Abstract: An overhead power and free conveyor system in which a carrier is propelled along a portion of the carrier track of the system in the conventional manner by a pusher on a driven chain engaging a driving dog on the carrier. The carrier is propelled along another portion of the carrier track of this system by a self-propelled tractor, with provision for transferring a carrier from one of these forms of propulsion to another. Preferably, the tractor travels on the carrier track when propelling a carrier or a train of carriers, which may be directly coupled to the tractor. Alternately, the tractor travels on the carrier track and pulls a tow bar, supported by a separate track, and equipped with a pusher engageable with the carrier driving dog.