The influence of road surface texture on the skid resistance under wet conditions

Due to their influence on traffic safety, skid resistance and drainage are important surface properties of a road and their optimization and durability is still focus of ongoing research. Under wet conditions, these two characteristics are connected as a wetted road cannot provide a sufficient skid resistance without a working drainage system. The wet friction is mainly affected by the road surface geometry and the water depth. Herein, we describe a novel numerical approach to study the influence of the surface texture - mainly the microtexture - on the wet friction coefficient. This method is based on the hysteresis effect, which is the main friction force on rough surfaces under wet conditions. We therefore use an already established friction model for dry surfaces and extend its range of application by an additional consideration of water films. A drainage model has been developed to calculate the water film thickness for a given road surface and geometry (pavement surface runoff model) as systematic measurements of water film thicknesses in situ are difficult. The water depth determines the number of contact points between the pavement and the tyre. Based on three-dimensional measurements of a surface texture, the friction coefficient is calculated. By this newly developed model approach, it is possible to identify the main factors influencing wet skid resistance in regard to the pavement surface microtexture and the water film thickness.