Friction measurements were made with a skid trailer at 70 mph (31 m/s) on 770 miles (1240 km) of rural, four-lane, controlled-access routes on the interstate and parkway systems in Kentucky. Each construction project was treated as a test section. Accident experience, friction measurements, and traffic volumes were obtained for each. Various relationships between wet-weather accidents and skid resistance were analyzed. Averaging methods were used as a means of developing trends and minimizing scatter. A moving average for progressively-ordered sets of five test sections yielded more definite results. The expression of accident occurrence which correlated best with skid and slip resistance was wet-weather accidents per 100 million vehicle miles (161 million vehicle kilometers). Accidents increased greatly as Skid Numbers (70 mph or 31 m/s) decreased from 27. Analysis of Peak Slip Numbers and accident occurrences indicated similar trends.

Report Date


Report Number

No. 408

Digital Object Identifier



Accepted for publication by the Transportation Research Board.