Vehicle Braking on Steep Down Grades: Field Experiment Results

Steep downgrades are known to increase accident rates yet little is published on how well vehicles brake and handle on steep downgrades. Braking tests were completed on grades of; 1, 7 13, 21 and 28 percent. The tested surfaces were asphalt, in both dry and wet conditions, with a car and a utility vehicle, with and without ABS brakes. The 13 percent grade was grooved and the test sequence repeated.

The braking tests found a non-linear decreasing relationship between the average coefficient of friction or drag factor and downgrade.

Pavement grooving on the 13 percent grade of a local road has eliminated the crash occurances for a two-year period. Testing showed that grooving also improved vehicle handling.