The possession of the results of a large number of truck crash tests around our practice makes the motor vehicle experts able to extend their expertise concerning deformation compatibility as well as crash analysis more reliably. The results of different types of crash tests (truck to car pile up, side collision, truck pile up on column of 3 cars) enabled the examination of the velocity-acceleration process, and deformation characteristics. During the crash test the debris spread and the beginnings of scratch marks, the brake marks and the geometrical location of the sliding marks in the post crash phase have been recorded. Analyzing the results of the crash tests, correlations were found between the position of the debris spread and scratch marks and the geometrical location of the real crash. Some of the crash tests have been reconstructed with the help of a modern finite elements method (FEM) computational program. With this program detailed information was obtained concerning the strains and the energy intake of the constituents of in the crash. On the basis of the evaluated test results and our experience in real crash accident reconstruction we have shown what the design limits are of the equipment for passive safety, rear underrun protection (RUP) corresponding to the valid regulations.