BACKGROUND. In recent years, increasing attention has been paid to improving car frontal design in order to minimise pedestrian injury. Many tests have been carried out using a free-flight instrumented headform projected against the car exterior. For pedestrians and other vulnerable road users, the bonnet should act as a cushion in an impact. AIMS OF THIS PAPER. General principles of bonnet design are stated. Particular attention is given to the issue of stiffness, and new implications are drawn. FINDINGS. Regarding bonnet stiffness, there is an optimum: too stiff, and the bonnet is injurious; not stiff enough, and the pedestrian’s head may bottom out, i.e., strike the very stiff structures in the engine compartment. In addition, the optimum bonnet stiffness will be different for different speeds of impact. CONCLUSIONS. There is a need for results covering the range of speeds at which serious pedestrian injuries occur. Theory does permit scaling of HIC (Head Injury Criterion) to different speeds, however, so not all speeds will need to be tested. Similar considerations apply to headform mass.T. P. Hutchinson, D. J. Searson, R. W. G. Anderson, J. K. Dutschke, G. Ponte and A. L. van den Ber
