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 other 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 is recommended to WSDOT. The new guideline is similar to those developed by other highway departments and is based on research conducted over the last 25 years. Most importantly, the new guideline provides WSDOT with a more realistic friction range for assessment of highway pavements.