A psychophysical method for determining the effect of studded tires on safety

A method was presented for determining the safety effect of studded tires independently of other driver and vehicle centered variables which covariate with the use of studs. It is based on psychophysical functions between the friction coefficient and accident risk, or driver behavior, separately produced for studded and unstudded cars. From the two functions, the effect of studded tires can be calculated at different levels of friction as far as the respective effect of studs on friction is known. A pilot study was conducted concerning the risk of skidding in a curve. The friction coefficient was periodically measured on an off-ramp of a motorway and, for each passing car, the spot speed and the use of studs was recorded. The probability of skidding, calculated from the distribution of safety margins, was plotted as a function of friction and the effects of studded tires and other driver and vehicle centered variables were demonstrated.