Traction tests were run during February, 1993 and 1994. The snow tests were conducted at a fairly constant temperature of -2 degrees C, and the ice tests at air temperatures ranging from -4 to -35 degrees C. The test vehicles were a standard midsize automobile and highway maintenance gravel trucks. The automobiles on packed snow at -6 degrees C have an average braking force coefficient of 0.35, a lateral force coefficient of 0.38, and a traction force coefficient of 0.20. The corresponding values for a straight truck are: 0.23, 0.35, and 0.15. An automobile on bare ice at -6 degrees C has an average braking force coefficient and lateral force coefficient of 0.09, and a traction force coefficient of about 0.08. The valves for the truck on bare ice in the same order are 0.06, 0.07, and about 0.04. A relationship was developed between the average braking force coefficient, ambient temperature, and the amount of standard highway winter aggregate used on the road. The influence of winter aggregate on ice gave an improvement of about 15% at a highway maintenance light application of 75 gm/m2, and about 30% at a heavy application rate of 150 gm/m2. Aggregate blow off tests on bare pavement estimated that at an application rate of 175 gm/m2 about 100 cars or 30 trucks would remove most of the winter aggregate from a bare road surface. (A)
Abstract