Of importance for the success of accident prevention campaigns is a definite knowledge of the causes of accidents. Attempts to reconstruct the actual events of accidents through subsequent investigations of the vehicles and at the scenes of the accidents often remain very unsatisfactory, since decisive traces and influences—the key to the solution of the problem—have been altered or are no longer there at all. Through presentation of practical examples and results of first-hand experiences, we will show the advantages of securing and evaluating traces of accidents at the scenes by technical experts for subsequent objective reconstruction of the events.The general method of securing traces, as practiced by the experts of our accident department, will be shown in great detail, as will be the thought processes employed by our experts in connection with suitable individual cases. The results obtained in this manner may be divided into three main categories in connection with the causes of accidents: 1. Human error. 2. Inadequacies of the traffic area, including other external circumstances. 3. Technical deficiencies of the vehicle that endanger traffic.