Evaluation of Surface Friction Guidelines for Washington State Highways

The Washington State Department of Transportation (WSDOT) determines wet-pavement surface friction characteristics by conducting skid-tests in accordance with applicable AASHTO and ASTM standards. The results of the skid-tests are used in conjunction with cther criteria to assist in selecting pavements for resurfacing (the primary criteria is wet-pavement accident rates). This paper examines literature from the United States and abroad on friction number guidelines for highways. On the basis of an analysis of the literature, a revised friction number guideline was developed. The new guideline is similar to those developed by other highway departments and is based on research conducted over the last 25 years.