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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 ApproachStarts 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 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 marksDegree 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 facilitiesEdge drop-off Sign placement Land use and

vulnerable user generators

Other factors

Roadside design Sign visibilityClear 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: 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 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?

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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.

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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

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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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