Search Results

The objective of this paper is to illustrate how the use of velocity diagrams of both vehicle and occupant motion can be of great assistance to the accident reconstructionist. The technique, best applied in the early stages of the reconstruction process, is recommended to (1) reduce the likelihood of arithmetic or equation misapplication errors, (2) permit estimates for such accident parameters as mutual crush and impact duration, and (3) provide insights into the critical issues of the reconstruction. For analyzing occupant motion, reasonably realistic models of compartment response are proposed based on either a cosine model or a model derived from the CRASH computer programs.

The computer program “IMPAC” (impact Momentum of a Planar Angled Collision) was developed for use in accident reconstruction to study the impact phase of a collision. It may be used for vehicle to vehicle or vehicle to fixed object impacts. Collisions are modeled as a vector impulse in two-dimensions taking place at a specified point in each two-dimensional vehicle. A common velocity is reached at this point for the inelastic collision with complete lockup. An optional condition is available to study sideswipe type collisions in which the colliding points are permitted to slide relative to each other at a prescribed speed along a defined plane of slip. The program has been validated by comparison with the data from 16 staged crash tests conducted by the NHTSA.

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.