Three body styles of diesel locomotive: cab unit, hood unit and box cab. These locomotives are operated by Pacific National in Australia.
R class steam locomotive number R707 as operated by the Victorian Railways of Australia.
A Green Cargo RC 4 class electric locomotive repainted in its original livery for the Swedish 150-year railway anniversary in 2006.

A locomotive or engine is a rail transport vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine,[1] first used in the early 19th century to distinguish between mobile and stationary steam engines.

A locomotive has no payload capacity of its own, and its sole purpose is to move the train along the tracks.[2] In contrast, some trains have self-propelled payload-carrying vehicles. These are not normally considered locomotives, and may be referred to as multiple units, motor coaches or railcars. The use of these self-propelled vehicles is increasingly common for passenger trains, but rare for freight (see CargoSprinter). Vehicles which provide motive power to haul an unpowered train, but are not generally considered locomotives because they have payload space or are rarely detached from their trains, are known as power cars.

Traditionally, locomotives pull trains from the front. Increasingly common outside North America is push-pull operation, where one locomotive pulls the train from the front and another locomotive pushes it from behind. In this arrangement the locomotive at the rear of the train is controlled from a control cab at the front of the train. Push-pull operation is generally infeasible in North America as, even if mid-train or tail-end "helpers" are provided, the front-end might have over {{convert|26,0* ; 1943: A synopsis of the Limulodidae (Coleoptera): a new family proposed for myrmecophiles of the subfamilies Limulodinae (Ptiliidae) and Cephaloplectinae (Staphylinidae). Annals of the Entomological Society of America, 36(3): 546-586. abstract full article at CHLA  

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