Transcript TRB ANB 25 User Liaison and Technology Transfer

Module 5
Selecting
Countermeasures
Safety Analysis in a Data-limited, Local
Agency Environment
July 22, 2013 - Boise, Idaho
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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
Principles
Evaluate
countermeasures
Consider
countermeasures
Identify target
crashes
• Manner of collision
(aka collision type)
• Crash severity
• Behavioral factors
Identify probable
contributing
factors
• Potential impact
• Link with contributing
factors
• Human
• Vehicle
• Roadway & Roadside
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Probable Contributing Factors
What it means
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

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Probable Contributing Factors
Examples
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

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Contributing
factors
Context (e.g.
land use &
users)
Site conditions
Target
crashes
Targeted
solutions
(countermeasures)
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Target Crashes
What it means

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
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Target Crashes
Examples
Run-off the road crashes
 Crashes involving pedestrians
 Red-light running crashes
 Angled crashes
 Drinking and driving crashes (behavioral)

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Target Crashes
Examples: expand perspective

Think about your state Strategic Highway
Safety Plan
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?
1.
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Countermeasure Selection
Factors that impact 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?
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Evaluate Countermeasures
Process

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
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Crash Modification Factor
CMF


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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Crash Reduction Factors
CRF

CRF vs. CMF
 If
the CMF = 0.9 then the CRF = 1-CMF=0.1
 Example:
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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Proven
countermeasures
address crashes in
focus areas:
• Intersections
• Pedestrians
• Roadway Departure
PROVEN COUNTERMEASURES
Infrastructure
FHWA Office of Safety
http://safety.fhwa.dot.gov/provencountermeasures/
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Roundabouts
Safety Edge
Corridor Access
Management
Medians & Pedestrian
Crossing Islands (Urban)
Backplates with
Retroreflective Borders
Pedestrian Hybrid Beacon
(HAWK)
Longitudinal Rumble
Strips & Stripes (TwoLane Roads)
Road Diet
Enhanced Delineation
& Friction for
Horizontal Curves
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Graphics: FHWA Office of Safety
Roundabouts
The 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.
Source: Washington State Department of Transportation
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Corridor Access Management
The Challenge


Conflict potential at atgrade 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
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Graphics: FHWA Office of Safety
Backplates with
Retroreflective Borders
The Challenge

Unintended RLR crashes
Safety Performance

15% reduction in all
crashes at urban,
signalized intersections
Source: FHWA Office of Safety
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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.
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Graphics: FHWA Office of Safety
Enhanced Delineation &
Friction for Horizontal Curves
The Challenge


Horizontal curves: 28% of all
fatal crashes
Safety Performance


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.


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 Edge
The 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
Source: FHWA Office of Safety
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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
Source: FHWA Office of Safety
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
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Pedestrian Hybrid Beacon
(HAWK)
The Challenge


Safety Performance
>70% pedestrian fatalities
at midblock locations
Vehicle speeds


>80% pedestrians die
when hit by vehicles ≥
40mph
<10% pedestrians die
when hit by vehicles @
20mph
Source: FHWA Office of Safety


Up to a 69% reduction in
pedestrian crashes
Up to a 29% reduction in
total roadway crashes
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Road Diet
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
Source: FHWA Office of Safety
ADT< 15,000
Safety Performance
•
•
•
Reduce # lanes for
pedestrians to cross:
reduce multiple-threat
crash
Reduce rear-end and sideswipe crashes
Improve speed limit
compliance  reduced
crash severity in event of a
crash
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Cost Effectiveness Evaluation
The how and the why
Reductions in crashes are considered cost
savings, or benefits
 Select countermeasures with the most
benefits
 Target total crashes, severe crashes, or
specific crash types

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Cost Effectiveness Evaluation
Basic steps

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.
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Value of Advanced Methods
Need-based targeted investment

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.
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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 resources
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End of Module 5
Questions?
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