This is the first report of SWOV Working Group "Tyres, road surfaces and skidding accidents". Skidding is considered to be an important contributory factor in traffic accidents. Skidding can in principle be prevented in two ways, viz: (1) reduction of the minimum necessary friction, and (2) increasing the available friction. The minimum necessary friction depends on the desired driving behavior which is affected mainly by factors associated with the road, the vehicle, other traffic and the weather. The available friction depends on the nature of the contact between the tire and the road surface. Various investigations have shown that, among other factors, the skidding resistance of the raod surface influences the likelihood of skidding and hence of an accident. However, it has not yet been possible, on the basis of these investigations, to determine a definite 'minimum necessary' value for the skidding resistance of a road surface. Nevertheless, the working group on tires, road surfaces and skidding accidents considers it very important for a fixed minimum skidding resistance for the surfaces of all roads in the netherlands to be recommended immediately, even if this value is provisional. Its conclusion is that--partly for the sake of uniformity--the guide value already employed by the state road laboratory for many years for state roads and recently also for secondary roads, should be recommended as a provisional guide value for the skidding resistance of all roads in the netherlands. This minimum skidding resistance for a wet road surface, expressed as the coefficient of friction, measured with a standardized patterned measuring tire at 86% longitudinal slip and a road speed of 50 km/h, is 0.51. However, the working group considers that more research is necessary before a definitive value can be recommended. It will also be necessary to seek other concrete measures which might reduce the incidence of skidding. A research program for this purpose is suggested. /Author/.
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