This synthesis report will be of interest to pavement design, construction, management, and research engineers, highway safety officials, and others concerned with pavement friction characteristics. It describes the current state of the practice and discusses the methods used for evaluating wet pavement friction characteristics of new and restored pavements. This synthesis reviews models used for measuring and evaluating friction and texture, causes for friction changes over time, and aggregate and mix design to provide adequate friction. Also presented are construction and surface restoration practices for providing good pavement surface characteristics. In addition, considerations of noise and ride quality are discussed when compromise may be required.

This report contains guidelines and recommendations for managing and designing for friction on highway pavements. The contents of this report will be of interest to highway materials, construction, pavement management, safety, design, and research engineers, as well as others concerned with the friction and related surface characteristics of highway pavements.

In 2012, Dynatest conducted friction testing for the Wisconsin Department of Transportation (WisDOT) on a representative subset of its State Trunk Highway Network. Friction testing was performed at 3,394 sites in accordance with ASTM E274 using a Dynatest 1295 Pavement Friction Tester. Testing was conducted using the ASTM E501 standard rib tire and skid numbers were adjusted (if necessary) to a speed of 40 mph (SN40R). The testing involved a variety of hot mix asphalt pavement mixtures (including stone matrix asphalt), concrete surface textures, pavement ages, and functional classifications throughout Wisconsin and the frictional characteristics were analyzed several different ways. In general, the weighted average SN40R for hot mix asphalt, stone matrix asphalt, and concrete pavements were 51.6, 42.5, and 49.5, respectively. The weighted average SN40R for the different functional classifications ranged from 50.4 to 55.5 for the rural classifications and from 41.4 to 49.9 for the urban classifications. The weighted average SN40R decreased slightly as HMA and concrete pavement ages increased. The average friction of SMA, on the other hand, was shown to increase slightly as the pavements aged. Lastly, some crash sites within the tested segments were identified and analyzed. The results showed that the frictional characteristics at these sites were comparable to other pavement sites throughout the state.