Earlier work on the application of optimization techniques for the crashworthiness design problem using a spring-mass simulation model was limited to selection of the stiffness of spring components to satisfy safety criteria. A drawback of this work was that the component dimensions could not be directly manipulated during optimization. Therefore, a new optimization capability, which determines the dimensions of the structural components, is developed to minimize the structural mass while meeting given safety criteria. Unlike the earlier work the present study uses both the nonlinear spring-mass model and beam models in a hybrid manner such that the optimizer interfaces with the spring-mass model, which in turn interfaces with the beam models to obtain force-deformation curves required as input. The number of computer runs for the computationally expensive beam models is significantly reduced by using an approximation concept. The feasibility of this approach is demonstrated through a practical example.