Vehicle crash investigators are regularly challenged to reconstruct the kinematics of collisions when there are no witnesses or there is conflicting witness testimony. Vehicle deformation, skid marks and contact points on the roadway and the roadside often permit a picture of the event to unfold. Vehicle speeds at collision are of major interest and are often estimated by studying skid marks, vehicle crush and vehicle displacement after initial collision. Some of the uncertainty in these calculations can be rectified if the vehicle in question has entered into a free-flight trajectory. Often the points of vehicle take off and landing are readily discernible and a calculation of the vehicle speed at take off can be made from the measured parameters of the trajectory.

This paper presents a solution to the fundamental equations of motion in terms of the horizontal range, the vertical height change and the angle of projection of the vehicle. Data are presented which quantify the speed at cake off in terms of these parameters and which will allow investigators who are unfamiliar with complex mathematical relationships to interpolate a solution for a measured set of parameters. The effects of aerodynamic drag on the vehicle are reviewed as they relate to the estimation of vehicle speed from the measured trajectory parameters.

Vehicle collisions involving free flight trajectories were investigated by The University of Western Ontario Multi-Disciplinary Accident Research Team and summaries of the findings are presented. These cases illustrate how this vehicle speed estimation technique can play a most valuable role in police and Coroners' investigations of such collisions.