Roadway Safety Management Process Prioritization of Improvement Projects Network Screening Countermeasure Selection Network Screening 6 7 9 5 8 4 Diagnosis Economic Appraisal Safety Effectiveness Evaluation
Methods for Identifying Sites The identification, examination and effective treatment of well-chosen sites will yield safety improvements…
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.
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
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
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
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
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
Determining deviant sites Expected crashes (based on EB method) Excess A Crashes per Unit Time SPF representing average for comparable sites (norm) Traffic Volume
Diagnosis • Crash Factors • Human • Roadway • Vehicle • Environmental • Collision Type • Run-off Road • Rear End • Head On • Sideswipe Same Direction
Site Review Methods • Engineering Road Safety Audits • Immediate improvements (maintenance) • Low cost safety improvements • High cost safety improvements • Crash history • Collision diagram
Motives for Action • Economic Efficiency • Professional and Institutional Responsibility • Fairness
Tools For Identifying Countermeasures • Engineering studies • Road safety audits • The Australian Safe Systems Approach • The Haddon matrix
Engineering Studies • 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
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.
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
The Haddon Matrix • Crash-Related Factor Categories • Human • Vehicle • Roadway • Environmental • Crash Time • Pre Crash • Crash • Post Crash
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.
The Haddon Matrix -- Exercise • Graduated Drivers Licensing • Airbags • Driver risk-taking propensity • Seat Belt Use • Distance to hospital • Electronic stability control • Driver age • Emergency Med. Svs. Training • GPS automatic crash notification • Rumble strips • Median barrier • Distance to roadside object
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
Countermeasure Sources:NCHRP Series 500 Guides • Countermeasures classified as: • Proven, • Tried, or • Experimental • Examples: • Relocate roadside objects (P) • Install shoulder rumble strips (T) • Delineate poles with retroreflective tape (E)
Countermeasure Sources:Highway Safety Manual • First edition released in 2010 • Provides practitioners with the best factual information and tools regarding safety consequencesof design decisions. • Sections • Part A: Safety knowledge • Part B: Safety management • Part C: Crash prediction models • Part D: Countermeasure selection and CMFs
Countermeasure Sources:Crash Modification Factors Clearinghouse
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
Question • When faced with many potential countermeasures, how does one choose which one(s) to implement?
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
Market Research for Targeting Countermeasures • Identifying sub-population characteristics • Easing language barriers • Customizing campaigns and programs
Market Research Techniques • What types of market research techniques can be used to target high crash risk groups?
Market Research Techniques • Focus groups • Surveys • Observational studies
Cost Effectiveness of Alternative Countermeasures Prioritize interventions and countermeasures based on effectiveness.
Major Topics • Countermeasure Costs and Benefits • Programming Projects • Qualitative Considerations • Countermeasure Evaluation
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?
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)
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
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
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
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
Countermeasure Benefits: Example Crash Costs Source: Highway Safety Manual, First Edition, Draft 3.1, April 2009.
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
Example Benefit-Cost Ratios Countermeasure benefits Benefit-cost ratio = Countermeasure costs http://www.dot.state.mn.us/trafficeng/otepubl/fundamentals/safetyfundamentals.pdf
Project Programming Techniques • Ranking • Weighting • Linear Programming
Other (Qualitative) Considerations • What are other considerations that can play a role in which countermeasures are implemented?
Other (Qualitative) Considerations • Design Standards • Tradeoffs • Familiarity • Constituent Concerns • How do we integrate these into science-based safety decisions?
Post-Implementation Evaluation • Evaluation is essential to establish countermeasure effectiveness • Funds should be set aside for scientific evaluation
Example Collision Diagram – After Countermeasure Was Installed Crashes decreased. Was all of the decrease due to the conversion to all way stop?