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Title:Effects of Aggregate Seal Coats on Skid Index Numbers & Accident Rates of Low Volume Roads in Utah
Authors:Prianka Seneviratne and John Bergener
University:Utah State University
Publication Date:May 1994
Report #:MPC-94-33
TRID #:00669028
Keywords:before and after studies, chip seals, countermeasures, crash rates, friction course, friction materials, low volume roads, rural highways, safety, seal coats, skidding, traffic safety
Type:Research Report – MPC Publications


This paper examines the effectiveness of applying chip seal friction courses in reducing accidents on low volume, rural roads. Chip sealing data from District 3 of the Utah Department of Transportation were used to examine accident rates before and after applying chip seal. Although accident rates generally decrease with an increase in skid numbers, existing linear and nonlinear relationships were found inappropriate to describe this trend. Nonlinear relationship between accident rate and skid number, estimated reductions in accident rates of more than 60 percent. However, before-and-after treatment accident rate comparisons using the data support these estimates only at statistically significant levels below 85 percent. The data indicate there is no definite relationship between accident rates and skid numbers on roads that were chip sealed.

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050