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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.

The National Highway Traffic Safety Administration maintains a large database containing data from nearly 1500 staged crash tests. A portion of that database tabulates information about the tests, vehicles, instrumented dummies, and barriers. That tabulated data has now been successfully loaded onto a desk-top Macintosh. Using a relational database program allows for fast and effective use of the database information. One application of the crash database was to investigate frontal pole barrier tests. The results from nineteen staged pole barrier tests were extracted from the database to evaluate various methods for relating the pre-impact speed to the observed crush. A common method for estimating speed involves calculation of the crush energy using the observed crush and crush parameters A and B (obtained from flat barrier tests). For frontal pole collisions, this method appears to under-estimate the impact speed by about 33%.

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.

A number of accidents involve a vehicle going off the edge of the road and becoming airborne. In these types of accident, the engineer is typically faced with the problem of estimating the velocity of the vehicle at launch, based on evidence defining the launch position and point of impact at the end of the flight. Two options have been available to evaluate the dynamics of such problems. The first is to treat the vehicle as a point mass, and use simple trajectory equations to define the flight path. This approach considers only the two translational degrees of freedom of the center of mass of the vehicle, and neglects effects of tire contact during launch. The second option is to carry out a full three-dimensional analysis. This approach treats the sprung mass of the vehicle as a rigid body, accounts for the four tire contact conditions, and possibly models the suspension and unsprung masses.

Many accidents involve questions regarding human visual performance. For example, drivers involved in accidents often report that they did not see what they hit, or that they saw it too late to do anything. In these cases, it is often necessary to determine if people or objects at the accident scene (pedestrians, motorcycles, other vehicles, debris, etc.) would have been visible to the reasonably alert person under conditions of a particular accident. This determination must be made with proper consideration of both inter- and intra-person variability The goal of accident reconstruction is to determine what happened in an accident, and why it happened. This process involves a thorough examination of the available evidence. More specifically, the investigator considers the physical evidence, accident reports, and statements of the involved parties and witnesses.