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

UNC HSRCUNC HSRCVHBVHB

Ryerson UniversityRyerson University(Bhagwant and Craig)(Bhagwant and Craig)

Project GoalsProject Goals

Develop new Accident Modification Develop new Accident Modification Factors where voids currently exist Factors where voids currently exist

Increase the Increase the level of predictive certaintylevel of predictive certainty for existing Accident Modification Factors for existing Accident Modification Factors

Coordination with other NCHRP and Coordination with other NCHRP and FHWA projectsFHWA projects

Completed TasksCompleted TasksPhase IPhase I– Literature ReviewLiterature Review– State Surveys and InterviewsState Surveys and Interviews

Research Results Digest 299Research Results Digest 299– Accident Modification Factors Knowledge Accident Modification Factors Knowledge

Matrix Matrix – List of 20 “credible” Accident Modification List of 20 “credible” Accident Modification

Factors Factors – High or Med-High level of predictive certainty High or Med-High level of predictive certainty

(LOPC)(LOPC)

Phase II EffortsPhase II Efforts

Empirical Bayes Before-After EvaluationsEmpirical Bayes Before-After Evaluations– Rural signal installationsRural signal installations– 4-lane to 3-lane conversions (Road diets) 4-lane to 3-lane conversions (Road diets) – Skid resistance treatmentSkid resistance treatment– Left-turn signal phasing Left-turn signal phasing – 8” to 12” signals 8” to 12” signals – Nighttime flash operation to normal Nighttime flash operation to normal – Double red signal heads (“Dollys”) Double red signal heads (“Dollys”) – Median width on divided roadwaysMedian width on divided roadways

Analysis-DrivenAnalysis-Driven Expert Panels Expert Panels– Urban/Suburban Urban/Suburban – Rural Multilane Rural Multilane

Cross-sectional modelsCross-sectional modelsGOAL – Develop Accident Modification FactorsGOAL – Develop Accident Modification Factors

StateState Treated SitesTreated SitesUnsignalized Unsignalized ReferenceReference

Signalized Signalized ReferenceReference

Years of Years of DataData

CaliforniaCalifornia 2828 2,3302,330 63631993-1993-20022002

MinnesotaMinnesota 1717 1,2581,258 21211991-1991-20022002

3-Leg Stop-Controlled 3-Leg Stop-Controlled (CA and MN independently)(CA and MN independently)

4-Leg Stop-Controlled 4-Leg Stop-Controlled (CA and MN independently)(CA and MN independently)

4-Leg Signalized 4-Leg Signalized (CA and MN combined)(CA and MN combined)

AllAll AllAll AllAll

Right-AngleRight-Angle Right-AngleRight-Angle Right-AngleRight-Angle

Left-TurnLeft-Turn Left-TurnLeft-Turn

Rear-EndRear-End Rear-EndRear-End Rear-EndRear-End

Rural Signal InstallationsRural Signal InstallationsSummary of data collectedSummary of data collected

Safety Performance Functions DevelopedSafety Performance Functions Developed

Rural Signal InstallationsRural Signal Installations

Crash Frequency Crash Modification Factors

(standard error) StateState TotalTotal Right AngleRight Angle Left TurnLeft Turn Rear EndRear End

CACA 0.778 (0.061)0.778 (0.061) 0.221 (0.036)0.221 (0.036) 0.433 (0.065)0.433 (0.065) 2.474 (0.373)2.474 (0.373)

MNMN 0.488 (0.027)0.488 (0.027) 0.228 (0.019)0.228 (0.019) 0.374 (0.063)0.374 (0.063) 1.300 (0.141)1.300 (0.141)

ALLALL 0.559 (0.025)0.559 (0.025) 0.227 (0.017)0.227 (0.017) 0.401 (0.047)0.401 (0.047) 1.579 (0.142)1.579 (0.142)

Rural Signal InstallationsRural Signal Installations

Economic Cost Crash Modifications Factors

CharacteristicCharacteristic Theta CostTheta Cost

AllAll 0.2650.265

CaliforniaCalifornia 0.3150.315

MinnesotaMinnesota 0.2470.247

3 leg3 leg 0.2860.286

4 leg4 leg 0.2640.264

2 lanes on major2 lanes on major 0.2650.265

4 lanes on major4 lanes on major 0.2650.265

AADT < 20,000AADT < 20,000 0.3140.314

AADT > 20,000AADT > 20,000 0.2530.253

Expected RA/Expected RE <=4.5Expected RA/Expected RE <=4.5 0.3240.324

Expected RA/Expected RE >4.5Expected RA/Expected RE >4.5 0.2150.215

Skid Resistant TreatmentSkid Resistant TreatmentSUMMARY OF DATA COLLECTEDSite TypeSite Type No. of SitesNo. of Sites

Treated IntersectionTreated Intersection 256256

Reference IntersectionReference Intersection 3,9933,993

Treated SegmentTreated Segment 36.3 miles36.3 miles

Reference SegmentReference Segment 1,242.4 miles1,242.4 miles

Data collected in New York State for 1994 to 2003.

SAFETY PERFORMANCE FUNCTIONS DEVELOPEDIntersectionsIntersections SegmentsSegments

TotalTotal TotalTotal

Wet-roadWet-road Wet-roadWet-road

Rear-endRear-end Rear-endRear-end

DryDry DryDry

Rear-end wet-roadRear-end wet-road Rear-end wet-roadRear-end wet-road

Right-angleRight-angle Rear-end dry-roadRear-end dry-road

Right-angle wet-Right-angle wet-roadroad Single vehicleSingle vehicle

  Single vehicle wet-Single vehicle wet-roadroad

Skid Resistant TreatmentSkid Resistant Treatment

Safety Effects At Intersections GroupingGrouping Total Total

(s.e.)(s.e.)Wet-Wet-road road (s.e.)(s.e.)

Rear-Rear-end end

(s.e.)(s.e.)

Dry Dry (s.e.)(s.e.)

Rear-Rear-end Wet end Wet

(s.e.)(s.e.)

Right-Right-angle angle (s.e.)(s.e.)

Right-Right-angle angle

Wet (s.e.)Wet (s.e.)

AllAll0.799 0.799

(0.028)(0.028)0.426 0.426

(0.030)(0.030)0.582 0.582

(0.034)(0.034)1.149 1.149

(0.051)(0.051)0.322 0.322

(0.041)(0.041)1.045 1.045

(0.078)(0.078)0.799 0.799

(0.123)(0.123)

3 leg signalized3 leg signalized0.667 0.667

(0.050)(0.050)0.372 0.372

(0.053)(0.053)0.554 0.554

(0.065)(0.065)0.959 0.959

(0.093)(0.093)0.261 0.261

(0.066)(0.066)0.787 0.787

(0.125)(0.125)0.470 0.470

(0.161)(0.161)

3 leg stop-controlled3 leg stop-controlled0.819 0.819

(0.048)(0.048)0.355 0.355

(0.046)(0.046)0.586 0.586

(0.057)(0.057)1.302 1.302

(0.095)(0.095)0.335 0.335

(0.075)(0.075)0.828 0.828

(0.218)(0.218)0.828 0.828

(0.218)(0.218)

3 leg yield-controlled3 leg yield-controlled0.590 0.590

(0.114)(0.114)0.217 0.217

(0.103)(0.103)0.304 0.304

(0.086)(0.086)1.392 1.392

(0.321)(0.321)0.221 0.221

(0.161)(0.161) n/an/a n/an/a

4 leg signalized4 leg signalized0.797 0.797

(0.052)(0.052)0.546 0.546

(0.070)(0.070)0.585 0.585

(0.068)(0.068)0.992 0.992

(0.081)(0.081)0.361 0.361

(0.084)(0.084)0.898 0.898

(0.117)(0.117)1.105 1.105

(0.294)(0.294)

4 leg stop-controlled4 leg stop-controlled1.271 1.271

(0.143)(0.143)0.597 0.597

(0.137)(0.137)0.943 0.943

(0.188)(0.188)1.754 1.754

(0.242)(0.242)0.482 0.482

(0.215)(0.215)1.687 1.687

(0.323)(0.323)0.829 0.829

(0.351)(0.351)

4 leg yield-controlled4 leg yield-controlled0.589 0.589

(0.216)(0.216)0.361 0.361

(0.371)(0.371)0.504 0.504

(0.248)(0.248)0.651 0.651

(0.273)(0.273) n/an/a n/an/a n/an/a

s.e means standard error n/a means not applicables.e means standard error n/a means not applicable

Skid Resistant TreatmentSkid Resistant TreatmentSafety Effects For Segments

GroupingGrouping Total Total (s.e.)(s.e.)

Wet-Wet-road road (s.e.)(s.e.)

Rear-Rear-end end (s.e.)(s.e.)

Dry Dry (s.e.)(s.e.)

Rear-Rear-end end Wet-Wet-road road (s.e.)(s.e.)

Rear-Rear-end end Dry-Dry-road road (s.e.)(s.e.)

Single-Single-vehicle vehicle (s.e.)(s.e.)

Single-Single-vehicle vehicle Wet-Wet-road road (s.e.)(s.e.)

AllAll 0.764 0.764 (0.023)(0.023)

0.434 0.434 (0.024)(0.024)

0.828 0.828 (0.043)(0.043)

1.003 1.003 (0.043)(0.043)

0.575 0.575 (0.055)(0.055)

0.977 0.977 (0.068)(0.068)

0.698 0.698 (0.040)(0.040)

0.399 0.399 (0.039)(0.039)

Rural 2 Rural 2 laneslanes

0.964 0.964 (0.073)(0.073)

0.852 0.852 (0.126)(0.126)

1.0471.047-0.149-0.149

1.167 1.167 (0.114)(0.114)

0.971 0.971 (0.256)(0.256)

1.235 1.235 (0.219)(0.219)

1.078 1.078 (0.141)(0.141)

1.125 1.125 (0.287)(0.287)

Rural >2 Rural >2 laneslanes

0.684 0.684 (0.032)(0.032)

0.346 0.346 (0.028)(0.028)

0.7760.776(-0.068)(-0.068)

0.875 0.875 (0.061)(0.061)

0.474 0.474 (0.079)(0.079)

0.838 0.838 (0.098)(0.098)

0.588 0.588 (0.046)(0.046)

0.292 0.292 (0.038)(0.038)

Urban 2 Urban 2 laneslanes

0.599 0.599 (0.082)(0.082)

0.260 0.260 (0.066)(0.066)

0.6120.612(-0.142)(-0.142)

0.992 0.992 (0.195)(0.195)

0.344 0.344 (0.145)(0.145)

0.695 0.695 (0.216)(0.216)

0.921 0.921 (0.232)(0.232)

0.523 0.523 (0.247)(0.247)

Urban > 2 Urban > 2 laneslanes

0.862 0.862 (0.038)(0.038)

0.538 0.538 (0.045)(0.045)

0.8660.866(-0.059)(-0.059)

1.132 1.132 (0.065)(0.065)

0.640 0.640 (0.084)(0.084)

1.120 1.120 (0.099)(0.099)

0.800 0.800 (0.083)(0.083)

0.615 0.615 (0.115)(0.115)

s.e means standard errors.e means standard error

Road Diets in Urban AreasRoad Diets in Urban Areas

Previously discussedPreviously discussed

Winston-Salem Empirical-Bayes Winston-Salem Empirical-Bayes EvaluationsEvaluations

TreatmentsTreatments– Left-turn signal phasingLeft-turn signal phasing

Permissive to protective/permissive LT phasingPermissive to protective/permissive LT phasing

Protective/permissive to protected LT phasingProtective/permissive to protected LT phasing

– 8” to 12” red signal heads8” to 12” red signal heads– Nighttime flash to normalNighttime flash to normal– Added double red signal heads (“dollys”)Added double red signal heads (“dollys”)

Identified treatment sites and reference groupIdentified treatment sites and reference group

Obtained crash data, geometric data, and traffic Obtained crash data, geometric data, and traffic volumes for treatment and reference sitesvolumes for treatment and reference sites

Winston-Salem Empirical-Bayes Winston-Salem Empirical-Bayes EvaluationsEvaluations

Permissive to protective/permissive Left TurnPermissive to protective/permissive Left Turn– 11 sites11 sites

Protective/permissive to protected Left TurnProtective/permissive to protected Left Turn– 4 sites4 sites

8” to 12” signal heads8” to 12” signal heads– 26 sites26 sites

Nighttime flash to normalNighttime flash to normal– 12 sites12 sites

Double red signal heads Double red signal heads – 8 sites8 sites

Winston-Salem Empirical-Bayes Winston-Salem Empirical-Bayes EvaluationsEvaluations

Safety Performance Function (SPF) for total Safety Performance Function (SPF) for total crashescrashes– Developed using reference groupDeveloped using reference group

Safety Performance Function (SPF) for target Safety Performance Function (SPF) for target crashes crashes – Could not be developed with available dataCould not be developed with available data– Used proportion of target crashes to adjust SPF for Used proportion of target crashes to adjust SPF for

total crashestotal crashes

Empirical Bayes analysis almost completeEmpirical Bayes analysis almost complete– Calibrate Safety Performance Functions separately Calibrate Safety Performance Functions separately

for before and after periodsfor before and after periods– Estimate percent change in crashesEstimate percent change in crashes

Median Width AMFMedian Width AMF

Current studies are not consistent Current studies are not consistent

Accident Modification Factor for median Accident Modification Factor for median width and validation of the approachwidth and validation of the approach

Preliminary assessment of states – WA, Preliminary assessment of states – WA, CA, MN, ILCA, MN, IL

Analysis-DrivenAnalysis-Driven Expert Panels Expert PanelsUrban-Suburban Arterials (NCHRP 17-26)Urban-Suburban Arterials (NCHRP 17-26)

25+ treatments addressed for segments and 25+ treatments addressed for segments and intersectionsintersections

– Geometrics (lane/shoulder widths, median type, etc.)Geometrics (lane/shoulder widths, median type, etc.)– Operations (signalization, speed limits, etc.)Operations (signalization, speed limits, etc.)– Other (lighting, roundabouts, etc.)Other (lighting, roundabouts, etc.)

Consensus on 9 Accident Modification FactorsConsensus on 9 Accident Modification Factors

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

Analysis-DrivenAnalysis-Driven Expert Panels Expert PanelsRural Multilane Roadways (NCHRP 17-29)Rural Multilane Roadways (NCHRP 17-29)

15+ treatments addressed for segments and 15+ treatments addressed for segments and intersectionsintersections

– Geometrics (median width/type, shoulder width/type, Geometrics (median width/type, shoulder width/type, turning lanes, alignment, etc.)turning lanes, alignment, etc.)

– Operations (signalization, speed limits, access, etc.)Operations (signalization, speed limits, access, etc.)– Other (lighting, roadside hazards, etc.)Other (lighting, roadside hazards, etc.)

Consensus on 3 Accident Modification FactorsConsensus on 3 Accident Modification Factors

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

Questions??Questions??