Improvement of Methods for Determing Pre-Crash Parameters from Skid Marks

摘要

This report presents the results of an experimental study, the goal of which was to validate and improve the methods currently used by accident reconstructionists to determine precrash parameters from skid marks. The three major issues concentrated on by this study were to validate or improve the currently used skid mark length versus prebraking speed formulas; to determine which method of measuring the coefficient of friction between the tire and the road produces the best results; and to see if unlocked wheels could produce skid marks. Six vehicles, three cars and three trucks, were tested during this study. The vehicles were tested with a variety of tire types and vehicle loadings on three different pavements. Both severe (wheels locked) and moderate (no wheels locked) stops were made from five speeds ranging from 10 to 60 mph. Prebraking speed, stopping distance and the length of the skid marks produced were determined for each stop. Stripchart recordings showing, as functions of time, distance travelled, speed, applied brake pedal force, longitudinal deceleration and the rotational rate of each wheel were also made. Regression analyses were performed to see how well the currently used skid mark length versus prebraking speed formulas and two modified forms of the currently used formulas fit the experimental data. These analyses showed that the currently used formulas provided an excellent fit to the test data. Furthermore, neither of the modified formulas were able to better explain the test data.