The objective sought in this research is the optimization of vehicle deceleration to minimize serious injury and fatalities for harnessed occupants. The injury criterion is head acceleration, which from biomechanical considerations is not permitted to exceed 80 G. Head injuries account for 70% of accident fatalities, and the most reliable indicator of such injuries is recognized to be head acceleration. Further biomechanical limitations on head motion appear to be the rate of change of acceleration which cannot exceed 1000 G/sec. and the injury severity index which is limited to the value 1000. From these criteria, a tentative selection of optimum head acceleration profiles for different vehicle impact speeds has been made. These traces serve as the desired output from a four-degree-of-freedom model of a lap-and-shoulder-belted front-seat occupant. It is required to find the vehicle deceleration input which causes this optimized head response during a crashing situation. The equations of motion for the occupant have been programmed on a digital computer, and the solutions presented graphically.The results show that the optimum vehicle deceleration waveform is a flat deceleration versus time history with a superimposed, early-impulse peak. This differs widely from present day car performance. A comparison of existing vehicle deceleration with the ideal traces suggests that the early-impulse criterion can be implemented in existing designs by moving the engine block forward. Simple calculations using collision models confirm this finding. Other recommended changes in the design of automobile forestructure include a lengthening of the front-end and a stiffened bumper to distribute impact loads. Using statistical data available from many sources, an empirical equation has been derived to show the savings in fatalities that would result using the optimized design.