The reconstruction of accidental impacts to the side structure of one or more accident vehicles often incorporates estimates of the energy absorbed by laterally struck vehicle(s). Such estimates generally involve considerably more issues than does the assessment of frontal or rear impact deformation energy. The sides of vehicles are, compared to the usual striking object, relatively broad, and they contain zones of varying stiffness supported by collapsible box structures. Side stiffnesses can vary widely, depending upon impact geometry. Most side impact crash tests that can readily be used to make estimates of side stiffness have been conducted by the National Highway Traffic Safety Administration (NHTSA). These tests are almost exclusively conducted against one particular area of the side structure, the damage sustained by test vehicles is generally poorly documented, and reported crush is obtained via procedures which contain measurement discontinuities as the severity of the impacts increase. Published “recommended” crush coefficients generally assume that the CRASH constant stiffness model holds over the complete range of crush depths. The concept of a Force Saturation model is recommended to deal with the more realistic structural behavior seen in practice at larger crush depths.This paper has two main objectives: (1) to summarize and critique the currently available side impact data base upon which side stiffness models and their associated coefficients have and can be based, and (2) to provide guidelines and insights into the development of reasonable energy estimates by use of improved crush models and crush measurement procedures.