An Introduction To Road Safety Engineering

by
Huy Huu Nguyen. PhD
1
Ho Chi Minh City, 20 Feb 2017
An Introduction to Road Safety
Engineering
Ho Chi Minh City University of Transport
Department of Transport Planning
----------------o0o-----------------

2
Objectives
 To introduce “Road Safety Engineering”
 To emphasize the important role of engineering approaches
 To introduce “Towards Safer Road” Manual
 To introduce some typical safety deficits with regards to
human factors
 To outline some key principle in planning and design of
safe road network

3
Global Road Safety
• The u er of road traffi deaths ea h year has not
increased – but remains unacceptably high at 1.24
million per year
• Predicted to grow to more than 4,000,000 annually by
2020 unless urgent action is taken
• 80% of road traffic deaths occur in middle-income
countries (72% population, 52% registered vehicles)
• Al ost 60% of road traffi deaths are among 15–44
year olds
• Vulnerable road users (especially motorcyclists!!!)
which have highest proportion of road traffic collisions
in low & middle-income countries
• No -fatal crash injuries are poorly documented
 Introduction

4
Vietnam Road Safety
Non-fatal crash injuries are poorly documented (under-reported)
Trends in Road Traffic Deaths
Source: 2011, NTSC Annual Reports
GDP (2010): 104.6 Billion USD
 Introduction

5
Safe System Approach
Source: Phillip Jordan, Road Safety
International, 2009
 The actual road crash is a result of humans, vehicles and
roads not working together.
 To reduce injury and death from road crashes we need to
have safer drivers, in safer vehicles, on safer roads.
 Road Safety Engineering

6
Figure 1. Changes in Objective and Subjective Safety
Source: HSM, 2009
Objective safety refers to use of
a quantitative measure which is
independent of the observer.
Subjective safety concerns the
perception of how safe a person
feels on the transportation
system.
Road Safety Engineering
focuses on Objective Safety
Crashes as the basis of safety
analysis

7
"a rare, random, multi-factorial event in
which one or more road users have failed to
cope with their environment.”
 Road crashes are:
 rare- 1 in 200 people injured every year
 random- impossible to predict where and
when the next crash will happen
 multi-factor- combination of behavioral,
vehicle and road factors.
 The multi-factor nature of crashes
suggests a chain of events involving:
 Behavioral (human) factors
 Vehicle factors
 Road factors

8
CHAIN OF EVENTS LEADING TO ACCIDENTS, Reichart (2001)

9
In this diagram, factors from four
categories (dark links) interact to
form a chain of events that link you
to crash.
Removing just one
factor breaks the chain
and may prevent the
crash!
Crash Chain
Source: MSF - Rider Handbook, 2007
Rider
Motorcycle
Traffic
Road & environment

10
Oval Safety
Source: MSF - Rider Handbook, 2007
Risk is reduced by
increasing your time
and space safety
margin.

11
“A process, based on analysis of road and traffic related accident
information, which applies engineering principles in order to identify road
design or traffic management improvements that will cost-effectively reduce
the cost of road accidents”
(Ken Ogden page 35 Safer Roads)

12
Our halle ge …
 To create a road environment which guides and controls all
road users, but forgives them when they make a mistake.
Figure 3. Crash Factors
Source: Highway Safety Improvement Program Manual, 2010
 Role of Engineering Approach

13
What do we do?

Road
safety
engineers
should
aim
to:
Guide
Warn
Forgive
Absorbing Pole
Inform
Control

14
The crucial role of engineering approaches
 In all countries, the police typically identify the main cause of road accidents as human
error.
 Vietnam is no exception with most of the accidents recorded by traffic police being
attributed to human error, and very few to road problems.
No, far from it; in many motorized countries engineers have led the
attack on road accidents with outstanding success.
Engineers play a leading role in road safety.

15
Why engineers play a leading role in road safety?
 There are four key reasons as follows
 Inconsistencies and complexities in the road design and road network will
significantly increase the difficulty of the road users' tasks and result in more road
accidents.
 Inappropriate planning of the road network in relation to land use and road
function will unnecessarily expose road users to the risk of road accidents.
 Road planning, design and engineering countermeasures can lead to significant
accident reductions and provide a more forgiving environment
 Road engineering improvements are relatively straightforward to implement and
they usually have an immediate effect.

16
4.1 An Integrated and Scientific Approach
 Road safety is the responsibility of many sectors and that an integrated approach
to national and local action is required.
 The most important are:
 A reliable and valid national road accident database
 A national road safety plan based on a scientific and rational diagnosis of the
road accident problem
 National and local coordinating agencies with the necessary authority and
resources to implement the plan
 Professional staff trained in the latest road safety approaches and technology
 Evaluation of the measures with feedback to the national plan
 Towards Safer Road

17
4.2 Accident Prevention and Reduction
 An important road safety concept is the distinction between Accident Prevention and
Accident Reduction.
Accident Prevention involves improved planning and design of new roads and related
developments to minimize road accidents and casualties.
Accident Reduction involves the application of cost effective measures to the existing
road network.
Source: AusRAP, 2012

18
“Experience over the fifty years in Europe has found that it is the application
of engineering and planning measures that has often been the most
successful approach in changing road user behavior.”
Urban Safety Management: Guidelines for Developing Countries, DFID, 2003
4.3 Road Accident Prevention by Improved Planning and Design
Source: AusRAP, 2012

19
Source: Timo Hoffmann, PTV Group, 2014

20
Source: Hills, B. L. and Baguley, C. J. (1992)
Examples of planning and engineering design that affect road-safety

21
The typical evolution of community design and street networks in the US. It began
with the grid (pictured left), but gradually developed into the 'tree' system (right) as
planners tried to incorporate more green and open spaces
http://www.dailymail.co.uk/sciencetech/article-2724023/
The more compact a city is, the lower the
levels of traffic fatalities!!!
The evolution of community design and street networks in the US

22
Street Network Types
Source: adapted from Marshall, W.E. and N.W. Garrick (2010) "Street Network Types and Road Safety", Urban Design International,
10.1057/udi.2009.31, April 21 2010.
https://people.hofstra.edu/geotrans/eng/ch6en/conc6en/street_network_types.html

23
Source: Brannolte, U. (2014)

24
Source: Brannolte, U. (2014)
Safety related Solutions for
intersection control
Roundabouts
have lowest
ACR

25
 Safe planning of road network is based on the three safety planning principles: Minimize exposure,
minimize risk, and minimize consequences.
Safe Network Shapes
Source: SWOV, 2001
Table 1. Score of three network structure on three indicators
Indicators
Grid network
(1)
Limited access
network (2)
Organic network
(3)
Road safety - + ++
Accessibility ++ + -
Costs - ++ +
 The score ‘-‘ indicates that an aspect has scored badly:
high costs, many accidents, poor accessibility
 The suitability of the three different network structures
can be judged by three indicators: Road safety,
accessibility, and costs.
(3) Organic network structure
(2) Limited access network
(1) Grid network structure

26
Intersection Planning (1)
 Traffic safety of intersection types
is determined by number of
conflict points.
 Multi-legged intersections should
not be used because of complex
traffic situation and unfavorable
sight angles.
 The fewer the potential conflict
points, the safer the intersection
will be.
 The speed-reducing effect of
roundabouts is caused by
deflection for entering traffic and
limited diameter of roundabout.
Source: SWOV, 2001
Figure 11. Intersection types and major conflict points of
each type

27
Spacing Between Public Street Intersections
(minimum spacing)

28
Source: SWOV, 2001
Figure 12. Areas of conflict at intersections with
different angles
 The angle of intersection should be as close as possible to 90 degrees. Angles other than
90 degrees cause the following safety problems:
 The area of conflict increases
 The visibility is limited
 Larger turning roadways are
required
 The exposure time through the
intersection increases

29
Examples of reconstruction of skew intersections
Source: SWOV, 2001

30
Road Hierarchy

31
Road Hierarchy

32
Safe Design of Roads
Figure 14. Driver expectancy

33
Safe Design of Roads
Figure 15. Intersection design
Safe design of intersections
must consider:
 Visibility
 Sight distances
 Clear road markings and
signing
 Islands and bollards to
protect drivers/pedestrians
 Restriction of turning
movements
 Segregated and safe routing
for pedestrians

34
4.4 Approaches to Accident Reduction
 There are four recognized approaches to accident reduction by the application
of cost effective treatments of existing roads. These are:
 Single sites: treatments of specific sites or short lengths of roads at
which accidents cluster;
 Mass action: application of a known remedy to locations which have
common accident factors;
 Route action: application of remedies to a road having above
average accident rate for that type or class of road;
 Area action: aggregation of remedial measures over an area with an
accident rate above a predetermined level; particularly aimed at
dealing with scattered accidents and usually in urban areas.

35
Nguyen Huu Huy. PhD
EU-Asia Road Safety Centre of Excellence (RoSCoE)
Office:
Prince of Songkla University
Sirindhorn Applied Engineering Research Building
Hat Yai, 90112
Thailand
Contact:
Phone: +84 939098090
E-mail: huycongtrinh@yahoo.com
Website: www.nice-roads.com
Thank You

An Introduction To Road Safety Engineering

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