This report documents and presents the results of a statistical analysis of accident data that attempts to provide a quantitative measure of the safety effects of studded tires on icy surfaces. Winter accident and driving data from two states, Minnesota and Michigan, were used in the study. Because a ban was placed on studded tires in Minnesota during the study period, a "before-and-after" type of analysis was possible for that State. Primary comparisons were made in terms of accident rates, using both accident data and exposure (time-on-road) data, nature of accident involvement as influenced by slippery roads, and the incidence of injury. Data from 91,275 winter accidents involving 36,639 autos were available for the analysis of tire effects. Even with this large sample, some of the most sought-after relationships did not prove to be statistically significant at the 0.05 level of confidence. The findings of the study tend, in general, to show a slight safety advantage for studded tires. Tables are presented that, with the use of local data can be applied to determine guidelines as to what changes in accident frequencies might be associated with the banning of studded tires. (Author/publisher)
Abstract