In dynamic conditions, the functional properties of internal combustion (IC) engines in steady thermal state depend on time histories of the quantities that characterize the intensity of engine operation. For the automotive engine, the most important process that determines the engine operation is the vehicle speed process. To evaluate the impact of the conditions of operation of motor vehicles on the properties of their IC engines, the investigation of passenger car speed processes in the conditions of typical vehicle use was taken up. The recorded speed vs. time curves were treated as realizations of stochastic processes and basic characteristics of the processes were determined. The vehicle motion was modelled as motion in the street congestion, urban, extra-urban, and high-speed traffic conditions. Based on empirical tests and analyses carried out, sets of passenger car speed vs. time curves have been proposed as realizations of model processes representing the vehicle motion in the conditions under consideration.