Support for the Elimination of Roadside Hazards: Evaluating Roadside Collision Data and Clear Zone Requirements

Over a three year period (2004‐2006), there were more than 60,000 crashes involving fixed objects (trees, utility poles, culverts, bridge piers, etc.) located within South Carolina roadsides. These fixed object crashes accounted for 20% of all crashes in South Carolina, and nearly 50% of all fatal crashes. In comparison, only 30% of fixed‐object crashes result in fatalities nationally. Responding to the growing concerns of roadside hazard involvement in crashes, SCDOT selected a research project to analyze roadside collision data, evaluate the sufficiency of current clear zones along state roadways, and assess the benefits associated with minimizing consequences of leaving the roadway by providing and maintaining adequate clear zones. Clemson University was selected to perform this work. After using a combination of crash data, SCDOT roadway inventory data, and geographic information system analysis tools to identify 287 sites of interest in 14 counties across the state, Clemson researchers surveyed the sites with an instrumented van to identify exact parameters for roadside slopes and distances to obstacles in the clear zones. Of the 287 sites surveyed, 131 were randomly selected and analyzed for clear zone requirements. Of these, only 12 met the criteria using automated software processing. Taking into consideration, variations in actual operating speeds and the presence of curves at these sites, six more would no longer meet clear zone requirements. The research team also analyzed 58 control sites. Control sites are areas that have no instances of fixed object crashes within the three year study period. For these 58 control sites, 47 met the minimum clear zone requirements, and only 11 did not. Using an odds ratio test for this sample, researchers determined that the odds of a site having a fixed object crash are 42 times higher if the minimum clear zone is not met. Considering the magnitude of the roadside hazard problem, and the deficiency of the clear zones in these areas, it appears that by providing recommended clear zones (or safe recovery areas) for motorists who leave the roadway, South Carolina could realize a notable decrease in roadway fatal and injury crashes. This is particularly significant realizing that many times it is for reasons other than driver error (i.e. blown tire, struck by another vehicle, avoiding an accident, avoiding deer, etc.).


  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Figures; Photos; References; Tables;
  • Pagination: 60p

Subject/Index Terms

Filing Info

  • Accession Number: 01151284
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-SC-09-01
  • Contract Numbers: SPR 667
  • Created Date: Feb 18 2010 11:10AM