Cost-effective geometric improvements for safety upgrading of horizontal curves

The purpose of this study was to determine the horizontal curve features which affect safety and traffic operations and to quantify the effects on accidents of various curve-related improvements. The primary data base developed and analyzed consisted of 10,900 horizontal curves in Washington State. Three existing federal data bases on curves were also analyzed. These data bases included the cross-section data base of nearly 5,000 miles (8,050 km) of roadway from 7 states, a surrogate data base of vehicle operations on 78 curves in New York State, and 3,277 curve segments from 4 states. Based on statistical analyses and model development, variables found to have a significant effect on accidents include degree of curve, roadway width, curve length, ADT, presence of a spiral, superelevation, and roadside condition. Curve flattening is expected to reduce accidents by up to 80 percent, depending on the amount of flattening. Widening lanes or shoulders on curves can reduce curve accidents by as much as 33 percent, while adding spiral transitions on curves was associated with a 5 percent accident reduction. Improving deficient superelevation can reduce accidents 10 percent or more, while the effects of specific roadside improvements were also quantified. An economic analysis was conducted to determine when curve flattening and/or widening are cost effective. An informational guide entitled "Safety Improvements on Horizontal Curves for Two-Lane Roads" (FHWA-RD-90-074) was developed in conjunction with this report to give specific guidance for the design of new curves and for upgrading existing curves.

  • Corporate Authors:

    United States. Federal Highway Administration. Office of Safety and Traffic Operations R&D

    McLean, Virginia  United States 
  • Authors:
    • Zegeer, C
    • Stewart, R
    • Reinfurt, D
    • Council, F
    • Neuman, T
    • Hamilton, E
    • Miller, T
    • Hunter, W
  • Publication Date: 1991-10


  • English

Media Info

  • Pagination: 237p
  • Serial:
    • Issue Number: FHWA/RD-90-021

Subject/Index Terms

Filing Info

  • Accession Number: 01404429
  • Record Type: Publication
  • Source Agency: ARRB
  • Files: ITRD, ATRI, USDOT
  • Created Date: Aug 23 2012 10:20PM