sentences:  Typical ballast tractor configurations employ an independent drawbar trailer, modular wheel-trailer units, or dolly trailer.An advantage of using ballast tractors is the ability to push-steer a trailer around a corner.A girder trailer, for example, is double-articulated so the front tractor can pull the load around a corner while the rear tractor pushes it through, thereby making the load more manoeuvrable than a simple towing configuration.