chapter 5.
Figure 4.22 – Examples of roadside furniture as hazards
As shown in Figure 4.22, these objects come in different shapes and sizes, from a single electrical box to
multiple poles. When evaluating poles, guidance provided in Sections 4.3.2.3 and 4.3.2.4 should be followed.
When evaluating foundations protruding from the ground, guidance provided in Section 4.3.2.5 should be
followed.
For electrical boxes and control cabinets, it is possible to use passively safe systems. These systems are
designed to break away to minimize the forces exerted on the impacting vehicle, as shown in Figure 4.23.
They are also designed with electrical connections which disconnect during an impact to eliminate the risk of
electrocution. More information on these systems is given in Chapter 5.
Figure 4.23 – Test performance of a passively safe control cabinet [8]

64. ROADSIDE DESIGN GUIDE
PAGE 64
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3.2.9 Drainage Pipes and Culverts
Drainage pipes and culvers are conduits which convey water flow through a roadway embankment or past
some other type of flow obstruction. Drainage pipes and culverts are constructed from a variety of materials
and shapes; from a single metal pipe to a multi-cell concrete box, as shown in Figure 4.24.
.
Figure 4.24 – Examples of a pipe (a) and a multi-cell box culvert (b) [9]
Pipes and culverts can be classified as either cross-drainage or parallel-drainage, according to their orientation
relative to the direction of travel, as shown in Figure 4.25.
Figure 4.25 – Cross and parallel drainage
Sections provide detailed guidance on the hazard assessment of cross and parallel drainage pipes and
culverts. In general, pipes and culverts located within the clear zone should be considered hazards if they are
not designed to be traversable. A pipe or culvert may be considered as non- traversable and therefore a
hazard, if:
• Its inlet and outlet is not matching the surface of the side slopes (see Figure 4.26);
• It has large gaps, into which a vehicle may fall and stop abruptly (see Figure 4.27);
• It has features such as headwalls or pipe ends protruding from the ground, which may
cause an errant vehicle to stop abruptly (see Figure 4.30); and if
• It is high enough (over 1m drop height see section 4.3.1.5) to be considered as a bridge
(see Figure 4.24).
Direction
of Travel

65. ROADSIDE DESIGN GUIDE
PAGE 65
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Cross Drainage Structures:
Cross drainage structures are designed to carry water underneath the roadway embankment and are in
perpendicular orientation to the direction of travel. A cross drainage structure can be anything from a single
pipe to a multi-cell box as shown previously in Figure 4.24.
Research [10] shows that a small cross drainage pipe, with a diameter equal to or less than 900mm, is
traversable and therefore not a hazard, as long as long as the pipe inlets are matched with the slope of the
embankment.
A pipe inlet which is protruding from the ground, as shown in Figure 4.26a, is a hazard and should be levelled
with the slope surface, as shown in Figure 4.26 .
Figure 4.26 – Hazardous (left) [9] and traversable (right) pipe inlets [11]
Cross drainage structures with an opening wider than 900mm are considered as non-traversable and a hazard
[2]. Figure 4.27 shows an example of a hazardous cross-drainage culvert with a large opening. An errant
vehicle reaching such a culvert may overturn on impact or fall into the opening and come to an abrupt stop.
Figure 4.27 – Example of a hazardous cross-drainage culvert; with a large opening
Hazardous culverts with large openings can be made traversable by covering the opening with appropriate
pipe runners or a safety grate, as shown in Figure 4.28.
Diameter < 900mm
✓

66. ROADSIDE DESIGN GUIDE
PAGE 66
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.28 – Traversable safety grate (left) [9] and pipe runners (right) [11]
Bar spacing and pipe diameter are important parameters when designing traversable pipe runners or bar
grates. Figure 4.29 shows the recommended design criteria for safety grates and pipe runners, by AASHTO
Roadside Design Guide [2].
Figure 4.29 – Design criteria for safety treatment of pipes and culverts [2]
Bar grates and pipe runners designed to the above criteria were crash tested at the Midwest Roadside Safety
Facility in United States [12]. These tests showed that vehicles can traverse cross-drainage structures with
grated-culvert end sections constructed of steel pipes spaced on 760 mm centres on slopes as steep as 1V:3H
and at speeds ranging from 30 km/h to 100 km/h. The results clearly demonstrated that the culvert safety
grates and pipe runners recommended in Figure 4.29 are traversable and meet the safety performance
guidelines set forth in NCHRP-350.
Modifications to the culvert ends to make them traversable should not significantly decrease the hydraulic
capacity of the culvert. Safety treatments should be hydraulically efficient. The 750mm bar spacing
recommended in this manual is not expected to significantly change the flow capacity of the culvert pipe unless
debris accumulates and causes partial clogging of the inlet. The designer should consider shielding the
structure with a barrier if significant hydraulic capacity or clogging
Span Length
Maximum 750mm
Up to 3.65 m.............................................................75 mm
3.65 - 4.90 m ............................................................87 mm
4.90 – 6.10 m........................................................... 100 mm
Pipe Runner Diameter

67. ROADSIDE DESIGN GUIDE
PAGE 67
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
problems could result. Where flood debris is not a concern for median drainage, much smaller openings
between bars may be acceptable and grates similar to those commonly used for drop inlets may be
appropriate.
Another potential hazard related to culverts is headwalls protruding from the ground, as shown in Figure 4.30.
Ideally, culverts should be level with the surface and no structural element, which may cause an impacting
vehicle to stop abruptly, should protrude from the ground. Such headwalls should be considered as hazards.
Figure 4.30 – Examples of hazardous culvert headwalls protruding from the ground [13]
Non-traversable cross drainage culverts located within the clear zone, as shown in Figure 4.31 are hazards.
Figure 4.31 – A cross-drainage culvert within the clear zone area
Once a hazardous cross drainage culvert is identified within the clear zone, the following treatment options
should be considered:
1. Remove the structure or extend it beyond clear zone. For inlets of pipes and culverts that
cannot be readily made traversable, designers may consider extending the structure so the
obstacle is located beyond the clear zone, as shown in Figure 4.32. However, this practice
does not completely eliminate the possibility of the pipe being hit. If the extended culvert
headwall is the only significant fixed object at the edge of the clear zone and the roadside is
generally traversable to the right-of-way line elsewhere, simply extending the culvert to
beyond the clear zone may not be the best alternative, particularly on freeways and
expressways. However, extending individual structures to the same minimum distance from

68. ROADSIDE DESIGN GUIDE
PAGE 68
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
traffic may be appropriate if the roadway has numerous fixed objects at the edge of the clear zone.
Figure 4.32 – Cross-drainage culvert extended beyond the clear zone
2. Cover the culvert with a traversable safety grate. The preferred treatment is to extend or
shorten the cross-drainage structure to intercept the roadway embankment and to match
the inlet slope to the front slope with a traversable safety grate or pipe runners, as shown in
Figure 4.33. The design of the safety grate and pipe runners should conform to the criteria
shown in Figure 4.29.
Figure 4.33 – Cross-drainage culvert changed with traversable design
3. Shield the structure with a barrier. If the hazardous drainage structure cannot be removed,
relocated or made traversable, then it should be shielded with an appropriate roadside
barrier, with an appropriate crash worthy terminal leading to it.
Parallel Drainage Structures:
Parallel drainage structures are those that are oriented parallel to the main flow of traffic. They are typically
used under driveways, access ramps, intersecting side roads, and median crossovers, as shown in Figure
4.34. As explained in Section 4.3.1.4, transverse/intersecting slopes should not exist on high speed, fully
access controlled roads such as motorways and expressways. Therefore parallel drainage structures should
not exist on these high speed roads either.

69. ROADSIDE DESIGN GUIDE
PAGE 69
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.34 – Example of a non-traversable parallel drainage structure [13]
As an errant vehicle is likely to impact the structure at approximately 90, parallel drainage structures represent
a potential hazard. Ideally, any parallel drainage structures will be located outside of the clear zone; however,
this will often not be practical because of the typical locations for these structures. In addition, the designer
must coordinate their design with that of the surrounding transverse slope (See section 4.3.1.4) to minimize
the hazard.
Research shows that parallel drainage pipes with a diameter equal to or less than 600mm are traversable [10]
and therefore not a hazard, as long as long as the pipe inlets are matched with the slope of the embankment
and the gradient of the transverse slope is 1V:6H or flatter, as recommended in Section 4.3.1.4.
Pipes with a diameter over 600mm are considered non-traversable and a hazard. However, just like cross
drainage structures, it is possible to make parallel drainage structures traversable via safety grates or pipe
runners, as shown in Figure 4.35.
Figure 4.35 – Traversable safety grate (left) [13] and pipes (right) [14]
Bar spacing and pipe diameter are important parameters when designing traversable safety grates. Research
has shown that for parallel drainage structures, a grate consisting of pipes set on 610mm centres will
significantly reduce wheel snagging [2]. Figure 4.36 shows a possible design for parallel safety grates,
recommended by AASHTO Roadside Design Guide [1].

70. ROADSIDE DESIGN GUIDE
PAGE 70
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.36 – Design criteria for safety treatment of parallel drainage structures [2]
Once a hazardous parallel drainage structure is located within the clear zone, the designer/engineer should
consider the following treatment options:
4. Remove the structures. The first treatment option to be considered is the removal of the
parallel drainage structure. Although this option completely eliminates the risk posed by this
hazard, it may not always be applicable due to drainage requirements. In low-volume
locations, such as local or collector roads, it may be possible to eliminate the parallel pipes
by constructing an overflow section on the intersecting side road.
5. Relocate the structure. The second treatment option to consider is the relocation of the
drainage feature to outside the clear zone, where it would be less likely to be reached by an
errant vehicle. Figure 21 presents a suggested design treatment.
Figure 4.37 – Alternate location for a parallel drainage culvert [2]
6. Cover the structure with a traversable safety grate. The third option is to make the drainage
feature traversable by matching its inlet to the slope surface and covering with a safety
grate or pipe runners as shown in Figure 4.36.

71. ROADSIDE DESIGN GUIDE
PAGE 71
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
7. Shield the structure with a barrier. If the hazardous drainage structure cannot be removed,
relocated or made traversable, then it should be shielded with an appropriate roadside
barrier, with an appropriate crash worthy terminal leading to it.
The following summarizes the preferred practices on the roadside safety treatment of parallel drainage
structures within the clear zone:
• Pipe diameter  450 mm. For these pipe sizes, a projecting end is acceptable.
• Pipe diameter > 450 mm to  600 mm. For these pipe sizes, the end of the pipe should match
the slope of the surrounding transverse slope. The opening to the pipe may remain.
• Pipe diameter > 600 mm. For these pipe sizes, the end of the pipe should match the
surrounding transverse slope, and the designer should provide grates across the opening.
This will reduce wheel snagging if an errant vehicle impacts the pipe end.
4.3.3 Non-deformable Continuous Objects
4.3.3.1 Fencing and Walls
Fencing and walls may be required along roads to protect drivers from unexpected intrusions from outside of
the right-of-way line. Fencing deters unauthorised and unsafe entry to the roadway by vehicles, pedestrians,
or animals.
Figure 4.38 – Pedestrian fencing along an urban road
Fence types used in Abu Dhabi include: woven wire, chain link, camel fence and pedestrian fences [6].
Fences and walls which are not designed to be passively safe should be considered hazards if they are located
within the clear zone. Unfortunately, currently there is no testing standard available specifically for the test of
such systems. For this reason engineering judgment should be used to assess the passive safety of such
systems. For more information on fencing, see Chapter
16.5 of Abu Dhabi Road Geometric Design Manual [6].

72. ROADSIDE DESIGN GUIDE
PAGE 72
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3.3.2 Retaining Walls
Retaining walls may be considered hazards, depending on the smoothness of the surface and whether the
surface of the wall is sturdy enough to resist the shock of the initial impact with a vehicle.
Generally, the following types of retaining walls should be considered a hazard:
• Retaining walls which are covered by decorative panels for aesthetic purposes, such as the
one shown in Figure 4.39. If these walls are not designed to resist structural loading such as
that from an errant vehicle, there is a risk of an impacting vehicle snagging and stopping
abruptly, instead of sliding along the surface.
• Retaining walls with structural elements protruding from the surface, which may cause
vehicle snagging, such as the one shown in Figure 4.40.
• Retaining walls with a non-smooth surface, such as the types made of stacked prefabricated
elements, with large protruding parts.
Conversely, a retaining wall may not be considered a hazard if it has a smooth surface which would not cause
vehicle snagging and let the impacting vehicle slide along the surface. An example of this may be a reinforced
concrete retaining wall.
Figure 4.39 – Potentially hazardous retaining wall; covered with decorative panels [6]
Figure 4.40 – A retaining wall; with structural elements protruding from the surface

73. ROADSIDE DESIGN GUIDE
PAGE 73
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
When a hazardous retaining wall is located within the clear zone, it should be shielded with a barrier. This may
either be achieved with an incorporated and integral concrete barrier shape, as shown in Figure 4.39, or with
a separate barrier system, placed offset from the shoulder, as shown in Figure 4.40.
In addition, the following will apply to the roadside safety aspects of retaining walls:
8. Flare rates. Use the same rates as those for concrete barrier. See Chapter 7.
9. End treatment. Preferably, the retaining wall will be buried in a back slope thereby shielding
its end. If this is not practical, use a crashworthy end treatment or crash cushion. See
Chapters 9 and 10.
4.3.3.3Noise Barriers
A noise barrier may take the form of an earth mound, a wall or solid fencing, or a combination of these. Noise
barriers with rigid structures should be considered as hazards, unless they are designed to be crashworthy in
accordance with NCHRP350 or MASH. Some designs use a concrete safety shape as an integral part either
of the noise barrier or as a separate roadside barrier.
Figure 4.41 – Example of a noise barrier
Noise barriers may be required to be located within a certain distance to the edge of the travelled way. Moving
them away from the road would necessitate a taller barrier, which may introduce problems associated with
wind loads and aesthetics. For these reasons relocating a noise barrier may not always be an applicable option
if it is located within the clear zone.
The traffic facing the end of a noise barrier should also be considered as a hazard, which poses the risk of a
head on collision. Caution should be exercised when locating noise barriers near gore areas.

74. ROADSIDE DESIGN GUIDE
PAGE 74
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.3.4 Bodies of Water
Bodies of water represent areas of high risk to road users due to the possible severe consequences of vehicle
submergence.
Still or flowing bodies of water such as, the sea, rivers, lakes, reservoirs, etc. with a water depth over 1m are
usually considered a hazard. When assessing bodies of water, engineer/designers should also evaluate the
sites where the water’s depth may rise over 1m during certain times of the year, due to seasonal events such
as heavy rain, tide and flooding.
Figure 4.42 – Permanent body of water
If the body of water under assessment is of any environmental significance, such as a reservoir, or source of
drinking water, it should also be assessed as a hazard with potential consequences to third parties. A vehicle
going into such a body of water may cause contamination, and affect others who use the water.
4.4 Hazards with Risk to Third Parties
4.4.1 Adjacent Roads and Carriageways
Median crossovers are the cause of some of the highest severity accidents. Especially for roads with high
traffic speeds and volume, a crossover incident poses the potential risk of multiple high speed collisions
involving several vehicles. For these locations, the adjacent carriageway not only poses a risk to the occupants
of an errant vehicle, but also to many others travelling on the other carriageway.
Adjacent roads with high speeds and heavy traffic, such as motorways, expressways and arterials, should be
treated as high risk hazards. The opposite side of dual carriageways should also be treated as adjacent roads
and therefore high risk hazards.
For divided roads, the median width represents the distance from the edge of the travelled way to the hazard
(adjacent road). If the median width is less than the required clear zone distance, and a barrier is not used,
the risk of a crossover incident reaches an unacceptable level.
Due to the right of way limits, it is often not possible to provide medians that are large enough to mitigate the
crossover risk without the need for barriers. For this reason median barriers are often required to mitigate the
risk of crossover incidents.

75. ROADSIDE DESIGN GUIDE
PAGE 75
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.4.2 Storage of Hazardous Material
Facilities such as chemical works, petroleum storage tanks or depots, facilities manufacturing or storing
hazardous chemicals in bulk may cause severe environmental and health problems if reached by an errant
vehicle. Such facilities should be treated as high risk hazards, and if they are located within the clear zone,
they should be removed, relocated or shielded by a barrier.
4.4.3 Places of Frequent Pedestrian Activity / Places of Public Gathering
Places of public gathering and frequent pedestrian activity are high risk third party hazards. Consequences of
an errant vehicle reaching a crowd would be extremely severe.
Examples of such places are:
• Heavily used public walkways,
• Schools,
• Residences,
• Businesses,
• Hospitals,
• Stadiums,
• Recreational facilities,
• Retail facilities,
• Factories, etc.
When evaluating these areas, the following parameters should be considered to assess the level of risk:
• Volume of pedestrian traffic: as the number of people using the area increases, so does
the probability of an errant vehicle hitting at least one person and therefore the consequences
of the incident.
• Type of pedestrians in the area: The area may be considered a higher risk in the presence
of specific type of pedestrians, such as school children.
• Geometry and characteristics of the road: Certain road geometries, such as a sharp
horizontal curve located at the end of a long straight, may increase the likelihood of a run-
off-the road incident. If the pedestrian area is located at such an area the risk would be higher.
• Type of traffic on the road: If high volumes of certain types of vehicles may cause even
more harm than the regular traffic, for example heavily laden freight vehicles, the pedestrian
area may be considered to be under higher risk
Once a high risk pedestrian area is identified, the following treatment options should be considered:
• Design and manage the road to minimise the likelihood of vehicles running off the road and
reaching the pedestrians
• Locate (or for existing facilities relocate) the pedestrian area beyond the clear zone

76. ROADSIDE DESIGN GUIDE
PAGE 76
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
• If previous options are not applicable, shield the pedestrian area with barrier.
On low-speed streets the practice is generally to separate pedestrians from traffic by a sidewalk separated
from the roadway by a raised curb. However, at speeds over 40km/h a vehicle may mount the curb for relatively
flat approach angles. Furthermore, it is generally impractical to separate pedestrians from the roadway with a
longitudinal roadside barrier. Thus, for streets with speeds over 40km/h, separating the sidewalk from the edge
of the roadway with a buffer space is encouraged [2].
When evaluating pedestrian activity, the designer/engineer should also consider the daily, weekly, and
seasonal fluctuations in the number of people using the area. If heavy pedestrian presence is expected only
for a short period of time for a specific event, such as a football match, concert etc., temporary barriers may
be considered instead of permanent installations.
Road user behaviour, including unauthorised pedestrian presence, as shown in Figure 4.43, should also be
considered. This type of risk should be eliminated through enforcement and by access control. For more
information on fencing, refer to Chapter 16.5 of the Abu Dhabi Geometric Design Manual.
Figure 4.43 – Example of unauthorised pedestrian presence at the side of a freeway
4.4.4 Cycle Lanes
Cycle lanes, similar to pedestrian facilities, may be considered as high risk hazards depending on factors such
as:
Frequency of Bicycle Traffic: Frequency is an important factor, because the probability of an errant vehicle
hitting a cyclist increases as the frequency of the cyclists on the cycle lane goes up. Conversely for infrequently
used cycle lanes or those designed with a roadside buffer, such as the one shown in Figure 4.44, even if a
vehicle runs off the road, the probability of it hitting a cyclist would be lower.
• Type of cyclists on the area: The area may be considered a higher risk in the presence of
specific type of cyclists, such as school children
• Geometry and characteristics of the road: Certain road geometries, such as a sharp
horizontal curve located at the end of a long straight, may increase the likelihood of a run-
off-the road incident. If the cycle lane is located near such an area the risk would be higher.

77. ROADSIDE DESIGN GUIDE
PAGE 77
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Figure 4.44 – Cycle lane
If a cycle lane is identified as high-risk, after the evaluation of the criteria mentioned above, the following
treatment options should be considered:
• Design and manage the road to minimise the likelihood of vehicles running off the road and
reaching the cycle lane
• Locate (or for existing facilities relocate) the cycle lane beyond the clear zone
• If previous options are not applicable, shield the cycle lane with a barrier.
4.4.5 Structures at Risk of Collapse
Some structures may pose the risk of collapsing on other road users if impacted by a vehicle, for example,
overhead bridges, pedestrian footbridges, gantries, high level masts, etc. A high energy impact, caused by a
heavy vehicle may cause significant damage to even the most rigid of structures, such as the one shown in
Figure 4.45.
A pedestrian footbridge, if collapsed due to a heavy vehicle impact, would not only harm the occupants of the
errant vehicle, but also the people who are on the footbridge and the road users on which the footbridge may
collapse. For this reason, these structures should always be considered high risk hazards. If these structures
cannot be removed, or relocated, they have to be shielded by an appropriately specified barrier.
Figure 4.45 – Abutment of a pedestrian footbridge

78. ROADSIDE DESIGN GUIDE
PAGE 78
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
4.4.6 Rail Lines
Although rare, if an errant vehicle collides with a train, the consequences are often catastrophic. The “Selby
Rail Crash” was a high-speed train accident, which occurred in England in 2001. This incident, where a high
speed train hit an errant vehicle from a nearby road bridge, caused 10 fatalities and 82 severe injuries [15].
Railway lines, including high speed rail, tram, light rail and others, should always be considered a high risk
hazard.
4.5 Summary and Conclusions
A hazard is a roadside feature or object that can cause physical, economic, time-based or strategic harm or
loss, if reached by an errant vehicle. Hazards that lie within the recommended clear zone area are under the
risk of being reached by errant vehicles, which may lead to injury or even fatal accidents.
This chapter presented an overview of the types and properties of roadside features that may be considered
hazards.
As a generalization, majority of the roadside hazards can be classified into one of the following categories:
A. Hazards with Consequences to Vehicle Occupants
a. Roadside Topography
i. Foreslopes
ii. Backslopes
iii. Ditches
iv. Transverse Slopes
v. Edges of Bridges and Retaining Walls
b. Non-deformable Single Obstacles
i. Trees
ii. Overhead Gantries and Cantilevers
iii. Roadside Sign Supports
iv. Luminaire Supports & CCTV Masts
v. Concrete Foundations Protruding from the Ground
vi. Bridge Piers, Abutments & Tunnel Portals
vii. Above Ground Equipment
viii. Drainage Pipes & Culverts
c. Non-deformable Continuous Obstacles
i. Retaining Walls
ii. Noise Barriers
iii. Fencing
iv. Permanent Bodies or Streams of Water
B. Hazards with Consequences to 3rd
Parties.
a. Adjacent Roads
b. Hazardous Material Storage
c. Places of Public Gathering & Pedestrian Activity
d. Heavily Used Bicycle Paths
e. Structures at Risk of Collapse

79. ROADSIDE DESIGN GUIDE
PAGE 79
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
f. Rail Lines
g. Areas of Environmental Concern
Information presented in this chapter does not cover every single possible roadside hazard and therefore
should be taken as a general guidance, rather than a definitive check-list. Engineering judgment should be
used to assess possible hazards on a case by case basis, prior to a final decision.
4.6 References
[1] CEDR, “SAVERS (Selection of Appropriate Vehicle Restraint Systems) - WP1: Defining the
Different Parameters which can Influence the Need and Selection of VRS (Unpublished
Report),” Conference of European Directors of Roads, 2014.
[2] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of
State Highway and Transportation Officials, 2011.
[3] TD19/06 Design Manual for Roads and Bridges, Volume2 Highway Structures: Design,
Section 2 Special Structures, Part 8, The Highways Agency, Transport Scotland, Welsh
Assembly Government, The Department for Regional Development Norther Ireland, 2006.
[4] FGSV, Traffic Management Work Group, “Guidlines for passive protection on roads by vehicle
restraint systems,” FGSV Verlag GmbH, Koln, 2009.
[5] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney,
NSW: Austroads, 2010.
[6] Abu Dhabi Department of Transport, Road Geometric Design Manual, Abu Dhabi: Abu Dhabi
Department of Transport, 2014.
[7] CEN, Eurpean Standard EN12767: Passive Safety of Support Structures for Road Equipment
- Requirements, Classification and Test methods, CEN, Eurpopean Committee for Standardization, 2007.
[8] Ritherdon & Company Ltd, “Ritherdon Passively Safe Cabinet,” [Online]. Available:
http://www.ritherdon.co.uk/products/passive-safety/passively-safe-cabinet-product.html.
[Accessed 16 07 2015].
[9] J. Schall, P. Thompson, S. Zerges, R. Kilgore and J. Morris, Hydraulic Design of Highway
Culverts, Third Edition, Washington, D.C.: U.S. Department of Transportation, Federal
Highway Administration, 2012.
[10] H. Ross, T. H. D.L. Sicking, H. Cooner, J. Nixon, S. Fox and C. Damon, “Safety Treatment of
Roadside Drainage Structures,” Transportation Research Record, no. 2060-08, 1982.
[11] Texas DoT, Hydraulic Design Manual, Texas Department of Transportation, 2014.
[12] D. Sicking, R. Bielenberg, J. Rohde, J. Reid, R. Faller and K. Polivka, “Safety Grates for

80. ROADSIDE DESIGN GUIDE
PAGE 80
04 IDENTIFICATION OF HAZARDS FIRST EDITION -DECEMBER 2016
Cross-Drainage Culverts,” Transportation Research Record, no. 2060, pp. 67-73, 2008.
[13] H. McGee, D. Nabors and T. Baughman, Maintenance of Drainage Features for Safety,
Washington D.C.: U.S. Department of Transportation, Federal Highway Administration, 2009.
[14] Cherokee Culvert, “www.cherokeeculvert.com,” 17 05 2016. [Online]. Available:
http://cherokeeculvert.com/end-treatments/.
[15] BBC, “BBC News,” 6 January 2003. [Online]. Available:
http://news.bbc.co.uk/1/hi/in_depth/uk/2001/selby_train_crash/default.stm. [Accessed 1 May
2015].

81. ROADSIDE DESIGN GUIDE
PAGE 81
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
5 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
5.1 Introduction
Passively safe support structures and traversable objects are those items of roadside furniture which have
been designed (and in many cases tested) so as to reduce the risk and severity of injury to road users in the
event of an impact.
“Roadside furniture” means any roadside objects used for the safety and control of traffic in addition to those
for assisting and informing the driver. This will include items such as highway signs, roadway lighting and traffic
signals.
As discussed in Chapter 2, it is always preferable, where practical and financially viable, to remove or relocate
a roadside hazard located within the clear zone of the roadside; however, there may be instances where this
is not possible. In such circumstances, consideration should therefore be to replace the existing hazard with a
passively safe support structure, or to make the hazard traversable.
This Chapter will examine the ways in which the performance of passively safe support structures and
traversable objects can be determined, how they should be implemented into the roadside, and how existing
hazards within the clear zone (for examples culverts) can be made traversable.
5.2 Passively Safe Support Structures
Chapter 4 details those items of roadside furniture, and roadside features which are considered to be
hazardous and should be reviewed as part of the clear zone approach.
The use of passively safe support structures may be effective in reducing the severity of support- related
crashes, if removal or relocation of the support structure is not feasible or financially viable. These types of
supports are designed to collapse or break away on impact, thereby reducing the severity of injury to the
occupants of an impacting vehicle, compared to those that could occur if the support was rigid.
However, due to the collapse modes of such systems, the risk to other people in the vicinity of the passively
safe support structure also needs to be considered. Therefore, the following issues also need to be considered
when specifying passively safe sign supports and their setback from the roadway:
• The area behind the support should be free of other hazards and, in the case of breakaway
supports, a run-out area may be required. It is not acceptable for an errant vehicle to pass
through a passively safe structure and then strike an additional hazard behind.
• There should be limited pedestrian activity in the vicinity of the support as any detached
elements from the support posts could pose a high level of risk to pedestrian and other
vulnerable road users (see Section 5.2.1).

82. ROADSIDE DESIGN GUIDE
PAGE 82
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
• The speed limit of the road, and which systems have been successfully tested to those speed
requirements;
• Whether the road is kerbed or un-kerbed, as any impact prior to that with a passively safe
support structure may influence the dynamic performance of the support structure;
• The location of the support structure (mid-block or at an intersection) as this will identify the
direction(s) in which the passively safe support structure may be struck. Some structures are
impact direction sensitive, and therefore the possible impact scenarios should be understood
and considered when selecting a passively safe support structure;
• Whether the support structure is to be located behind a road safety barrier as this will assist
in determining the level of safety which needs to be provided by the support structure;
• Maintenance, repair and replacement requirements and associated costs [1].
The damaged support and any elements that detach under impact should not pose a risk to other road users,
and any level of risk should be quantified before the use of a passively safe support structure is included within
any roadside design. This may involve locating them at the property line (urban and rural) or in an easement
(rural). In general, impact absorbing poles should be favoured over slip-base ones in areas of low traffic speed,
parking and in areas with large amounts of pedestrian activity. This is because the impact absorbing poles do
not become detached from their base during an impact, whereas the slip-base ones do. Therefore, the slip-
base systems have a higher risk of moving further than their base and collapsing on top of pedestrians or other
vulnerable road users.
Location of sign structures is important for road user safety. Factors such as road geometric alignment, sight
lines and decision distances should be considered to make sure the road users are provided with enough time
to read, understand and safely execute any manoeuvre required.
5.2.1 Types of Passively Safe Support Structures
There are a number of support structures often present in the roadside which can be made passively safe,
including:
• Supports for small and large roadside signs
• Gantries and cantilever sign supports (albeit in a small number of situations)
• Lighting columns
• Supports for traffic signals and surveillance cameras
• Emergency telephones
There are two main designs of passively safe support structures:
a) Slip-base and non-energy absorbing supports such as that shown in Figure 5.1 and Figure
5.2 are designed to breakaway at their base upon impact, allowing the vehicle to pass beneath the support to
minimise damage to the impacting vehicle and reduce the risk of injury to the vehicle occupant(s). This may
be achieved by a slip plane, plastic hinge, fracture element, or a combination of these features. These can be
uni-directional, bi- directional, or omni-directional, and details on these three subtypes can be found within
Section 5.2.2.3.

83. ROADSIDE DESIGN GUIDE
PAGE 83
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
b) Energy absorbing supports collapse on impact by an errant vehicle and are designed to
decelerate an impacting vehicle in a controlled way. In some cases this means that the
vehicle will stop at the base of the support. These deformable supports are designed to
remain in the ground after being struck as shown in Figure 5.3 and Figure 5.4.
Figure 5.1 – Example of a slip-base support
The two types of passively safe sign supports outlined in this section are typically integrated into, or promoted
as, proprietary systems. However, in addition to these designs of supports, there are a number of non-
proprietary sign supports which are deemed to be passively safe, and which are therefore also not considered
to represent a roadside hazard. These are:
• Steel posts that do not exceed the equivalent section properties of a tubular steel post having
an external diameter of 89 mm or less and a wall thickness of 3.2 mm or less [2], and
• Wood posts with dimensions of 100 mm x 100 mm or less [3].

84. ROADSIDE DESIGN GUIDE
PAGE 84
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.2 – Example of a slip-base pole mechanism
Figure 5.3 – Example of the failure mechanism for an energy absorbing support

85. ROADSIDE DESIGN GUIDE
PAGE 85
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.4 – Examples of impact absorbing poles
5.2.2 Small Roadside Signs and Their Supports
There are some circumstances where the size and therefore weight of a sign exceeds that which can be
supported by a single sign support, and this will depend on the design of the support structure selected. Advice
in this regard will be provided by the manufacturer of the support structure, and in such cases more than one
sign support should be used.
The Abu Dhabi Standard Drawings Manual contains details for structural supports for traffic control devices.
The Abu Dhabi MUTCD identifies practices for the selection, location, and design of highway signs. For
roadside safety applications, the following will apply to highway signs.

86. ROADSIDE DESIGN GUIDE
PAGE 86
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Small roadside signs are usually defined as those supported by one or more posts and which have a sign
panel not greater than 5 m2
in area [3]. The supports for small roadside signs are typically installed in one of
the following ways:
• Set in a precast cylindrical concrete base,
• Driven directly into the soil,
• Set in drilled holes, or
• Mounted on top of a separately installed base.
Unless successfully impact tested to the requirements of NCHRP 350 or MASH (see Section 5.2.8), sign
supports should not be braced as this can significantly affect the impact performance of an otherwise
acceptable design, especially in the case of yielding supports (see Figure 5.5). To avoid the need for bracing,
larger breakaway or multiple breakaway posts should be considered when it is necessary to increase the
strength of a support structure.
Figure 5.5 – Braced sign support [4]
The breakaway mechanisms for small sign supports consist of yielding, fracture or a slip-base design. The
most commonly used small sign support hardware and the characteristics of each are described in the
following sections. The mode of breakaway will be determined by the performance of the sign support during
the impact testing of the system.
Sign supports, gantries, cantilever sign supports, VMS and traffic light supports shall be designed according
to Abu Dhabi “Road Structures Design Manual” [4]. For issues not covered, the “AASHTO Standard
Specifications for Structural Supports for Lighting Signs, Luminaires and Traffic Signals” [5] shall be used.
5.2.2.1 Yielding supports for small signs
Yielding supports for small signs typically consist of:
• U-channel steel posts,
• Perforated square steel tubes,
• Thin-walled aluminium tubes, or
• Thin-walled fibreglass tubes.
Examples of these are presented in Figure 5.6.

87. ROADSIDE DESIGN GUIDE
PAGE 87
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
U-Channel Steel Post Perforated Square Steel Tube
Thin Walled Aluminium or Fibreglass Tube
Figure 5.6 – Examples of yield supports for small signs
To prevent the sign from twisting due to wind loading, a steel plate may be bolted or welded to the pipe
support. Experience from the US has shown a suitable plate size for such applications to be

88. ROADSIDE DESIGN GUIDE
PAGE 88
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
100 mm  300 mm  6 mm [3]. It is more difficult to predict the performance of yielding supports than other
support types as their dynamic behaviour can vary according to factors such as:
• The soil resistance,
• Variations in the depth of embedment,
• The size of the sign which is attached to the sign support,
• Stiffness of the sign support, and
• Mounting height of the sign.
5.2.2.2 Fracturing supports for small signs
Fracturing sign supports are those posts connected at ground level to a separate anchor. Anchors for steel
pipe and steel post systems are normally driven into the ground. Wood posts are typically set in drilled holes
and backfilled [3].
The breakaway feature for wood posts with dimensions greater than 100 mm x 100 mm can be achieved
through the process of drilling two 38 mm diameter holes near the ground level perpendicular to the flow of
traffic, and filled with expanding Styrofoam to prevent post deterioration [7]. It is recommended by the Federal
Highways Administration (FHWA) in the US that such holes are drilled 10.2cm (4”) and 45.7cm (18”) from the
ground, as shown in Figure5.7.
Figure 5.7 – Drilled holes in wooden posts

89. ROADSIDE DESIGN GUIDE
PAGE 89
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
5.2.2.3 Slip-base supports for small signs
Slip-base designs are designed to break/shear when impacted by an errant vehicle, detaching the main part
of the sign support from an anchorage in the ground. The scheme designer should use engineering judgement
to consider where the disconnected post may land following an impact. Slip-base designs can be classified as
unidirectional (i.e. they are designed to work in one orientation only), multidirectional (i.e. they are designed to
be impacted in more than one direction) or omnidirectional (i.e. they can impacted in any direction).
Unidirectional and multidirectional design should be installed in those locations where they can only be
impacted in the direction for which they have been designed (and tested). Conversely, omnidirectional slip-
bases can be installed in any location as they have been designed (and tested) to be impacted in any direction.
The most basic types of unidirectional breakaway supports for small signs are horizontal and inclined slip
bases, which use a 4-bolt slip base inclined in the direction of traffic at 10 to 20 degrees from horizontal, as
shown in Figure 5.8. As shown during full scale impact testing, the slip- bases have been designed so that on
impact the sign will move upward to allow the impacting vehicle to pass under it and not hit the windshield or
the top of the car, thus reducing the risk of injury to the occupants of the impacting vehicle. The inclined slip-
base can only be impacted in one direction, as shown by the red arrow. For this reason, neither the horizontal
nor the inclined slip- base designs should be used in medians, traffic islands, or other locations where impacts
from more than one direction are possible.
The multidirectional slip-base shown in Figure 5.8 is designed to function in two directions. This is indicated
by the red arrows. Multidirectional or omnidirectional bases (as shown in Figure 5.9) should be used in the
following locations:
• Channelizing islands;
• Intersections;
• Medians;
• Ramp terminals; and
• Other locations where a sign may be impacted from several directions.
Unlike rigid supports for small signs, there is a number of installation and maintenance problems which can
arise for slip-base systems, and these include:
• Wind and other vibration loads may cause the bolts in the slip base to loosen;
• The clamping bolts, which have low torque requirements, may “walk” or migrate from the
slots under wind loading;
• Over-torqueing of the bolts within the slip-base assembly.

90. ROADSIDE DESIGN GUIDE
PAGE 90
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.8 – Examples of unidirectional (top) and multidirectional (bottom) slip bases
Figure 5.9 – Example of an omnidirectional passively safe support before (left) and during (right)
impact
5.2.3 Large Roadside Signs and Their Supports
Large roadside signs are those which have a sign panel greater than 5 m2
in area. Due to their size and the
resulting wind loading and weight, large roadside signs will generally be supported by more than one post.

91. ROADSIDE DESIGN GUIDE
PAGE 91
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
The breakaway mechanisms for the supports of large signs consist of fracture or a slip-base design. Typically,
the supports for large signs do not have a yielding mechanism. Further details of these failure mechanisms
can be found within Section 5.2.2.
5.2.3.1 Supports for large signs with an upper hinge design
A number of supports for large signs incorporate an upper hinge design – by this it is meant that there is a
designed saw cut through the web of the post to the rear flange and a slotted fuse plate on the expected impact
side. The rear flange then acts as a hinge when the post rotates upwards in the event of an impact, as
demonstrated in Figure 5.10. Slotted plates may be used on both sides of the post if impacts are expected
from either direction, thus making it multidirectional. An example of such a sign support is shown in Figure
5.11.
Figure 5.10 – Example of the failure mechanism for an upper hinge design
Due to the functional nature of supports with an upper hinge, there are a number of restrictions for their use:
• All signs should not be installed in such a way as to interfere with the functioning
mechanism of the post;
• Supplementary signs should not be installed below the hinges if the supplemental sign is
likely to strike the windshield of an impacting vehicle;
• The total mass of the support structure and any connected signs between the bottom of the
hinge and the top of the shear plate of the breakaway base should not exceed 270 kg [3];
• The hinge should be at least 2 m above the ground so that no portion of the sign or upper
section of the support is likely to penetrate the windshield of an impacting vehicle.

92. ROADSIDE DESIGN GUIDE
PAGE 92
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.11 – Example of a support for a large sign with a hinge
5.2.3.2 Slip-base supports for large signs
The mechanism and operational requirements for slip-base supports for large signs are the same as those for
small signs. For more details, refer to Section 5.2.2.
5.2.4 Gantries and Cantilever Sign Supports
Due to the size and/or quantity of signage which they support, overhead gantries (see Figure 5.12) and
cantilevers (see Figure 5.13) are often substantial structures and can in many circumstances span multiple
lanes of freeways or expressways. However, due to their substantial nature, it is often very difficult to make
the supports passively safe and hence, their posts can often represent significant hazard to road users. It is
for this reason that the posts of gantries and cantilever sign supports should be considered significant roadside
hazards, and dealt with in line with the requirements of Chapter 2 (i.e. remove, relocate or protect with a vehicle
restraint system).
Figure 5.12 – An example of an overhead gantry

93. ROADSIDE DESIGN GUIDE
PAGE 93
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.13 – An example of a cantilever sign
There are a number of passively safe gantries (see Figure 5.14) available on the market, and these have
the following advantages [8]:
• Lightweight construction;
• Passive safety – as shown by full scale impact testing conducted by TRL on behalf of
the UK Highways Agency in 2005 (shown in Figure 5.14);
• Strength;
• Quick installation;
• No maintenance (for aluminium systems);
• A fully engineered and developed design using proven components;
• Factory fabrication with good quality control of materials and components;
• Easy to recycle when the gantry is no longer needed.
Figure 5.14 – Example of a passively safe gantry [7]

94. ROADSIDE DESIGN GUIDE
PAGE 94
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
However, despite these advantages, in the event of an impact these may have serious consequences for other
road users. This may be the gantry falling down over or across the road and in some cases, following traffic
impacting the gantries and/or supported signs which would then lie in the carriageway. Hence, before
implementing a passively safe gantry across a carriageway, the risks associated with its installation, and any
subsequent impact must be ascertained and quantified. If in any doubt, a vehicle restraint system should be
provided in front of the legs of the gantry, even if it is a passively safe system. It should be noted that the
placement of overhead sign structures is important for driver safety. Consider sight lines, decision distance,
and road alignment to provide the motorists with sufficient time to read, interpret, and safely execute any
manoeuvres required [7].
Necessary vertical and horizontal clearances should be provided for gantries and cantilevers; i.e. 6.5m vertical
and 9.0m horizontal clearance. These requirements are presented in Abu Dhabi Manual for Uniformed Traffic
Control Devices (MUTCD).
5.2.5 Passively Safe Lighting Columns (Luminaires)
The Abu Dhabi Road Lighting Manual presents a detailed discussion on roadway lighting with respect to:
• The requirement to provide lighting and lighting columns;
• The requirements for locating the lighting columns; and
• The design of lighting columns to provide the required level of luminance and uniformity.
5.2.5.1 The Height and Mass of Passively Safe Lighting Columns
The height of the lighting column to be used in a particular location(s) will depend on the length of the arm at
the top of the lighting column and the intensity of the light given by the luminaire, however, as a general rule,
lighting columns typically used in Abu Dhabi are 10 m or 14 m in height. A typical installation of lighting columns
in the median of the E20 (Airport Freeway is shown in Figure 5.15.
Figure 5.15 – Example of 14m high lighting columns installed in the median
Following the risk assessment and mitigation approach within Chapter 2, if 10 m and 14 m lighting poles cannot
be removed or relocated outside of the clear zone, it may be possible to make them passively safe, and a
number of such products are available in the market. A level of passive

95. ROADSIDE DESIGN GUIDE
PAGE 95
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
safety can be achieved through either use of a slip-base, or by making the lighting column energy absorbing
in its overall design (for example by designing it to yield on impact). More details about these passively safe
failure modes can be found in Section 5.2.1.
The height of passively safe lighting columns should generally not exceed 12.5m on roadsides. However, on
central reservations, 15m and 18 m high poles can be used [8]. This is due to:
• The approximate maximum height of currently accepted hardware; and
• The height that can accommodate modern lighting design practices when foundations are
set at approximately the roadway grade.
On a limited number of roads, where adequate luminescence cannot be provided by using 18m high lighting
columns, high masts (which are 25 m high) are used. Due to their height, these lighting columns are very rigid
and therefore present a significant risk to road users. It is for this reason that these lighting columns should
always be protected by a safety barrier [3].
Following the clear roadside principals in Chapter 2, designers should also consider the use of high-mast
lighting columns as these can be used to both reduce the number of lighting columns within the roadside, as
well as enabling the columns to be placed further away from the travelled carriageway. High-mast lighting
columns are fixed-base systems which are not passively safe. Where used, such systems should be located
outside of the clear zone or shielded with an appropriately specified barrier and should be located away from
the natural impact side of the roadway (e.g. the inner side of a loop interchange). As with all roadside hazards,
high-mast lighting columns should be located sufficiently far behind the barrier in such a way that in the event
of an impact, the deflection of the barrier will not interfere with the lighting column. This distance will be
determined by the dynamic performance of the barrier during full-scale impact testing to NCHRP350 or MASH
(see Chapter 6).
The mass of a breakaway lighting column should not exceed 450 kg to reduce the potential for serious
consequences [3].
5.2.6 Passively Safe Traffic Signal and Surveillance Camera Supports
The Abu Dhabi Traffic Signals, Electronic Warning, and Information Systems Manual presents a detailed
discussion on the design of these elements.
Traffic signal supports and surveillance cameras are a special situation where the use of a passively safe
support structure may not be suitable for a number of reasons. The first is that the signals will typically be
installed in areas of high traffic volumes and, in some cases, high pedestrian volumes (refer to Figure 5.16
and Figure 5.17). As a result any detached elements are likely to pose an unacceptably high level of risk to
these parties. In addition, the confusion and level of risk posed by the absence of a traffic signal is also likely
to be high in the event of an impact.
For these reasons, the use of a passively safe support for a traffic signal or a surveillance camera is only likely
to be suitable in a limited number of applications, following the application of engineering judgement. In the
majority of cases, traffic signals and surveillance cameras should not be made passively safe, but should be
moved away from the edge of the carriageway as far as

96. ROADSIDE DESIGN GUIDE
PAGE 96
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.16 – The complex siting of traffic signs
reasonably practicable, and located behind a safety barrier system; however, this will depend on site conditions
and available space, posted speed, vehicle movements, and the movement of vulnerable road users such as
pedestrians and cyclists.
Figure 5.17 – The siting of surveillance cameras
5.2.7 Emergency Telephones
5.2.7.1 Purpose and Need for Emergency Telephones
Emergency telephones provide motorists with a means of reporting incidents, which may include an incident,
a disabled vehicle obstructing a roadway or other emergencies for which assistance is needed.
In general, emergency telephones should be provided on freeways with high traffic volumes (>50,000 ADT).
When determining the need for telephones in this situation, the effect of incidents on congestion and safety is
the main consideration. In rural areas, traffic volumes are generally lower and congestion is not normally a
primary consideration.

97. ROADSIDE DESIGN GUIDE
PAGE 97
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Factors that need to be considered before placing an emergency telephone include isolation of the road from
abutting properties (e.g. limited access), the time required to obtain medical assistance, any history of high
incident rates, road geometry, roadside topography, issues with the provision of telecommunications cables,
and climate.
During the planning of an emergency telephone system, consultations should be held with organisations
responsible for the operation and servicing of the system, such as the telecommunications supplier, the
intended operator, and the emergency services. More details on post supports for emergency telephones are
provided in Section 5.2.7.2.
5.2.7.2 Locating Emergency Telephones
Given the rise in mobile communications the need for emergency telephones is likely to decrease over time;
however, engineering judgement should be applied as to the need for such telephones, taking into account
factors such as mobile telephone connectivity coverage.
The location of emergency telephones is determined by the acceptable walking distance for motorists to
safely and conveniently use the service, the level of risk in using it, and the location of major features (e.g.
interchanges) that may increase the need for the service at the particular site. Pedestrian movements
across freeways and other high-speed roads should be strongly discouraged. Therefore, emergency/help
telephones should generally be placed in pairs, directly opposite each other (there should not be more than
a lateral displacement of 50m between opposite telephones) as shown in Table 5.1.
Table 5.1 – An example of spacing of emergency telephones
Road type Situation Spacing (m) Consideration
Urban freeway
General application 1000 Maximum walking distance 500 m
Special circumstances 1200
Increased because of difficulty in providing
safe access. Not for general use.
Critical road sections
400 Particularly vulnerable to congestion.
200 Severe network and safety implications
Rural freeway
General (< 10,000 AADT) 4000 Lower probability of incidents
Higher volume (>10,000
AADT)
2000 Depends also on site circumstances
In addition the following factors should also be considered before locating an emergency telephone:
• Telephones should only be installed on the right-hand side of the roadway where there are
up to two lanes per roadway;
• Telephones should be installed on both sides of the roadway where there are three or more
lanes per roadway provided that a vehicle can stand clear of through traffic on the median
side (i.e. there is a wide shoulder or an emergency parking bay available);
• Locations within interchanges should allow access by users of ramps as well as the main
roadway, and pedestrians should not be required to cross a heavily trafficked entrance or exit
ramp;
• Where no roadside barrier is present, the telephone should be located just outside the
shoulder, preferably outside of the clear zone;

98. ROADSIDE DESIGN GUIDE
PAGE 98
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
• Isolated sections of roadside barrier should not be introduced solely for the protection of a
telephone. Where a continuous roadside barrier is present, the telephone should be placed
near the end of the barrier;
• It desirable that emergency telephones are oriented so that the user faces the oncoming
traffic while operating the telephone;
• Emergency telephones should be situated at or near each major road feature, such as a
major interchange on a freeway or a major intersection on a highway. In such cases,
telephones are placed on the departure side of the feature;
• Approaching drivers should have adequate sight distance to the telephone;
• Visibility of the site from surveillance cameras should also be maintained;
• Access to telephone lines should be considered whilst determining the location of an
emergency telephone;
• Ambient noise levels should not unduly affect telephone usage;
• The location of lighting columns and signs must not conflict with the site proposed for the
telephone. However, at the same time road lighting must provide adequate illumination of the
telephone and phones should be placed within 10m on the approach side of a street lighting
pole. If street lighting is not provided, or is inadequate for identification and/or operation of
the telephone, special provisions may be needed to enable operating instructions to be
followed;
• Existing or planned vegetation must not obscure telephones or the vision of camera coverage
of the site;
• The topography of the ground in the vicinity of the telephone should also be considered and,
where possible, emergency telephones should be located in areas with a gradient of 1:6 or
flatter (locations on steep batters are unsuitable);
• All emergency telephones should be numbered to assist callers reporting incidents, and to
provide unambiguous identification of the site for the deployment of emergency services and
maintenance staff.
Emergency telephones should be readily identifiable from the road during the day and at night from a distance
that enables drivers to stop safely.
5.2.8 EN12767, NCHRP350 and MASH Performance Classifications for
Passively Safe Supports
All passively safe structures shall have demonstrated compliance with the European requirements of EN12767
[2] and/or the American recommendations in either NCHRP350 [10] or MASH [11] and additional local
conditions for the Abu Dhabi Road Network. Evidence of this shall be presented and approved by the
Overseeing Organization prior to the use of these systems. Only systems approved by the Overseeing
Organization shall be used.
After January 1, 2011, newly-tested passively safe support structures must be evaluated in accordance with
either EN12767 or MASH. However, support structures that were accepted before the adoption of MASH by
using criteria contained in NCHRP350 may remain in place and may continue to be manufactured and
installed.

99. ROADSIDE DESIGN GUIDE
PAGE 99
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
The European standard EN12767 classifies the support structures according to three main categories:
• Impact Speed;
• Energy Absorption; and
• Occupant Safety.
All EN12767 tests are carried out with a 900kg test vehicle; impacting the support structure head- on, as shown
in Figure 5.18.
There are four different types of tests; all with different impact speeds as shown in Table 5.2. All systems must
first be tested with an impact speed of 35km/h. This low speed test is designed to demonstrate if the failure
mechanism works, even in low energy impacts. A secondary impact test, with an impact speed of either 50,
70 or 100km/h, then follows. This secondary test determines the system’s Impact Speed Class, as shown in
Table 5.2.
Figure 5.18 – Example of an EN12767 test
Table 5.2 – EN12767 impact speed categories [2]
Speed Class km/h Impact Speeds km/h
50 35 and 50
70 35 and 70
100 35 and 100
An important measure of performance for a passively safe support structure is the amount of energy
absorbed during the impact. The lower the impact absorption, the higher the safety is likely to be. As an
example, a regular support structure would absorb all the energy during an impact and therefore the impact
force is exerted into the vehicle and then to the occupants; causing injury. In EN12767, the energy
absorption characteristic of a system is assessed through the reduction in the speed of the vehicle, as a
result of the impact. Depending on the amount of reduction, the product is classified as either High Energy
Absorbing (HE), Low Energy Absorbing (LE) or Non Energy absorbing (NE), as shown in Table 5.3.

100. ROADSIDE DESIGN GUIDE
PAGE 100
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Table 5.3 – EN12767 energy absorption categories [2]
Impact Speed (km/h) 50 70 100
Energy Absorption Category Exit speed, ve (km/h)
HE ve = 0 0 ≤ ve ≤ 5 0 ≤ ve ≤ 50
LE 0 < ve ≤ 5 5 < ve ≤ 30 50 < ve ≤ 70
NE 5 < ve ≤ 50 30 < ve ≤ 70 70 < ve ≤ 100
In addition, EN12767 also requires passively safe products to be classified by their impact severity. During the
test, longitudinal and angular accelerations are measured through accelerometers installed on the test vehicle.
The occupant safety is then assessed through severity indices, which are based on the accelerometer
measurements. Following are the indices, which are used to evaluate occupant safety in EN12767:
• Acceleration Severity Index (ASI): A concept which has been developed for assessing
occupant impact severity for vehicles involved in collisions with road restraint systems;
• Theoretical Head Impact Velocity (THIV): A concept where the theoretical velocity of the
impact of an occupant’s head with the interior surface of the vehicle is assessed as a
measure of impact severity.
Once the ASI and THIV are calculated, the Occupant Severity Level is then determined as shown in Table 5.4.
The lower the ASI and THIV values are, the higher the occupant safety would be. Therefore, the Occupant
Severity Level 3 provides the highest level of safety, which is followed by Levels 2 and 1.
Table 5.4 – EN12767 occupant safety classification [2]
Energy
Absorption
Categories
Occupant
Severity Level
Speeds
Mandatory Low Speed Test at
35km/h
Speed Class Impact Test at 50,
70 or 100km/h
Maximum Value Maximum Value
ASI THIV (km/h) ASI THIV (km/h)
High Energy
Absorbing
(HE),
1 1,0 27 1,4 44
2 1,0 27 1,2 33
3 1,0 27 1,0 27
Low Energy
Absorbing (LE)
1 1,0 27 1,4 44
2 1,0 27 1,2 33
3 1,0 27 1,0 27
Non Energy
absorbing
(NE),
1 1,0 27 1,2 33
2 1,0 27 1,0 27
3 0,6 11 0,6 11
4
No
requirement
No
requirement
Impact speed - exit speed
<3km/h
In addition, during the test the structure must ensure that:

101. ROADSIDE DESIGN GUIDE
PAGE 101
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
• The test item shall behave in a manner predicted by the manufacturer, in terms of shearing
or detaching, deforming only, or deforming and shearing;
• The test item or detached elements, fragments or other major debris from the test item shall
not penetrate the occupant compartment. The windscreen may be fractured but shall not be
penetrated;
• The vehicle shall remain upright for not less than 12 m beyond the impact point with a (roll
angle) less than 45º and a (pitch angle) less than 45º. Roll and pitch refer to the angle of
change along x and y axes respectively, as shown in Figure 5.19.
For testing to the American requirements of NCHRP350 or MASH, the breakaway support must perform in a
predictable manner when struck head-on by an 820 kg car (NCHRP350) and/or an 1100 kg car and a 2270 kg
pickup truck (MASH), at a speed from 30 km/h to 100 km/h [2]. In addition, the testing is conducted to ensure
that:
• When impacted, the structural support must react in a predictable manner by breaking away,
fracturing or yielding;
Figure 5.19 – Pitch and Roll Angles
• No components must penetrate or show potential to penetrate the occupant compartment
of the test vehicle;
• The vehicle must remain stable and upright during and after the impact;
• There must be no significant deformation or intrusion of the windshield or passenger
compartment;
• Limits are placed on the transverse and longitudinal components of the occupant impact
velocity to avoid the possibility of serious injury.
These specifications also establish a maximum stub height of 150 mm. This reduces the possibility of snagging
the undercarriage of a vehicle after a support has broken away from its base.
5.2.9 Selection Criteria for Passively Safe Support Structures
In Abu Dhabi, breakaway supports can be used on roads with a design speed equal to, or greater than 80
km/h.

102. ROADSIDE DESIGN GUIDE
PAGE 102
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Where a passively safe support is to be used, it shall have been tested to an impact speed which reflects the
posted speed limit of the road. Within NCHRP350 and MASH, the maximum designated test speed is 100km/h.
For roads with a speed limit equal to or in excess of 100km/h, the passively safe structure shall have been
tested to 100km/h.
When choosing an EN12767 system, the following should be considered, with regards to Energy Absorption
characteristics. Category NE supports provide a lower risk of injury to vehicle occupants than HE or LE, and
can be the most appropriate choice on non-built up roads with insignificant volumes of non-motorized users
(NMUs). Category LE and HE supports reduce the risk of secondary incidents and collision with NMUs, as the
vehicle exit speed is lower, and thus can have advantages on built-up roads where there is a significant volume
of NMUs. [12]
Category NE supports are generally slip-base systems. Slip-base supports are mostly suitable for locations
where vehicle speeds are greater than 60 km/h and are the preferred type of frangible poles [13]. Due to the
risk posed from detached elements from the slip-base systems, impact absorbing supports are suited to
locations where it is undesirable for a pole to fall to the ground, such as in high pedestrian use areas or where
the median or traffic island in which the pole is located is narrow and traffic volumes are high [13]. Impact
absorbing supports are usually category LE in EN12767. In areas where pedestrians are likely to exist, the
volume of pedestrian traffic should be reviewed to determine if a slip-base support will present a greater
potential hazard to the pedestrian traffic than a non-breakaway support will to the vehicular traffic. This should
be ascertained using engineering judgement and experience. Locations where the hazard potential to
pedestrian traffic may be greater than the risk to vehicle occupants will include:
• Parking lots;
• Tourist attractions;
• School zones; or
• Central business districts and local residential neighbourhoods where the posted speed
limited is 50 km/h or less [3].
In these locations, non-passively safe supports and lighting columns may be a better choice. Non- passively
safe supports are generally category HE in EN12767. Other locations that typically require the use of non-
breakaway bases, regardless of the pedestrian traffic volume, are rest areas and combined light and traffic
signal poles.
In some rare cases an engineer may consider placing a passively safe support structure within the working
width of a barrier. However, whilst they are designed to reduce the risk of injury to road users in the event of
an impact, passively safe products should not be placed within the working width of a safety barrier (or
equivalent for other vehicle restraint system types). One such case is shown in Figure 5.20; where there is an
existing barrier to shield the rock face but not enough space beyond the working width of the barrier to place
a support structure. In this case an engineer may be tempted to place a passively safe system, within the
working width, as there is not enough space to place a rigid one behind the working width. The safety of this
kind of installation is debatable; as these systems are designed and tested to work without secondary impacts.

103. ROADSIDE DESIGN GUIDE
PAGE 103
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.20 – Passively safe supports should not be installed in the working width of a safety
barrier
5.2.10 Application Criteria for Passively Safe Supports
The Abu Dhabi Standard Drawings Manual presents the hardware details for the safe installation of
roadside furniture such as highway signs, lighting columns, and traffic signals.
Following the approach detailed within Chapter 3, before specifying the use of any type of support structure
within the roadside or median, the following points should be considered [1]:
• Avoid placing poles close to the roadway - Any roadway improvement that involves
reconstruction of utility services should take the opportunity to avoid placement of poles close
to the roadway. This proactive approach will avoid problems rather than having to rectify them
in future. Where possible, poles should be located as far away from the roadside as possible
to minimise the risk of an errant vehicle hitting them;
• Pole removal – In all cases, poles should be removed wherever possible. It should be noted
however, that on tangents to curves where there is a crash history, the removal of a pole may
lead to crashes migrating to the next available pole. When considering removal of a pole with
a crash history it is important to understand why vehicles are leaving the road and take action
to keep vehicles on the road;
• Undergrounding cables – The relocation of utility services to underground ducts and
removal of the poles is the most effective option for the treatment of hazardous poles;
• Rationalisation of pole functions - It may be possible to rationalise the number of poles
along a road corridor by combining separate functions and services onto common poles. For
example, traffic signals, road lighting and large signage may be supported by the same poles.
Power cables, telecommunication services and spotlights can share common poles.
However, care must be taken so as not to overload the post and, in the case of passively

104. ROADSIDE DESIGN GUIDE
PAGE 104
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
safe sign supports, adversely affect their impact performance characteristics. It may be possible to place all
poles on the side of the road that has the better safety performance or least risk. This may involve changing
the poles from side to side as the crash risk changes along a curved route;
• Reducing pole numbers by increasing spacing - Increased pole spacing provides areas
for errant vehicles to pass between poles as shown in Figure 5.21.
• The effective gaps for vehicles to pass through are dependent on the width of the vehicle and
the exit angles. If increased pole spacing is used to reduce the roadside risk then designers
should check that the poles being removed to increase pole spacing are those that have
been involved in crashes or have the higher risk. It would be counterproductive to remove
poles which have not been a hazard but leave the high-risk poles in place;
Relocation - Pole relocation needs to target areas where the run-off-road crashes are likely, for example on
the approach to curves, the outside of curves, near lane merges, lane terminations, adjacent to exits from
roundabouts and intersections. Research [1] has confirmed the belief that the number of crashes decreases
as poles are moved further from the roadway. The expected percentage reduction in pole crashes with
increasing distance from the roadway is shown in Table 5.5.
Figure 5.21 – Reducing pole numbers by increasing spacing

105. ROADSIDE DESIGN GUIDE
PAGE 105
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Table 5.5 – Percentage reduction in pole crashes with increasing distance from the roadway [1]
Distance from roadway
before relocation (m)
Distance from roadway after relocation (m)
1.8 2.4 3.0 3.7 4.6 5.2 6.1 7.6 9.1
0.6 50 58 64 68 72 74 77 80 82
0.9 35 46 53 58 64 67 70 74 77
1.2 22 35 44 50 57 60 65 69 73
1.5 11 26 36 43 51 55 59 65 69
1.8 0 17 28 36 45 49 54 61 65
2.1 8 20 29 39 44 50 57 62
2.4 0 13 23 33 39 45 53 58
3.0 0 11 23 29 37 45 52
3.3 5 18 25 33 42 49
3.7 0 14 20 29 39 46
4.0 9 16 25 35 43
4.3 4 12 21 32 40
4.6 0 8 17 29 37
Example: A lighting pole is located 1.8m from the edge of the travelled way. If the pole is relocated to 5.2m
from the edge of the travelled way, a 49% reduction is expected in the number of crashes with the pole; using
Table 5.5.
5.2.10.1 Foundation Requirements for Passively Safe Systems
In many cases, the performance of a passively safe support will be dependent on the foundations surrounding
the support. In some cases, the design of the support system will be such that any movement or rotation of
the support in the ground may inhibit (or in extreme cases, stop) the safe functioning of the passively safe
device. For this reason it is essential that the promoter of the system is requested to provide details of the
foundation requirements for their system, prior to its installation. In those cases where the system has not been
tested in the soil type into which it is to be installed, the promoter should be asked to provide supporting
evidence to ensure that the full performance of the system can be realised in the foundation into which it is to
be installed.
As shown through full-scale impact testing, slip-base mechanisms (see Section 5.2.2.3) are designed to
release when impacted at a typical bumper height of about 500mm and properly to activate if loaded in shear
rather than bending stress. For this reason, slip-base systems should only be installed in areas where the
foreslope is limited to 1V:6H. Supports placed on foreslopes that are between 1V:4H and 1V:6H are only
acceptable when the face of the support is within 600mm of the intersection of the shoulder slope and the
foreslope, as shown in Figure 5.22.
No passively safe supports should be located in drainage ditches where erosion of the ditch could affect the
proper operation of the breakaway mechanism. A vehicle entering the ditch could also be inadvertently guided
into the support.

106. ROADSIDE DESIGN GUIDE
PAGE 106
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Intersection of shoulder slope and fore slope
Less than 600mm Acceptable
Passively Safe Support Structure Foreslope between 1V:4H and
1V:6H
Greater than 600mm Not Acceptable
Figure 5.22 – Use of passively safe support structures on slopes
5.2.10.2 Electrical Disconnection of Passively Safe Lighting columns,
Traffic Signals and Illuminated Signs
For passively safe lighting columns, traffic signals and illuminated signs, a power supply will be required into
to provide the power for the lighting systems. In many passively safe designs, the associated electrical
connections are also designed to disconnect in the event of an impact, and then subsequently easy to
reconnect.
There are a range of different commercially available electrical isolation solutions, and these fall into three
broad categories [8]:
Pull-out plug – This solution utilises a rugged plug and socket assembly mounted within the signal pole at
ground level. In the event of an impact, the plug assembly will be pulled apart due to the movement of the
pole, therefore achieving electrical isolation of the pole. Both LE and NE products will probably give the
movement needed to separate a pull-out plug system. If the broken post was effectively tethered by the
electrical supply, this would interfere with the movement of the post and the vehicle might overrun the post, or
a restrained post might hit a windscreen [8]. A HE support may not give the movement needed to separate a
plug system depending on the rotation of the post in the ground.
Circuit breaker – This method obtains electrical isolation by using a current sensor to ascertain if the electrical
current drawn exceeds a present threshold. If a fault state is achieved, isolators automatically turn off the
power within a maximum duration of 0.4 seconds.
Impact sensor – Similar to the circuit breaker system, the impact sensor is mounted in the pole, which in the
event of a vehicle striking the pole, is used to activate isolators mounted in the traffic signal cabinet.
Any exposed electrical connection (when detached from the support structure), can pose a risk of electrocution
to the occupant of the errant vehicle, other road users and/or emergency services attending the scene. For
this reason the electrical circuit controlling the power to the mounted system should operate with a maximum
disconnection time of 0.4 seconds when fault conditions occur [2]. In addition, the electrical disconnection
should take place in a location which is as close to the foundation as practicable.

107. ROADSIDE DESIGN GUIDE
PAGE 107
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
5.2.10.3 Locating Passively Safe Sign Supports
Although the Abu Dhabi MUTCD specifies the general location of large roadside signs, the designer has to
apply engineering knowledge with regard to the exact placement of any given sign. Further guidance on the
locating of posts can be found within Section 5.2.10.
It should be borne in mind that once struck, the sign can become a maintenance problem, requiring repair. It
is for this reason that even passively safe sign supports should be located where they are least likely to be hit
and, when feasible, outside the clear zone. Furthermore, the continuous wind buffeting caused by passing
vehicles may create fatigue problems on the threaded components of sign supports, if they incorporate such
components. To overcome this problem, passively safe signs should wherever possible be placed so that the
edge of the sign is not closer than 1.2 m from the carriageway edge [12].
5.2.10.4 Locating Passively Safe Lighting Columns
It may be the case that the design of the lighting is such that lighting columns are needed to be place in high
risk locations such as gore areas, traffic islands, off ramps, and intersections. At all times, the safety
implications of locating the lighting column should be considered using engineering judgement and if possible,
the lighting column should be moved to a location which would represent a lower level of risk to the road user.
This may mean removing the lighting column. In cases where the column cannot be moved, engineering
judgement should be applied to determine the best solution to reduce the risk posed to road users.
Figure 5.23 gives an example of a poor location of a lighting column as there is little protection given to road
users on the main line of the road, those turning right, or those turning from the road on the right onto the main
line. In such a location, it would be prudent to consider removing the lighting column (an example of which is
shown in Figure 5.24), moving it behind the safety barrier further down the road, or to consider the use of a
crash cushion in front of the lighting column and signs. Note that in the example shown in Figure 5.24, the
large posts and raised kerb will also present a hazard and hence, this is still not an optimised solution.
Figure 5.23 – Example of poor lighting column positioning at a traffic island

108. ROADSIDE DESIGN GUIDE
PAGE 108
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
Figure 5.24 – An example of a traffic island with no lighting columns
In both of the examples shown in Figure 5.23 and Figure 5.24 further risk assessment and remedial work
should be undertaken to reduce the risk to road users from the unprotected signs located on the island (unless
they are passively safe). Such a risk assessment should assess each of the possible vehicle approaches, and
the hazards which may exist within that road space. Possible speeds and angles of impact should be
considered, and the probability and consequences of each scenario assessed. Remedial measures should
then be undertaken to reduce these risks to a point which is as low as reasonably practicable (refer to Chapter
2).
Because of the potential hazard to road users posed by the rigid nature and large size of lighting columns, the
general approach to lighting is to use breakaway supports wherever possible. All new lighting columns located
within the clear zone of a roadway (refer to Chapter 3) where no pedestrian facilities exist will be placed on
breakaway supports, unless they are located behind or on a barrier or protected by crash cushions, which are
necessary for other roadside safety reasons. Engineering judgement should also be applied to lighting columns
located outside the clear zone to assess whether they too should be passively safe if there is a reduced
probability of them being struck by errant vehicles.
A luminaire support will generally fall near the line of the path of an impacting vehicle with the mast arm usually
rotating so it points away from the roadway when resting on the ground. This action generally prevents the
pole from going into other traffic lanes. However, these falling poles may endanger bystanders such as
pedestrians and bicyclists or other motorists and these risks should be quantified before the specification of
passively safe lighting columns (refer also to Section 5.2.1).
5.2.10.5 Locating Passively Safe Traffic Signals and Surveillance
Cameras
Due to the need to provide information and instructions to road users, designers will have only limited options
available in determining acceptable locations for the placement of traffic signal and surveillance pedestals,
signal and surveillance poles, pedestrian detectors, and control cabinets, as shown in Figure 5.25.
Considering roadside safety, these elements should be placed as far from the roadway as practical. However,
due to visibility requirements, limited mast-arm lengths, limited right-of-way, or pedestrian requirements, traffic
signal and surveillance equipment often must be placed relatively

109. ROADSIDE DESIGN GUIDE
PAGE 109
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
close to the travelled way as shown in Figure 5.25. Note that in the example of Figure 5.25 risks to road users
are also posed from the trees and the other roadside posts/lighting columns.
Figure 5.25 – Example of a surveillance camera and control cabinet
When placing passively safe traffic signals and surveillance cameras, the requirements of Chapter 3 should
be considered, and the hazard should be placed outside of the calculated clear zone. However, it is not only
the support which poses a risk to road users, it may also be the associated control cabinet.
In determining the location of the control cabinet, the designer should consider the following:
• The controller cabinet should be placed in a position so that it is unlikely to be struck by
errant vehicles. It should be outside the clear zone, if practical;
• The controller cabinet should be located where it can be easily accessed by maintenance
personnel;
• The controller cabinet should be located so that a technician working in the cabinet can see
the signal indications in at least one direction;
• The controller cabinet should be located where the potential for water damage is
minimized;
• The controller cabinet should not obstruct intersection sight distance;
• The power service connection should be reasonably close to the controller cabinet [3]
A good example of locating the control cabinet can be seen in Figure 5.25 where the cabinet is located away
from the edge of both carriageways, and between two rigid objects (trees) which will provide protection to the
cabinet, in the absence of a barrier system. However, ease of access to the cabinet by a maintenance team
should also be considered.
5.3 Traversable Obstacles
As identified in Chapter 4, there are a number of roadside hazards which relate more to the geometry of the
roadside, rather than to specific types of hazards or items located within it. Such roadside geometry cannot be
made ‘passively safe’ in the purest sense of the word, instead they

110. ROADSIDE DESIGN GUIDE
PAGE 110
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
can be made traversable, i.e. they have been designed such that a vehicle can cross over them whilst limiting
the risk of injury to the vehicle’s occupants.
Obstacles which can be made traversable include:
• Culverts and drainage structures;
• Transverse slopes;
• Ditches.
The following sections, and those referenced therein, give details of how these features can be made
traversable. Where a roadside feature exists which is not specifically covered by these sections, the
engineering approach explained within these sections should be adapted for the feature under review.
5.3.1 Culverts and Drainage Structures
For further details on design methods for making culverts and drainage structures traversable, refer to Section
4.3.2.9.
In summary, culverts and drainage structures can be made traversable by using one or more of the following
approaches:
• Extend the culvert opening beyond the clear zone with smooth, traversable earth graded
transitions;
• Provide a traversable end section; and/or
• Shield the culvert with a roadside barrier and a crashworthy end treatment facing oncoming
traffic.
5.3.2 Transverse Slopes
For further details on traverse slopes, refer to Section 4.3.1.4. Transverse slopes can be traversable by
making them as flat as practical, ideally with a gradient of 1V:6H or flatter.
5.3.3 Ditches
For further details on roadside ditches, refer to Section 4.3.1.3. Roadside ditches can be made traversable by
ensuring that they have a smooth and relatively flat ditch, with rounded corners. Those ditches which are
considered to be traversable are shown in grey in Figure 4.7.
5.4 Summary and Conclusions
Where a hazard exists within the clear zone and it cannot be removed or relocated outside of the clear zone,
consideration should be given to making the hazard passively safe or traversable. In both cases, the objective
is to reduce the risk to road users from the impact of striking a roadside object or topographical feature.
Roadside hazards which can be made passively safe include:
• Supports for small and large roadside signs;
• Gantries and cantilever sign supports (albeit in a small number of situations);

111. ROADSIDE DESIGN GUIDE
PAGE 111
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
• Lighting columns;
• Supports for traffic signals and surveillance cameras;
• Emergency telephones.
Roadside topography which can be made traversable includes:
• Culverts and drainage structures;
• Transverse slopes;
• Ditches.
There are two main types of passively safe support structures:
• Slip-base and non-energy absorbing supports are designed to breakaway at their base upon
impact, allowing the vehicle to pass beneath the support to minimise or avoid injury to vehicle
occupants;
• Energy-absorbing supports collapse on impact by an errant vehicle, and are designed to
decelerate an impacting vehicle to a controlled way.
When using slip-base supports, consideration should be given to whether the system is unidirectional (i.e. they
are designed to work in one orientation only), multidirectional (i.e. they are designed to be impacted in more
than direction) or omnidirectional (i.e. they can impacted in any direction). Unidirectional and multidirectional
should be installed in those locations where they can only be impacted in the direction for which they have
been designed (and tested). Conversely, omnidirectional slip bases can be installed in any location as they
have been designed (and tested) to be impacted in any direction.
Slip-base mechanisms are designed to release when impacted at a typical bumper height of about 500mm
and properly activates if loaded in shear rather than bending stress. For this reason, slip- base systems should
only be installed in areas where the foreslope is limited to 1V:6H. Supports placed on foreslopes that are 1V:4H
through 1V:6H are only acceptable when the face of the support is within 600mm of the intersection of the
shoulder slope and the foreslope. In addition, no passively safe supports should be located in drainage ditches
where erosion of the ditch could affect the proper operation of the breakaway mechanism. A vehicle entering
the ditch could also be inadvertently guided into the support.
In addition, when utilising a slip-base system, the hazard posed from detached parts of slip-base systems,
should be considered, in particular the risk posed to other road users, in particular pedestrians. This may
restrict the use of slip-base systems in some locations.
All passively safe system used should meet the testing requirements of EN12767, NCHRP350 or MASH.
Where a passively safe support is to be used, it shall have been tested to an impact speed which reflects the
speed limit of the road. Within NCHRP350 and MASH, the maximum designated test speed is 100km/h. For
roads with a speed limit equal to or in excess of 100km/h, the passively safe structure shall have been tested
to 100km/h.
5.5 References
[1] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney,

112. ROADSIDE DESIGN GUIDE
PAGE 112
05 PASSIVELY SAFE SUPPORT STRUCTURES &
TRAVERSABLE OBSTACLES
FIRST EDITION -DECEMBER 2016
NSW: Austroads, 2010.
[2] CEN, Eurpean Standard EN12767: Passive Safety of Support Structures for Road Equipment -
Requirements, Classification and Test methods, CEN, Eurpopean Committee for
Standardization, 2007.
[3] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of
State Highway and Transportation Officials, 2011.
[4] Abu Dhabi Department of Transport, Road Structures Design Manual, First Edition, Abu Dhabi:
Department of Transport,
[5] AASHTO Standard Specifications for Structural Supports for Lighting Signs, Luminaires and
Traffic Signals, Fifth Edition, Washington D.C.: American Association of State Highway and
Transportation Officials, 2009
[6] Federal Highway Administration, Maintenance of Signs and Sign Supports, Washington D.C.:
US Department of Transportation, January 2010.
[7] Alberta Infrastructure and Transportation, Roadside Design Guide, Alberta Infrastructure and
Transportation, November 2007.
[8] The Passive Revolution, Designing Safer Roadsides, A Handbook for Engineers, Exeter, UK:
Hemming Information Services in association with The Passive Revolution and Traffic
Engineering & Control, 2008.
[9] G. Williams, J. Kennedy, J. Carroll and R. Beesley, “The use of passively safe signposts and
lighting columns, PPR342,” Transport Research Laboratory, Wokingham, UK, August, 2008.
[10] NCHRP, “NCHRP Report 350, Recommended Procedures for the Safety Performance
Evaluation of Highway Features,” Transportation Research Board, National Research Council,
Washington DC, 1993.
[11] FHWA, “Manual for Assesing Safety Hardware (MASH),” [Online]. Available:
http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/ctrmeasures/mash/.
[Accessed 23 02 2015].
[12] BSI, “Passive safety of support structures for road equipment - Requirements, classification
and test methods,” British Standards Institution, October 2009.
[13] Roads & Transport Authority, Roadside Design Guide for Dubai, First Edition, Dubai: RTA,
2008.

113. ROADSIDE DESIGN GUIDE
PAGE 113
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
6 DESCRIPTION OF ROADSIDE, MEDIAN AND
BRIDGE BARRIERS
6.1 Introduction
Previous chapters have shown that once the width of the clear zone has been defined (Chapter 3), and it has
been identified as being a hazard (Chapter 4), the preferable way of reducing the risk to road users from the
hazard is to remove it completely, or to move it outside of the clear zone (Chapter 2). If this is not possible, the
hazard should be made passively safe or traversable in line with the recommendations of Chapter 5. If, and
only if all of these options are not available, or not economically viable (refer to Chapter 12) should a vehicle
restraint system be installed. Due to the risk posed to road users from the presence of a barrier, safety barrier
systems should only be used as a last resort.
There are many different barrier systems available on the market today. Historically, safety barriers were
primarily developed by the national road authorities and the available systems on the market were limited to a
few designs. These “non-proprietary” systems were the first of their kind and have seen widespread application
around the world. However, over the last few decades, with the help of standardized impact testing and a
competitive market place, the number of systems developed by private companies, i.e. “proprietary” systems,
has far surpassed the number of the non- proprietary ones. The level of safety has also benefited from the
increased number of systems, as the barrier manufacturers keep developing better performing systems to
position themselves ahead of their competition within the market.
Due to these reasons, it is no longer a valid approach for a designer/engineer to limit themselves to, and
memorize the properties of a certain number of non-proprietary systems. Due to the ever improving nature of
the available systems, it is not practical or possible to provide the details of every single system in this Guide
either. Therefore the designer/engineer should be able to interpret the performance characteristics and
installation requirements of every system on a case by case basis. To help the designer/engineer achieve that,
this Chapter provides an overview to the classification and the properties of safety barrier systems.
Safety barriers can be classified into different categories by several of their properties. These include:
A Classification by Impact Test Performance:
o Classification by Containment Level;
o Classification by Working Width & Dynamic Deflection;
o Classification by Vehicle Intrusion;
o Classification by Impact Severity;
B Classification by Developer of the System:
o Proprietary Systems;
o Non-Proprietary Systems;

114. ROADSIDE DESIGN GUIDE
PAGE 114
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
C Classification by Rigidity & General Design:
o Flexible Systems;
o Semi-Rigid Systems;
o Rigid Systems.
The classifications shown above are applicable to roadside, median and bridge barriers. Therefore, the
information presented in this Chapter is applicable to all roadside, median and bridge barriers. All of these
classifications are explained in detail in the following sections, to help the designer/engineer develop an overall
understanding of the road safety barrier systems.
Detailed information on the impact testing standards accepted by the Abu Dhabi Department of Transport, i.e.
MASH & NCHRP-350, is also provided within the following sections.
The information presented in this Chapter focuses on the types and properties of safety barriers only. Guidance
into the selection and application criteria of these systems is provided in Chapter 7
– Selection and Application of Roadside, Median and Bridge Barriers.
6.2 Safety Barrier Elements
Figure 6.1 shows the different components of a length of safety barrier installation. Further details of roadside,
median and bridge barriers can be found within this Chapter, whilst further details of terminals can be found
within Chapter 9, and details of transitions are in Chapter 10. It should be noted that Figure 6.1 is only indicative
to show the various elements of the safety barrier, and does
not provide guidance with regard to the layout and specification of safety barrier systems. Further details of
this can be found within Chapter 7.
Roadside barriers, in general, can be located along the side of roads to provide three main functions:
• To shield errant vehicles from natural hazards along the roadside; or
• To shield errant vehicles from man-made obstacles along the roadside; or
• To shield 3rd parties located along the roadside from errant vehicles.
Median barriers, in general, are installed to provide one of the following three functions:
• On a divided carriageway to separate opposing traffic;
• On roadways to separate through traffic from local traffic; or
• To separate through traffic from a frontage road.
Two sided Median barriers are designed to redirect vehicles striking either side of the barrier. Bridge
barriers are intended to prevent a vehicle from running off the edge of a bridge.

115. ROADSIDE DESIGN GUIDE
PAGE 115
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
* Components shown in the figure are not to scale and are for demonstrative purposes only.
Figure 6.1 - Definition of the components of a length of safety barrier
Roadside Barrier: A longitudinal barrier used to shield roadside
obstacles or non-traversable terrain features. It may occasionally be
used to protect pedestrians or “bystanders” from vehicle traffic.
Transition: A section of barrier between two different barriers or, more
commonly, where a roadside barrier is connected to a bridge railing or to
a rigid object such as a bridge pier. The transition should produce a
gradual stiffening of the approach rail so vehicular pocketing, snagging,
or penetration at the connection can be avoided.
Bridge Barrier: A longitudinal barrier whose primary function is to
prevent an errant vehicle from going over the side of the bridge structure
Median Barrier: A longitudinal barrier used to prevent an errant vehicle
from crossing the highway median.
Terminal: A terminal is essentially a crashworthy anchorage, a device
used to anchor a flexible or semi-rigid barrier to the ground. Being
crashworthy, terminals are normally used at the end of a barrier that is
located within the clear zone or that is likely to be impacted by errant
vehicles.

116. ROADSIDE DESIGN GUIDE
PAGE 116
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
6.3 Classification of Safety Barriers by Performance
6.3.1 Overview
Perhaps the most important and relevant type of classification for safety barriers is the performance
classification. The performance classification is assessed and demonstrated through a series of standardised
full scale impact tests, such as the one shown in Figure 6.2. These impact tests not only prove whether a
barrier performs satisfactorily under certain impact conditions, but they also provide a controlled way of
accurately measuring certain impact characteristics of the system under test. These important impact
characteristics, such as dynamic deflection, working width, zone of intrusion and impact severity levels, provide
the vital information that a designer/engineer needs when designing the roadside geometry and selecting an
appropriate barrier system. These impact characteristics, which are explained in further detail in the following
sections, are often more relevant to the roadside designer/engineer than the individual dimensions of the
system.
Figure 6.2 – Impact testing of a roadside safety barrier
At the moment there are two main established impact test standards, which are used widely around the world.
These are:
• The American Guidelines - MASH [1] (previously NCHRP350 [2]); and
• The European Standard – EN1317 [3].
Due to the reasons explained in Chapter 1, the selected impact test guidelines for the safety barriers to be
used in the Abu Dhabi Road Network are MASH and NCHRP350. All safety barriers (used in the roadside,
median and on the edge of bridges) shall have demonstrated compliance with the American recommendations
in either NCHRP Report 350 (FHWA, 2004) or MASH (AASHTO, 2009) and additional local conditions for the
Abu Dhabi Road Network. Evidence of this shall be presented and approved by the Overseeing Organization
prior to the use of these systems. Only systems approved by the Overseeing Organization shall be used.
Performance classification according to these guidelines is presented in more detail in the following sections.
A brief overview of the EN1317 standard is also provided in Section 6.3.4, for informative purposes only. This
is further expanded in Appendix A.

117. ROADSIDE DESIGN GUIDE
PAGE 117
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
6.3.2 NCHRP350 and MASH Performance Classifications
After January 1, 2011, newly-tested safety barriers must be evaluated in accordance with MASH. However,
vehicle restraint systems that were accepted before the adoption of MASH by using criteria contained in
NCHRP Report 350 may remain in place and may continue to be manufactured and installed.
In order to meet the requirements of NCHRP350, or MASH, the safety barrier must demonstrate that it can
successfully decelerate (and in some cases redirect) an impacting vehicle without the unsafe detachment of
elements. During such times, the impacting vehicle should maintain an upright orientation, whilst meeting the
requirements of two severity indices; Occupant Impact Velocity (OIV) and Occupant Ride-down Acceleration
(ORA). The portion of the end treatment included in a barrier’s length-of-need must have re-directional
characteristics similar to those of the barrier to which it is attached.
The purpose of NCHRP350 and MASH is to present uniform guidelines for the impact testing of both
permanent and temporary highway safety features and recommended evaluation criteria to assess test results.
It should be noted that both NCHRP350 and MASH are guidelines and not formal standards and hence, they
only provide advice on the way in which testing should be conducted.
6.3.3 Test Types in NCHRP350 and MASH
The guidelines of NCHRP350 and MASH contain a number of Tables and Figures to explain the testing which
was undertaken to demonstrate the performance of a particular vehicle restraint system. This is based on over
40 years of experience from those involved within the industry, on an International basis. The underlying
philosophy in the development of the guidelines is that the testing conditions should represent the “worst case.”
This is particularly true for the determination of the impact weight, speed and angles of the tests.
For example, the weight of the small passenger car test vehicle was selected to represent approximately the
98th percentile of passenger type vehicles in the USA; i.e. only two percent of vehicles weigh less than the
specified test weight. The impact speed and angle combination represents approximately the 92.5 percentile
of real-world crashes [2]. The test requirements for longitudinal barrier systems are included in Table 6.1 and
Table 6.2.
When the combined effects of all testing parameters are considered, the testing represents the extremes of
impact conditions to be expected in real-world situations. At the same time, the existence of consistent
guidelines ensures that there is a level platform on which to test, and therefore ultimately compare, the
performance of different products.
It is also implicitly assumed that, if a roadside safety feature performs satisfactorily at the two extremes, for
example at TL-1 and TL-6, then the feature would also work well for all impact conditions in between, such as
TL-2, TL-3, TL-4 and TL-5. This assumption has shown to be reasonable for most roadside safety features [2].
Following an impact test to the requirements of NCHRP350 or MASH, the performance of the tested system
is evaluated in terms of the stability of the impacting vehicle; risk of injury to the occupants inside the impacting
vehicle, the structural adequacy of the safety feature, the exposure to workers and pedestrians that may be
behind a barrier or in the path of debris resulting from impact with a safety feature, and the post-impact
behaviour of the test vehicle.

118. ROADSIDE DESIGN GUIDE
PAGE 118
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Table 6.1 - Test requirements for NCHRP350 [2]
Test Level
Test conditions
Test vehicles
Vehicle speed
(km/h)
Impact angle
(°)
TL-1
820-kg passenger car
2000-kg pickup truck
50
50
20
25
TL-2
820-kg passenger car
2000-kg pickup truck
70
70
20
25
TL-3
820-kg passenger car
2000-kg pickup truck
100
100
20
25
820-kg passenger car 100 20
TL-4 2000-kg pickup truck 100 25
8,000-kg single-unit truck 80 15
820-kg passenger car 100 20
TL-5 2000-kg pickup truck 100 25
36,000-kg semi-trailer truck 80 15
820-kg passenger car 100 20
TL-6 2000-kg pickup truck 100 25
36,000-kg tanker truck 80 15
Table 6.2 - Test requirements for MASH [1]
Test Level
Test conditions
Test vehicles
Vehicle speed
(km/h)
Impact angle
(°)
TL-1
1100-kg passenger car
2270-kg pickup truck
50
50
25
25
TL-2
1100-kg passenger car
2270-kg pickup truck
70
70
25
25
TL-3
1100-kg passenger car
2270-kg pickup truck
100
100
25
25
TL-4
1100-kg passenger car
2270-kg pickup truck
10,000-kg single-unit truck
100
100
90
25
25
15
TL-5
1100-kg passenger car
2270-kg pickup truck
36,000-kg semi-trailer truck
100
100
80
25
25
15
TL-6
1100-kg passenger car
2270-kg pickup truck
36,000-kg tanker truck
100
100
80
25
25
15

119. ROADSIDE DESIGN GUIDE
PAGE 119
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
If a system successfully meets these parameters, its performance during the impact test is then classified by:
• Containment Level;
• Deflection Distance;
• Zone of Intrusion;
• Impact Severity Level.
Further details of these classifications are given in the following sections. These factors can then be used to
specify the performance of the system which is required at a particular site. It is therefore emphasised that for
a particular road safety application, it is not a product which should be specified, but the performance
requirements of the safety measure which is to be installed. Once the performance requirements of a particular
site are specified, a product which meets the requirements can be selected from the Abu Dhabi Department
of Municipal Affairs and Transport’s list of accepted proprietary products.
Other factors that should be evaluated in the design of a safety feature, include aesthetics, cost (initial and
maintenance), and durability (ability to withstand environmental conditions, wind- induced fatigue loading, sand
accumulation, effects of moisture, ultraviolet radiation, etc.). These are not addressed by these testing
standards, as this is not their purpose. However, the designer/engineer should evaluate the importance of
these factors on a site-by-site basis through engineering judgment.
6.3.3.1 Classification by Containment/Test Level
The containment/test level of a safety barrier relates specifically to the combination of weight, impact angle
and speed of test vehicle which the barrier has shown to successfully contain and redirect under full scale
impact testing to NCHRP350 or MASH. Reference should be made to Table 6.1 and Table 6.2 for further
details on the testing requirement for each containment/test level.
For example, if a barrier was shown to contain an 1100kg passenger car at 100km/h and 25 degrees, and a
2270kg pickup truck at 100km/h and 25 degrees, the system would be classified as a ‘TL-3’ safety barrier
under the criteria defined in MASH (Table 6.2).
It can also be observed from these tables, that the higher test levels require successful performance with
heavier impact vehicles or higher impact speeds. Therefore, the higher test levels prove successful
performance with higher energy impacts.
The TL-1 & TL-2 systems have been developed primarily for passenger cars and pick-up trucks for roads
where the speed limit isn’t over 50km/h or 70km/h respectively. These systems provide less protection
compared to the systems which are designed to the higher test levels. The most commonly used barriers
around the world today are the TL-3 systems [6]. TL-4 and TL-5 systems are generally designed for heavier
vehicles, weighing up to 10,000 and 36,000kg respectively. TL- 6 systems are also designed for impacts with
vehicles up to 36,000kg, but for the TL-6 test a tanker truck is used, whereas for the TL-5 test a semi-trailer
truck is used.
The higher test level barriers (TL-4 and over) are usually more expensive compared to the lower test level
ones. However, they may be justified for locations with high traffic volumes, higher traffic speeds, poor road
geometry, significant volume of heavy vehicle traffic and 3rd
party risk nearby

120. ROADSIDE DESIGN GUIDE
PAGE 120
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
(See Chapter 4, Section 4.4). On the other hand, a TL-3 system may not be cost effective for locations with
low traffic speed and volume. In such locations a TL-2 or a TL-1 system may be enough to contain the likely
range of vehicle impacts.
For design of barriers and railings refer to “AASHTO-LRFD Bridge Design Specifications” [4] and “AASHTO
Standard Construction Specifications” [5].
6.3.3.2 Classification by Deflection Characteristics
Deflection characteristics are among the most important features of a safety barrier. The amount of deflection,
which a system shows during an impact, changes from one design to another.
In general, barrier systems with higher deflection characteristics, i.e. flexible systems (see Section 6.5.1),
would dissipate the energy of a crash more and therefore lower the impact forces imposed upon the vehicle
occupants. On the other hand, systems with higher deflection would require more clear space behind them to
work safely. This is because, an errant vehicle can still reach the hazard behind and experience a secondary
impact, as shown in Figure 6.3, if the distance between the hazard and the barrier is less than the barrier’s
deflection distance. For this reason, depending on the available space on the site, the designer/engineer may
need to choose a system which has less deflection (see Chapter 7 for application requirements).
Figure 6.3 – A hazard, located within the deflection distance of the safety barrier
The deflection characteristics of a safety barrier are determined through full scale impact testing and are
expressed with the following properties:
• Dynamic Deflection: is the maximum dynamic lateral displacement of the traffic face of the
barrier that occurs during impact [1], as shown in Figure 6.4;
• Working Width: is the distance between the traffic face of the barrier before the impact and
the maximum lateral position of any major part of the system or vehicle, during the impact
as shown in Figure 6.4.
Both dynamic deflection and working width are determined through the analysis of high speed video coverage,
recorded during the impact test. The designer/Engineer can find this information through the promoter of the
system or within the test report.

121. ROADSIDE DESIGN GUIDE
PAGE 121
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
(See Chapter 4, Section 4.4). On the other hand, a TL-3 system may not be cost effective for locations with
low traffic speed and volume. In such locations a TL-2 or a TL-1 system may be enough to contain the likely
range of vehicle impacts.
For design of barriers and railings refer to “AASHTO-LRFD Bridge Design Specifications” [4] and “AASHTO
Standard Construction Specifications” [5].
6.3.3.1 Classification by Deflection Characteristics
Deflection characteristics are among the most important features of a safety barrier. The amount of deflection,
which a system shows during an impact, changes from one design to another.
In general, barrier systems with higher deflection characteristics, i.e. flexible systems (see Section 6.5.1),
would dissipate the energy of a crash more and therefore lower the impact forces imposed upon the vehicle
occupants. On the other hand, systems with higher deflection would require more clear space behind them to
work safely. This is because, an errant vehicle can still reach the hazard behind and experience a secondary
impact, as shown in Figure 6.3, if the distance between the hazard and the barrier is less than the barrier’s
deflection distance. For this reason, depending on the available space on the site, the designer/engineer may
need to choose a system which has less deflection (see Chapter 7 for application requirements).
Figure 6.3 – A hazard, located within the deflection distance of the safety barrier
The deflection characteristics of a safety barrier are determined through full scale impact testing and are
expressed with the following properties:
• Dynamic Deflection: is the maximum dynamic lateral displacement of the traffic face of the
barrier that occurs during impact [1], as shown in Figure 6.4;
• Working Width: is the distance between the traffic face of the barrier before the impact and
the maximum lateral position of any major part of the system or vehicle, during the impact
as shown in Figure 6.4.
Both dynamic deflection and working width are determined through the analysis of high speed video coverage,
recorded during the impact test. The designer/Engineer can find this information through the promoter of the
system or within the test report.

122. ROADSIDE DESIGN GUIDE
PAGE 122
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 6.4 – Working Width and Dynamic Deflection for two example systems
The working width is important in that it determines the space that must be maintained between the hazard
and the barrier. If a hazard were allowed to remain within the deflection distance of a barrier, the longitudinal
movement of an errant vehicle can still carry it into that obstacle. It is for that reason that no hazard (which
cannot be removed, relocated or made passively safe/transferable) should be present within the working width
of a safety barrier system.
It is essential that the deflection distance available on site is known, and that the deflection distance quoted by
the promoter for their system is less than the available distance on site. If a barrier must be located immediately
adjacent to the hazard, a rigid barrier may be the only viable option.
6.3.3.2 Classification by Zone of Intrusion (ZOI)
The Zone of Intrusion (ZOI) is the region measured above and behind the face of a barrier system where an
impacting high sided vehicle or any major part of the system (i.e. part over 2kg in mass) was seen to encroach
during an impact, as shown in Figure 6.5. Hence, there is a risk that an impacting vehicle may also encroach
into this space in the event of an incident.
The ZOI is determined following the full scale impact test of the system, in a similar way to the deflection
distance, as shown in Figure 6.6.

123. ROADSIDE DESIGN GUIDE
PAGE 123
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 6.5 – Zone of intrusion for higher vehicles
Figure 6.6 – Zone of intrusion as seen during an impact test
The ZOI is an important measurement to make, as it will assist with identifying the space within which there
should be no hazard, even in the event of a vehicle rolling on the top of the safety barrier system. This is
particularly important in the case of safety barriers located in front of bridge piers where there is a risk (to be
mitigated) of an impacting vehicle striking the barrier, rolling on the top of the barrier, and subsequently striking
the bridge pier. The barrier height and profile and the vehicle size, speed, and angle of impact determine the
amount of intrusion behind the barrier. The designer should try to accommodate this additional distance behind
the barrier, especially for applications with a Test Level of 4 and higher. This is because the heavy vehicles
for which the TL- 4 and higher systems are designed for (see Table 6.2) usually have significantly wider zones
of intrusion, caused by their height and size, as shown in Figure 6.6. The cargo box located at the back of
heavy vehicles lean much further over the barrier during an impact, compared to the cab, as shown in Table
6.3. This can especially be a problem in the vicinity of bridge piers.
It may not always be possible to move bridge piers beyond the clear zone and therefore a barrier is often
required to shield the errant vehicles from an impact with the pier. From a roadside safety perspective a TL-3
barrier is generally considered sufficient to protect majority of the passenger vehicles from a pier. However, a
TL-3 barrier is not likely to be enough to stop a heavy vehicle, which may then continue and hit the bridge pier.
This can especially be a problem if the bridge is known to have structural issues, as the impact may cause
significant damage. Therefore, a TL-4 or higher containment level barrier may be required.
Before Impact During Impact
Zone of

124. ROADSIDE DESIGN GUIDE
PAGE 124
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Table 6.3 – Examples of ZOI width for selected barrier types and test levels*
Test
Level
Barrier Type
Barrier Height
Range (Bh) in mm
Zone of Intrusion
Width (ZOIw) in mm
TL-2
Concrete 508-686 711
Concrete 686-1067 305
TL-3
Sloped-face
Concrete
762-813 457
Vertical
Concrete
737-813 610
Combination
of concrete
and steel
889-1067 610
Steel tubular
rails on curb
813-864 457
Steel tubular
without
curbs
705-914 762
TL-4 All 737-1067
864
(ZOIw_cab)
2030
(ZOIw_cargo)
* Adapted from AASHTO Roadside Design Guide [5]

125. ROADSIDE DESIGN GUIDE
PAGE 125
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
As guidance, in the USA, the AASHTO LRFD Bridge Design Specifications [7] set out the requirements for
design evaluation and rehabilitation of bridges. According to these specifications, bridge piers that are within
9m of the travelled way should be designed to withstand a large impact load or be shielded with a barrier. The
following height guidelines from the AASHTO LFRD Bridge Design Specifications are based on offset from the
travelled way to the face of the pier [6]:
• A 1370mm high barrier located 3m or less from the pier; or
• A 1070mm high barrier located more than 3m from the pier [7].
These values are only given as general guidance. The engineer/designer can identify the ZOI of individual
systems by referring to the crash test reports and high speed videos. This way, the required distance between
the barrier and the pier can be adjusted according to the impact behaviour of the individual product.
Narrowing of the roadway is not preferred on high-speed facilities to accommodate additional clearance for
ZOI. For example, do not reduce the shoulder width to gain additional clearance behind the barrier to meet the
ZOI guidelines. In those cases where the height of the hazard does not exceed the height of the barrier, the
ZOI is not considered to be relevant.
6.3.3.3 Classification by Impact Severity Level
Another important characteristic of a safety barrier is the impact severity level. As explained in Chapter 2, a
roadside barrier should also be considered as a hazard and it should only be used if the consequences of
hitting the barrier are expected to be less than hitting the hazard behind. Every barrier has different impact
characteristics and some absorb the impact energy better than the others, therefore exerting less impact forces
on the occupants of the errant vehicle. Rigid barriers for example (see Section 6.5.3) do not deflect as much
during an impact, as the flexible barriers (see Section 6.5.1) would and therefore usually higher forces are
exerted on the vehicle occupants during an impact with a rigid system.
The impact severity level of a system is determined through full scale impact testing. Due to the cost, reliability
and design of impact test dummies, occupant risk in NCHRP350 and MASH is assessed by the response of a
theoretical unrestrained front seat occupant whose motion, relative to the occupant compartment is determined
by the vehicle’s accelerations. The ‘point mass’ occupant is assumed to move through space until it strikes a
hypothetical part of the vehicle’s interior, and subsequently is assumed to then experience the remainder of
the vehicle’s acceleration pulse by remaining in contact with the vehicle interior. The two performance factors,
which determine the impact severity level for a barrier, are:
a) Occupant Impact Velocity (OIV): Which is the lateral and longitudinal component of
occupant velocity at the time when it impacts the vehicle’s interior;
b) Occupant Ride-down Acceleration (ORA): Which is the highest lateral and longitudinal
component of the resultant vehicular acceleration averaged over a 10ms interval following
the impact
Methods for calculating these values can be found in both NCHRP350 [2] and MASH [1]. Table 6.4 presents
the preferred and maximum allowable OIV & ORA Values from MASH.

126. ROADSIDE DESIGN GUIDE
PAGE 126
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Table 6.4 - Preferred and maximum allowable OIV & ORA values from MASH [1]
Occupant Impact Velocity (OIV) Limits
Component Preferred Maximum Allowable
Longitudinal and Lateral 9.1 m/s 12.2 m/s
Longitudinal 3.0 m/s 4.9 m/s
Occupant Ride-down Acceleration (ORA) Limits
Component Preferred Maximum Allowable
Longitudinal and Lateral 15.0 G 20.49 G
* For more information on test types, please refer to MASH [1]
OIV and ORA provide a method of ranking the severity of the impact with the safety barrier system, and give
an indicative guide to the level of injury which might be expected from an impact with an errant vehicle
(assuming all of the impact parameters are the same as those under which the safety barrier was tested). In
general terms, the lower the value of OIV and ORA for a particular system, the lower the risk of injury would
be to the vehicle occupants in the event of an impact.
6.3.1 The European Standard EN1317
Whilst vehicle restraint systems used within Abu Dhabi should be successfully tested to the requirements of
NCHRP350 and MASH, for completeness, reference is also made to the European Standard for the testing of
road restraint systems, EN1317 (see also Appendix A).
The European standard has been prepared by the European Committee for Standardization (CEN). During
the initial drafting of EN1317 in the mid-1990s, developments within the preparation of NCHRP350 were
followed closely by the standards writers in Europe, and every effort was made to harmonize the impact
performance standards (e.g. using the same or similar testing conditions and evaluation criteria). However,
given the inherent differences in highway and traffic conditions between the United States and EU, differences
between the U.S. guidelines and CEN standards arose. The gap between these two sets of requirements has
opened even further in the preparation of the MASH and latest published versions of EN1317 [8].
Despite a number of attempts, no equivalence can be found between testing to NCHRP350/MASH and
EN1317. Due to the different testing methods, test vehicle types and speeds, the use of both EN1317 and
NCHRP350/MASH products on the same scheme is strongly discouraged.
EN1317 is split into a number of different parts, each concentrating on a different product sector, the latest
published versions of which are outlined below:
• EN1317-1: 2010 - Terminology and general criteria for test methods;
• EN1317-2: 2010 - Performance classes, impact test acceptance criteria and test methods
for safety barriers including vehicle parapets;
• EN1317-3: 2010 - Performance classes, impact test acceptance criteria and test methods
for crash cushions;
• ENV1317-4; 2002 - Performance classes, impact test acceptance criteria and test methods
for terminals and transitions of safety barriers;

127. ROADSIDE DESIGN GUIDE
PAGE 127
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• EN1317-5:2007+A2 2012 - Product requirements and evaluation of conformity for vehicle
restraint systems;
• TR1317-6: 2012 - Pedestrian parapets.
It should be noted that there is a move to split the requirements of ENV1317-4 into two documents, one which
will solely cover the requirement for transitions (TR1317-4) and another which will solely cover the
requirements for terminals (EN1317-7). Whilst drafts of these new parts have been prepared, they are currently
awaiting publication.
6.1 Classification of Safety Barriers as Non Proprietary or Proprietary
All vehicle restraint systems (i.e. safety barriers, motorcyclist protection devices, terminals, crash cushions
and transitions) can be categorised as being either proprietary or non-proprietary.
6.4.1 Non-Proprietary (Generic) Systems
For many years, the FHWA in the USA and European countries such as the UK and Germany developed
vehicle restraint systems. Some of these designs were tested at the time to the appropriate standards, whilst
some were not. However, once the designs of these generic (non- proprietary) systems had been concluded,
they were ‘handed over’ to industry for them to fabricate the products and promote them, without patents.
Previously these non-proprietary systems have been accepted for use by the Abu Dhabi Department of
Municipal Affairs and Transport, and they are detailed in the Abu Dhabi Standard Drawings Manual.
Application of these systems over time has meant that there is a great deal of experience in the use (and
restrictions of use) of these products. However, in many cases there is a lack of continued support for these
products in terms of future development and the design and testing of transitions and connections to such
systems. Due to the lack of continuous development, many of these systems were tested in accordance with
the older versions of impact test standards and therefore usually with lighter vehicles which are not
representative of today’s vehicle fleets. For this reason, the impact performance of such systems with the
heavier and higher speed modern vehicles would be questionable.
Since these systems were developed by national road authorities, they were generally developed to fit the
specific needs of their own network and geographic conditions. Therefore, they may not always fit the local
conditions in other countries. This can especially be an issue in Abu Dhabi, where local conditions such as
extreme heat, corrosive soils and sandy roadsides may require certain characteristics such as better corrosion
resistance, free flow of sand, etc. This can lead to difficulties in the provision of a continuous level of safety,
as these systems are not continuously supported by the original designer to fit the needs of different local
conditions.
6.4.2 Proprietary Systems
In general, proprietary systems are commercially available and as such they are sold and promoted by
individual companies. As a result, such systems are often very competitively priced, and designed and tested
to the standards of NCHRP350 or MASH or EN1317.
Due to the worldwide competition, private barrier manufacturers need to continuously improve their systems
to position themselves ahead of their competition. This leads to a continuous improvement in the safety level
of barrier systems available in the market. Today, many proprietary

128. ROADSIDE DESIGN GUIDE
PAGE 128
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
systems perform better than the similar non-proprietary designs. For example, it is common to find proprietary
systems which achieve same containment level as a non-proprietary system, but with less deflection and lower
impact severity levels.
Proprietary systems are often tested or re-tested to the latest version of the impact test standard, to position
their products ahead of their competition. This means that these products are often tested with heavier vehicles
and vehicles with higher centres of gravity, which represent the modern vehicle fleets better than the older
standards.
As the design of the system belongs to the manufacturer, they will often provide their own guidance as to the
suitability of the system in a certain location, and provide details of the training required for installation and
maintenance requirements for their products. The manufacturers can also choose to develop or modify their
systems to perform better within the local conditions. This gives a level of assurance and accountability from
the manufacturer as to the performance of the system which they have placed on the market. As such,
proprietary systems are preferred to non- proprietary systems.
To use a proprietary roadside barrier, the system must have been accepted for use on the Abu Dhabi road
network by the Abu Dhabi Department of Municipal Affairs and Transport, or its representatives. In order to be
deemed acceptable, the manufacturer will be required to supply full test reports and videos of their system(s)
to the Department of Municipal Affairs and Transport for assessment against the relevant testing standard
(either NCHRP350 or MASH) mention EN1317.
In addition, questions regarding the suitability of the product for local conditions must also be completed in a
satisfactory way, supported by evidence where possible. Note that whilst the acceptance of a product in
another territory (e.g. by Federal Highways in the USA or awarded a CE mark within Europe) may be
considered as part of the approval process, this will be no guarantee of acceptance for use by the Abu Dhabi
Department of Municipal Affairs and Transport, due to its local needs and road conditions. A list of those
approved products deemed to be acceptable for use on the AD DoT road network is available.
6.2 Classification of Safety Barriers by Rigidity
Historically, safety barriers have been grouped into three categories as flexible, semi-rigid and rigid, according
to their deflection characteristics resulting from an impact. This type of classification is an approximate one,
based on general characteristics of the system and therefore does not rely on a quantifiable relationship. This
classification has been useful in explaining the advantages and disadvantages of certain type of systems, at
a time when the available systems on the market were limited to a certain number of non-proprietary designs.
Today however, with the increased number of varied proprietary systems available on the market, the
boundaries between the flexible, semi-rigid and rigid categories have been blurred. Therefore, a more
meaningful and the recommended type of classification is the performance based one, which is presented in
Section 6.3.
The classification by rigidity is also included in this design guide for informative reasons. The following sections
give general information into flexible, semi-rigid and rigid barrier systems.

129. ROADSIDE DESIGN GUIDE
PAGE 129
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
6.5.1 Flexible Systems
Flexible barrier systems have been historically characterised by relatively high deflections upon impact, which
dissipate the energy of a crash and result in lower impact forces imposed upon the vehicle occupants. This
behaviour can often result in lower levels of injury risk to vehicle occupants when compared with semi-rigid
and rigid barrier systems. Whilst the specific performance of a barrier system will vary from one barrier to
another, flexible barriers often display good control of vehicle trajectories after impact, which assists in
redirecting an errant vehicle on a path along the line of the barrier. This minimises the likelihood of secondary
impacts with other vehicles.
The primary advantages of flexible barrier systems is the low deceleration forces which are imparted onto the
vehicle occupants, effective vehicle containment, redirection over a wide range of vehicle sizes and installation
conditions, and low initial cost. Damaged posts are usually easily replaced because these are often located in
plastic sleeves in concrete foundations.
However, once hit by an errant vehicle, the length of damaged section is often longer for flexible systems than
more rigid designs. Unlike more rigid systems, flexible systems usually require immediate repair after an impact
as they lose their functionality after the first impact, and therefore they are the most dependant on continuous
monitoring and maintenance.
Wire rope safety barrier (WRSB) systems have historically been shown as the most commonly used type of
flexible barrier on the AD DoT road network, an example of which can be seen in Figure 6.7.
Figure 6.7 - Wire Rope Safety Barrier – an example of a flexible safety barrier
The WRSB normally comprises three or four strands of tensioned cable, held in the designed heights by flexible
posts. The design principle is the redirection of the impacting vehicle, once sufficient tension is developed in
the cables. There are many different proprietary designs available on the market today, some of which are
shown in Figure 6.8, through indicative profiles.
As can be seen from the figure, the number and the configuration of cable positioning change from one product
to another. Depending on the design, the cables may be:
• Positioned on one side of posts throughout the installation;
• Positioned on the opposite side of each consecutive post;
• Positioned inside the posts;

130. ROADSIDE DESIGN GUIDE
PAGE 130
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• Or intertwined.
Apart from the ones where the cables are positioned on a single side of the posts throughout the installation,
the WRSB are designed to contain impacts from both sides and are therefore commonly used as median
barriers.
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.8 – Examples of WRSB profiles
It is not possible to make a general statement about the impact performance characteristics of different cable
configurations, i.e. it is not possible to say that one configuration is safer than the other. The engineer/designer
should refer to the test results and manufacturer’s specifications to compare different products. The majority
of the WRSB systems available on the market today are tested to TL-3; however, there are also TL-4 systems
available.
The height of the individual cables is important and changes from one system to another. A typical system can
have an upper cable height of 580mm to 720mm from the ground level [9]. The cable heights are generally
designated as the result of numerous crash tests and computer simulations to provide the optimum
performance. If the cables are too low, an impacting vehicle may go over the barrier; whereas if the cables are
too high, an impacting vehicle may go under the barrier. For this reason it is very important that the cable
heights of the installed system is the same as the crash tested one.
Another important property is the post spacing. Although the main aim of the posts in a flexible system is to
keep the cables at the designated height and easily bend under the vehicle impact, they do also add stiffness
to the overall system. As the post spacing decreases, the stiffness of the system increases and therefore the
deflection of the system decreases. A lot of the proprietary systems are available in different post spacing
configurations to provide systems with different

131. ROADSIDE DESIGN GUIDE
PAGE 131
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
working widths. However, as the number of posts increase, so does the cost of the system. As a very general
guidance, a typical WRSB system can have post spacing anywhere between 1.8m to 3.2m.
Depending on the type of soil, the post may be driven directly to the ground, installed in sockets which are
driven into the ground or installed in sockets with concrete casings, as shown in Figure
6.9. Type and the depth of foundation required changes from one design to another, and therefore the selection
should be made according to the manufacturer’s instructions. However, as a very general guidance, a typical
WRSB system can have foundation depths anywhere between 400mm to 1,000mm, although these may need
to be increased where sandy or weak soil conditions exist.
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.9 – Examples of WRSB foundation types
The majority of the WRSB systems available on the market today are designed to have higher tensions on the
cables, compared to the first WRSB designs. During the evolution of these systems, it was understood that by
applying higher tension to the cables, lower deflections can be achieved under impact. As the cables are
already tensioned before the impact, it takes less deflection for the system to build the necessary tension to
redirect the errant vehicle. For this reason, it is important that the tensions on the cables are kept within the
acceptable limits. These limits change from one product to another and every product should be tensioned to
the manufacturer’s specifications. This is especially important in Abu Dhabi, where the high temperatures can
cause the cables to expand and therefore decrease the tension. The tension in the cables can be increased
or decreased through cable tensioners located at the anchorages (see Figure 6.7) or on the cables, depending
on the design and length of installation.
A negative effect of using tensioned cables is that it limits the road geometries on which the systems can be
installed. This is especially true on tight horizontal curves, where the high tension can bend the posts; and on
sag vertical curves, where the high tensions can lift the cables from the posts and increase the cable height to
unacceptable limits. The minimum allowable horizontal curve radius for WRSB installation changes from one
design to another, but as a general guideline 200m can be indicated as the recommended minimum for most
systems [9].

132. ROADSIDE DESIGN GUIDE
PAGE 132
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
The length of the tested system makes a considerable difference in the deflection characteristics. It is known
that short test installations, such as 100-150m, can demonstrate lower deflections compared to longer
installations such as 250-300m. This is because, in short installations, the tension builds up with less deflection
and some of the tension is shared by the ground anchors located at the ends of the system. As a result, WRSB
systems should ideally not be installed on the roadside, in lengths longer than the ones used during the impact
test. If they are installed in longer lengths, they may deflect further than the distances recorded during the
impact test; which may cause errant vehicles to reach the hazards behind the barrier.
Another type of flexible system is the weak post w-beam barrier, an example of which is shown in Figure 6.10.
This system behaves like a low tension WRSB, i.e. the barrier posts are weak and designed to bend easily
during an impact, without too much resistance. Naturally, this system does not incorporate blockouts, as these
would increase the stiffness of the posts and therefore would be against its working principle. The posts are
placed far apart and their main function is to keep the w-beam at the required height rather than adding
significant stiffness to the system. Variations of this system have been successfully tested to TL-2 and TL-3
[5]. The weak posts used in these systems are similar to those of the WRSB designs. Similar to the WRSB,
the required beam height, foundation depth and post spacing would change from one system to another, and
therefore the system installed on the roadside should be the same as the system tested during the full-scale
crash test. Please refer to the individual details of products provided by manufacturers. However, as a very
general guidance, a typical weak post system can have post spacing of around 3.8m, a beam height of around
710mm and a foundation depth of around 900mm.
Figure 6.10 – Weak Post W-Beam Barrier
In sandy areas, the open design of the wire rope system prevents drifting on or alongside the roadway.
However the local experience shows that the sand accumulation is still a problem with the weak post w-beam
system. Therefore designer/engineer should assess the potential sand accumulation of a system, on a product-
by-product basis; independent of its rigidity classification. Such accumulation of sand against the face of a
barrier can, in itself, present a risk of injury to road users, as shown in Figure 6.11.

133. ROADSIDE DESIGN GUIDE
PAGE 133
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 6.11 – Effect of barrier type on sand accumulation
The disadvantages of flexible systems include their sensitivity to correct height installation and maintenance,
their reduced effectiveness on the inside of horizontal curves, the clear area needed behind the barrier to
accommodate the deflection of the system upon impact, and the comparatively long lengths of barrier that are
non-functional and in need of repair following a major impact.
6.5.2 Semi-Rigid Systems
Semi-rigid barriers have been historically classified as the systems which are positioned between the flexible
and rigid categories, based on their deflection characteristics. The majority of w-beam (excluding the weak
post systems) and the thrie-beam systems available on the market today can be categorised as semi-rigid
barriers, an example of which can be seen in Figure 6.12.
Figure 6.12 - Strong post W-Beam Barrier with block out
These systems have historically been shown to be the most commonly used type of semi-rigid barrier within
the AD DoT road network. Resistance in these systems results from a combination of tensile and flexural
stiffness of the rail and the bending or shearing resistance of the posts. There

134. ROADSIDE DESIGN GUIDE
PAGE 134
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
are many different proprietary designs available on the market today, which are developed from the original
non-proprietary w-beam systems, some of which are shown in Figure 6.13, through indicative profiles. The
majority of the proprietary w-beam systems available on the market are successfully tested to either TL-3 or
TL-4.
As can be seen from the figure, these systems can have different beam profiles, but the most common ones
are the w-beam and the thrie-beam. The thrie-beam is known to provide increased rigidity compared to the w-
beam, however, the overall performance of these systems would change from one design to another. The
beams can either be connected directly to the steel posts or they can be connected through steel, plastic or
wooden blockouts. Blockouts are used to prevent a vehicle from snagging on the (generally) stiff posts of the
system and to maintain rail alignment (and therefore reduce the risk of vaulting) in the event of an impact.
Some proprietary systems feature double blockouts in their design as an energy absorbing mechanism or to
increase the post offset.
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.13 - Examples of single sided W-Beam profiles
Beam height is important and is usually measured from the ground to the top of the beam, as shown in Figure
6.13. Required beam height changes from one design to another. But as a rough guidance, a typical w-beam
system can have a beam height of around 700mm to 800mm; whereas a thrie-beam system can have a beam
height around 800mm to 850mm. The cable beam heights are generally designated as the result of numerous
crash tests and computer simulations to provide the optimum performance. If the beam is installed too low, an
impacting vehicle may go over the barrier; whereas if the beam is installed too high, an impacting vehicle may
go under the barrier. For this reason it is very important that the beam height of the installed system is the
same as the crash tested one.

135. ROADSIDE DESIGN GUIDE
PAGE 135
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Another important property is the post spacing. As the post spacing decreases, the stiffness of the system
increases and therefore the deflection of the system decreases. This effect is demonstrated in Table 6.5,
through very general, indicative values for selected systems. The table shows the effect of changing the post
spacing on the maximum deflection. The values shown here are based on two sources. The first source is the
results of a computer simulation using the Numerical Analysis of Roadside Design (NARD) Program. The
second source is the full scale impact tests carried out by the Kansas Department of Transportation. Both, the
simulations and the full scale impact tests shown in the table were carried out with a 2,000kg passenger car
at an impact angle and speed of 25° and 97km/h [6]. As can be seen from the table, barriers deflect more once
the post spacing is increased. The values shown in this table are very general and for indicative purposes only.
A lot of the proprietary systems are available in different post spacing configurations to provide systems with
different working widths. However, as the number of posts increases, so does the cost of the system. As a
very general guidance, a typical w-beam system can have post spacing anywhere between 0.6 m to 5.0m.
The designer/engineer should refer to the crash test reports for each individual product to determine the
maximum deflection and working width. Impact tested products should not be modified on site to alter their
post spacing, as doing so effectively creates a new system, and therefore further impact testing is required.
Table 6.5 – Effect of post spacing on barrier deflection*
Barrier Type
Impact
Angle (°)
Post Spacing
(mm)
Maximum Deflection (mm)
Simulation
Result
Impact Test
Result
Single W-
beam
25 1,905 907 754
25 952 541 597
Double W-
beam
25 952 437 498
25 476 320 N/A
Single Thrie-
Beam
25 1,905 716 N/A
25 952 480 N/A
* Adapted from AASHTO Roadside Design Guide [6]
It is often possible to find double sided versions of a lot of the designs available on the market. The double
sided systems are designed to be used in the median as they can withstand impacts from both sides. The
addition of the second beam on the opposite side increases the rigidity and as a result affects the impact
characteristics of the system. For this reason, the double sided versions of the single sided w-beam designs
should also be impact tested. Experience shows that the double sided versions of single sided w-beam design
often successfully pass the same test levels with less deflection. Figure 6.14, shows some indicative profiles
of the common double sided w-beam systems.

136. ROADSIDE DESIGN GUIDE
PAGE 136
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.14 - Examples of double sided W-Beam profiles
Similar to WRSB systems, the w-beam posts can be driven directly to the soil, placed in sockets which are
driven into the soil or placed in concrete casings (see Figure 6.9). The type and depth of the foundation required
changes from one design to another and therefore, a selection should be made according to the manufacturer’s
instructions. However, as very general guidance, a typical w-beam system can have foundation depths
anywhere between 1,000mm to 1,200mm.
Semi-rigid barriers deform or deflect upon impact but to a lesser extent than flexible systems. When struck by
an errant vehicle, the support posts are designed to bend/collapse and the barrier rail to deform and act as a
belt to absorb some of the impact force. The tensile forces developed in the barrier rail assist in redirecting
the impacting vehicle. Resistance is achieved through the combined flexure and tensile strength of the rail.
In terms of advantages and disadvantages, semi-rigid barriers are positioned between flexible and rigid
systems.
• Their initial cost is usually higher than the flexible ones but lower than the rigid ones;
• Depending on the severity of impact, semi-rigid barriers usually retain a level of functionality
(albeit reduced) after a slight/moderate collision, thereby eliminating the need for immediate
repair [6]. This makes the semi-rigid systems more durable compared to the flexible ones.
Therefore, they are less dependent on maintenance and immediate repair, compared to the
flexible systems. However, they are not as durable or maintenance-free as the rigid systems;
• In terms of impact forces exerted on to vehicle occupants, semi-rigid systems, in general,
provide a smoother deceleration compared to rigid systems. However, the flexible systems
provide even smoother deceleration than the semi-rigid systems;

137. ROADSIDE DESIGN GUIDE
PAGE 137
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• In terms of the deflection characteristics, semi-rigid systems are generally positioned
between flexible and rigid systems. Although every system is different from another, generally
speaking, semi-rigid systems achieve the same test levels with less deflection, compared to
flexible systems. On the other hand, semi-rigid systems generally deflect more, compared to
rigid systems. This can be seen as an advantage against the flexible systems and a
disadvantage against the rigid systems, in locations where the clear space behind the barrier
is limited.
6.5.3 Rigid Systems
Rigid barriers have historically been categorised as systems which do not deflect or deform to any significant
extent when impacted. Impacts with rigid barrier systems tend to be more severe than the impacts with more
flexible systems due to lack of deflection. This leads to higher forces exerted on the occupants of the impacting
vehicle and hence to a higher risk of injury. Although this assumption is generally valid, a more reliable
comparison between different systems can be achieved by looking at the impact severity parameters OIV and
ORA, as explained in Section 6.3.3.4.
Systems with higher impact severity parameters should be restricted to locations where there is a very limited
width for barrier deflection or where there the risk to third parties is greater than the risk to vehicle occupants.
The most commonly used rigid barrier systems within Abu Dhabi are concrete barriers, examples of which are
shown in Figure 6.15. The majority of the concrete barriers available on the market today are successfully
tested to TL-4 and TL-5.
Figure 6.15 – Examples of roadside (left) & median (right) concrete barriers
Figure 6.16 presents some of the most common profiles available on the market today. Profile of a concrete
barrier has a significant effect on the way it redirects errant vehicles. For example, the F- Shape barrier was
developed as a modified version of the New Jersey type and is often seen as a safer system for smaller
vehicles, due to redirection characteristics. Some profiles provide higher containment levels, whereas others
provide lower impact severity.

138. ROADSIDE DESIGN GUIDE
PAGE 138
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.16 - Examples of double sided concrete barrier profiles
As can be seen from the figure, some of the concrete barriers are designed to be surface mounted, such as
the Dutch Step Profile, whereas others may require to be partially embedded under the surface level, such as
the F-Shape and some may require significant foundations, such as the Vertical Wall. Some designs are
installed as free-standing systems while others utilise ground anchorages to keep the barrier from moving
during the impact. These foundation requirements change from one design to another and therefore, reference
should be made to the manufacturer’s specifications for each individual system.
Concrete barriers are also available as single sided systems, to be used as roadside barriers. Figure 6.17
shows some of the common single sided concrete barrier profiles available on the market today.
Height is an important property of concrete barriers and changes from one design to another. Typical height
of an F-Shape and New Jersey barrier is 810mm, whereas Dutch Step design is usually 900mm; single slope
barriers are 1076mm and a vertical wall can be around 1400mm. The barrier heights are generally designated
as the result of numerous crash tests, two of which are shown in Figure 6.18. Figure 6.18 shows two of the
impact tests carried out during the development of the vertical wall barrier in UK. The barrier shown on the left
had a height of 810mm and the impacting vehicle overturned. This system was later modified to a height of
1400mm, as shown on the right and the vehicle was successfully contained. For this reason it is very important
that the heights of the installed system is the same as the crash tested one.

139. ROADSIDE DESIGN GUIDE
PAGE 139
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.17 - Examples of single sided concrete barrier profiles
Figure 6.18 – Effect of concrete barrier height on impact performance
Due to their rigid nature, and their ability to successfully contain vehicles with minimal damage, the cost to
maintain and repair rigid barriers over their life (often quoted as 50 years) is less than for semi-rigid and flexible
systems [9]. However, it is often the case that the cost of initially installing rigid systems will be greater than
for semi-rigid and flexible systems with the same containment capability.
Concrete barriers can be installed in two methods, precast or cast in-situ, as shown in Figure 6.19. In precast
systems, the individual concrete blocks are built at a factory and joined together on site. This type of concrete
barrier takes less time to install compared to in-situ alternative. The connection details between the individual
blocks changes from one system to another and is of vital importance. The Engineer/Designer should make
sure the connections are done in-line with the original design and the system on the road is installed to the
same standard as the impact tested system.

140. ROADSIDE DESIGN GUIDE
PAGE 140
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
The in-situ concrete barriers are cast on the site via mobile slip form machines. The installation in this type of
system takes longer compared to pre-cast systems; however, the resulting barrier often provides higher
performance due to its continuous structure.
Figure 6.19 – Examples of in-situ (left) [10] and pre-cast (right) concrete barriers
Pre-cast systems utilise a number of different interlocking mechanisms to connect individual concrete blocks.
These mechanisms often require a block to be slid over the edge of the next one to create an interlocking
connection. Some of these are patented systems and are unique to specific manufacturers. A representation
of such an interlocking mechanism is shown in Figure 6.20.
Figure 6.20 – Example of a pre-cast concrete barrier connection mechanism
Concrete barriers can be installed in a number of different ways, as shown in Figure 6.21. The in- situ systems
are often cast on asphalt or gravel bases and are free-standing. Pre-cast systems can be embedded within a
layer of asphalt, placed on a gravel or asphalt base or they can be anchored to the ground. Embedding the
system within a layer of asphalt adds additional resistance against lateral movement during impact, and
therefore helps decrease the deflection. On the other hand, the freestanding pre-cast systems may deflect
during an impact, depending on the specific design.

141. ROADSIDE DESIGN GUIDE
PAGE 141
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
This free movement usually decreases the impact severity for vehicle occupants; however, more space is
required behind the barrier to accommodate the extra deflection. Some systems incorporate ground anchors
to fix the concrete blocks to the ground. This adds stiffness to the freestanding pre-cast system and usually
eliminates the lateral deflection during an impact. It is not possible to state that one foundation type is generally
better than the others. The designer/engineer should evaluate each foundation according to the properties and
requirements of each individual site.
It is important to make sure that the barrier installed on the roadside has the same foundation set- up as the
one which was impact tested. This is because changing the type of foundation used can cause noticeable
difference in impact performance levels, such working width or impact severity. For example, a pre-cast system
which was embedded in asphalt may show no deflection during the impact test. However, the same system
may show deflection, if it is tested in free standing installation. In such cases, further impact testing may be
required to demonstrate the effects of change in foundation. Proprietary concrete barrier manufacturers often
test their systems with different foundation combinations and create selections of different performance levels
with the same profiles. Further detail about individual systems should be provided by the manufacturers.
Figure 6.21 – Examples of concrete barrier foundations
A disadvantage of the concrete systems is that they do not allow the free flow of sand and therefore can cause
sand accumulation on the edges of the barrier, as shown in Figure 6.22.
Figure 6.22 – Sand accumulation on the side of a closed profile concrete barrier

142. ROADSIDE DESIGN GUIDE
PAGE 142
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
A rigid barrier can be considered for freeways, truck roads, and expressways in the following cases:
• to shield objects close to the roadway where deflection space is limited;
• On truck roads where there is a high volume (10% or more) of heavy trucks [12];
• To minimize repair and maintenance;
• To reduce headlight glare into nearby buildings or other sensitive areas;
• To reduce headlight glare between frontage roads and the mainline, especially where the
alignment directs headlights at opposing traffic; and
• Areas where it is especially critical to contain errant vehicles.
Where a concrete barrier is used as a rigid barrier system, the following considerations should be made:
• For roadside and bridge applications, the safety shape should be located on the traffic side
with (if present), the vertical face on the back;
• Concrete barriers can be backfilled behind the barrier, as shown in Figure 6.23, to provide
lateral support and to further reduce deflection in the event of an impact;
Figure 6.23 – Example of a concrete median barrier with backfill
• Due to the rigid nature of the system, taller vehicles such as HGVs and buses may roll on the
top of the barrier (see ZOI in Section 6.3.3.3). This should be considered when specifying the
concrete barrier system, and the distance between the front of the barrier system and the
hazard located behind it;
• Due to their rigid nature, concrete barriers should ideally only be located in places where the
anticipated angle of impact is less than 15 degrees to reduce the risk of injury to vehicle
occupants in the event of an impact. These are mainly high speed dual carriageway roads;
• Concrete barriers must not be located more than 4 m from the edge of the nearest traffic lane
because greater distances increase the risk of higher angle collisions with the barrier [9];
• For a concrete barrier to be effective, the barrier must be able to resist the impact load through
a combination of moment and shear loads. To achieve this, a minimum length of barrier is
required. Achieving this minimum length depends on the type of system, method of
anchorage of the barrier and the detail of the connections between elements of the

143. ROADSIDE DESIGN GUIDE
PAGE 143
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
system. Therefore designer/engineer should refer to the installation guidelines of the system, as
recommended by the manufacturer.
Bridge barriers are also considered as rigid systems. Due to the higher risks associated with the consequences
of falling off the side, bridge barriers are usually designer to containment level of TL-4 and higher. These
systems can be made of concrete, aluminium, steel or a combination of concrete and metal. Some of the
common profiles are shown in Figure 6.24, for indicative purposes.
*Profiles are not to scale and are shown for indicative purposes only.
Figure 6.24 – Examples of common bridge barrier profiles
Concrete systems are generally known for their ability to contain heavier vehicles and lower maintenance
costs, as they require virtually no maintenance for most hits. Concrete barriers such as New Jersey, F-Shape,
Single Slope and Vertical wall are considered to be MASH TL-5 bridge railings when adequately reinforced
and built to a minimum height of 1,067mm [6]. However, these systems are heavy and introduce a permanent
load on the bridge, which should be considered during the bridge design. Sometimes metal sections are added
on top of the concrete to increase the height of the system and therefore the containment level.
Metal bridge barriers can be made of aluminium or steel. The metal systems, especially the aluminium ones,
are lighter than concrete alternatives and therefore introduce less loading on the bridge. However, they are
more likely to be damaged during impacts than the concrete ones and therefore have higher maintenance
costs. In general, steel systems can contain heavier vehicles than the aluminium one do; although this would
change from one design to another. Aluminium systems available on the market are mostly tested up to TL-4,
whereas it is possible to find TL-5 steel systems. Bridge barriers available on the market are predominantly
proprietary systems and therefore the design details can change dramatically from one system to another.
Further information should be provided by the manufacturer.
6.3 Summary and Conclusions
Safety barriers can be classified into different categories by several of their properties. These include:
• Impact Test Performance:

144. ROADSIDE DESIGN GUIDE
PAGE 144
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
o Containment Level;
o Working Width & Dynamic Deflection;
o Vehicle Intrusion;
o Impact Severity.
• Developer of the System:
o Proprietary Systems;
o Non-Proprietary Systems;
• Rigidity and General Design:
o Flexible Systems;
o Semi-Rigid Systems;
o Rigid Systems.
Of all these classifications, the most important and relevant ones are the performance classifications. The
performance classification of a system is determined through full scale impact testing. Performance of barrier
systems should be specified in terms of containment/test level (i.e. the weight and speed of vehicle for which
the system has been successfully tested), deflection distance (i.e. the distance which the barrier deflects under
impact), zone of intrusion (i.e. the distance above and behind the barrier where a higher vehicle may roll into),
and impact severity (i.e. how high is the risk of injury to the occupant of a vehicle in the event of an incident).
The recommended impact test guidelines for Abu Dhabi are MASH and NCHRP350.
Barrier systems can be designated as either proprietary (i.e. they are owned by a manufacturer) or non-
proprietary (i.e. they are patent free). Proprietary systems are to be preferred as they are tested to the latest
standards and will have a great amount of supporting information in terms of site suitability, training and
maintenance requirements.
Historically, barrier systems have been categorised as flexible, semi-rigid and rigid. With the increase of the
number and variety of available systems on the market, the boundaries between these categories have
disappeared. Therefore a more meaningful and recommended classification is the performance based one.
Each type of barrier has its place on the Abu Dhabi Road Network. However, care must be taken to ensure
that the minimum performance requirements specified for a particular barrier type are correct and that the
barrier selected meets or exceeds these minimum requirements.
Only barrier systems accepted by the Abu Dhabi Department of Municipal Affairs and Transport are permitted
to be installed on the road network.
6.4 References
[1] FHWA, “Manual for Assesing Safety Hardware (MASH),” [Online]. Available:
http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/ctrmeasures/mash/.
[Accessed 23 02 2015].

145. ROADSIDE DESIGN GUIDE
PAGE 145
06 DESCRIPTION OF ROADSIDE, MEDIAN &
BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
[2] NCHRP, “NCHRP Report 350, Recommended Procedures for the Safety Performance
Evaluation of Highway Features,” Transportation Research Board, National Research Council,
Washington DC, 1993.
[3] CEN, “EN 1317 Road Restraint Systems - Part 2: Performance classes, impact test acceptance
criteria and test methods for safety barriers including vehicle parapets,” CEN (European
Committee for Standardization), Brussels, 2010.
[4] AASHTO-LRFD Bridge Design Specifications, 7th
Edition, Washington D.C.: American
Association of State Highway and Transportation Officials, 2014.
[5] Standard Specifications for Highway Bridges, 17th
Edition, Washington D.C.: American
Association of State Highways and Transportation Officials, 2005.
[6] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of
State Highway and Transportation Officials, 2011.
[7] American Association of State Highway and Transportation Officials, AASHTO LRFD Bridge
Design Specifications, Washington DC: AASHTO, 2010.
[8] Roadside Safety Design Comittee, “Transportation Research Circular E-C172,” Transportation
Research Board, Washington D.C., 12 July 2012.
[9] RTA, Roadside Design Guide for Dubai, First Edition, Dubai: Roads and Transport Authority,
2008.
[10] G. Williams, “Whole Life Cost-Benefit Analysis for Median Safety Barriers,” TRL, 2008.
[11] Delta Bloc, Delta Bloc International GmbH, [Online]. Available:
http://www.deltabloc.co.uk/en/Product-
Categories/Permanent_Safety_Barriers8/pproducts/0.html. [Accessed 06 09 2015].
[12] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney, NSW:
Austroads, 2010.

146. ROADSIDE DESIGN GUIDE
PAGE 145
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
7.1 Overview
Chapter 6 has given details of the different types of barriers which are available (i.e. flexible, semi- rigid or
rigid), the testing which is required of these barriers to NCHRP350 or MASH, and the way in which these
barriers can be classified following the testing. Barriers are typically classified according to their level of
containment, their deflection characteristics, and their impact severity level.
This Chapter details the way in which these performance classifications should be specified for a particular
location to ensure that the barrier installed (under testing conditions) has shown to be capable of providing a
level of risk reduction which is acceptable.
Furthermore, in order to ensure that a level of performance is maintained in the event of an impact, an overview
of the maintenance and inspection requirements for barrier systems is also provided, giving examples of those
issues more regularly witnessed on the Abu Dhabi road network, reasoning why such issues are not
acceptable and more importantly, what can be done to remedy the situation.
7.2 Selection Criteria
The selection of a barrier system for a particular location should be primarily governed by safety considerations
and secondarily by cost. In general, more flexible barriers will have the lowest lateral deceleration rates and
will perform better at gradually redirecting an errant vehicle. However, when a flexible system has an impact,
it will usually require repair work before it will function properly again. In areas with frequent accidents, this
may result in a significant accumulation of time during which the barrier is not operational, thus increasing risk
to other road users. Also, the regular presence of repair crews must be considered as a potential hazard, both
for the motorist and for the workers themselves. In such circumstances, use of a semi-rigid barrier or a rigid
concrete barrier may be warranted, which require less repair work.
The safety of a given barrier system will also vary, depending on the type of vehicle involved. It is partly for
that reason that proprietary barrier systems are preferred as they will have been tested to a particular test level
in accordance with NCHRP350 or MASH and hence, the impact parameters for which the barrier has
demonstrated performance will be known.
As stated in Chapter 3, the preference should always be to remove or relocate hazards from clear zones where
practical rather than simply installing barriers.
Because of their size, buses and large trucks are not well protected by flexible barrier systems and even if
they contain a larger impacting vehicle, the extra vehicle weight may cause larger than normal deflections. If
the cable is adjacent to an embankment, large vehicles may still reach the slope. With their higher centres of
gravity, they will be more likely to roll over, even on relatively mild slopes. Rigid barriers function best for large
vehicles, and higher barriers reduce the chance

147. ROADSIDE DESIGN GUIDE
PAGE 146
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
that the large vehicles will flip over the barrier. The designer should review the distribution of vehicle types
expected as a factor in selecting appropriate barrier types.
Factors that should be considered in the selection of the type of barrier to be used at a specific site include:
• Restraint requirements (i.e. performance capability);
• Dynamic deflection and clearance;
• Site conditions;
• Traffic volumes and percentage of heavier vehicles;
• End treatments (see Chapter 9);
• Sight distance (see Chapter 5 of the Abu Dhabi Road Geometric Design Manual);
• Costs;
• Maintenance;
• Aesthetics; and
Table 7.1 and Table 7.2 outline these requirements. The following sections elaborate on these considerations.
7.2.1 Containment Requirements
The primary purpose of all roadside barriers is to prevent a run-off-the-road vehicle from striking a fixed object
or terrain feature that is less forgiving than striking the barrier itself. Containing and redirecting the impacting
vehicle using an appropriate and well-specified barrier system accomplishes this.
Because the dynamics of an impact crash are complex and will vary wildly from impact to impact, the most
effective means of assessing barrier performance is through full-scale impact tests based on a similar testing
and assessment requirements. By standardising such tests, designers can compare the safety performance
of alternative designs. Traditionally, most roadside barriers have been developed and tested for passenger
cars and offer marginal protection when struck by heavier vehicles at high speeds and at other than flat angles
of impact. Therefore, if the safety of the occupants of passenger vehicles is the primary concern, flexible barrier
systems will normally be selected. However, locations with high traffic volumes, high speeds, high-crash
experience, and/or a significant volume of heavy trucks and buses may warrant a higher performance level
barrier, which is typically more rigid. This is especially important if barrier penetration by a vehicle is likely to
have serious consequences, for example, when there is a high consequence third party located behind the
barrier.
The initial determination that needs to be made is the level of containment that the barrier must provide at a
given site. The “basic” level is to provide for light passenger vehicles, including four- wheel drive vehicles and
light commercial vehicles, and this is accomplished in many cases by specifying TL-3 longitudinal barriers
(although this will depend on the speed of the road). Similarly, TL-2 barriers may be appropriate on lower
speed roadways where design speeds are 70 km/h or less.

148. ROADSIDE DESIGN GUIDE
PAGE 147
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Table 7.1 - Selection criteria for roadside barriers
Criteria Comments
1. Containment requirements
(Performance Capability)
The barrier must be structurally able to contain and redirect an
errant vehicle, and hence the appropriate Test Level (TL) should
be selected.
2. Deflection distance and
clearance
Adequate deflection distance must be available so that the barrier
can deflect on impact without contacting rigid objects behind the
barrier. This will also require consideration of the Zone of Intrusion
(ZOI).
3. Site Conditions The slope approaching the barrier, slope behind the barrier, and
distance from travelled way may preclude the use of some barrier
types, as too might the ground conditions into which the barrier
will be installed.
4. Cost Standard barrier systems are relatively consistent in cost, but
special-use systems can cost significantly more.
5. Traffic Volumes and percentage
of heavier vehicles
A high volume of traffic on the road will increase the exposure of
the barrier system to impacts (both collision and nuisance hits).
Roads with a higher percentage of heavier vehicles will require the
provision of barrier with a higher test level (level of containment)
6. Maintenance
a. Routine The barrier should not require a significant amount of routine
maintenance.
b. Collision Damage Generally, flexible systems require significant repair after a
collision, semi-rigid systems have fewer repair requirements and
rigid systems or higher performance railings require an even
smaller amount of repair, sometimes nil. [1]
c. Nuisance Hits Flexible barriers will require the most frequent attention for
nuisance hits (e.g. mowers, minor vehicular encroachments).
Semi-flexible barriers will require repairs where nuisance hits
cause kinks or tears. Rigid barriers will seldom require repairs for
nuisance hits.
d. Materials Storage The fewer the number of different systems used, the fewer
inventory items/storage space required.
e. Simplicity Simpler designs, in addition to costing less, are more likely to be
repaired properly by field personnel.
7. Compatibility The barrier system selected may need to be connected to other
systems and/or terminals.
8. Aesthetics There may be some instances where the appearance of the
barrier, or the ability to see through the barrier may influence the
choice of barrier used.
9. Field Experience The performance and maintenance requirements of existing
systems should be monitored to identify problems that could be
lessened or eliminated by using a different barrier type.

149. ROADSIDE DESIGN GUIDE
PAGE 148
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Table 7.2 – Key considerations in barrier selection
Barrier
Type
Consideration
Flexible
Length
Length of the tested WRSB makes a considerable difference on deflection characteristics. It is known that short test
installations, such as 100-150m, can demonstrate lower deflections compared to longer installations such as 250-
300m. This is because in short installations the tension builds up with less deflection, and some of the tension is
shared by the ground anchors located at the ends of the system.
Therefore, for proposed installations which are longer than the ones used during the impact test, the
designer/engineer should consider the potential effect on the maximum deflections. Similarly, the minimum length of
installation at full height (excluding transitions from the end anchors to full height) should be in-line with the
manufacturer’s specifications. The manufacturer and road authority should be consulted when determining
anchorage spacing.
Horizontal
curves
The WRSB manufacturer should be consulted in case of proposed installations on horizontal curves with less than
600m radius. This is because the high tension on the ropes may bend the posts and cause problems with rope height
and tension during or after an impact. The minimum recommended horizontal curve radius is around 200m for most
WRSB installations.
Vertical
curves
The WRSB manufacturer should be consulted in case of proposed installations on vertical curves, where the high
tensions can lift the cables from the posts or the posts from their sockets at the bottom of the curve and increase the
cable height to unacceptable limits. In cold weather this effect can be more apparent due to the contraction of the
cables. Cables which are higher than acceptable limits can cause the impacting vehicle to go under the barrier. This is
especially more likely at the bottom of sag vertical curves, where the front suspension of an impacting vehicle would
be more likely to get compressed; lowering the impact height of the vehicle.
Ground
Slope
Ground slope on which the WRSB will be installed can be a limiting factor. Generally, a slope of 1V:10H is considered
as the maximum acceptable ground slope. The WRSB manufacturer should be consulted in case of proposed
installations on slopes steeper than 1V:10H.
Transition
The WRSB systems should not be connected directly to other, more rigid systems, unless the safety of the transition
is proven through full scale impact testing. This is because the combination of the high deflections of a WRSB with the
lower deflection of a stiffer system can cause pocketing, when hit by errant vehicles; i.e. the impacting vehicle can be
directed to a head-on collision with the end of the stiffer system. However, WRSB may be installed in close proximity
to rigid or semi-rigid barriers provided that there is sufficient distance between the barriers to accommodate the
dynamic deflection.
Semi
-rigid
Length
To perform satisfactorily, barriers must have sufficient length to enable the tension to be developed through the
system and into the foundations and/or anchorages as impact occurs. For proprietary systems, the minimum
length of a barrier system should be stated within the manufacturer’s installation manual. However, as a general
guide, for semi-rigid systems, the barrier should have at least 30 m of barrier section; exclusive of terminal
sections and/or transition sections.
Horizontal
curves
W-beam and Thrie-beam barriers are known to contain errant vehicles relatively well on the outside of curves, as the
concave shape helps the development of tension in the rail. The inside of the small radius curves may be a bit more
problematic as it becomes more difficult to develop the tension, without significant deflections. However, this
problem is usually specific to installations, such as the corners of intersections, for which appropriate designs are
available (see section 7.4.3).
Kerbs
When installing a barrier in the vicinity of a kerb, the barrier face should ideally be in-line with the kerb. If this is not
achievable, the barrier should be placed a certain distance away from the kerb face, depending on the traffic speed.
Further information is available in section 7.3.6.
Rigid
Length
The minimum length of installation should be stated within the manufacturer’s specifications. However, as a general
guide, for rigid systems, this value is likely to be around 20-30m.
Horizontal
curves
Rigid barriers are known for their higher impact severities, due to lack of deflection. For this reason, they should
generally be avoided in locations where they are likely to get hit in high impact angles, such as outside of small
radius horizontal curves. However, it is not always possible to avoid this in all situations, particularly on loop ramps
at urban freeway interchanges. At least on loops ramps, the impact speeds are expected to be relatively low.
Drainage
Water outlets should be provided under the system to help discharge storm water from the road pavement.

150. ROADSIDE DESIGN GUIDE
PAGE 149
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Due to the high number of variables and local considerations to be made, the decision whether to install a
barrier system with a higher level of containment (TL3 or greater) will largely depend on engineering
judgement, and consideration of the following points:
• High percentage of heavy vehicles in traffic stream (i.e. on truck roads);
• Routes where hazardous materials (such as chemicals, solvents, pesticides, oils (except
edible ones), nuclear waste) are transported;
• Adverse geometrics, such as sharp curvature, that are often combined with poor sight
distance
• Severe consequences associated with penetration of a barrier by a large vehicle; and
• For bridge parapets, the height of the bridge, and the type of hazard located below the bridge.
With regard to the specific case of median barrier systems, a proprietary TL-3 barrier (capable of redirecting
passenger cars, vans and light trucks) will be adequate in most cases. However, consideration should be given
to the bulleted points above when determining the test level of the barrier to be installed, especially if the result
of a heavy vehicle penetrating a median barrier is likely to be catastrophic. In such cases the use of a
proprietary TL-4 or TL-5 median barriers should be specified as these have an increased capability to contain
and redirect large vehicles.
Further, with regard to the specific case of bridge barriers:
A. TL-4. This is the standard Abu Dhabi bridge rail on most bridges. Its use is appropriate,
except for those conditions identified in point C below where a TL-5 bridge rail should be
used.
B. TL-5. This performance level should be designated for:
• All truck roads;
• All roads with significant truck volumes (say, 100 DDHV or higher); and
• All other sites where a TL-5 rail can address a specific concern (e.g. truck lean over,
potential catastrophic consequences for heavy vehicle penetration).
C. TL-6. This is the highest performance level and it is only considered for the rare cases
where a route is regularly used by high numbers (say, 100 DDHV or higher) of tankers or
similar vehicles and there are hazards with risk to third parties (See Chapter 4, Section 4.4)
within the vicinity of the travelled way.
7.2.2 Deflection Distance Requirements
As detailed within Section 6.3.3.2 the distance which the barrier deflects during the NCHRP350/MASH testing
will be reported for every proprietary product. The deflection distance is important in that it determines the
space that must be maintained between the hazard and the barrier. If a hazard were allowed to remain within
the deflection distance of a barrier, as shown in Figure 7.1, the longitudinal movement of an errant vehicle can
still carry it into that obstacle. It is for that reason that no hazard (which cannot be removed, relocated or made
passively safe/transferable) should be present within the deflection distance of a safety barrier system.

151. ROADSIDE DESIGN GUIDE
PAGE 150
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.1 - Examples of hazards located within the deflection distance of the barrier
Field experience has shown that, during impact, a large truck or similar high-centre-of-gravity vehicle can lean
over more rigid barrier systems, and therefore intrude behind the rear face of the barrier system. The Zone of
Intrusion (ZOI) is the clear area that should be provided behind the barrier and beyond its dynamic deflection
distance to account for this behaviour, and more details regarding the determination of this area is given within
Section 6.3.3.3. The designer should consider the ZOI when locating a barrier to shield a rigid object, such as
a bridge pier or sign support. In some cases, however, providing a separation between the barrier and the
object will not be practical. In critical areas, it then may be desirable to use a higher performing barrier or, for
a concrete barrier, to increase the barrier height to minimize vehicular overhang in a crash. In the specific case
of median barriers, relatively wide, flat medians are suited for flexible or semi-rigid barriers, if the deflection
distance of the barrier system is less than one-half of the width of the median. Narrow medians, where little or
no deflection is acceptable, within heavily travelled roadways usually require a rigid barrier.
7.2.3 Impact Severity Level Requirements
Section 6.3.3.4 provides details of the severity indices (OIV and ORA) which are calculated during impact
testing to NCHRP 350 and MASH. These provide a method of ranking the severity of the impact with the safety
barrier system, and give an indicative guide as to the level of injury which might be expected from an impact
with an errant vehicle (assuming all of the impact parameters are the same as those under which the safety
barrier was tested). In general terms, the lower the value of OIV and ORA for a particular system, the lower
the risk of injury would be to the vehicle occupants in the event of an impact. For proprietary systems used
within the Abu Dhabi Department of Municipal Affairs and Transport’s road network, preference should be
given to those systems meeting the ‘preferred’ values within Table 6.4. No systems exceeding the ‘maximum’
values within Table 6.4 shall be used without prior approval of the Abu Dhabi Department of Municipal Affairs
and Transport with all of the values being detailed on the Abu Dhabi Department of Municipal Affairs and
Transport’s list of accepted vehicle restraint systems.

152. ROADSIDE DESIGN GUIDE
PAGE 151
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.2.4 Site Considerations
Site conditions will often influence the choice of barrier type. Regardless of the type of barrier being used, it
is preferable that the slope in front and behind of the barrier is essentially flat (1V:10H or flatter) because the
requirements of NCHRP350 and MASH are such that safety barriers have (generally) only been tested in such
configurations. The result on an impact with a specific barrier in a slope is generally unknown.
If the barrier is to be placed on a slope steeper than approximately 1V:10H, a flexible or semi-rigid type should
be used to reduce the severity of impact between the errant vehicle and the barrier system - this is likely to
increase due to additional lateral forces on the vehicle as a result of travelling across the slope. However, no
barrier should be placed on any slope steeper than 1V:6H. Instead, the barrier should be placed closer to the
edge of the carriageway (where the gradient is likely to be less), or remedial works undertaken to flatten the
running surface prior to the barrier location. The full width between the traffic lanes and a concrete barrier
should be suitably paved to ensure optimum barrier performance.
7.2.5 Cost Considerations
Full details regarding the economic evaluation of different treatment options (which can equally be applied to
different barrier systems under review) can be found in Chapter 12. The selection of a barrier should consider
the life cycle costs of optional systems. The initial capital cost of the barrier is only one component of economic
evaluation. Repair and future maintenance costs may vary substantially for different systems. The initial cost
of the system will still be an important budgetary and project management consideration. In general, the initial
cost of a system increases as rigidity and strength increase, but repair and maintenance costs usually
decrease with increased strength.
Where clear space will allow, a flexible or semi-rigid median barrier may be the best choice due to the less
severe impacts which will result, if a barrier can be located in the centre of a median where it is less likely to
be hit and repairs do not necessitate closing a lane of traffic. However, a rigid barrier (requiring no significant
routine maintenance or repair) is recommended if a barrier must be located immediately adjacent to a high-
speed, high-volume traffic lane, or if there is a high density of heavier vehicles (refer to Section 7.2.1).
7.2.6 Traffic Considerations
Higher traffic volumes increase the probability of a barrier impact, both in terms of a heavy impact, but also in
terms of nuisance strikes. However, it is not just the impact itself which should be considered, but also the
effects of the resulting repair works. Closing lanes to work (particularly in the case of median barriers) causes
more traffic complications where traffic volumes are high. Therefore, in high-traffic volume locations, rigid
barriers are generally preferred because they usually provide continuous, crashworthy service without
generating maintenance and repair.
Where there is a high volume of heavy vehicles (for example on a truck road) or a history of heavy vehicle,
cross-median crashes, a rigid barrier is preferred because it is more likely to contain and redirect heavy
vehicles. Maintenance and repairs are not usually required after a hit. The designer must also consider the
Zone of Intrusion (see Section 6.5.4) for the system, together with the other performance requirements detailed
in Section 7.2.

153. ROADSIDE DESIGN GUIDE
PAGE 152
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.2.7 Installation, Maintenance and Inspection Requirements
For all proprietary system, installation, maintenance and inspection requirements should be provided by the
promoters associated with the barrier system. They should also have an established training scheme for the
operatives undertaking these activities.
Maintenance factors that need to be considered before selecting a particular barrier system include:
• Routine maintenance of the barrier;
• Damage repair;
• Effect of the barrier on road and roadside maintenance (pavement overlays for example);
• Material and component requirements (e.g. stockpiling of spare parts); and
• Experience of maintenance repair crews.
It is desirable that the number of different roadside barrier systems used in Abu Dhabi be limited. This practice
has advantages in that maintenance personnel need to be familiar with and trained to inspect and maintain a
limited number of systems and stocks of replacement parts are more easily managed. However, at the same
time, a wide variety of products give designers choice in the products which they can use, as a result
competition will increase and costs reduce.
Rigid systems are generally not damaged during impact and therefore have lower maintenance requirements
and associated costs. Therefore, rigid barriers may be advantageous on urban freeways and expressways
where maintenance workers are particularly vulnerable. However, this advantage is offset to some extent by
the likelihood of more serious crashes and a greater level of subsequent traffic disruption.
Flexible systems generally become ineffective following an impact. In the case of a wire rope safety fence,
many hundreds of metres of barrier may become ineffective following an impact on the system. However,
flexible systems can be relatively easy to repair even when a significant number of posts are damaged during
impact. The combination of concrete ground sockets, slotted posts and the cables used for wire rope systems
enables damage to be quickly repaired.
Repair maintenance is usually a more important factor for median barriers than roadside barriers. One or more
high-speed lanes will normally need to be closed in order to repair or replace damaged barriers because
median barriers are typically installed closer to the travelled way. This creates a safety concern for both the
repair crew and for motorists using the road. Consequently, a rigid barrier system is likely to be preferable in
many median applications, particularly for high- volume urban freeways and expressways where the barrier
must be located in close proximity to the traffic lane.
7.2.8 Compatibility Requirements
The total roadside barrier system, including bridge rails, must function effectively as a unit. As a result, impact
tested transitions should be used when the approach roadside barrier significantly differs in strength, height,
and deflection characteristics from the connected system (refer to Chapter 9). In certain circumstances, the
barrier will also need to demonstrate a level of compatibility with other features, such as:
• Local terrain;
• Lighting columns and overhead sign supports; and

154. ROADSIDE DESIGN GUIDE
PAGE 153
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• Bridge piers.
Figure 7.2 (left) shows a lack of compatibility between a concrete barrier and the kerb located in front of it – in
this case there is a lack of continuity in protection, caused by the gap in the barrier as a result of the location
of the overhead sign support. Ideally, the support would be removed or moved rearwards from the edge of the
carriageway, however, if this is not possible, an acceptable solution would be to install a short length of profiled
steel plate (as shown in the right-hand side photograph). Whilst this does not provide complete continuity, it
does address of the need to have a gap in the barrier, whilst maintaining the profile of the barrier system and
reducing the risk of pocketing.
Figure 7.2 - Lack of Cmcpatibility between barrier and overhead sign support (left) and a possible
solution (right)
7.2.9 Aesthetic and Environmental Considerations
While aesthetics are a concern, they are not normally the controlling factors in the selection of a roadside
barrier, except in environmentally sensitive locations (e.g. recreational areas, parks). In these instances, a
natural-looking barrier that blends with its surroundings may be appropriate, as shown in Figure 7.3. However,
it should be ensured that the barrier still meets the structural and performance specifications. Aesthetics may
also be important in tourist or recreational areas. In some situations, barriers that blend with the surroundings
may be preferred.
The designer should make every effort in the treatment of all structures, including bridge rails, to reflect the
Islamic design and culture. Design concepts should be easily implemented. Also, incorporate the construction
considerations into the architectural treatment concepts. Architectural elements should be functional, durable,
and easily maintained. Desirably, maintain a sense of continuity throughout the entire highway corridor.
Lack of Compatibility
A Possible Solution

155. ROADSIDE DESIGN GUIDE
PAGE 154
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.3 - An example of a bridge parapet designed to incorporate aesthetic considerations
Environmental factors may be important to consider in the selection process. For example, barriers with
considerable frontage area may contribute to drifting of sand in some areas. Figure 7.4 shows that whilst
drifting and blown sand can be an issue for road user visibility, it is clear that, due to the open nature of some
barriers, it can be less of a risk to road users if the sand is permitted to blow through the barrier system. This
should be compared to Figure 7.5 where the solid face of the concrete barrier acts as a barrier to the flow of
the sand and hence, sand is seen to accumulate on the face of the barrier. This accumulated sand will be
detrimental to the safety of road users as it will reduce the ability of the barrier system to function as designed.
Hence, in areas where drifting sand is frequent and large in volume, barriers with an open design should be
considered.
Figure 7.4 - The Effect of Drifting Sand

156. ROADSIDE DESIGN GUIDE
PAGE 155
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.5 - Sand accumulation on the face of a concrete barrier
In a similar way, open profile barriers should be preferred in areas liable to flooding to allow the passage of
water through the system. Of course, the provision and maintenance of drainage solutions in these areas
should be reviewed when flooding is an issue.
Certain types of steel barrier will deteriorate in corrosive or abrasive environments; typically the soils in Abu
Dhabi are generally extremely corrosive due to the resistivity of the soil, the temperature and humidity, and
high winds.
Soil Resistivity is a measure of how much the soil can resist the flow of electricity. Corrosiveness of a soil can
be rated according to its resistivity; smaller resistivity results in more severe corrosivity rating. The soil
resistivity in Middle Eastern sandy desert environment is usually less than 2000ohm cm, which makes it
severely corrosive as shown in Table 7.3.
Table 7.3 - Soil Corrosivity Scale [2]
Soil Resistivity Range (Ω cm) Corrosivity Rating
0 – 2000 Severe
2000 - 10000 Severe to moderate
10000 - 30000 Mild
30000 and above Not likely
Temperature and humidity are important factors in soil corrosivity. High yearly means of temperatures and
humidity contribute to Abu Dhabi’s very corrosive environment. Wind velocity is relatively high in coastal
regions; sometimes with blowing sand (as shown in Figure 7.4). The combination of all of these properties
creates a very corrosive environment, which tests the durability of road safety systems and in particular, their
foundations.
Acceptable solutions such as protective coatings or thicker gauge metal could be utilised. The posts used for
a particular location will depend on two main aspects:
• The performance requirements and design of the barrier system;

157. ROADSIDE DESIGN GUIDE
PAGE 156
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• The local ground conditions.
Within the manufacturer’s installation manual, guidance will be given with regard to the post types which are
suitable for their system (as this will vary from system to system). The evaluation of the ground conditions and
the foundations available at a particular location can be found in Section 7.3.7.
The corrosion effects of weathering of steel can be seen by the deterioration of the post in Figure
7.6. These weathering effects will be lessened if the steel post is installed with a concrete sleeve around it
although the rate of degradation will vary depending on the local conditions of the site.
Figure 7.6 - Example of a corroded barrier post
The high corrosivity of the soils in Abu Dhabi has led the Authorities to use concrete foundations for some
items of roadside furniture, which protrude above ground level. These should not exceed 150mm. Concrete
foundations will protect the electrical connections of objects such as luminaire supports, by cutting their contact
with the ground, as shown in Figure 7.7. However, care must be taken that this will not interfere with the
dynamic performance of systems, particularly passively safe devices. Further details on restrictions and
requirements in such cases can be found in Section 4.3.2.5.
Figure 7.7 - Electrical cabinet on a raised concrete base

158. ROADSIDE DESIGN GUIDE
PAGE 157
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.2.10 Field Experience
There is no substitute for documented proof of a barrier’s field performance. If a particular barrier system is
working satisfactorily and does not require an extraordinary amount of maintenance, there is little reason to
select and install another barrier for which these characteristics are not conclusively known. It is particularly
important that impact performance and repair cost data be maintained by appropriate personnel and that the
information is made available to design engineers charged with selecting and installing traffic barriers.
The manner in which a barrier performs in the field, and how this relates to the original full scale testing can
be identified by reviewing experience from impacts with barrier systems where available and by documenting
the resulting damage and repair costs. In general, designers should consider using only a few different
roadside barrier systems on any particular scheme. The advantages of this practice include:
• The systems in use have been proven effective over the years;
• The site-specific design details are better understood;
• Construction and maintenance personnel are familiar with the systems;
• Parts and inventory requirements are simplified when only a few different types of barrier
are routinely used; and
• End terminals and transition sections for normal installations also can be standardized.
7.3 Application Criteria for Roadside, Median and Bridge Barriers
After consideration of Chapters 3 and 4, and determining that the system cannot be made passively safe or
traversable in accordance with Chapter 5, consideration should be given to the performance of the barrier
needed of a particular application, in line with the guidance in Chapter 6, and Section 7.2.
This Section presents guidelines with regard to the way in which the barrier system should then be designed.
However, it is emphasised that at all times within the design process, engineering judgement should be applied
and the final design thoroughly reviewed before implementation.
When determining the placement of a barrier system, either in the roadside, median, or on a bridge structure,
the following detailed aspects of the barrier design should be made:
• Length of need;
• Minimum length and gaps in barriers:
• Lateral placement from the edge of the travelled way;
• Shy line offset;
• Barrier deflection distance;
• Effect of kerbs; and
• Foundation conditions.

159. ROADSIDE DESIGN GUIDE
PAGE 158
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
The following points should also be considered with particular reference to roadside barriers (refer to Section
7.4):
• Effect of embankments;
• Rate of flare;
• The presence of a short radius; and
• Sight distance.
In addition, the following points should be considered with particular reference to median barriers (refer to
Section 7.5):
• Terrain effects on the lateral placement of median barriers;
• Superelevated sections;
• Fixed objects within the median;
• Emergency and maintenance crossings;
• Gates; and
• Glare screens.
Furthermore, the following points should be considered with particular reference to bridge parapets (refer to
Section 7.6):
• Material type;
• Hardware attachments;
• Additional lateral placement considerations;
• Heights of bridge parapets;
• Fixation to bridge decks.
These factors are discussed in the following sections.
7.3.1 Length of Need
A barrier must be extended a sufficient distance upstream and/or downstream from the hazard to safely protect
a run-off-the-road vehicle. Otherwise, the vehicle could travel behind the barrier and impact the hazard. The
determination of the LON, adjustments, graphical representations and solved examples are shown in the
appendix at the end of this Guide.
Vehicles depart the road at relatively small angles (as demonstrated by the relatively small impact angles
specified for testing within NCHRP350 and MASH). These flat angles of departure result in the need to extend
the barrier a significant distance upstream from the hazard.
Many factors combine to determine the appropriate length of need for a given roadside condition. These
include:
• The distance to the outside limit of the hazard (LA) or the clear zone (LC), whichever is
smaller;
• The distance between the edge of travelled way and the barrier (L2);

160. ROADSIDE DESIGN GUIDE
PAGE 159
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• The runout length (LR), which is based on the design speed (V) and the traffic volume on
the facility;
• The length of hazard (L1), as measured parallel to the roadway;
• Whether or not the barrier is on a flare; and
• On two-way facilities, whether or not the barrier needs to be extended to provide protection
for the traffic in the opposing direction.
Figure 7.8 and Figure 7.9 illustrate the variables that will determine the barrier length of need. Figure 7.8
applies to a roadway with traffic moving in one direction or to a two-way roadway where the hazard is not within
the clear zone of the opposing direction of travel. For two- way, two-lane undivided highways, all barrier ends
should be terminated with an approved crashworthy end terminals (see Chapter 9). Figure 7.9 applies to a
two-way undivided facility where the roadside hazard is within the clear zone of the opposing direction of traffic.

161. P
AGE
160
07
S
ELECTION
AND
A
PPLICATION
OF
R
OADSIDE
,
M
EDIAN
A
ND
B
RIDGE
B
ARRIERS
L1 = Length of hazard
Notes:
 Use appropriate crashworthy terminal. See Chapter 9. Note that the Length of need starts 3.81m downstream of
the terminal.
 Use acceptable anchorage terminal. See Chapter 9.
 The use of the 25° angle to locate the end of the trailing barrier end will be determined on a case-by-case basis
depending on site conditions.
L2
= Distance to barrier LC
= Clear zone
LA = Distance to back of hazard L3 = Distance
to front of hazard LR = Runout length
X = Length needed for approach end
R
OADSIDE
D
ESIGN
G
UIDE
3.81m
L
1
Figure
7.8
-
Barrier
length
of
need
layout
(one-way
or
dual
two
way
divided
roadways)
F
IRST
E
DITION
-D
ECEMBER
2016

162. P
AGE
161
07
S
ELECTION
AND
A
PPLICATION
OF
R
OADSIDE
,
M
EDIAN
A
ND
B
RIDGE
B
ARRIERS
L2
= Distance to barrier LC
= Clear zone
Notes:
 Use appropriate crashworthy terminal. See Chapter 9. Note that
the Length of need starts 3.81m downstream of the terminal.
 If Lc for opposing traffic < LA, then X = 0 for opposing traffic.
LA = Distance to back of hazard L3 = Distance to front of hazard LR =
Runout length
X = Length needed for approach end
R
OADSIDE
D
ESIGN
G
UIDE
3.81m
Figure
7.9
-
Barrier
length
of
need
layout
(two-way
roadways)
F
IRST
E
DITION
-D
ECEMBER
2016

163. ROADSIDE DESIGN GUIDE
PAGE 162
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.3.2 Minimum Length and Gaps in Barriers
To perform satisfactorily, barriers must have sufficient length to enable the strength to be developed
through the system and into the foundations and/or anchorages as impact occurs. Hence, even if the
length of need is shorter, the installation length of a barrier system should at least be the minimum
length of the barriers systems. Designers should, therefore, check that the distance between the
leading and trailing points of need is greater than the minimum length of barrier for the chosen barrier
type. The lengths to be considered in the design of roadside barriers are the [3]:
• Terminal lengths;
• Transition length; and
• Minimum length of barrier.
For proprietary systems, the minimum length of a barrier system should be stated within the
manufacturer’s installation manual. However, as a general guide, for semi-rigid systems, the barrier
should have at least 30m [1] of barrier section exclusive of terminal sections and/or transition sections.
For flexible systems, the minimum length is 60m [4], exclusive of the terminal or transition sections.
For rigid barriers, a minimum length of 20-30m may be suitable [1].
Likewise, short gaps between runs of barrier are undesirable. This is because short gaps introduce
discontinuities into the system, and increase the risk for errant motorists; as they can hit the ends of
the barriers. These barrier ends should be shielded by crashworthy terminals (see Chapter 9). A single
gap requires two terminals (one for each end) and the cost of two crash-worthy terminals is likely to be
more than the cost of a short distance of standard barrier section. Ultimately, the cost effectiveness of
each option will depend on the costs of terminals and the standard section of barrier and also on the
length of the gap. The evaluation should be done by the designer/engineer for each scenario. However
as a rough guidance, gaps of less than 60m between barrier termini should be connected into a single
run, unless a gap is required for access, in which case the end of the barriers should be terminated
using appropriate terminal designs.
7.3.3 Lateral Placement
Barriers in themselves can be hazardous to errant vehicles, it is just that the risk of injury, and severity
of injury should be less than that resulting from an impact with the hazard located behind the barrier
system. However, the lateral position of a barrier can greatly affect the outcome on an incident, either
affecting the probability of the incident occurring, or the severity of injuries resulting from an impact.
This equally applies to roadside, median and bridge barrier systems.
As a general rule, a roadside barrier should be placed as far from the travelled way as practical, while
maintaining the proper operation and performance of the system [5]. This way, a wider clear area is
provided, which would increase the chances of an errant vehicle to regain control, without hitting the
barrier. Furthermore, the designer/engineer should understand the following effects, with regards to
the lateral placement of barriers:

164. ROADSIDE DESIGN GUIDE
PAGE 163
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
• As the distance from the edge of the travelled way increases, the proportion of errant vehicles
which are likely to reach the distance decreases (see Chapter3, Figure 3.1). This means that,
barriers which are placed closer to the edge of the travelled way are more likely to get hit by
errant vehicles, compared to ones which are placed further away. Therefore, the barriers
which are located closer to the edge of the travelled way are likely to be impacted more
frequently than the ones located further away. This, in effect, is likely to cause higher property
damage costs for road users and higher maintenance costs for road authorities, and as a
result, increase the risk of injury to road workers during maintenance and repair;
• Barriers which are located closer to the edge of the travelled way, on average, are likely to
get hit at higher speeds than the ones located further away. This is simply because barriers
which are located further away will provide more empty space, along which the errant vehicle
can slow down, before reaching the barrier;
• Experience shows that barriers which are located closer to the edge of the travelled way are
likely to get hit at lower impact angles, whereas the barriers which are located further away
are likely to get hit at higher impact angles [1]. This is because the errant vehicles do not
always follow a straight line as they leave the road. In scenarios, where an errant vehicle
follows a curved path, the angle of impact would increase as the distance of the barrier from
the edge of the road increase. This can especially be a problem for rigid systems, such as
concrete barriers, as high impact angles, combined with the rigid nature of the system can
increase the impact severity. Therefore, consideration should be taken, when placing rigid
systems further away from the road. However, by their nature, rigid systems are more likely
to be chosen, in locations where the lack of space does not permit other systems, due to
working width requirements. Therefore, rigid barriers are likely to be located close to the edge
of the travelled way anyway;
• Barriers which are placed too close to the edge of the travelled way may cause drivers to
consider them as hazards and to shy away from barrier and drive closer to the lane on the
other side. The net effect is a reduction in traffic speed, which affects the capacity of the road.
The distance from the edge of the travelled way beyond which a roadside barrier will not be
perceived as a hazard and result in motorists reducing speed or changing vehicle position on
the roadway, which is referred to as the shy-line offset [5]. Further information on the shy-line
offset is provided in Section 7.3.4;
• There is an increased risk of sideswipe crashes if lane widths less than 3.65m are used next
to barriers. This occurs because drivers tend to move away from the barrier and may
encroach into adjoining travel lanes;
• Drivers will travel at moderate speeds close to long lengths of barrier; however, this is
generally only successful in a high-stress driving environment (e.g. tunnels and bridges)
where drivers are attentive and ready to react quickly to risks;
• Driving close to barriers increases the stress of the driving task and cannot be sustained for
long periods.

165. ROADSIDE DESIGN GUIDE
PAGE 164
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
In addition to operational considerations, a roadside barrier and its foundation should not [1]:
• interfere with any utilities, drainage conduits or structures; or
• impair access of personnel or machinery to any utilities, drainage conduits or installation or
structures.
The lateral position of a barrier is influenced by the [1]:
• Road cross-section (e.g. need for shoulder and/or kerb);
• Barrier-to-hazard clearance (see Section 7.3.5);
• Shy line offset (see Section 7.3.4);
• Trajectory of vehicles when crossing kerbs and slopes (see Section 7.3.6); and
• Desire to avoid nuisance damage (frequent strikes).
Depending on the local circumstances, it may be preferable to provide the same shoulder width
adjacent to barriers as is provided elsewhere along a road as this will provide the road user with a
consistent roadside geometry. However, consider the provision of a wider shoulder (e.g. 3m to 4m from
the edge of the adjacent traffic lane to the barrier) to provide space for vehicles parked on the nearside
to open their doors and/or to provide space for maintenance vehicles to stand clear of the traffic lane
[1].
In some cases, the distance between the edge of the travelled way and the hazard may be limited, in
which case, the designer must consider how the available space will be best used and what type of
barrier is most suitable for the particular situation. Where space is limited, and discretionary parking or
emergency stopping is not essential, it may be preferable to provide a reduced shoulder width in front
of the barrier, provided that the shy line principle (refer to Section 7.3.4) is given adequate
consideration [1].
When a vehicle passes over a kerb or a slope, its trajectory and/or the height of the vehicle may be
affected and this may, in turn, affect the way in which the vehicle interacts with the barrier system. For
that reason it is important to consider the effect of the kerb strike and/or slope geometry on the lateral
placement of the barrier system. Further details of these issues are considered in Sections
7.3.6 and 7.4.1.
The barrier offset should match or exceed the desirable shoulder width on the roadway for the service
life of the infrastructure element being designed. For example, for a new bridge, the projected traffic
volume for the next 50 years is of interest. It is normal practice on new bridge designs to provide
sufficient width such that widening would not be required in the 25 to 30 years following construction
[6]. As long as the barrier is located beyond the perceived shoulder of a roadway, it will have minimum
impact on driver speed or lane position [5].
7.3.4 Shy line offset
When roadside features such as bridge railings, parapets, retaining walls, fences or roadside barriers
are located too close to traffic, drivers in the adjacent traffic lane tend to reduce speed, drive off-centre
in the lane, or move into another lane. The distance from the edge of the travelled way beyond which
a roadside object will not be perceived as a hazard and results in motorists

166. ROADSIDE DESIGN GUIDE
PAGE 165
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
reducing speed or changing vehicle position on the roadway is referred to as the shy-line offset [5].
Table 7.4 provides suggested shy line offsets based on design speed.
Where possible, barriers should be located outside of the shy-line, particularly where relatively short
lengths of barrier are used. For long, continuous runs of barriers, this offset distance is not as critical,
especially if the barrier is first introduced beyond the shy-line and gradually transitioned toward the
roadway [1].
However, there is also some evidence available that the presence of a safety barrier may influence the
operating speed of traffic. Research has shown that the mean traffic speed on sections of road with
median road safety barriers is higher than similar sections of road without median road safety barriers.
Experience in Sweden is that traffic speeds increased on a narrow road after construction of a median
wire rope road safety barrier [1].
Shy-line offset distance is seldom a controlling criterion for barrier placement. It will have minimum
impact on driver’s speed or lane position as long as the barrier is located beyond the perceived
shoulder of a roadway. However, the shy-line offset should not be used to determine the shoulder
width. Where a roadside barrier is needed to shield an isolated condition, adherence to the uniform
clearance criteria is not critical; however, barrier deflection distance (7.3.5) needs to be considered. It
is more important in these cases that the barrier is located as far from the travelled way as practical.
Table 7.4 - Suggested shy-line offset
Design speed (km/h) Shy line offset (m)
140 3.8
130 3.7
120 3.2
110 2.8
100 2.4
90 2.2
80 2.0
70 1.7
60 1.4
50 1.1
Source: Adapted from AASHTO Roadside Design Guide [5]
7.3.5 Barrier deflection distance
When a vehicle strikes a roadside barrier, the dynamic deflection of a barrier varies according to the
characteristics of the impacting vehicle, impact speed, angle of impact and the characteristics of the
barrier system. Sufficient lateral clearance should be provided between the barrier and a hazard to
accommodate the appropriate dynamic deflection [1]. Further information regarding the determination
of the deflection distance for barrier systems during impact testing at NCHRP350 and MASH can be
found in Sections 6.3.3.2 and 7.2.2. The designer needs to consider the distance a barrier will deflect
upon impact as a critical factor in the selection and lateral placement of barrier, in particular if the
obstruction being shielded is a rigid object.

167. ROADSIDE DESIGN GUIDE
PAGE 166
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
When deciding on the lateral placement of a barrier, the designer/engineer should ensure that the
distance between the front face of the barrier and the hazard is wider than the working width of the
barrier, as shown in Figure 7.10. This way, enough clear space will be provided behind the barrier, to
prevent a secondary impact with the hazard.
Figure 7.10 – Barrier placement in front of hazards
For vehicles with a relatively high centre-of-gravity the Zone of Intrusion (ZOI) should also be
considered so that the roll of the vehicle will not enable it to strike a hazard located at the rear of the
barrier. When deciding on the lateral placement of a barrier, the designer/engineer should ensure that
the distance between the front face of the barrier and the hazard is wider than the zone of intrusion
width (ZOIw) of the barrier, as shown in Figure 7.11. More details regarding the ZOI can be found in
Section 6.3.3.3.
In some cases, the available space between the barrier and the hazard may not be adequate and in
these cases, a different barrier system should be specified. This will generally mean that a more rigid
barrier system will need to be used for the particular application.

168. ROADSIDE DESIGN GUIDE
PAGE 167
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.11 – Consideration of ZOI in barrier placement
When used in front of embankments, sufficient space should be provided between the back of posts
and the embankment, as shown in Figure 7.12. This is done to ensure that adequate soil support is
provided behind the posts to obtain proper operational characteristics of the barrier.
Figure 7.12 - Barrier placement in front of embankments
Limited test results indicate that the offset distance for embankments is not as critical as it is for rigid
objects. A 600mm distance is desirable for adequate post support, but this may vary depending on the
slope of the embankment, soil type, expected impact conditions, post cross section and embedment,
and the type of barrier system. Increasing the embedment length of barrier posts by 300mm or more
can compensate for the reduced soil foundation support near the slope break point [5], as too can the
use of posts with soil plates’ located at the bottom of the posts to increase the area of interaction
between the post and the supporting ground. However, the

169. ROADSIDE DESIGN GUIDE
PAGE 168
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
designer/engineer should not carry out any modifications to impact tested systems without consulting
the manufacturer and the highways authority.
Figure 7.13 - Different generic post types (from left to right: standard post, long post,
standard post with pressure plate, longer post with pressure plate)
7.3.6 Lateral Placement of Barriers behind Kerbs
Kerbing has been shown to be a major contributor to the vaulting and destabilization of impacting errant
vehicles, particularly at high speeds and with higher kerbs. When the tyres of an errant vehicle strike
a kerb, the impact tends to bounce the vehicle upwards, which can contribute to vaulting or penetration
of the rail. This effect contributes to destabilization. When the destabilizing or vertical bounce effects
act in combination with either the destabilizing effects of striking a rigid barrier or the large deflection
of a flexible barrier system, unsatisfactory results may occur and the barrier may be breached, and the
vehicle not contained.
When a vehicle strikes a kerb, the resulting trajectory of the impacting vehicle depends upon several
variables:
• Size, weight and suspension characteristics of the vehicle;
• Size of the impacting vehicle’s tyres;
• The impacting vehicle’s impact speed and angle; and
• The height, shape and the overall installation of the kerb itself.
Barrier/kerb combinations should be discouraged on high speed roads. At those locations where a kerb
might be considered an appropriate solution (e.g. for drainage or delineation), alternative treatments
should be considered when a roadside barrier system is to be installed. In particular, where a rigid
barrier is used, a kerb will impart a vertical force to the vehicle, the dynamic effect of which could
adversely affect the performance of the barrier [7].
Where there are no feasible alternatives, the designer should consider using a 100mm or less sloping
kerb and/or consider stiffening the barrier to reduce the potential deflection. Kerbs with a lower height
are preferred in all cases, and again, if the kerb can be removed, this is the most preferable action.
Ground Level
60
0m
m
900m
m
Soil Plate

170. ROADSIDE DESIGN GUIDE
PAGE 169
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
On lower-speed facilities (i.e. less than 70km/h), a vaulting potential still exists, but the risk of such an
occurrence is lessened [5]. Engineering judgement should be applied on a case-by-case basis for each
situation considering the anticipated speeds and consequences of vehicular penetration.
7.3.6.1 Recommended Installation Procedures for Semi-Rigid W-Beam
Barriers In-line with a Kerb
When using a semi rigid barrier in combination of a sloping-face kerb, the ideal way of installation is to
have the front face of the barrier flush with the front face of the kerb. The recommended types of kerbs
to be used in these types of installations differ according to the design speed of the road. These are
shown in Figure 7.14 and explained further below. Note that the height of the barrier must be measured
from the pavement surface and should be in accordance with the manufacturer’s installation
instructions for the product.
• Design Speed < 80km/h: A semi-rigid w-beam barrier can be used with any combination of
a sloping-faced kerb that is 150mm or shorter if installed in-line with the front (traffic) face of
the barrier for design speeds up to80 km/h;
• Design Speed 80 to 100km/h: For design speeds above 80 to 100km/h, a 100mm or shorter
sloping kerb is recommended for installations where the face of the kerb is flush with the face
of the barrier;
• Design Speed > 100km/h: For design speeds greater than 100 km/h, the sloping kerb face
should be 1V:3H or flatter and no higher than 100mm although the use of kerbs on roads
with a design speed of 100km/h or greater is discouraged.
Figure 7.14 – Placement of w-beam barriers in-line with kerbs
7.3.6.2 Recommended Installation Procedures for Semi-Rigid W-Beam
Barriers - Set-back from a Kerb
When using a semi rigid barrier in combination of a sloping-face kerb, the ideal way of installation is to
have the front face of the barrier flush with the front face of the kerb (as explained in Section 7.3.6.1).
However, it may not always be possible to install the barrier in-line with the front face of the kerb. In
such cases the barrier may be installed at a set-back, which provides enough space for the suspension
and bumper of the errant vehicle to come back to their normal pre-departure

171. ROADSIDE DESIGN GUIDE
PAGE 170
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
state, before reaching the barrier. Once the suspension and bumper have returned to their normal
position, impacts with the barrier are not as adversely affected. The minimum recommended set- back,
and the maximum recommended kerb height for such installations differ according to the design speed
of the road. These are shown in Figure 7.15 and explained further below. Note that in case of set-back
installations, the height of the barrier must be measured from the top surface of the kerb and should
be in accordance with the manufacturer’s installation instructions for the product.
• Design Speed < 70km/h: For design speeds less than 70 km/h, sloping-face kerbs of
150mm or lower may be used as long as the face of the barrier is located flush with or at
least 2.5m behind the face of the kerb;
• Design Speed 70 to 80km/h: At design speeds between 70 and 80 km/h, a minimum lateral
offset distance of 4m is required to allow the vehicle suspension to return to its normal pre-
departure state. Once the suspension and bumper have returned to their normal position,
impacts with the barrier are not as adversely affected. Sloping-face kerbs of 100mm or lower
may be used as long as the face of the barrier is flush with the face of the kerb or located at
least 4m behind the kerb;
• Design Speed > 80km/h: Set-back installations are not recommended for roads with a
design speed over 80km/h. In such locations, in-line installations should be preferred, as
explained in Section 7.3.6.2.
Figure 7.15 - Placement of w-beam barriers set-back from kerbs
Note that in all cases, it is assumed that the running surface between the front edges of the kerb and
the barrier is flat (i.e. 1V:3H or flatter). If this is not the case, engineering judgement, taking into account
the consideration the points raised within this Section and within Section 7.4.1, should be used to
evaluate any adjustment which might need to be made to the height of the safety barrier beam in order
for it to function and perform as designed.
7.3.7 Foundation Conditions
For many barrier systems, the interaction of a post with the ground in which it is located can have a
significant effect on the dynamic performance of the barrier system. It is for that reason that the

172. ROADSIDE DESIGN GUIDE
PAGE 171
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
performance of the barrier in the ground into which it is to be installed should be understood. This may
not necessarily mean that the barrier will be tested within the soil (although this is preferable), but in
some cases it will be possible for manufacturers and promoters to demonstrate the change in
performance (if any) due to the installation in different ground. The testing requirements within
NCHRP350 and MASH provide details on the different types of soils into which guardrails for testing
could be installed, and on the requirements for the associated compaction of the soil [3], [7].
For proprietary systems, the effect of different ground conditions and the ways in which different ground
conditions can be dealt with will be contained within the manufacturer’s installation manual. On the Abu
Dhabi Department of Municipal Affairs and Transport road network, all soil should be compacted or
stabilised such that there is additional foundation support provided by the soil surrounding the posts.
Whilst not applying in all cases, in general terms many systems (particularly flexible systems) work by
the post to rail connections breaking on impact (as designed), and the impacting vehicle travelling over
the resulting line of posts, bending them to ground level as the vehicle passes over them. At this time,
the beam of the barrier system is maintained at a constant height by the posts in front of, and behind,
the impacting vehicle. Therefore, in order for the system to perform as designed, the ability of the
ground to withstand the impact forces (applied through the post) and for the ground to not move during
the event, is critical to the performance of the barrier system. There are two ways in which this can be
achieved:
1. Regulate the material into which the post of the barrier is located on the roadside so that it
mirrors that into which the barrier was installed during full scale testing; and
2. Understand the ability of the ground to withstand the impact forces.
The first way, i.e. recreating the ground conditions as it was tested, is generally considered an
unrealistic solution. This is due to two reasons. The first one is the difficulty of recreating the same
ground conditions in different places, due to the differing local conditions and the effects of compaction,
ground water table, humidity, etc. The second reason is the high costs involved. Instead, it is
recommended to measure the quasi-static properties of the soil and to ensure that these meet
minimum values. This is the technique often employed within the installation manual for proprietary
systems.
The design of the test procedure for ground conditions has been in use within the UK for many years,
and is detailed within the British Standard BS7669-3 [8]. An alternative testing method (involving an
instrumented post and a trolley can be found in Annex B of MASH [7], however, this test method is
tailored for test house use, and not for use on the roadside. The UK test method is commonly known
as the ‘push/pull’ test, and requires and incremental load to be applied to the top of a post (not
connected to the beam of a barrier at the time of testing). This incremental load can either be applied
through pushing or pulling the top of the post, as shown in Figure 7.16.
The process for undertaking the push post testing (which is the most commonly used of the two
methods) is explained in BS7669-3: Vehicle Restraint Systems - Part 3: Guide to the Installation,
Inspection and Repair of Safety Fences [8]:

173. ROADSIDE DESIGN GUIDE
PAGE 172
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.16 - Push testing of a driven (left) [9] and a surface mounted (right) post
7.3.8 Common Installation, Maintenance and Inspection Issues
Whilst every attempt is made to install, maintain and inspect the barrier systems on the Abu Dhabi road
Network in accordance with best practice, a number of common issues with regard to the way in which
barrier systems had been installed prevail. The following sections outline these issues, and offer
solutions for ways in which these issues can be avoided in the future.
7.3.8.1 Problems with Lap Joints in W-Beams
For W-beam barriers, the way in which adjacent rails are lapped is of extreme importance. Beams
which are lapped incorrectly are known to fail at the joints on impact, subsequently impaling impacting
vehicles and greatly increasing the risk of severe injuries to the vehicle occupants. An example of an
incorrect lap-joint barrier beam overlap is shown in Figure 7.17. In all cases, the lap of the barrier
should be such that, in the direction of traffic, the end of the first barrier encountered is located in front
of the approach end of the second barrier encountered, as shown in the right hand picture in Figure
7.17.
Figure 7.17 - The lap of adjoining w-beam rails

174. ROADSIDE DESIGN GUIDE
PAGE 173
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.3.8.2 Lack of Continuity in Barrier Systems
One of the fundamental requirements for the predictable performance of a barrier is for a continuous
length of barrier to be provided, and for all components of the barrier to work in unison in the event of
an impact. As a result, longitudinal barrier elements which are not connected will represent a risk of
injury to road users in the event of an impact. This is the case where barrier beams have been removed
by operatives (for example to gain access through the barrier for the purposes of irrigation, as shown
in Figure 7.18).
Figure 7.18 - Lack of continuity in a w-beam barrier
7.3.8.3 Beam Height Issues
The height to which a guard rail should be set will be contained within the manufacturer’s installation
manual, and this should be followed. If, for any reason, such a height is not achievable, this should be
reported to the manufacturer and resolution should be sought. Such resolution may be a change in
post type or, in extreme cases, may mean that a different barrier solution should be found. Barriers
which are set too low are more likely to be traversed and climbed over by an impacting vehicle. Hence,
with a barrier which has been installed too low, there is a risk of the barrier being overcome, and the
hazard at the rear of the barrier being struck and/or traversed. This is likely to result in an increase in
risk of injury to the vehicle occupants. Therefore, the height of a barrier must be set in accordance with
the manufacturer’s specifications.
In many cases the manufacturer’s specification for the height of the barrier beam will assume that the
running surface between the edge of the carriageway and the front face of the beam will be relatively
flat (i.e. 1V:10H or flatter). Due to site constraints, this may not be the case and hence, in such
circumstances, engineering judgement may need to be applied when setting the height of the safety
fence, taking into account the likely orientation and height of an errant when impacting the barrier. This
is of particular importance for barrier systems with beams where the compatibility between the vehicle
and the barrier is more important than for those systems (such as concrete systems) whose
performance is less dependent on the height of the impacting vehicle due to their wide impact face.

175. ROADSIDE DESIGN GUIDE
PAGE 174
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.3.8.4 Foundation and Compaction Related Issues
The installation of barrier systems, particularly for semi-rigid systems, the posts of safety barrier
systems may be provided with an integral concrete foundation, as shown in Figure 7.19.
Reinforced concrete strip footings that have been structurally designed are acceptable to support
barrier systems where the relevant road authority has accepted a base plated post version. When
placed in concrete strips, the posts should be able to deflect laterally during an impact.
Figure 7.19 - Steel posts supplied with integrated concrete foundations
To ensure appropriate performance of the concrete foundations and the post and rail systems ground
conditions must be compacted properly to ensure the foundations do not become extracted from the
ground upon vehicle impact as shown in Figure 7.20. For w-beam barriers, a potential improvement to
the soft soil conditions is to install the system with 2100mm trie-beam posts instead of the standard
1800mm posts [1].
Figure 7.20 - Effect of uncompacted soil on a barrier impact

176. ROADSIDE DESIGN GUIDE
PAGE 175
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Another problem observed with the foundations was exposed concrete foundations on some of the
barrier systems, as shown in Figure 7.21. This may be either due to erosion of the supporting sandy
surface sand with wind, or due to inadequate installation in the first place. Please refer to Section 7.3.7
for further information.
Figure 7.21 – Concrete foundations protruding out off the ground
In locations where surface mounted posts are required (for example on bridge decks), fasteners
specified by the manufacturer must be used. This was not the case in the installation shown in Figure
7.22. In this case, small screws have been used instead of larger holding down bolts for the installation.
As a result, instead of the post remaining affixed to the ground and the post screw (between the post
and the rail) breaking on impact, as designed, the post has been pulled out of the ground, remaining
attached to the beam. This could pose a serious risk to road users and will significantly affect the
performance characteristics of the barrier system.
Figure 7.22 - Use of incorrect fixings for a surface mounted post

177. ROADSIDE DESIGN GUIDE
PAGE 176
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.4 Additional Application Criteria for Roadside Barriers
7.4.1 Placement on slopes
Terrain conditions between the travelled way and the barrier can have significant effects on the barrier’s
impact performance. Generally, acceptable impact conditions at the moment of impact occur when all
of the wheels of the vehicle are on the ground and its suspension system is neither compressed nor
extended. Such is the vehicle’s orientation and stability at the time of impact during the testing to
NCHRP350 and MASH – testing under which the performance characteristics of the barrier systems
are determined.
Similar to crashes involving kerbing, a wide range of factors will influence the behaviour and trajectory
of errant vehicles as they traverse slopes (e.g. suspension stiffness, vehicle weight, speed of impact,
angle of impact). Consequently, there is uncertainty about where to position barriers so that [7]:
• The vehicle does not vault over the barrier; or
• The vehicle does not go under the barrier with consequent snagging on the barrier supports
and other problems.
Figure 7.23 illustrates the bumper trajectory as a car leaves the travelled way and crosses the shoulder
and the embankment. The primary area of concern is the zone where the bumper height is likely to be
above that of normal bumper height. A barrier placed in this zone can be expected to be struck at a
point higher than had it been installed on a level surface and, unless it has been designed for such
impacts, its performance may be inadequate, and the barrier may fail to successfully contain and/or
redirect an errant vehicle.
Figure 7.23 also illustrates parameters (∆HS, ∆HM, ∆H2, LM, and L) for determining bumper heights.
Values ∆HS and ∆H2 are important because most roadside barriers are placed between the edge of
the shoulder and 0.6m off the shoulder.
Table 7.5 contains trajectory data for rounded embankments for 100km/h encroachments at angles of
25 and 15 degrees. These numbers were obtained primarily from computer simulation [5].
Figure 7.24 shows an example application of Table 7.5, to determine the areas to avoid on a 1V:6H
slope for barrier installation. In general, barrier installations on 1V:6H slopes are not recommended.
Slopes in front of a barrier should be 1V:10H or flatter [10]. This also applies to the areas in front of the
flared section of barrier and to the area approaching the terminal ends, as shown in Figure B.5 in
Appendix B.
A rounded slope configuration will reduce the risk of an errant vehicle becoming airborne and affords
the driver more control over the vehicle. Typically 1.2m to 1.8m is used for slope rounding and this can
generally be obtained as part of the slope grading and vegetation establishment.
The type of barrier is also important as the performance of those systems with a very open profile (such
as wire rope and steel post and rail systems) is likely to be more affected by the height of an impacting
vehicle than for closed profile systems (such as concrete barriers). In these cases the area of
compatibility between vehicle and barrier is much increased and therefore closed systems may be
more preferable in locations where they are installed in a slope location.

178. ROADSIDE DESIGN GUIDE
PAGE 177
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.23 - Design parameters for vehicle encroachments on slopes [5]
Figure 7.24 – Barrier placement considerations on 1V:6H embankments Table 7.5 -
Example bumper trajectory data
Encroachment
Angle
(degrees)
Embankment
Slope (V:H)
L (m) ∆HS (mm) ∆H2 (mm)
∆HM
(mm)
Lm (m)
25 1V:6H 9.1 102 122 175 6.1
25 1V:4H 10.7 102 122 200 7.0
25 1V:3H 12.2 102 122 200 7.0
25 1V:2H 12.2 102 122 200 7.0
15 1V:6H 7.0 48 71 114 4.9
15 1V:4H 7.9 48 71 175 5.5
15 1V:3H 8.5 48 71 210 6.1
15 1V:2H 10.1 48 71 244 7.6

179. ROADSIDE DESIGN GUIDE
PAGE 178
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.4.2 Rate of Flare
Motorists are less likely to perceive roadside barriers to be a hazard if the barrier is introduced gradually
to the roadside environment through the use of a “flare”, i.e. the line of the barrier at the beginning of
the terminal is set back a distance from the travelled way and is then gradually brought closer to the
line of the travelled way. Consequently, some end terminals are designed to be flared away from the
approaching traffic. The flare rate is the ratio of the length of the flared part of the barrier (measured
parallel to the road) to the barrier offset [1].
Using a flared barrier in advance of a roadside hazard may be advantageous. A barrier may be flared
to:
• Locate the barrier terminal farther from the travelled way;
• Minimize a driver’s reaction to an obstacle near the roadway by gradually introducing a
parallel barrier installation;
• Transition a roadside barrier closer to the roadway because of an obstacle; or
• To reduce the total length of barrier need.
Also following should be considered:
• A flared barrier results in increased impact angles with the potential for greater severity of
impact;
• A flared barrier increases the likelihood that the vehicle will be redirected into the opposing
lane of traffic or across the roadway;
• The grading required to provide 1V:10H or flatter slopes in front of the flared section of
barrier may interfere with roadside drainage and/or may require additional right of way.
The flare rate is typically expressed as a ratio (a:b), as shown in Figure 7.25. For example, a flare rate
of 19:1 means that for every one metre travelled rearwards from the edge of the carriageway (b), the
line of the barrier should be such that 19 metres are travelled along the carriageway (a).
As indicated, one disadvantage is that a flare will increase the vehicular angle of impact, although some
w-beam barriers have been successfully crash tested with flare rates as high as 1:7 [5]. It will also
increase the amount of earthwork needed to provide 1V:10H slopes in front of the barrier and
approaching the terminal. When choosing how much to flare the barrier, the designer will need to strike
a balance between the length of the barrier and how far the installation projects toward the ditch and
the corresponding need for flattening the approach slopes.

180. ROADSIDE DESIGN GUIDE
PAGE 179
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.25 – Flare rate layout
Table 7.6 presents suggested flare rates for roadside barriers based on design speed and barrier type.
It should be noted that the flare rate values required for rigid and semi-rigid barrier installations within
the shy-line, yield smaller flare angles, compared to situations where they are located outside the shy-
line. It should also be noted that for proprietary systems, the manufacturer should provide details of
the recommended flare rate for their system within their accompanying installation manual.
Flatter flare rates (i.e. those with a lesser gradient) may be used, particularly where extensive grading
of the existing ground surface would be required to obtain a flat approach to the barrier from the
travelled way. Note that the recommended flare rate for barriers within the shy-line is approximately
twice that for barriers located outside the shy-line distance [5]. This is more applicable where the
approach roadway is wider than the roadway near the obstacle and has an offset less than the
suggested shy-line offset. For example, if an approach roadway is wider then a bridge roadway, the
designer should use flatter flare rates based on inside the recommended shy- line values.
Another disadvantage to flaring a barrier installation is the increased likelihood that a vehicle will be
redirected back into or across the roadway following an impact. This situation is especially undesirable
on single carriageways where the impacting vehicle could be redirected into oncoming traffic.

181. ROADSIDE DESIGN GUIDE
PAGE 180
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Table 7.6 - Suggested flare rates for barrier design
Design
speed
(km/h)
Flare rate for
barrier
inside shy line (a:b)
Shy-line
Offset
Flare rate for barrier at or beyond
shy line
Rigid
(a:b)
Semi-rigid
(a:b)
Flexible
(a:b)
140 38:1 3.8 26:1 21:1 50:1
130 35:1 3.7 24:1 19:1 50:1
120 32:1 3.2 22:1 17:1 50:1
110 30:1 2.8 20:1 15:1 50:1
100 26:1 2.4 18:1 14:1 50:1
90 24:1 2.2 16:1 12:1 50:1
80 21:1 2.0 14:1 11:1 50:1
70 18:1 1.7 12:1 10:1 50:1
60 16:1 1.4 10:1 8:1 50:1
50 13:1 1.1 8:1 7:1 50:1
Source: Adapted from AASHTO Roadside Design Guide [5].
7.4.3 Short Radius Barriers at Intersections
A side road or entrance within the length of need of a barrier installation poses a severe challenge to
the design of a safe roadside. This is especially true if the intersection is located close to a bridge.
Figure 7.26 demonstrates these difficulties through three example scenarios. Scenario a) shows a
standard barrier installation which can be used to shield motorists from hazards such as rigid roadside
furniture, a river, road, railway or the end of a rigid bridge barrier. In this scenario a minimum length of
barrier is required both to stop errant vehicles reaching the hazards (see Section 7.3.1) and due to the
minimum length of installation required for the barrier to work as intended (see Table 7.2).
Scenario b) introduces a side road connection within close proximity to the bridge. The close proximity
of the side road does not allow enough space for the minimum length of installation required. In such
a scenario, the only hazards located in the vicinity of the intersection can be rigid roadside furniture.
Intersection corners often have hazardous roadside furniture installed, such as traffic signs, signals,
electrical cabinets, utility poles, etc. These hazards, should either be removed, relocated or made
passively safe (see Chapter 2), if possible. This way the need for the barrier could completely be
eliminated.
However, in scenarios where the intersection is located close to a bridge, which is located over a higher
risk hazard such as a river, railway or another road, it may not be possible to eliminate the need for a
barrier. This is because, as shown in Scenario c), even if the ends of the rigid barriers

182. ROADSIDE DESIGN GUIDE
PAGE 181
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
a)
b)
c)
Figure 7.26 – Difficulties of barrier placement at intersections
on the bridge are shielded with crash cushions, there is still a high risk of an errant vehicle reaching
the high risk hazard, i.e. the river, railway or the other road, because the length of need requirements
are not met.
In all scenarios, the preferred solution is to close or relocate the intersecting road and install the
required length of barrier with an appropriate transition and a crashworthy terminal (i.e. scenario “a” in
Figure 7.26). However, it may not always to close or relocate the intersecting road.

183. ROADSIDE DESIGN GUIDE
PAGE 182
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
In such cases, a short radius barrier installation may be considered, as shown in Figure 7.27. The
difficulty with the short radius barrier installations is the potential of high angle impacts, which is likely
to cause high severity outcomes for regular rigid and semi-rigid systems; whereas flexible systems are
unsuitable for such small radii. A vehicle impacting the radius at a high angle and speed may penetrate
the barrier, or vault over the barrier after the posts lean back, creating a ramping effect. Where
penetration or vaulting does not occur, the vehicle may be decelerated at an excessive rate. However,
there are some short radius barrier systems, which are specifically designed and successfully crash
tested for these situations. Examples of these systems are shown in Figure 7.28 and Figure 7.29. The
principle of these systems is to provide acceptable rate of deceleration for vehicles impacting at high
angles. This is achieved by:
• The use of break-away (may be wooden) posts at 2.0m spacing;
• Omitting blockouts;
• Not providing washers on the mushroom-headed bolts connecting the rail to blockouts. [1]
When using short radius barriers, it should be remembered that they should only be used if the
alternative of removing the side road is not applicable. When they are the only choice, the use of a
short radius barrier system will impose constraints on how close it can be installed to a bridge, what
radius can be used, and how far it must run along the intersecting side road. When terminating the
radius barrier system, the barrier on the intersecting roadway should be completed to any required
length of need and terminated with an appropriate end treatment.
Figure 7.27 – Possible solution to barrier placement at intersections

184. ROADSIDE DESIGN GUIDE
PAGE 183
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Source: Adapted from Austroads Guide to Road Design [1]
Figure 7.28 - Short radius barrier at intersection (2.5 m to 10 m radius)
5. Remove blockouts

185. ROADSIDE DESIGN GUIDE
PAGE 184
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Source: Adapted from Austroads Guide to Road Design [1]
Figure 7.29 - Short radius barrier at intersection ( to 10 m radius)
7.4.4 Sight Distance
Concrete barriers and, to a lesser extent, w-beam barriers can obstruct visibility. Barriers located close
to intersections can impede the safe intersection sight distance and minimum gap sight distance
available to drivers attempting to select a safe gap in traffic on the major road. This issue applies to
barriers located on the verge and barriers located in medians [3]. Where barriers are needed on the
inside of curves, the horizontal sight distance should be checked in accordance with the criteria for
stopping sight distance. The designer should check to determine if barrier conflicts exist on a given
curve and should carefully weigh the alternatives before selecting the barrier configuration.

186. ROADSIDE DESIGN GUIDE
PAGE 185
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Options to consider are:
• Offsetting the barrier to the inside of the curve enough distance to obtain the required sight
distance;
• Flattening or extending roadside slopes so the barrier may be moved farther from the
travelled lanes;
• Using open systems (such as wire rope) as opposed to the more closed systems (such as
concrete barrier);
• Reducing the height of barriers (retesting may be needed to establish any effect on the
revised ZOI for the system) and overall performance; and
• Providing overhead lighting to aid night-time visibility.
7.5 Additional Application Criteria for Median Barriers
Many of the general barrier application criterion identified previously in Section 7.3 can be equally
applied to median barrier systems. However, this Section builds upon these requirements and identifies
specific areas for consideration and modification to deal with the specific hazards and alignment issues
which may arise from locating a barrier within the median. In particular, this Section addresses the
issues of:
• Terrain effects on the lateral placement of median barriers;
• Super-elevated sections;
• Fixed objects within the median;
• Emergency and maintenance crossings, i.e. Gates; and
• Glare screens.
7.5.1 Guidelines for the Need of Median Barrier
Median cross-over crashes are those of particularly high consequences. Therefore, additional
consideration should be given when assessing the need for a barrier in the median. Figure 7.30 shows
recommended guidelines for the use of median barriers on high-speed, fully controlled- access
roadways, such as freeways and expressways. As can be seen from the figure, a median barrier is
recommended for roads with more than 20.000 ADT, a median width less than 9m.
For locations with an ADT more than 20,000 and a median width between 10m to 15m, a median
barrier should be considered based on local conditions. In such locations a decision should be made
through a cost/benefit analysis or engineering judgment, by considering factors such as history of
cross-over incident in the area, horizontal and vertical alignment, expected future traffic, median terrain
configuration, the need to prevent U turn, etc.
For medians with less than 20.000ADT and width less than 15m, or a median width of more than 15m
and for any ADT volume, a barrier is optional. Even if a median barrier is not deemed necessary today,
the median should be left in a state where a barrier can be installed in the future, if necessary for
reasons such as increase of ADT over 20.000 or increase in the frequency of cross-over crashes.

187. ROADSIDE DESIGN GUIDE
PAGE 186
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
* May be used for purposes such as providing a restriction to prevent illegal U turns.
Figure 7.30 - Recommendations for median barriers on high speed, fully controlled-access
highways
Example:
Comment if a median barrier is required or not.
Road Type: Multilane Divided
Design ADT: 12,000 per direction
Design Speed: 140km/h
Horizontal Alignment: Straight
BARRIER
OPTIONAL*
but normally not
Optional
BARRIER
CONSIDERED
based on
engineering
judgement of
siteconditions

188. ROADSIDE DESIGN GUIDE
PAGE 187
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Solution:
Using Figure 7.30 for:
• ADT: 12,000+12,000 = 24,000 for both directions
• Median Width: 8.0m
A Barrier is recommended.

189. ROADSIDE DESIGN GUIDE
PAGE 188
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.5.2 Terrain Effects on the Lateral Placement of Median Barriers
As detailed within Section 7.4.1, barriers perform best when an impacting vehicle has all of its wheels
on the ground at the time of impact, and its suspension system is neither compressed nor extended,
i.e. the vehicle is in a stable condition. This is the way in which barrier systems are tested and hence,
their performance (under defined impact conditions) is known. Therefore, the effect of terrain is a major
factor to consider when locating a median barrier. As a result, consideration should be given to the
following aspects when determining the placement of such barriers, and engineering judgement should
be applied in all cases:
• The most desirable median is one that is relatively flat (i.e. slopes of 1V:10H or flatter) and
free of objects. The median barrier then can be placed at the centre of the median. Placement
guidelines are necessary when these conditions cannot be met. However, a rigid barrier
should not be used in the middle of wide medians (i.e. greater than 3.0 m to 4.0 m from the
edge of the traffic lane) because of the likelihood of higher impact angles and resultant higher
severity of impacts [1]. A flexible barrier located on both sides of the median has the
advantage that it maximises the opportunity to contain deflections within the median.
However, a central location has the advantages in that [1]:
o Debris from damaged barriers is less likely to encroach into the carriageway;
o Sight distance past the barrier on curves is maximised;
o The barrier sustains less nuisance impacts than a barrier on the side of the median;
and
o The cost is less than a barrier on both sides of a median.
• Features within the median between the travelled way and the barrier can have a significant
effect on the barrier’s impact performance. Kerbs and sloped medians (including super-
elevated sections) are two prominent features that deserve attention. Refer to Section 7.3.6
for further guidance regarding the use of barriers in conjunction with kerbs. Uncompacted
ground conditions and drainage swales can impart a roll moment on a traversing vehicle, and
the slopes in the median can affect the performance of the barrier as the vehicle suspension
is compressed. A vehicle that traverses one of these features prior to impact may go over or
under the barrier or snag on the support posts of a strong- post system.
• Figure 7.31 illustrates the basic median sections for which placement guidelines are
presented:
o Depressed medians or medians with a ditch section (Median Section I);
o Stepped medians or medians that separate travelled ways with significant
differences in elevation (Median Section II); and
o Median embankments (Median Section III).
7.5.2.1Depressed medians or medians with a ditch section (Median
Section I)
Firstly the slope and the ditch sections should be examined in line with the recommendations within
Chapter 3 to determine if a roadside barrier is warranted (if the slopes and ditches cannot be

190. ROADSIDE DESIGN GUIDE
PAGE 189
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
made traversable). In such cases that a barrier is warranted the barrier should be located as indicated
below, with reference to Figure 7.31:
Figure 7.31 - Recommended barrier placement in non-level medians [5]

191. ROADSIDE DESIGN GUIDE
PAGE 190
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Illustration 1: A roadside barrier should be placed near the shoulder on each side of the median (as
shown at locations “b” and “d”), if both slopes require shielding (i.e. the ditch is non- traversable). A
median barrier should be placed at “b,” if only one slope requires shielding (e.g. S2). In this situation, a
rigid or semi-rigid barrier is typical.
Illustration 2: This applies where neither slope requires shielding but either one or both are steeper
than 1V:10H. In such cases the median barrier should be located on the side with the steeper slope.
This will typically be a rigid or semi-rigid system.
Illustration 3: If both slopes are relatively flat, the median barrier should be located at or near the
centre of the median (at “c”) if vehicle override is unlikely. The designer can use any type of median
barrier having an appropriate test level for the application, if its dynamic deflection is not greater than
one-half the median width. It is not generally desirable to locate the barrier in the drain at the centre of
wider medians because of the potential for debris to accumulate around the barrier and adversely
affect flow within the drain. There is also potential for the post foundations to be affected due to sodden
soil within the drain [1].
When locating a barrier in a non-level application, the manufacturer/promoter of the system should be
consulted to ascertain whether the system would be suitable for such an application.
7.5.2.2Stepped medians or medians that separate travelled ways with
significant differences in elevation (Median Section II)
For this section, the following placement criteria apply, with reference to Figure 7.31:
Illustration 4: If the embankment slope is steeper than approximately 1V:10H, the median barrier
should be located “b.”
Illustration 5: If the slope contains obstacles or consists of a rough rock cut, a roadside barrier should
be located at both “b” and “d.” This section may have a retaining wall at “d.” If so, the base of the wall
should be smooth and continuous – where possible the profile should reflect that of a successfully
tested concrete barrier system.
Illustration 6: If the cross slope is flatter than approximately 1V:10H, a barrier should be located at or
near the centre of the median.
7.5.2.3 Median embankments (Median Section III)
For this section, the following placement criteria apply, with reference to Figure 7.31:
Illustration 7: This type of median design should not be considered to be a barrier or to provide positive
protection against crossover crashes. A barrier should be installed and located at “b” and “d” if both
slopes are not traversable. If retaining walls are used at “b” and “d,” contour the base of the wall should
be smooth and continuous – where possible the profile should reflect that of a successfully tested
concrete barrier system.
If the slopes are traversable, and it is considered that a vehicle could pass over the apex of the median
(indicated by “c”), a non-rigid median barrier may be placed at the apex of the cross section. For non-
traversable slopes, a barrier should be placed adjacent to the shoulder of each carriageway. If retaining
walls are used adjacent to each carriageway, it is recommended that the base of the wall be
constructed to the external shape of the preferred standard concrete barrier [1].

192. ROADSIDE DESIGN GUIDE
PAGE 191
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
7.5.3 Barrier Orientation on Super-elevated Sections
Figure 7.32 illustrates the preferred orientation of the centreline of a barrier based on the roadway
slope on a super-elevated section.
Figure 7.32 - Example of preferred barrier orientation on super-elevated sections
7.5.4 Fixed Objects within the Median
Several important factors are related to safety-shape concrete median barriers. For high-angle, high-
speed impacts, passenger size vehicles may become partially air-borne and, in some cases, may reach
the top of the barrier. Fixed objects (e.g. luminaire supports) on top of the wall may cause snagging or
separate from the barrier and detach into opposing traffic lanes. Even for shallow-angle impacts, the
roll angle toward the barrier imparted to high-centre-of-gravity vehicles may be enough to permit
contact by the top portion of the cargo box with fixed objects on top of or immediately behind the wall.
For this reason, it is important that consideration is given to the identified Zone of Intrusion (ZOI) for
the barrier system being used, and a barrier system specified for which hazards will not be located
within the ZOI (more details of which can be found in Section 6.5.4)
If there is a hazard in the median such that it is outside of the clear zone for one carriageway, but within
the clear zone of the other carriageway the barrier should be treated as a roadside barrier (refer to
Sections 7.3 and 7.4). Bridge piers, lighting columns, trees and overhead sign support structures are
examples of objects that are often located in a median. These are often numerous and hence, a
continuous barrier should generally be provided within the median as shown in Figure 7.33. This will
then also counter the risks posed by illegal U-turns through the median.

193. ROADSIDE DESIGN GUIDE
PAGE 192
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
Figure 7.33 - Continuous median barrier
7.5.5 Emergency and Maintenance Crossings
There are various options available to create an emergency/maintenance crossing, however, it should
be noted that emergency and (in particular) maintenance crossings are non-preferred and, in many
cases, are now being closed due to the risk to road users who perform illegal U-turns through such
openings, see Figure 7.34. Note that in this Figure, there is no transition between the steel barrier
system and the concrete units and thus the end of the concrete units represent a hazard to road users.
Emergency/maintenance crossings may take the form of a gate or a removable barrier, and a typical
example of a gate is shown in Figure 7.35. Note that this gate is also available with a length of 10m
and other lengths too.
Figure 7.34 - The closure of an emergency access with permanent concrete barrier units
Each of the two options (to install a gate or a removable barrier) varies in cost and ease of operation.
In those locations where an emergency/maintenance crossing point is permitted, consideration must
be given to the protection of road users from the risks posed by the ends of the barriers, as well as to
the flare rates used at the crossing. Note that the flare rates must not exceed the requirements of
Table 7.6.

194. ROADSIDE DESIGN GUIDE
PAGE 193
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN
AND BRIDGE BARRIERS
FIRST EDITION -DECEMBER 2016
For emergency crossings, the main requirement is the speed with which the emergency crossing can
be opened and operational; and this will depend on the option chosen. It will also depend on whether
special equipment or personnel are required to operate or open the emergency crossing. In most
cases, a time of less than 30 minutes to open the gate or dismantle a permanent safety barrier would
be desirable.
For maintenance crossings, speed may not be as much of an issue as the opening can be planned.
Where regular maintenance is required, then it may be beneficial to provide permanent maintenance
crossings at each end that can be opened and closed quickly. For other situations, there are two
options:
• Provide a maintenance crossing from the outset; or
• Create a maintenance crossing only when required (i.e. take down or break out the
permanent system; this can often by the most cost effective solution.

195. ROADSIDE DESIGN GUIDE
Figure 7.35 - Example of a median gate (12m)
PAGE 194
07 SELECTION AND APPLICATION OF ROADSIDE, MEDIAN AND BRIDGE BARRIERS FIRST EDITION -DECEMBER 2016

196. ROADSIDE DESIGN GUIDE
PAGE 195
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
7.5.6 Glare Screens
Headlight glare may be defined as a sensation experienced when a person’s vision is interrupted by
a light source that has a much higher intensity than the surrounding area. It is frequently cited as a
major contributing factor in night time crashes that occur on unlighted highways [5]. By definition, glare
screens are most often installed on median barriers, and an example of this can be seen in Figure
7.36.
Figure 7.36 – The use of glare screens in the median
The magnitude and severity of headlight glare depends on various combinations of a wide variety of
factors, including:
• Headlight systems, which includes the headlight configuration, mounting height, and output
intensity;
• Roadway features, which include the roadway alignment, geometrics, and pavement
reflectivity;
• Transmission media, which includes the atmosphere and physical features through which
the light must pass, such as windshields and eyeglasses; and
• Human variables, which include driver’s age, visual ability, and fatigue.
Depending on the severity and effect glare has on a driver, it may be classified as discomfort or
disability glare, defined as follows:
• Discomfort glare does not necessarily impair the vision. However, it frequently causes drivers
to become tense and apprehensive, which increases the level of fatigue and may lead to
driver error. This type of glare is common and usually occurs where median or outer separator
widths are greater than approximately 10m.
• Disability glare definitively impairs a driver’s vision, frequently causing temporary blindness;
consequently, it should be addressed whenever practical. Disability glare occurs usually
where median or outer separator widths are less than approximately 10 m in width or on
horizontal curves.

197. ROADSIDE DESIGN GUIDE
PAGE 196
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
7.5.6.1 The Need for Glare Screens
As indicated, headlight glare from opposing traffic can be bothersome and distracting. Glare screens
are not needed in properly lighted areas, but glare screens can be used with median barriers to
eliminate headlight glare when no other practical alternative exists (e.g. wider median, outer
separation, highway lighting, landscaping). The designer should consider if the following conditions
exist when determining the need for a glare screen:
• Unlighted divided highways where design speeds are 80 km/h or greater and medians 10 m
or less in width;
• Horizontal curves on divided highways;
• Points where the separation between a mainline and frontage road is minimal and alignment
is such that mainline traffic is affected by the lights of vehicles using the frontage road;
• Points of transition that create critical glare angles between opposing vehicles;
• Locations where night time crash rates are unusually high; and
• Any location where conflicting light sources cause a distorted or confusing view of the driver’s
field of vision.
The typical application of glare screens is on urban freeways with narrow medians and high traffic
volumes. Another application is between on/off ramps at interchanges where the two ramps adjoin
each other. Here, the sharp radii and the narrow separation may make headlight glare especially
bothersome. The designer should consider the use of glare screens at these sites.
7.5.6.2 Glare screen types
The following describes the glare screens used:
• Concrete glare screen: Where a glare screen is warranted for a section of roadway with
concrete barrier, the designer may specify a concrete glare screen, which simply involves
increasing the barrier height. This type of glare screen is advantageous on high-volume
routes due to its low maintenance (Figure 7.37);
• Glare screen blades (as shown in Figure 7.36): As an alternative to the concrete glare
screen, a series of thin vertical blades may be mounted on top of the concrete barrier. The
designer must specify the spacing, height, and longitudinal spacing of the blades on the
plans.
7.5.6.3 Glare screen design
The following applies to the design of a glare screen:
• Glare screens must not be used as a wind shield nor should they detract from the aesthetics
of the highway;
• Glare screens should be durable and easy to maintain;
• Glare screens should be designed for a cut-off angle of 20°. This is the angle between the
median centreline and the line of sight between two vehicles travelling in opposite directions,
as shown in Figure 7.37. The glare screen should be designed to block the headlights of
oncoming vehicles up to the 20° cut-off angle. On horizontal curves, the

198. ROADSIDE DESIGN GUIDE
PAGE 197
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
design cut-off angle should be increased to allow for the effect of curvature on headlight direction:
Cut-off Angle (in degrees) = 20 + 1746.8
R
where: R = radius of horizontal curve of the road, in metres;
• Glare screens may reduce the available horizontal sight distance. For curves to the left, the
designer will need to check the middle ordinate to determine if adequate stopping sight
distance will be available;
• When determining the necessary glare screen height, the designer may ignore the effect of
sag vertical curvature;
• The upper and lower elevations of the glare screen must be such that light does not shine
over or under the barrier. The height of glare screens may be established by examining the
following factors:
o Height of driver’s eye in relation to the pavement (1080 mm for passenger vehicles
and 2.3 m for large trucks);
o Height of the headlights of various size vehicles in relation to the pavement;
o Changes in elevation across the entire roadway width including the median.
• The preceding steps address the design of glare screen. However, the calculation of detailed
height requirements does not imply that the height of glare screen should vary repeatedly
from location to location along a road scheme. The height of glare screen used should
encompass the needs of the entire road scheme, or road scheme segment.
• Prior to affixing a glare screen to the top of a proprietary system, the manufacturer/promoter
should be consulted to ascertain whether the addition of the glare screen will detrimentally
affect the dynamic performance of the barrier system.
7.6 Additional Application Criteria for Bridge Barriers
Many of the general barrier application criterion identified previously in Section 7.3 can be equally
applied to bridge barrier systems. However, this Section builds upon these requirements and identifies
specific areas for consideration and modification to deal with the specific hazards and alignment
issues which may arise from locating barriers on bridges. In particular, this Section addresses the
issues of:
• Material type of bridges;
• Hardware attachments to bridges;
• Additional lateral placement considerations;
• Heights of bridge parapets;
• Fixation to bridge decks.
Bridge rails generally need to be designed to provide higher levels of containment compared to other
longitudinal barriers due to the higher risk and likely consequences of an impact on a bridge structure.
High risk situations include bridges over other roads, deep water and railways, and for high
overpasses. Bridge rails in these situations need to provide greater resistance against the possibility
of penetration or the chances that a vehicle will roll over the top of the barrier. Vehicles with greater
mass or higher centre of gravity are particularly at risk [7].

199. ROADSIDE DESIGN GUIDE
PAGE 198
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
7.6.1 Material type
Figure 7.37 - Cut-off angle for glare screens
Bridge rails manufactured from both precast (see Figure 7.38) or cast in-situ concrete or manufactured
from metal (see Figure 7.39) are available today; however, despite the lower dead weight load of
metal systems, concrete bridge barriers are often used in Abu Dhabi. The advantages of concrete
bridge rails include:

200. ROADSIDE DESIGN GUIDE
PAGE 199
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
• Better ability to contain heavy vehicles;

201. ROADSIDE DESIGN GUIDE
PAGE 200
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
• Lower maintenance costs; and
• Much simpler structural connection to the bridge deck.
Figure 7.38 – An example of a precast concrete bridge barrier
Figure 7.39 – An example of a steel bridge barrier
7.6.2 The Attachment of Hardware to Bridge Barriers
Hardware attachments to bridge rails may include:
• Pedestrian and bicycle railings;
• Traffic enforcement cameras;
• Sign supports;
• Luminaire poles;

202. ROADSIDE DESIGN GUIDE
PAGE 201
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
• Large sign support structures;
• Fences; and
• Decorative features (see Figure 7.40).
Figure 7.40 – Example of decorative features attached to a bridge parapet
Bridge rails that are impacted by high centre-of-gravity vehicles may lean over and extend past the
top of the bridge rail. The clear area that should be provided behind a bridge rail and beyond its
dynamic deflection distance to account for this behaviour is called the Zone of Intrusion (ZOI),
additional information for which is included in Section 6.3.3.3. Hardware attachments placed on
bridges at sensitive sites such as overpasses where debris could fall onto the paths of roadway traffic
below should be avoided unless the attachments are placed outside of the ZOI.
7.6.2.1 Additional Lateral Placement Considerations
A full, continuous shoulder should be provided across a bridge to maintain a uniform clearance to
roadside elements. The approach railing should have the appropriate flare rate shown in
Table 7.6 when the bridge railing is located within the recommended shy-line offset distance (see
Table 7.4). For new bridges, kerbs should not be installed in front of bridge barriers due to the
instability which they can induce into impacting vehicles prior to the impact with the bridge railing (refer
to Section 7.3.6).
An impact tested transition should be used between the approach barrier and the end of the bridge
rail (refer to Chapter 11).
In urban areas, pavements are typically present on a bridge and at lower speeds; this sidewalk is
separated from the adjacent roadway by a vertical kerb, which is typically 150 mm to 200 mm high
(refer to Figure 7.41). However, at higher speeds, the vertical kerb will interfere with the proper
vehicular/bridge rail interaction. Therefore, the following should apply to the location of a bridge rail in
combination with a sidewalk:

203. ROADSIDE DESIGN GUIDE
PAGE 202
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
• On roads with a speed limit  70 km/h: The bridge rail is typically located on the outside
edge of the sidewalk;
• On roads with a speed limit  80 km/h: The bridge rail should be located between
pedestrians and traffic; i.e. between the roadway portion of the bridge deck and the sidewalk.
There should be no kerb present between the roadway and the sidewalk.
Figure 7.41 – Presence of a pavement on a bridge structure
7.6.3 Heights of Bridge Barriers
A concern that must be considered in selecting a bridge barrier is its height. A railing may have
adequate strength to prevent physical penetration (which will be demonstrated during impact testing)
but unless it also has adequate height, an impacting vehicle or its cargo may roll over the railing or
onto its side, away from the railing after redirection. Whilst full scale impact testing will give an
indication as to the likelihood of such an occurrence taking place, this is only under predefined impact
parameters and will not take into account the variations in impact conditions likely when the barrier
system is put into service.
In the USA, there are two main concrete barrier types in service, the basic F-shape and the New
Jersey shape which have an overall height of 815 mm. When designing a scheme which incorporates
bridge barriers, the designer should evaluate whether a bridge barrier rails higher than the standard
815 mm is warranted. The issues that may merit this include:
• The need for a TL-5 or TL-6 barrier system;
• The need to address the overhang of large trucks into the ZOI – this will be of particular
interest on truck roads where the probability of a higher vehicle impacting the bridge barrier
is increased.
When selecting a proprietary system, the height of the barriers under consideration must be
obtained and considered within the design process, with engineering judgement applied to
the associated risk of using barriers with different heights. As a guide,
Table 7.7 indicates the recommended range of heights of parapets to be specified for particular
applications.

204. ROADSIDE DESIGN GUIDE
PAGE 203
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
Table 7.7 - Recommended bridge parapets heights
Application Height of Parapet
For all bridge barriers, except as below: 840mm to 1067mm
For all bridges and structures over railways carrying freeways or
expressways
1067mm to 1250 mm
For all other bridges and structures over railways, except as below: 1067mm to 1500 mm
For cycle ways immediately adjacent to the bridge barrier 1067mm to 1400 mm
For TL-5 or TL-6 barriers 1067mm to 1500 mm
For automated railways and where there is a known vandalism
problem over railways
1067mm to 1800 mm
7.6.4 Fixation to Bridge Decks
The importance of ground conditions has been identified in Section 7.3.7; however, the considerations
only cover posts located within ground. For the specific case of bridge barriers it is likely that a different
style of fixation to the bridge deck will be required. Figure 7.42 shows an example of bridge deck posts
and Figure 7.43 a fixing method often used to attach the bridge barrier posts to a bridge deck.
Figure 7.42 – Fixation of bridge deck posts
As with all post designs, bridge barrier posts should be installed in accordance with the
manufacturer’s instructions – this includes both the fixings, and any adhesives which are specified
for the installation process.

205. ROADSIDE DESIGN GUIDE
PAGE 204
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
*Drawing not to scale, not structural, and shown for indicative purposes only.
Figure 7.43 – Typical metal barrier on bridge deck
In the case of concrete barriers on the edge of bridges, these should be connected to the bridge deck
and if precast, adjacent units should also be connected to ensure that the barrier system functions
and performs as designed (and tested), and that the concrete units do not fall from the bridge in the
event of an impact. Examples of typical in-situ and pre-cast concrete bridge barrier installations are
shown in Figure 7.44 and Figure 7.45 respectively.
*Drawing not to scale, not structural, and shown for indicative purposes only.
Figure 7.44 – Typical cast in-situ concrete barrier on bridge deck

206. ROADSIDE DESIGN GUIDE
PAGE 205
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
*Drawing not to scale, not structural, and shown for indicative purposes only.
Figure 7.45 – Example of a pre-cast concrete barrier on bridge deck
7.7 Upgrading Roadside, Median and Bridge Barriers
Inadequate (generally older) barriers will normally fall into one of two categories:
• Those that have structural inadequacies (i.e. they are showing signs of degradation); or
• Those that are functionally inadequate with regard to design and/or placement.
Designers should remain up-to-date with current barrier standards, designs, products and guidelines
in addition to investigating promising new research findings. However, there is no substitute for field
data or crash records to evaluate the performance of an existing barrier systems.
Whilst this Section does not provide detailed guidance on the review of existing barrier systems, care
should be taken to follow the manufacturer’s inspection and maintenance manuals for their systems.
The information contained within the following sections is generic and should be used to supplement
the product specific requirement.
7.7.1 Barriers with Structural Inadequacies
Structural inadequacies are characterised by reduced performance when barriers are struck. The
most obvious structural inadequacies include:
• Lack of blockouts for a strong-post system without specific design features to
accommodate this configuration;
• Weakened posts;

207. ROADSIDE DESIGN GUIDE
PAGE 206
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
• Substandard or obsolete roadside barriers;
• Missing components;
• Inadequate post spacing;
• Inadequate, non-conforming, or non-existent end treatment;
• Inadequate transition section;
• Damaged rail; or
• Corroded rail.
7.7.2 Barriers with Design/Placement Inadequacies
Design or placement inadequacies increase the likelihood of reduced performance from an
otherwise acceptable barrier system. Some of the most common deficiencies are:
• Barriers that are improperly placed on slopes or behind kerbs;
• Barriers, which are not really necessary at a location and could be removed;
• Barriers with deflection distances that exceed the distance between the rail and the
shielded fixed object;
• Barriers that are too long or too short to adequately shield an obstacle or non-traversable
terrain feature;
• Barriers that are too high or too low;
• Median barriers located in a steep (see Section 7.5.2) depressed median or a median with
surface irregularities where:
o The barrier can be moved near the shoulder’s edge (i.e. Figure 7.31, Illustration 1 or
2);
o The barrier can be relocated to a position, where the terrain between the edge of
the travelled way and the barrier has an acceptable slope; or
o The shoulder can be extended to the lateral distance desired and the barrier can be
placed on the shoulder.
• Strengthening bridge rails to the appropriate performance level by:
o Adding new rails, and posts if required, in front of the existing bridge rail;
o Improving anchorage of the bridge rail to the bridge deck;
o Strengthening the rail and/or posts.
• Increasing the bridge rail height to meet the requirements of the desired performance level;
• Removing or shielding of bridge rail appurtenances that have the potential for causing
vehicle snagging; or
• Eliminating kerbs, which have a detrimental effect on bridge rail-vehicle interaction.

208. ROADSIDE DESIGN GUIDE
PAGE 207
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
7.7.3 Establishing priorities of upgrading needs
Obsolete roadside, median and bridge barriers are often upgraded as part of reconstruction projects.
These devices may also be considered for replacement as part of system-wide safety improvement
projects. In each case, the designer should determine the scope and extent of the barrier upgrade to
be accomplished. The major factors that should be considered include, but not limited to:
• The nature and extent of barrier deficiency;
• Crash history;
• The results of any retesting of the product, or similar products; and
• The cost-effectiveness of recommended improvements.
These factors are interrelated, and the designer should rely on experience and judgement to reach a
preferred solution. The first step is an analysis of the continued need for an existing barrier. If it is
cost-effective to eliminate the shielded object by removal, relocation, or redesign, this is the option of
choice. If the feature requiring shielding cannot be eliminated, the designer should assess the
adequacy of the existing barrier installation. If the barrier is essentially non-functional (i.e. it cannot
reasonably be expected to function satisfactorily under most expected impacts), it should be upgraded
to current criteria.
Common deficiencies include:
• Installations that are too short, too low, or too high to be effective;
• Non-typical barrier types;
• Barriers improperly installed on slopes or behind kerbs; and
• Transition sections and end treatments.
In some cases, these deficiencies will be so obvious that the appropriate course of action is readily
apparent; but many times the deficiencies may be marginal and a decision may be based on
engineering judgement or an economic analysis. This may include further evaluation to verify critical
design details (e.g. base plate connections, anchor bolts, material brittleness, welding details,
reinforcement development). Then the past crash history at a specific site or an in-service
performance evaluation with a specific feature can be considered with respect to the cost of upgrading
the barrier. If the defective barrier is located on a road where the traffic speeds and volumes are
relatively low and therefore the impacts are less likely, then a temporary solution may be to delineate
the defective section.
7.7.4 Specific Issues with Bridge Barriers
Older bridge barrier systems may have a kerb or walkway between the travel lane and the bridge
railing. The kerb or the walkway may cause an impacting vehicle to go over the barrier or impact it
from an unstable position and subsequently roll over. In such installations, steel and aluminium
designs may cause snagging, as the vehicle may hit the gaps between the beams in abrupt angles.
This can produce high deceleration forces potentially leading to occupant injuries. This type of issue
can be detected through an analysis of available crash reports.

209. ROADSIDE DESIGN GUIDE
PAGE 208
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
In some cases, existing bridge barriers currently installed do not meet the requirements of the testing
standards NCHRP350 or MASH. In such cases, it may not be practical, or cost effective to completely
replace the barrier system installed. Instead, it may be more appropriate to apply a retrofit solution to
the location.
Retrofit designs refer to changes, modifications, and additions to existing bridge railings that elevate
these railings to acceptable performance levels. These designs may:
• Eliminate snagging potential;
• Increase the strength of the railing;
• Provide an acceptable transition from the approach rail to the bridge rail itself;
• Provide longitudinal continuity to the system; and
• Reduce or eliminate undesirable effects of kerbs or narrow walkways in front of the bridge
rail.
A number of specific retrofit concepts that can be adapted to numerous types of obsolete designs
have been developed and tested within the USA [5]. A number of these designs are in place within
the Abu Dhabi road network and hence, these approaches may be implemented where justified.
These solutions relate to:
• Concrete retrofit (safety shape or vertical);
• W-beam/thrie-beam retrofits; and
• Metal post-and-beam retrofits.
7.7.4.1 Concrete retrofit (safety shape or vertical)
If an existing substandard bridge barrier is located on a bridge, one retrofit technique is to construct
a concrete barrier in front of the bridge barrier (if there is sufficient space). Details of this retrofit
solution are given in Figure 7.46.
This design is most effective when the existing railing can remain in place and does not require
extensive modifications. The concrete safety shape commonly used for new construction often can
be added to an existing substandard bridge railing as an economical retrofit design:
• If the structure can carry the additional dead load; and
• If the existing railing configuration can meet the anchorage and impact forces needed for the
retrofit barrier.
Although a vertical-faced retrofit can cause relatively high deceleration forces for high-angle impacts,
its addition to the top of an existing kerb creates an effective barrier. A protruding kerb that may
contribute to vehicular vaulting in shallow angle impacts should not be installed in front of the concrete
shape as this may cause considerable wheel and suspension system damage.
7.7.4.2 Continuation of Approach Roadside Barrier Beam
One potential retrofit improvement consists of rebuilding the approach roadside barrier to current
standards, providing an acceptable transition section and continuing the metal beam rail element
across the structure to provide railing continuity. Where kerbs are present on the bridge, the retrofit
railing can be blocked out to minimize the possibility of a vehicle ramping over the bridge railing.

210. ROADSIDE DESIGN GUIDE
PAGE 209
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
Carrying an approach roadside barrier across the structure is an inexpensive, short-term solution to
inadequate bridge railings. This treatment can be particularly effective on low-speed roadways. It can
also significantly improve the impact performance of an obsolete railing, although it may not bring an
existing bridge railing into full compliance with applicable crash test requirements. Continuous metal-
beam rails across a structure also eliminate one of the major problems of a bridge-rail/transition-rail
design - adequate anchorage to prevent the approach rail from pulling out when struck. When the
approach barrier is extended across the bridge, the only transition design elements that remain critical
are gradual stiffening and elimination of a snagging potential.
Figure 7.46 – Installation of a reinforced concrete block in front of an existing (substandard)
rail [5]
7.7.4.3 Metal post-and-beam retrofits
A metal post-and-beam retrofit railing mounted at the kerb edge may be appropriate to use on an
existing structure with a raised kerb or walkway.
The crash test specimen for the post attachment to the kerb or bridge deck can be a yielding design
that eliminates bridge deck damage in high-angle, high-speed impacts. Metal rail elements should
line up with the face of the kerb and the elements should be spaced to minimize the likelihood of
vehicle intrusion and subsequent snagging on the posts.
This design has the advantage that it separates motor vehicles from pedestrians who are using the
sidewalk on a bridge. In many cases, the existing bridge railing can be used or converted to a
pedestrian railing.

211. ROADSIDE DESIGN GUIDE
PAGE 210
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
7.8 Summary and Conclusions
7.8.1 Summary and Conclusions Applicable to all Types of Barriers
Factors that should be considered in the selection of the type of barrier to be used at a specific site
include:
• Restraint requirements (i.e. performance capability);
• Dynamic deflection and clearance;
• Site conditions;
• Traffic volumes and percentage of heavier vehicles;
• End treatments
• Sight distances;
• Costs;
• Maintenance;
• Aesthetics; and
• Field experience.
With regard to the containment requirements for barrier systems, the “basic” level is to provide for
light passenger vehicles, including four-wheel drive vehicles and light commercial vehicles, and this
is accomplished by specifying TL-3 longitudinal barriers. The decision whether to install a barrier
system with a higher level of containment will largely depend on engineering judgement, and
consideration of the following points:
• High percentage of heavy vehicles in traffic stream (i.e. on truck roads);
• Hazardous materials routes;
• Adverse geometrics, such as sharp curvature, that are often combined with poor sight
distance;
• Severe consequences associated with penetration of a barrier by a large vehicle; and
• For bridge parapets, the height of the bridge, and the type of hazard located below the bridge.
With regard to the specific case of bridge barriers, the following identifies Abu Dhabi practices for the
selection of a bridge rail restraint requirement:
A. TL-4. This is the standard Abu Dhabi bridge rail on most bridges. Its use is appropriate,
except for those conditions identified in point C below where a TL-5 bridge rail should be
used.
B. TL-5. This performance level should be designated for:
• All truck roads;
• All roads with significant truck volumes (say, 100 DDHV or higher); and

212. ROADSIDE DESIGN GUIDE
PAGE 211
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
• All other sites where a TL-5 rail can address a specific concern (e.g. truck lean over,
potential catastrophic consequences for heavy vehicle penetration).
C. TL-6. This is the highest performance level and it is only considered for the rare cases
where a route is regularly used by high numbers (say, 100 DDHV or higher) of tankers or
similar vehicles and there are hazards with risk to third parties (see Chapter 4, Section 4.4)
within the vicinity of the travelled way.
No hazard (which cannot be removed, relocated or made passively safe/transferable) should be
present within the deflection distance of a safety barrier system.
For proprietary systems used on the Abu Dhabi Department of Municipal Affairs and Transport road
network, preference should be given to those systems meeting the ‘preferred’ values for the impact
severity parameters OIV and ORA. No systems exceeding the ‘maximum’ values for OIV and ORA
shall be used without prior approval of the Abu Dhabi Department of Municipal Affairs and Transport
(see Chapter 6, Section 6.3.3.4).
It is preferable that the slope in front of the barrier is essentially flat (1V:10H or flatter) because the
requirements of NCHRP350 and MASH are such that safety barriers have (generally) only been tested
in such configurations. The result on an impact with a specific barrier in a slope is generally unknown.
Maintenance factors that need to be considered before selecting a particular barrier system include:
• Routine maintenance of the barrier;
• Damage repair;
• Effect of the barrier on road and roadside maintenance (pavement overlays for example);
• Material and component requirements (e.g. stockpiling of spare parts); and
• Experience of maintenance repair crews.
With regard to specific maintenance issues identified within the Abu Dhabi road network, the following
advice is recommended:
• In all cases, the lap joint of a barrier should be such that, in the direction of traffic, the end of
the first barrier encountered is located IN FRONT of the approach end of the second barrier
encountered;
• All lap joints should incorporate all eight of the fasteners required;
• No barrier components should be cut or drilled on site;
• Longitudinal barrier elements which are not connected will represent a risk of injury to road
users in the event of an impact;
• The manufacturer’s installation instructions should be followed at all times, with particular
reference to installation height; and
• Soil should be sufficiently compacted around the base of barrier posts, and none of the
concrete foundations should be exposed above ground level.

213. ROADSIDE DESIGN GUIDE
PAGE 212
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
When determining the placement of a barrier system, either in the roadside, median, or on a bridge
structure, the following considerations should be made (see Section 7.3):
• Length of need (see Section 7.3.1);
• Minimum length and gaps in barriers (see Section 7.3.2);
• Lateral placement from the edge of the travelled way (see Section 7.3.3);
• Shy-line offset (see Section 7.3.4);
• Barrier deflection distance (see Section 7.3.5);
• Effect of kerbs (see Section 7.3.6); and
• Foundation conditions (see Section 7.3.7).
7.8.2 Summary and Conclusions Specific to Roadside Barriers
The following points should also be considered with particular reference to roadside barriers (refer
to Section 7.4):
• The effect of embankments (see Section 7.4.1);
• The rate of flare (see Section 7.4.2);
• The presence of a short radius (see Section 7.4.3); and
• The sight distance (see Section 7.4.4).
7.8.3 Summary and Conclusions Specific to Median Barriers
In addition, the following points should be considered with particular reference to median barriers
(refer to Section 7.5):
• Terrain effects on the lateral placement of median barriers (see Section 7.5.2);
• Super-elevated sections (see Section 7.5.3);
• Fixed objects within the median (see Section 7.5.4);
• Emergency and maintenance crossings (see Section 7.5.5);
• Glare screens.
7.8.4 Summary and Conclusions Specific to Bridge Barriers
Furthermore, the following points should be considered with particular reference to bridge barriers
(refer to Section 7.6):
• Material type (see Section 7.6.1);
• Hardware attachments (see Section 7.6.2);
• Additional lateral placement considerations (see Section 7.6.2.1);
• Heights of bridge parapets (see Section 7.6.3); and
• Fixation to bridge decks (see Section 7.6.4).

214. ROADSIDE DESIGN GUIDE
PAGE 213
07 SELECTION AND APPLICATION OF ROADSIDE,
MEDIAN AND BRIDGE BARRIERS
FIRST EDITION-DECEMBER 2016
7.8.5 Summary and Conclusions on Upgrades to Barriers
When planning upgrades to roadside, median and bridge barriers, the structural and functional
inadequacies should be considered in relation to the:
• Nature and extent of barrier deficiency;
• Crash history;
• The results of any retesting of the product, or similar products; and
• The cost-effectiveness of recommended improvements.
7.9 References
[1] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney,
NSW: Austroads, 2010.
[2] V. Hock, R. Lampo, S. Johnston and J. Myers, “Corrosion Mitigation and Materials Selection
Guide for Military Construction in a Severely Corrosive Environment,” US Army Corps of
Engineers, Construction Engineering Research Laboratory, 1988.
[3] NCHRP, “NCHRP Report 350, Recommended Procedures for the Safety Performance
Evaluation of Highway Features,” Transportation Research Board, National Research
Council, Washington DC, 1993.
[4] Vicroads, “The use of Wire Rope Safety Barrier (WRSB), RDN 06-02 C,” Vicroads, Victoria,
2015.
[5] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of
State Highway and Transportation Officials, 2011.
[6] Alberta Infrastructure and Transportation, “Roadside Design Guide,” 2007.
[7] AASHTO, “Manual for Assessing Safety Hardware,” Ammerican Association of State
Highway and Transportation Officials, Washington DC, 2009.
[8] British Standards, “BS7669-3: Vehicle Restraint Systems - Part 3: Guide to the Installation,
Inspection and Repair of Safety Fences,” BSI, 1994.
[9] R. Setchell, “Eastern Daily Press,” [Online]. Available:
http://www.edp24.co.uk/polopoly_fs/1.867564!/image/1569740063.jpg_gen/derivatives/land
scape_490/1569740063.jpg. [Accessed 5 5 2016].
[10] J. W. Hutchinson, “The Significance and Nature of Vehicle Encroachments on Medians of
Divided Highways,,” in Highway Engineering Series No 8, Urbana, IL, University of Illinois,
1962.

215. ROADSIDE DESIGN GUIDE
PAGE 213
08 Motorcyclist Protection Systems First Edition-December 2016
8 MOTORCYCLIST PROTECTION SYSTEMS
8.1 Introduction
Motorcyclists impacting roadside barriers has been raised by motorcyclists’ groups throughout the
world, and studied in road safety research for more than a decade.
The problem is largely based on the fact that a vast majority of the vehicle restraint systems installed
along the roads today are not primarily designed with motorcyclists in mind. As such, these barriers
are not specifically designed to stop errant riders from reaching the hazards behind, and may
themselves pose a risk to motorcyclists due to exposed posts, sharp edges and corners.
Motorcycle to barrier impacts are infrequent, but high severity accidents. According to 2012 UK data,
motorcycles (2.86 fatal accidents per billion vehicle mile) were approximately 48 times more likely to
become involved in a fatal barrier accident than cars (0.06 fatal accidents per billion vehicle mile) [1].
In 2005, motorcycle crashes were found to be the leading source of fatalities in guardrail crashes in
the USA. In terms of fatalities per registered vehicle, motorcycle riders were dramatically
overrepresented in the number of fatalities resulting from guardrail impacts. Motorcycles comprised
only 2% of the vehicle fleet, but accounted for 42% of all fatalities resulting from guardrail collisions.
From 2000 to 2005, approximately one in eight motorcyclists who struck a guardrail were fatally
injured – a fatality risk over 80 times higher than for car occupants involved in a collision with a
guardrail [2].
In order to reduce risk of injury to a motorcyclist when impacting a safety barrier, a number of
Motorcyclist Protection Systems (MPS) have been developed throughout Europe. This has led to the
further development of a European Technical Specification for the testing of such devices (TS1317-
8:2012). Details of TS1317 are given in Section 8.4 of this chapter. At the time of writing of this
document, there was no standardised crash test methodology available according to the American
guidelines NCHRP-350 or MASH. The TS1317-8 is currently the only standardised way of impact
testing the MPS and therefore it is the chosen way of assessing MPS for this design guide.
However, the installation of an MPS onto an existing barrier system will result in additional cost, and
a careful evaluation has to be made in order to ensure that the use of public funding for the installation
of such systems is best utilised to achieve the highest benefit to cost ratio among many possible
alternative safety measures. Consideration is also given to the effect that the addition of the MPS may
have on the performance of the barrier when impacted by other roads users (car drivers for example).
This Chapter provides information on the types of MPS available on the market today and the
performance assessment of these through the European testing standard TS1317-8:2012.
Recommendations on the locations where these systems may be required are also presented. Finally
guidance on the selection and application of MPS is given.

216. ROADSIDE DESIGN GUIDE
PAGE 214
08 Motorcyclist Protection Systems First Edition-December 2016
8.2 Road Safety Barriers from Motorcyclists’ Point of View
The majority of the roadside safety barrier systems in use today are designed to bring passenger cars
and/or heavy vehicles to a controlled and safe stop. However, when struck by errant motorcyclists,
these systems may fail to provide protection, and could contribute towards serious or fatal injuries.
Research shows that there are two dominant types of motorcycle to barrier accidents [1]. In the first
type, motorcyclists hit the barrier while sliding on the ground, having fallen from their motorcycle. In
this type of accident, the impact mainly occurs with the lower section of the barrier. In the second type,
motorcyclists hit the barrier at an upright position while they are still on the motorbike. In this type of
accident, the impact mainly occurs with the upper section of the barrier.
A steel guardrail, as shown in Figure 8.1, does not provide the necessary protection for a motorcyclist,
as errant riders who are sliding on the ground, can easily go between the posts and under the rail to
reach the hazard behind the barrier. Hitting the barrier itself is not an acceptable option either, as the
exposed barrier posts constitute the leading cause of injury in motorcycle to barrier accidents [3].
Figure 8.1 – A W-beam barrier from a motorcyclist’s perspective [4]
The type of barrier post can have an important effect on the outcome of a motorcyclist-to-barrier
impact. I-beam posts, such as the IPE posts (I-beam posts manufactured according to European
standard EN10025), as shown in Figure 8.2, are known to be the most aggressive design from a
motorcyclist safety perspective, due to sharp edges and corners, which can cause significant injuries.
Sigma, Z or C profile barrier posts, as shown in Figure 8.2, are less aggressive alternatives, with no
exposed edges on the impact side. However, even these posts are not completely safe for errant
riders impacting them.
For riders who hit the barrier at an upright position, the sharp corners located at the top of the posts
also pose a significant danger. The Norwegian Public Roads Administration’s Handbook 231
[5] has identified the top of the posts as being particularly hazardous for motorcyclists if they become
dismounted from their motorcycle during an impact and fall on top of these; a view shared by Gibson
and Benetatos [6] and Duncan et al [7].

217. ROADSIDE DESIGN GUIDE
PAGE 215
08 Motorcyclist Protection Systems First Edition-December 2016
Figure 8.2 – Types of barrier posts from a motorcyclist’s perspective
Wire rope is another common barrier type which poses similar dangers to errant motorcyclists as the
W-beam systems do. Contrary to popular belief among motorcyclists, research shows that it is the
exposed posts which pose the biggest danger, not the wire ropes [1]. For example a study carried out
in the USA by Daniello and Gabler found that there was no significant difference in the percentage of
killed or seriously injured (KSI) for riders involved in motorcycle collisions with W- beam (40.1% KSI)
and cable barriers (40.4% KSI) [8]. Duncan et al. have stated that there is no substantial evidence to
show that wire rope barriers pose a greater risk to motorcyclists than the objects from which they are
designed to shield the road user, such as trees, posts, or oncoming traffic [7]. Duncan et al also added
that there is no evidence of the “cheese cutter effect” during injury events.
Figure 8.3 – Wire rope barrier from a motorcyclist’s perspective
Concrete barriers, unlike the steel alternatives, do not feature any sharp edges or corners which may
cause injuries to motorcyclists. Especially for low angle impacts, an errant rider can simply slide along
or over the barrier without getting caught in any sharp features. This characteristic makes concrete a
more motorcyclist friendly choice over steel; especially for median applications, where the angles of
impact are more likely to be narrow. Also, unlike steel systems, concrete barriers do not let errant
riders to pass through and reach the hazard located behind.

218. ROADSIDE DESIGN GUIDE
PAGE 216
08 Motorcyclist Protection Systems First Edition-December 2016
Figure 8.4 – Concrete barrier from a motorcyclist’s perspective
A study in the USA by Gabler, using 2005 Fatality Analysis Reporting System data, found that the
fatality risk in motorcycle to guardrail collisions (12.4%) is almost 1.5 times higher than the fatality risk
in a motorcycle to concrete barrier collision (7.9%) [8]. However, concrete barriers are not perfectly
motorcycle-friendly either. In 2007, the Spanish Motorcyclists Association “Association Mutua
Motera”, carried out a full-scale crash test for a “New Jersey” profile concrete barrier [9], as shown in
Figure 8.5 (see Section 8.4 for impact testing of MPS). The results of the test have shown a head
injury criteria value of more than 1.5 times the acceptable limit (Head Injury Criterion
i.e. HIC is the index representing the head injury risk and it is calculated by using the accelerations
acting on the head of the dummy, which are recorded during the test [10]). This shows that concrete
barriers, although more desirable than steel systems from a motorcyclist safety perspective, are not
as safe as dedicated motorcyclist protection systems.
Figure 8.5 – Impact test of a new jersey profile concrete barrier [9]

219. ROADSIDE DESIGN GUIDE
PAGE 217
08 Motorcyclist Protection Systems First Edition-December 2016
8.3 Types of Motorcyclist Protection Systems
There are currently more than thirty different MPS designs available on the market today [1] and these
can be categorized into one of three main categories: continuous MPS, discontinuous MPS and
barriers with motorcyclist protection incorporated in their design.
8.3.1 Continuous Motorcyclist Protection Systems (CMPS)
CMPS are the most common type currently being manufactured and promoted around the world. In
this type of MPS, a secondary protective element is fitted underneath the main longitudinal of the
barrier system, as shown in Figure 8.6.
Figure 8.6 – Example of a continuous MPS, Bike Guard from Highway Care Ltd. [11]
This type of system provides continuous protection of the posts, to errant motorcyclists impacting the
barrier while sliding along the ground, having fallen from their motorcycles. However, these systems
do not provide any protection from the top of the barrier and are therefore less effective for motorcycle
impacts in upright position.
CMPS available on the market today come in many different designs and materials, including metal,
as shown in Figure 8.6, plastic, as shown in Figure 8.7, and composite materials, as shown in Figure
8.8. From a performance perspective, it is not possible to say if one material is safer than the others.
The designer/engineer should asses the performance of individual systems through impact test
results (see Section 8.4), regardless of the material type. However, from a durability perspective,
some materials may be a better fit for the environmental conditions in Abu Dhabi, i.e. high
temperatures and humidity. For this reason, the designer/engineer should assess each system on a
product by product basis.
Figure 8.7 – Example of a plastic CMPS, DR46 from SNOLINE [12]

220. ROADSIDE DESIGN GUIDE
PAGE 218
08 Motorcyclist Protection Systems First Edition-December 2016
Figure 8.8 – Example of a composite CMPS, BASYC [13]
Installation requirements of CMPS vary from one system to another. Some CMPS are connected
directly to the barrier posts, as shown in Figure 8.7, some are connected directly on to the main beam,
as shown in Figure 8.6. Some systems are designed to be connected to the posts through simple
cable ties, as shown in Figure 8.7, while others my require special equipment for the installation, as
shown in Figure 8.8. The ease of installation, depends on the requirements of the specific system.
The designer/engineer should refer to the manufacturers specifications and installation manual to
assess the ease of installation for each indivdual system.
*Profile is not to scale and is shown for indicative purposes only.
Figure 8.9 – Example of a typical CMPS profile
Most CMPS are designed to be installed on to more than one type of barrier system. For example, it
is possible to install the Bike Guard and the DR-46 systems, as shown in Figure 8.6 and Figure
8.7 respectively, on to various types of guardrail, including w-beam and open box beam systems.
However, the added MPS may cause a difference in the impact performance of the barrier, on to
which it is attached. For this reason, the MPS and the barrier should be tested together, according to
MASH or NCHRP-350, to prove the acceptable performance of a specific combination (see Section
8.4).

221. ROADSIDE DESIGN GUIDE
PAGE 219
08 Motorcyclist Protection Systems First Edition-December 2016
The main advantage of these systems is that they can be fitted easily under the existing barrier
installations, without the need of replacing them. A disadvantage of these systems is that they can be
problematic at the areas prone to sand accumulation, as they wouldn’t allow the sand to flow under
the system. For this reason they ideally should not be installed in areas of potential sand
accumulation. Another potential disadvantage is the installation limitations at very sharp horizontal
curves. The minimum radius of curvature, which the system can be installed at, changes from one
design to another.
8.3.2 Discontinuous Motorcyclist Protection Systems (DMPS)
The DMPS focus only on the most aggressive element of a barrier system, the post. These are
discontinuous systems where each post is covered individually, as shown in Figure 8.10.
Figure 8.10 – Example of a discontinuous MPS application on a W-beam barrier, Motoprotec
from Motoprotec Security Systems [14]
Similar to CMPS, these systems only provide protection for errant riders sliding along the ground.
They generally do not provide protection for from the top of the barrier and are therefore less effective
for motorcycle impacts in upright position.
DMPS available on the market today also come in different designs and materials, including plastic,
foam and other composite materials. The designer/engineer should asses the performance of
individual systems through impact test results (See Section 8.4), regardless of the material type.
However, from a durability perspective, some materials may be a better fit for the environmental
conditions in Abu Dhabi, i.e. high temperatures and humidity. For this reason, the designer/engineer
should assess each system on a product by product basis. Most DMPS are also designed to be
installed on to more than one type of barrier system, such as the W-beam shown in Figure 8.10 and
the wire rope systems shown in Figure 8.11. The applicability is often based on the profile of the
barrier posts, as shown in Figure 8.2, and changes from one design to another.

222. ROADSIDE DESIGN GUIDE
PAGE 220
08 Motorcyclist Protection Systems First Edition-December 2016
Figure 8.11 – Example of discontinuous MPS application on a wire rope barrier in South
Australia [15]
DMPS, similar to CMPS, are relatively easy to install systems. Unlike some DMPS designs, CMPS
are not limited by the minimum horizontal curvature of the road. It can be installed at even the sharpest
curves. DMPS designs do not completely obstruct the lower section of the barrier and therefore allow
the windblown sand to freely pass through. This makes it a better alternative at areas prone to sand
accumulation.
8.3.3 Barriers with Motorcyclist Protection Incorporated in Design
This tested proprietary system is a barrier with motorcyclist protection incorporated in their
fundamental design. As shown in Figure 8.12, these systems do not feature any exposed posts,
corners or sharp edges. In addition to providing protection for sliding riders, unlike other alternatives
they also provide protection for the riders impacting the barrier in an upright position.
Figure 8.12 – Example of a barrier with motorcyclist protection incorporated in its design,
CUSTOM from CSM SpA
They are currently the least frequent MPS type on the market and are likely to be more expensive and
more time consuming to install than the other alternatives, as they would require a complete
replacement of the existing barrier. However, the additional level of safety provided may justify their
application. Similar to CMPS, these systems are not recommended in areas of potential sand
accumulation as they wouldn’t allow the sand to blow through.

223. ROADSIDE DESIGN GUIDE
PAGE 221
08 Motorcyclist Protection Systems First Edition-December 2016
8.4 Performance Assessment of Motorcyclist Protection Systems
Currently the common standardized way of assessing the performance of a MPS is the European
Technical Specification TS1317-8 “Motorcycle road restraint systems which reduce the impact
severity of motorcyclist collisions with safety barriers” [10]. TS1317-8 succeeds and is a combination
of both the Spanish Test Standard UNE-135900 and Test Protocol of the French test house LIER.
NCHRP350 and MASH do not include any methods for the impact performance assessment of MPS.
Therefore TS1317-8 is the recommended guidance of the MPS performance assessment for Abu
Dhabi.
The recommended procedure is to test a MPS first according to TS1317-8 to assess its impact
performance for motorcyclists. Since TS1317-8 tests are only carried out with test dummies sliding
on the ground, they do not contradict with MASH and NCHRP350 methodologies. If the MPS shows
satisfactory performance from a motorcyclist safety perspective, then the combination of the MPS and
the barrier, to which it will be attached, should be tested as one system, according to MASH or
NCHRP350. This secondary level of testing is required to demonstrate that the addition of MPS does
not adversely affect the performance of the barrier during impacts with other vehicles.
TS1317-8 specifies requirements for the impact performance of systems designed for the reduction
of impact severity for motorcyclists. Currently TS1317-8 considers only the scenario of a rider
impacting a barrier whilst sliding along the ground, having fallen from their motorcycle. Other incident
scenarios, such as riders impacting the barrier while still on their motorcycle are not yet considered in
TS1317-8. The systems reviewed by TS1317-8 are those fitted to barriers, or barriers that have
inherent rider protection or risk reduction capability.
8.4.1 TS1317-8 Test Types
The full-scale impact tests in TS1317-8 consist of launching a Hybrid III Test Dummy with a modified
shoulder at a given speed against a barrier with an MPS installed. At the moment of impact, the
dummy is sliding with its back and legs in contact with ground in a stable way, as shown in Figure
8.13 . The dummy is equipped with a helmet and dressed in motorcyclist safety clothes in accordance
with the requirements specified in the technical specification.
Figure 8.13 – Example of an EN1317-8 test configuration [10]
During the test, accelerations, forces and moments acting on the head and neck are measured with
instrumentation inside the dummy. High and normal speed cameras are used to capture test

224. ROADSIDE DESIGN GUIDE
PAGE 222
08 Motorcyclist Protection Systems First Edition-December 2016
footage that describes the behaviour of the MPS, barrier and dummy. Main performance indicators of
a TS1317-8 test are Speed and Severity Level classification.
8.5 Selection Criteria
Once the decision for the installation of a MPS is made, following criteria should be used in deciding
the type of MPS to be installed.
8.5.1 Compatibility with the Existing Barrier
It is not possible to install every MPS on to every barrier system available in the market. The chosen
MPS should be compatible with the existing barrier.
Compatibility should also be assessed from a performance perspective. Adding an MPS to an existing
barrier can have some adverse effects during an impact with a car. This concern was supported by
tests carried out in BAst, Germany [18]. The testing indicated that there would be an increased
probability of a car climbing up the barrier due to the addition of the lower secondary rail, although the
results of the testing were still deemed to meet the requirements of the European Barrier Test
Standard EN1317-1&2. This is why a MPS ideally should not be installed on the road, without testing
the combination of barrier + MPS as a single system through MASH or NCHRP350. If the combination
passes the tests, then there would be significantly less worry for a vehicle to climb over the barrier.
It should be noted that different MPS-barrier combinations can result in different impact
characteristics. Therefore, it is important to test the complete systems both to a MPS testing standard
(TS1317-8) & a barrier testing standard (MASH or NCHRP-350 for Abu Dhabi) before installation.
In all cases, the compatibility of an MPS with a barrier system should be checked with the
manufacturer/promoter of the system, prior to installation. This may result in a different MPS and/or
barrier being selected for a particular application.
8.5.2 Areas of Potential Sand Accumulation
As explained in Section 8.3.1, continuous motorcyclist protection systems can cause problems in
areas of blowing sand. These systems do not allow the free movement of sand and therefore may
cause accumulation under the barrier. Consideration should be given for the selection of an
appropriate MPS in such areas. From a motorcyclist’s point of view, ideally, the designer/engineer
should try to eliminate the risk by removing or relocating the hazards, in such areas. If this is not
possible, then a barrier design, which would allow the free movement of the sand, can be considered.
This is likely to be a WRSB system, due to their better performance in letting the sand to flow
underneath. If this is the case, then the posts of the WRSB should be shielded with an appropriate
MPS, such as the example shown in Figure 8.11.
8.6 Application Criteria
8.6.1 Common Locations Where a Motorcyclist Protection System may
be required
Motorcycle to barrier accidents are rare but high severity incidents. Due to their rarity, covering the
whole network with MPS is often not feasible from a cost effectiveness perspective. However, due

225. ROADSIDE DESIGN GUIDE
PAGE 223
08 Motorcyclist Protection Systems First Edition-December 2016
to the high severity of these incidents, well targeted MPS installations are likely to provide high
cost/benefit ratio. For this reason it is important to identify the most common locations of motorcycle
to barrier incidents. Once identified, these locations can then be evaluated for the installation of a
MPS.
Following are the common locations of motorcycle to barrier accidents, based on international best
practice, which should be evaluated for the installation of a MPS:
8.6.1.1 Sharp Bends on Single Carriageways
On single carriageways, the most common locations for motorcycle-to-barrier incidents are sharp
bends, especially the ones with a horizontal curve radius less than 200m, as shown in Figure 8.14.
These locations are even more susceptible to motorcycle-to-barrier incidents if one or more of the
contributing characteristics, which are presented in Section 8.6.1.3, exist.
Figure 8.14 – Example of a sharp bend on a single carriageway [4]
On single carriageways, the following areas should be prioritised for the evaluation of a MPS
installation:
• Left hand bends with a curve radius of 200m or less – in such cases the rightside barrier
provision should be prioritised for assessment;
• Right hand bends with a curve radius of 200m or less – in such cases the leftside barrier
provision should be prioritised for assessment.
8.6.1.2 Vicinity of Interchanges on Dual Carriageways
Research shows that on high speed dual carriageway roads, such as freeways and expressways,
motorcycle-to-barrier accidents occur most commonly at the vicinity of the interchanges [1], such as
the one shown in Figure 8.15.
Motorcycle-to-barrier accidents also occur on uninterrupted straight (horizontal curve radius
>2000m) sections of dual carriageways. However, due to the relatively low number of incidents
compared to the very long stretch of dual carriageways on the network, it is not feasible to prioritise
these sections for MPS installation.
On an interchange, the following areas should be prioritised for the evaluation of a MPS
installation:

226. ROADSIDE DESIGN GUIDE
PAGE 224
08 Motorcyclist Protection Systems First Edition-December 2016
On Ramps/Slip Roads:
• On left hand bends with a curve radius of 200m or less – in such cases the rightside barrier
provision should be prioritised for assessment;
• On right hand bends with a curve radius of 200m or less – in such cases the leftside barrier
provision should be prioritised for assessment.
Figure 8.15 – Areas to be considered for MPS installation on an interchange [16]
8.6.1.3 Additional Road Characteristics for the use of a Motorcyclist
Protection System
Enhanced prioritisation should also be given to areas where one or more of the following
characteristics exist:
a) Locations with a known history of motorcycle-to-barrier accidents;
b) Routes regularly travelled by motorcyclists/where the percentage of motorcyclist traffic is
high;
c) Locations where the barrier system is located close to the edge of the carriageway;
d) Inadequate geometric design, such as reverse and/or insufficient super-elevation, as shown
in Figure 8.16;
Areas to be considered
for a MPS installation

227. ROADSIDE DESIGN GUIDE
PAGE 225
08 Motorcyclist Protection Systems First Edition-December 2016
Figure 8.16 – Examples of reverse/inadequate super-elevation [17]
e) Consecutive curves with changing direction and horizontal curve radii, such as mountain
terrain, as shown in Figure 8.17, A).;
• This is a physically challenging combination for the riders. It is easier to make an error
and miss the correct line during the successive direction changes;
f) Sharp horizontal curves located at the end of long straights, without a sufficient transition
spiral, as shown in Figure 8.17, B);
• The long straight gives enough distance for reaching higher speeds, while judging the
brake point before the sharp curve can be tricky for riders. This combination is also
against rider expectations;
g) Consecutive curves in the same direction, with decreasing radius, as shown in Figure 8.17,
C);
• It is very hard to judge and keep the correct cornering line in this combination as the
correct line changes suddenly in the middle of the corner. This design is also against
rider expectations;
Figure 8.17 - High risk horizontal road alignment combinations for motorcyclists [17]
h) Locations with poor sight distance;
i) Locations likely to experience sand accumulation and skidding;
j) Locations where other hazards to motorcyclists exist, subject to engineering judgment.
8.6.2 Assessment of the Need for a Motorcyclist Protection System
Once an area of potential motorcycle-to-barrier incidents is identified, the following treatment options
should be evaluated; listed in order of decreasing level of desirability from a road safety perspective.
1) Investigate the methods that would decrease the probability of a motorcyclist leaving the
carriageway (e.g. improving road surface, improved signage or better visibility);

228. ROADSIDE DESIGN GUIDE
PAGE 226
08 Motorcyclist Protection Systems First Edition-December 2016
2) Where possible, eliminate the need and remove the barrier:
a. Remove any existing hazard(s);
b. Move any existing hazard(s) further from the carriageway;
c. Make the hazard(s) passively safe for an impact by a motorcyclist (as there is no
published testing standard to ascertain the passive safety performance of roadside
hazards through an impact by motorcyclist, engineering judgement should be used
to make this assessment);
3) If the barrier cannot be removed, then installation of an MPS, compliant with TS1317-8,
should be considered.;
4) If the installation of an MPS cannot be justified (for example due to a cost benefit analysis),
then a review of the proximity of any remaining hazards to the front face of the barrier
should be carried out to ascertain whether the working width of the system could be
increased by the removal of posts from the barrier system. The removal of the posts would
decrease the probability of an impact by a motorcyclist, and thus reduce the risk of injury.
8.7 Maintenance and Inspection Requirements
Motorcyclist Protection Systems should be inspected in line with the manufacturer’s Installation and
Maintenance manual. MPS, in general, are relatively simple systems which are attached to the
existing barriers. The majority of the MPS available on the market today require little regular or routine
maintenance. However, it is important that periodic maintenance checks are performed, in line with
the manufacturer’s recommendations so that each installed unit remains fully functional. It may be
time and cost-effective to carry out the MPS inspection together with the inspection of the barrier
system, which they are attached to. Similar to safety barriers, maintenance and inspection
requirements for an MPS should be provided by the promoter associated with the system. They should
also have an established training scheme for the operatives undertaking these activities.
The majority of the available MPS are designed to remain functional after an impact by an errant
motorcyclist sliding on the ground. However, due to their flexible nature, impact with a vehicle may
easily cause enough damage to render a MPS ineffective. Similar to their installation, repair of MPS
is relatively quick and easy, even when a significant length of the system is damaged.
Ideally, MPS should not be used in areas where they can cause potential sand accumulation.
Accumulated sand would not only render the MPS ineffective, but it can also adversely affect the
impact performance of the barrier, which it is attached to (See Section 7.2.10).
Some MPS, similar to a W-beam barrier, are designed in the form of rails which need to be lapped in
a certain direction. Guidance given in Section 7.2.8.1 also applies to these systems. Therefore, correct
lapping of the systems should also be checked during inspections.
Some MPS are made of materials, which may be more sensitive to heat than others, such as plastic,
composites, etc. If such a system is chosen for installation, the effect of the high temperatures and
humidity observed in Abu Dhabi should be checked during inspection. MPS should not deform or get
affected by heat in any other way.
8.8 Summary and Conclusions
The majority of the barrier systems are not designed to provide protection for motorcyclists.
Motorcycle-to-barrier impacts are rare but high severity incidents. In order to reduce risk of injury to

229. ROADSIDE DESIGN GUIDE
PAGE 227
08 Motorcyclist Protection Systems First Edition-December 2016
a motorcyclist when impacting a safety barrier, a number of Motorcyclist Protection Systems (MPS)
have been developed.
MPS available on the market can be grouped into three categories:
• Continuous MPS;
• Discontinuous MPS;
• Barriers with MPS incorporated in design.
Performance of a MPS can be assessed through the European Technical Specification TS1317-8.
Main performance indicators of a TS1317-8 test are Speed and Severity Level classification.
The need for a MPS should be assessed for road sections with a higher risk of a motorcycle-to- barrier
incident. Locations to prioritise for an assessment are:
• Areas with a history of motorcycle-to-barrier accidents;
• Sharp bends in single carriageways;
• Vicinity of Interchanges on dual carriageways, with a special focus on ramps.
Once an area for possible motorcycle-to-barrier accidents is identified, it should be evaluated for a
MPS installation. A MPS is only recommended if the barrier cannot be removed.
Once the decision to install a MPS is made, the type should be selected according to:
• Compatibility with the existing barrier;
• Potential risk of sand accumulation.
The chosen MPS should be compatible with the existing barrier. Adding a MPS to an existing barrier
can have some adverse effects during an impact with a car. This is why, ideally, a MPS should not be
installed on the road, without testing the combination of barrier + MPS as a single system through
MASH or NCHRP350.
CMPS can cause problems with sand accumulation and therefore should not be used in areas prone
to blowing sand.
MPS should be inspected in line with the manufacturer’s installation and maintenance manual. The
majority of the available MPS are designed to remain functional after an impact by an errant
motorcyclist sliding on the ground.
Some MPS are made of materials, which may be more sensitive to heat than others. If such a system
is chosen for installation, the effect of the high temperatures and humidity observed in Abu Dhabi
should be checked during inspection.
8.9 References
[1] C. Erginbas and G. Williams, “Motorcyclists and Barriers on the Highways Agency Road
Network,” TRL (Unpublished), 2015.
[2] H. C. Gabler, “THE RISK OF FATALITY IN MOTORCYCLE CRASHES WITH ROADSIDE
BARRIERS,” Virginia Tech, United States, 2007.

230. ROADSIDE DESIGN GUIDE
PAGE 228
08 Motorcyclist Protection Systems First Edition-December 2016
[3] M. Mcdonald, “Motorcyclists and Roadside Safety Hardware,” in A2A04 Summer Meeting,
2002.
[4] FEMA, “New Standards for Road Restraint Systems for Motorcyclists - Designing Safer
Roadsides for Motorcyclists,” Federation of European Motorcyclists' Associations, 2012.
[5] Norwegian Public Roads Administration, “MC Safety Design and Operation of Roads and
Traffic Systems,” Directorate of Public Roads, Norway, 2004.
[6] T. Gibson and E. Benetatos, “Motorcycles and Crash Barriers,” NSW Motorcycle Council, New
South Wales, 2000.
[7] C. Duncan, B. Corben and N. &. T. C. Truedsson, “Motorcycle and Safety Barrier Crash-
Testing: Feasibility Study,” Accident Research Centre, Monash University, 2000.
[8] A. Daniello and H. C. Gabler, “Effect of Barrier Type on Injury Severity in Motorcycle-to-Barrier
Collisions in North Carolina, Texas, and New Jersey,” Transportation Research Record:
Journal of the Transportation Research Board, p. pp. 144–151, 2011.
[9] J. C. Toribio, “Barreras rígidas de hormigón Comportamiento ante el impacto de motoristas
(Rigid Concrete Barriers, Behaviour on the Impact of Motorcyclists),” Asociacion Mutua Motera
, pp. 62-65, 2008.
[10] CEN, CEN/TS 1317-8, Road Restraint Systems - Part 8: Motorcycle Road Restraint Systems
Which Reduce the Impact Severity of Motorcyclist Collisions with Safety Barriers, Brussels:
CEN, European Committee for Standardization, 2012.
[11] EuroRAP, “Barriers to change: designing safe roads for motorcyclists,” EuroRAP,
Basingstoke, 2008.
[12] SNOLINE, “www.snoline.com,” [Online]. Available: http://www.snoline.com/dr46-1. [Accessed
2015 09 15].
[13] BASYC Systemas de Seguridad Vial, [Online]. Available: http://www.basyc.eu/. [Accessed
2015 09 15].
[14] World Highways, “www.worldhighways.com,” [Online]. Available:
http://www.worldhighways.com/categories/road-markings-barriers-workzone-
protection/features/crash-cushion-design/. [Accessed 15 09 2015].
[15] Governmen of South Australia Depratment of Planning, Transport and Infrastructure,
“www.dpti.sa.gov.au,” [Online]. Available:
http://www.dpti.sa.gov.au/towardszerotogether/safer_roads/building_safer_roads. [Accessed
15 09 2015].
[16] Abu Dhabi Department of Transport, Road Geometric Design Manual, Abu Dhabi: Abu Dhabi

231. ROADSIDE DESIGN GUIDE
PAGE 229
08 Motorcyclist Protection Systems First Edition-December 2016
Department of Transport, 2014.
[17] FGSV, “Merkblatt zur Verbesserung der Verkehrssicherheit auf Motorradstrecken (Leaflet to
Improve Road Safety on Motorcycle Roads),” Forschungsgesellschaft für Straßen und
Verkehrswesen, 2007.
[18] BAST, “Einsatzkriterien für Schutzeinrichtungen mit geringerem Verletzungsrisiko für
Motorradfahrer. Bundesanstalt für Strassenwesen,” BAST, 2004.

232. ROADSIDE DESIGN GUIDE
PAGE 258
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
6 CRASH CUSHIONS
6.1 Overview
A crash cushion is a crashworthy safety device, which is designed to protect errant vehicles from the
high severity outcomes of impacting fixed objects. In a similar way to energy absorbing terminals,
this is achieved by gradually decelerating the impacting vehicle to a safe stop, before reaching the
fixed hazard. All crash cushions are designed to provide protection for head-on impacts; however,
some of them also provide further protection by redirecting a vehicle away from the fixed object when
impacted on the side.
Crash cushions are stand-alone objects and therefore, unlike terminals, are generally not connected
to the end of guardrails. Like other safety hardware, crash cushions primarily serve to lessen the
severity of an impact rather than prevent impacts from occurring in the first place.
Ideal places for crash cushion installations are locations where fixed objects within the clear zone
cannot be removed, relocated, or made passively safe. Gore areas (i.e. diverge areas) and medians,
are places where crash cushions are most commonly used. This is because these places often have
hazards such as sign supports or ends of rigid barriers, which may not always be made passively
safe or shielded with a crash-worth terminal. One such location is shown in Figure 10.1. In this gore
area the end of the rigid barrier poses a risk of head-on collision for errant vehicles, therefore a crash
cushion can be used to improve the safety of road users. Figure 10.2 shows an example of a crash
cushion application on another gore area. Note, that in this example the crash cushion provides
protection from the ends of the rigid barrier and the gantry located behind.
Figure 10.1 - Lack of crash cushion at gore area

233. ROADSIDE DESIGN GUIDE
PAGE 259
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.2 - Application of crash cushion at gore area
A crash cushion may be suitable for deployment in front of an isolated obstruction, which cannot be
removed, relocated or be protected by an adequate length of longitudinal safety barrier. In North
America particularly, crash cushions have widely been deployed for many years to protect drivers
from isolated structures and other potentially hazardous features, particularly at the approach to gore
areas. Such structures and hazardous features should also be equipped with a crash cushion in Abu
Dhabi, as shown in Figure 10.3.
Figure 10.3 - An example of a crash cushion used to shield a single object in Abu Dhabi
Only proprietary crash cushions (i.e. those which are promoted by manufacturers and their
representatives) should be used, as these will have been carefully designed and tested by their
associated manufacturers. More details on the differences between proprietary and non- proprietary
systems can be found in Section 6.4.
This Chapter briefly explains the design principles behind crash cushions and where their use may
be considered. Descriptions, design procedures, selection guidelines, and placement
recommendations for systems that have been successfully crash tested also are provided.

234. ROADSIDE DESIGN GUIDE
PAGE 260
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
6.2 Types of Crash Cushions
There are numerous different types of crash cushion systems available on the market today. These
systems can be classified into several categories based on their design principles. These include:
• Design Principle, i.e. Kinetic Energy vs. Conservation of Momentum;
• Gating vs. Non-Gating;
• Redirective vs. Non-Redirective;
• Sacrificial, Reusable or low maintenance/Self-Restoring.
A crash cushion may have more than one of these properties. For example, a crash cushion may be
categorised as non-gating, redirective, and reusable at the same time. Given the different mode of
operation of different crash cushion types, it is essential that the correct system is used in any
particular situation. In all cases, the manufacturer or promoter of the system should be consulted to
ensure that the crash cushion proposed is suitable for the application under which it is to be used.
10.2.1 Crash Cushion Types by Design Principles
The purpose of a crash cushion is to slow down an impacting vehicle into a controlled stop by
dissipating the impact energy. Crash cushions can be divided into two categories according to the
design principle through which they achieve the controlled deceleration of the impacting vehicle.
These categories are:
• The systems which are designed according to the work-energy principle; and
• The systems which are designed according to the conservation of momentum principle.
Both of these types are outlined in the following sections.
10.2.1.1 Crash Cushions based on Kinetic Energy Principle
The crash cushions which are based on kinetic energy principle utilise crushable or plastically
deformable components, to convert the kinetic energy of an impacting vehicle into other forms of
energy such as, mechanical, potential, heat and sound. As the impact progresses, some of the
kinetic energy of the vehicle is converted into mechanical energy through the deformation of the
vehicle and crash cushion components. Some of these components will convert the kinetic energy
into potential energy and deform back towards their pre-impact shapes towards the end of the
impact. This is similar to the working principle of a spring. Some of the kinetic energy is converted
into heat by the friction between the system components and the vehicle. And finally, some of the
kinetic energy is converted into sound, through the noise generated during the impact.
These types of systems are also referred to as ‘compression’ systems. The majority of the crash
cushions available on the market today are designed to the kinetic energy principles, such as the
example shown in Figure 10.4. This type of crash cushion is required to be fixed to a rigid surface or
support structure to provide the necessary resistance during a collision. This fixing is usually
achieved in the form of ground anchors or other connections to the object behind, such as the
connection to a road safety barrier, as shown in Figure 10.4. All systems have their own unique
designs and therefore products must be installed in accordance with the manufacturer’s
recommendations.

235. ROADSIDE DESIGN GUIDE
PAGE 261
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.4 – Example of a crash cushion based on the Kinetic Energy Principle
10.2.1.2 Crash Cushions based on Conservation of Momentum
Principle
The crash cushions which are based on the conservation of momentum principle (sometimes
referred to as the ‘inertial’ type) utilise materials of expendable mass, such as sand, into which the
kinetic impact energy of the vehicle can be transferred during the collision. The material of
expendable mass is often kept in containers such as drums or buckets, as shown in Figure 10.5. As
the impacting vehicle collides with each container, the expandable mass located inside the container
is shifted and dispersed around the crash by the transfer of momentum from the vehicle to the mass.
Usual practice is to provide an increasing amount of mass within each row of containers, and / or
increase the number of containers from the impact face of the system towards the back. The net
effect of this layout is a gradual increase in the amount of mass within the system and therefore a
gradual decrease of speed for the impacting vehicle.
Figure 10.5 – Example of a crash cushion based on the Conservation of Momentum
Principle [1]
Historically, this type of system was mainly used in the United States. However, over the years, with
the development of numerous crash cushions which are based on the kinetic energy principle, the
use of these systems has declined. This is mainly due to the following disadvantages of these types
of systems:
• They occupy considerably more space than other available crash cushions;
• They are sacrificial by design, i.e. they are usually not functional after an initial impact (see
Section 10.2.4);

236. ROADSIDE DESIGN GUIDE
PAGE 262
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
• The dispersion of sand upon impact can create a safety and maintenance problem;
• If not sealed properly, the amount of sand within each container can increase due to the
drifting sands and sand storms observed in Abu Dhabi. This can affect the impact behaviour
of the system.
However, these systems do have the following advantages:
• They do not require to be fixed to a rigid surface or support structure, as they are designed
to be free-standing;
• This is the only type of crash cushion the design of which can be determined analytically.
10.2.2 Gating vs. Non Gating Crash Cushions
In a similar way to terminals, crash cushions can also be classified as either being ‘gating’ or ‘non-
gating’, as shown in Figure 10.6.
Gating crash cushions are designed to allow vehicles impacting near the beginning or nose of the
system to safely pass through the unit and travel behind the cushion, as shown in Figure 10.6.
As crash cushions (unlike terminals) are often installed close to the hazards from which they are
protecting road users, gating crash cushions are not preferred. Vehicles that pass through a gating
treatment are directed into the area behind the end treatment. It is therefore necessary to ensure
that this run-out area should:
• Contain no fixed hazards (e.g. poles and trees);
• Be traversable, with a lateral slope of 4:1 or flatter:
• Extended parallel to the barrier/terminal at least for a distance of 18 m beyond the point of
need for the barrier/terminal;
• Be at least 6 m wide [2].
If a runout area cannot be provided or would be smaller than the required dimension, a non-gating
system should be used.
Non-gating crash cushions, when impacted on either end by a vehicle, will not allow the vehicle to
pass through or over it, but instead contain or redirect the vehicle along the travelled way. Depending
on their characteristics, non-gating crash cushions can further be categorised as redirective or non-
redirective (see Section 10.2.3).
10.2.3 Redirective vs. Non-Redirective Crash Cushions
Further to the classification of being gating or non-gating, a crash cushion can also be classified as
being either ‘redirective’ or ‘non-redirective’, as shown in Figure 10.7.
‘Redirective’ crash cushions have been designed so that when impacted by a vehicle on the side
they will redirect the vehicle along the travelled way (in the direction that it was originally travelling).
The classification of a crash cushion as redirective or non-redirective is based on the performance
of the system during side impacts. On the other hand, the classification of gating or non-gating is
based on the performance during impacts with near the beginning or nose of the system.

237. ROADSIDE DESIGN GUIDE
PAGE 263
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Therefore, it is possible for a redirective system to be either gating or non-gating. Such systems are
preferred in all locations as they also offer positive performance for side impacts.
Figure 10.6 - Gating and non-gating crash cushions
‘Non-Redirective’ crash cushions are designed so that when impacted by a vehicle on their side,
they will either allow the vehicle to pass through or contain the vehicle within the system, as shown
in Figure 10.7. These systems are designed to safely accommodate most impacts with the front of
the crash cushion, but they do not have the capability to redirect vehicles impacting near the rear.
As a result, most non-redirective cushions are designed to be wider than the hazard to be shielded
and are typically used farther from traffic where the risk of high-energy impacts near the rear of the
cushion is lower [3]. The non-redirective systems are predominantly the ones which are designed
according to the conservation of momentum principle, i.e. the barrel and sand systems, and therefore
they are predominantly gating systems. This is also recognised by NCHRP-350 and MASH, which
do not describe any impact tests which are applicable to non-redirective non-gating systems (see
Section 10.3.1).
Traffic Flow
Traffic Flow
Traffic Flow
Traffic Flow

238. ROADSIDE DESIGN GUIDE
PAGE 264
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.7 - Redirective and non-redirective crash cushions
10.2.4 Sacrificial, Reusable or Low Maintenance / Self-Restoring
Crash Cushions
Crash cushions can also be grouped into three categories according to the amount of repair required
to return the system back into a crashworthy state after an impact. These are:
• Sacrificial crash cushions;
• Reusable crash cushions; and
• Low maintenance / self-restoring crash cushions.
A ‘sacrificial crash cushion’ is a crash cushion designed for a single impact before requiring
significant repair and replacement of components. In general, a sacrificial crash cushion will require
the replacement of the system following an impact. Most examples of this type of system absorb
impact energy by crushing steel rail elements. Other devices contain energy absorbing

239. ROADSIDE DESIGN GUIDE
PAGE 265
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
elements which are designed to permanently deform on impact, gradually decelerating the impacting
vehicle and bringing any impacting vehicle to a controlled stop.
This may include components such as plastic cartridges containing foam, sand or water, as indicated
in Figure 10.8. Major components of sacrificial crash cushions are destroyed by impacts, but it should
be noted that other parts may still be reusable.
Figure 10.8 - Examples of energy absorbing cartridges in crash cushions [1], [4]
A ‘reusable crash cushion’ is a crash cushion system for which some of the major components have
been designed to be reusable after an impact. However, some of the components will need to be
replaced after an impact to ensure that the crash cushion is maintained to produce the original level
of performance in a subsequent impact. In locations where designers expect to have frequent
impacts these devices are likely to have a great cost/benefit ratio, and are therefore more
appropriate.
The category of ‘Low Maintenance / Self-restoring Crash Cushions’ contains those crash cushion
systems that suffer very little, if any, damage upon impact and which are designed to be easily pulled
back into their full operating condition, an example of which is given in Figure 10.9. Alternatively,
they can partially rebound after an impact and may only need an inspection to ensure that no parts
have been damaged or misaligned. As with any crash cushion system, inspections should be
undertaken in line with the manufacturer’s requirements, as detailed within their Installation,
Inspection and Maintenance manual.
Figure 10.9 - Example of a self-restoring crash cushion

240. ROADSIDE DESIGN GUIDE
PAGE 266
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
There are relatively high levels of cost associated with the initial purchase and installation of such
crash cushion systems. But there are subsequent low levels of repair and maintenance. This means
that these types of crash cushions should be installed in high-speed, high-traffic volume ramps or
medians (where there is an anticipated high frequency of high severity incidents) to reduce the risk
to road users and the exposure of maintenance workers to the traffic (during repairs).
For all crash cushion systems it is essential that all of the components and fixings for the crash
cushion are checked for damage following an impact, and if necessary appropriate repairs are made
to ensure that the crash cushion is restored to full working order.
Requirements for the inspection and repair of crash cushions should be provided by the
manufacturer of the proprietary system within their Installation, Inspection and Maintenance manual.
Where there are any questions or doubts regarding damage to a component, this should be checked
with the manufacturer of the system. If in any further doubt, the component should be replaced. All
replacement parts should be provided by the manufacturer (or their representatives).
6.3 NCHRP350 and MASH Performance Classifications
All crash cushions shall have demonstrated compliance with the American recommendations in
either NCHRP Report 350 [5] or MASH [3] and additional local conditions for the Abu Dhabi Road
Network. Evidence of this shall be presented and approved by the Overseeing Organization prior to
the use of these systems. Only systems approved by the Overseeing Organization shall be used.
After January 1, 2011, newly-tested crash cushions must be evaluated in accordance with MASH.
However, crash cushions that were accepted before the adoption of MASH by using criteria
contained in NCHRP Report 350 may remain in place and may continue to be manufactured and
installed.
In order to meet the requirements of NCHRP350, or MASH, the crash cushion must demonstrate
that it can successfully decelerate (and for redirective, non-gating crash cushions, redirect) the
impacting vehicle without the unsafe detachment of components. During the impact testing event,
the impacting vehicle should maintain an upright orientation, whilst meeting the requirements of two
severity indices; OIV and ORA. More details regarding these severity indices can be found in Chapter
6, Section 6.3.3.4.
10.3.1 Test Types
NCHRP Report 350 and MASH contain recommended procedures for evaluating the performance
and test procedures for crash cushions. The testing of a crash cushion requires the successful
completion of a series of full-scale impact tests. Table 10.1 and Table 10.2 show the parameters for
the most commonly available impact test level (TL-3). Each test configuration is described in terms
of the type and mass of the impacting vehicle, impact point, speed and angle of impact.
As can be seen from Table 10.1, according to NCHP350 for re-directive crash cushions, some test
types are only recommended for gating systems, some are only recommended for non-gating
systems and some are recommended for both. According to MASH however, all the test
configurations for redirective crash cushions listed in Table 10.2 are recommended for both gating
and non-gating systems; with the only difference being the evaluation criteria of the test outcome.
The non-gating systems are expected to contain or redirect the vehicle or bring the vehicle to a
controlled stop, whereas the performance of gating systems are considered acceptable in case of

241. ROADSIDE DESIGN GUIDE
PAGE 267
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
redirection, controlled penetration or controlled stopping of the test vehicle. For non-redirective crash
cushions however, both NCHRP350 and MASH specify tests which are only applicable for gating
systems. There are no tests described for non-redirective and non-gating systems. This is because
a system is unlikely to be both non-redirective and non-gating at the same time.
Table 10.1 - Test requirements for TL-3, NCHRP350 [5]
Test
Level
Feature Type
Impact Conditions
Impact Point
Vehicle
Impact
Speed
(km/h)
Impact
Angle
(°)
TL-3
Redirective
Crash
Cushions
G/NG 820kg Car 100 0 Head-on at ¼ vehicle width
G/NG 700kg Car 100 0 Head-on at ¼ vehicle width
G/NG 2000kg Pickup
Truck
100 0 Head on, centre
G/NG 820kg Car 100 15 on nose of cushion
G/NG 700kg Car 100 15 on nose of cushion
G/NG 2000kg Pickup
Truck
100 15 on nose of cushion
G 820kg Car 100 15 at the critical impact point
G 700kg Car 100 15 at the critical impact point
G 2000kg Pickup
Truck
100 20 at the critical impact point
NG 820kg Car 100 15 at the critical impact point
NG 700kg Car 100 15 at the critical impact point
NG 2000kg Pickup
Truck
100 20 at the critical impact point
NG 2000kg Pickup
Truck
100 20 at the critical impact point
G/NG 2000kg Pickup
Truck
100 20 at ½ cushion length
Non-Redirective
Crash
Cushions
G 820kg Car 100 0 at ¼ vehicle width
G 700kg Car 100 0 at ¼ vehicle width
G 2000P 100 0 Head on, centre
G 820kg Car 100 15 on nose of cushion
G 700kg Car 100 15 on nose of cushion
G 2000kg Pickup
Truck
100 15 on nose of cushion
G 2000kg Pickup
Truck
100 20 at ½ cushion length
Notes:
G/NG – Applicable for gating and non-gating crash cushions

242. ROADSIDE DESIGN GUIDE
PAGE 268
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
G – Applicable for gating crash cushions only
NG – Applicable for non-gating crash cushions only

243. ROADSIDE DESIGN GUIDE
PAGE 269
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Table 10.2 - Test requirements for TL-3, MASH [3]
Test
Level
Feature Type
Impact Conditions
Impact Point
Vehicle
Impact
Speed
(km/h)
Impact
Angle
(°)
TL-3
Redirective
Crash
Cushions
G/NG 1100kg Car 100 0 Head-on at ¼ vehicle width
G/NG 2270kg Pickup
Truck
100 0 Head on, centre
G/NG 1100kg Car 100 5/15 on the nose of the cushion
G/NG 2270kg Pickup
Truck
100 5/15 on the nose of the cushion
G/NG 1100kg Car 100 15 at the critical impact point
G/NG 2270kg Pickup
Truck
100 25 at the critical impact point
G/NG 2270kg Pickup
Truck
100 25 at the critical impact point
G/NG 2270kg Pickup
Truck
100 25 at the critical impact point
G/NG 1500kg Car 100 0 Head on, centre
Non-Redirective
Crash
Cushions
G 1100 kg Car 100 0 Head-on at ¼ vehicle width
G 2270kg Pickup
Truck
100 0 Head on, centre
G 1100 kg Car 100 5/15 on nose of cushion
G 2270 kg Pickup
Truck
100 5/15 on nose of cushion
G 2270 kg Pickup
Truck
100 20 at critical impact point
G 1500kg Car 100 0 Head on, centre
Notes:
G/NG – Applicable for gating and non-gating crash cushions
G – Applicable for gating crash cushions only
NG – Applicable for non-gating crash cushions only
Table 10.1 and Table 10.2 also present the impact point for each test configuration. It can be seen
that some of the tests are carried out at the critical impact point. For crash cushions, the critical
impact point is described as the point where the behaviour of the system changes from redirecting
the impacting vehicle to either capturing the vehicle (for non-gating systems) or allowing it to gate
through the system (for gating systems) [3]. The critical impact point is often first estimated through
computer simulations and then identified through a series of full scale crash tests described in
NCHRP350 and MASH.
All test levels include the testing of cars and light duty commercial vehicles up to the size of a pickup
truck. The pickup truck is similar to many of the four-wheel-drive vehicles currently using the road
network within Abu Dhabi and hence the reliance on the NCHRP350 and MASH test methods. These
test methods do not include tests involving larger vehicles such as single unit trucks and semitrailers.

244. ROADSIDE DESIGN GUIDE
PAGE 270
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
L2
L1
10.3.2 Containment Level
TL-1 provides test requirements for vehicle impact speeds of 50km/h, TL-2 provides for vehicle
impact speeds of 70km/h and TL-3 (which is the basic level) provides for vehicle impact speeds of
100km/h (refer to Tables Table 10.1 to Table 10.2). Guidance on which TL is appropriate for which
location is provided in Figure 10.11.
10.3.3 Deflection Characteristics
Adequate clearance of the crash cushion to any fixed object or an area used by motorists or NMUs,
that is, behind the installation, shall be provided. This is not only the footprint of the crash cushion
system being used, but also the distance into which the crash cushion is likely to deflect in the event
of an impact by an errant vehicle. As shown in Figure 10.10, the deflection distance of a crash
cushion will typically be wider, but shorter than that of the crash cushion footprint, and therefore the
overall deflection zone required for the crash cushion will be a combination of both zones (with the
length of the undeformed system L1, and the width of the deformed system W2). The minimum area
required to accommodate both the footprint of the system and the required deflection area will vary
from system to system, and will be included within the manufacturer’s Installation manual. Due to
the space requirements for a particular system, this requirement may preclude the use of certain
crash cushions.
Crash Cushion
footprint W1
Crash Cushion
deflection zone W2
Minimum Required
Space for Crash W2
Cushion
L1
Figure 10.10 - The minimum required space for a crash cushion
10.3.4 Impact Severity Level
Following the impact testing of a crash cushion (independent of its type and performance
characteristics), the impact severity level of the system will be reported in terms of the OIV and ORA.
More details on OIV and ORA are given in Chapter 6, Section 6.3.3.4. For all crash cushions, the
impact severity level shall be as low as practicable to reduce the risk of injury to the occupants of
errant vehicles. For systems tested to NCHRP Report 350 or MASH, lower values for OIV and ORA
should be sought (refer to Chapter 6, Section 6.3.3.4).
W2 > W1
L1 > L2

245. ROADSIDE DESIGN GUIDE
PAGE 271
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
6.4 Selection Criteria
The most appropriate crash cushion should be selected by considering:
• The speed limit of the road (see Section 10.4.1);
• The gating characteristic of the crash cushion (see Section 10.2.2 & 10.4.2);
• The space available for installation of the crash cushion (see Section 10.4.3);
• The cost considerations of the project, including but not limited to:
o Maintenance and inspection requirements (see Section 10.4.4.1);
o The selection of Reusable, Sacrificial or Self Restoring Crash Cushions (See
Section 10.4.4.2);
o The capacity of the system to absorb nuisance hits (see Section 10.4.4.3).
There may be locations where the application of a crash cushion may not be appropriate. Risk
reduction may be better provided by the installation of an approved guardrail equipped at its
approach end with an impact tested terminal (refer to Chapter 9). Section 10.6 provides further
guidance about the decision between using a crash cushion or a terminal.
Once the classification of a crash cushion has been determined in accordance with guidance
provided in this section, available products meeting the specification should be identified from the
Abu Dhabi Department for Transport’s list of approved proprietary products.
With regards to the crash cushion selected, the manufacturer should declare (within their Installation
and Maintenance requirements), the space required for the installation of the crash cushion, together
with the additional space required for the displacement of the crash cushion in the event of an impact.
It is essential that this information is acquired from the manufacturer prior to a final decision being
made about which crash cushion to install at a particular location.
10.4.1 Speed Class
When selecting a particular terminal system, it is important to consider the conditions under which
the system has been tested; one of the most important factors being the speed class under which it
has demonstrated compliance. Guidance on which Test Level is appropriate for which location is
provided in Figure 10.11.
In those cases where the speed limit of the road exceeds 100km/h (the testing speed for TL-3
products), the manufacturer/promoter of the system should be contacted to ascertain whether any
additional testing has been undertaken at higher speeds and/or whether there is any in-service
experience with vehicles impacting at greater speeds. Where such evidence is presented, with
positive results, this should be taken into account when specifying product and such products
preferred.

246. ROADSIDE DESIGN GUIDE
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
60 or
70km/h
More
than
70km/h
Is adequate runout distance
available behind the crash
cushion?
adequate runout distance
available behind the crash
cushion?
Speed Limit of Road Is adequate runout distance
available behind the crash
cushion?
50km/h
or less
Yes
No
Yes
No
Yes
No
Figure 10.11 - Crash cushion minimum performance decision tree
PAGE 271
MINIMUM PERFORMANCE
TL-3, non-gating only
Any TL-3
TL-2, non-gating only
Any TL-2
TL-1, non-gating only
Any TL-1

247. ROADSIDE DESIGN GUIDE
PAGE 272
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
10.4.2 Selection of Gating and Non Gating Crash Cushions
The selection of gating and non-gating crash cushions should be based on the requirements detailed
within Figure 10.13, with reference to Figure 10.6. It should be noted that the runout distance for
each crash cushion will vary by product and as such, the manufacturer should be consulted and this
information requested if it is not presented within the product documentation (for example within the
product installation manual). If this is not available, the recommended runout distance for a gating
crash cushion is 18x6m for 100km/h sites. In general terms, if the runout distance behind the crash
cushion is not adequate, a non-gating crash cushion must be used.
10.4.3 Space Available for Installation
When selecting a crash cushion for a particular application, one of the main factors to consider is
the physical size of the crash cushion. This is not just the footprint which the crash cushion occupies,
but also the space into which the crash cushion is likely to deflect in the event of an impact by an
errant vehicle (also refer to Section 10.3.3 and Figure 10.10). Both of these dimensions should be
available from the manufacturer, and it must be ensured that there is sufficient space available on
site.
Adequate clearance of the crash cushion to any fixed object or an area used by motorists or NMUs
(that is, behind the installation) shall be maintained and not compromised. In some situations, this
may preclude the use of certain crash cushions. The crash cushion installed should be wider than
the hazard it protects such that it fully shields the hazard. In the extreme case this may mean that
the width of the crash cushion is wider than the hazard that it is located in front of, as shown in Figure
10.12. Whilst such an arrangement is not preferred, it must be ensured that the alignment of the side
of the crash cushion reflects that of any barrier at the rear of the crash cushion when travelling in the
direction of the main line traffic. Whilst in the example in Figure 10.12 protection is given from the
end of the concrete barrier, it would have been preferable to reduce the width of the crash cushion
such that the alignment of the right hand side of the cushion was such that it aligned with the barrier
at its rear.
Figure 10.12 - Selection of crash cushion width to protect road users from hazards
Edge of rear of crash
cushion
Edge of hazard at
rear of crash cushion

248. ROADSIDE DESIGN GUIDE
PAGE 273
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
In all cases, the result of the full-scale impact testing (to NCHRP350 and/or MASH) will indicate any
anticipated movement of the rear of the crash cushion, and any movement of components of the
crash cushion behind the rear back plate of the crash cushion. Both of these should be considered
when locating the crash cushion. In many cases, manufacturers will provide guidance on the
‘protected zone’ offered by the crash cushion, i.e. the area into which hazards should be located.
10.4.4 Cost Considerations
Cost considerations should not just include the initial cost of purchasing the crash cushion, but should
also include the costs associated with installation, maintenance, and repair or replacement costs.
This can vary significantly depending on the structural characteristics of the crash cushion. It should
also be noted that site preparation costs can be significant when accommodating certain systems.
At locations where frequent impacts with the crash cushion are expected, life-cycle costs for repairing
or replacing a crash cushion system also may become a significant factor in the selection process.
The following sections give further details about the crash cushion properties which would affect their
life-time costs and therefore affect their selection for a given application.
10.4.4.1 Maintenance and Inspection Requirements
The maintenance considerations for crash cushions will include routine maintenance, maintenance
after an impact and the need to stock and maintain spare parts for the system. Due to the need to
repair crash cushions quickly after they have suffered damage caused by an impact (due to their
location in front of rigid non-deformable hazards) there is an associated need to have a ready supply
of spare parts for the systems, and local, trained maintenance operatives to carry out the works. This
will be checked during the approval of proprietary systems onto the Abu Dhabi List of Approved
Products, but the designer should check with the supplier that this is still the case during the
procurement procedures. The maintenance characteristics of each crash cushion will, in many
cases, play an important role in the selection process.
Many of the more commonly available proprietary crash cushion systems require little regular or
routine maintenance. However, it is important that periodic maintenance checks are performed in
line with the manufacturer’s recommendations so that each installed unit remains fully functional. It
is possible that damage can occur to the crash cushion as the result of a minor impact which could
have a significant effect on the dynamic performance of the crash cushion in the event of a second
impact. In addition, if a crash cushion is located in an area that is accessible to pedestrians,
vandalism may be a problem, and therefore checks should be made to ensure that the crash cushion
is undamaged. Again, full details of the frequency and the requirements of each inspection can be
found within the manufacturer’s Installation and Maintenance Manual.
The frequency and extent of impact maintenance at each crash cushion location should be
maintained as they dictate the most effort and expenditure during the life of an installation. If a
particular site has a relatively high frequency of crashes, using a crash cushion that has some degree
of reusability or self-restoration is recommended, whilst the reasoning behind the number of impacts
should be established to identify whether there are any other road safety measures which could be
implemented to reduce the number of impacts (for example, changes to road alignment, improved
signage, the use of road surfaces with greater friction properties). Similarly, if nuisance strikes on
the crash cushion are relatively common, a crash cushion with redirection

249. ROADSIDE DESIGN GUIDE
PAGE 274
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
capability should reduce or eliminate the maintenance effort for minor repairs or partial replacement
of a system.
10.4.4.2 Selection of Reusable, Sacrificial or Self-restoring Crash
Cushions
The expected crash frequency is an important factor to consider when selecting the type of crash
cushion to be installed at a site. A higher frequency of impacts will increase the life-time costs, as
each impact will generate a new repair cost. The repair cost will change dramatically for sacrificial,
reusable and self-restoring systems. Therefore, the frequency of accidents becomes an important
factor when selecting between these systems. The Annual Daily Traffic (ADT) has been shown to
be a good indicator for expected impact frequency. The higher the ADT, the more impacts with the
crash cushion is expected. The proximity of the crash cushion to the edge of the travelled way will
also affect the number of impacts, as more impacts are expected for installations located closer to
the traffic. Furthermore, the location of the crash cushion will affect the costs associated with lane
closures for repairs. Systems which are close to the road can necessitate lane closures, whereas
this may be avoided for locations where the crash cushion is further away from the edge of the
travelled way. Figure 10.13 provides a decision tree for the crash cushion type selection, based on
these considerations.
Due to the low initial cost, but greater level of repair required (in the event of an impact), sacrificial
crash cushions should only be used in areas where the risk of impact is low. It should be noted
however, that whilst many of the components of a sacrificial crash cushion will be permanently
deformed in an impact (and will require replacement), due to the testing requirements of NCHRP350
and MASH, such systems will afford the same level of risk reduction as equivalent reusable crash
cushions.
Sacrificial crash cushions are generally recommended for areas with an ADT of less than 25,000,
with a low history or expectation of impacts occurring during the lifetime of the crash cushion and in
locations which are greater than 3m from the travelled way and/or outside of the clear zone (refer to
Figure 10.13) [6].
Reusable crash cushions are generally recommended for areas with an ADT of less than 25,000,
which have a history or expectation of one or fewer impacts each year and which are greater than
3m from the travelled way. They are also suited for locations where there is an unlimited repair time
(Refer to Figure 10.13) [6].
Self-restoring crash cushions are generally recommended for areas with an ADT of 25,000 or more,
with a history or expectation of multiple impacts each year and locations within 3m of the travelled
way. They are also suited to sites requiring night repairs and/or with repair time limitations [6].
10.4.4.3 Capacity to Absorb Nuisance Hits
Crash cushions, similar to terminals, are susceptible to nuisance crashes, i.e. small, low speed
impacts. It is preferable if the crash cushion can withstand a number of nuisance crashes and
continue to perform satisfactorily before requiring any repair. Crash cushions which can withstand
nuisance crashes better are likely to lead to less repair costs, and this helps their cost- effectiveness
through the lifetime of the installation.

250. ROADSIDE DESIGN GUIDE
PAGE 275
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.13 - Crash cushion type decision tree [6]
Less than
25,000
Low
History or
expectation of
impacts
Location greater than 3m
away from the travelled way
and/or outside clear zoneIs
Yes
Yes
Low Maintenance and/or Self
Restoring Crash Cushion
More than
or equal to
25,000
Low Maintenance and/or Self
Restoring Crash Cushion
Location greater than 3m
away from the travelled way
and/or outside clear zone
Reusable Crash Cushion
One or fewer
each year
Low Maintenance and/or Self
Restoring Crash Cushion
Average Daily Traffic
Sacrificial Crash Cushion
TYPE of CRASH CUSHION

251. ROADSIDE DESIGN GUIDE
PAGE 276
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
6.5 Application Criteria
10.5.1 Evaluation of Site Characteristics
Due to the nature of crash cushions and the way in which they are designed to function, it is essential
to consider their dynamic performance when locating them, ensuring that adequate space for the
crash cushion to shield non-removable fixed objects is considered. This is not just the footprint of
the crash cushion, but also the space required for the cushion to deform and deflect into when
impacted, and consideration on the likely vehicle trajectory following an impact.
It should be noted that the footprint and space required for the designed performance operation of
the crash cushion should be obtained from the manufacturer prior to the selection of a crash cushion
type. This is likely to be contained within the manufacturer’s Installation and Maintenance manual.
When addressing the need for a crash cushion for a particular location, the following are examples
of areas where a crash cushion should be considered:
• Concrete barrier end;
• Guardrail end;
• Bridge pier;
• Bridge rail;
• Toll booth;
• Exposed work area – workers of equipment.
To ascertain the space available for the locating of the crash cushion at such sites (refer to Figure
10.10), , the width and height of the hazard should be calculated.
Several additional factors should be considered in the placement of a crash cushion, and these are
as follows:
10.5.1.1 Site Grading for Crash Cushions
All crash cushions shall have been designed and tested to NCHRP350 and/or MASH, and therefore
their performance has only been demonstrated on level site conditions. As such, their performance
on an excessively sloped non-level site is unknown and could produce undesirable vehicular
behaviour. Therefore, when installed on site, crash cushions should be placed on a base or
pavement slightly sloped to facilitate drainage; however, the cross slope should not exceed the value
determined by the manufacturer and specified within their Installation and Maintenance manual (as
highlighted in Figure 10.14).
10.5.1.2 Curbs
Again, due to the testing requirements of NCHRP350 and/or MASH, the performance of a crash
cushion has only been demonstrated on level site conditions, and therefore, their performance on a
raised surface (with a curb for example) is unknown and could produce undesirable vehicular
behaviour. Therefore, for new constructions, crash cushions should not be built on raised surfaces
with curbs, unless this has been specified by the manufacturer.

252. ROADSIDE DESIGN GUIDE
PAGE 277
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.14 - Cross slope should not exceed 5% in front of a crash cushion
Existing crash cushion locations should be reviewed to determine if the presence of a curb is likely
to affect the performance of the unit, and if so, appropriate modifications should be made when
roadway rehabilitation occurs. In such cases, the views of the manufacturer should be sought to
ascertain the effect which the curb may have on the dynamic performance of the crash cushion.
10.5.1.3 Surface
Many crash cushion systems require anchoring into a paved, bituminous, or concrete pad. This
requirement, together with the fixings of the crash cushion to the surface, will be determined and
specified by the manufacturer within their Installation and Maintenance manual, based on the results
of impact testing.
10.5.1.4 Location
The crash cushion must not infringe on the travelled way. There should be a minimum of 600mm
behind crash cushion systems, as shown in Figure 10.15, and in front of the hazard to allow access
to the system – this distance may be extended by the manufacturer’s specification.

253. ROADSIDE DESIGN GUIDE
PAGE 278
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.15 - Distance between rear of crash cushion and hazard
In all cases, the crash cushion should be located as far away as possible from the hazard located in
front, to ensure that in the event of a head-on impact with the crash cushion, the deformed crash
cushion does not enter into the space occupied by the hazard. Additionally, the crash cushion should
not be located so far in front of the hazard that a snagging point is generated between the rear of
the crash cushion and the front face of the hazard. Both, sound engineering judgement and risk
analysis techniques should be applied to ensure that the placement is safe.
Guidance on locating the crash cushion in relation to the hazard will be available from the
manufacturer of the crash cushion, and should be adhered to in all cases.
In all cases, the possible impact scenarios for the site requiring a crash cushion should be
understood, together with an understanding as to whether an impact is likely from only one side (for
example if installed in the roadside), or both sides (for example if installed in the median, or within a
gore area). Most crash cushions are designed for impacts on either side, but prior to the selection of
a particular system, it must be checked whether the crash cushion design will be suitable for the
application.
10.5.1.5 Bridge joints
The use of all crash cushions over bridge expansion joints or deflection joints should be avoided
because movement in these joints could create destructive strains on the crash cushion. This may
be avoided by choosing a different length of crash cushion (whilst maintaining the required ‘Test
Level’), or by re-examining the layout of the site, and choosing other options (for example guardrails
and a full height terminal).
10.5.1.6 Delineation of Crash Cushions
The designer must ensure that all crash cushion delineation is provided to ensure the crash cushion
is clearly visible to approaching traffic. Examples of ways in which a crash cushion can be delineated
are shown in Figure 10.16; note, that this can include the use of plastic delineation bollards.
Min 600mm

254. ROADSIDE DESIGN GUIDE
PAGE 279
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.16 - Examples of crash cushion delineation
10.5.2 The use of Crash Cushions in Gore Areas
As can be seen from many of the figures within this Chapter, one of the main applications for crash
cushions in the Emirate of Abu Dhabi is to protect road users from the hazard presented by the end
of safety barriers at nosings and gore areas. It is recommended that the required space for crash
cushion installation for these locations should be considered from the preliminary design stage. This
should be done to prevent any compatibility issues between the selected crash cushion and the final
design, caused by the lack of required space.
Figure 10.17 and
Table 10.3 give recommendations for the area which should be made available for crash cushion
installation. Although it depicts a gore area, the same approach could be applied to other types of
objects from which road users will need to be shielded. Note that the dimensions shown in
Table 10.3 are not definitive and are provided for guidance only. The manufacturer should always
be consulted to ascertain whether there are any specifications specific to their product, prior to the
finalisation of the scheme design.
Figure 10.17 - Guidelines for the provision of crash cushions at gore areas [6]

255. ROADSIDE DESIGN GUIDE
PAGE 280
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Table 10.3 - Dimensions for the provision of crash cushions in gore areas [6]
Design
Speed
on
Main
Line
(km/h)
Dimensions for Crash Cushion, Reserve Area (in metres)
Preferred
Minimum
Unrestricted Conditions Restricted Conditions
N L F N L F N L F
50 3.5 5 1.5 2.5 3.5 1 2 2.5 0.5
80 3.5 10 1.5 2.5 7.5 1 2 5 0.5
110 3.5 17 1.5 2.5 13.5 1 2 8.5 0.5
130 3.5 21 1.5 2.5 17 1 2 11 0.5
N = for preliminary design purposes, an assumed width of space necessary for placement of crash cushions
L = for preliminary design purposes, an assumed length of space necessary for placement of crash cushions
F = for preliminary design purposes, an assumed maximum width of a fixed object that will need to be shielded with a
crash cushion
As can be seen from
Table 10.3, the dimensions are given for three different scenarios. These scenarios are:
• Preferred: These are the preferred dimensions to be provided, if other concerns such as
cost, available space, etc. are not an issue. This is the optimal solution;
• Minimum for Unrestricted Conditions: These are the minimum recommended
dimensions to be provided, if the concern of cost is not an issue;
• Minimum for Restricted Conditions: These are the minimum recommended dimensions
to be provided, if the cost of providing more space cannot be justified.
6.6 The Decision to use Crash Cushions or Energy Absorbing
Terminals
This Chapter has discussed the use of crash cushions and given examples of where their use will
be to the benefit of road safety. Chapter 9 has also considered the provision of energy absorbing
terminals. In any respect, both types of device are very similar in both their function, their mode of
operation, and the resulting levels of safety afforded to road users. There will be times, when the
designer/engineer will need to choose between a crash cushion or a terminal (or two terminals). This
decision will often have to be made based on the size and location of the hazard, the space available
for installation and the cost associated with each system.
Terminals will generally be the system of choice for locations where the traffic is found only on one
side of the device, such as the roadsides. Generally, for one sided installations, terminals will be
cheaper than crash cushions and the required space for installation will be less, although this would
ultimately depend on the individual systems.

256. ROADSIDE DESIGN GUIDE
PAGE 281
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
For locations where the traffic is found on both sides of the device, such as medians and gore areas,
the decision between a terminal and a crash cushion will be determined on factors such as the width
of the hazard, available space and cost. As explained in Chapter 9, Section 9.2.5, there are double
sided terminals available on the market. However, these systems are relatively narrower than the
crash cushions, and therefore the main limiting factor for these systems is likely to be the maximum
allowable distance between the barriers located on each side of the median or gore area. This is
demonstrated through two example locations shown in Figure 10.18.
The location shown on the top image has a double sided terminal installed on a gore area, whereas
the location shown on the bottom image has a crash cushion installed on another gore area. It can
be seen for the double sided terminal installation that the barriers located on each side are positioned
much closer to each other, compared to the situation behind the crash cushion installation. It can
also be observed that the crash cushion does not only provide protection from the ends of the semi-
rigid barriers, but it also provides protection from the traffic sign located behind. To be able to
accommodate the traffic sign, the barriers located on each side need to be a certain distance away
from each other.
This distance required to accommodate the traffic sign is likely to be wider than the maximum design
width of a double sided terminal. Therefore, a crash cushion is the natural choice for the location. To
be able to use a double sided terminal on this location, the barriers located on each side would need
to be elongated further upstream of the gore area, until they are positioned close enough to
accommodate the terminal. Such an application increases the length of the installation. The required
space to accommodate the extra length of installation may not be available, which in turn eliminates
the double sided terminal as a viable option. When a crash cushion is to be connected to roadside
barriers, as shown in Figure 10.18, appropriate transition sections should be provided between the
crash cushion and the two barrier ends.

257. ROADSIDE DESIGN GUIDE
PAGE 282
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.18 - The use of terminals and crash cushions at nosings
In locations where the width of the hazard, or the distance between barriers is enough to
accommodate either a double sided terminal or a crash cushion, the decision should be made based
on the criteria explained in Section 10.4, and also in Chapter 9, Section 9.4,. These include factors
such as, compatibility with the barrier system to be connected, cost, maintenance requirements,
capacity to absorb nuisance hits, gating or non-gating character of the system, the space required
for installation and the space available on site.
For the special case of concrete barrier ends located on gore areas and medians, such as the ones
previously shown in Figure 10.1 and Figure 10.2, crash cushions are likely to be the system of choice.
To be able to use double sided terminals on these locations, a section of steel barrier would need to
be elongated from each side of the gore area until they meet in the middle, and the ends of these
steel barrier sections would need to be connected to the concrete barrier through appropriate
terminals. Such an application would often require a considerable amount of space and added cost,
which would make the crash cushion a better choice in general.
In other cases, for example, where there is a requirement for the end treatment to provide an
anchoring function for the connected guardrail system, only a terminal could be used as generally,
crash cushions are not designed to perform such a function.
6.7 Example applications
Figure 10.19 gives examples of locations where crash cushions should have been installed (but have
not), whilst Figure 10.20 demonstrates good applications of crash cushions used in Abu Dhabi.
These give an indication of both poor and appropriate applications, with regards to crash cushion
provision.

258. ROADSIDE DESIGN GUIDE
PAGE 283
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
Figure 10.19 - Examples of areas which should be equipped with a crash cushion
Figure 10.20 - Examples of appropriate median crash cushion applications
6.8 Summary and Conclusions
Crash cushions should be used at locations where fixed objects cannot be removed, relocated, or
made passively safe, or be protected by an adequate length of longitudinal safety barrier, for example
in gore areas and nosings.
All crash cushions used should be successfully tested to NCHRP350, MASH and/or EN1317-3, and
approved by the Overseeing Organisation. In all cases, the TL rating of the terminals should be
applicable for the speed limit of the road on which it is being used. In addition, the choice of crash
cushion type should be based on the ADT and incident history of the site. Crash cushions should be
located, installed, inspected and maintained in accordance with the manufacturer’s instructions.
Crash cushions should be located sufficiently far in front of a hazard to ensure that in the event of a
head-on impact with the crash cushion, the deformed crash cushion does not infringe on the space
occupied by the hazard. However, the crash cushion should not be located so far in front of the
hazard that a snagging point is generated between the rear of the crash cushion and the front face
of the hazard. Typically, a distance of 0.6m between the back of the crash cushion and the
✓ ✓
✓

259. ROADSIDE DESIGN GUIDE
PAGE 284
10 CRASH CUSHIONS FIRST EDITION -DECEMBER 2016
front face of the hazards will meet both of these criteria; however, the distance required will vary
from product to product. Hence, the manufacturer’s installation manual should be consulted for
details relating to the specific requirements for the crash cushion being installed.
Adequate clearance of the crash cushion from any fixed object or an area used by motorists or NMUs
(that is, behind the installation) shall be maintained and not compromised. This should take into
account the area required for the footprint of the crash cushion, and the area into which the crash
cushion will deflect in the event of an impact. In some situations, this may preclude the use of certain
crash cushions.
6.9 References
[1] Roads & Transport Authority, Roadside Design Guide for Dubai, First Edition, Dubai: RTA,
2008.
[2] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney, NSW:
Austroads, 2010.
[3] AASHTO, Manual for Assesing Safety Hardware (MASH), Washington D.C.: American
Association of State Highway and Transportation Officials, 2009.
[4] Laura Metaal Road Safety, “TAU Permanent redirective crash cushion,” [Online]. Available:
http://laurametaal.nl/en/content/guard-rail-double-sided/guard-rail-double-sided/guard-rail-
double-sided/guard-rail-double-6. [Accessed 10 09 2015].
[5] NCHRP, “NCHRP Report 350, Recommended Procedures for the Safety Performance
Evaluation of Highway Features,” Transportation Research Board, National Research Council,
Washington DC, 1993.
[6] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of State
Highway and Transportation Officials, 2011.

260. ROADSIDE DESIGN GUIDE
PAGE 285
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
7 TRANSITIONS
7.1 Overview
A transition is a section of barrier between two different barriers or, more commonly, where a
roadside barrier is connected to a bridge railing or to a rigid object such as a bridge pier or parapet.
The aim of a transition is to provide a gradual change in stiffness from one system to another so
vehicular pocketing, snagging, or penetration at the connection can be avoided.
A transition is required for any location where one type of vehicle restraint system is required to be
connected to another, such as at approaches to bridge locations and between a rigid and semi rigid
barrier system. This is typically between two barrier systems of different rigidity, but the same
principles should also apply for the transition between a terminal and a safety barrier.
In general, the purpose of a transition is:
• To provide a safe connection between two types of vehicle restraint systems;
• To provide a gradual change in stiffness from one system to another;
• To protect traffic from a head-on collision with the end of another vehicle restraint system.
Without a correctly designed and implemented transition, there is a risk of an abrupt change in
deflection performance characteristics, creating a risk of pocketing and/or snagging which in turn
represents a high level of risk to road users. ‘Pocketing’ means that (on impact) a flexible system on
the approach end of the transition may deflect so far that the impacting vehicle then strikes the end
of the more rigid system connected at the other end of the transition, as shown in Figure 11.1.
Figure 11.1 – An example of vehicle pocketing

261. ROADSIDE DESIGN GUIDE
PAGE 286
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
Where practicable, vehicle restraint systems must be physically connected together, and the
transition used to complete this connection should be designed so as to provide a gradual change
in stiffness, height, profile and/or containment from one barrier to another.
The connection between two safety barriers having the same type, cross-section and material, is not
considered a transition, as long as the deflection characteristics of the two different connected
systems are matched.
7.2 Types of Transitions
The Abu Dhabi Standard Drawings Manual presents one example of a transition (between a single
rail steel corrugated beam and a rigid concrete barrier (refer to Section 11.6.2.4).
A list of accepted transitions may be obtained from the Abu Dhabi Department of Municipal Affairs
and Transport’s list of Accepted Vehicle Restraint Systems. In addition, individual
manufacturers/promoters may also be able to give details of transitions appropriate for their systems
which have been accepted for use in other countries.
There are ten factors which will constitute a transition:
• Change in deflection characteristics;
• Change in material;
• Change in overall shape;
• Change in shape and/or dimensions of the supporting posts (by increasing the thickness of
the material used and/or by increasing the overall dimensions of the posts’ crosssection);
• Change in shape and/or size of beam;
• Change in containment (TL) level;
• Change in overall height;
• Change in individual rail height (for example if connecting two guardrails, one with a beam
height of 610mm, and another with a rail height of 750mm);
• Change in lateral stiffness (i.e. the system is made more rigid and there is therefore a risk
of pocketing between the two systems);
• Change in vehicle restraint system type.
In order to design an effective transition between two vehicle restraint systems, each of these factors
should be considered, and further guidance on how this could be achieved is given in Section 11.6.

262. ROADSIDE DESIGN GUIDE
PAGE 287
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
7.3 NCHRP350 and MASH Performance Classifications
All transitions shall have demonstrated compliance with the American recommendations in either
NCHRP 350 [1] or MASH [2] and additional local conditions for the Abu Dhabi Road Network.
Evidence of this shall be presented and approved by the Abu Dhabi Department of Municipal Affairs
and Transport prior to the use of these systems. Only systems approved by the Abu Dhabi
Department of Municipal Affairs and Transport shall be used.
In all cases, and due to the high number of transitions which could exist between systems,
acceptance of a transition can be based on one or more of the following methods (in order of
preference):
• Full scale impact testing to the requirements of NCHRP350 or MASH (refer to Section
11.4);
• Virtual testing to the requirements of the European Technical Report TR16303-4;
• Good engineering judgement based on the design rules within Section 11.6.
However, it is emphasised that in all cases, transitions should be approved by the Abu Dhabi
Department of Municipal Affairs and Transport prior to specification and installation.
Virtual testing (more commonly known as computer simulation) can be used to demonstrate the
anticipated dynamic performance of a transition, however the development, use and interpretation
of computer simulation is a specialised subject. As a result, European standardisation groups have
developed a Technical Report (TR16303-4) which gives guidance for the conduct of those working
with virtual testing. The TR identifies minimum requirements for the models which are used for the
simulation, and provides details on how these should be validated so that the result of the virtual
testing can be relied upon.
Whilst vehicle restraint systems used within Abu Dhabi should be successfully tested to the
requirements of NCHRP350 and MASH, for completeness, reference is also made to the European
Standard for the testing of road restraint systems, EN1317 in Chapter 6, Section 6.3.4 and Appendix
A.
7.4 Test Types
NCHRP Report 350 and MASH contain recommended procedures for the testing of transitions.
Testing of a transition requires the successful completion of a series of full-scale impact tests, the
parameters for which are shown in Table 11.1.
As shown in Table 11.1, all transition testing should be conducted at the critical impact point (CIP).
For transitions, the CIP is described as the point that maximizes the risk of test failure [2]. The CIP
is often estimated by the test house through computer simulations or use of specialist software such
as The Barrier VII [3]. Further information about the identification of CIP can be found in NCHRP 350
and MASH.
The following sections describe transition performance characteristics in further detail:

263. ROADSIDE DESIGN GUIDE
PAGE 288
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
Table 11.1 - Test requirements for NCHRP350
Test Level
Impact Conditions
Impact Point
Vehicle
Impact Speed
(km/h)
Impact
Angle (°)
NCHRP350
TL-3
Basic Level
820kg Car 100 20 At CIP
700kg Car 100 20 At CIP
2000kg Pickup Truck 100 25 At CIP
TL-4 820kg Car 100 20 At CIP
700kg Car 100 20 At CIP
2000kg Pickup Truck 100 25 At CIP
8000kg Single Unit Truck 80 15 At CIP
TL-5 820kg Car 100 20 At CIP
700kg Car 100 20 At CIP
2000kg Pickup Truck 100 25 At CIP
36000kg Tractor/van-type 80 15 At CIP
TL-6 820kg Car 100 20 At CIP
700kg Car 100 20 At CIP
2000kg Pickup Truck 100 25 At CIP
36000kg Tractor/tank-type 80 15 At CIP
MASH
TL-3
Basic Level
1100kg Car 100 25 At CIP
2270kg Pickup Truck 100 25 At CIP
TL-4 1100kg Car 100 25 At CIP
2270kg Pickup Truck 100 25 At CIP
10000kg Single Unit Truck 90 15 At CIP
TL-5 1100kg Car 100 25 At CIP
2270kg Pickup Truck 100 25 At CIP
36000kg Tractor/van-type 80 15 At CIP
TL-6 1100kg Car 100 25 At CIP
2270kg Pickup Truck 100 25 At CIP
36000kg Tractor/tank-type 80 15 At CIP
7.5 Selection Criteria
In many cases, the selection of a transition will be greatly limited as it is likely that there will only be
a small number of possible solutions for connecting one vehicle restraint system to another.
However, there are a number of factors which should be considered before the selection of any
proposed transitional arrangement. These are, as a minimum:
• The vehicle restraint systems to be connected as transitions will typically only be suitable for
the connection of two specific systems, and will not be of a generic design;
• The containment requirements for the transition (refer to Section 11.5.1);
• The deflection characteristics of the transition (refer to Section 11.5.2);
• The impact severity level of the transition (refer to Section 11.5.3);
• Maintenance and inspection requirements (refer to Section 11.5.4); and

264. ROADSIDE DESIGN GUIDE
PAGE 289
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
• Cost considerations (refer to Section 11.5.5).
Once the classification of the transition has been determined, available transitions of this
classification should be identified from the Abu Dhabi Department for Transport’s list of approved
proprietary products.
It is possible that in a number of cases, a suitable transition may not exist. In such cases the
promoters/manufacturers of the two vehicle restraint systems to be connected should be contacted
to ensure that a transition can be developed and approved by one (or more) of the methods identified
within Section 11.3.
Where no agreement can be reached between the two promoters/manufacturers, each vehicle
restraint system should be terminated in accordance with the requirements of Chapter 9. However,
it is emphasised that this is a non-preferred arrangement and in all cases, designers should strive to
encourage promoters/manufacturers to develop approved transitions.
11.5.1 Containment Requirements
TL-1 provides test requirements for vehicle impact speeds of 50km/h, TL-2 provides for vehicle
impact speeds of 70km/h and TL-3 (which is the basic level) provides for vehicle impact speeds of
100km/h (refer to Table 11.1). T-L 4, TL-5 and TL-6 provide for tests with larger vehicles such as
single unit trucks and semitrailers to determine the performance of transitions with such vehicle types
and masses.
The containment level of a transition should not be less than the lower of the two connected systems
(for example, if a transition is to connect TL-3 and TL-4 systems, the minimum containment level for
the transition is TL-3). Where a transition spans more than one containment class (for example where
a TL-3 system is connected to a TL-5 system), it is the manufacturer’s choice whether to test the
system at either the same containment level as either of the two connected barriers (i.e. TL-3 or TL-
5), or the intermediate containment level (i.e. TL-4). Furthermore, as a general rule, the containment
level of a transition between a terminal and a safety barrier should match that of the connected safety
barrier (typically TL-3).
11.5.2 Deflection Requirements
Following the impact testing of a transition (independent of its type and performance characteristics),
the working width and dynamic deflection of the system is determined and reported, as described in
Chapter 6, Section 6.3.3.2. The assessment of the dynamic performance is undertaken through the
analysis of high speed video coverage, recorded during the impact test.
Both of these measurements are very important when selecting the design and site of a transition
as it is important to ensure that if the transition is impacted by an errant vehicle on the road, the risk
of the system deflecting and impacting the hazard behind the transition and/or another road user or
road worker is minimised to a level which is as low as reasonably practicable. As explained in Section
7.3.5 of Chapter 7, the distance between the front face of the system to the hazard should be less
than the working width of the system. This is to prevent the impacting vehicles reaching the hazard
as a result of the deflection in the system. The criteria explained in Section
7.3.5 are equally applicable to transitions.

265. ROADSIDE DESIGN GUIDE
PAGE 290
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
If there is insufficient space available, consideration should be given to the use of a different
transition and thus, different vehicle restraint systems at either end of the transition.
Furthermore, the dynamic deflection (see Section 6.3.3.2) of a transition should not exceed the size
of the larger dynamic deflection of the two connected systems [4]. This is to prevent pocketing. The
dynamic deflection of a transition should be between the dynamic deflections of the two systems it
connects.
11.5.3 Impact Severity Level Requirements
Following the impact testing of a transition (independent of its type and performance characteristics),
the impact severity level of the system will be reported in terms of the OIV and ORA. These provide
a method of ranking the severity of the impact with the transition, and give an indicative guide as to
the level of injury which might be expected from an impact with an errant vehicle (assuming all of the
impact parameters are the same as those under which the system was tested). Further explanation
of the severity indices can be located within Chapter 6, Section 6.3.3.4.
For transitions, the impact severity level shall be as low as practicable to reduce the risk of injury to
the occupants of errant vehicles. For systems tested to NCHRP Report 350 or MASH, lower values
for OIV and ORA should be preferred, as shown in Table 3 of Section 7.2.3.
11.5.4 Maintenance and Inspection Requirements
All transitions should be maintained and inspected in line with the manufacturer’s recommendations.
These should be contained within the documentation supplied by the transition, and are likely to
reflect the requirements for the connected vehicle restraint systems. Any non- proprietary transitions
should be inspected every two years as a minimum.
11.5.5 Cost Considerations
As with all roadside safety systems, cost considerations should not just include the initial cost of
purchasing the crash cushion, but should also include the costs for installation, maintenance, repair
or replacement.
Unlike other barrier elements however, the number of alternative systems available for an acceptable
installation will be limited for transitions. There are many different types of roadside and bridge
barriers available on the market today. Each combination of these systems requires a unique
transition. The costs of developing a transition is considered high compared to the number of
potential applications. This means high development costs for low sales figures for the
manufacturers. Therefore, the cost considerations are less likely to be the decisive factor for the
transition selection, as there are often no alternatives available.
7.6 Application Criteria
The design of a transition between two connected vehicle restraint systems will require engineering
judgement, experience and knowledge of the vehicle restraint systems to be connected.

266. ROADSIDE DESIGN GUIDE
PAGE 291
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
There are no specific rules which should be followed in the design of new transitions, however, there
are a number of factors and International best practice which should be considered and incorporated
within the design process. These specific points are highlighted below:
1. The general rule for transitions is that where practicable, vehicle restraint systems must be
physically connected together, and the transition used to complete this connection should be
designed so as to provide a gradual change in stiffness, height, profile and/or containment
from one barrier to another. This is the fundamental approach to be taken within the design
of a transition.
2. A more rigid roadside barrier transition can be provided through reducing post spacing (see
Figure 11.2); by using posts with a larger cross section or posts which go further into the
ground; and/or by using stronger or an increased number of rail elements. The use of a wider
rail system such as thrie beam may also be used. Such methods are frequently used by the
designers of proprietary products to decrease the deflection characteristics of their products.
However, as an example, within the UK, the 1.7 m length of a standard post is increased to
1.95 m if additional stiffness is required. The use of reduced post spacing on the approach
to a more rigid barrier system can be seen within Figure 11.2.
3. Transitions should be designed to minimise the likelihood of snagging by an errant vehicle
and one from the opposing lane on a two-way facility. ‘Snagging’ means that a vehicle
impacts a flexible barrier system, which deflects to such an extent that the vehicle then
impacts the approach end of the connected barrier system. This may result in very rapid
deceleration of the errant vehicle, greatly increasing the risk to the occupants of the errant
vehicle.
4. In addition to the risk posed by the end of a barrier, a vehicle’s wheels may also become
snagged on the posts of the connected system. The snagging of a vehicle may be mitigated
through the use of block-outs between the rail and the posts of the barrier system, or through
the addition of a secondary rail underneath the main containment rail(s), known as a ‘rubbing
rail’. An example of such a rubbing rail is shown in Figure 11.2.
5. The face of the approach rail transition should be smooth. Projections from the face of the
barrier should be avoided wherever possible, and in any case limited to 25mm [5], as shown
in Figure 11.3.

267. ROADSIDE DESIGN GUIDE
PAGE 292
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
Figure 11.2 – An example of reduced post spacing and a rubbing rail
Direction of Traffic
Traffic face of Barrier A
Figure 11.3 – Projections on the face of a transition
6. To ensure that significant changes in deflection do not occur within a short distance, the
transition section should be sufficiently long. Generally, the transition length should be 10 to
12 times the difference in the lateral deflection of the two systems being connected by the
transition [6]. For example, if the deflection of Barrier A is 2.3 m, and the deflection of
connected Barrier B is 1.2 m, the transition should be between 11-13 m in length.
7. A transition such as that shown in Figure 11.4 is unacceptable for a number of reasons,
including the protrusion greater than 25 mm at the base of the transition, and the lack of a
gradual change in stiffness from the concrete barrier, to the steel beam, and back to the
concrete barrier. A more acceptable transition is that shown in Figure 11.5, where there is a
much better and controlled increase in stiffness, and a lack of protrusions due to the
alignment and design of the transition.
Figure 11.4 – An unacceptably short transition
Max 25 mm
Traffic face of Barrier B

268. ROADSIDE DESIGN GUIDE
PAGE 293
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
Figure 11.5 – Transitional design with increasing stiffness
8. The effect of impacting the departure end of the downstream barrier, and the resulting
deflection should be assessed using a risk based approach, examining the likely effect of
impacts along the length of the transition, and the probability and severity of any resulting
injury. Figure 11.6 shows a number of examples where an impact on the departure end of
the upstream barrier will result in the barrier deflecting and redirecting the errant vehicle onto
the approach end of the downstream barrier. Such details are unacceptable, and the two
connected systems should work together to contain and redirect an errant vehicle.
Figure 11.6 – Unacceptable transition details
9. The transition should be designed so that the height of the transition increases smoothly and
continuously from the lower system to the higher one. An example of such an arrangement
can be seen in Figure 11.7. International experience has shown that any steps or slopes
should not be greater than 8% [7].
Approach end of
downstream barrier
Departure end of
upstream barrier
Approach end of
downstream barrier
Departure end of
upstream barrier

269. ROADSIDE DESIGN GUIDE
PAGE 294
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
Figure 11.7 – An example of changes in connected barrier height
10. Drainage features (e.g. curbs, raised inlets, curb inlets, ditches) in front of the barrier in the
transition area may initiate vehicle instability that can, in some instances, adversely affect the
crashworthiness of the transition. The slope between the edge of the travelled lane and the
barrier should be no steeper than 1V:10H [6].
11.6.1 Connections
The strength of each connection between two different barriers should not be less than the strength
of the joint between consecutive beams in the lower containment barrier (typically the lap joint of a
TL-3 barrier). This can be demonstrated by testing or by calculations. Tests and calculations should
include combined longitudinal and bending forces if they both exist in a vehicle impact.
Experience from within the UK has shown that as a general rule, any connection between TL-1, TL-
2 or TL-3 barriers should be capable of transmitting a tensile force of 330kN [8]. Furthermore, any
connection between a TL-4, TL-5 or TL-6 barriers should be capable of transmitting a tensile force
of 500kN [8]. Connections which are not capable of transmitting such forces are likely to break in the
event of an impact, and these tensile force restrictions will provide designers with proven in-service
and in-testing guidance for the design of connections.
It must also be ensured that at each end of a transition there is a physical connection to another
vehicle restraint system, or a terminal. It is not acceptable to leave unprotected end of systems,
neither on the approach or departure end of the transition (as shown in Figure 11.8). The
arrangement shown in Figure 11.8 is unacceptable for a number of reasons, notably that the two
systems are not connected together. There is a risk of an errant vehicle impacting the ramped end
of the concrete barrier, and launching, possibly into the column located behind the concrete barrier.
There is also no increase in stiffness or anchorage at the end of the steel guardrail and hence, any
impact close to the departure end of the steel barrier is likely to deflect the steel barrier such that an
errant vehicle could impact the ramped concrete end with the centreline of the vehicle. An
arrangement such as that shown in Figure 11.16a should have been installed at this location – this
would include the removal of the ramped concrete end, a physical and sufficiently robust connection
(capable of transmitting a tensile force of 330kN) of the steel guardrail into the

270. ROADSIDE DESIGN GUIDE
PAGE 295
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
concrete, and a closing of the post spacing just prior to the concrete barrier to increase the barrier’s
stiffness.
Figure 11.8 – Example of a poor transition (unconnected barrier systems)
11.6.2 Specific Transitional Arrangements
There are a number of transitional arrangements that require additional consideration and
engineering judgement to be applied to ensure they can be dealt with in an appropriate way. These
are explained in the following sections.
11.6.2.1 Safety Barrier to Bridge Parapet Transitions
Within the design of a transition, any exposed ends of bridge parapet systems should be flared
backwards, away from the traffic face of the parapet at an angle of 45° [9] as shown in Figure 11.9,
unless the rail is close to the main rail of the connecting barrier system. It should be noted that, where
practical, instead of flaring back rails, it is preferable to transition all rails so as not to leave any
exposed rail ends.
Figure 11.9 – An example of a flared back top parapet rail
11.6.2.2 Wire Rope Safety Barrier to Semi-rigid Barrier
When it comes to the provision of a transition between a WRSB and a w-beam barrier, there are
different approaches utilised internationally. The first type of approach is to install both the WRSB
and the W-beam side by side for a distance, as shown in Figure 11.10. This is the type of transition

271. ROADSIDE DESIGN GUIDE
PAGE 296
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
which is recommended by the New Zealand Transport Agency [10]. In this application, the length of
overlap depends on the individual lengths of the WRSB and W-beam transitions. This is because
the end point of the W-beam terminal must align with (as shown in Figure 11.10) or overlap the point
of redirection of the WRSB system (i.e. the point where the WRSB terminal ends and standard
section of WRSB begins). The idea is to provide a standard section of at least one of the barrier
types along the whole transition and to keep the re-directional capabilities throughout the whole
arrangement. It should be noted that the W-beam terminal to be used for this type of transition is a
full height, parallel and an energy absorbing system. It is recommended that the offset between the
front face of the W-beam and the centreline of the WRSB should be 825mm at the upstream end of
W-beam, as shown in Figure 11.10. This offset comprises:
• 225mm (450/2, nominal WRSB footing);
• 100mm clearance; and
• 500mm semi-rigid barrier timber or I-section posts, and blockout [10].
*Figure is not to scale and shown for indicative purposes only.
Figure 11.10 – Example of a WRSB to W-beam transition by overlapping installation
The second type of application is to install the WRSB and the W-beam side by side with enough
distance to ensure that they will perform completely independently from each other during an impact.
This is also the type of arrangement which is recommended for transitions between WRSB and
concrete barriers, and therefore it is explained in further detail in Section 11.6.2.3. This is the type of
transition arrangement which requires the largest amount of space and therefore may not be
applicable at all locations.
The final type of transition arrangement features a section where the WRSB is physically connected
on to the W-beam, as shown in Figure 11.11. This type of arrangement was originally developed by
the South Dakota Department of Transportation to provide a transition between the strong post W-
beam and low-tension WRSB systems [11]. In 1998, this system was tested in accordance with
NCHRP 350 [1] and successfully met the evaluation criteria of TL-3. However, over the following
years the low-tension WRSB system became a less preferred option with the emergence of the high-
tension proprietary WRSB systems. Over the years several manufacturers of the high-tension
proprietary systems have introduced modified versions of the South Dakota design to fit the needs
of their individual systems. Several of these designs were technically assessed and approved for
use in the USA by the FHWA [11].

272. ROADSIDE DESIGN GUIDE
PAGE 297
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
The original design utilised special steel straps to transition the individual cables of the low-tension
WRSB system over and under the W-beam. These cables were then connected to a ground anchor
located behind the W-beam. In the new designs for the high-tension WRSB systems, the need for a
ground anchor is eliminated. This is because each of the cables is attached directly on to the W-
beam rail element by special anchors. The design of these anchors change from one system to
another and therefore further detail should be provided by the individual manufacturer.
For both the original and the new designs, the post spacing of the WRSB is reduced to half for usually
a length of around 12-13 posts, as the WRSB approaches the W-beam connection. This is done to
increase the stiffness and therefore decrease deflection on the approach to the W-beam. The length
of this section will depend on the post spacing of individual system and the transition arrangement.
The W-beam terminals used in these transitions are full-height, and energy absorbing systems. The
W-beam terminal is installed in a flared arrangement. This is done to provide more deflection space
between the WRSB and the w-beam terminal. The area leading to the w-beam terminal should have
a ground slope of 1V:10H or flatter, in-line with the requirements explained in Chapter 9, Section
9.5.3.

273. ROADSIDE DESIGN GUIDE
PAGE 298
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
*Figure is not to scale and shown for indicative purposes only.
Figure 11.11 - Example of a WRSB to W-beam transition

274. ROADSIDE DESIGN GUIDE
PAGE 299
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
11.6.2.3 Wire Rope Safety Barrier to Concrete Barrier
Due to the very flexible nature of wire rope, and the very rigid nature of concrete barriers, these
systems should not be connected directly to each other. Concrete and WRSB are rarely connected
to each other and therefore the number of available designs are limited. The international best
practice to combat this problem consists of untested design recommendations [12], [10]. The
recommended application is to overlap a section of concrete barrier and WRSB, in a configuration
where the distance between the two systems at any point is less than the dynamic deflection (see
Chapter 6, Section 6.3.3.2) of the WRSB. This configuration is shown in Figure 11.12.
*Figure is not to scale and shown for indicative purposes only.
Figure 11.12 - An example of a transition between wire rope barrier and a concrete barrier
In the figure the distance ‘A’ represents the minimum acceptable distance between the concrete
barrier and WRSB. This value should be less than the dynamic deflection of the WRSB. This is to
ensure that enough space is provided behind the WRSB, so in the event of an impact from Approach
1, the barrier would not deflect all the way into the concrete barrier. This prevents a secondary impact
with the concrete barrier. As explained in Chapter 6, Section 6.5.1, the dynamic deflection will change
greatly from one WRSB system to another. Therefore, this value should be provided by the
manufacturer.
The distance ‘B’, shown in Figure 11.12, should also be less than the dynamic deflection of the
WRSB system. This is to ensure that in the event of an impact from the Approach 2, the WRSB does
not deflect into the opposing travelled way. This way a secondary impact with oncoming vehicles is
prevented. As shown in the figure, the measurement for ‘B’ should be made between the edge of
the travelled way and the first point on WRSB, which can be reached by an errant vehicle coming
from Approach 2. The angle of approach can be taken as the impact test angle corresponding to the
test level of the specific WRSB. For example, for a TL-3 WRSB, the approach angle can be taken
as 25° to represent the highest angle, to which the system was tested. The impact angles for different
test levels are provided in Chapter 6, Section 6.3.3. Finally, the flare rate of the WRSB should be
within the appropriate limits. More information on flare rates can be found in Chapter 7, Section 7.4.2.

275. ROADSIDE DESIGN GUIDE
PAGE 300
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
11.6.2.4 Steel Barrier Approaches to Concrete Barriers
Connections between semi-rigid steel barriers and rigid concrete barriers are particular areas of
concern as they present the potential for a high risk of pocketing and resulting injury. It is for this
reason that the Abu Dhabi Department of Municipal Affairs and Transport has developed a standard
detail for such transitions, as shown in Figure 11.14.
Full details of this transition can be found within Drawing Number R-24 of the Abu Dhabi Standard
Drawings Manual [13]. This is a well-designed transition as there is a gradual increase in post
spacing (and therefore barrier stiffness) on the approach to the rigid barrier system (shown in red),
and a clear connection (capable of withstanding a 330kN loading) into the concrete barrier (shown
in orange). The plan view shows that there is also continuity in the alignment of the barriers through
the transition (shown in green) and no excessive protrusions within the design. However, the
transition could be further improved as the differences in profile between the steel and concrete
systems introduces an exposed step at the end of the concrete barrier which would still prove to be
an area of injury risk for the occupants of an errant vehicle. This area is highlighted on Figure 11.13.
This could be overcome by introducing an additional (rubbing) rail below the main rail and/or by
connecting the barrier into a vertically faced concrete barrier. Both of these approaches have been
implemented within the design shown in Figure 11.2 and will greatly reduce the risk to road users.
The drawing in Figure 10.13 also makes it clear that this transition is only valid for connecting
concrete and semi-rigid guardrail type designs.
Figure 11.13 – Exposed step of concrete barrier

276. ROADSIDE DESIGN GUIDE
PAGE 301
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
Figure 11.14 - The Abu Dhabi Department of Municipal Affairs and Transport standard detail for transition from guardrail to rigid concrete barrier [13], Refer to latest version.

277. ROADSIDE DESIGN GUIDE
PAGE 302
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
11.6.3 Example applications
Figure 11.15 demonstrates a number of inappropriate transition details
a) Steel to Concrete Barrier b) Steel to Concrete Bridge
c) Steel to Concrete Barrier d) Wire Rope to Steel Barrier
Figure 11.15 – Examples of inappropriate transitions
There are a number of reasons why each of the transitions within Figure 11.15 does not meet the
guidance within this Section with regard to the design of transitions:
Figure 11.15a: In this Figure it is clear that there is no physical connection between the two barrier
systems, no decrease in post spacing (and therefore stiffening of the steel guardrail) prior to the
concrete section and, due to the change in profile between the two barrier systems, a risk to road
users from striking the end of the concrete barrier. In the event of an impact close to the end of the
steel guardrail, it is likely that the beam will deflect to an extent such that an errant vehicle will still
strike the end of the concrete barrier. Under such circumstances, the detail shown in Figure 11.14
would reduce road user risk (although this detail in itself could be better designed as explained
above).
Figure 11.15b: This Figure is very similar in detail to that seen in Figure 11.15a, however, the
consequences of the poor detail are likely to be higher due to the larger concrete face which poses
the risk to road users. In addition, this Figure shows the importance of correct alignment between
the two sections of connected barrier. A detail similar to that within Figure 11.14 would reduce the
risk to road users at this location.
Figure 11.15c: This Figure is slightly improved on the detail within Figure 11.15a, however still not
acceptable. Whilst the end of the guardrail beam now overlaps with the end of the concrete barrier,
there is still no physical connection between the two systems. Hence, whilst the risk of injury to road
users is lower than in the case shown in Figure 11.15a, the lack of connection means that, again, in
the event of an impact towards the end of the steel guardrail, it is likely that the beam will

278. ROADSIDE DESIGN GUIDE
PAGE 303
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
deflect to an extent that an errant vehicle will still strike the end of the concrete barrier. This detail
could be improved by Figure 11.14.
Figure 11.15d: In this final figure there is no connection between the wire rope fence and the end of
the steel barrier system. Whilst this in isolation is not a significant problem, the barriers have been
overlapped in such a way that, due to the large deflection of the wire rope system and the lack of
movement in the terminal section of the steel guardrail, any impact towards the end of the wire rope
system is likely to deflect the wire rope in such a way that the errant vehicle will still strike the end of
the terminal.
In order to reduce the risk to road users at this point, the barriers should either be connected as
shown in Figure 11.11 or overlapped such that the systems can function independently, as shown
in Figure 11.10 or Figure 11.12. It should be noted that if the second option is to be followed, the
requirements for a full height terminal (given in Chapter 9) should be applied.
Figure 11.16 demonstrates improved transition details, as witnessed in Abu Dhabi.
Figure 11.16 – Example of appropriate transition between a w-beam and a concrete barrier
7.7 Summary and Conclusions
A transition is required for any location where one type of vehicle restraint system is required to be
connected to another.
In general, transitions are required:
• To provide a safe connection between two vehicle restraint systems;
• To protect traffic from a head-on, or angled collision with the end of another vehicle
restraint system.
As a general rule and where practicable, vehicle restraint systems must be physically connected
together, and the transition used to complete this connection should be designed to provide a
✓

279. ROADSIDE DESIGN GUIDE
PAGE 304
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
gradual change in stiffness, height, cross-sectional shape and/or containment from one barrier to
another.
In general, the rigidity of the W-beam systems can be increased by reducing the post spacing, by
using posts with a larger cross section, and/or by using stronger or an increased number of rail
elements.
Transitions should be designed to minimise the probability of snagging by an errant vehicle and one
from the opposing lane on a two-way facility. The snagging of a vehicle may be mitigated through
the use of block-outs between the rail and the posts of the barrier system, or through the addition of
a secondary rail underneath the main containment rail(s), known as a ‘rubbing rail’.
To ensure that significant changes in deflection do not occur within a short distance, the transition
section needs sufficient length.
The transition should be designed so that the height of the transition increases seamlessly from the
lower system to the higher one. The face of the approach rail transition should be smooth.
Drainage features in front of the barrier in the transition area may initiate vehicle instability that can,
in some instances, adversely affect the crashworthiness of the transition. The slope between the
edge of the travelled lane and the barrier should be no steeper than 1V:10H.
In all cases, and due to the high number of transitions which could exist between systems,
acceptance of a transition should be based on one or more of the following methods (in order of
preference):
• Selection of proprietary transition systems which have had full scale impact testing to the
requirements of NCHRP350 or MASH (see Clause 11.3);
• Virtual testing to the requirements of the European Technical Report TR16303-4;
• Good engineering judgement based on the design rules within Section 11.6.
However, it is emphasised that in all cases, transitions should be approved by the Abu Dhabi
Department of Municipal Affairs and Transport prior to specification and installation.
7.8 References
[1] NCHRP, “NCHRP Report 350, Recommended Procedures for the Safety Performance
Evaluation of Highway Features,” Transportation Research Board, National Research Council,
Washington DC, 1993.
[2] AASHTO, Manual for Assesing Safety Hardware (MASH), Washington D.C.: American
Association of State Highway and Transportation Officials, 2009.
[3] H. E. Ross, H. S. Perera, D. L. Sicking and R. P. Bligh, “National Cooperative Highway Research
Program, Report 318: Roadside Safety Design for Small Vehicles,” Transportation Research
Board, Washington, D.C., 1989.
[4] CEN, “EN 1317 Road Restraint Systems - Part 4: Performance classes, impact test acceptance
criteria and test methods for terminals and transitions of safety barriers,” European Committee
for Standardization, Brussels, 2002.

280. ROADSIDE DESIGN GUIDE
PAGE 305
11 TRANSITIONS FIRST EDITION -DECEMBER 2016
[5] Alberta Infrastructure and Transportation, Roadside Design Guide, Alberta Infrastructure and
Transportation, November 2007.
[6] AASHTO, Roadside Design Guide, 4th Edition, Washington D.C.: American Association of State
Highway and Transportation Officials, 2011.
[7] CEN, “EN 1317 Road Restraint Systems- Part 4 - Draft Ammendments,” Unpublished Draft -
Eurpoean Committee for Standardization, Brussels, 2014.
[8] BSI, “BS6779-1, Highway parapets for bridges and other structures - Part 1: Specification for
vehicle containment parapets of metal construction,” British Standards Institution, London, 1998.
[9] TD19/06 Design Manual for Roads and Bridges, Volume 2 Highway Structures: Design, Section
2 Special Structures, Part 8, The Highways Agency, Transport Scotland, Welsh Assembly
Government, The Department for Regional Development Northern Ireland, 2006.
[10] NZ Transport Agency, “Technical Memorandum, Road Safety Hardware Series, TM-2013, Wire
Rope Safety Barrier Transitions,” New Zealand Transport Agency, Nov 2014.
[11] FHWA, “Memorandum on the Cable Barrier Transitions to W-Beam Guardrail,” US Department
of Transportation, Federal Highway Administration, Washington DC, 2006.
[12] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney, NSW:
Austroads, 2010.
[13] Abu Dhabi DoT, Standard Drawings for Road Projects - Part 3: Road Structures, Abu Dhabi:
Abu Dhabi Department of Transport, 2014.

281. ROADSIDE DESIGN GUIDE
PAGE 306
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
8 ECONOMIC ASSESSMENT
8.1 Introduction
Although the number of fatalities from roadside crashes is decreasing every year in the Emirate of
Abu Dhabi, roadside crashes account for a significant portion of the total fatal highway crashes.
Approximately 15 percent are the result of a single vehicle run-off-the-road crash. These casualties
represent a significant loss for the country’s economy and an immeasurable emotional loss for the
families of people who are involved with the incidents.
A significant proportion of these roadside casualties may be prevented by good engineering and
design practices, which would improve the level of safety and decrease the severity of accidents.
From this perspective, well targeted roadside safety improvements can generally be seen as highly
beneficial investments. However, the funds allocated to safety treatments are usually limited and
there are often more than one treatment options applicable to a site. Furthermore, every roadside is
different and the costs and benefits of a certain safety treatment would change from one site to
another. Therefore, the engineer/designer should evaluate the potential safety treatments through
economic assessment on a site-by-site basis so that the highest amount of benefits can be gained
from a limited amount of funds.
There are several methods developed around the world for comprehensive economic assessment
of roadside safety treatments; such as Road Safety Analysis Program (RSAP) [1] in USA, Highway
Safety Manual (HSM) [2] methodology in USA, Road Restraint Risk Analysis Program (RRRAP) [3]
in UK, SAVERS Tool [4] in Europe and the Austroads methods [5] in Australia. These methods all
provide useful ways through which a designer/engineer can carry out economic analysis. However,
almost all of these methods are developed to cater for their respective local conditions, by using
local data. For example, the accident prediction models, which constitute the basis of all these
models, are often developed or calibrated by using local accident, traffic and road geometry data.
Therefore, they may not be as reliable when applied to the local conditions in other regions, including
the Emirate of Abu Dhabi. Furthermore, comprehensive economic analysis often requires a large
amount and variety of data, which currently is not available for every type of road in Abu Dhabi.
Therefore, the designer/engineer may not always have enough data to be able to use the
methodologies mentioned above.
Due to these limitations, this chapter provides a general guidance on roadside safety economic
assessment process, which can help designers/engineers, who only have access to a limited amount
of data. However, designer/engineer can also use the presented methodology to carry out more
detailed economic analyses, if there is enough data to support it. References are also made to the
international methods mentioned above, for those who want to explore further on the related topics.
In the future, as more data become available, the Abu Dhabi Department of Transport may introduce
more comprehensive economic analysis requirements.

282. ROADSIDE DESIGN GUIDE
PAGE 307
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
8.2 Abu Dhabi Roadside Design Guide Economic Assessment
Process
Economic assessment is an integral part of the Abu Dhabi Roadside Design Guide risk mitigation
approach. A brief overview of the economic analysis process and its standing within the whole risk
mitigation approach was presented in Chapter 2. This chapter provides the necessary tools to help
the designer/engineer achieve the steps presented in Chapter 2.
Figure 2.10 shows the recommended economic analysis process for this Guide. As can be seen
from the figure, the process explained in this chapter begins once a number of treatment options are
identified to mitigate the risk posed by a roadside hazard.
Stage 1 - Assessment of Economic Feasibility
Figure 12.1 – Overview of the economic assessment process
It should also be verified that the considered treatment options are physically practicable. Chapter
2, Figure 2.10 explains the general approach to risk mitigation. First, the alternative treatment options
are shown i.e. remove, relocate, make passively safe, use barrier, delineate hazard. Then physical
practicability of these options is checked. Only the ones which are physically practicable are carried
to the economic assessment stage. Economic Analysis is only a part of this whole process. Therefore
the flowchart shown in this chapter is only focusing on the economic assessment and the treatment
prioritisation.
As can be seen from Figure 2.10, the economic assessment process consists of two main stages:
Calculate BCR for Physically Practicable Treatment Options
BCR<1 BCR≥1
Treatment is Not
Economically Justified
Treatment Economically
Justified
Stage 2 - Treatment Prioritization
Non-Monetary
Considerations
By Incremental By Risk
BCR Reduction
Engineering Judgment
Choose the appropriate treatment option

283. ROADSIDE DESIGN GUIDE
PAGE 308
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
• Stage 1: Assessment of economic feasibility for each treatment option;
• Stage 2: Prioritization of economically feasible treatment options.
Stage 1: The first stage includes the assessment of economic feasibility of each option to make sure
the expected benefits of a safety treatment outweigh its costs. The recommended method for
checking this is a Benefit Cost Ratio (BCR) Analysis. Necessary guidance to carry out this analysis
is presented in Section 12.3. Any project with a BCR less than 1.0 is considered not feasible and
therefore is not economically justified. The assessment continues with the treatment options with
BCR equal to or greater than 1.0.
Stage 2: The second stage includes the selection between one of the economically justified
treatment options. This selection is not straightforward and requires a multi layered assessment with
the priorities changing from one site to another. Depending on the project and site requirements, a
designer/engineer may need to rank or assess the treatment options from one or more of the
following perspectives:
• By benefit cost ratio, as explained in Section 12.4.1;
• By the amount of risk reduction, as explained in Section 12.4.2;
• By non-monetary considerations, as explained in Section 12.4.3.
Once the options are assessed through these considerations, the designer/engineer should assess
and choose the most suitable treatment for the specific site.
8.3 Benefit Cost Ratio Analysis
BCR Analysis is a systematic process for calculating, and comparing the benefits and costs of a
proposed project or investment. It has two main purposes:
• To determine if an investment decision is sound (i.e. the justification for/ feasibility of the
decision). This involves comparing the total expected cost of the counter-measure against
the total expected benefits, to see whether the benefits outweigh the costs, and by how much;
and
• To provide a basis for comparing alternative projects. This involves comparing the total
expected costs of the different options against their total expected benefits, to assess the
most economically advantageous option.
The BCR is the ratio of the total benefits relative to the total costs of a project, both expressed in
monetary terms. It summarises the overall value for money of a project proposal. All benefits and
costs are expressed in discounted present values. If the BCR exceeds 1.0, then the project is
considered viable and potentially a good investment; the higher the BCR the more economically
advantageous the investment is likely to be. However, the BCR figure can be misleading when
comparing different options. For example, a high BCR may be a consequence of a very small
scheme with low costs but relatively high benefits generating a high BCR. Meanwhile a large
investment may generate very high benefits, but at a very high cost as well as generating a relatively
low BCR. It is therefore essential only to compare similar schemes in investment decisions, for
example projects of a similar size or value. So, in addition to considering the BCR, the total net
benefits as well as the overall costs should also be considered when comparing alternative
investments in the decision making process.

284. ROADSIDE DESIGN GUIDE
PAGE 309
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
To calculate the BCR, the following procedures should be undertaken:
A. Calculate the Benefits of the Treatment Option
Step 1. Determine the expected crash rate without the treatment (Section 12.3.1.1)
Step 2. Determine the expected reduction in crash rate caused by the treatment (Section
12.3.1.2)
Step 3. Calculate the estimated annual monetary value of reduction in crashes (Section
12.3.1.3)
Step 4. Calculate the Present Value of the benefits (PVbenefits) (Section 12.3.3)
B. Calculate the Costs of the Treatment Option
Step 5. Estimate the annual costs of the treatment (Section 12.3.2)
Step 6. Calculate the Present Value of the costs (PVcosts) (Section 12.3.3)
C. Calculate the BCR for the Treatment Option
Step 7. Calculate the BCR using Equation 12.1
Equation 12.1
Where:
BCR = Benefit-Cost Ratio
PVbenefits = Present value of project benefits
PVcosts = Present value of project costs
A summary of the BCR calculation process is presented in
Figure 12.2. Following sections provide the necessary guidance on the individual steps of BCR
calculation.

285. PAGE 310 FIRST EDITION -DECEMBER 2016
12 ECONOMIC ASSESSMENT
ROADSIDE DESIGN GUIDE
Figure 12.2 – Calculation of the Benefit Cost Ratio (BCR)
Treatment Benefits Treatment Costs
Crash Records or
Prediction Model
CrashModification
Factors
Cost of Crashes
Discount Rate (%)
Project Life (Years)
Step 7
Calculate the
Benefit Cost Ratio
(BCR)
Step 6
Calculate the Present Value of the
Costs (PVcosts)
(Section 12.3.3)
Other
costs
Design and Maintenance
Construction costs costs
Step 5
Estimate the annual costs of the
treatment (AVcosts)
(Section 12.3.2)
Calculate the Present Value of the
benefits (PVbenefits)
(Section 12.3.3)
Step 4
Calculate the estimated annual
Step 3 monetary value of reduction in crashes
(AVbenefits) (Section 12.3.1.3)
Determine the expected reduction in
Step 2 crash rate with the treatment (Nwt)
(Section 12.3.1.2)
Determine the expected crash rate
without the treatment (Nwot) (Section
12.3.1.1)
Step 1

286. ROADSIDE DESIGN GUIDE
PAGE 311
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
y
12.3.1 Assessment of Treatment Benefits
The first part of a BCR calculation involves the assessment of project benefits. Main benefits of a
roadside safety treatment include reduction in either or both the number and/or the severity of
crashes. Another benefit of reducing the number of crashes is the reduction in traffic disruptions,
which are caused as a result. Benefits of reduction in traffic disruptions are usually included within
the unit costs of crashes and therefore, additional calculations are usually not necessary. The
following sections explain the individual steps involved in calculating the benefits caused by a
treatment.
12.3.1.1 Determination of the Expected Crash Rate
The first step in assessing treatment benefits is the estimation of the expected crash rate (number
of crashes per year) at the roadside under evaluation, without any treatments. This can be achieved
through two types of approaches:
• Estimation through observed/historic crash frequency;
• Estimation through statistical methods.
In the first approach, historic crash data is used as an indicator for future crashes. This may be
established from the DoT’s crash database. This type of approach is often the only available method
of estimation in the absence of any other methodology or detailed data. This is currently the case in
Abu Dhabi and therefore the use of historic crash frequency is the recommended approach within
this Guide. An advantage of using observed crash frequency is the ease of understandability, as
these values are easier to interpret then statistical models.
On the other hand the designer/engineer should be aware of the limitations of using historic crash
data. These limitations are mainly related to the lack of predictability and natural variations in crash
data over time. Roadside crashes are random events and their frequencies naturally fluctuate over
time at any given site. The random nature of the crashes means that short-term crash frequencies,
such as for one or two years, are not reliable for the estimation of the long term situation. As shown
in Figure 12.3, if a two year period of crashes was used as the sample to estimate the crash
frequency, it would be difficult to know if this two year period represents a typically high, average, or
low crash frequency.
Long-Term
Average
Crash Frequency
Figure 12.3 – Effect of short-term and long term observed crash frequency
Short-Term
Observed Crash Frequenc Average Crash
Short-Term
Average Crash
Frequency
Years

287. ROADSIDE DESIGN GUIDE
PAGE 312
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
For roadside safety projects, generally a three or five year period is considered appropriate to
determine the average number of injury and fatal crashes per year for the base case (existing
conditions). It may be appropriate to adjust the base case crash rate to account for an expected
future increase in the frequency of crashes due to traffic growth (an example of this is demonstrated
in Section 12.3.4). For newly build roads, where there would not be any history of crashes, the
designer/engineer can estimate the average crash frequency, based on historic data of similar
roadways or facilities.
Example:
The number of crashes observed at a site is as shown in Figure 12.4. The observed crash frequency
for this site can be estimated as follows:
12
11
10
9
8 Average crash
Frequency
7
6
5
4
1 2 3 4 5 6
Year
Figure 12.4 – Example average crash frequency estimation
The second approach in the estimation of crashes is the use of statistical methods. These methods
are usually based on regression analyses and require detailed local traffic and road geometry data
to develop and calibrate. This type of comprehensive data is currently not available at Abu Dhabi
and the authors are not aware of any statistical crash prediction models developed for the local
conditions. However, these models can be developed in the future and therefore the
designer/engineer should keep up to date with latest developments and publications on this area.
Currently there are a number of international economic and risk assessment tools/manuals which
are widely used in different parts of the world. These tools/manuals make use of different statistical
models for the prediction of the number of crashes. However, these models are developed and
calibrated for their respective local traffic and road conditions and therefore they are not directly
applicable to the Abu Dhabi road network. References to these tools/manuals are provided; with a
brief description of each. Further information can be obtained from the individual sources.
Number
of
Crashes
Observed

288. ROADSIDE DESIGN GUIDE
PAGE 313
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
• AASHTO - Highway Safety Manual (HSM) [2]: The AASHTO HSM is a three volume
manual, which arguably provides the most comprehensive guidance on quantitative safety
analyses, among the resources available today. Part C of HSM provides a comprehensive
guide to prediction of crashes through development of Safety Performance Functions (SPFs).
SPFs are statistical base models, which are used to estimate the average crash frequency
for a facility type with specified base conditions. Once the SPFs are developed, the predicted
crashes for the base case are then adjusted for specific road characteristics through the use
of Crash Modification Factors (CMFs). The final step of the HSM prediction methods is the
calibration of the estimated crashes for local conditions through the use of a Calibration
Factor.
• Road Safety Analysis Program (RSAP) [1]: The RSAP is a computer program for
performing benefit-cost analysis on roadside design alternatives. The RSAP was originally
developed under NCHRP Project 22-9 and distributed with the 2002 edition of the AASHTO
Roadside Design Guide [6]. The RSAP encroachment module uses a two-step process to
estimate crash frequency. The first step involves estimating a base or average encroachment
rate based on highway type and then multiplying the encroachment rate with the traffic
volume to estimate encroachment frequency. The next step is to adjust the base
encroachment frequency to account for specific highway characteristics that affect
encroachment rates.
• Austroads Guide to Road Design – Part 6 [5]: Part 6 of the Austroads Guide to Road
Design: Roadside Design, Safety and Barriers include a crash frequency prediction model in
Section 4.6. The Austroads prediction model is very similar to the RSAP approach and the
reference is made to the RSAP base encroachment model as one of the recommended
resources. Similar to the RSAP method, the base encroachment rate is then adjusted through
several factors to predict the number of crashes on a specific road configuration. The
adjustment factors used in this model are developed to cater for the local conditions in
Australia.
• Road Restraint Risk Analysis Program (RRRAP) [3]: The RRRAP is roadside risk
assessment software developed as part of the UK design standard Design Manual for Roads
and Bridges (DMRB). The crash frequency prediction module used in RRRAP is similar to a
SPF as described in the HSM. The RRRAP is developed for the UK roads having a speed
limit of 50mph or greater and ADT of 5000 or greater.
• Selection of Appropriate Vehicle Restraint Systems (SAVeRS) [4]: SAVeRS was a cross
border funded research project for the Conference of European Directors of Roads. The final
result of the SAVeRS project was an Excel based barrier selection tool. This tool included a
run-off-road crash prediction module, which was developed and calibrated for Austria, Great
Britain, UK, Ireland, Italy and Sweden, using HSM methodology. The final tool of the SAVeRS
Project can be found at www.saversproject.com.

289. ROADSIDE DESIGN GUIDE
PAGE 314
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
12.3.1.2 Determination of the Reduction in Crash Rate Caused by the
Proposed Treatment
The second step in assessing the treatment benefits is the estimation of the amount of reduction in
crash rate caused by the proposed safety treatment. This is achieved through the use of Crash
Modification Factors (CMFs). A CMF is the ratio of the crash frequency of a site under two different
conditions and it represents the relative change in crash frequency due to change in one specific
condition, as shown in Equation 12.2. Therefore a CMF may serve as multiplicative factor to compute
the expected number of crashes after implementing a given treatment at a specific site, as shown in
Equation 12.3.
Equation 12.2
Where:
CMF = Crash Modification Factor
Nexpected A = Expected Average Crash Frequency with Site ConditionA
Nexpected B = Expected Average Crash Frequency with Site Condition B
Equation 12.3
Where:
Nwt = Expected Average Crash Frequency at the site with treatment
Nwot = Expected Average Crash Frequency at the site without treatment
With no change of conditions at a site, the value of CMF is 1.00. A CMF value less than 1.00 means
the treatment alternative reduces the estimated average crash frequency in comparison to the base
condition. A CMF value of more than 1.00 means the treatment alternative increases the estimated
average crash frequency in comparison to the base condition. The relationship between a CMF and
the expected percent change in crash frequency is shown in Equation 12.4. It should be noted that
the % reduction in crash frequency, as shown in Equation 12.4, is also referred to as a Crash
Reduction Factor (CRF) within the literature.
Equation 12.4
Example:
• If a CMF=0.85, then the expected percent change is 100 x (1.00 – 0.85) = 15%, indicating a
reduction in expected average crash frequency by 15%;
• If a CMF=1.25, then the expected percent change is 100 x (1.00 – 1.25) = - 25%, indicating
a 25% increase in expected average crash frequency.
CMFs are generally presented for the implementation of a particular treatment or an alternative
design. Examples include relocating a hazard beyond the clear zone, using passively safe lighting
columns, installing a semi-rigid barrier, changing the rigidity of a barrier, etc.
CMFs for different treatments are established by research studies, which have evaluated the effects
of applying roadside safety treatments. CMF development has been a hot topic in road safety
research for over two decades and there are many CMFs available in the published

290. ROADSIDE DESIGN GUIDE
PAGE 315
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
literature for many different types of treatments. Ideally, if available, the CMFs which are developed
with local data, for local conditions should be used. However, currently there are no CMFs developed
specifically for Abu Dhabi. In the future, as more data become available, research studies may
develop CMFs, which are specific to Abu Dhabi. Therefore, the engineer/designer should be
responsible of keeping their knowledge up to date. In the absence of local alternatives, internationally
developed CMFs may be used. However, when using these CMFs, the designer/engineer should
refer to the source research and understand the conditions under which the CMFs were estimated.
Some CMFs are developed for a particular type of crash, for example only run-off-road crashes,
while others may relate to all crashes recorded at a site. Similarly, some CMFs are developed to
predict certain types of incident severity, such as fatal crashes, injury crashes, property-damage only
crashes, whilst others are developed for all crashes, without the detail of severity. Sometimes
multiple CMFs may be available for the same treatment, from different research studies. In such a
case the designer/engineer should analyse and choose the one which suits the site under evaluation.
There are new CMFs being developed every day. The designer/engineer should check for new
research for updated and better fitting CMFs. A good resource for finding up to date CMFs is the
website: Crash Modification Factors Clearinghouse [7], which is funded by the U.S. Department of
Transport Federal Highway Administration and maintained by the University of North Carolina
Highways Safety Center. This website is a regularly updated online database of published CMFs,
including the CMFs from the HSM. It includes a search function, through which the designer/engineer
can find specific CMFs for many different types of safety treatments. References are also made to
each individual research, for more detailed information on each of the CMFs published on the
website.
Another good resource for CMFs is the Austroads Research Report – Improving Roadside Safety
[8]. This report provides a comprehensive literature review into the available roadside safety related
CMFs. There are many useful CMFs identified and presented within this report.
Table 12.1 presents a list of CMFs, which are selected from the international literature available. The
table does not contain every single published CMF to date and it is provided for guidance only. It is
the responsibility of the designer/engineer to understand the limitations by referring to the source
research. If they become available in the future, the designer/engineer should prefer CMFs which
are developed for local conditions.

291. ROADSIDE DESIGN GUIDE
PAGE 316
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Table 12.1 – Example roadside safety related CMFs from the literature
Type of Treatment CMF
Severity
Level
Crash
Type
Source
Hazard Removal, Relocation, Modification
Clear Zone Related
Remove or relocate fixed
hazards outside of clear
zone
0.29
Fatal
&
Injury
Run-off-
road
[9]
Relocate hazard (utility pole) -
increase in lateral offset by
1.5m
0.67 Injury
Run-off-
road
crashes
into utility
poles
[10]
On two-lane rural
roads, increase
roadside recovery
distance by:
1.5m 0.87
All Crashes*
Run-off-
road
[11]
2.4m 0.79
3.0m 0.75
4.6m 0.65
Reducing the number of hazards
Reduce
number
of poles
per
km
from 38 to 25 per
km
0.75
All Crashes*
All Crashes [11]
from 25 to 13 per
km
0.75
from 38 to 13 per
km
0.5
Traversable Side Slopes
On
Rural
two-
lane
roads
Flatten
Side Slope
from
1V:2H
to 1V:4H 0.90
All Crashes* Single
Vehicl
e
[2]
to 1V:5H 0.85
to 1V:6H 0.79
to 1V:7H 0.73
Flatten
Side Slope
from
1V:3H
to 1V:4H 0.92
to 1V:5H 0.86
to 1V:6H 0.81
to 1V:7H 0.74
Flatten
Side Slope
from
1V:4H
to 1V:5H 0.94
to 1V:6H 0.88
to 1V:7H 0.81
Flatten
Side Slope
from
1V:5H
to 1V:6H 0.94
to 1V:7H 0.86
Flatten
Side Slope
from
1V:6H
to 1V:7H 0.92

292. ROADSIDE DESIGN GUIDE
PAGE 317
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
On
Rural
multilan
e
highway
s
Change
Side Slope
from
1V:7H
1V:7H or
flatter 1.00
All Crashes*
All Crashes [2]
to 1V:6H 1.05
to 1V:5H 1.09
to 1V:4H 1.12
to 1V:2H
or steeper 1.18
* All Crashes include Fatal, Injury and Property Damage Only

293. ROADSIDE DESIGN GUIDE
PAGE 318
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Table 12.1 - Example roadside safety related CMFs from the literature (continued)
Type of Treatment CMF
Severity
Level
Crash
Type
Source
Hazard Removal, Relocation, Modification
Drainage Structures
Lengthen or extend culvert further
away from the road 0.56
All
Crashes* All
Crashes
[12]
Widen and flatten culvert outlets 0.00
Fatal
&
Injury
All
Crashes
[13]
Passively Safe Poles
Replace rigid pole with passively
safe poles (slip-base, impact
absorbing, etc.)
0.6
All
Crashes*
Run-off
Road
Crashes
on
Straight
[14]
0.4 Fatal All
Crashes
[9]
0.7 Injury All
Crashes
[9]
Move utility services
underground
0.6
All
Crashes* All
Crashes
[12]
Remove lighting poles in urban
area
0.6 Injury All
Crashes
[15]
Hazard Shielding
Roadside & Median Barriers
New semi-rigid roadside
barrier installation
0.7
All
Crashes*
Run-off-
road
[16]
0.44 Fatal
0.77 Injury
0.74 Fatal
&
Injury
0.66
Propert
y
Damag
e Only
Semi-rigid roadside barrier
installation on inside of
curves
0.72
Fatal
&
Injury
All
Crash
Types
[9]

294. ROADSIDE DESIGN GUIDE
PAGE 319
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Semi-rigid roadside barrier
installation on outside of
curves
0.37
Fatal
&
Injury
All
Crash
Types
[9]
Changing barrier along
embankment to less
rigid type
0.68 Injury Run-off-
road
[2]
0.59 Fatal
* All Crashes include Fatal, Injury and Property Damage Only

295. ROADSIDE DESIGN GUIDE
PAGE 320
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Table 12.1 - Example roadside safety related CMFs from the literature (continued)
Type of Treatment CMF
Severity
Level
Crash
Type
Source
Hazard Shielding
Roadside & Median Barriers (continued)
Installation of continuous
flexible barrier on
roadsides ad in medians
on a
rural
freewa
y
0.21 Injury
Run-
off-
road
and
cross-
median
head-
on
[17]
0.13
Seriou
s
Injury
on an
urban
freewa
y
0.14 Injury
0.17
Seriou
s
Injury
For ADT of
20,000 to
60,000 on
multilan
e
divided
highway
s
Install any type of
median barrier
0.57 Fatal
All Crashes [2]
0.7 Injury
1.24
All
Crashes*
Install steel median
barrier
0.65 Injury
Install cable median
barrier
0.71 Injury
Crash Cushions
Install Crash Cushion
0.31 Fatal
Fixed
object
Impact
s
[18]
0.31 Injury
0.54
Propert
y
Damag
e Only
* All Crashes include Fatal, Injury and Property Damage Only
Example:
The expected average crash frequency without treatment (Nwot) with a fixed object at a roadside
is estimated to be 4 injury crashes per year. It is planned to install a crash cushion in front of the
hazardous object to decrease the frequency of injurious accidents. Using
Table 12.1, a CMF=0.31 is chosen to estimate the decrease in injury accidents with fixed object
impacts, caused by a crash cushion installation.
Using Equation 12.3,
Nwt = Nwot× CMF

296. ROADSIDE DESIGN GUIDE
PAGE 321
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Nwt = 4 × 0.31 = 1.24 injury crashes per year

297. ROADSIDE DESIGN GUIDE
PAGE 322
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Therefore, the reduction in injury crash frequency, due to the installation of a crash cushion is
estimated as: 4.0 − 1.24 = 2.76 injury crashes per year. In other words a 69% reduction in the number
of accidents with an injurious outcome is expected.
12.3.1.3 Conversion of Benefits into a Monetary Value
Once the reduction in the annual crash frequency due to a treatment is estimated, these values
should then be converted into a monetary value. This can be achieved by multiplying the estimated
reduction in the crash frequency with the average societal cost of crashes as shown in Equation
12.5.
Equation 12.5
Where:
y = Year in the service life of the treatment
AVbenefits(y) = Annual Monetary Value of Benefits for year y
Cc = Average Societal Cost of a Crash
Nwt (y)= Expected Average Crash Frequency at the site for year y with treatment
Nwot (y) = Expected Average Crash Frequency at the site for year y without treatment
As can be seen from Equation 12.5, in order to calculate the monetary benefits of a treatment,
average societal crash costs (Cc) are required. Table 12.2 provides the average crash costs by
severity for Abu Dhabi. This table is only provided as an example. The designer/engineer should
always justify the reasoning behind the selected crash costs for a specific project.
Table 12.2 –Average societal costs of crashes [19]
Accident Type by Severity Per Crash (AED)
Fatal 2,596,212
Serious Injury 1,044,122
Moderate Injury 111,262
Minor Injury 49,508
Weighted Average for All Injuries including Fatal 460,413
Property Damage Only (PDO) 10,418
As can be seen from Table 12.2, the average societal costs may be available for individual types of
accidents by severity. Therefore Equation 12.5, in theory, can be applied to calculate the AVbenefits for
crash types of different severity. However, CMFs and the expected crash frequency estimations do
not always differentiate between fatal, serious and slight injury accidents. As a result, it is usually not
possible to estimate the number of expected crashes individually for different types of severity. For
this reason the usual practice is to establish an average societal cost that is representative of a
combined fatal/injury crash. This can be achieved by weighting the average crash costs by the
number of crashes in each type of severity. This is done for the 2009 values

298. ROADSIDE DESIGN GUIDE
PAGE 323
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
and the average crash cost for all fatal and injury accidents is estimated as AED 460,413, as shown
in Table 12.2.
Example:
The crash cushion installation shown in the previous example was estimated to reduce the number
of injury/fatal crashes by 2.76 per year. Assuming that this installation will increase the number of
PDO crashes by 2.00 per year; what is the annual monetary benefit (AVbenefit) associated with this
crash cushion installation?
Using Table 12.2 as a reference for Cc and applying Equation 12.5 for Injury and PDO crashes
separately:
AVbenefits for Injury/Fatal crashes: 2.76 x AED 460,413 = AED 1,270,740 per year
AVbenefits for PDO crashes: - 2.00 x AED10,418 = - AED 20,836 per year
Total AVbenefits for all crashes: AED1,270,740 - 20,836 = AED 1,249,904 per year
12.3.2 Assessment of Annual Treatment Costs
Estimating the project costs associated with implementing a treatment should follow the same
procedure as developing cost estimates for other highway construction projects. The expected costs
are likely to differ between sites and each treatment. The cost of implementing a treatment will
include a range of factors; for example, rights of way acquisition, material costs, earthworks, utility
relocation etc. All such costs should be included in the BCR Analysis. These include, but may not
be limited to:
• Project development, design and management;
• Rights of way costs, including land acquisition;
• Construction costs;
• Traffic management during construction;
• Operating costs;
• Maintenance costs; etc.
Some of these costs, such as construction costs, would occur at the beginning of the project while
the others, such as maintenance, occur over the life time of the project. These should be estimated
as annual costs (AVcosts) for each year and discounted into a present value as explained in Section
12.3.3.
12.3.3 Project Present Value of Costs and Benefits
Previous sections (12.3.1 and 12.3.2) presented the methodology to estimate the annual values (AV)
of treatment costs and benefits. However, in economic analysis all costs and benefits incurred in
future years should be discounted to an equivalent Present Value (PV). This is done to reflect the
value of money over time. Due to depreciation and the society’s preferences for current consumption
over long term investments, the benefits which will occur in the future are valued less

299. ROADSIDE DESIGN GUIDE
PAGE 324
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
today. Adjustment of annual monetary values into present values is achieved through the use of a
present worth factor (Fp), as shown in Equation 12.6, Equation 12.7 and Equation 12.8.
Equation 12.6
Equation 12.7
Where:
PVbenefits = Present value of project benefits
PVcosts = Present value of project costs
AVbenefits(y) = Annual Monetary value of project benefits for year y
AVcosts (y) = Annual Monetary value of project costs for year y
y = Year in the service life of the treatment
Ep = Number of years (evaluation period or project life) for which the annual costs are to be
discounted.
Fp (y) = Present worth factor for year y
Equation 12.8
Where:
Fp(y) = Present worth factor for year y
y = Year in the service life of the treatment
i = Discount Rate (i.e., if the discount rate is 5 percent, i = 0.05)
12.3.4 Example BCR Calculation
The example presented in this section illustrates the process for calculating the benefits and costs
for three alternative safety treatments at a problematic road section. This example does not belong
to a real case study, but rather it is designed to demonstrate the processes involved in a BCR
calculation. The values presented in this example, such as costs of individual countermeasures, or
the expected crash frequency, may not be accurate in terms of real world values. The
designer/engineer should therefore not use any of the values presented in this example in their BCR
calculations.
Background Information:
The roadside along a section of highway is under safety evaluation. The initial assessment revealed
that the rigid lighting columns along the road are all located within the clear zone. Engineers have
identified the following three treatment options to mitigate the risk posed by the lighting columns:
• Treatment Option 1: Relocate the rigid lighting columns beyond the clear zone;

300. ROADSIDE DESIGN GUIDE
PAGE 325
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
• Treatment Option 2: Replace the rigid lighting columns with a passively safe alternative
design;
• Treatment Option 3: Shield the rigid lighting columns with a semi-rigid barrier;
The Facts:
The roadway agency has analysed the crash history along the road under evaluation and decided
the following frequency is a good estimation of the expected casualty crashes (fatal/injury) with rigid
lighting poles, if the roadside is left in its current condition:
• Nwot = 0.4 casualty crashes per year.
A 2% annual increase in the crash frequency is also estimated, as a result of the expected future
increase in traffic volume in the area.
Following a literature review, the following CMFs were identified as suitable for the proposed
treatment options (see Table 12.1):
CMF1 = 0.29, “Remove or relocate fixed hazards outside of clear zone, for fatal & injury, run-off-
road crashes [9]”
• CMF2 = 0.60 “Replace rigid pole with passively safe poles (slip-base, impact absorbing,
etc.), for fatal & injury, Run-off Road Crashes on Straight [14]”
• CMF3 = 0.74 “New semi-rigid roadside barrier installation, for fatal & injury, run-off-road
crashes [16]”
The roadway agency finds the societal crash costs shown in Table 12.2 acceptable. The agency
decided to conservatively estimate the economic benefits of countermeasures. Therefore, they are
using the average injury crash cost (i.e. the weighted average of all severities including fatal) as the
crash cost value (Cc) representative of the predicted fatal and injury crashes.
• Cc= AED460,413
The discount rate (i) is accepted as the following:
• i = 4.0%
The evaluation period (Ep) is selected as the following:
• Ep= 10 years – Please note that 10 years is chosen, to keep the length of calculations and
the space required for this example at a reasonable limit. In reality, the design life of the
treatment is likely to be chosen as the analysis period.
The costs of each treatment option are estimated as follows:
• Treatment Option 1: An initial construction cost of AED 166,800, with negligible annual
costs in the following years.
• Treatment Option 2: An initial construction and equipment cost of AED 150,000, with an
annual repair and maintenance cost of AED 6,255 in the following years.

301. ROADSIDE DESIGN GUIDE
PAGE 326
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
• Treatment Option 3: An initial construction and equipment cost of AED 120,000, with an
annual repair and maintenance cost of AED 21,016 in the following years.
Solution:
Step 1: Calculate the expected frequency of crashes with (Nwt) and without (Nwot) treatment
Expected crash frequency without any treatment (Nwot) is calculated for each year, as shown in Table
12.3. The initial crash frequency of 0.4 crashes per year is adjusted with an annual increase of 2%
to include the effect of expected increase in traffic volume in the area.
Once the expected crash frequency (Nwot) for each year is estimated, the individual CMFs for each
treatment are used with Equation 12.3 to calculate the expected crash frequencies (Nwt) after each
treatment, as shown in Table 12.3.
It can be seen that, relocation of the hazard is estimated to provide the highest reduction in crash
frequency. This is followed by the use of passively safe columns and the use of a semi-rigid barrier.
Table 12.3 – Estimated annual reduction in crash frequency by each treatment
Year
in
Servic
e Life
(y)
Expected
Crash
Frequency
without
Treatment
(Nwot)
(Crashes/Yea
r)
Treatment 1 -
Hazards removed
or relocated
beyond
clear
zone
Treatment 2 -
Hazards made
passively safe
Treatment 3 -
Hazards
shielded with a
semi-rigid
barrie
r
CMF1
Expected
Crash
Frequenc
y (Nwt1)
CMF2
Expected
Crash
Frequenc
y (Nwt2)
CMF3
Expected
Crash
Frequenc
y (Nwt3)
1 0.40 0.2
9
0.12 0.6
0
0.2
4
0.7
4
0.3
0
2 0.41 0.2
9
0.12 0.6
0
0.2
4
0.7
4
0.3
0
3 0.42 0.2
9
0.12 0.6
0
0.2
5
0.7
4
0.3
1
4 0.42 0.2
9
0.12 0.6
0
0.2
5
0.7
4
0.3
1
5 0.43 0.2
9
0.13 0.6
0
0.2
6
0.7
4
0.3
2
6 0.44 0.2
9
0.13 0.6
0
0.2
6
0.7
4
0.3
3
7 0.45 0.2
9
0.13 0.6
0
0.2
7
0.7
4
0.3
3
8 0.46 0.2
9
0.13 0.6
0
0.2
8
0.7
4
0.3
4
9 0.47 0.2
9
0.14 0.6
0
0.2
8
0.7
4
0.3
5
10 0.48 0.2
9
0.14 0.6
0
0.2
9
0.7
4
0.3
5

302. ROADSIDE DESIGN GUIDE
PAGE 327
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Tota
l
4.38 1.27 2.63 3.24
Step 2: Calculate the annual monetary benefits (AVbenefits) caused by reduction in crash rate
for each treatment
Equation 12.5 is used to estimate annual monetary benefits for each year, as shown in

303. ROADSIDE DESIGN GUIDE
PAGE 324
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Table 12.4:
Table 12.4 – Annual monetary benefits of change in crashes caused by each treatment
Year
in
Servic
e Life
(y)
Average
Cost of a
Crash (Cc)
(AED)
Treatment 1 Treatment 2 Treatment 3
Average
Reductio
n in
Crash
Frequenc
y (Nwot-
Nwt1)
Annual
Monetar
y
Benefits
(AVbenefits)
(AED)
Average
Reductio
n in
Crash
Frequenc
y (Nwot-
Nwt2)
Annual
Monetar
y
Benefits
(AVbenefits
) (AED)
Average
Reductio
n in
Crash
Frequenc
y (Nwot-
Nwt3)
Annual
Monetar
y
Benefits
(AVbenefits
) (AED)
1 460,413 0.28 130,75
7
0.1
6
73,666 0.10 47,883
2 460,413 0.29 133,37
2
0.1
6
75,139 0.11 48,841
3 460,413 0.30 136,04
0
0.1
7
76,642 0.11 49,817
4 460,413 0.30 138,76
1
0.1
7
78,175 0.11 50,814
5 460,413 0.31 141,53
6
0.1
7
79,739 0.11 51,830
6 460,413 0.31 144,36
7
0.1
8
81,333 0.11 52,867
7 460,413 0.32 147,25
4
0.1
8
82,960 0.12 53,924
8 460,413 0.33 150,19
9
0.1
8
84,619 0.12 55,002
9 460,413 0.33 153,20
3
0.1
9
86,312 0.12 56,103
10 460,413 0.34 156,26
7
0.1
9
88,038 0.12 57,225
Step 3: Convert the annual monetary benefits (AVbenefits) into present value of benefits
(PVbenefits)
Equation 12.6 is used to convert the annual monetary benefits (AVbenefits) into present value of
benefits (PVbenefits) for each treatment, as shown in Table 12.5.
Table 12.5 – Converting annual values to present values (benefits)
Treatment 1 Treatment 2 Treatment 3

304. ROADSIDE DESIGN GUIDE
PAGE 325
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Year
in
Servic
e Life
(y)
Present
Wort
h
Facto
r (Fp)
Annual
Monetar
y Costs
(AVcosts)
(AED)
Present
Value of
Costs
(PVcosts)
(AED)
Annual
Monetar
y Costs
(AVcosts)
(AED)
Presen
t Value
of
Costs
(PVcosts)
(AED)
Annual
Monetar
y Costs
(AVcosts)
(AED)
Presen
t Value
of
Costs
(PVcosts)
(AED)
1 1.00 130,75
7
130,757 73,666 73,666 47,883 47,883
2 0.92 133,37
2
123,310 75,139 69,471 48,841 45,156
3 0.89 136,04
0
120,939 76,642 68,135 49,817 44,288
4 0.85 138,76
1
118,613 78,175 66,824 50,814 43,436
5 0.82 141,53
6
116,332 79,739 65,539 51,830 42,601
6 0.79 144,36
7
114,095 81,333 64,279 52,867 41,781
7 0.76 147,25
4
111,901 82,960 63,043 53,924 40,978
8 0.73 150,19
9
109,749 84,619 61,830 55,002 40,190

305. ROADSIDE DESIGN GUIDE
PAGE 325
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
9 0.70 153,20
3
107,638 86,312 60,641 56,103 39,417
10 0.68 156,26
7
105,568 88,038 59,475 57,225 38,659
Tota
l
1,158,90
4
652,903 424,387
Step 4: Convert the annual monetary costs (AVcosts) into present value of costs (PVcosts)
Table 12.6 presents the estimated annual project costs for each one of the treatment options.
Please observe that Treatment Option 1 is estimated to have only an initial construction cost, while
Treatment Options 2 & 3 are estimated to have initial construction, equipment, annual
maintenance and crash repair costs. Once the annual costs are estimated, Equation 12.7 is then
used to convert the annual monetary costs (AVcosts) into present value of costs (PVcosts) for
each treatment, as shown in Table 12.6
Table 12.6 - Converting annual values to present values (costs)
Year
in
Servic
e Life
(y)
Presen
t
Worth
Factor
(Fp)
Treatment 1 Treatment 2 Treatment 3
Annual
Monetar
y Costs
(AVcosts)
(AED)
Presen
t Value
of
Costs
(PVcosts)
(AED)
Annual
Monetary Costs
(AVcosts) (AED)
Presen
t Value
of
Costs
(PVcosts)
(AED)
Annual
Monetar
y Costs
(AVcosts)
(AED)
Presen
t Value
of
Costs
(PVcosts)
(AED)
1 1.0 166,80
0
166,80
0
150,000 150,00
0
120,00
0
120,00
0
2 0.9 0 0 6,255 5,783 21,016 19,430
3 0.9 0 0 6,255 5,561 21,016 18,683
4 0.9 0 0 6,255 5,347 21,016 17,965
5 0.8 0 0 6,255 5,141 21,016 17,274
6 0.8 0 0 6,255 4,943 21,016 16,609
7 0.8 0 0 6,255 4,753 21,016 15,970
8 0.7 0 0 6,255 4,570 21,016 15,356
9 0.7 0 0 6,255 4,395 21,016 14,766
10 0.7 0 0 6,255 4,226 21,016 14,198
Tota
l
166,800 194,719 270,251
Step 5: Calculate the BCR
Once the present value of costs (PVcosts) and benefits (PVbenefits) are estimated, the BCR can then
be calculated for each treatment option by using Equation 12.1, as shown in Table 12.7.
Table 12.7 – Calculation of the BCR for each treatment option

306. ROADSIDE DESIGN GUIDE
PAGE 326
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Treatment 1 Treatment 2 Treatment 3
PVcosts (AED) 166,800 194,719 270,251
PVbenefits (AED) 1,158,904 652,903 424,387
BCR 6.9 3.4 1.6

307. ROADSIDE DESIGN GUIDE
PAGE 327
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Discussion of Results:
This example demonstrated BCR calculations for three alternative treatment options. The results
show that all treatment options are economically feasible as the BCR for all are over 1.00. Of the
three options, relocation of the hazards is expected to provide the highest BCR with a value of 6.9.
However, in reality, relocating lighting columns beyond the clear zone may not be applicable. This is
because the lighting columns should be located within a certain distance from the travelled way to
fulfil their intended function. Normally, this option could have been discarded even before going into
lengthy BCR calculations. However, it was included in this example on purpose to show the effects
of such a treatment.
Among the two practicable treatment options, use of passively safe lighting columns provides the
highest BCR with 3.4, while shielding the existing columns with a barrier provides a BCR of 1.6. The
use of passively safe columns is the likely choice of treatment for this situation, as it provides higher
benefits for lower costs.
It can also be observed that the initial cost of using passively safe columns is estimated to be higher
than the initial cost of a semi-rigid barrier installation. However, as the annual maintenance and crash
repair costs for the barrier are estimated to be higher, the use of passively safe columns is expected
to be the cheaper option over the 10 year analysis period. These numbers were selected on purpose
to show that the option with the cheapest initial cost may not always be the cheapest over a longer
period. In reality the initial and following annual costs of a barrier and a passively safe column would
change from one product to another.
8.4 Treatment Prioritization Methods
Once the CBR Analysis is complete, the designer/engineer can identify the treatment options which
are not economically feasible and eliminate these from further consideration. The following task is to
choose one of the economically feasible options for application. At this stage the designer/engineer
may choose to make a decision based on one or more of the following considerations:
• Economic effectiveness – Ranking by Incremental BCR;
• The amount of risk reduction – Ranking by Risk Reduction;
• Non-monetary considerations.
Each site is different and the importance of one of these considerations may be higher for some sites
than the others. Therefore, the designer/engineer should be aware of them all and make an informed
decision based on engineering judgment to choose the best option for the specific site. To help with
the decision process, the designer/engineer may choose to rank and prioritize the treatment options
based on these criteria. This section provides guidance into how these rankings can be carried out.
12.4.1 Ranking by Incremental BCR
The first way of ranking treatment options is through their economic effectiveness. A good measure
for economic effectiveness is the BCR. At this point of economic assessment, BCR for each
treatment option will already be available to the designer/engineer. A simple way of comparing
alternative treatment options is simply ranking them by their BCR in decreasing order.

308. ROADSIDE DESIGN GUIDE
PAGE 328
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
The project with the highest BCR is estimated to provide the highest monetary return with respect to
the investment required. This type of ranking is easy to interpret when the project with the highest
benefits is also the project with the lowest cost, as was the case with the example shown in Section
12.3.4.
However, there are some situations where it is not straightforward to choose one treatment option
over the other, simply by comparing their BCR. As previously explained in Section 12.3, a high BCR
may be a consequence of a very low cost treatment, such as delineation of a hazard, with relatively
high benefits. Meanwhile a more expensive treatment, such as installation of a crash cushion, may
generate very high benefits, but at a higher cost and therefore generate a lower BCR. One such
example is shown in Table 12.8. In this example Treatment 1 has a higher BCR (5.00) compared to
Treatment 2 (2.00). However, Treatment 2 provides much higher benefits (AED 100,000) compared
to Treatment 1 (AED50,000). In such a situation, choosing only by BCR alone would lead to a very
simple treatment, which would not lead to a significant improvement. On the other hand, to choose
Treatment 2, the designer/engineer should be able to justify the extra costs required. In such cases
an Incremental BCR Analysis can be used to make more informed decisions.
Table 12.8 – Example situation, where BCR does not provide a clear choice
Treatment 1 Treatment 2
PVcosts (AED) 10,000 50,000
PVbenefits (AED) 50,000 100,000
BCR 5.00 2.00
Incremental BCR Analysis is an extension to the individual BCR calculations for alternative treatment
options. Incremental CBA provides the designer/engineer a method through which they can compare
alternative treatment options and assess if the additional cost required to implement an alternative
treatment are justified by the added benefits.
To calculate the incremental CBA the following procedures should be undertaken:
Step 1. Calculate the BCR for all alternative treatment options.
Step 2. Arrange all alternative treatment options with a BCR>1.0, in ascending order based on
their estimated cost (PVcosts). The project with the lowest cost is ranked first.
Step 3. Calculate the incremental B/C ratio (BCRb/a) of the second treatment option with respect
to the first one, using Equation 12.9:
Equation 12.9

309. ROADSIDE DESIGN GUIDE
PAGE 329
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Where:
BCRb/a = Incremental BCR of treatment option b with respect to option a
PVbenefits_a , PVbenefits_b = Present value of benefits for treatment options a and b
PVcosts_a , PVcosts_b = Present value of costs for treatment options a and b
a = treatment option with the lower cost compared to option b
b = treatment option with the higher cost compared to option a
Step 4. If the BCRb/a > 1.0, the additional funds required to implement option b rather than a yield
more benefit than the incremental increase in cost. Therefore option b is preferred over a.
Analysis continues with the comparison of b to the next treatment option in the list.
If the BCRb/a < 1.0, the additional funds required to implement option b rather than a yield
less benefit than the incremental increase in cost. Therefore option b is not preferred over
a. Analysis continues with the comparison of a to the next project in the list.
If the costs (PVcosts) for two options are equal, the option which provides higher benefits for
the same cost is preferred. Analysis continues with the comparison of the chosen option
with the next one on the list. This process is repeated. The project selected in the final
pairing is considered to be the best investment on economic grounds.
Step 5. Continue Steps 3 and 4 until a comparison with the last (highest cost) treatment option in
the list. Treatment option selected in the last comparison is considered the best economic
investment.
Step 6. Once the best economic investment is identified, steps 2 to 5 can be repeated for the
remaining options to identify the second best investment. This process can be repeated
until the ranking of every treatment option is identified.
Example:
Calculate the incremental BCR for the example shown in Table 12.8.
Using Equation 12.9, BCRtreatment2/treatment1 = (100,000 – 50,000) / (50,000 – 10,000) = 1.25
The result shows that the added funds required for the implementation of treatment Option 2 over
Option 1 yield more benefit than the incremental increase in cost. Therefore Option 2 is the better
economic investment.
Example:
Table 12.9 shows an example of a typical incremental BCR analysis. In this example there are four
alternative treatment options to choose from. As can be seen from the table, alternative treatment
options are listed from left to right with an order of increasing costs (PVcosts). The analysis starts with
the comparison of the second cheapest option, Treatment 2, with the cheapest option,

310. ROADSIDE DESIGN GUIDE
PAGE 330
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
Treatment 1. Using Equation 12.9, the BCR2/1 is calculated as 1.25. This value is over 1.00 therefore
Treatment 2 is preferred over Treatment 1.
The analysis continues with the comparison of Treatment 2 with the next one, which is Treatment
3. Again using Equation 12.9, BCR3/2 is calculated as 0.40. This value is less than 1.0 and therefore
the added cost of Treatment 3 over Treatment 2 is not justified by the relative increase in benefits.
Treatment 2 is still the preferred option.
The analysis continues with the comparison of Treatment 2 with the next one on the list, which is
Treatment 4. Once again using Equation 12.9, BCR4/2 is calculated as 7.40. This value is over 1.0
and therefore Treatment 4 is preferred over Treatment 2. Since Treatment 4 is the last option in the
list, there are no more comparisons to make, therefore it can be concluded that Treatment 4 is the
best economic investment among the alternatives.
Table 12.9 – Example of incremental BCR selection
To achieve a full economic ranking of all treatment options, Treatment 4 is removed from the table
and the process described above is repeated for the remaining options. This will show that the
second best economic investment is Treatment 2. Treatment 2 is then removed from the list for the
final comparison, which reveals that Treatment 1 is the third best economic investment. Therefore,
the economic ranking of the alternative treatment options is as follows:
1. Treatment Option 4
2. Treatment Option 2
3. Treatment Option 1
4. Treatment Option 3
12.4.2 Ranking by Risk Reduction
The second way of ranking treatment options is by the amount of risk reduction provided. As
previously shown in Table 12.8, a treatment option with the highest BCR does not necessarily
provide the highest amount of risk reduction. Cost effectiveness is essential for a well targeted road
safety treatment. However, this should be achieved while providing an acceptable level of benefits,
i.e. reduction in the number and/or severity of crashes. To ensure this, local road authorities can
often set targets for minimum acceptable risk. For example in UK, roadside design

311. ROADSIDE DESIGN GUIDE
PAGE 331
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
decisions are done through the software RRRAP [3]. The RRRAP calculates the risk for each
treatment option and expresses the risk in equivalent fatalities per 100million vehicle km travelled. If
the risk after a treatment is expected to be above a certain value (this value is currently not public
information), the level of risk and therefore the treatment option is considered unacceptable [20].
Similarly the road authority or the designer/engineer may choose to rank the alternative treatment
options from a number of different risk reduction measures. These measures include:
• Monetary value of treatment benefits;
• Total number of crashes reduced;
• Number of fatal and incapacitating injury accidents reduced;
• Number of fatal and injury crashes reduced.
As an outcome of a ranking procedure, the project list is ranked high to low on any one of the above
measures. At this point the road authority or the designer/engineer may choose to set a certain level
of risk reduction as a minimum and eliminate any treatment options which do not provide the
minimum desired level of risk reduction. Many simple improvement decisions, especially those
involving only a few sites and a limited number of project alternatives for each site can be made by
reviewing rankings based on two or more of these criteria.
Example:
Table 12.10Table 12.10 presents an example scenario which demonstrates how the amount of risk
reduction provided can affect the final decision, in treatment selection. According to this scenario,
the road authority has a set goal of decreasing the frequency of injury accidents by 50% within the
next 10 years. A problematic site is chosen for safety improvements. There are three alternative
treatment options identified to decrease the frequency of injury crashes observed at the site.
Table 12.10, the first treatment option is estimated to provide a 35% reduction, while treatment
options 2 and 3 are estimated to provide 60% and 70% reduction respectively. In-line with their
casualty reduction targets, the road authority does not consider a 35% reduction high enough.
Therefore treatment option 1 is discarded. An incremental BCR is calculated between options 2 and
3 as follows:
BCRtreatment3/treatment2 = (350,000 – 300,000) / (190,000 – 150,000) = 1.25
As the BCR is larger than 1.0, the treatment option 3 is chosen over treatment 2.
Table 12.10 – Example of ranking by risk reduction
Treatment
Option 1
Treatment
Option 2
Treatment
Option 3
% Reduction in Crashes 35% 60% 70%
PVcosts (AED) 14,000 150,000 190,000
PVbenefits (AED) 175,000 300,000 350,000
BCR 12.5 2.0 1.8

312. ROADSIDE DESIGN GUIDE
PAGE 332
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
However, this selection could have been different if the road authority did not have a specific
percentage of risk reduction set as a threshold value. In such a situation the treatment option 1 would
not have been discarded. In that case, the results of an incremental BCR analysis shows that the
added funds required for the implementation of treatment options 2 and 3 over option 1 doesn’t yield
more benefit than the incremental increase in cost. Therefore, Option 1 is chosen as the better
economic investment.
BCRtreatment2/treatment1 = (300,000 – 175,000) / (150,000 – 14,000) = 0.92; 0.92<1.00
BCRtreatment3/treatment1 = (350,000 – 175,000) / (190,000 – 14,000) = 0.99; 0.99<1.00
As demonstrated within this example, some roadside safety treatments may provide a good value
for money. However, the amount of risk reduction provided may not always be considered enough.
12.4.3 Non-Monetary Considerations
In most cases, the main benefits of applying a roadside safety treatment can be quantified in
monetary terms; i.e. the monetary gains expected due to a reduction in crash frequency, severity,
and the associated repair costs. However, implementing safety counter-measures can have several
impacts some of which cannot be evaluated using monetary criteria. These are nevertheless
important and should form part of the decision-making process. Examples to non- monetary impacts
include the following:
• Public demands & road user needs;
• Public perception of road safety improvements;
• Meeting established community objectives to improve safety or accessibility along a
particular route or in a certain area;
• Air quality, noise, visual intrusion or other environmental considerations;
• Aesthetics;
• Experience from other, similar sites;
• In-service performance of treatment options.
As these considerations cannot be quantified, their effect in the final decision should be evaluated
on a case by case basis through engineering judgment. For example, aesthetics may be of a
significant importance in the selection of a certain type of treatment over the other alternatives around
areas of natural beauty, land marks, major tourist attractions, etc. while it may not be an important
factor in a remote rural area of no special importance. In some cases the designer/engineer may
choose to apply a certain treatment option to satisfy the public demand, although it may not be the
best option from an economic perspective. For example, one may choose to install a motorcyclist
protection system on a certain location to satisfy the demands of a motorcyclist action group.
Non-monetary considerations can be of significant importance in the final decision; however, the
designer/engineer should always ensure that an adequate level of safety is provided.
12.4.4 Selection of an Appropriate Treatment Option
Once the risk reduction and BCR ranking, and the non-monetary assessment of treatment options
are complete, the designer/engineer should find a balance between the risk reduction, cost

313. ROADSIDE DESIGN GUIDE
PAGE 333
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
effectiveness and non-monetary considerations. As each site is different, in some scenarios
monetary constraints will be the decisive factor, in others amount of risk reduction may be, and in
some unique situations, non-monetary considerations may be more important than cost
effectiveness. It is therefore up to the DoT to specify which is the priority for the specific project, and
up to the designer/engineer to fulfil these requirements, ensuring that engineering judgment should
be used to find the optimal solution that fits the needs of the particular site. More information on the
final selection of the optimal roadside treatment is provided in Chapter 2.
8.5 Summary and Conclusions
This chapter provides a general guidance to the designer/engineer on roadside safety economic
assessment process. Comprehensive economic analyses usually require a considerable amount of
data and local crash prediction models, which are not available for Abu Dhabi at the moment. Due
to these limitations, the guidance provided in this Chapter is aimed for designer/engineer, which may
not have access to a wide range of data. References are also made to more comprehensive
international methods and tools.
The economic assessment process starts with the assessment of economic feasibility for each
treatment option identified for the roadside under evaluation. Recommended method for this
assessment is benefit/cost ratio (BCR). BCR calculation involves the following steps:
• Assessment of Treatment Benefits;
o Determination of the Expected Crash Rate;
o Determination of the Reduction in Crash Rate Caused by the Proposed Treatment;
o Conversion of Benefits into a Monetary Value;
• Assessment of Treatment Costs;
• Discounting of Costs and Benefits;
• Calculation of BCR.
Each of these steps is supplemented with example calculations, which demonstrates all steps
included in a BCR analysis. References are also made to international resources, to help the
designer/engineer identify key parameters, such as crash modification factors (CMFs) & average
crash costs, in the absence of local values.
Once the BCR for each treatment option is calculated, the ones with a BCR less than 1.0 are
eliminated from the analysis, as these are considered as economically infeasible. The assessment
then continues with prioritization of the economically feasible treatment options from different
perspectives. Guidance is given to help the designer/engineer to assess and/or rank the treatment
options, based on the following criteria:
• Economic effectiveness;
• The amount of risk reduction;
• Non-monetary considerations.
Following the assessments based on these criteria, the designer/engineer can then choose the most
appropriate treatment option for the site under evaluation, based on engineering judgment.

314. ROADSIDE DESIGN GUIDE
PAGE 334
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
8.6 References
[1] K. K. Mak and D. L. Sicking, “NCHRP 492 - Roadside Safety Analysis Program (RSAP)
Engineer's Manual,” Transportation Research Board, Washington, D.C., 2003.
[2] AASHTO, Highway Safety Manual, 1st Edition, Washington D.C.: American Association of
Highway and Transportation Officials, 2010.
[3] TD19/06 Design Manual for Roads and Bridges, Volume2 Highway Structures: Design, Section
2 Special Structures, Part 8, The Highways Agency, Transport Scotland, Welsh Assembly
Government, The Department for Regional Development Norther Ireland, 2006.
[4] CEDR, “SAVERS (Selection of Appropriate Vehicle Restraint Systems),” Conference of
European Directors of Roads, 2015.
[5] Austroads, Guide to Road Design Part 6: Roadside Design, Safety and Barriers, Sydney, NSW:
Austroads, 2010.
[6] AASHTO, Roadside Design Guide, Washington D.C.: American Association of Highway and
Transportation Officials, 2002.
[7] University of North Carolina Highway Safety Research Center, “Crash Modification Factors
Clearinghouse,” U.S. Department of Transport Federal Highway Administration, [Online].
Available: http://www.cmfclearinghouse.org/. [Accessed 26 10 2015].
[8] C. Jurewicz, L. Steinmetz, C. Phillips, G. Veith and J. McLean, “Improving Roadside Safety,
Stage 4 - Interim Report (AP-R436-14),” Austroads, Sydney, Australia, 2014.
[9] A. Gan, J. Shen and A. Rodriguez, “Update of Florida crash reduction factors and
countermeasures to improve the development of district safety improvement projects: final
report,” Florida Department of Transportation, Tallahassee, FL, USA, 2005.
[10] C. V. Zageer, “SETTING PRIORITIES FOR REDUCING UTILITY POLE CRASHES,”
Transportation Research Circular, no. E-C030, pp. 9-31, 2001-4.
[11] C. Zegeer, J. Hummer, D. Reinfurt, L. Herf and W. Hunter, “Safety cost-effectiveness of
incremental changes in cross-section design: informational guide, report FHWA/RD-87/094,”
Federal Highway Administration, Washington, DC, USA, 1987.
[12] Federal Highway Administration, Toolbox of countermeasures and their potential effectiveness
for roadway departure crashes, Washington, DC, USA: FHWA, 2008.
[13] B. Corben and S. Newstead, Evaluation of the 1992-1996 Transport Accident Commission
funded accident blackspot treatment program in Victoria, report 182, Melbourne, Vic.: Monash
University Accident Research Centre, 2001.
[14] Roads and Traffic Authority, Accident reduction guide Part 1: accident investigation and
prevention, report TD2004/RS01, Sydney, NSW: RTA, 2004.
[15] VicRoads, ‘Road safety program: guidelines for the selection of projects under the road
conditions sub-program (incorporating accident blackspot projects, mass action projects,

315. ROADSIDE DESIGN GUIDE
PAGE 335
12 ECONOMIC ASSESSMENT FIRST EDITION -DECEMBER 2016
railway level crossing projects)’, Kew, Vic: VicRoads, 1990.
[16] Arizona Department of Transportation, Traffic engineering policies, guides and procedures:
section 231: benefit/cost ratio economic analysis, Phoenix, AZ, USA: Arizona DOT, 2009.
[17] N. Candappa, A. D’Elia, B. Corben and S. Newstead, Evaluation of the effectiveness of flexible
barriers along Victorian roads: final report, report 291, Clayton, Vic: Monash University Accident
Research Centre, 2009.
[18] R. Elvik, A. Hoye, T. Vaa and M. Sorensen, The handbook of road safety measures, 2nd edition,
Bingley, UK: Emerald, 2009.
[19] Abu Dhabi Department of Transport, Summary of Crash and Injury Costs, 2009.
[20] Mouchel Parkman, “Guidance on the use of the Road Restraint Risk Assessment Process
(RRRAP) associated with TD 19/06,” Mar 2011. [Online]. Available:
http://www.standardsforhighways.co.uk/tech_info/rrrap.htm. [Accessed 20 October 2015].

316. ROADSIDE DESIGN GUIDE
PAGE 335
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
9 URBAN ROADSIDE DESIGN
9.1 Introduction
Previous chapters have provided a detailed description of the main approaches to safe roadside
design for roads outside built-up areas. However, when considering roads in urban areas, there are
some important differences that have to be taken into account. In particular:
• Speed limits and traffic speeds are often lower;
• Traffic volumes are likely to be higher than for equivalent roads in rural areas;
• Traffic speeds vary more between peak and off-peak periods;
• There will be greater numbers of pedestrians and cyclists in the vicinity of the road, and
needing to cross;
• Intersections and driveways will be much more closely spaced;
• The edge of the carriageway will often be curbed;
• Parking, pick-up and set-down (e.g. taxis) and loading will often take place at the curb side;
• Bus stops will be more commonplace, with associated signposts and shelters at the curb
side and stationary buses;
• There will be more street furniture and facilities used by pedestrians, such as seating,
refuse bins, public telephones;
• Where shops and cafes are present, there are likely to be additional signs, including
advertising boards;
• Public utilities install roadside poles and equipment cabinets, and more roadworks for
maintenance and installation.
Crucially, space is more constrained, with the width available for the highway already limited by
existing developments. This means there is often less space available for separating vehicles from
pedestrians and cyclists, in providing clearance zones and in meeting the requirements for sightlines.
This Chapter therefore discusses how the issues listed above are taken into account in roadside
design in urban areas, and identifies where the practices described elsewhere in this guide may
need to be modified. It is strongly recommended that when planning any urban highway scheme, an
initial assessment is made of these local factors at an early stage in the design process. In particular,
gathering information on pedestrian and cycle demand, including an assessment of desire lines (the
most direct routes between the main origins and destinations) will make it easier to ensure that their
needs are taken into account in the design, and that conflicts can be avoided.

317. ROADSIDE DESIGN GUIDE
PAGE 336
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
9.2 Hazards on the Sidewalk
With constrained space next to the roadside the sidewalk becomes a natural location for many
features that have the potential to present hazards to road users. These include poles for road signs
and signals; utility poles and cabinets; bus stops and shelters; refuse bins; public seating and cycle
parking. Where streets are significantly used for shopping or cafes there may be advertising boards
and stalls/kiosks for street vendors. There may also be pedestrian guard railings, and trees.
It is important to distinguish between hazards to errant vehicles encroaching on to the sidewalk, and
hazards to pedestrians on the sidewalk. In the latter case the main risk is from errant vehicles,
although consideration also needs to be given to the risks (including trips and falls) to pedestrians,
and the obstruction caused by poorly designed features on the sidewalk. Strategies to minimise risk
of conflict between motor vehicles and pedestrians are detailed in Section 13.4.
From the perspective of vehicles travelling along the carriageway, the following hazards are
presented by features on the sidewalk [1]:
• Collision in the event that the vehicle leaves the carriageway;
• Reduced sightlines;
• Adverse impacts on lane position, including encroachment into adjacent or opposing lanes
if drivers feel it necessary to increase their passing distance;
• The risk of contact with protruding parts of the vehicle (e.g. mirrors) and the overhang of
long vehicles.
It is recommended that a minimum clear-zone of 0.5m should be provided (0.9m at intersections) to
avoid the problems listed above. Ideally, this should be 1.2m from the curb [1]; research undertaken
in the United States in 2008 showed that 80% of crashes in an urban environment involved an object
with lateral offset equal to or less than 1.2m [2]. The clear-zone value of 0.5m should be considered
the minimum standard and where space constraints permit the value of 1.2m should be used,
especially at a number of potential high risk zones as detailed in Section 13.3.2.
In most urban environments breakaway designs are not necessary, they should generally be used
for structures less than 1.8m from the curb on roads with a posted speed limit of 80km/h or above,
which will be limited to urban Expressways and Freeways. However, the use of breakaway designs
can still be considered for lower speed roads if necessary, especially in higher risk zones. There are
exceptions to the use of breakaway designs, for example except for bus shelters or locations with
very high pedestrian flows (the risk to pedestrians arises chiefly from the errant vehicle rather than
anything they might hit, and with the exception of crash barriers, the majority of features that might
be installed in the footway are not intended to stop stray vehicles and would not be effective in doing
so even if designed not to break).
For roadside furniture, the following examples generally are not considered a roadside hazard in the
urban environment at operating speeds less than 60km/h:
• Street furniture such as pedestrian railing, bollards, bins, benches;
• Furniture not within the roadside clear zone; and
• Furniture located behind a roadside barrier.

318. ROADSIDE DESIGN GUIDE
PAGE 337
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
9.3 Evaluation of Safety of Individual Sites
13.3.1 Identification of Risk Factors
Given the diversity of roadside environments found in an urban area it cannot be assumed that a
single approach will be suitable at all locations within a particular scheme. Analysis of road crash
statistics shows that they are not wholly randomly distributed, with some particular locations often
standing out as experiencing more frequent crashes. There can be quite significant local variations
in speed and road geometry, as well as factors that lead to pedestrians being exposed to much
greater risk in particular places, for example near bus stops, schools, or where there is greater
demand for pedestrians to cross. If the higher risk locations can be identified, then they can be given
priority for safety improvements. One approach is to increase the clearance distances described in
0 at sensitive locations, so there is less risk of errant vehicles striking roadside objects.
When evaluating sites for potential increased risk the factors below should be considered.
Crash history- where available, crash statistics and police records should be assessed to identify
places where a disproportionate number of crashes have occurred.
Traffic speed- crash severity is much greater at higher speeds, which in urban areas are most likely
to occur when speeds are not constrained by congestion or engineering measures. For this reason
the 85th
percentile for off-peak speeds should be used. In urban areas this may be higher than the
design speed for the road.
Proximity to curb- where parking, or a cycle lane, or some other untrafficked margin keeps the
main traffic flow away from the curb, this space can be included in the clearance zone, and such a
location would be considered at lower risk of encroachment.
Pedestrians- it is important to identify significant pedestrian flows, including both alongside the road,
where they congregate and places where they cross. Consideration should also be given to where
children are most likely to be found.
Cyclists- cyclists are at greatest risk at intersections, and this applies where cyclists are given
dedicated routes alongside links as well as when they are sharing the road with other vehicles. Street
furniture and other roadside features can obstruct cyclists, or their sightlines to the main traffic flow,
and present an increased risk in the event of a crash.
13.3.2 Sites Requiring Increased Clearance Distances
There are particular locations where greater clearances should be allowed than the minimum
recommendations given in section 13.2. These include the outside of curves and locations where
the curb is dropped, for example at pedestrian crossings and driveways. Consideration should also
be given to the need to maintain sightlines at turnings. These are discussed in greater detail in the
sub sections below.

319. ROADSIDE DESIGN GUIDE
PAGE 338
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
13.3.2.1 On Horizontal Curves
Hazards next to curved sections of road should be regarded as presenting greater risks. Vehicles
are more likely to leave the carriageway on the outside of curves and there is a greater likelihood of
encroachment by overhanging long vehicles. It is therefore recommended that greater clearance
distances are provided at such high risk locations.
It is recommended that at least 1.8m lateral clearance is provided from the face of the curb on the
outside of a curve whilst maintaining 1.2m offset elsewhere. Where there is no vertical curb provision
then this clearance should be increased to 3.6m [1]. Figure 13.1 shows an example of a curbed
curve.
A further consideration is to ensure that the drivers’ line of sight is maintained around the curve. As
such a clear zone should also be maintained on the inside of the curve, albeit over a shorter distance,
as shown in Figure 13.1 [1]. Obstructions on the inside of a horizontal curve, which continue for a
considerable length and interfere with the line of sight on a continuous basis, can include roadside
barriers, walls and buildings. However, in general, obstructions such as traffic signs and utility poles
are not considered for this purpose.
Figure 13.1 – Lateral offset for objects at horizontal curves on curbed facilities [1]
13.3.2.2 At Merge Locations
Lane merge locations, which in urban areas include places such as the ends of bus stop bays,
present an increased risk of conflict between vehicles on the road, and hence of vehicles leaving the
road, especially if they fail to merge and continue in their previous path to avoid a crash.
It is recommended that a 3.7m clear zone is maintained in the vicinity of the taper point, as shown
in Figure 13.2. Research shows that longitudinal placement of objects within approximately 3.1m of
the taper point, increases the frequency of roadside crashes in this location [1]. For this reason it is
recommended that the clear zone should be extended at least 3.1m beyond the taper point as shown
in Figure 13.2.

320. ROADSIDE DESIGN GUIDE
PAGE 339
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Figure 13.2 – Lateral offset at merge locations [1]
13.3.2.3 At Driveways
The risk of roadside crashes is increased at driveways, for several reasons. As at any intersection
there is greater risk of conflict between vehicles entering or leaving the driveway and those on the
main carriageway. There is also a loss of delineation of the edge of the carriageway where there is
no white line, which is common in urban areas, increasing the risk that drivers will misjudge the
boundary of the road, leading to increased risk of collision with objects on the far side of the driveway.
Furthermore, at driveways there is no curb to provide redirection of errant vehicles. For these
reasons increased clearance zones are recommended on the far side of the driveway, a lateral offset
of 3.0 to 4.6m should be provided [1]. Furthermore, visibility triangles for vehicles exiting the driveway
should be clear of obstructions; these should be relocated, removed or lowered. The offset distance
will vary along with the extent of the visibility triangle depending on the design or operating speed of
the major road, as specified in the relevant design standards. The lateral offsets at driveways are
shown in Figure 13.3.
Figure 13.3 – Lateral offset at driveways [1]

321. ROADSIDE DESIGN GUIDE
PAGE 340
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
13.3.2.4 At Intersections
Crashes disproportionately occur at intersections, where there is greater potential for conflicting
manoeuvres, as well as a greater concentration of roadside infrastructure, such as signposts, traffic
signal poles and cabinets, lighting; and potentially traffic islands and bollards. The risk of errant
vehicles leaving the carriageway is increased by the presence of dropped curbs at pedestrian
crossings. Furthermore, there is a risk that turning vehicles will not follow the intended turning path
and will encroach into the sidewalk area, with greater risk of collision with roadside objects.
Design approaches for managing these risks are described below.
• Objects on the inside of turning movements should be as far as possible from the curb. It is
recommended that a clearance zone of 1.8m (with a minimum of 0.9m) is provided [1];
• Where there are dropped curbs for pedestrian crossings, objects should not be positioned
in the path that an errant vehicle would follow if directed up the access ramp [1];
• Traffic islands should be clearly visible to drivers while not encroaching in their path, and
should conform to the appropriate design guidance [3].
Similar to driveways in Section 13.3.2.3, adequate sight distance should be available for a driver to
perceive potential conflicts and to perform the actions needed to negotiate the intersection safely. A
visibility triangle is determined that allows a driver approaching an intersection to observe the actions
of vehicles on the crossing leg(s). This involves establishing the needed sight triangle by determining
the legs of the triangle on the two crossing roadways. Within this clear sight triangle, any object that
would obstruct the driver’s view should be removed, lowered or lateral offset increased. The
obstructions can include buildings, parked or turning vehicles, trees, hedges, plantings, signs, fences
and retaining walls.
Figure 13.4 provides details for constructing and measuring visibility triangle and the subsequent
offset requirements. The lateral offset will vary depending on the design or operating speed of the
major road and the intersection layout, as specified in the relevant design standards.
Figure 13.4 – Clear sight viewing triangle for viewing traffic approaching from the left [3]

322. ROADSIDE DESIGN GUIDE
PAGE 341
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
13.3.2.5 Roundabouts
Special consideration should be applied to roundabouts with regard to the lateral offset of objects.
Similar to horizontal curves, there is an increased likelihood of encroachment by overhanging long
vehicles. It is therefore recommended that greater clearance distances are provided these locations.
Furthermore, the position of objects relative to the curbs at a roundabout is influenced by speed and
possible errant vehicles. In particular, give care to the placement of objects along the exit leg of the
roundabout to consider potential paths of errant vehicles and within the central island on the entry
legs.
It is recommended that at least 1.2m lateral clearance is provided from the face of the curb on the
outside of a roundabout through the circulatory carriageway. Where possible objects should not be
placed alongside the exit leg through the exit radius, but where necessary the clearance of 1.2m
should be maintained. On entry to the roundabout any poles or other furniture in the direct path of a
potential errant vehicle should be of breakaway or frangible design.
9.4 Pedestrian Facilities
Pedestrian facilities include:
• Sidewalk/pathways;
• Pedestrian crossing locations;
• Pedestrian crossing design (type of crossing);
• Dropped curbs (curb ramps).
Sidewalks and pedestrian facilities generally do not pose a hazard to motorists. The safety concern
for locating these facilities adjacent to the road is the risk to the pedestrians using the facilities.
Guidance for the use of sidewalks on urban streets is in the Abu Dhabi Road Geometric Design
Manual [3].
Table 13.1 describes common strategies for eliminating or minimizing motor vehicle–pedestrian
crashes at roadside locations.
The approach taken to design should take into account the local context and function of the road or
street. For higher speed roads, such as urban freeways, the ‘movement’ function dominates, and
the focus would be on physically separating pedestrians from the traffic flow. For a shopping or
residential street in an urban centre the ‘place’ function dominates, and the focus would be on
reducing traffic speed and flow, giving space to pedestrians and facilitating freedom of movement.
An additional feature of the roadside environment is a pedestrian buffer area (often referred to as a
buffer strip). As shown in Figure 13.5, the pedestrian buffer is a physical distance separating the
sidewalk and the vehicle travelled way. Buffer areas often accommodate on-street parking, transit
stops, street lighting, planting areas for landscape materials, and common street features. Buffer
strips may be either planted or paved, and they are encouraged for use between urban roadways
and their companion sidewalks.

323. ROADSIDE DESIGN GUIDE
PAGE 342
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Table 13.1 - Design strategies to protect pedestrians in motor vehicle crashes [1]
Purpose Strategy
Reduce motor vehicle–pedestrian crash
likelihood at roadside locations
• Provide continuous pedestrian facilities
• Provide safe crossing facilities that are
conveniently located for desire lines
• Install pedestrian refuge medians or
channelized islands
• Offset pedestrian locations away from
travelled way with pedestrian buffers
• Physically separate pedestrians from
travelled way at high-risk locations
• Improve sight distance by removing objects
that obscure driver or pedestrian visibility
Reduce severity of motor vehicle–pedestrian
crashes at roadside locations
• Reduce roadway design speed, operating
speed, or both in high pedestrian volume
locations
Figure 13.5 – Example of a pedestrian buffer area
Guidance on recommended clearance distances between pedestrians and vehicular traffic has been
issued in the Roadside Design Guide for Dubai, reproduced, but amended to suit Abu Dhabi
requirements, in Table 13.2.

324. ROADSIDE DESIGN GUIDE
PAGE 343
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Table 13.2 - Clearances between pedestrians and vehicular traffic [4]
Road class
Desirabl
e
Clearanc
e
Minimu
m
Clearanc
e
Absolute
Minimum
Clearance
Comments
Freeway
Equal to or
greater than
the clear
zone width
(see Ch.
3)
Equal to
the clear
zone width
(see Ch. 3)
Where it is absolutely
necessary to provide
for pedestrians within
the right-of-way the
clearance may only be
reduced if
appropriate vehicle
restraint systems are
installed.
As a general rule pedestrians
should not have access to
the right-of-way. However, if
a sidewalk or walkway is
required, pedestrians are to
be excluded from access to
the roadway by means of a
suitable barrier.
Expressway
Equal to or
greater than
the clear
zone width
(see Ch.
3)
Equal to
the clear
zone width
(see Ch. 3)
Where it is absolutely
necessary to provide
for pedestrians within
the right-of-way, the
clearance may only be
reduced if
appropriate vehicle
restraint systems are
installed.
Pedestrians are in general to
be excluded from
expressways by suitable
barrier and fencing or grade
separation. Where access is
required connecting
walkways should be provided
with vehicle restraint system
separation.
Arterial
Roads
Equal to or
greater than
the clear
zone width
(see Ch. 3)
Speed limit
≥80 km/h:
2.0m
Speed limit
<80 km/h:
1.2m
Speed limit ≥ 80
km/h: 1.2m
Speed limit < 80
km/h: 0.5m
If curbside parking is
permitted, the sidewalk may
extend to the back of the
curb. On high speed roads (≥
80 km/h) the provision of
suitable barriers should be
considered if pedestrian
activity is high and minimum
clearance cannot be
achieved.
Collector
Roads
Equal to or
greater than
the clear
zone width
(see Ch.
3).
Sidewalk can be immediately
adjacent to curb
Often there will be a
parking lane which provides
separation between
pedestrians and moving
vehicles.
Local Roads Sidewalk can be immediately adjacent to curb
Generally there will be a
parking lane which provides
separation between
pedestrians and moving
vehicles.

325. ROADSIDE DESIGN GUIDE
PAGE 344
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Bridges
Speed limit >60km/h: install a vehicle restraint
system at the curb line between sidewalk and
traffic lanes
Speed limit ≤60km/h*: sidewalk may extend to the
curb line*
Sidewalks should not be
provided on bridges on
roads which do not have
pedestrian access,
including freeways and
expressways.
*A vehicle restraint system can be provided for roads with a speed limit ≤60km/h if deemed necessary for the
safety of pedestrians where activity is high. The barrier shall be designed as a normal longitudinal roadside
safety barrier and located at a suitable offset relative to the curb. See Section 13.6 for further details.
When planning pedestrian facilities consideration should also be given to:

326. ROADSIDE DESIGN GUIDE
PAGE 345
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
• Comfort and security- surface quality, ensuring satisfactory lighting, ensuring that routes are
overlooked and do not provide places of concealment;
• Capacity- considering flows and the effective width of the sidewalk when obstacles are taken
into account. The recommended widths for sidewalks and determining levels of comfort are
detailed in the Abu Dhabi Road Geometric Design Manual [3]. The manual details the four
primary zones that constitute the pedestrian realm, which are illustrated in Figure 13.6 and
the required widths for each of the realm elements for various contexts are detailed in Table
13.3;
• The needs of people with impaired vision or mobility, in particular in relation to surface quality,
avoidance of trip hazards and obstacles, dropped curbs at crossings, and provision of tactile
surfaces in line with the appropriate standards. The Abu Dhabi Urban Street Design Manual
[5] provides guidance on the use and provision of tactile surface treatments whilst Figure
13.7 shows typical tactile provision at curb ramps;
• The presence of children, particularly near schools and play areas;
• Sight lines to the traffic lanes, especially at crossings;
• Bus stops, including access from sidewalk where not adjacent to the road, and providing a
comfortable and secure waiting area that does not congest the sidewalk.
Figure 13.6: Pedestrian realm elements [5]

327. ROADSIDE DESIGN GUIDE
PAGE 346
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Table 13.3: Width for pedestrian realm zones [3]
Street Family Frontage Through Furnishing Cycle Track Edge*
Min Max Min Max Min Max Min Max Min Max
City Context
Boulevard 0.5 1.5 2.8 4.0 1.2 3.5 1.5 2.5 0.2 2.0
Avenue 0.5 1.5 2.4 4.0 1.0 3.0 1.5 2.5 0.2 2.0
Street 0.5 1.5 2.4 3.0 1.0 2.4 1.5 2.5 0.2 2.0
Access lane n/a n/a 1.8 2.5 n/a n/a n/a n/a 0.2 1.5
Town Context
Boulevard 0.5 1.5 2.4 3.5 1.2 3.0 1.5 2.5 0.2 2.0
Avenue 0.5 1.5 2.0 3.0 1.0 2.4 1.5 2.5 0.2 2.0
Street 0.5 1.5 2.0 2.4 1.0 2.0 1.5 2.5 0.2 2.0
Access lane n/a n/a 1.8 2.5 n/a n/a n/a n/a 0.2 1.5
Commercial Context
Boulevard 0.5 1.5 2.4 3.5 1.2 3.0 1.5 2.5 0.2 2.0
Avenue 0.5 1.5 2.0 3.0 1.0 2.4 1.5 2.5 0.2 2.0
Street 0.5 1.5 2.0 2.4 1.0 2.0 1.5 2.5 0.2 2.0
Access lane n/a n/a 1.8 2.5 n/a n/a n/a n/a 0.2 1.5
Residential Context
Boulevard 0.5 1.0 1.8 3.5 1.2 2.0 1.5 2.5 0.2 2.0
Avenue 0.5 1.0 1.8 3.0 1.2 2.0 1.5 2.5 0.2 2.0
Street n/a n/a 1.8 3.4 n/a n/a 1.5 2.5 0.2 2.0
Access lane n/a n/a 1.8 3.4 n/a n/a n/a n/a 0.2 1.5
Industrial Context
Boulevard 0.3 0.5 2.0 3.6 1.2 2.4 1.5 2.5 0.2 2.0
Avenue 0.3 0.5 2.0 3.4 1.0 2.4 1.5 2.5 0.2 2.0
Street 0.3 0.5 2.0 3.0 1.0 1.5 1.5 2.5 0.2 2.0
Access lane n/a n/a 1.8 2.5 n/a n/a n/a n/a 0.2 1.5
* Edge zone must be a minimum of 1.5 m where there is on-street parking or a cycle track. It may only go
down to 0.2 m when sufficient room is available for signing, lighting, and utilities within an adjacent
Furnishings zone.
Figure 13.7 – Typical curb ramp and tactile strip configuration [3]
The provision of safe and convenient crossing facilities in the right location is essential for
managing crashes in the roadway. Crossing facilities need to follow desire lines as closely as

328. ROADSIDE DESIGN GUIDE
PAGE 347
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
possible, and to be part of legible routes, so that pedestrians make use of them naturally when
following the most obvious route to where they are going. If use of a formal crossing facility involves
a long detour, or takes a route that is not readily discernible, then pedestrians will be more likely to
attempt to cross the traffic flow at a place of their own choosing, which may lead to increased risk of
collisions. If suitably located the use of formal crossing points can be further reinforced through good
design of the sidewalk environment: ensuring that crossing points are visible and easily identified,
are clear of obstructions, use dropped curbs to improve comfort. Typical details of a raised crossing
is provided in Figure 13.8
Figure 13.8: Typical raised crosswalk (avenue) [3]
9.5 Bicycle Facilities
This Section gives a brief overview on bicycle facilities. For more detailed information please refer
to “Abu Dhabi Road Geometric Design Manual [3]”, “Abu Dhabi Urban Planning Council Urban

329. ROADSIDE DESIGN GUIDE
PAGE 348
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Street Design Manual [5]”, “Abu Dhabi Walking and Cycling Master Plan [6]” and “AASHTO Guide
for Development of Bicycle Facilities [7]”.
There is a wide range of type of facilities intended for use by cyclists, with many different examples
found across the world. Provision ranges widely in the extent to which cyclists are separated from
other traffic, with examples including:
• Sharing the roadway with other vehicles with no specific facilities, sometimes assisted by
speed reduction measures such as traffic calming;
• Sharing wide outside vehicle lanes;
• Shared use of bus lanes;
• Cycle lanes within the carriageway;
• Physical separation within the carriageway;
• Fully segregated off-carriageway cycle tracks, as shown in Figure 13.9;
• Off-road cycle tracks separate from the road network, which may be shared with
pedestrians.
Figure 13.9 – A fully segregated off-carriageway cycle track
The most appropriate form of facility for a particular location will need to take account of a range of
local factors, including traffic flow and speeds, cycle demand, and the space available. A street
categorisation can be used as the basis for suggesting which forms of infrastructure could be most
appropriate, as shown in Table 13.4, which is based on an example from Transport for London
London Cycle Design Standards [8].
The more the ‘movement’ function for a street dominates, the greater the traffic speed and flow that
would be expected, and hence the greater degree of separation that would be considered
appropriate. In locations with a ‘higher place’ function, such as a Souk, a scheme design might focus
on how cycling can help to bring people to the space, and then to spend time there, whilst at the
same time how motorised traffic is calmed to reduce speeds and make the place more inviting.
Where the vehicle through-movement is dominant and the place is ‘low’, the design for cycling

330. ROADSIDE DESIGN GUIDE
PAGE 349
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
should address both capacity and safety issues including managing conflict with other vehicle types
and pedestrians, cycle priority and the minimization or avoidance of delay.
In Table 13.4 the types of cycling intervention are categorised according to the ‘degree of separation’
they offer between cyclists and motor vehicles. Where the street has a higher movement function,
improved level of service for cyclists can be achieved by greater user separation and by traffic
calming measures.
Table 13.4 - Indicative range of cycling provision by type of street [8]
High movement
low place
Medium movement
medium place
Low movement
high place
Degree of separation Principal
Arterials
Minor
Arterials
Collector
/
Local
Street
Principal
Arterials
Minor
Arterials
Collector
/
Local
Street
City
Center
Commercial
boulevard
Souk
/
Park
Full segregation
(e.g. cycle track, segregated lane)
Dedicated on carriageway lanes
(markings or ‘light’ separation)
Shared on-carriageway lanes
(bus lanes, wide vehicle lanes)
Sharing with other vehicles
(shared with normal traffic lane)
It is very important to recognise that a disproportionate number of cycle crashes take place at
intersections, where they are most likely to come into conflict with motorised vehicles. This is also
the case even where cycle tracks are otherwise segregated from traffic, as cyclists often lose priority
at intersections and find themselves positioned on the inside of turning vehicles when segregation
ends.
Although outside the scope of this Guide, cycle-friendly intersection design is therefore fundamental
to the development of safe cycle route networks. From the perspective of roadside design, the
position of junctions and crossings needs to be taken into account, including the detail of how cyclists
re-join the carriageway, sightlines to the vehicle carriageway the location of dropped curbs and the
position of street furniture and other features.
Further design considerations:
• Cycle tracks are commonly provided at the roadside close to trip attractors (e.g. shops, public
transport interchanges), but can cause obstruction and represent a hazard. Where practical
their installation should respect the clear zone advice set out in this document;

331. ROADSIDE DESIGN GUIDE
PAGE 350
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
• Separate signposts might be provided for cyclists, these should be treated in the same way
as other features in terms of respecting clearance distances and avoiding causing obstruction
to cyclists or pedestrians;
• Where cycle tracks are provided outside the main vehicle carriageway this space should also
be kept clear of obstructions, and where possible a clear zone of 0.5m [5] maintained to
reduce the risk of injury to cyclists in the event of an off-road fall, or conflict with pedestrian;
• Wide shoulders and bicycle lanes provide an additional clear area adjacent to the travelled
way, so these features provide a secondary safety benefit for motorists and can be included
as part of the clear zone. These bicycle facilities also will improve the resulting sight distance
for motor vehicle drivers at intersecting driveways and streets;
• The minimum lateral clearance of 0.5m shall be used for objects adjacent to segregated cycle
track or shared path, however 1.0m is desirable to ensure enough clearance is present taking
into account extent of handlebars past the edge of the path, especially through curves where
cyclists may lean further outside the edge.
The Abu Dhabi Urban Planning Council Urban Street Design Manual [5] provides a number of
diagrams detailing the design of cycle facilities in the urban environment, including at intersections.
Reference should be made to this document, and other design standards, when considering bicycle
scheme designs. An example of typical cycle facility design is reproduced in Figure 13.10 and this
shows the use of a ‘buffer zone’ between pedestrian and cyclists where a segregated track is
provided, this reduces the potential for conflict and provides protection to pedestrians. All cycle tracks
should be free of obstructions with a minimum lateral clearance to obstructions of at least 0.5m.
Figure 13.10 – Typical bicycle facilities [5]
Bicycle parking racks are often made of solid materials that do not break-away and are secured to
the ground to prevent theft. The non-yielding nature of this street furniture item has the potential to
increase injury severity if a run-off crash were to occur. Table 13.5 describes common strategies for
eliminating or minimizing motor vehicle–bicycle crashes at roadside locations and improving bicycle
safety.

332. ROADSIDE DESIGN GUIDE
PAGE 351
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Table 13.5 - Design strategies for bicycles [1]
Purpose Strategy
Reduce likelihood of an crash • Use wider curb lanes.
• Provide segregated facilities with clear buffer
zones.
• Increase operational offsets.
• Highlight bicycle paths with coloured
pavement, especially at intersections.
• Provide advanced stop lines at signalised
intersections to allow cyclists to move ‘first’
and reduce potential for conflict.
• Provide colour contrasting material at
potential conflict zones to highlight likelihood
of encountering other users.
Reduce severity of an crash • Locate bicycle racks away from the edge of the
curb to reduce chance of vehicle strikes.
9.6 Roadside Safety Barriers in Urban Areas
13.6.1 Determining use of roadside safety barriers
Pedestrians or bicyclists may require shielding by a roadside safety barrier (vehicle restraint system)
where they are considered to be exposed to a higher than normal risk of being struck by an errant
vehicle. Where a pedestrian/bicyclist facility either exists or is proposed for an existing site that has
run-off-road crash history, an assessment of pedestrian, bicyclist, and bystander exposure should
be undertaken so that crash reductions for alternative treatments can be considered (Section13.3).
In the evaluation, the designer should consider the combination of factors that would require
shielding of the facility including the:
• Number and type of path users (e.g. whether large numbers of people congregate in or
pass through the area, the presence of young school children);
• Factors that make the site more hazardous than other sites along the road (e.g. road
geometry and characteristics that would increase the risk of run-off-road events);
• Type of traffic that may cause a run-off-road event to be particularly severe (e.g. high
numbers of heavy vehicles);
• Situations where a roadside barrier may be appropriate are:
• Intermediate and high-speed roads where a path is within the clear zone;
• Heavily trafficked shared-use paths separated by less than 4 m from an adjacent heavily
trafficked lane, especially if the geometry is substandard (see also section 13.4);

333. ROADSIDE DESIGN GUIDE
PAGE 352
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
• Sites where there is expected to be large numbers of bystanders congregated adjacent to
the road beyond the clear zone (e.g. schoolyard, sporting facilities) and the consequences
of a crash are expected to be high.
Placing a roadside safety barrier in a pedestrian environment imposes compromises and trade-offs
between vehicle occupant safety and pedestrian/bicyclist safety. Evaluation of the trade-offs
between vehicular and pedestrian/safety should include factors contributing to the relative risk for
each user class. These include exposure of individuals and expected severity of each crash
category. To evaluate the expected severity of any crashes, consider the operating speed of the
roadway facility, the treatment under consideration, and the nature of any particular traffic barrier.
As discussed previously, analysis of speeds should refer to the off-peak, when speeds are likely to
be higher, and the most severe crashes are likely to occur.
Where there is a need to provide a roadside safety barrier between a path and roadway traffic, it is
important that the rear of the barrier is not a hazard for pedestrians and bicyclists. Designers should
ensure that:
• The barrier should be kept as far from pedestrians and cyclists as possible, with good
clearance provided between the rear of the barrier and the path;
• No sharp edges, burrs or other potential hazards (e.g. protruding bolts) exist;
• Where sufficient clearance cannot be provided, bicyclists are protected from “snagging” on
posts by the provision of suitably designed rub rails;
• Where sufficient clearance cannot be achieved, consideration is given to the need to increase
the height of the barrier either to prevent errant bicyclists from falling over the barrier and into
a traffic lane or to discourage pedestrians from jumping over the barrier to cross the road at
an unsafe location.
Where the objective is to prevent cyclists and pedestrians from encroaching onto a traffic lane from
an adjacent sidewalk or cycles track rather than to protect path users from errant vehicles, or errant
vehicles from roadside hazards, then a pedestrian fence should be adequate, see Section 13.7.5.
Where bridges are present in urban areas these usually include a sidewalk, but space for separation
is limited, so bridge roadside barriers are often used to protect pedestrians. At lower speeds, the
sidewalk is separated from the adjacent roadway by a vertical curb, which is typically 150 mm to 200
mm high. However, at higher speeds, the vertical curb will interfere with the proper vehicular/bridge
safety barrier interaction. Therefore, the following will apply to the location of a bridge safety barrier
in combination with a sidewalk:
11. Speed  70 km/h. The bridge rail is typically located on the outside edge of the sidewalk;
12. Speed  80 km/h. Place the bridge rail between pedestrians and traffic; i.e. between the
roadway portion of the bridge deck and the sidewalk. For the 815-mm concrete barrier rail,
the rail must have a metal handrail on the top of the barrier to reach the required 1050mm
height for a pedestrian rail. A 1250mm pedestrian or 1400mm bicycle rail [9] is then used at
the outside edge of the sidewalk. For this arrangement, the roadway and sidewalk portions
of the bridge deck are at the same elevation.
For further details on the provision at bridges please refer to Chapter 7 of this manual.

334. ROADSIDE DESIGN GUIDE
PAGE 353
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
13.6.2 Roadside Safety Barrier Warrants
In addition to protecting pedestrian and cyclists from errant vehicles, safety barrier may also be
warranted in the urban environment on the basis that it reduces the severity of potential crashes. A
barrier may be deemed appropriate in the urban environment if:
• There is reasonable probability of a vehicle leaving the road at that location;
• The cumulative consequences of the vehicle leaving the road outweigh the cumulative
consequences of impacts with the barrier.
Greater consideration should also be given based on the adjoining land use. Schools, playgrounds,
and parks located on the outside of curves may warrant the additional protection of a safety barrier.
Consideration should also be given to protecting commercial and residential premises that are close
to the right-of-way, particularly where there is a history of run-off crashes.
13.6.3 Common Urban Barrier Treatments
13.6.3.1 Roadside and Median Barriers
The use of standard highway barrier systems may not always be applicable in some urban
environments, especially those where the speed limit is <70km/h. In these circumstances alternative
measures of separating opposing flows of traffic should be considered, including the use of medians,
raised or flush, with flush only being considered on high speed roads that will only be encountered
on freeways or expressways.
When introducing a median that has plantings, barriers or fencing installed it is imperative that
intersection sight distance is maintained. In such circumstances the plantings or other features in
the median should be terminated or the height adjusted in advance of the intersection.
13.6.3.2 Crash cushions
Where applicable, crash cushions should always be considered at urban locations where fixed
objects cannot be relocated, removed or longitudinal barrier systems cannot be safely introduced.
The use of crash cushions as opposed to standard longitudinal barriers is potentially more
appropriate for protecting fixed objects, especially those at exit ramps, gores, ends of median
barriers, bridge piers and abutments. This is particularly the case where the increase in maintenance
levels, right-of-way constraints and varying traffic flows creates situations that limit where removing
or relocating objects is possible.
There are a number of crash cushions that are appropriate for narrow or constrained width
conditions, as detailed in Chapter 10 of this Guide. When introducing a crash cushion where curbs
are present the issue of vaulting will need to be taken into consideration, as detailed in Chapter 7 of
this Guide.

335. ROADSIDE DESIGN GUIDE
PAGE 354
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
9.7 Common Urban Roadside Features
13.7.1 Curbs
13.7.1.1 High Upstand Curbs
Roads in urban areas will commonly have upstand curbs to separate pedestrians from the main
carriageway. The curb is also usually adjacent to a gutter so has a role in drainage. Curbs in urban
areas are usually 150mm (6”), but a lower 100mm (4”) curb will often suffice if drainage is the primary
function. Typical curb design for an upstand curb is provided in Figure 13.11.
Figure 13.11 – Typical details of an upstand curb [3]
While curbs will deter drivers from encroaching into the pedestrian space, they have only limited
effectiveness in redirecting errant vehicles, particularly at speeds greater than 40km/h. Larger SUV
style vehicles will more easily mount the curb than smaller cars, so the prevalence of these vehicle
types needs to be taken into account. Because of the limited redirectional capability, the guidance
on clear zones in Section 13.2 should be followed as far as possible. Traffic speed needs to be taken
into account, therefore, where the speed is 70km/h or less, fixed objects should be located as far
from the roadway as practical, but in no case closer than 500mm from the face of the curb. Curbs
should not be used on facilities where the design speed is 70km/h or greater [3]. Where sidewalks
are adjacent to the curb (i.e. there is no buffer area), locate all appurtenances behind the sidewalk.
When a vehicle mounts the curb it will travel approximately 2.5m before its suspension returns to its
normal state. This increases the risk of it vaulting any barriers it might hit, so vehicle restraint system
should be installed either immediately adjacent to the curb or at least 2.5m away [1].
13.7.1.2 Vehicle Barrier Curbs
Vehicle barrier curbs, or treif kerbs as they are often referred, can be used on urban roads with a
speed limit ≤60km/h to prevent vehicles mounting the curb [4]. This type of curb has high profile
(typically 280mm or greater) and has proven effective at redirecting vehicles at speeds up to 60km/h
at impact angles up to five degrees. At speeds greater than this the curbs effectiveness of redirecting
is reduced and in turn acts as hazard to errant vehicles by providing an overturning opportunity so
should not be used on roads with a speed limit >60km/h [4]. Figure 13.12 provides typical details of
a vehicle barrier curbs.
This type of curb should predominately be used in areas of high pedestrian use to provide additional
protection from any possible errant vehicles. However, in providing this type of curb it

336. ROADSIDE DESIGN GUIDE
PAGE 355
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
needs to be understood that the curb height is an impediment to pedestrians in crossing the road
and the following considerations should be taken into account:
• If implemented provide the curb on both sides of the road, and the median if present, to
ensure pedestrians do not become ‘stranded’ in the road. This may occur if one side of the
road has standard upstand curbs;
• If used in the vicinity of pedestrian crossing care should be taken at the dropped curb location
to ensure the gradient of the drop is not excessive and impede use. Transition to upstand
kerbs and then to dropped curbs may be required.
Figure 13.12 – Typical details of vehicle barrier curbs [3]
13.7.2 Shoulders & Sidewalks
Where space permits, urban roads may have a paved shoulder between the traffic lanes and the
curb. They increase separation of traffic from the curb and any sidewalk present, so their width
should be counted as part of the clear-zone. Shoulders have the advantage of reducing the likelihood
of errant vehicles leaving the road, however they have the disadvantage of encouraging higher
speeds, because of the perceived greater road width that results. The decision to include a shoulder,
and the width provided, should therefore take into account considerations of the purpose of the road
or street, the overall urban design objectives, and hence the traffic speeds that are appropriate to
provide for in the design.
13.7.3 Traffic Islands & Medians
Traffic movements are often separated by features such as traffic islands and median strips. Clearly
these, and any additional objects, such as lighting columns or signposts, placed within them, present
a hazard to errant vehicles. The guidance on clearance zones and lateral offsets given earlier in this
Chapter should therefore be applied to these features.
Specific design considerations for medians and islands are [1]:
• Widening the median will help reduce the likelihood of errant vehicles colliding with any
objects placed within it;
• The severity of crashes can be reduced by ensuring that only breakable items are located in
medians or islands, or by shielding rigid objects with vehicle barrier curbs (trief curbs) on low
speed roads. On an urban freeway or expressway vehicle restraint systems should be
implemented if an appropriate clear zone cannot be achieved.

337. ROADSIDE DESIGN GUIDE
PAGE 356
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
13.7.4 Gateways
Gateway treatments are a combination of features used to create a sense of arrival to place and can
take many forms. They are used at the perimeter of a local area to inform road users they are
entering a slow speed environment and that they can expect to encounter localized features intended
to induce a traffic calming effect. Gateways are used to emphasize the change in character of the
road environment and its use.
Gateways can take many forms and use structures or features such as lighting units, raised planting,
trees, walls and public art features, to illustrate the approach to a gateway. Many of these features
could be considered hazardous roadside features. The operating speed on approach to a gateway
is a key design consideration in determining what features can be used and subsequently how far
they must be set back from the road.
• Where approach speeds are high (>70km/h) then clear-zone guidance as detailed in Chapter
3 of this Guide shall be applied;
• In low speed locations fixed features can be used and placed closer to the road, but must
maintain the 0.5m minimum lateral clearance, with greater clearance provided where site
conditions allow;
• The use of speed reduction signs, both upright and pavement markings, tactile road
pavement surfaces and other gateway treatments will aid in reducing speed and the
likelihood of run-off crashes [1].
An example gateway design incorporating audio tactile pavement surface treatment, pavement
marking speed limit reinforcement, reduced width running lanes and accompanying mature trees is
detailed in Figure 13.13.
Figure 13.13 – Example gateway layout
13.7.5 Pedestrian Fencing
A high proportion of pedestrian casualties occur from crashes when pedestrians are crossing the
road away from formal crossing points. While, as discussed in Section 13.4, the starting point for
resolving this problem is to ensure satisfactory provision of safe crossing places, pedestrian fencing
(or restraint systems as they are often referred) have a role in discouraging crossing away from
formal crossings at high risk locations, for example mid-block crossing on major streets. Furthermore
pedestrian fencing should be used for the following purposes:
• Assist in directing pedestrians to formal and safe crossing locations;

338. ROADSIDE DESIGN GUIDE
PAGE 357
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
• Prevent pedestrians entering the road and conflicting with vehicular traffic where pedestrian
activity is high;
• To exclude pedestrians from high volume and speed roads, urban freeways and
expressways with speed limit >80km/h.
Figure 13.14 details a typical use of pedestrian fencing to prevent pedestrians crossing a busy three
lane main street by installing the fencing between the service road and main road. In this instance
the fencing will direct pedestrians along the sidewalk to the next formal crossing location.
Figure 13.14 – Example pedestrian fencing restricting crossing over a main street
In addition to their use in preventing pedestrians from crossing at high risk locations, pedestrian
fencing has a role at particular locations where pedestrian flows need to be managed, or
encroachment by groups of pedestrians discouraged. Examples include [3]:
• Outside schools;
• At busy bus stops to keep queuing passengers away from the roadway;
• Where off-road pedestrian or cycle routes join routes adjacent to the carriageway, and
there is a risk of vulnerable road users over-running into the traffic.
On high speed roads pedestrian fencing can be installed in tandem with road safety barrier within
the median and edge of the road to discourage pedestrians crossing these roads.
There are number of types of pedestrian fencing that can be used to contain and direct pedestrians.
The principle design considerations include [3]:
• Fencing should be constructed from vertical members, as far as it is practical, to restrict the
ease at which people can climb the fence;
• Rigid horizontal members should be avoided to limit the potential for fence components to
spear through a vehicle;
• Fencing located in a clear zone must not be hazardous to vehicle occupants or pedestrians.
The fencing should not be designed to resist penetration by a vehicle;
• All fencing shall have a lateral offset of 0.5m minimum from the curb, but where space
allows this should be increased. If a large area is left between the road and the fencing

339. ROADSIDE DESIGN GUIDE
PAGE 358
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
then landscaping or pedestrian deterrent surface treatment should be used in the space so
it is not attractive for pedestrian use.
A major downside to pedestrian fencing is their visual impact on the streescape. A range of
construction materials can be used to improve their appearance, and hedges can also be used to
this effect. Fencing can also present an additional crashes risk themselves- cyclists and powered
two wheeler users in particular. Fencing at intersections can result in cyclists being trapped if caught
on the inside of turning vehicles. There is also evidence that the presence of fencing can encourage
drivers to increase their speed, because they perceive the risk of crash with pedestrians to be
reduced [10].
With these disadvantages the use of fencing is inappropriate on streets with an important ‘place’
function, for example where there are shops, cafes and public spaces. Restricting the movements
of pedestrians too much in such areas would be detrimental to the intended uses of the street,
including the viability of businesses. Consideration should therefore be given to measures to reduce
the speed of the traffic so as to reduce the risk to vulnerable roads users, and also to improve the
quality of the environment.
13.7.6 Anti-glare Screens
Anti-glare screens are provided to eliminate light from oncoming vehicle headlights. They must be
designed in such a way that light directed towards the driver at oblique angles (12° to 20°) is reduced
whilst relatively maintaining an open vision (around 70°) in the sideways direction [9].
The height to effectively screen headlight glare from all types of vehicles on level ground is 2.0m [9].
The screens can be either standalone systems or mounted on top of safety barriers.
There are a number of types of anti-glare systems that can be used. The principle design
considerations and roadside design guidance include [9]:
• Standalone anti-glare screens (not mounted on barrier systems) used on roads with a speed
limit >80km/h located in a clear zone must not be hazardous to vehicle occupants in a run-
off crash and must not resist vehicle penetration;
• Standalone anti-glare screens (not mounted on barrier systems) used on roads with a speed
limit ≤60km/h shall have a minimum lateral clearance of 0.5m. Where space permits this
should be widened to 1.2m. If a large area is left between the road and the screen then
landscaping or pedestrian deterrent surface treatment should be used in the spaces so it is
not attractive for pedestrian use, as the height of the screen may mask some pedestrians
and encourage use close to the carriageway where the risk of strikes from passing vehicles
is heightened;
• Where mounted upon safety barriers it is essential that the anti-glare screen and its fittings
do not detrimentally effect the operational safety requirements of the barrier system;
• Anti-glare screening may lose its effectiveness where there are severe undulations of the
highway alignment, particularly where there are high proportions of large goods vehicle
traffic. In such instances increased height screens may be appropriate;
• Where the highway alignment contains tight left-hand curves the anti-glare screens may
restrict sight distance leading to potential greater risks. In such instances the screen provision
will need to be reviewed to ensure appropriate sight distances are maintained throughout;

340. ROADSIDE DESIGN GUIDE
PAGE 359
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
• Anti-glare screens can be particularly effective alongside major streets where service roads
are present and when during the hours of darkness opposing headlamps on the nearside
cause confusion.
13.7.7 Street Furniture
Street furniture includes items provided for the use and comfort of people using the space adjacent
to the road, or interchanging with public transport, or to improve the aesthetic appeal of the
streetscape. Examples include:
• Seating for public use;
• Litter (rubbish) bins;
• Public art;
• Public telephones;
• Planters;
• Bicycle parking;
• Bus shelters;
• Street vendor kiosks and stalls.
Some of these might be temporary, placed there by owners of the frontages, and may be difficult for
the highway authority to influence. Where their design and installation can be controlled the advice
set out in Section 13.2 should be followed, ensuring satisfactory clearance zones and the use (where
applicable) of breakable construction.
The main impacts of street furniture will be on the pedestrian space, so consideration should be
given to the issues discussed in section 13.4, in particular on ensuring adequate usable width for the
observed pedestrian flows is maintained, avoiding creating trip hazards and obstacles, especially for
those with impaired vision or mobility, and ensuring satisfactory sight lines to the vehicle lanes,
especially at crossing points. Where practical, street furniture should be provided as far from the
carriageway as possible, preferably within a service strip outside of the through zone of the
pedestrian area. Furthermore, street furniture should be placed so it does not restrict sight distance
for all road users including cyclists and pedestrians at dedicated crossing locations [1].
13.7.8 Utility Poles
Because of the constrained space next to urban roads, and limited rights-of-way for utility companies,
utility poles are commonly installed alongside the carriageway. These present very significant
hazards for errant vehicles, and can also obstruct the sidewalk and any off-carriageway cycle track.
Some poles have steel guy wires to provide additional support, which present additional hazards, as
vehicles can strike them and they can be hard to see trip hazards for pedestrians, especially with
impaired vision. Unlike signposts, utility poles are not suited to breakable construction. While utilities
can sometimes be relocated underground, this is very expensive so roadside poles cannot usually
be removed completely. The risk they present can be managed however, through [1]:
• Avoiding locations with high crash risks;
• Positioning them as far as possible from the vehicle lanes;

341. ROADSIDE DESIGN GUIDE
PAGE 360
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
• Avoiding access points and junctions where sight lines can be restricted, and turning vehicles
may be more likely to encroach;
• Placing them on the inside of turns in the road, as errant vehicles will more usually leave the
road on the outside of curves.
Risks can also be reduced by locating poles where they would be protected by another feature, such
as a roadside barrier. Utility poles are also often used for street lighting and for traffic a sign, which
helps to reduce street clutter and avoids the additional risk that would otherwise arise from the
signposts and lighting columns that would otherwise be needed.
13.7.9 Lighting & Visibility
Roadside lighting in urban areas must serve two purposes- illuminating both the carriageway and
the adjacent pedestrian sidewalk. Adequate pedestrian lighting is necessary for comfort and security,
as well as safety by ensuring they are visible to drivers. This imposes different requirements for the
distribution of light from street lighting columns, which will need to be shorter (i.e. 10m) and more
closely spaced than in a purely highway environment (where 25m columns can be used). However,
this increases the number of lighting poles that need to be installed next to the carriageway. Locating
them on the side of the sidewalk furthest from the carriageway will reduce the risk that errant vehicles
will collide with them, while offering the advantage that light will fall onto the sidewalk.
When considering lighting design and provision the illumination levels of pedestrian crossings are of
great importance, particular zebra crossings. In these instances pedestrians should be sufficiently
backlit by adjacent lighting units to ensure their visibility to approaching vehicles.
More detailed guidance is provided in the Abu Dhabi Road Lighting Manual [11].
Because of the potential hazard, the general approach to lighting standards is to use breakaway
supports wherever possible. All new lighting standards located within the clear zone of a roadway
where no pedestrian facilities exist will be placed on breakaway supports, unless they are located
behind or on a barrier or protected by crash cushions in gore areas, which are necessary for other
roadside safety reasons. Poles outside the clear zone on these roadways should also be breakaway
where there is a possibility of being struck by errant vehicles.
On roadways where pedestrian facilities exist, review the volume of pedestrian traffic to determine if
a breakaway support will present a greater potential hazard to the pedestrian traffic than a non-
breakaway support will to the vehicular traffic. Examples of locations where the hazard potential to
pedestrian traffic may be greater include:
• Parking lots;
• Tourist attractions;
• School zones;
• Central business districts and local residential neighbourhoods where the posted speed
limited is 50 km/h or less.
In these locations, non-breakaway supports may be a better choice. Other locations that typically
require the use of non-breakaway bases, regardless of the pedestrian traffic volume, are rest areas
and combined light and traffic signal poles.

342. ROADSIDE DESIGN GUIDE
PAGE 361
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
13.7.10 Sign Posts
In urban areas there can be a lot of constraints on where signposts can be located. Sign posts at the
roadside present a hazard to errant vehicles, but can also cause obstructions to pedestrians if
located on the sidewalk. Similar considerations apply to traffic signal poles, where there is even less
choice of location. In both cases poles must be placed in a location that minimizes pedestrian
conflicts and does not reduce the sidewalk width below minimum. Clearly, if the opportunity is taken
to fix signs to existing posts, for example lighting columns, where this is practicable, then street
clutter and the number of hazards at the roadside can be minimised.
As is generally the case for sign posts next to the highway, breakaway construction is usually
recommended (see Chapter 5) for posts with diameter greater than 89mm. The greatest risk to
pedestrians arises from the errant vehicles themselves rather than anything they might strike, and
sign posts are not designed to stop stray vehicles. However, there are some locations, especially
where large numbers of pedestrians congregate, where a different conclusion might be reached.
To assess whether this is the case on roadways where pedestrian facilities exist, the process and
the examples of hazardous locations is same as that detailed in Section 13.7.9.
13.7.11 Landscaping, trees and shrubs
Landscaping forms an important part of the streetscape in terms of providing high quality and
attractive areas, improving the user environment and subsequently encouraging greater use and
time spent in an area. Furthermore, mature trees can provide an essential part in providing shade to
lower ambient temperatures.
However, large mature trees and other forms of landscaping including raised planters and decorative
rocks can be hazardous to errant vehicles. Landscaping can also have a detrimental effect on
sightlines
Trees with a mature trunk size greater than 100mm in diameter are classified as fixed roadside
objects. When introduced (or expected to grow to and above this size) these should be located in
conformance with the clear zone standards specified in Chapter 3 or road safety barrier provided on
Urban Expressways and Freeways where there high operational and 85th
percentile speeds. The
clear zone standards must also be applied to other landscaping that are likely to be hazardous to an
errant vehicle on higher speed urban roads.
On lower speed roads with a posted speed limit of 60km/h or less, the use of safety barrier is not
required and a minimum lateral clearance of 1.0m shall be applied to allow for vehicle overhang and
clearance of high vehicles. However, greater distance should be considered for the following reasons
[1]:
• Use of the adjacent lane, for example if parking is permitted a greater distance shall be
employed to allow easy access and egress;
• The provision of a suitable border area to take into account watering, root damage and
maintenance requirements so as not to impact on adjacent travel lanes.
In some cases vehicle barrier curbs is an option to shield landscaping that is within the clear zone in
urban areas. This is especially the case where there is a known run-off crash history or potential high
risk zones as detailed in Section 13.3.2. See section 13.7.1 for details on curb use.

343. ROADSIDE DESIGN GUIDE
PAGE 362
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
Sight distance standards specified in the Road Geometric Design Manual for Abu Dhabi [3] must be
adhered to in the design process and future growth and required maintenance regimes are
determined and established. Critical locations include intersections, driveways, pedestrian crossings
and median openings. However, points that must be considered are [1]:
• Landscaping shall allow full visibility for all users at driveways and intersections. Any
landscaping within the required visibility sight distance shall be removed, relocated or
lowered;
• Landscaping of very small traffic islands should be discouraged to reduce maintenance costs,
closure of traffic lanes and safety of maintenance personnel.
9.8 Summary & Conclusions
Urban areas are very diverse, with a wide range of traffic speeds and flows, road widths and
geometry, road user types and street environments. Pedestrians and cyclists will occur in much
greater numbers, with dedicated infrastructure of their own, needing both to travel along links and
also to cross them. In many locations, especially residential areas and town centres, the road
environment is part of a public space, used for social purposes and interactions, not merely as a
transport facility. It is therefore helpful to the design process to assess a location in terms of its
‘movement’ and ‘place’ function, as this has implications for the relative priority given to traffic
capacity and provision for pedestrians and cyclists, and for the vehicle speeds that are considered
appropriate.
Due to varied nature of the urban environment space is more constrained that means there is often
less space available for separating vehicles from pedestrians and cyclists and in providing clearance
zones and in meeting the requirements for sightlines detailed elsewhere in this Guide and therefore
need to be modified.
This Chapter has provided the details of the minimum lateral clearance of roadside object of 0.5m,
with a desirable extended 1.2m clearance where there are no space constraints, and widened even
further in high risk areas such as curves and intersections. These distances must be adhered to for
all urban design schemes.
In certain circumstances roadside and median safety barrier can be used in low speed urban
environments where there is a specific need to counter known run-off crash locations, where there
is increased chance of conflict (curves) and where high numbers of pedestrian are expected. Each
site will need to be assessed individually to ascertain the suitability of providing the barrier
considering the possible trade-offs. Roadside and median safety barriers should be used on high
speed urban Expressways and Freeways where adequate clearance zone treatments cannot be
applied.
Pedestrian and cycle facility requirements have also been provided relating to the placement of street
furniture and other hazards. Where possible, separation and segregation of users should be applied
to provide protection and reduce conflict. The through zones of these facilities should be clear of
objects, preferably with the use of a service strip. The minimum lateral clearance for pedestrians and
cyclists to objects should be the minimum 0.5m and preferably widened for cycle tracks and paths
to 1.0m.
This Chapter has also provided guidance on the introduction and design considerations for a number
of roadside objects and possible treatments that are affected by clearance zones or items within the
extent of clearance zones. Each site where schemes are designed are likely to vary to

344. ROADSIDE DESIGN GUIDE
PAGE 363
13 URBAN ROADSIEDDESIGN FIRST EDITION -DECEMBER 2016
some extent but the recommendations and guidance set out should be adhered to in all conditions to
ensure a safe and practical urban streetscape environment for all road users. This may mean the use of
breakaway infrastructure or vehicle curbs in certain scenarios or revised entry treatments at gateways
taking into account traffic flows and speeds.