A method and a system for controlling a displacement device for a fifth wheel coupling disposed on a tractor vehicle are described, wherewith the displacement device has a lower structure having at least one guide rail oriented in the direction of travel, a movable carriage which supports the fifth wheel coupling and engages the guide rail(s), and a control device connected to a motorized drive unit for displacing the carriage and also connected to an adjusting member for fixing the carriage with respect to the guide rail(s); wherewith a measurement is made for determining the angle between the tractor and semi-trailer, the measurement signal is converted in the control device to a control signal, and thereby an operation of the motorized drive unit and/or the adjusting member is initiated. The underlying problem of the invention was to devise a method and a control system which minimize the risk of the semi-trailer striking against the cab of the tractor. One way in which this problem is solved according to the invention is that, from the measurement signal, an angular or distance timewise rate of change is generated in the control device, or such a timewise rate of change is transmitted to the control device.