We shall discuss the problem of rail vehicle safety studies using simulation methods. The contemporary methods and criteria used for safety assessment of railway vehicles by railways Europe are shown, whereas special attention is paid to the criteria and research programs applied to the vehicle approval procedures in Poland. Taking advantage of these safety criteria and codes of practice, a number of computer simulations have been conducted in order to study the safety issues. Presented results of the computer simulations include a rail vehicle running on a tangent and curved track for different simulation parameters such as: running velocity, load level, condition of wheel profiles, track irregularities. The track irregularities represent different maintenance quality levels which are set according to UIC518 code. In this paper there has also been made a comparison between the results of computer simulation safety assessment studies and the measurements taken in real conditions during the safety tests of a Shimmns(s) type freight vehicle.