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Crash Reduction Factors for Countermeasures Issue Briefs and Desktop Reference

Crash Reduction Factors for Countermeasures Issue Briefs and Desktop Reference. Maurice Masliah, Ph.D. Senior Researcher iTRANS Consulting (905) 882-4100 ext 5295 mmasliah@itransconsulting.com. Prepared by iTRANS Consulting. Updated Issue Briefs. Intersections. Traffic Signals.

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Crash Reduction Factors for Countermeasures Issue Briefs and Desktop Reference

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  1. Crash Reduction Factors for CountermeasuresIssue Briefs and Desktop Reference Maurice Masliah, Ph.D. Senior Researcher iTRANS Consulting (905) 882-4100 ext 5295 mmasliah@itransconsulting.com Prepared by iTRANS Consulting

  2. Updated Issue Briefs Intersections Traffic Signals April 2004 September 2007 FHWA

  3. New Issue Briefs Pedestrian Roadway Departure FHWA

  4. New Product: Desktop Reference FHWA

  5. What is a CRF? • Crash Reduction Factor • Percentage crash reduction that might be expected after implementing a countermeasure • CRF of 25 means a 25% reduction in crashes • CRF of -20 means a 20% increase in crashes FHWA

  6. Issue Briefs: Purpose • One CRF for each countermeasure • The “best” available CRF (accuracy and precision checks) • Additional information relevant to the CRF (traffic control, area type, etc.) FHWA

  7. Desktop Reference: Purpose • Multiple CRFs for the same countermeasure (where available) • CRF functions • Additional information such as study type, number of observations, CRF range (high - low) FHWA

  8. Poll Question 1 How useful do you think the Issue Briefs will be to you? • Not very useful • Somewhat useful • Very useful • Best thing since sliced bread FHWA

  9. Product PurposeIowa DOT Tom Welch State Transportation Safety Engineer Iowa Dept of Transportation FHWA

  10. Roadway Departure Issue Brief Purpose CRFs How to Use FHWA

  11. Roadway Departure CRF Example • CRF = 38(10)17 FHWA

  12. CRF 38 Remove or relocate fixed objects outside the clear zone CRF Example Expected crashes without treatment Expected crashes with treatment FHWA

  13. CRF Example • CRF = 38(10)17 • Bold type means a rigorous methodology was used to estimate the CRF, and the standard error is relatively small • (10 ) is the standard error for this CRF • 17is the reference number* * details at the end of the Issue Brief FHWA

  14. CRF Confidence Interval • Estimation of confidence interval [38(10)17]  2 standard errors from the CRF 18% (38 - 2 X 10) and 58% (38 + 2 X 10) • Expected safety effect of the countermeasure: between 18% and 58% FHWA

  15. Poll Question 2 How many of you use CRFs in your work? • I use CRFs • I don’t but I think there are others in my agency who do • I don’t use and don’t know anyone in my agency who does use CRFs FHWA

  16. Example ApplicationDouglas County Keary B. Lord Assistant Director/ Traffic Operations Division Manager FHWA

  17. Accuracy • Accuracy is the proximity of the estimate of the CRF to the true value • Two types of bias affect accuracy: 1. Regression to the mean bias 2. Traffic volume bias FHWA

  18. Precision • Precision is the degree to which repeated estimates of the CRF are similar to each other • Measure of precision: standard error of CRF FHWA

  19. Reliability • Reliability is defined here as the combination of precision and accuracy • CRFs that pass the reliability test are shown in bold font FHWA

  20. Reliability Selection Criteria and Thresholds FHWA

  21. Number of CRFs and Bold CRFs **Very few published CRFs are considered reliable! FHWA

  22. Poll Question 3 • Internal documentation • FHWA Issue Briefs • Other published sources • Other (please use message board to explain) Where do you get your CRFs from? FHWA

  23. CRF Proper Use and Limitations Colorado DOT TBD – Bryan Allery/Jake Kononov Colorado Dept of Transportation FHWA

  24. Highway Safety Improvement Program (HSIP) • Implementation • Planning • Evaluation (3) A comparison of accident numbers, rates, and severity observed after the implementation of a highway safety improvement project with the accident numbers, rates, and severity expected if the improvement had not been made. FHWA

  25. HSIP & CRFs • Evaluation legislation specifies the information needed to produce CRFs • Our review of HSIPs has not found any states which tie their evaluation work with CRF generation • Potential to link tasks currently being conducted with improving knowledge of effectiveness of countermeasures FHWA

  26. Strategic Highway Safety Plan (SHSP) • CRFs should be part of the process of selecting countermeasures • Intersections as an emphasis area within a SHSP • Task team identifies left-turn crashes at intersections as an overrepresented crash type • What are appropriate countermeasures? FHWA

  27. Strategic Highway Safety Plan (SHSP) • Review of Intersection Issue Brief for left-turn crash CRFs • Provide protected left turn phase 16(2)19 • Install left-turn lane (physical channelization) 249 • Install cameras to detect red-light running 45(6)27 • Identify intersection locations and conduct a cost-benefit analysis FHWA

  28. Future Direction – What’s Next? • Accident Modification Factors and Functions (rather than CRFs) • Increase in number of studies that evaluate safety effects of countermeasures • More stringent criteria in adoption of AMFs • New tools FHWA

  29. What is an AMF? • Accident Modification Factor • Multiplier representing the expected change in crashes • CRF of 25 equals an AMF of 0.75 • CRF of -20 equals an AMF of 1.20 FHWA

  30. Accident Modification Functions • Today, CRFs / AMFs for most countermeasures are noted as constants • However, CRFs / AMFs are really functions of environmental variables: • Traffic volume • Traffic mix (trucks, pedestrians, bicyclists) • Road geometry • Operational conditions FHWA

  31. More Stringent Inclusion Criteria • Highway Safety Manual inclusion process: • Accuracy and precision of AMFs • Standard error of 0.1 or less indicates AMF that is sufficiently accurate, precise, and stable • Companion AMFs with standard errors of 0.2 - 0.3 are also included • indicating the potential safety effects of the treatment on other facilities, or other crash types and severities FHWA

  32. Future Direction • Periodical Update of Issue Briefs and Desktop Reference • Search new information: • current research projects:http://rip.trb.org/ • government-funded documents published:http://www.ntis.gov/search/index.asp? • bibliographic databasehttp://ntlsearch.bts.gov/tris/index.do FHWA

  33. New Tools and New AMFs • Low Cost Safety Improvements Pooled Funds Study • Highway Safety Manual (HSM) • SafetyAnalyst • Interactive Highway Safety Design Model (IHSDM) FHWA

  34. Thank YouQuestions? FHWA

  35. FHWA

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