The presented research is focused on the analysis of running properties of a rail motor unit using a multibody simulation program in order to evaluate forces in a wheel/rail contact and a derailment quotient. The main part of the research represents simulations of a rail motor unit running on a real railway track in the Simpack multibody program. Attention is paid to the evaluation of the obtained results. The topic of the research, i.e. performing dynamic analysis and evaluation of forces using simulation software, is closely related to the broader context of railway vehicles and wheel-rail interaction. The study aims to use a computational tool to simulate the operation of a railway vehicle. It includes creating a rail vehicle model (a rail motor unit), setting its parameters, and implementing simulations to analyse the dynamic behaviour of the rail vehicle running on a real railway track section.