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Rear impacts in the crash test data base compiled by the NHTSA are analyzed and compared to the CRASH3 rear stiffness coefficients. The CRASH3 values do not represent the test data adequately. This is because the values were derived from limited data, and because some of the rear moving barrier test data were miscoded as fixed barrier tests. A review of the larger NHTSA data base does not support the CRASH3 assumption that vehicles of similar size (wheelbase) have similar rear stiffness characteristics. Therefore, it is important when reconstructing individual accidents to use crash test data specific to the vehicles involved. Repeated rear fixed barrier test data on four vehicles are analyzed to study the data trend at speeds below and above the NHTSA test data. Constant stiffness and constant force models are compared and a combination of the two is shown to fit available test data.

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.