Water Depth Influence on Pavement Friction

The effects of various water depths (obtained with a rain simulator) on the friction properties of various pavement textures have been determined at different levels of vehicular speeds, tire-tread depths, tire pressures, and tire types. Within the range of the experimental data gathered, increasing water depth beyond that required to inundate the pavement surface macrotexture does not significantly affect skid numbers. Increases in tire-tread depth and surface texture increases skid numbers, whereas, increases in vehicle speed decreased skid numbers. The effects of tire inflation pressure were of limited significance within the range tested. A water depth of 0.02 in. (0.51 mm) appears acceptable for routine friction measurements. A surface macrotexture of about 0.04 in. (1.02 mm) should be considered minimum for high-speed facilities unless the surface is an open-graded or porous draining type. A minimum tread-depth requirement of about 0.06 in. (1.52 mm) should be included in vehicle inspection requirements.