In this paper, the application of UHF RFID in automatic vehicles identification is studied by the means of a new simulation framework. The system under study consists of the stationary readers with antennas mounted over the road lanes and vehicles license plates equipped with passive EPC Class 1 Generation 2 UHF RFID tags. The simulation includes protocol settings, antennas parameters, and propagation media conditions. Propagation analysis considers Doppler shift to compute the path loss of moving tags properly. The estimations of an inventory round duration, the number of rounds the tag participates in and the tag identification probability are provided. The paper presents vehicles identification probabilities computed for different protocol settings and movement speeds. In particular, it was shown that a vehicle could be identified with 0.9 probability by EPC values only when the vehicle speed is 120 km/h or even more. If the vehicle is identified with both EPC and TID banks values, the same 0.9 probability is achievable when the vehicle speed is under 90 km/h. The results of the simulation coincide with the experiment results involving the city buses.