The use of passenger car skid mark length as a measure of vehicular energy dissipation is widespread. In actual emergency braking maneuvers, the relationship between deceleration, initial speed and time is non-linear. In addition, substantial energy is dissipated by the vehicle prior to the production of visible skid marks.This paper discusses these relationships for passenger cars engaged in emergency braking. Specifically, this paper reports the results of an empirical study relating changes in velocity and acceleration during braking maneuvers. The test results are then correlated to skid length and energy dissipation in order to permit accurate skid mark signature analysis.