It is becoming more and more complex and time consuming to have a newly developed vehicle meet the safety requirement these days. On the other hand, with the aid of computers and software technology, detailed crash simulation are possible. ISUZU MOTORS LTD. has applied these to the passenger car from the early stages of development in order to optimize the car's behavior in the 35MPH frontal barrier test. Crash simulations were performed by using the detailed full vehicle FEM model and the crash simulation program PAM-CRASH. This simulation focussed on the collapsing mode of the front structure, especially on the front of the side rails and the attached parts. Section forces, accelerations, and deformed shapes were investigated and optimized to improve energy absorption. The effect was confirmed by the experimental barrier test. This procedure contributed greatly to reducing the time required for development as well as the number of prototype vehicles needed.