NCHRP Crash Reduction Factors for Traffic Engineering and ITS Improvements UNC HSRC VHB Ryerson University (Bhagwant and Craig)

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

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)

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

State Treated Sites Unsignalized Reference Signalized Reference Years of Data California282, Minnesota171, Leg Stop-Controlled (CA and MN independently) 4-Leg Stop-Controlled (CA and MN independently) 4-Leg Signalized (CA and MN combined) AllAllAll Right-AngleRight-AngleRight-Angle Left-TurnLeft-Turn Rear-EndRear-EndRear-End Rural Signal Installations Summary of data collected Safety Performance Functions Developed

Rural Signal Installations Crash Frequency Crash Modification Factors (standard error) StateTotal Right Angle Left Turn Rear End CA (0.061) (0.036) (0.065) (0.373) MN (0.027) (0.019) (0.063) (0.141) ALL (0.025) (0.017) (0.047) (0.142)

Rural Signal Installations Economic Cost Crash Modifications Factors Characteristic Theta Cost All0.265 California0.315 Minnesota leg leg lanes on major lanes on major AADT < 20, AADT > 20, Expected RA/Expected RE <= Expected RA/Expected RE >

Skid Resistant Treatment SUMMARY OF DATA COLLECTED Site Type No. of Sites Treated Intersection 256 Reference Intersection 3,993 Treated Segment 36.3 miles Reference Segment 1,242.4 miles Data collected in New York State for 1994 to SAFETY PERFORMANCE FUNCTIONS DEVELOPEDIntersectionsSegments TotalTotal Wet-roadWet-road Rear-endRear-end DryDry Rear-end wet-road Right-angle Rear-end dry-road Right-angle wet- road Single vehicle Single vehicle wet- road

Skid Resistant Treatment Safety Effects At Intersections Grouping Total (s.e.) Wet- road (s.e.) Rear- end (s.e.) Dry (s.e.) Rear- end Wet (s.e.) Right- angle (s.e.) Right- angle Wet (s.e.) All (0.028) (0.030) (0.034) (0.051) (0.041) (0.078) (0.123) 3 leg signalized (0.050) (0.053) (0.065) (0.093) (0.066) (0.125) (0.161) 3 leg stop-controlled (0.048) (0.046) (0.057) (0.095) (0.075) (0.218) 3 leg yield-controlled (0.114) (0.103) (0.086) (0.321) (0.161) n/an/a 4 leg signalized (0.052) (0.070) (0.068) (0.081) (0.084) (0.117) (0.294) 4 leg stop-controlled (0.143) (0.137) (0.188) (0.242) (0.215) (0.323) (0.351) 4 leg yield-controlled (0.216) (0.371) (0.248) (0.273) n/a n/an/a s.e means standard error n/a means not applicable

Skid Resistant Treatment Safety Effects For Segments Grouping Total (s.e.) Wet- road (s.e.) Rear- end (s.e.) Dry (s.e.) Rear- end Wet- road (s.e.) Rear- end Dry- road (s.e.) Single- vehicle (s.e.) Single- vehicle Wet- road (s.e.) All (0.023) (0.024) (0.043) (0.043) (0.055) (0.068) (0.040) (0.039) Rural 2 lanes (0.073) (0.126) (0.114) (0.256) (0.219) (0.141) (0.287) Rural >2 lanes (0.032) (0.028) 0.776(-0.068) (0.061) (0.079) (0.098) (0.046) (0.038) Urban 2 lanes (0.082) (0.066) 0.612(-0.142) (0.195) (0.145) (0.216) (0.232) (0.247) Urban > 2 lanes (0.038) (0.045) 0.866(-0.059) (0.065) (0.084) (0.099) (0.083) (0.115) s.e means standard error

Road Diets in Urban Areas Previously discussed

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

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

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

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

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 Consensus on 9 Accident Modification Factors Follow-up work on additional Accident Modification Factors (e.g., roadside hazards, speed) Follow-up work on additional Accident Modification Factors (e.g., roadside hazards, speed)

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 Consensus on 3 Accident Modification Factors Follow-up work identified for additional Accident Modification Factors (access, shoulder type) within both projects Follow-up work identified for additional Accident Modification Factors (access, shoulder type) within both projects

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