Transcript TRB ANB 25 User Liaison and Technology Transfer Subcommittee

Module 4
Diagnosis of Sites
with Potential for
Safety Improvement
Safety Analysis in a Data-limited, Local
Agency Environment
July 22, 2013 - Boise, Idaho
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Module 4 Objectives
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Develop and use diagnostics
Describe different approaches to safety and how
diagnostics differ across these approaches
List studies that can support diagnostics
 Site
visits
 Collision diagrams
 Assessment of human factors
 Road safety audits/ assessments
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Diagnostic Questions
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What are the characteristics of the areas of interest
identified in Module 3?
 Geometry, roadside, safety features, operational
characteristics
What are the characteristics of the people involved in the
crashes?
 User age, purpose of trips, mode choice, safe/unsafe
behaviors
What are the characteristics of the crashes themselves?
 Over-represented crash types and characteristics
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Site-specific & systemic approaches
Site-Specific Approach
Systemic Approach
Starts with the identification of sites that
has potential for improvement based on
comparisons with similar sites
Starts with the identification of similar sites
that can be treated with a proven low-cost
countermeasure
Analysis of a particular site that was
selected based on a safety performance
measure
Identify sites with similar characteristics
that can be targeted with a particular
proven low cost countermeasure
Identify target crashes based on site
diagnostics and then selects a
countermeasure or combinations of
countermeasures to reduce the risk of
target crashes occurring or the severity of
these crashes
Address a particular collision type that is
often associated with fatal and serious
injuries
Countermeasure cost varies greatly and
can be for short, medium or long-term
implementation
Select and install one particular low cost
treatment at many similar sites to target a
specific crash contributing factor.
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Site-specific & systemic approaches

Most agencies use a combination of these
approaches
 to
treat locations with the highest potential for
improvement
 to reduce risk of possible events by
implementing low cost treatments system
wide (systemic)

Often, a combination of strategies can
have the greatest return on investment in
safety (benefit-cost ratio)
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Site-specific Diagnosis

We can gather information for diagnosis
through one or more of these methods:
 Site
visit
 Crash history
 Local knowledge
 Crash Analysis Safety Study (would include
site visits and incorporating local knowledge)
 Road safety audit/road safety assessments
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Road Safety Studies

A road safety study may require several
elements or activities (the nature of the
site governs what is needed):
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
Crash history analysis
Site observations: user behavior, specific
traffic control features, changes in traffic
flow and characteristics over different times
of the day
 Operating speed study
 Other
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Traffic volume counts
Access management study
Origin-destination study
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Site Visits
GEOMETRIC
DESIGN
TRAFFIC
CONTROL
OPERATIONS
EVIDENCE OF
CRASHES
Superelevation
Intersection control
Left turn storage
Skid marks
Degree of curvature
Passing guidance
Acceleration areas
Damaged signs
Site distance
Pavement markings
Deceleration areas
Crash debris
Pavement friction
Striping
Weaving (merging &
diverging)
New fences
Shoulder width
Lane width
Facilities and
features for
vulnerable users
Crash impact marks
on side of trees,
utility poles, etc.
Shoulder slope
Lane alignment
Transit facilities
Edge drop-off
Sign placement
Land use and
vulnerable user
generators
Roadside design
Sign visibility
Clear zones
Sign conditions
Other factors
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Creating Collision Diagrams

Building a collision diagram from crash
reports
 Reflect
actual roadway geometry and features
and scale to the extent possible
 Symbols used for various crash types

Denoting severity level, vehicle type, other
variables
 Labeling:
what information are you interested
in or would be most relevant for your site?
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Creating
Collision
Diagrams
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Creating Collision Diagrams
Symbols & summary tables
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Creating Collision Diagrams
Individual collisions can be listed on a
collision summary
 This can be done by hand on a paper
form, in readily available presentation
software, or by using diagraming software
 The most important: the diagram should
help us distinguish patterns or specific
characteristics of crashes at the site
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Creating Collision Diagrams
Example of summary for collision diagram
STUDY PERIOD: 1/1/08-12/31/08
CITY: Springfield
ROADWAY: Center Street
COUNTY: Orange
INTERSECTION: Main Street
SOURCE: Local Law Enforcement
No.
Date
Time
Type
Ped
Bike
Fatal
Injuries
Prop
Damg
Day/
Night
Wet/
Dry
Contrib
Cause
1
1/6
7:30
PM
Left
Turn
0
0
1
$2500
Night
Dry
FTYROW
2
1/21
12:15
PM
Rear
End
0
0
2
$1500
Day
Dry
FTC
3
2/6
2:30
PM
Left
Turn
0
0
1
$3000
Day
Dry
FTYROW
4
4/1
4:50
PM
Angle
0
0
0
$2000
Day
Dry
FTYROW
5
4/30
8:25
PM
Left
Turn
0
0
0
$2500
Night
Dry
FTYROW
6
5/16
5:30
PM
Rear
End
0
0
2
$1000
Day
Wet
FTC
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Interpreting Collision Diagrams

The value of collision diagrams: identifying
 Relative
frequency of crash types (crash
manner)
 Which approaches/ movements have the highest
crash involvement
 Days of week or times of day that are
overrepresented
 Geometric design issues that may be also
contributing
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What can we
learn from
the diagram?
Is any
information
missing?
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Users and context
Understanding the Users

Who are involved in crashes at this location?
Consider the following:
 Vulnerable users (peds, bikes, motorcycles, users
with disabilities)
 Driver ages (young, mature)
 Trip types (commuters, recreational trips, school
trips)
 Different modes, including transit and freight
vehicles

Why are they behaving the way they are?
What are their needs?
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Human Factors
2nd Edition of the Human Factors Guidelines
NCHRP Report 600
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What are the errors that drivers and users are
making?
Is driver expectation violated?
What are we expecting the driver to do?
 Judging distance and speed
 Inattentional blindness
 Visibility
 Etc.
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Local Knowledge
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The local community uses the facility the most –
and can offer valuable insights
Examples:
 Law enforcement:
crash locations where people are killed or
seriously injured
 Locations and particular crash types (DUI,
speeding, etc.)

 Local
maintenance staff know objects being
continually hit and replaced or how often
sight-distance blocking foliage is trimmed, etc.
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Road Safety Audits
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Independent, multi-disciplined group: engineers, law
enforcement, planners, elected officials, user group
advocates, educators, etc.
Planned or existing facilities (most beneficial for planning
or early in the design process)
Includes site visit
Consider multiple modes and their interactions
Consider human factors
Both diagnose (this module) and recommend
countermeasures (next module)
Result in a report of findings and recommendations
presented to facility owner
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Making the connection
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Diagnosis is our tool to identify
 Which
of the fatal and serious injury crashes are
the most common?
 What are the most common contributing factors?
 Who are the users we need to consider?

Diagnosis is the key to identifying the most
appropriate countermeasure/ combination of
countermeasures for target crash types and
considering the context in the process (the
role of the facility, land use, etc.)
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Summary
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Two ways to approach diagnosis: at individual
sites, or at similar sites across the system
Several means of gathering data for diagnosis
 Crash
history and diagrams
 Site visits
 Road safety study to gather volume, traffic patterns,
speeds, etc.
 RSAs and local knowledge

Aim to identify contributing factors to crashes
before you can choose appropriate
countermeasures
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End
Module 4
Questions?
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