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''See also: Locomotive (Software).''
A 'locomotive' is a railway 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").
A locomotive has no payload capacity of its own, and its sole purpose is to move the train along the tracks. In contrast, some trains have self-propelled payload-carrying vehicles. These are not normally considered locomotives, and may be referred to as multiple units or railcars. The use of these self-propelled vehicles is increasingly common for passenger trains, but very 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 in local passenger service is push-pull operation, where a locomotive pulls the train in one direction and pushes it in the other, and is optionally controlled from a control cab at the opposite end of the train.
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Contents

Origins

Locomotives vs. multiple units

Advantages of locomotives

Advantages of multiple units

Classification by motive power

Steam

Diesel locomotives

Gas turbine-electric

Electric

Magnetic levitation

Hybrid

Experimental

Classification by use

See also

External links

References

Origins

The first successful locomotives were built by Cornish inventor Richard Trevithick. In 1804 his unnamed steam locomotive hauled a train along the tramway of the Penydarren ironworks, near Merthyr Tydfil in Wales. Although the locomotive hauled a train of 10 tons of iron and 70 passengers in five wagons over nine miles (14 km), it was too heavy for the cast iron rails used at the time. The locomotive only ran three trips before it was abandoned. Trevithick built a series of locomotives after the Penydarren experiment, including one which ran at a colliery in Tyneside where it was seen by the young George Stephenson.^[1]

The first commercially successful steam locomotive was Matthew Murray's rack locomotive, ''The Salamanca'', built for the narrow gauge Middleton Railway in 1812. This was followed in 1813 by the ''Puffing Billy'' built by Christopher Blackett and William Hedley for the Wylam Colliery Railway, the first successful locomotive running by adhesion only. Puffing Billy is now on display in the Science Museum in London, the oldest locomotive in existence.^[2]
In 1814 George Stephenson, inspired by the early locomotives of Trevithick and Hedley persuaded the manager of the Killingworth colliery where he worked to allow him to build a steam-powered machine. He built the ''Blücher'', one of the first successful flanged-wheel adhesion locomotives. Stephenson played a pivotal role in the development and widespread adoption of steam locomotives. His designs improved on the work of the pioneers. In 1825 he built the ''Locomotion'' for the Stockton and Darlington Railway which became the first public steam railway. In 1829 he built ''The Rocket'' which was entered in and won the Rainhill Trials. This success lead to Stephenson establishing his company as the pre-eminent builder of steam locomotives used on railways in the United Kingdom, the United States and much of Europe.^[2]
''See also'': History of rail transport,

Locomotives vs. multiple units

Advantages of locomotives

There are many reasons why the motive power for trains has been traditionally isolated in a locomotive, rather than in self-propelled vehicles.^[4] These include:

★ 'Ease': should the locomotive fail, it is easy to replace it with another. Failure of the motive power unit does not require taking the entire train out of service.

★ 'Maximum utilization of power cars': idle trains waste costly motive power resources. Separate locomotives enable costly motive power assets to be moved around as needed.

★ 'Flexibility': large locomotives can be substituted for small locomotives where the grades are steeper and more power is needed.

★ 'Obsolescence cycles': separating the motive power from payload-hauling cars enables one to be replaced without affecting the other. At times locomotives have become obsolete when their cars were not, and vice versa.

Advantages of multiple units

There are several advantages of multiple unit (MU) trains compared to locomotives.

★ 'Energy efficiency': Multiple units are more energy efficient than locomotive-hauled trains and more nimble, especially on grades, as much more of the train's weight (sometimes all of it) is placed on driven wheels, rather than suffer the dead weight of unpowered coaches.

★ 'No need to turn locomotive': Many multiple units have cabs at both ends or are arranged so that a set of cars has cabs at both ends, so that the train may be reversed without uncoupling/re-coupling the locomotive, giving quicker turnaround times, reducing crew costs, and enhancing safety.

★ 'Reliability': As multiple unit trains have multiple engines, the failure of one engine does not prevent the train from continuing its journey. A locomotive drawn passenger train typically only has one power unit, meaning the failure of this causes the train to be disabled. However, some locomotive hauled passenger trains may utilize more than one locomotive, as do most locomotive hauled freight trains, and are able to continue at reduced speed after the failure of one locomotive.

★ 'Safety': Multiple units normally have completely independent braking systems on all cars, meaning the failure of the brakes on one car does not prevent the brakes throughout the train from operating safely.

Classification by motive power

Locomotives may generate their power from fuel (wood, coal, petroleum or natural gas), or they may take power from an outside source of electricity. It is common to classify locomotives by their source of energy. The common ones include:

Steam

Main articles: steam locomotive




In the 19th century the first railway locomotives were powered by steam, usually generated by burning coal. Because steam locomotives included one or more steam engine, they are sometimes referred to as "steam engines". The steam locomotive remained by far the most common type of locomotive until after World War II.^[2]
The first steam locomotive was built by Richard Trevithick; it first ran on 21 February 1804, although it was some years before steam locomotive design became economically practical.¹. The first commercial use of a steam locomotive was The Salamanca on the narrow gauge Middleton Railway in Leeds in 1812. The locomotive ''Fairy Queen'', built in 1855 runs between New Delhi and Alwar in India and is the oldest steam locomotive in regular (albeit tourist-only) service in the world, and the oldest steam locomotive operating on a mainline. ^[6].^[7]
The all-time speed record for steam trains is held by an LNER Class A4 4-6-2 Pacific locomotive of the LNER in the United Kingdom, number 4468 ''Mallard'', which pulling six carriages (plus a dynamometer car) reached 126 mph (203 km/h) on a slight downhill gradient down Stoke Bank on 3 July 1938^[8]. Aerodynamic passenger locomotives in Germany attained speeds very close to this ^[9], and this is generally believed to be close to the practicable limit for a direct-coupled steam locomotive.
Before the middle of the 20th century, electric and diesel-electric locomotives began replacing steam locomotives. Steam locomotives are less efficient than their more modern diesel and electric counterparts and require much greater manpower to operate and service.^[10] British Rail figures showed the cost of crewing and fuelling a steam locomotive was some two and a half times that of diesel power, and the daily mileage achievable was far lower. As labour costs rose, particularly after the second world war, non-steam technologies became much more cost-efficient. By the end of the 1960s-1970s, most western countries had completely replaced steam locomotives in passenger service. Freight locomotives generally were replaced later. Other designs, such as locomotives powered by gas turbines, have been experimented with, but have seen little use.
By the end of the 20th century, almost the only steam power still in regular use in North America and Western European countries was on heritage railways specifically aimed at tourists and/or railroad enthusiasts, known as railfans or train spotters, although some narrow gauge lines in Germany which form part of the public transport system, running to all-year-round timetables retain steam for all or part of their motive power. Steam locomotives remained in commercial use in parts of Mexico into the late 1970s. Steam locomotives were in regular use until 2004 in the People's Republic of China, where coal is a much more abundant resource than petroleum for diesel fuel. India switched over from steam-powered trains to electric and diesel-powered trains in the 1980s, except heritage trains. In some mountainous and high altitude rail lines, steam engines remain in use because they are less affected by reduced air pressure than diesel engines.
As of 2006 DLM AG (Switzerland) continues to manufacture new steam locomotives.^[11]

Diesel locomotives

Main articles: Diesel locomotive


Starting in the 1940s, the diesel-powered locomotive began to displace steam power on North American railroads. Following the end of World War II, diesel power began to appear on railroads in many countries, By the 1960s, few major railroads continued to operate steam locomotive . ''(See Dieselization)''
As is the case with any vehicle powered by an internal combustion engine, diesel locomotives require some type of power transmission system to couple the output of the prime mover to the driving wheels. In the early days of diesel railroad propulsion development, electric, hydraulic and mechanical power transmission systems were all employed with varying degrees of success. Of the three, electric transmission proved to be most practical, and, except for some diesel-hydraulic locomotives manufactured for lower power applications, nearly all modern Diesel-powered locomotives are diesel-electric.
Diesel locomotives require considerably less maintenance than steam, with a corresponding reduction in the number of personnel needed to keep the fleet in service. The best steam locomotives spent an average of three to five days per month in the shop for routine maintenance and running repairs . Heavy overhauls were frequent, often involving removal of the boiler from the frame for major repairs. In contrast, a typical diesel locomotive requires no more than eight to ten hours of maintenance per month and may run for many years between heavy overhauls .
Diesel units are not as polluting as steam power; modern units produce low levels of exhaust emissions. Diesel-electric locomotives are often fitted with "dynamic brakes" that use the traction motors as generators during braking to assist in controlling the speed of a train on a descending grade.

Gas turbine-electric

Main articles: Gas turbine-electric locomotive