Role of Safety Performance Functions in the Highway
- Slides: 20
Role of Safety Performance Functions in the Highway Safety Manual July 29, 2009
Presentation Overview • SPF Application in Part C: Predictive Method • SPF Application in Part B: Roadway Safety Management Process
Safety Performance Functions in Part C – Predictive Method
SPFs in Part C – Predictive Method
Summary Data Needs for SPF Application • SPF for specific facility type • AADT • Length • Site characteristics to adjust with AMFs – Roadway – Intersection • Local Calibration Factor • Crash data for EB Method application
Application of SPFs in Part C 1. 5 -mi rural two-lane Tangent roadway segment 10, 000 veh/day 0% grade Local calibration factor = 1. 10 6 driveways per mi 10 -ft lane width 4 -ft gravel shoulder Roadside hazard rating = 4 Nobserved = 10 crashes/year • Objective: - Calculate predicted average crash frequency (Npredicted)
Predictive Method Sample Application Step 1 - Base Conditions Estimate (Nspf) Crashes/year Step 2 – Estimate Predicted Average Crash Frequency Crashes/year
Safety Performance Functions in Part B – Roadway Safety Management
SPFs and Part B – Roadway Safety Management
Chapter 4 – Network Screening
Chapter 4 – Network Screening
Chapter 4 – Network Screening • Excess Predicted Average Crash Frequency Using SPFs
Chapter 7 – Economic Appraisal • Estimate Crash Reduction on Suburban Arterial Intersection
Estimate Crash Reduction • Predicted Crashes - INTERSECTION – Predict Future Crash Frequency with SPF Data needs: SPFs, Future AADT, Length – Apply AMFs and Calibration Factor to Account for Local Conditions Data needs: AMFs for existing condition, local calibration factor • Predicted Crashes - ROUNDABOUT – Apply AMF to Account for Alternate Conditions (Roundabout) Data needs: AMFs for alternate condition
Estimate Monetary Benefit Crash Severity Fatality (K) Comprehensiv e Crash Costs $4, 008, 900 Disabling Injury (A) $216, 000 Fatal/Injury (K/A/B) $158, 200 Possible Injury (C) $44, 900 • Convert crash difference to monetary benefits Evident Injury (B) $79, 000 and estimate annual savings of improvement PDO (O) $7, 400 Source: Crash Cost Estimates by Maximum Police-Reported Injury Severity within Selected Crash Geometries, FHWA - HRT - 05 -051, October 2005.
Summary of Data Needs for SPF Application • Applicable SPF • AADT • Length • Local Geometric/Operational Conditions and Corresponding AMFs • Local Calibration Factors • Historical crash data for EB Method Application
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SPFs in Part C – Predictive Method Expected Average Crash Frequency from EB Approach Observed Crash Counts Predicted Average Crash Frequency from SPF Equation
Predictive Method Sample Application • Step 3 – Estimate Expected Average Crash Frequency Crashes/year
Chapter 9 - Safety Effectiveness Evaluation