Road traffic safety is affected by several factors, such as skid resistance and deviations in the longitudinal and/or transverse profile of a pavement surface, especially when they result in water accumulation and standing on pavement surfaces. Problems in safe operation of vehicles may create also light reflectivity and dirt on the road surface (debris, foreign objects, fuel and fuel oil rests). Although all of the above mentioned factors can provide an important hazard to road traffic safety, a key role has pavement slipperiness. Road pavement surfaces must therefore ensure adequate levels of friction and skid resistance for the vehicle’s tyres travelling on them. especially in wet conditions. Already a thin film of water on road surface considerably reduces level of friction and increases accident risk. In order to obtain information about the pavement surface condition and to verify road safety conditions, two important parameters are usually routinely assessed: friction coefficient and texture depth. Results from measurements of friction and texture depth in the UK showed that friction falls with speed. They also showed that friction on surfaces with a low texture depth falls more rapidly with speed than for high-textured surfaces, and that a loss of friction at slow speeds is highly affected by texture depth. The friction coefficient is calculated by dividing the force resisting to motion in the plane of the interface by the load acting perpendicular to that interface. A particular coefficient is related to the specific tyre, speed of measurement, water film thickness and other measuring conditions that affect it, so specific terms and measurements are used for describing road surface behaviour under standardised conditions. (Author/publisher)
Abstract