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", and is a shortened form of the term locomotive engine,. 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. 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 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 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.
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.
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.
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 led 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.
There are many reasons why the motive power for trains has been traditionally isolated in a locomotive, rather than in self-propelled vehicles. 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.
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 engines, 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.
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.. 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 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.
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. Aerodynamic passenger locomotives in Germany attained speeds very close to this and due to the difficulties of adequately balancing and lubricating the running gear, this is generally thought 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. 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.
Starting in the 1940s, the diesel-powered locomotive began to displace steam power on 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 electrical generators during braking to assist in controlling the speed of a train on a descending grade.
In 1894, a Hungarian engineer Kálmán Kandó developed high-voltage three phase alternating current motors and generators for electric locomotives; he is known as the father of the electric train. His work on railway electrification was done at the Ganz electric works in Budapest. He was the first who recognised that an electric train system can only be successful if it can use the electricity from public networks. After realising that, he also provided the means to build such a rail network by inventing a rotary phase converter suitable for locomotive usage.
The electric locomotive is supplied externally with electric power, either through an overhead pickup or through a third rail. While the capital cost of electrifying track is high, electric trains and locomotives are capable of higher performance and in some cases lower operational costs than steam or diesel power. Electric locomotives, because they tend to be less technically complex than diesel-electric locomotives, are both easier and cheaper to maintain and have extremely long working lives -- there are many examples of electric locomotives operating for more than half a century with minimal overhaul, and it is not unusual for electric locomotives to be operating close to their centenary.
The world speed record for a wheeled train was set in February 2007 by a French TGV which reached a speed of 575 km/h (357 mph).
Some electric locomotives can also operate off battery power to enable short journeys or shunting on non-electrified lines or yards. Battery-powered locomotives are used in mines and other underground locations where diesel fumes or smoke would endanger crews, and where external electricity supplies cannot be used due to the danger of sparks igniting flammable gas. Battery locomotives are also used on many underground railways for maintenance operations, as they are required when operating in areas where the electricity supply has been temporarily disconnected. However, the cost and weight of batteries prohibit using battery-powered locomotives on extended runs.
A turbine offers some advantages over a piston engine. The number of moving parts is much smaller, and the power to weight ratio is much higher. A turbine of a given power output is also physically smaller than an equally powerful piston engine, allowing a locomotive to be very powerful without being inordinately large. However, a turbine's power output and efficiency both drop dramatically with rotational speed, unlike a piston engine, which has a comparatively flat power curve.
Gas turbine locomotives are very powerful, but also tend to be very loud. Union Pacific Railroad operated the largest fleet of gas turbine-electric locomotives in the world, and was the only railroad to use them for hauling freight in regular service. Most other GTELs have been built for small passenger trains, and only a few have seen any real success in that role.
After the 1973 oil crisis and the subsequent rise in fuel costs, gas turbine locomotives became uneconomical to operate, and many were taken out of service. This type of locomotive is now rare.
Magnetic levitation (maglev) trains are electrically powered, using an open motor which floats the train above the track without the use of wheels. This replaces rolling friction with electromagnetic drag. Very few systems are in service and the construction cost is relatively high. A major disadvantage of maglev trains is their incompatibility with existing rail infrastructure, requiring the construction of new, special-purpose tracks.
The first commercial maglev trains ran in the 1980s in Birmingham, United Kingdom, providing a low-speed shuttle service between the airport and the railway station. Despite the interest and excitement, the system was shut down due to a lack of spare parts and replaced by wheeled cablecars a few years later.
A hybrid locomotive is a Locomotive that uses an on-board rechargeable energy storage system (RESS) and a fuelled power source for propulsion.
Hybrid trains typically are powered either by Fuel Cell technology or the diesel-electric hybrid which reduces fuel consumption through regenerative braking and switching off the hydrocarbon engine when idling or stationary (as used in automobiles such as the Toyota Prius).
There are other forms of motive power in experimental use.
Parry People Movers make an experimental light rail railcar powered by energy stored in a flywheel. The flywheel is powered from an onboard battery-driven motor or internal combustion engine and is also recharged through regenerative braking. A proposed alternative is to recharge the flywheel from external electric motors installed at station stops. Although this would increase installation costs it would substantially reduce the weight of the vehicles. It would cost less than providing a continuous electrical supply.
Parry People Movers have been tested on several railways, including the Ffestiniog Railway, the Welsh Highland Railway and the Welshpool and Llanfair Light Railway. The first mainstream timetable service for the flywheel railcar was launched in February 2006 providing the Sunday service on the short link between Stourbridge junction and Stourbridge Town in the United Kingdom.
Most steam locomotives are reciprocating units, in which the pistons are coupled to the drivers (driving wheels) by means of connecting rods. Therefore, the combination of starting tractive effort and maximum speed is greatly influenced by the diameter of the drivers. Steam locomotives intended for freight service generally have relatively small diameter drivers, whereas passenger models have large diameter drivers (as large as 84 inches in some cases).
With diesel-electric and electric locomotives, the gear ratio between the traction motors and axles is what adapts the unit to freight or passenger service, although a passenger unit may include other features, such as head end power (aka hotel power) or a steam generator.
Some locomotives are designed specifically to work mountain railways, and feature extensive additional braking mechanisms and sometimes rack and pinion. Steam locomotives built for steep rack and pinion railways frequently have the boiler tilted relative to the wheels, so that the boiler remains roughly level on steep grades.