Abstract: The present invention comprises two control lines parallel to a rail for guiding self-propelling moving bodies. These lines are divided into sections in staggered relationship between which portions of conductor are placed. Sliding contacts, connected to the moving body, travel over the control lines to detect the state of voltage of one and to short circuit the other. A relay reverses the detection and the short circuit on passage of the sliding contacts on each of the portions of conductor. The invention is applicable to the field of handling.