Prior side impact modelling studies concentrated on characterizing the structural and occupant resl)onses in perpendicular (90 degrees) and oblique (60 degrees) impacts where the striking vehicle's bumper engaged the door of the struck vehicle. In this model, the two colliding vehicles were modelled with three masses (representing the striking vehicle, and the struck vehicle's door and passenger compartment) and the struck car occupant was modelled with four masses (representing the pelvis, rib, spine and head body segments) from which the lateral motions of the vehicle and the occupant were obtained. While this model worked satisfactorily, only a limited number of variables could be parametrically assessed to determine their influence on occupant responses. It became apparent that a number of refinements were necessary to thoroughly investigate the effects of structural improvements and other injury mitigation concepts on occupant thoracic responses.

A new model was, therefore, developed with fifteen masses and thirty-one connecting energy absorbing elements which more closely simulated the interaction of the side door and adjoining structure o[ passenger cars and the interaction of the door with the occupant in side impacts. The most important additions were:​ (a) inclusion of rate sensitive factors in the energy absorbing elements, (b) inclusion of inner and outer door masses to account for the penetration distance between the exterior and interior door surfaces, (c) inclusion of upper and lower load paths for the door and the A/B pillars, (d) inclusion of door inner core energy absorbing elements to account for the internal stiffness and the stiffness of the interior door surface, and (e) inclusion of coupling stiffncss between the pelvis and spine body segments which was assumed to have a negligible effect on occupant responses in the earlier model.

Simulation studies were performed with the new model to compare the responses obtained in side impact tests of various models of production cars conducted by the National Highway Traffic Safety Administration (NHTSA). Specifically, a VW-Rabbit, Nissan-Sentra, Honda-Civic, Chevrolet-Celebrity and Chevrolet-Spectrum were simulated using the new model. Additionally, side impact tests of Ford-LTD's conducted by Motor Vehicle Manufacturers Association (MVMA) were also simulated.

With the aid of this model. various vehicle characteristicsa nd their effects on the thoracic response of an unrestrained occupant were investigated. These included:​ striking vehicle stiffness and its geometry, door internal structural characteristics of struck vehicles and internal geometry, stiffness characteristics of A/B pillars, a nd occupant's lateral seating positions. From the above parametric changes, the interactions of the occupant and the door structure were evaluated in an attempt to explain the occupant response differences seen in production car tests.