In many cases we have to estimate the speed of the vehicles involved in an accident. The aim of this paper is to make a brief presentation of some cases solved on the question of speed and dynamics using different methods and presenting the estimated error obtained. So in the paper it will be taken into account the indication of tachograph diagram with pros and cons, assuming that this indication is only informative as far as the tachograf is not specially designed as an accident recording device. In the paper it will be included the reconstruction of the accident using PC Crash features in optimization method to reduce the error regarding the trajectory and rest position. For validation of this analysis we will provide also a video record from a high resolution surveillance camera versus the simulation of the accident.