diagnosis of sites with potential for safety improvement 1 module 4 safety analysis in a...
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Diagnosis of Sites with Potential for Safety Improvement
Module 4
Safety Analysis in a Data-limited, Local Agency Environment
July 22, 2013 - Boise, Idaho
Module 4 Objectives 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 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 approachesSite-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) 5
Site-specific Diagnosis We can gather information for diagnosis
through one or more of these methods: Site visitCrash history Local knowledgeCrash 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): 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
Traffic volume counts Access management study Origin-destination study
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Site VisitsGEOMETRIC 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
Other factors
Roadside design Sign visibility
Clear zones Sign conditions
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Creating Collision Diagrams
Building a collision diagram from crash reportsReflect actual roadway geometry and features
and scale to the extent possible
Symbols used for various crash types Denoting severity level, vehicle type, other
variablesLabeling: 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 DiagramsSymbols & 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 DiagramsExample 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 PedBike
Fatal Injuries Prop Damg
Day/Night
Wet/Dry
ContribCause
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: identifyingRelative frequency of crash types (crash
manner)Which approaches/ movements have the highest
crash involvementDays of week or times of day that are
overrepresentedGeometric 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 contextUnderstanding 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? 18
Human Factors2nd Edition of the Human Factors Guidelines NCHRP Report 600
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 blindnessVisibilityEtc.
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Local Knowledge
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.20
Road Safety Audits 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 owner21
Making the connection
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 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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