Estimation of Effects of Reduced Salting and Decreased Use of Studded Tires on Road Accidents in Winter

Abstract

The effect on road accidents of reduced salting was estimated on the basis of accident risks on bare (free of ice and snow) and slippery roads and the changes that decreased salting causes in the proportions of vehicle kilometers driven on different road surface conditions. That the risk in slippery conditions may depend on the frequency of such conditions was also taken into account. The effects of studded tires on accidents were estimated on the basis of data from mail surveys and case study accidents. The effects of the use of studded tires on driving behavior were studied in real traffic so that drivers were unaware that their driving was being monitored. The final conclusions were drawn by combining results from a number of studies. Even though the results from a single study were often more indicative than conclusive, the studies together resulted in reasonably clear implications of the direction and magnitude of the effects. It was concluded that decreasing the use of salt or studded tires from the present level (approximately 95 percent of cars use studded tires and approximately 10 T of salt is used per road kilometer each winter) would increase injury accidents in winter. Accidents would increase 26 to 30 percent if salting were decreased by 80 percent and only 20 percent if cars were equipped with studded tires.