Effects of Operating Speed and Posted Speed Limit in Conjunction with Roadway Geometric Design on Safety Performance for High-Speed Rural Highways and Freeways

Estimating the speed-crash relationship has long been of interest in roadway safety analysis. Because of the many contributing factors – such as roadway geometry and context, weather conditions, human factors, and vehicle type distribution – that influence both speeds and crashes, the relationship cannot be adequately established without considering the corresponding roadway geometric features, the dynamics of the vehicle and tire, and accounting for their effects on speeds and crashes. While a significant amount of research has been conducted to identify relationships between roadway design elements and crashes, research that has considered the contribution of operating speeds or posted speed is limited. A general subjective understanding of the contribution of operating speed of a highway or freeway, through the dynamics of the vehicle, on the severity of a crash (higher speeds are associated with more severe crashes) is known. What is desired is a quantitative understanding of how speed (both operating and posted) in conjunction with roadway geometry relates to the likelihood of a crash and crash severity. This research would build on existing research to explore the relationships among design elements, speed, vehicle dynamics, and crashes on high-speed rural highways and freeways. These relationships will help inform future design guidance, posted speed practices, and potential safety countermeasures, which are related to desired outcomes for multiple AASHTO Committees, such as Design, Traffic Engineering, and Safety. The greater availability of speed data along with innovative statistical analysis techniques provides the opportunity to better consider operating speed in understanding the safety relationships among geometric design, traffic volume, posted speed limit, and crashes. The objectives for this research include (1) identifying the relationship(s) among roadway geometric characteristics, speed (posted and operating), and safety for high-speed rural highways and freeways; (2) determining the relative contribution of speed (posted or operating) with various roadway geometric characteristics on safety for high-speed rural highways and freeways; and (3) determining if existing crash modification factors for geometric elements can be modified with a speed component (operational, posted), or if a speed related crash modification factors (CMFs) can be developed.


  • English


  • Status: Proposed
  • Funding: $950000
  • Contract Numbers:

    Project 15-82

  • 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: 20220607
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01846129
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 15-82
  • Files: TRB, RIP
  • Created Date: May 23 2022 3:02PM