The increase in the carrying capacity and cargo capacity of the road train is achieved mainly by lengthening the base of the semi-trailer. At the same time, with the lengthening of the base of the semi-trailer, the overall length of the road train increases and, as a result, its maneuvering performance decreases. For road trains, the location of the coupling device on the tractor frame is selected as constant and maximum, ensuring unhindered folding of the links of the transport train at any turning radii that take place in operational conditions. At the same time, the maximum removal of the coupling device from the cab and other overall parts of the tractor is necessary only at large folding angles at small turning radii of the road train. The considerable space between the semi-trailer and the tractor cab negatively affects the operational characteristics of the road train - maneuvering, dynamic, economic. Various types of mechanical, hydraulic, pneumatic and other devices are recommended to regulate the displacement of the trailer hitch and maintain its optimal value. The article proposes a method for determining the minimum required displacement of the coupling device and the semi-trailer leaning on it from the tractor cab during unsteady movement on a turn for a road train with a semi-trailer. The analysis of the interdependencies of the folding angles of the road train, the angle of rotation of the controlled wheels during the rotation of the road train by 90 ° with a stationary fixed location of the hitch on the frame of the tractor and with a movable hitch that provides the optimal distance between the tractor and the semi-trailer during rotation.