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Two widely used computer programs developed for the analysis of vehicle collisions are CRASH and SMAC. This paper reviews stiffness parameters which are used in the application of these programs, and methods to select these parameters. The paper also introduces a rational method to select stiffness parameter KV for the SMAC program. The CRASH program expresses the vehicle force-crush relationship as FC = A + B*CR, where FC is the force per unit width, and CR is the vehicle residual crush. The “stiffness parameters,” A and B, define a linear relation with a zero-crush intercept. For collinear impacts, these parameters are used in determining crush energy, which in turn is used in determining changes in velocities of the impacting vehicles. Over the years, considerable effort has been expended by numerous researchers to determine A and B for a variety of vehicles, and a substantial body of vehicle crash test data has been developed and analyzed to this end.

This paper describes a straight-forward, automated approach to performing sensitivity analyses using Monte Carlo simulation techniques. Probability distributions are assigned to key input parameters, and results are expressed in the form of probability distributions of each of the desired output parameters. With this technique, it is possible to obtain quantitative results regarding the probability of results being within selected ranges. The approach is fast and automated, and provides a rational basis for dealing with uncertainty and ranges of parameters in accident reconstruction analyses.