This research uses aluminum foam and numerical optimization method to improve vehicle energy absorption. The front part of the rail where axial compression is dominant and three parts where global bending collapse is dominant, were reinforced by filling empty sections with aluminum foam. The existing sheet metal reinforcing elements were removed. The nonlinear explicit finite element code PAM-CRASH was used to carry out the crash simulations. Two single-objective optimization problems were performed for the aluminum foam-filled front side rail of a passenger car under impact condition to maximize the specific energy absorption, i.e., to maximize the internal energy and minimize the component weight simultaneously. The crash optimization problems were solved by using a sequential quadratic programming method, where the required functions are approximated by using design of experiments (DOE) and response surface method (RSM). In addition, the trigger on the front part of the rail was redesigned so that the peak wall force response was reduced dramatically while maintaining the required resistance in low speed crash. The results show that about 40% increase in energy absorbed and 30% increase in specific energy absorption were obtained. This research demonstrates a new way of achieving large increase in the energy absorption while maintaining high weight efficiency in crashworthiness analysis using lightweight metallic core such as aluminum foam or honeycomb.