Dr.Makendran Chapter -II Accident Studies & Collision Diagram .pdf

CENGRTE7301- ROAD SAFETY AND
ACCIDENT ANALYSIS
Chapter –II
Accident Studies & Collision Diagram
Dr. MakenDran M.E., Ph.D.
Assistant Professor
Road and Transportation Engineering
Department of Civil Engineering
Wollega University, Nekemte, Ethiopia 1

Content
This Chapter covers one of the most important negative
impact of transportation system, namely the accidents.
 Some salient accident statistics
 Causes of accidents
 Accident data collection
 Accident investigation
 Accident Analysis
 Fundamental Definitions of Terms
 Accident patterns
 Collision Diagrams
 Construction of Collision Diagram
 Crash Diagnosis
2

Introduction
• The problem of accident is a very acute in highway
transportation due to complex flow pattern of vehicular
traffic, presence of mixed traffic along with
pedestrians.
• Traffic accident leads to loss of life and property. Thus the
traffic engineers have to undertake a big responsibility of
providing safe traffic movements to the road users and
ensure their safety.
• Road accidents cannot be totally prevented but by
suitable traffic engineering and management the accident
rate can be reduced to a certain extent.
• For this reason systematic study of traffic accidents are
required to be carried out.
• Proper investigation of the cause of accident will help
to propose preventive measures in terms of design and
control. 3

Objectives of accident studies
Some objectives of accident studies are listed below:
1. To study the causes of accidents and suggest
corrective measures at potential location
2. To evaluate existing design
3. To compute the financial losses incurred
4. To support the proposed design and provide economic
justification to the improvement suggested by the
traffic engineer
5. To carry out before and after studies and to
demonstrate the improvement in the problem.
4

Causes of road accidents
• The various causes of road accidents are:
1.Road Users - Excessive speed and rash driving, violation of traffic
rules, failure to perceive traffic situation or sign or signal in
adequate time, carelessness, fatigue, alcohol, sleep etc.
2.Vehicle - Defects such as failure of brakes, steering system, tyre
burst, lighting system .
3.Road Condition - Skidding road surface, pot holes, ruts.
4.Road design - Defective geometric design like inadequate sight
distance, inadequate width of shoulders, improper curve design,
improper traffic control devices and improper lighting,.
5.Environmental factors -unfavorable weather conditions like mist,
snow, smoke and heavy rainfall which restrict normal visibility and
and makes driving unsafe.
6.Other causes -improper location of advertisement boards, gate of
level crossing not closed when required etc..
5

Accident statistics
• The statistical analysis of accident is carried out
periodically at critical locations (or) road stretches which
will help to arrive at suitable measures to effectively
decrease accident rates.
• It is the measure (or estimates) of the number and severity
of accident.
• These statistics reports are to be maintained zone-wise.
• Accident prone stretches of different roads may be assessed
by finding the accident density per length of the road.
• The places of accidents are marked on the map and the
points of their clustering (BLACK SPOT) are determined.
6

Accident statistics (Contd…)
• By statistical study of accident occurrence at a
particular road or location or zone of study for a long
period of time.
• it is possible to predict with reasonable accuracy
the probability of accident occurrence per day or
relative safety of different classes of road user in that
location.
• The interpretation of the statistical data is very important
to provide insight to the problem.
7

Accident data collection
a) The accident data collection is the first step in the accident study.
b) The data collection of the accidents is primarily done by the police.
c) Motorist accident reports are secondary data which are filed by
motorists themselves.
The data to be collected should comprise all of these parameters:
1. General
2. Location
3. Details of vehicle involved
4. Nature of accident
5. Road and traffic condition
6. Primary causes of accident
7. Accident cost

The data to be collected should comprise all of these parameters:
1. General - Date, time, person involved in accident, classification of
accident like fatal, serious, minor
2. Location - Description and detail of location of accident
3. Details of vehicle involved - Registration number, description of
vehicle, loading detail, vehicular defects
4. Nature of accident - Details of collision, damages, injury and casualty
5. Road and traffic condition - Details of road geometry, surface
characteristics,type of traffic, traffic density etc..
6. Primary causes of accident - Details of various possible cases
(already mentioned) which are the main causes of accident.
7. Accident cost - Financial losses incurred due to property damage,
personal injury and casualty
Accident data collection (Contd…)

• These data collected need proper storing and retrieving for the
following purpose. The purposes are as follows:
1.Identification of location of points at which unusually high
number of accident occur.
2.Detailed functional evaluation of critical accident location to
identify the causes of accidents.
3.Development of procedure that allows identification of hazards
before large number of accidents occurs.
4.Development of different statistical measures of various
accident related factors to give insight into general trends, common
casual factors, driver profiles, etc.
Accident data collection (Contd…)

Accident investigation
The accident data collection involves extensive investigation which
involves the following procedure:
1.Reporting: It involves basic data collection in form of two
methods:
a. Motorist accident report
b. Police accident report
2.At Scene-Investigation
3.Technical Preparation
4.Professional Reconstruction
5.Cause Analysis

Accident investigation (Contd…)
1. Reporting: It involves basic data collection in form of two methods:
a. Motorist accident report - It is filed by the involved motorist involved in all
accidents fatal or injurious.
b. Police accident report - It is filed by the attendant police officer for all
accidents at which an officer is present. This generally includes fatal accidents
or mostly accidents involving serious injury required emergency or hospital
treatment or which have incurred heavy property damage.
2. At Scene-Investigation: It involves obtaining information at scene such as
measurement of skid marks, examination of damage of vehicles, photograph of final
position of vehicles, examination of condition and functioning of traffic control
devices and other road equipment's.
3. Technical Preparation: This data collection step is needed for organization and
interpretation of the study made. In this step measurement of grades, sight
distance, preparing drawing of after accident situation, determination of
critical and design speed for curves is done.
4. Professional Reconstruction: In this step effort is made to determine from
whatever data is available how the accident occurs from the available data. This
involves accident reconstruction which has been discussed under Section No.7 in
details. It is professionally referred as determining behavioral or mediate
causes of accident.
5. Cause Analysis: It is the effort made to determine why the accident occurred from
the data available and the analysis of accident reconstruction studies..
What are the steps in involved in Accident investigation (Contd..)

Accident data analysis
• The purpose is to find the possible causes of accident related
to driver, vehicle, and roadway. Accident analyses are made
to develop information such as:
1.Driver and Pedestrian - Accident occurrence by age groups
and relationships of accidents to physical capacities and to
psychological test results.
2.Vehicle - Accident occurrence related to characteristic of
vehicle, severity, location and extent of damage related to
vehicles.
3.Roadway conditions - Relationships of accident occurrence
and severity to characteristics of the roadway and roadway
condition and relative values of changes related to roadways.

Accident data analysis (Contd…)
It is important to compute accident rate which reflect
accident involvement by type of highway.
These rates provide a means of comparing the relative
safety of different highway and street system and traffic
controls.
Another is accident involvement by the type of drivers
and vehicles associated with accidents.

• The five KABCO crash severity levels are:
• K - Fatal injury: an injury that results in death;
• A - Incapacitating injury: any injury, other than a fatal injury,
which prevents the injured person from walking, driving or
normally continuing the activities the person was capable of
performing before the injury occurred;
• B – Non-incapacitating evident injury: any injury, other
than a fatal injury or an incapacitating injury, which is evident to
observers at the scene of the accident in which the injury
occurred;
• C - Possible injury: any injury reported or claimed which is not
a fatal injury, incapacitating injury or non-incapacitating evident
injury and includes claim of injuries not evident;
• O – No Injury/Property Damage Only (PDO).
Fundamental Definitions of Terms

Collision Diagrams
Collision diagrams are used to display and identify similar
accident patterns.
They provide the following information are as follows
The type and number of accidents;
Including conditions such as time of day, day of week,
Climatic conditions,
Pavement conditions, and
Other information critical to determining the causes of
safety problems.
• Accident reports should be organized by year of occurrence
and accident type for the analysis period.

How to Construction of Collision Diagram
Sketch the location diagram for either an intersection or roadway
section using a standard form, details are as follows

How to Construction of Collision Diagram

How to mark the Collisions diagram at Junction ?

• The purpose of site/crash diagnosis is: to develop an
understanding of factors that may lead to crashes.
• It begins with a review of crash data that may identify
any patterns in the types of crashes and/or severity of
crashes that have occurred.
• The activities included in the diagnosis step provide
an understanding of crash patterns, past studies, and
physical characteristics before potential
countermeasures are selected.
• The intended outcome of a diagnosis is :the
identification of the causes of the collisions and
potential safety concerns or crash patterns that can
be evaluated further
Purpose of crash diagnosis/Collision Diagram?

How many steps involved in Crash Diagnosis?
The diagnosis procedure involves the following three steps
Step 1: Safety Data Review
Step 2: Assigning Supporting Documentation
Step 3: Assess Field Conditions

• The diagnosis procedure involves the following three
steps
Step 1: Safety Data Review
• Review crash types, severities, and environmental
conditions to develop summary descriptive statistics for
pattern identification and,
• Review crash locations.
Step 2: Assigning Supporting Documentation
• Review past studies and plans covering the site vicinity to
identify known issues, opportunities, and constraints.
Step 3: Assess Field Conditions
• Visit the site to review and observe multi-modal
transportation facilities and services in the area,
particularly how users of different modes travel through
the site.
What are the steps involved in Diagnosis procedure?

1. SAFETY DATA REVIEW
• Compiling and reviewing three to five years of safety data is suggested to
improve the reliability of the diagnosis.
• The safety data review considers:
• Descriptive statistics of crash conditions (e.g., counts of crashes by
type, severity, and/or roadway or environmental conditions); and
• Crash locations (i.e., collision diagrams, condition diagrams, and crash
mapping).
• 1.1 Descriptive Crash Statistics
Crash databases generally summarize crash data into 3 categories:
A. Information about the crash,
B. The vehicle in the crash,
C. Peoples in the crash.
In this step, crash data are reviewed and summarized to identify potential
patterns.

1. SAFETY DATA REVIEW (Contd…)

Crash severity – KABCO levels
K – Fatal injury
A – Incapacitating injury
B – Non-incapacitating evident injury
C – Possible injury
O – Property damage only (PDO)

1. SAFETY DATA REVIEW(Contd…)

S.No. Date Time Type Ped Bike Fatal Injuries Day/ Night Wet/Dry
1 1/6/2008 7:30 p.m. Left Turn 0 0 1 Night Dry
2 1/21/2008 12:15 p.m. Rear End 0 0 2 Day Dry
3 2/6/2008 2:30 p.m. Left Turn 0 0 1 Day Dry
4 4/1/2008 4:50 p.m. Angle 0 0 0 Day Dry
5 4/20/2008 8:25 p.m. Left Turn 0 0 0 Night Dry
6 5/16/2008 5:30 p.m. Rear End 0 0 2 Day Wet
7 5/26/2008 9:00 p.m. Angle 0 0 1 Night Dry
10 9/1/2008 10:00 a.m. Left Turn 0 0 0 Day Dry
12 10/30/2008 3:25 p.m. Rear End 0 0 1 Day Dry
13 11/11/2008 6:30 p.m. Rear End 0 0 0 Night Wet
1. SAFETY DATA REVIEW…

 Bar charts, pie charts, or tabular summaries are useful for
displaying the descriptive crash statistics.
 The purpose of the graphical summaries is to make patterns visible.

1.2 Summarizing Crashes by Location
• Collision Diagram
A collision diagram is: 2D plan view representation of the crashes
that have occurred at a site within a given time period.
A collision diagram simplifies the visualization of crash
patterns.
Crash clusters or particular patterns of crashes by collision
type (e.g., rear-end collisions on a particular intersection
approach) may become evident on the crash diagram that
were otherwise overlooked.
1. SAFETY DATA REVIEW(Contd…)

Collusion diagram
 From the collusion diagram illustrates total crashes occurring
during the study time period.
 The diagram shows the location of each crash, as well as the crash
type. The crashes are numbered in sequential order, starting with
the most recent.
 As shown in Collusion Diagram, there are multiple driveways on
the south side of the study roadway (First Avenue). The collision
diagram identifies the majority of the crashes are rear end
collisions or left turn collisions with vehicles entering the
driveways.
 The collision diagram helps with identifying patterns, but it may
not provide enough information to identify the contributing
factors. The next step is to conduct a field investigation to
determine what might be causing these crashes.

• Crash Mapping
• Electronic databases of roadway network and
geocoded crash data can be integrated with a
Geographic Information Systems (GIS) database.
• GIS allows data to be displayed and analyzed
based on spatial characteristics.
• Evaluating crash locations and trends with GIS is
called crash mapping.
1. SAFETY DATA REVIEW…

ASSESS SUPPORTING
DOCUMENTATION

2.ASSESS SUPPORTING DOCUMENTATION
• Assessing supporting documentation is the second
step in the overall diagnosis of a site.
• The goal of this assessment is :to obtain and review
documented information or personal testimony of local
transportation professionals that provides additional
perspective to the crash data review.
• The supporting documentation may identify new safety
concerns or verify the concerns identified from the
crash data review.

The following types of information may be useful as supporting
documentation to a site safety assessment:
• Current traffic volumes for all travel modes;
• As-built construction plans;
• Relevant design criteria and pertinent guidelines;
• Inventory of field conditions (e.g., traffic signs, traffic control devices, number
of travel lanes, posted speed limits, etc.);
• Relevant photo or video logs;
• Maintenance logs;
• Recent traffic operations and/or transportation studies conducted in the vicinity
of the site;
• Land use mapping and traffic access control characteristics;
• Historic patterns of adverse weather;
• Known land use plans for the area;
• Records of public comments on transportation issues;
• Roadway improvement plans in the site vicinity; and,
• Anecdotal information about travel through the site.

3. ASSESS FIELD CONDITIONS
• The diagnosis can be supported by a field
investigation.
• Field observations can serve to validate safety
concerns identified by a review of crash data or
supporting documentation.
• During a field investigation, firsthand site information
is gathered to help understand motorized and non-
motorized travel to and through the site.
• Careful preparation, including participant selection and
coordination, helps get the most value from field time.

3. ASSESS FIELD CONDITIONS
• Roadway and roadside characteristics
• Traffic conditions
• Traveler behavior
• Roadway consistency
• Land uses
• Weather conditions
• Evidence of problems

Road Reconstruction
The number of vehicles on the road increases from year to
year, which introduces complications into organization of
traffic, sharply reduces the operation and transportation
characteristic of roads and lead to the growth of accident rate.
This leads to the need of re constructing road.
The places of accidents need to be properly
marked so that the reconstruction can be
planned accordingly.

Before After Reconstruction
Road Reconstruction (Contd….)

Reconstruction process may
also include construction of a
new road next to the existing
road, renewal of pavement
without changing the
horizontal alignment or profile
of the road, reconstruction a
particular section of road.
Few more examples of
reconstruction of selected
road section to improve traffic
safety are shown in Figure
42:14.

Channelization
• The Channelization of traffic at intersection
separates the traffic stream travelling in different
direction, providing them a separate lane that
corresponds to their convenient path and
spreading as far as possible the points of conflict
between crossing traffic streams.
• The traffic lanes are separated by marking
relevant lines or by constructing slightly elevated
islands.
• Proper Channelization reduces confusion and its
leads to reduce the accidents.

Figure. Channelized Intersection Ensuring safety

Case Study: Crash Pattern
Analysis
Countermeasure Identification
Example:- For Reference purpose

Crash patterns should be identified through an analysis of the
crash data for specific locations.
The crash patterns can be identified using a collision diagram,
collision summary, field reviews, input from other disciplines, and
other information.
When conducting a crash analysis, it is useful to create a summary
table of the crashes that occurred during the study period.
The table could include a summary of the pavement conditions,
crash type, lighting conditions, number of injuries or fatalities,
and any other relevant information, such as driver-related facts
(i.e., age, gender, restraint use).
The summary table can provide insight for identifying crash
patterns. An example collision summary is shown in Next
Table 3.1
Case Study: Crash Pattern Analysis (Contd….)

Case Study: Crash Pattern Analysis
An example collision summary is shown in Table 3.1
STUDY PERIOD: 1/1/08-12/31/08 CITY: Springfield
ROADWAY: Center Street COUNTY: Orange
INTERSECTION: Main Street SOURCE OF DATA: Local Law Enforcement
No. Date Time Type
Ped
Bike Fatal
Injurie
s
Property
Damage
Day/
Night
Wet/
Dry Contributing Cause
1 1/6/2008 7:30 p.m. Left Turn 0 0 1 $2,500 Night Dry FTYROW*
2 1/21/2008 12:15 p.m. Rear End 0 0 2 $1,500 Day Dry Followed too Closely
3 2/6/2008 2:30 p.m. Left Turn 0 0 1 $3,000 Day Dry FTYROW
4 4/1/2008 4:50 p.m. Angle 0 0 0 $2,000 Day Dry FTYROW
5 4/20/2008 8:25 p.m. Left Turn 0 0 0 $2,500 Night Dry FTYROW
6 5/16/2008 5:30 p.m. Rear End 0 0 2 $1,000 Day Wet Followed too Closely
7 5/26/2008 9:00 p.m. Angle 0 0 1 $2,500 Night Dry FTYROW
10 9/1/2008 10:00 a.m. Left Turn 0 0 0 $2,500 Day Dry FTYROW
12 10/30/2008 3:25 p.m. Rear End 0 0 1 $1,000 Day Dry Followed too Closely
13 11/11/2008 6:30 p.m. Rear
End
0 0 0 $1,500 Night Wet Followed too Closely
14 1/21/2008 5:00 p.m. Left
Turn
0 0 0 $3,000 Day Dry FTYROW
15 12/19/2008 4:55 p.m. Left
Turn
0 0 3 $2,000 Day Dry FTYROW
Total
No.
Ped/
Bike Fatal Injuries Angle
Left
Turn
Rear
End
Side
Swipe
Out of
Control Night Wet
15 0 0 9 2 9 4 0 0 4 2
100% 0% 0% 60% 13% 60% 27% 0% 0% 27% 13%
* FTYROW – Failed to Yield Right-of-Way.

• Table 3.1 summarizes the date and time of each collision, the crash type,
injuries, time of day (day or night), and the contributing cause reported by the
law enforcement officer.
• This summary can help identify any dominant crash types or prevailing
conditions.
• It may also be beneficial to summarize driver-related information such as age,
gender, restraint use, level of impairment, etc.
• As shown in Table 3.1, left turn collisions appear to be a significant problem at
this intersection, comprising 60 percent of the crashes during the one-
year time period shown.
• In addition, it is sometimes helpful to compare site specific crash summaries
to statewide averages to identify trends or overrepresentation.
• In this case, there were no apparent trends in crashes occurring at night
(27 percent) or on wet pavement conditions (13 percent).
• Although a crash summary provides some insight on potential issues, the next
step is to develop a collision diagram to better understand what is occurring
on a study roadway segment or intersection.
Case Study: Crash Pattern Analysis (Contd….)

Collision Diagram
Transportation professionals prepare collision diagrams to demonstrate the flow and direction of travel to
further illuminate the circumstances surrounding crashes.
The collision diagram provides a visual representation of the crash data and can help identify
crash patterns. Figure 3.3 shows an example collision diagram.
Figure 3.3 illustrates 19 crashes
occurring during the study time
period. The diagram shows the location
of each crash, as well as the crash type.
As shown in Figure 3.3, there are multiple
driveways on the south side of the study
roadway (First Avenue). The collision
diagram identifies the majority of the
crashes are rear end collisions or left
turn collisions with vehicles entering the
driveways.
The collision diagram helps with
identifying patterns, but it may not
provide enough information to identify
the contributing factors.
Figure 3.3 Collision Diagram

Dr.Makendran Chapter -II Accident Studies & Collision Diagram .pdf

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