Freeway Segment Safety Performance Function (SPF) Development

This report documents the Ohio Department of Transportation’s effort to improve the reliability of safety decision-making through the development of planning-level and project design-level safety performance functions (SPFs). Planning-level SPFs will replace calibrated versions of national SPFs in Safety Analyst to support network screening. Project design-level SPFs will replace previously calibrated versions of the Highway Safety Manual (HSM) Chapter 18 SPFs through estimation of Ohio-specific SPFs, adjustment factors (AFs), and a one-directional approach to freeway safety analysis. This research evaluated the performance of the calibrated HSM predictive method against an Ohio-specific bidirectional predictive method, Ohio bi-directional SPFs for base conditions used in combination with HSM AFs, and a one-direction predictive method. The results indicated the one-direction predictive method provided reliable predictions for all crash types and severities when compared to the baseline of the calibrated version of the HSM predictive method. The one-direction method is easier to implement on complex alignments, provides a broad set of AFs, but does exclude some factors that may be relevant to practitioners. Additional factors may be considered along with the one-direction predictive method, as needed, as external crash modification factors to the predictive method.


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Bibliography; Figures; Maps; Tables;
  • Pagination: 153p

Subject/Index Terms

Filing Info

  • Accession Number: 01780922
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/OH-2021-20
  • Contract Numbers: 33808
  • Created Date: Aug 31 2021 11:18AM