Safety Impacts of Intersection Sight Distance

The provision of appropriate intersection sight distance (ISD) is an important element in intersection design. The approach to the determination of ISD in American Association of State Highway and Transportation Official's (AASHTO's) A Policy of Geometric Design of Highways and Streets (known as the “Green Book”) is based on gap-acceptance developed in the 1996 NCHRP Report 383: Intersection Sight Distance. This approach includes the ability to more easily calculate ISD for both passenger cars and trucks by allowing the selection of an ISD “design vehicle.” Calculations of ISD using this approach yield different results than those calculated with earlier methods. However, past research efforts to analyze and quantify the safety impacts of ISD have produced inconsistent results, making it difficult to fully evaluate the different approaches. The quantification of these safety impacts would allow better design evaluations that include variations in available ISD. It would also provide the opportunity to evaluate the potential safety impacts of the ISD criteria in the Green Book. Transportation agencies would benefit from guidance on incorporating the safety impacts of intersection sight distance into the decision-making process. The objective of this research is to determine the relationships between safety and available ISD and to develop guidelines for transportation agency decision making. The guidelines should be applicable to unsignalized intersections (no control, yield control, and stop control on the minor road). It is expected that the research and guidelines will address the following elements: (1) Identification of appropriate definitions and methods to measure ISD; (2) Quantification of the relationship between safety and available ISD (i.e., Crash Modification Factors and other appropriate functions); and (3) Guidance to transportation agencies on how to apply these functions to evaluate the safety impacts of available sight distance.


  • English


  • Status: Completed
  • Funding: $450000
  • Contract Numbers:

    Project 17-59

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Parker, Stephan

  • Performing Organizations:

    Vanasse Hangen Brustlin, Incorporated

    P.O. Box 9151, 101 Walnut Street
    Watertown, MA  United States  02471-9151
  • Principal Investigators:

    Eccles, Kimberly

  • Start Date: 20120514
  • Expected Completion Date: 0
  • Actual Completion Date: 20170331
  • Source Data: RiP Project 29076

Subject/Index Terms

Filing Info

  • Accession Number: 01541912
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-59
  • Files: TRB, RiP
  • Created Date: Oct 29 2014 1:00AM