A self-propelled vehicle that pulls or pushes a train of unpowered vehicles along a rail track. It carries no passengers or cargo itself, but serves only to propel the train. The use of a locomotive avoids the difficulty of coordinating the movement of a train of self-powered carriages or wagons and the necessity of unloading, replacing, and reloading one carriage in a train should its engine fail. A locomotive also increases the flexibility of the rail system, in that additional locomotives can be added where needed, and the size and type of locomotive can be chosen to suit the load to be moved.