A train is a form of rail transport consisting of a series of vehicles that usually runs along a rail track to transport cargo or passengers. Motive power is provided by a separate locomotive or individual motors in self-propelled multiple units. Although historically steam propulsion dominated, the most common modern forms are diesel and electric locomotives, the latter supplied by overhead wires or additional rails. Other energy sources include horses, engine or water-driven rope or wire winch, gravity, pneumatics, batteries, and gas turbines. Train tracks usually consist of two running rails, sometimes supplemented by additional rails such as electric conducting rails and rack rails, with a limited number of monorails and maglev guideways in the mix. The word 'train' comes from the Old French trahiner, from the Latin trahere 'pull, draw'.
There are various types of trains that are designed for particular purposes. A train may consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit (or occasionally a single or articulated powered coach, called a railcar). The first trains were rope-hauled, gravity powered or pulled by horses. From the early 19th century almost all were powered by steam locomotives. From the 1910s onwards the steam locomotives began to be replaced by less labor-intensive and cleaner (but more complex and expensive) diesel locomotives and electric locomotives, while at about the same time self-propelled multiple unit vehicles of either power system became much more common in passenger service.
A passenger train is one which includes passenger-carrying vehicles which can often be very long and fast. One notable and growing long-distance train category is high-speed rail. In order to achieve much faster operation over 500 km/h (310 mph), innovative Maglev technology has been researched for years. In most countries, such as the United Kingdom, the distinction between a tramway and a railway is precise and defined in law. The term light rail is sometimes used for a modern tram system, but it may also mean an intermediate form between a tram and a train, similar to a heavy rail rapid transit system except that it may have level crossings.
A freight train (also known as a goods train) uses freight cars (also known as wagons or trucks) to transport goods or materials (cargo). Freight and passengers may be carried in the same train in a mixed consist.
Rail cars and machinery used for maintenance and repair of tracks, etc., are termed maintenance of way equipment; these may be assembled into maintenance of way trains. Similarly, dedicated trains may be used to provide support services to stations along a train line, such as garbage or revenue collection.
Steam locomotive-hauled passenger train
British Rail Class 390 Electric multiple unit train
A Transperth B-series train
Passengers travelling on the roof of a train in South Sudan
There are various types of trains that are designed for particular purposes. A train can consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit (or occasionally a single or articulated powered coach, called a railcar). Trains can also be hauled by horses, pulled by a cable, or run downhill by gravity. Special kinds of trains running on corresponding special 'railways' are atmospheric railways, monorails, high-speed railways, maglev, rubber-tired underground, funicular and cog railways.
A passenger train may consist of one or several locomotives and coaches. Alternatively, a train may consist entirely of passenger carrying coaches, some or all of which are powered as a "multiple unit". In many parts of the world, particularly the Far East and Europe, high-speed rail is used extensively for passenger travel. Freight trains are composed of wagons or trucks rather than carriages, though some parcel and mail trains (especially Travelling Post Offices) are outwardly more like passenger trains.
Trains can also be 'mixed', comprising both passenger accommodation and freight vehicles. Such mixed trains are most likely to occur where services are infrequent, and running separate passenger and freight trains is not cost-effective, though the differing needs of passengers and freight usually means this is avoided where possible. Special trains are also used for track maintenance; in some places, this is called maintenance of way.
In the United Kingdom, a train hauled by two locomotives is said to be "double-headed", and in Canada and the United States it is quite common for a long freight train to be headed by three or more locomotives. A train with a locomotive attached at each end is described as 'top and tailed', this practice typically being used when there are no reversing facilities available. Where a second locomotive is attached temporarily to assist a train up steep banks or grades (or down them by providing braking power) it is referred to as