Post-impact deformation has long been used to assess the severity of vehicular impact. If similar deformation of a similarly impacted vehicle has been experimentally observed, the speed change during a subject impact may be estimated.Crush energy is the usual intermediary, and all crush energy methods to date use the same physical model, that of the energy of compression of a uniformly, but not necessarily linearly, elastic region of an otherwise rigid vehicle. This paper reviews the various inferences historically associated with this “standard model,” including some which oversimplify or fail to follow logically from the model.It is concluded that treatments which are more complete or which do follow logically from the standard model can easily be derived. Improved treatments, which more closely duplicate the effects which must be present in the subject, “real-world” impact, are presented. Application of these relationships to a spectrum of experimental data is not within the scope of this paper.