Vehicle occupant movement and impact with the interior in frontal collisions – the ‘second collision’

Abstract

This paper describes the movement of vehicle occupants in moderate speed (25–35 mph) frontal crashes. In these collisions, the occupant compartment is usually unintruded. Therefore, the occupant movement may be expressed relative to the movement of the rear (or undeformed) portion of the vehicle. The paper begins with a review of the dynamics of the undeformed portion of a vehicle during a collision. The occupant movement is then studied by examining the effects of the restraints (i.e. the seat, the seat belt and the air bag) upon the occupant. Interestingly, with only a few simplifying assumptions, the analysis leads to governing equations involving only elementary functions. It thus enables the hand computation and evaluation of occupant movement by accident reconstructionists. An illustration, with specific numerical data, is given. The efficacy of seat belts and the timely deployment of air bags are demonstrated.