The Simulation Model of Automobile Collisions (SMAC) computer program was developed by Calspan Corporation as an aid with which to accurately reconstruct road accidents. Part of the overall objective of the research has been to make the system “user oriented” so that users without an engineering background can operate it with ease. This has necessitated developing a START program which automatically runs the SMAC program from a minimum of input data and an iteration routine designed to optimize the input values of velocities to provide a “best fit” reconstruction to the available scene data.A summary of how the START program works is given; however, emphasis is placed in the paper on the development of the iterative routine. The theory behind the routine is given and a number of examples are then presented to show how it works. For each example the results of each successive iteration are given to illustrate the manner in which the program converges to an acceptable reconstruction.This paper is based on research performed under Contract No. DOT-HS-5-01124 with the National Highway Traffic Safety Administration. The contents of the paper reflect the views of the author, who is responsible for the facts and accuracy of the data presented herein, and do not necessarily reflect the official views or policy of the Department of Transportation.