Better Measures of the Effect of Traffic Speed on Crash Frequency and Severity for the Highway Safety Manual

A key gap in the body of knowledge contained in both the first edition and the forthcoming second edition of the Highway Safety Manual (HSM) is the limited consideration of traffic speed effects in the predictive models for most facility types. It is well-established that crash severity increases with vehicle speed, and speed may also influence crash frequency. However, because speed is correlated with nearly every other variable used in HSM predictive methods, traditional regression models do not effectively capture speed relationships and may even produce counterintuitive results. Improving how speed effects are incorporated into these models will result in more realistic and actionable outputs. Research is needed to identify effective ways to include traffic speed in HSM predictive models, thereby increasing their accuracy and alignment with the Safe System Approach. Given the strong correlation between speed and various roadway and intersection characteristics, alternative approaches to quantifying speed effects—beyond standard regression modeling—should be explored. The objective of this research is to formulate and develop predictive methods that realistically account for the effects of traffic speed on both crash frequency and severity, with the aim of inclusion in a future edition of the HSM. The research will involve a comprehensive review of prior studies on speed-safety relationships (from both U.S. and international sources), evaluation of alternative modeling approaches, quantification and comparison of model results, and development of predictive methods using the most promising strategies. Ultimately, this research will support transportation agencies in their efforts to eliminate fatalities and serious injuries, many of which involve excessive speed, and will aid in the development of context-sensitive roadway designs that promote safe operating speeds.

• Record URL:
  • http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=5872
• Supplemental Notes:
  • Contract to a Performing Organization has not yet been awarded.

Language

• English

Project

• Status: Proposed
• Funding: $750,000.00
• Contract Numbers:

  Project 17-139

• Sponsor Organizations:

  National Cooperative Highway Research Program

  Transportation Research Board
  500 Fifth Street, NW
  Washington, DC  United States  20001

  American Association of State Highway and Transportation Officials (AASHTO)

  444 North Capitol Street, NW
  Washington, DC  United States  20001

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Project Managers:

  Deng, Zuxuan

• Start Date: 20250526
• Expected Completion Date: 0
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Crash rates; Crash severity; Predictive models; Traffic speed
• Identifier Terms: Highway Safety Manual
• Subject Areas: Highways; Planning and Forecasting; Safety and Human Factors;

Filing Info

• Accession Number: 01956569
• Record Type: Research project
• Source Agency: Transportation Research Board
• Contract Numbers: Project 17-139
• Files: TRB, RIP
• Created Date: May 28 2025 10:16AM