High-speed train in Shanghai, ChinaThere are three types of modern locomotive—electric, diesel-electric and diesel. High-speed trains, such as the French Train à Grande Vitesse (TGV) or the China Railways High-Speed "Harmony", are normally electrically powered with a power car at each end and specially designed carriages. Diesel locomotives are normally used only for shunting and on low-speed local trains.
How trains work
On an electric locomotive, the wheels are moved by electric motors. The electricity comes either from overhead cables or from an electrified third rail. On a diesel-electric locomotive, the wheels are also driven by electric motors, but the electricity is generated by a diesel engine. On a diesel locomotive, a diesel engine drives the wheels via a mechanical transmission.Cutaway illustration of an electric power carHigh-speed trains are powered by electric current, collected from an overhead cable by a pantograph. A transformer converts the very high-voltage electricity in the overhead cable to the lower voltage needed by the motors in the power car. Electronic circuits in the locomotive control how the electricity flows to the motors, and thus the speed of the train. An auxiliary power unit supplies power for utilities such as lighting and air conditioning.
High-speed trains travel much faster than most other trains—usually more than 200 km/h (125 mph). The first high-speed train, the Japanese Shinkansen (“bullet train”), started services in 1964. Others include the French Train à Grande Vitesse (TGV) and German InterCity Express (ICE). Many high-speed expresses run on purpose-built tracks, including the Shinkansen trains.
Where purpose-built straight tracks are not possible, speeds can be increased by using tilting trains. These tilt inwards as they go round curves at high speed in the same way as motorcyclists do on the road.
Train à Grande Vitesse
The French high-speed train, the Train à Grande Vitesse, or TGV, holds the world speed record for a train travelling on rails. During a test run without passengers between Paris and Strasbourg in 2007, the TGV reached a speed of 574.8 km/h (360 mph). The TGV regularly runs at speeds of 300 km/h (188 mph). The 425-kilometre (265-mile) journey from Paris to Lyon takes less than 2 hours.A TGV, showing its interior features The TGV's high speed is made possible by its streamlined design, its high-powered electric motors and its relatively low weight. Its motors are powered by electric current via a long arm called a pantograph that connects to an overhead cable. The two power cars, one at either end of the train, together with its eight passenger cars, are all carefully streamlined, so the train uses up no more energy than an ordinary train.
A TGV driver's cabThe TGV has trucks of four wheels, called bogies, set between the carriages. This design allows the train to bend slightly as it goes around corners at high speed. Also, fewer wheels are needed, so reducing friction.
Computers effectively drive the TGV. The driver checks the train’s progress on a computer screen and gives instructions by using a keyboard. A radio links on-board computers with the signalling centre and other trains on the track. This means the driver does not even have to slow down to check and react to lineside signals. Computers also operate the brakes, air-conditioning and other equipment.
The high-speed TGV can travel up slopes four times as steep as most other trains. So the new tracks built for it could be much straighter, saving much of the cost of constructing a level track across hilly country. Having tracks without sharp curves also avoids the need to slow down for corners.A TGV's gradient, compared to other trains
A Trans-Siberian express train
The longest scheduled train service is the Trans-Siberian Express, which runs on the Trans-Siberian Railway, from Moscow to Vladivostok, a port city on the Sea of Japan, a distance of 9297 kilometres (5810 miles). The complete journey takes almost eight days. Hauled by steam locomotives, the first train ran on the route in 1914. The line was electrified in the 1960s.
Electric trains are useful in places where smoke or fumes cannot easily escape into the air. Many large cities have electric trains which run under the ground, linking different parts of the city. They are known as rapid transit, underground, subway, metro or metropolitan railways. They have good acceleration in order to move quickly between closely spaced stations. The first underground trains ran in London in 1863. Originally steam-powered, they are now electric.
Many towns and cities have trams (known as streetcars in the USA): rail vehicles that run on tracks along the city streets. They are usually powered by electricity, supplied from an overhead pantograph or sometimes an electrified third rail. The St Charles Line, which runs through the US city of New Orleans, is the oldest continuously operating tram line in the world. Steam services began in 1835, and the line was electrified in 1893.
Consultant: Chris Oxlade
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