NCHRP 17-25 Crash Reduction Factors for Traffic Engineering and ITS Improvements

1. NCHRP 17-25Crash Reduction Factors for Traffic Engineering and ITS Improvements UNC HSRC VHB Ryerson University (Bhagwant and Craig)

2. Project Goals • Develop new Accident Modification Factors where voids currently exist • Increase the level of predictive certainty for existing Accident Modification Factors • Coordination with other NCHRP and FHWA projects

3. Completed Tasks • Phase I • Literature Review • State Surveys and Interviews • Research Results Digest 299 • Accident Modification Factors Knowledge Matrix • List of 20 “credible” Accident Modification Factors • High or Med-High level of predictive certainty (LOPC)

4. Phase II Efforts • Empirical Bayes Before-After Evaluations • Rural signal installations • 4-lane to 3-lane conversions (Road diets) • Skid resistance treatment • Left-turn signal phasing • 8” to 12” signals • Nighttime flash operation to normal • Double red signal heads (“Dollys”) • Median width on divided roadways • Analysis-Driven Expert Panels • Urban/Suburban • Rural Multilane • Cross-sectional models • GOAL – Develop Accident Modification Factors

5. Rural Signal Installations Summary of data collected Safety Performance Functions Developed

6. Rural Signal Installations

7. Rural Signal Installations

8. Skid Resistant Treatment

9. Skid Resistant Treatment s.e means standard error n/a means not applicable

10. Skid Resistant Treatment s.e means standard error

11. Road Diets in Urban Areas Previously discussed

12. Winston-Salem Empirical-Bayes Evaluations • Treatments • Left-turn signal phasing • Permissive to protective/permissive LT phasing • Protective/permissive to protected LT phasing • 8” to 12” red signal heads • Nighttime flash to normal • Added double red signal heads (“dollys”) • Identified treatment sites and reference group • Obtained crash data, geometric data, and traffic volumes for treatment and reference sites

13. Winston-Salem Empirical-Bayes Evaluations • Permissive to protective/permissive Left Turn • 11 sites • Protective/permissive to protected Left Turn • 4 sites • 8” to 12” signal heads • 26 sites • Nighttime flash to normal • 12 sites • Double red signal heads • 8 sites

14. Winston-Salem Empirical-Bayes Evaluations • Safety Performance Function (SPF) for total crashes • Developed using reference group • Safety Performance Function (SPF) for target crashes • Could not be developed with available data • Used proportion of target crashes to adjust SPF for total crashes • Empirical Bayes analysis almost complete • Calibrate Safety Performance Functions separately for before and after periods • Estimate percent change in crashes

15. Median Width AMF • Current studies are not consistent • Accident Modification Factor for median width and validation of the approach • Preliminary assessment of states – WA, CA, MN, IL

16. Analysis-Driven Expert Panels • Urban-Suburban Arterials (NCHRP 17-26) • 25+ treatments addressed for segments and intersections • Geometrics (lane/shoulder widths, median type, etc.) • Operations (signalization, speed limits, etc.) • Other (lighting, roundabouts, etc.) • Consensus on 9 Accident Modification Factors • Follow-up work on additional Accident Modification Factors (e.g., roadside hazards, speed)

17. Analysis-Driven Expert Panels • Rural Multilane Roadways (NCHRP 17-29) • 15+ treatments addressed for segments and intersections • Geometrics (median width/type, shoulder width/type, turning lanes, alignment, etc.) • Operations (signalization, speed limits, access, etc.) • Other (lighting, roadside hazards, etc.) • Consensus on 3 Accident Modification Factors • Follow-up work identified for additional Accident Modification Factors (access, shoulder type) within both projects

18. Questions??