Safety Benefits of Paved Shoulders

Single vehicle run-off-road (ROR) crashes are the largest type of fatal passenger vehicle crash in the United States (NCHRP 500 2003). In Iowa, ROR crashes accounted for 36% of rural crashes and 9% of total crashes in 2006. Run-off-road crashes accounted for more than 61.8% of rural fatal crashes and 32.6% of total fatal crashes in Iowa in 2006. Paved shoulders are a potential countermeasure for ROR crashes. Several studies are available which have generally indicated that paved shoulders are effective in reducing crashes. However, the number of studies that quantify the benefits are limited. The research described in this report evaluates the effectiveness of paved shoulders. Model results indicated that covariate for speed limit was not significant at the 0.05 confidence level and was removed from the model. All other variables which resulted in the final model were significant at the 0.05 confidence level. The final model indicated that season of the year was significant in indicating expected number of total monthly crashes with a higher number of crashes occurring in the winter and fall than for spring and summer. The model also indicated that presence of rumble strips, paved shoulder width, unpaved shoulder width, and presence of a divided median were correlated with a decrease in crashes. The model also indicated that roadway sections with paved shoulders had fewer crashes in the after period as compared to both the before period and control sections. The actual impact of paved shoulders depends on several other covariates as indicated in the final model such as installation year and width of paved shoulders. However, comparing the expected number of total crashes before and after installation of paved shoulders for several scenarios indicated around a 4.6% reduction in the expected number of monthly crashes in the after period.

  • Record URL:
  • Corporate Authors:

    Iowa State University, Ames

    Center for Transportation Research and Education, 2711 South Loop Drive
    Ames, IA  United States  50011-8664

    Iowa Department of Transportation

    800 Lincoln Way
    Ames, IA  United States  50010
  • Authors:
    • Hallmark, Shauna L
    • McDonald, Thomas J
    • Tian, Ye
    • Andersen, David J
  • Publication Date: 2009-1-1


  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Figures; References; Tables;
  • Pagination: 63p

Subject/Index Terms

Filing Info

  • Accession Number: 01149546
  • Record Type: Publication
  • Report/Paper Numbers: InTrans Project 05-239
  • Created Date: Jan 14 2010 4:32PM