Deflection Angle Effect on Continuous Driver Performance Along Horizontal Curves

Horizontal curves make up only a small share of mileage in the United States, yet accounted for 23% of all fatal crashes. Overall, research has shown that the average crash rate for horizontal curve locations is approximately three times the average crash rate for the tangent section. Thus, it is important to understand how drivers can more safely transverse these sections of roadways, such as slowing to a safe speed. Drivers’ speed at horizontal curves is due, in part, to their perception of the way in which curves look upon approach. This perception is linked to the curve radius and deflection angles of horizontal curves. Previous research found that on the tangent section before a curve began, drivers cruised at their highest speeds before slowing most significantly right before the start of the curve (Point of Curvature). Following this, drivers increased their speed slightly until the midpoint of the curve, before exiting the curve at approximately the same speed as the midpoint. However, to date, research has not considered a continuous study of driver speed throughout the entire length of a curve in terms of the impact of the curve deflection angle alone. Thus, it is not known how the intensity of a curve impacts driver performance throughout the time a driver spends traversing the length of a curve, and what the relationship between speed, lane position, curve radii, and deflection angle is throughout each portion of a horizontal curve, from the tangent section prior to the curve, through the tangent section following the curve. The focus of the proposed study is to investigate the relationship between varying deflection angles at horizontal curves, at both minimum radii and above minimum radii, on driver speeds and lateral positioning. The most vital anticipated benefit of this research is the reduction of fatal and serious injury crashes through implementing countermeasures in a cost-effective manner at identified critical locations along horizontal curves of varying deflection and radii. These countermeasures could be implemented only on the most critical sections of roadway to be most cost-effective, which is critical for the 77% of roadway miles in the U.S. owned and operated by local governments. For example, high friction surface treatments, guardrails, and/or rumble strips could be placed only on the sections of a curve where most critical, either in terms of speed, brake timing, lateral position, or acceleration/deceleration. This would make these safety countermeasures much more accessible for local and state governments. Further, this research provides comprehension of driver performance continuously along horizontal curve corridors, which would allow researchers to make more informed decisions regarding the development of future countermeasures along horizontal curves.


  • Status: Inactive
  • Funding: $50000
  • Contract Numbers:


  • Sponsor Organizations:

    Office of the Assistant Secretary for Research and Technology

    University Transportation Centers Program
    Department of Transportation
    Washington, DC  United States  20590
  • Managing Organizations:

    University of Iowa, Iowa City

    National Advanced Driving Simulator, 2401 Oakdale Blvd
    Iowa City, IA  United States  52242-5003
  • Performing Organizations:

    University of Massachusetts, Amherst

    Baystate Roads Program, 214 Marston Hall
    Amherst, MA  United States  01003
  • Principal Investigators:

    Ai, Chengbo

    Fitzpatrick, Cole

  • Start Date: 20200901
  • Expected Completion Date: 20210831
  • Actual Completion Date: 0
  • USDOT Program: University Transportation Centers

Subject/Index Terms

Filing Info

  • Accession Number: 01738854
  • Record Type: Research project
  • Source Agency: Safety Research Using Simulation University Transportation Center (SaferSim)
  • Contract Numbers: 69A3551747131
  • Files: UTC, RiP
  • Created Date: May 6 2020 4:44PM