The “IMPAC” collision algorithm is a comparatively simple application of momentum conservation in a collision. This 2-D model may be used in a number of applications: to reconstruct car to car collisions, to study car to barrier collisions, to evaluate proposed crash test conditions, to refine and check reconstruction calculations made using the “damage” option of “Crash3”, or as a predictor for the “SMAC” program to reduce the number of runs required to obtain a reconstruction. The program also provides a means of rapidly evaluating questions of sensitivity of results to changes in input. The essential features of the model are reviewed herein and two collision configurations are examined. The most recent version of the program provides output for purposes of comparison with the method employed by the “Damage” option of the “Crash3” program.