Abstract: A conveyor system comprising a conveyor track, a conveyor movable along said track, a free track and a plurality of carriers movable along the free track. The conveyor has longitudinally spaced pusher and holdback dogs mounted thereon. Each carrier comprises spaced trolleys and a tie bar interconnecting the trolleys. A trailing trolley has a pusher movably mounted thereon for movement into and out of the path of the pusher and holdback dogs. A bumper is mounted on the carrier at the front end thereof so that it engages a preceding carrier or an obstacle. The bumper and the retractable pusher are interconnected such that upon engagement of the bumper with the preceding carrier or obstacle the pusher is retracted out of the path of the pusher dog.