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A locomotive is a rail transport that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, push–pull operation has become common, and in the pursuit for longer and heavier freight trains, companies are increasingly using distributed power: single or multiple locomotives placed at the front and rear and at intermediate points throughout the train under the control of the leading locomotive.
The first full-scale working railway steam locomotive was built by Richard Trevithick in 1802. It was constructed for the Coalbrookdale ironworks in Shropshire in England though no record of it working there has survived. On 21 February 1804, the first recorded steam-hauled railway journey took place as another of Trevithick's locomotives hauled a train from the Penydarren ironworks, in Merthyr Tydfil, to Abercynon in South Wales. Accompanied by Andrew Vivian, it ran with mixed success. The design incorporated a number of important innovations including the use of high-pressure steam which reduced the weight of the engine and increased its efficiency.
In 1812, Matthew Murray's twin-cylinder rack locomotive Salamanca first ran on the Wagonway rack-and-pinion Middleton Railway; this is generally regarded as the first commercially successful locomotive. Another well-known early locomotive was Puffing Billy, built 1813–14 by engineer William Hedley for the Wylam Colliery near Newcastle upon Tyne. This locomotive is the oldest preserved, and is on static display in the Science Museum, London. George Stephenson built Locomotion No. 1 for the Stockton & Darlington Railway in the north-east of England, which was the first public steam railway in the world. In 1829, his son Robert built The Rocket in Newcastle upon Tyne. Rocket was entered into, and won, the Rainhill Trials. This success led to the company emerging as the pre-eminent early builder of steam locomotives used on railways in the UK, US and much of Europe. The Liverpool & Manchester Railway, built by Stephenson, opened a year later making exclusive use of steam power for passenger and goods trains.
The steam locomotive remained by far the most common type of locomotive until after World War II.Ellis, p. 355 Steam locomotives are less efficient than modern diesel and electric locomotives, and a significantly larger workforce is required to operate and service them. British Rail figures showed that the cost of crewing and fuelling a steam locomotive was about two and a half times larger than the cost of supporting an equivalent diesel locomotive, and the daily mileage they could run was lower. Between about 1950 and 1970, the majority of steam locomotives were retired from commercial service and replaced with electric and diesel–electric locomotives. While North America transitioned from steam during the 1950s, and continental Europe by the 1970s, in other parts of the world, the transition happened later. Steam was a familiar technology that used widely-available fuels and in low-wage economies did not suffer as wide a cost disparity. It continued to be used in many countries until the end of the 20th century. By the end of the 20th century, almost the only steam power remaining in regular use around the world was on .
The first internal combustion rail vehicle was a kerosene-powered draisine built by Gottlieb Daimler in 1887, but this was not technically a locomotive as it carried a payload.
The earliest gasoline locomotive in the western United States was built by the Best Manufacturing Company in 1891 for San Jose and Alum Rock Railroad. It was only a limited success and was returned to Best in 1892.
The first commercially successful petrol locomotive in the United Kingdom was a petrol–mechanical locomotive built by the Maudslay Motor Company in 1902, for the Deptford Cattle Market in London. It was an 80 hp locomotive using a three-cylinder vertical petrol engine, with a two speed mechanical gearbox.
In 1903, the Hungarian Weitzer railmotor was the world's first petrol-electric locomotive.
Various collection methods exist: a trolley pole, which is a long flexible pole that engages the line with a wheel or shoe; a bow collector, which is a frame that holds a long collecting rod against the wire; a pantograph, which is a hinged frame that holds the collecting shoes against the wire in a fixed geometry; or a contact shoe, which is a shoe in contact with the third rail. Of the three, the pantograph method is best suited for high-speed operation.
Electric locomotives almost universally use axle-hung traction motors, with one motor for each powered axle. In this arrangement, one side of the motor housing is supported by plain bearings riding on a ground and polished journal that is integral to the axle. The other side of the housing has a tongue-shaped protuberance that engages a matching slot in the truck (bogie) bolster, its purpose being to act as a torque reaction device, as well as a support. Power transfer from motor to axle is effected by spur gearing, in which a pinion on the motor shaft engages a bull gear on the axle. Both gears are enclosed in a liquid-tight housing containing lubricating oil. The type of service in which the locomotive is used dictates the gear ratio employed. Numerically high ratios are commonly found on freight units, whereas numerically low ratios are typical of passenger engines.
Electricity is typically generated in large and relatively efficient Power station, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches and .
Electric locomotives usually cost 20% less than diesel locomotives, their maintenance costs are 25–35% lower, and cost up to 50% less to run.
The first electrically worked Rapid transit line was the City & South London Railway, prompted by a clause in its enabling act prohibiting use of steam power. It opened in 1890, using electric locomotives built by Mather & Platt. Electricity quickly became the power supply of choice for subways, abetted by the Sprague's invention of multiple-unit train control in 1897.
The first use of electrification on a main line was on a four-mile stretch of the Baltimore Belt Line of the Baltimore & Ohio (B&O) in 1895 connecting the main portion of the B&O to the new line to New York through a series of tunnels around the edges of Baltimore's downtown. Three Bo+Bo units were initially used, at the south end of the electrified section; they coupled onto the locomotive and train and pulled it through the tunnels. B&O Power, Sagle, Lawrence, Alvin Stauffer
DC was used on earlier systems. These systems were gradually replaced by AC. Today, almost all main-line railways use AC systems. DC systems are confined mostly to urban transit such as metro systems, light rail and trams, where power requirement is less.
In 1894, Hungarian engineer Kálmán Kandó developed a new type 3-phase asynchronous electric drive motors and generators for electric locomotives. The new 3-phase asynchronous electric drive motors were more effective than the synchronous electric motors of earlier locomotive designs. Kandó's early 1894 designs were first applied in a short three-phase AC tramway in Evian-les-Bains (France), which was constructed between 1896 and 1898. In 1918, Kandó invented and developed the rotary phase converter, enabling electric locomotives to use three-phase motors whilst supplied via a single overhead wire, carrying the simple industrial frequency (50 Hz) single phase AC of the high voltage national networks.
In 1896, Oerlikon installed the first commercial example of the system on the Lugano Tramway. Each 30-tonne locomotive had two motors run by three-phase 750 V 40 Hz fed from double overhead lines. Three-phase motors run at constant speed and provide regenerative braking, and are well suited to steeply graded routes, and the first main-line three-phase locomotives were supplied by Brown (by then in partnership with Walter Boveri) in 1899 on the 40 km Burgdorf—Thun line, Switzerland. The first implementation of industrial frequency single-phase AC supply for locomotives came from Oerlikon in 1901, using the designs of Hans Behn-Eschenburg and Emil Huber-Stockar; installation on the Seebach-Wettingen line of the Swiss Federal Railways was completed in 1904. The 15 kV, 50 Hz , 48 tonne locomotives used transformers and rotary converters to power DC traction motors.
Italian railways were the first in the world to introduce electric traction for the entire length of a main line rather than just a short stretch. The 106 km Valtellina line was opened on 4 September 1902, designed by Kandó and a team from the Ganz works. The electrical system was three-phase at 3 kV 15 Hz. The voltage was significantly higher than used earlier and it required new designs for electric motors and switching devices. The three-phase two-wire system was used on several railways in Northern Italy and became known as "the Italian system". Kandó was invited in 1905 to undertake the management of Società Italiana Westinghouse and led the development of several Italian electric locomotives.
Such locomotives are used where a conventional diesel or electric locomotive would be unsuitable. An example is maintenance trains on electrified lines when the electricity supply is turned off. Another use is in industrial facilities where a combustion-powered locomotive (i.e., Steam locomotive or diesel-powered) could cause a safety issue due to the risks of fire, explosion or fumes in a confined space. Battery locomotives are preferred for mines where gas could be ignited by Trolley pole units Electric arc at the collection shoes, or where electrical resistance could develop in the supply or return circuits, especially at rail joints, and allow dangerous current leakage into the ground. Battery locomotives in over-the-road service can recharge while absorbing dynamic-braking energy.
The first known electric locomotive was built in 1837 by chemist Robert Davidson of Aberdeen, and it was powered by (batteries). Davidson later built a larger locomotive named Galvani, exhibited at the Royal Scottish Society of Arts Exhibition in 1841. The seven-ton vehicle had two direct-drive , with fixed electromagnets acting on iron bars attached to a wooden cylinder on each axle, and simple commutators. It hauled a load of six tons at four miles per hour (6 kilometers per hour) for a distance of . It was tested on the Edinburgh and Glasgow Railway in September of the following year, but the limited power from batteries prevented its general use.Renzo Pocaterra, Treni, De Agostini, 2003
Another example was at the Kennecott Copper Mine, Latouche, Alaska, where in 1917 the underground haulage ways were widened to enable working by two battery locomotives of tons. In 1928, Kennecott Copper ordered four 700-series electric locomotives with on-board batteries. These locomotives weighed 85 tons and operated on 750-volt overhead trolley wire with considerable further range whilst running on batteries. The locomotives provided several decades of service using Nickel–iron battery (Edison) technology. The batteries were replaced with lead-acid batteries, and the locomotives were retired shortly afterward. All four locomotives were donated to museums, but one was scrapped. The others can be seen at the Boone and Scenic Valley Railroad, Iowa, and at the Western Railway Museum in Rio Vista, California. The Toronto Transit Commission previously operated a battery electric locomotive built by Nippon Sharyo in 1968 and retired in 2009.
London Underground regularly operates battery–electric locomotives for general maintenance work.
Freight locomotives are normally designed to deliver high starting tractive effort and high sustained power. This allows them to start and move long, heavy trains, but usually comes at the cost of relatively low maximum speeds. Passenger locomotives usually develop lower starting tractive effort but are able to operate at the high speeds required to maintain passenger schedules. Mixed-traffic locomotives (US English: general purpose or road switcher locomotives) meant for both passenger and freight trains do not develop as much starting tractive effort as a freight locomotive but are able to haul heavier trains than a passenger locomotive.
Most steam locomotives have reciprocating engines, with pistons coupled to the driving wheels by means of connecting rods, with no intervening gearbox. This means the combination of starting tractive effort and maximum speed is greatly influenced by the diameter of the driving wheels. Steam locomotives intended for freight service generally have smaller diameter driving wheels than passenger locomotives.
In diesel-electric and electric locomotives the control system between the and adapts the power output to the rails for freight or passenger service. Passenger locomotives may include other features, such as head-end power (also referred to as hotel power or electric train supply) or a steam generator.
Some locomotives are designed specifically to work steep grade railways, and feature extensive additional braking mechanisms and sometimes rack and pinion. Steam locomotives built for steep Rack railway frequently have the boiler tilted relative to the locomotive frame, so that the boiler remains roughly level on steep grades.
Locomotives are also used on some high-speed trains. Some of them are operated in push-pull train with trailer at another end of a train, which often have a cabin with the same design as a cabin of locomotive; examples of such trains with conventional locomotives are Railjet and Intercity 225.
Also many high-speed trains, including all TGV, many Talgo (250 / 350 / Avril / XXI), some Korea Train Express, ICE 1/ICE 2 and Intercity 125, use dedicated , which do not have places for passengers and technically are special single-ended locomotives. The difference from conventional locomotives is that these power cars are integral part of a train and are not adapted for operation with any other types of passenger coaches. On the other hand, many high-speed trains such as the Shinkansen network never use locomotives. Instead of locomotive-like power-cars, they use electric multiple units (EMUs) or diesel multiple units (DMUs) – passenger cars that also have traction motors and power equipment. Using dedicated locomotive-like power cars allows for a high ride quality and less electrical equipment; but EMUs have less axle weight, which reduces maintenance costs, and EMUs also have higher acceleration and higher seating capacity. Also some trains, including TGV PSE, TGV TMST and TGV V150, use both non-passenger power cars and additional passenger motor cars.
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