Advancing Safety Prediction Methodologies for Horizontal Curves

Statistics from the Fatality Analysis Reporting System (FARS) indicate that more than 25 percent of fatal crashes occur at horizontal curves, with most of these crashes being roadway departures. Although researchers and practitioners agree that curvature plays a role in crash frequency and severity, safety performance functions (SPFs) and severity distribution functions for horizontal curves have not been thoroughly investigated or widely implemented.  The American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) provides SPFs of various facility types for segments and intersections, but not for curve segments. Rather, curves are evaluated by applying an adjustment factor (AF) to estimate the predicted crash frequency of a curve segment. Unfortunately, not all the SPF models within the HSM have AFs for horizontal curves. Recent studies have been implemented to develop AFs for curve segments of certain facility types to begin filling this gap. However, applying a horizontal curve AF to an existing segment SPF assumes that the underlying prediction model of a tangent segment only needs to be adjusted to appropriately estimate a horizontal curve’s influence on the segment’s safety performance. This method may not be the best way to assess the safety performance of horizontal curves. A more thorough investigation may reveal that common geometric attributes used to estimate the safety performance of tangent segments have a different degree of influence on the safety performance of horizontal curves. Taking this possibility further, the attributes most important for predicting the safety performance of a horizontal curve may differ due to context (rural versus urban), facility type, or other factors such as geometric and operational characteristics, and roadside elements. Therefore, additional research is needed to better understand the attributes that most influence the safety performance of horizontal curves. The objective of this research is to develop a guide and a tool to quantify the safety performance of horizontal curves using geometric and operational characteristics for applications across a range of highway activities including planning, design, operations, and safety management At the minimum, the research shall:  (1) Advance the predictive safety performance methodologies for horizontal curves on rural and urban freeways, rural and urban multilane divided roadways, rural and urban multilane undivided roadways, and rural and urban two-lane undivided roadways.  (2) Develop and validate a statistically valid predictive methodology to quantify the safety performance of locations with curves for use by state and local transportation agencies to help evaluate the likely safety performance of different horizontal curves at a given location. The study should consider geometric and operational characteristics of contiguous highway segments and various facility types. Consideration should be given to different horizontal curve types such as simple curves, compound curves, reverse curves, and broken-back curves.  Accomplishment of the project objective will require completion of the following tasks, at a minimum.  


  • English


  • Status: Active
  • Funding: $350000
  • Contract Numbers:

    Project 17-117

  • 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

  • Performing Organizations:

    Texas Transportation Institute

    Texas A&M University System
    3135 TAMU
    College Station, TX  United States  77843-3135
  • Principal Investigators:

    Geedipally, Srinivas

  • Start Date: 20240308
  • Expected Completion Date: 20260307
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01845545
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-117
  • Files: TRB, RIP
  • Created Date: May 17 2022 11:30AM