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Selecting Countermeasures

Module 5

Safety Analysis in a Data-limited, Local Agency Environment

July 22, 2013 - Boise, Idaho

Learning Objectives

Define key concepts: Probable contributing

factors Target crashes

List and discuss the steps in the countermeasure selection process

Explain what a crash modification factor (CMF) is and how it is used in countermeasure selection

Explain the importance of cost effectiveness evaluation

Discuss the steps in the cost effectiveness evaluation

Describe other considerations in the countermeasure selection process

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Countermeasure Selection

Identify target crashes• Manner of collision

(aka collision type)• Crash severity• Behavioral factors

Identify probable contributing factors• Human • Vehicle• Roadway & Roadside

Consider countermeasures • Link with contributing

factors

Evaluate countermeasures• Potential impact

Principles

LINKAGE

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Probable Contributing Factors

The ‘cause’ of a crash is very difficult to determine

Crash reports allow us to identify probable contributing factors

Crash reports reflect common factors that were present

What it means

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Probable Contributing Factors

Driver inattention – slower response time Driver under the influence of alcohol

and/or drugs – reduces driver capabilities Too high a speed for prevailing conditions Failure to yield right of way at a traffic

signal when turning left/right Younger drivers – inexperience may

create higher crash involvement risk

Examples

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Target crashes

Contributing factors

Context (e.g. land use & users)

Site conditions

Targeted solutions (counter-

measures)

Target Crashes

Key considerations:A countermeasure usually only change one or

a subset of the crashes at a site

A countermeasure may increase some crash groupings and reduce other crash groupings

What it means

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Target Crashes

Run-off the road crashes Crashes involving pedestrians Red-light running crashes Angled crashes Drinking and driving crashes (behavioral)

Examples

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Target Crashes

Think about your state Strategic Highway Safety Plan1. What are the priorities in the plan?2. Are there any of the priorities that are more

prevalent on the types of facilities in your city/town/county or region?

3. Who are participating in the development of the SHSP? Can you partner with them?

Examples: expand perspective

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Countermeasure Selection

Cost-effectiveness: Limited resources Desire the largest reduction in fatalities and

serious injuries possible Context:

High-speed facility with limited access? Rural town centers with vulnerable users? Suburban arterial with driveway accesses?Urban central business district?

Factors that impact selection

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Evaluate Countermeasures

Considerations when selecting a countermeasure: Impact on target crashes (CMF)

Frequency & severity – are we reducing the overall severity of crashes

Economic impact Short, medium or long-term

Reliability (proven vs. experimental)Other tradeoffs that can’t be measured

Process

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Crash Modification Factor

Value that quantifies the impact on crashes/ crash groupings/ severities

Example: CMF=0.9

If fatal and injury crashes in a particular crash type] Before treatment = 20 crashes per year Then after treatment = 20 x 0.9=18 crashes per year

Advantage: modification indicates that countermeasures increase or decrease crashes

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CMF

Crash Reduction Factors

CRF vs. CMF If the CMF = 0.9 then the CRF = 1-CMF=0.1Example:

If fatal and injury crashes in a particular crash type: Before treatment = 20 crashes per year Reduction in crashes = 20 x 0.1= 2 crashes per

year

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CRF

PROVEN COUNTERMEASURESInfrastructure

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Proven countermeasures address crashes in focus areas:• Intersections• Pedestrians• Roadway Departure

FHWA Office of Safetyhttp://safety.fhwa.dot.gov/provencountermeasures/

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Roundabouts

Corridor Access Management

Backplates with Retroreflective Borders

Longitudinal Rumble Strips & Stripes (Two-Lane Roads)

Enhanced Delineation & Friction for Horizontal Curves

Safety Edge

Medians & Pedestrian Crossing Islands (Urban)

Pedestrian Hybrid Beacon (HAWK)

Road Diet

Graphics: FHWA Office of Safety

RoundaboutsThe Challenge Est. 300k signalized

intersections in US 1/3 intersection fatalities

@ signalized int 2,300 ped fatalities

RLR: ≈700 annual fatalities

Safety Performance Two-way STOP to

roundabout: up to 82% reduction in severe (injury/fatal) crashes & 44% in all crashes

Signal to roundabout: up to 78% reduction in severe (injury/fatal) crashes & 48% reduction in all crashes.

17Source: Washington State Department of Transportation

Corridor Access Management

The Challenge Conflict potential at at-

grade intersections (driveways, public roads)

Number & types of conflict influence safety performance

Safety Performance 5-23% reduction in all

crashes along two-lane rural highways, and

25-31% reduction in severe (injury/fatal) crashes along urban/suburban arterials

18Graphics: FHWA Office of Safety

Backplates with Retroreflective Borders

The Challenge Unintended RLR crashes

Safety Performance 15% reduction in all

crashes at urban, signalized intersections

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Source: FHWA Office of Safety

Graphics: FHWA Office of Safety

Longitudinal Rumble Strips & Stripes (Two-Lane Roads)

The Challenge Roadway departure

crashes: 53% of fatal crashes annually

Inattentive drivers veering out of the travel lane

Safety Performance Center line rumble strips on:

rural two-lane roads: 44% reduction of head on / fatal and injury crashes.

urban two-lane roads: 64% reduction of head-on / fatal and injury crashes.

Shoulder rumble strips on rural two-lane roads: 36% reduction of run-off-road fatal and injury crashes.

20Graphics: FHWA Office of Safety

Enhanced Delineation & Friction for Horizontal Curves

The Challenge Horizontal curves: 28% of all

fatal crashes

Chevron signs, curve warning signs, and/or sequential flashing beacons: anticiapated 38-43% reduction in all fatal and injury crashes.

Chevron signs on horizontal curves: anticipated 16% reduction in non-intersection fatal and injury crashes.

Safety Performance

New fluorescent curve signs or upgrading existing curve signs to fluorescent sheeting: anticipated 25% reduction in non-intersection fatal and injury crashes.

Providing static combination horizontal alignment/advisory speed signs can generate a 13% reduction in all injury crashes.

Refinishing pavement with microsurfacing treatment can bring about a 43% reduction in all fatal and serious injury crashes.

FHWA CMF Clearinghouse

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Safety EdgeThe Challenge Studies suggest crashes

involving edge drop-offs: 4x more likely to be fatal on similar roads

Safety Performance Eliminates tire scrubbing:

associated with loss of control of a vehicle

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Source: FHWA Office of Safety

Medians & Pedestrian Crossing Islands (Urban/Suburban)

The Challenge >70% pedestrian fatalities

at midblock locations Vehicle speeds

>80% pedestrians die when hit by vehicles ≥ 40mph

<10% pedestrians die when hit by vehicles @ 20mph

Safety Performance Installing raised medians

or pedestrian refuge areas at marked crosswalks:

anticipated 46% reduction in pedestrian crashes

unmarked crosswalk locations: anticipated 39% reduction in pedestrian crashes

23Source: FHWA Office of Safety

Pedestrian Hybrid Beacon(HAWK)

The Challenge >70% pedestrian fatalities

at midblock locations Vehicle speeds

>80% pedestrians die when hit by vehicles ≥ 40mph

<10% pedestrians die when hit by vehicles @ 20mph

Safety Performance

Up to a 69% reduction in pedestrian crashes

Up to a 29% reduction in total roadway crashes

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Source: FHWA Office of Safety

Road DietThe Challenge >70% pedestrian fatalities

at midblock locations Vehicle speeds

>80% pedestrians die when hit by vehicles ≥ 40mph

<10% pedestrians die when hit by vehicles @ 20mph

Safety Performance• Reduce # lanes for

pedestrians to cross: reduce multiple-threat crash

• Reduce rear-end and side-swipe crashes

• Improve speed limit compliance reduced crash severity in event of a crash

25Source: FHWA Office of Safety

ADT< 15,000

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Cost Effectiveness Evaluation

Reductions in crashes are considered cost savings, or benefits

Select countermeasures with the most benefits

Target total crashes, severe crashes, or specific crash types

The how and the why

Cost Effectiveness Evaluation

When evaluating countermeasures, compare the benefits to the cost to implement, creating a B/C ratio.The benefits are the reduction in the

frequency and severity of the target collision type(s)

The larger the B/C ratio, the better the rate of return.

Basic steps

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Value of Advanced Methods

The advanced statistical methods in the HSM allows us to account for regression to the mean. This gets us closer to spending our resources on safety where it is most needed, i.e. where we’ll more likely to achieve the performance.

Need-based targeted investment

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Tools & Resources (Module 6)

FHWA CMF Clearinghouse usRAP FHWA Resources for Local Agencies

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www.cmfclearinghouse.org

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usRAP Tools Software for Network Screening Able to:

Review an entire highway network and identify improvement locations

Identify cost-effective highway infrastructure improvements

Software is simple and easy to use Required input data can be assembled

with moderate effort

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usRAP Tools Software for Network Screening Identifies:

Potential locations for safety improvement projects Candidate project types

Web-based and easily accessible To be demonstrated later in the workshop Software access and training are available

through AAA Foundation for Traffic Safety

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Summary: Module 5

Match countermeasures to target crash type(s) and severity

Crash Modification Factors (CMFs) A CMF of 0.9 means we can expect to see 90% of

the target crash type(s) & severities after implementation

Economic evaluation of the countermeasure(s) allows us to assess return on investment

Tools and resources37

End of Module 5

Questions?

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