The effects of geometric design and traffic characteristics on accidents on two-lane rural roads with a moderate average daily traffic (ADT) between 400 and 3000 vehicles per day were studied for two data sets. Geometric design elements were aggregated into "bundles" or groups frequently found together in the field as a result of design policies. Advanced multivariate analysis techniques were used to explore their relationships with accident experience. It was found that accidents interact in such a complex way with ADT that the rate of accidents per mile-year is superior to the conventional rate of accidents per vehicle-mile for models developed from typical accident data files. Models using almost 20 geometric and traffic variables explained about 70 percent of the variance in accident frequency on several hundred road sections. Of this, ADT accounted for 30 percent and intersections and driveway frequency about 25 percent more. Models using ADT, access density, and geometric bundles made up of up to 5 design variables performed as well as the 20-variable models. Simple categorical models using only the bundles explained approximately 50 percent of the variance in accident density in both data sets. Illustrative mathematical models were also developed. Off-road accidents increase with ADT exponentiated to .5 to .9; the exponent increases as bundle characteristics become worse. Comparison of sections with the best and worst accident records showed the strong influence of the geometric design bundles on accident experience. Results of the research indicate that treating geometric and roadside elements as clusters rather than individually is a worthwhile approach for safety improvement programs.

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 51-61
  • Monograph Title: Evaluation Methods and Design and Operational Effects of Geometrics
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00457201
  • Record Type: Publication
  • ISBN: 0309039169
  • Report/Paper Numbers: HS-039 598
  • Files: TRIS, TRB
  • Created Date: Aug 31 1990 12:00AM