Abstract: A spring biased over-center linkage transmits a biasing force to opposite guide wheels in alternate sequence for maintaining a selected one of the guide wheels in contact with one of two parallel guide surfaces, depending upon whether the vehicle is operative in a left or a right follower mode. A steering assembly controls the direction of travel of the vehicle in response to the position of the selected one guide wheel as it follows the contour of the cooperative guide surface. A double-acting reciprocative operator positions the over-center linkage at left and right bias positions for left and right follower mode operation, respectively. A spring provides over-center bias to the over-center linkage and constitutes the sole source of biasing force. The apparatus is suitable for use with a vehicle in an automated transportation system in which the vehicle travels along a predetermined travel path or a guideway.