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Role of Safety Performance Functions in the Highway Safety Manual

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.

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Role of Safety Performance Functions in the Highway Safety Manual

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  1. Role of Safety Performance Functions in theHighway Safety Manual July 29, 2009

  2. Presentation Overview SPF Application in Part C: Predictive Method SPF Application in Part B: Roadway Safety Management Process

  3. Safety Performance Functions in Part C – Predictive Method

  4. SPFs in Part C – Predictive Method

  5. SPF for specific facility type AADT Length Site characteristics to adjust with AMFs Roadway Intersection Local Calibration Factor Crash data for EB Method application Summary Data Needs for SPF Application

  6. Application of SPFs in Part C • Objective: • Calculate predicted average crash frequency (Npredicted)

  7. Predictive Method Sample Application Step 1 - Base Conditions Estimate (Nspf) Crashes/year Step 2 – Estimate Predicted Average Crash Frequency Crashes/year

  8. Safety Performance Functions inPart B – Roadway Safety Management

  9. SPFs and Part B – Roadway Safety Management

  10. Chapter 4 – Network Screening

  11. Chapter 4 – Network Screening

  12. Chapter 4 – Network Screening Excess Predicted Average Crash Frequency Using SPFs

  13. Estimate Crash Reduction on Suburban Arterial Intersection Chapter 7 – Economic Appraisal

  14. 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

  15. Estimate Monetary Benefit Convert crash difference to monetary benefits and estimate annual savings of improvement Source: Crash Cost Estimates by Maximum Police-Reported Injury Severity within Selected Crash Geometries, FHWA - HRT - 05-051, October 2005.

  16. 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

  17. Thank you! www.highwaysafetymanual.org

  18. SPFs in Part C – Predictive Method Observed Crash Counts Expected Average Crash Frequency from EB Approach Predicted Average Crash Frequency from SPF Equation

  19. Predictive Method Sample Application • Step 3 – Estimate Expected Average Crash Frequency Crashes/year

  20. Chapter 9 - Safety Effectiveness Evaluation

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