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BackgroundThe winter tyre type have various effects on traffic safety. These effects have been analysed in three separate studies published between December 2014 – December 2015.MethodsThe main questions of the 3 studies were a): what’s the safety difference between studded tires and studless tires and b) how can we promote traffic safety connected to winter tires? The study number 1, “Studded and studless tires in fatal wintertime road accidents” was based on accident data analysis. The study 2, “The socio-economical consequences of Ice grip approval” was based on literature analysis. The study 3, “The winter tyre type effects on the grip and wear of packed snow and ice” was a field test study.ResultsIn Finland, 12% of the traffic exposure of passenger cars and vans in winter is driven by studless winter tires. If everyone in Finland would use studded tires, we would have one deadly accident per year less.There is no ice grip demands for the winter tires used in Finland. If such demand will be deployed today, there will be 0.5 million € yearly societal savings per year. If the use of studless tires increase as planned, the effects of ice grip approval will be multifold.Studded tires have an external safety effect, they make ice more rough. According to tests in test field, 50% of studded tires ensured good friction conditions for all kind of winter tires.ConclusionsUse of studded tires offer still remarkable traffic safety benefits in winter time. Because there seem to be need to decrease the proportion of studded tires in large cities (studded tires may promote air quality problems), it’s still important to understand, how we can minimise the negative traffic safety effects of this decrease. By deploying ice grip demands, we can be assured, that the approved studless tires meet the winter traffic demands. It’s also important to remember, that if the proportion of studded tires will fall below 50%, there is high risk for increasing slipperiness.

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.