Computer techniques are applied in all areas of vehicle design having an influence over the speed of the design process and the efficiency and coherence of the design itself. The deployment of analytical methods removes the need for some test work and changes the role of much of the rest.A restraint system design has implications for several vehicle areas: body design; seat design; interior trim and hardware; and steering system; and must be considered against all these as well as the structural crashworthiness of the vehicle.At the concept stage, computer methods outline the implications of the functional specification so it can be modified if found to be unreasonable or inconsistent. As the vehicle design progresses, the requirements of the restraint system are broadly defined using programs to assess comfort and dynamic performance.Initial sled test work is based on the realistic possibilities as determined from the dynamic simulations, and the results of these tests serve to refine the model and improve background data. These tests are deliberately kept simple, and the computer model is used to study the effects of different impact conditions and component designs. This information is fed to design areas. This sequence of test and simulation is repeated in conjunction with prototype vehicle tests. The process means that sled tests have been effectively used and their combination with computer simulations gives a better understanding of, and confidence level in, the restraint system performance in the full vehicle test.