A Localized Safety Performance Functions Approach Accounting for “Within” Tennessee Variations on Freeways & Interchanges

The Tennessee Department of Transportation (TDOT) is adopting the Highway Safety Manual (HSM) as a resource to assess the safety performance on Tennessee (TN) roadways. The HSM (2010) provides Safety Performance Functions (SPFs) to predict crash frequency on several types of roadway facilities, e.g., segments and intersections. HSM recommends that transportation agencies develop either their own jurisdiction-specific SPFs or calibrate the default HSM SPFs using local data. The rationale behind this is that the HSM SPFs were developed using data from a few states in the U.S., which may not be representative of other states due to potential variability in conditions. To assist with implementing HSM procedures, the University of Tennessee has worked closely with TDOT to develop TN-specific SPFs for various types of rural and urban roadway segments in Phases I and II of the project. This phase (III) relates to SPFs for freeway segments and interchange ramps in Tennessee. The study 1) develops calibration factors (CFs) for freeway segments (interstates and expressways) and interchange ramps, 2) estimates TN-specific SPFs for freeway segments and interchange ramps, and 3) provides “highly localized” SPFs for freeways. A unique aspect of this study is dealing with heterogeneity by investigating the spatial and temporal variations in crash frequencies and associated factors using statistical models, known as geographically and temporally weighted regressions. The results reported in this study are ready for implementation by TDOT, e.g., by using crash prediction tools supplied as part of this project. The report also lists recommendations for enhancing safety analysis in TN.

• Record URL:
  https://www.tn.gov/content/dam/tn/tdot/long-range-planning/research/final-reports/res2020-final-reports/RES2020-04_Part1_Final_Report_Approved.pdf
• Corporate Authors:

  University of Tennessee, Knoxville

  Center for Transportation Research
  Conference Center Building
  Knoxville, TN  United States  37996-4133

  Tennessee Department of Transportation

  James K. Polk Building
  Fifth and Deaderick Street
  Nashville, TN  United States  37243-0349

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Khattak, Asad
  • Mohammadnazar, Amin
  • Patwary, A Latif
  • Ahmad, Numan
  • Haque, Antora
  • Mahdinia, Iman
• Publication Date: 2022-2

Language

• English

Media Info

• Media Type: Web
• Edition: Final Report
• Features: Appendices; Figures; References; Tables;
• Pagination: 125p

Subject/Index Terms

• TRT Terms: Calibration; Crash rates; Freeways; Highway safety; Interchanges; Safety analysis
• Identifier Terms: Highway Safety Manual; Safety Performance Functions; Tennessee Department of Transportation
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01846972
• Record Type: Publication
• Report/Paper Numbers: RES2020-04
• Files: TRIS, ATRI, USDOT, STATEDOT
• Created Date: May 25 2022 9:35AM