Driver Reaction to a Technical Safety Measure—Studded Tires

An investigation was conducted to determine if drivers of vehicles with studded tires are making use of the increased coefficient of friction on icy roads to maintain a higher speed or to drive at a higher level of safety than do drivers with unstudded tires. Speeds, following-distances, and presence of studded tires were checked on several thousand vehicles in real traffic during early morning hours. The sample studied consisted of drivers in traffic between a suburb and the town of Uppsala. The measurements were carried out with traffic analyzers and studded-tires indicators on two consecutive curves. Studies were made in both dry and icy road conditions. The safety level was calculated in the following ways: (1) the quotient between coefficient of friction used and the maximum friction available in the curve, and (2) the quotient between actual speed and the highest possible speed in the curve. The results showed that, although drivers with vehicles equipped with studded tires are driving somewhat faster than drivers with unstudded tires in icy (low friction) road conditions, this increase in speed does not lead to lower safety. On the contrary, drivers with studded tires are, on the average, driving with larger safety margins than drivers with unstudded tires. In dry (high friction) road conditions, no clear differences in safety or speed were found.