Safety Performance of Complex Interchanges

Many service interchanges include custom designs that do not fit into the traditional interchange definitions in the AASHTO Green Book, which makes it challenging to predict and compare the relative predicted crash frequency of different interchange forms. Complex interchanges involving isolated ramps, direct high-occupancy vehicle (HOV) connections, direct connections to frontage roads, ramp termini closely spaced or clustered with cross street/frontage road intersections, ramps connecting to nearby developments, and/or other customizations are becoming more common. The Highway Safety Manual (HSM) provides crash prediction for interchange elements such as simple ramps and basic ramp termini configurations, but does not provide a comprehensive crash prediction methodology that can be applied to the large number of interchanges that are not typical basic design. Research is needed to identify and quantify the relationship between each conflict point type at service interchanges on the overall crash frequency of the interchange. The research should generate a methodology consistent with the HSM to develop customized safety performance functions (SPFs) for complex or new interchange designs, including those not identified in the AASHTO Green Book or HSM. The product of the research will be a series of crash prediction models for the various interchange elements, implementable within the mechanics of the HSM. This is relevant to the AASHTO HSM Committee as it will contribute to future updates to the HSM. Gaps remain within the HSM predictive methodology regarding applications to the various interchange configurations being used. Research should generate a building-block approach, incorporating the fundamentals of interchange planning and design, and may provide more timely direction than the traditional approach of developing an independent SPF for each form. As interchange forms are continuously expanded and modified to address safety concerns and other needs, agencies have limited documentation on how to quantitatively assess the safety effects of different interchange configurations and major changes (such as converting or adding ramps to a median high occupancy/toll (HOT) access to an existing interchange crossroad or ramps connecting multiple roads).


  • English


  • Status: Proposed
  • Funding: $700000
  • Contract Numbers:

    Project 17-129

  • 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:

    Zhao, Yi

  • Start Date: 20230725
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01888637
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-129
  • Files: TRB, RIP
  • Created Date: Jul 25 2023 8:09AM