Road Safety Management Process

Module 4-1

Roadway Safety Management Process

4

5

6

7

8

9

Network

Screening

Diagnosis

Countermeasure Selection

Economic

Appraisal

Prioritization of

Improvement Projects

4 5 6 7 8 9

Safety Effectiveness

Evaluation

Network

Screening

Module 4-1

Methods for Identifying Sites

The identification, examination and effective treatment of well-chosen sites will yield safety improvements…

3

Module 4-1

Methods for Identifying Sites

Goal – Identify and rank “sites with promise” • Those sites that, if treated, will experience decreases in

crashes

Example methods• Public involvement? Political pressure?

• High crash frequency history

• High crash rate

• Severity-weighted frequency (based on crash costs)

• Excess crashes

• Etc.

4

Module 4-1

Example: Excess Crashes

Compare actual crashes to expected crashes for this category of sites (e.g., two-lane rural intersections)

More details in Unit 4

5

Module 4-1

Network Screening

Identify sites that may benefit the most from a treatment

Establish Focus• Specific crash types (e.g., wet weather crashes)• Specific facility types (e.g., intersections)• Specific area/corridor

Select reference population• Groups of sites with similar characteristics

Select performance measures

Select screening method and do the screening

Module 4-1

Performance Measures

13 performance measures listed in the Highway Safety Manual

Range from very simple measures based on average crash frequency to advanced measures based on the empirical Bayes method

Module 4-1

How to Select a Performance Measure?

Data Availability• Is traffic volume data available?

• Are Safety Performance Functions available? If no, can they be estimated?

Does the performance measure account for Regression-to-the-Mean Bias

Module 4-1

How to Identify Sites with Promise?

Expected Number of Crashes

Excess Expected Difference compared to the average for comparable sites (also called deviation from the norm)

• Can be used Identify deviant sites

Can use empirical Bayes method to estimate expected crashes

Module 4-1

Determining deviant sitesC

rash

es p

er U

nit T

ime

Traffic Volume

A

Expected crashes (based on EB method)

SPF representing average for comparable sites (norm)

Excess

Module 4-1

Diagnosis

Crash Factors

• Human

• Roadway

• Vehicle

• Environmental

Collision Type

• Run-off Road

• Rear End

• Head On

• Sideswipe Same Direction

Module 4-1

Site Review Methods

Engineering Road Safety Audits• Immediate improvements (maintenance)

• Low cost safety improvements

• High cost safety improvements

Crash history• Collision diagram

Module 4-1

Example Collision Diagram

Module 4-1

Motives for Action

Economic Efficiency

Professional and Institutional Responsibility

Fairness

COUNTERMEASURE SELECTION

Module 4-1

Tools For Identifying Countermeasures

Engineering studies

Road safety audits

The Australian Safe Systems Approach

The Haddon matrix

Module 4-1

Step 1: Examine the Crash Data

Step 2: Conduct a Field Study

Step 3: Identify Potential Countermeasures

Step 4: Prioritize Countermeasures

Step 5: Implement the Chosen Countermeasure(s)

Step 6: Evaluate the countermeasure impact

17

Engineering Studies

Module 4-1

Road Safety Audits

Used for Roadway Corridors, Both Existing and New (Canada)

Characteristics of RSAs• A formal examination with a structured process;

• Conducted independently by professionals who are not currently involved with the project;

• Completed by a team of qualified professionals representing appropriate disciplines;

• Focuses solely on safety issues; and

• Examines the transportation site with respect to all potential road users.

18

Module 4-1

The Australian “Safe Systems Approach”

How?• Safer vehicles

• Safety roads and roadsides

• Controlling speeds

Can’t Prevent All Crashes

But Try To Assure No Serious Injuries or Deaths

Module 4-1

The Haddon Matrix

Crash-Related Factor Categories • Human

• Vehicle

• Roadway

• Environmental

Crash Time• Pre Crash

• Crash

• Post Crash

20

Module 4-1

The Haddon Matrix (cont.)

Can be use to • Categorize existing treatments to identify cells with few

• Categorize factors (e.g., fatigue, ambulance delay) to generate new treatments.

21

Element Pre Crash Crash Post Crash

Human

Vehicle/Equipment

Road/Physical Environment

Module 4-1

The Haddon Matrix -- Exercise1. Graduated Drivers Licensing

2. Airbags

3. Driver risk-taking propensity

4. Seat Belt Use

5. Distance to hospital

6. Electronic stability control

7. Driver age

8. Emergency Med. Svs. Training

9. GPS automatic crash notification

10. Rumble strips

11. Median barrier

12. Distance to roadside object

22

Element Pre Crash Crash Post Crash

Human

Vehicle/Equipment

Road/Physical Environment

Module 4-1

The Haddon Matrix (cont.)

23

Element Pre Crash Crash Post Crash

HumanGDL

Risk Taking

Driver Age

Seat Belt Use Driver Age

Vehicle/Equipment

Electronic Stability Airbags GPS Auto-Notification

Road/Physical Environment

Rumble Strips

Distance to Object

Median Barrier

Distance to Object

Distance to Hospital

EMS Training

Module 4-1

Sources for Potential Countermeasures

Roadway Countermeasures

• NCHRP Series 500

• Highway Safety Manual, Part D

• FHWA Crash Modification Factor Clearinghouse

• FHWA list of suggested (proven) countermeasures

NCHRP Report 617, Accident Modification Factors for Traffic Engineering and ITS Improvements

Behavioral Countermeasures

• Countermeasures That Work

Module 4-1

Countermeasure Sources:NCHRP Series 500 Guides

Countermeasures classified as:1. Proven, 2. Tried, or3. Experimental

Examples:• Relocate roadside objects (P)• Install shoulder rumble strips (T)• Delineate poles with

retroreflective tape (E)

Module 4-1

Countermeasure Sources:Highway Safety Manual First edition released in

2010

Provides practitioners with the best factual information and tools regarding safety consequences of design decisions.

Sections• Part A: Safety knowledge

• Part B: Safety management

• Part C: Crash prediction models

• Part D: Countermeasure selection and CMFs

Module 4-1

Countermeasure Sources:Crash Modification Factors Clearinghouse

Module 4-1

Countermeasure Sources:FHWA Suggested Countermeasures (2008) Road safety audits Rumble strips and

rumble stripes Median barriers Safety edge Roundabouts Left and right turn

lanes at stop-controlled intersections

Yellow and all red change intervals at traffic signals

Median and pedestrian refuge areas in urban and suburban areas

Walkways

Module 4-1

Countermeasure Sources:NHTSA “Countermeasures That Work”

Module 4-1

Question

When faced with many potential countermeasures, how does one choose which one(s) to implement?

Module 4-1

Comparing Countermeasures

Subjective comparisons• Which will garner the most public support?

• Which is most appropriate for the area?

Objective comparisons• Expected effectiveness -> decreases in crashes (CMFs)

• Expected costs -> installation and maintenance

Module 4-1

Market Research for Targeting Countermeasures

Identifying sub-population characteristics

Easing language barriers

Customizing campaigns and programs

Module 4-1

Market Research Techniques

What types of market research techniques can be used to target high crash risk groups?

Module 4-1

Market Research Techniques

Focus groups

Surveys

Observational studies

Cost Effectiveness of Alternative CountermeasuresPrioritize interventions and countermeasures based on effectiveness.

Module 4-1

Major Topics

Countermeasure Costs and Benefits

Programming Projects

Qualitative Considerations

Countermeasure Evaluation

Module 4-1

Countermeasure Costs

Startup or installation costs• Example?

Ongoing operational or maintenance costs• Example?

Resilience/staying power (“usable life”)• Which countermeasures would have shorter staying

power? Which would be longer?

Module 4-1

Countermeasures Benefits

Crashes prevented – use CMFs to estimate if available

Changes in crash severity• Signals and red light cameras

• Cable median barriers

Other benefits not related to safety (e.g., reduced delay)

Module 4-1

Countermeasure Benefits:Crash Modification Factors Crash modification factor (CMF) is a multiplicative

factor used to compute the expected number of crashes after implementing a given countermeasure at a specific site.

CMF =

CMF > 1 indicates an expected increase in crashes

CMF < 1 indicates an expected decrease in crashes

Expected crashes with countermeasure

Expected crashes without countermeasure

Module 4-1

Countermeasure Benefits: Issues in developing CMFs Isolating specific treatments or populations

Data availability• Detailed data not collected (e.g., installation date, etc)

• Countermeasure not installed anywhere yet

Time

Money

Module 4-1

Countermeasure Benefits: Tools and Resources for CMFs Highway Safety Manual

CMF Clearinghouse

SafetyAnalyst

The Interactive Highway Safety Design Model (IHSDM)

NCHRP Report 622, Effectiveness of Behavioral Highway Safety Countermeasures

Module 4-1

Countermeasure Benefits: Assigning Monetary Value to Crashes Prevented

Complex Process

Rules of Thumb

Fatal plus Serious Injury vs. minor injury plus PDO Costs

Cost Effectiveness

Module 4-1

Countermeasure Benefits: Example Crash Costs

Killed – K $4,008,900

Disabling Injury – A $216,000

Evident Injury – B $79,000

Possible Injury – C $44,900

Property Damage Only – O $7,400

Source:  Highway Safety Manual, First Edition, Draft 3.1, April 2009.

Module 4-1

Benefit and Cost Analysis

Striving for the most effective use of limited safety funds (“bang for the buck”)

Rank competing projects

Methods• Benefit-cost ratio

• Present value of benefits

Module 4-1

Example Benefit-Cost Ratios

http://www.dot.state.mn.us/trafficeng/otepubl/fundamentals/safetyfundamentals.pdf

Countermeasure benefits

Countermeasure costsBenefit-cost ratio =

Module 4-1

Project Programming Techniques

Ranking

Weighting

Linear Programming

Module 4-1

Other (Qualitative) Considerations

What are other considerations that can play a role in which countermeasures are implemented?

Module 4-1

Other (Qualitative) Considerations

Design Standards

Tradeoffs

Familiarity

Constituent Concerns

How do we integrate these into science-based safety decisions?

Module 4-1

Post-Implementation Evaluation

Evaluation is essential to establish countermeasure effectiveness

Funds should be set aside for scientific evaluation

Module 4-1

Example Collision Diagram – After Countermeasure Was Installed

Crashes decreased. Was all of the decrease due to the conversion to all way stop?

Module 4-1

Countermeasure Evaluation:A Limited Primer Methods for developing CMFs (i.e., evaluating

countermeasures)• Study of sites/groups where a treatment is implemented

(a “before-after” evaluation where a change has occurred)

• Comparison of some sites/subjects with treatment vs. other similar sites/groups without treatment (e.g., median widths)o No real change has occurredo Usually involves developing a predictive model with lots of factorso There are difficulties with developing true measure of the treatment

effect

We will just look at first type – evaluations where something really changed (i.e., a treatment was implemented)

Module 4-1

Countermeasure Evaluation:Goal and False Causes

• Goal – Measure true effect of a countermeasureo We want to be sure that the observed change is due to the

countermeasure alone

• What other factors could cause the change?

Module 4-1

Countermeasure Evaluation:Goal and False Causes

• Goal – Measure true effect of a countermeasureo We want to be sure that the observed change is due to the

countermeasure alone

• What other factors could cause the change?o Other “treatments” at the same time (e.g., primary seat-belt law at

the same time as adding a protected left-turn phase to intersections)

o Changes in AADTo Regression to the meano Underlying trends in crashes (e.g., economy-related changes)o Others

• So how do we control for/discount these other “causes”?

Module 4-1

Countermeasure Evaluation:Controlling for Other Causes “Before vs. After” is misleading

Should be, “Estimated After (without treatment) vs. Observed After (with treatment).

How well we estimate the after (without treatment) crashes defines the strength of the evaluation

Different ways to estimate the after (without treatment) crashes• Use only the observed after treatment crashes (assume nothing

changes – weakest)

• Use of similar comparison groups to estimate (can use SPF prediction based on comparison group)

• Use of Empirical Bayes to estimate (weighted between predicted and observed)

• Randomly assign large group of similar sites to treatment or control group (like a drug study) and estimate based on non-treated control group

Module 4-1

That’s all!• Lots of hard work in planning, collecting data, statistical

analysis and interpretation of results

• BUT, when you are reading evaluation reports, just remember:

The strength of the study results depends on how well After-Crashes Without Treatment were estimated!

Evaluation – Summary