Relationships Between Pre-Skidding and Pre-Braking Speed

This paper investigates the accuracy of vehicle pre-braking speed estimates based upon tire/roadway coefficient of friction (drag factor) measurements and skid mark measurements. Data was collected to determine if there were any correlations between pre-braking speeds and pre-skidding speeds. Braking tests were performed on three vehicles using various measurement devices including an accelerometer, a fifth wheel, a radar gun, and a shot marker (bumper gun) system. The vehicle speeds, braking distances, skid mark distances, and deceleration histories were recorded. From this data, coefficients of friction for the tested road surface were evaluated. The coefficients of friction were then used in combination with the measured skid mark distances to calculate the vehicle pre-skidding speeds. The calculated pre-skidding speeds were then compared to the actual pre-braking speeds of the vehicles in order to establish the accuracy of the calculation methodology. A correlation between the calculated pre-skidding speed and the actual pre-braking speed was established for the study data.