A gravity railroad or gravity railway is a railroad on a slope that allows cars carrying minerals or passengers to coast down the slope by the force of gravity alone. The speed of the cars is controlled by a braking mechanism on one or more cars on the train. The cars are then hauled back up the slope using animal power, a locomotive or a stationary engine and a cable, a chain or one or more wide, flat iron bands. A much later example in California used 4 ft 8+1⁄2 in standard gauge steam engines to pull gravity cars back to the summit of Mt. Tamalpais.

A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the use of these self-propelled vehicles is increasingly common for passenger trains, but rare for freight trains.