The analysis of work of different subsystems of automatic control of speed of rolling wagons is conducted in automated control system by marshaling yards. New scientific approach is formed about determination of potential of speed of wind at flowing around of carriages for the increase of exactness calculation of speed exit wagons from park brake position. Calculates the rate of exit from the park brake position suggested taking into account the revised rates of meteorological conditions. The mathematical model allows us to calculate the value of the potential speed at any point of the park based on the variable value of the wind speed at height, difficult terrain hump, wagons influence are on the ways of sorting the park, the deformation field of wind speed in the flow of terrain sorting park, deformation field wind speed flow of cars on the tracks screening park. Worked out method maybe in future to use for calculation of speed of exit of wagons in from park brake position.