Developing Jurisdiction-Specific SPFs and Crash Severity Portion Functions for Rural Two-Lane, Two-Way Intersections

Transportation agencies rely on the Highway Safety Manual's (HSM) scientific predictive procedures to quantify road safety; however, the HSM methods may not be accurate for use by local jurisdictions. This study used data from rural two-lane, two-way intersections in South Dakota to compare jurisdiction-specific safety performance functions (SPFs) and HSM SPFs to determine which functions were more accurate when used locally. Jurisdiction-specific SPFs—without the use of a calibration factor—were found to be most accurate. The study also compared fixed severity proportion with a severity proportion function calibrated by local data. The authors assumed that the site-specific severity proportion would be more appropriate than a fixed value because the former reflects the relationship between severity proportion and site characteristics. However, results showed that the severity proportion function did not contribute significantly to prediction accuracy. The conclusion offers certain level of assurance for practitioners who are more likely to use a fixed injury severity proportion as a viable alternative to a site-specific severity proportion.


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  • Accession Number: 01725147
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Dec 17 2019 2:13PM