There are three types of modern locomotive - electric, diesel-electric and diesel. On an electric locomotive, the wheels are moved by electric motors (normally one for each pair of wheels). The electricity usually comes from overhead cables, but sometimes from an electrified third rail. On a diesel-electric locomotive, the wheels are also driven by electric motors, but the electricity comes from a generator driven by a powerful diesel engine. On a diesel locomotive, a diesel engine drives the wheels via a mechanical transmission. Diesel locomotives are normally used only for shunting and on low-speed local trains. The fastest express trains, such as the French Train a Grande Vitesse (TGV), are normally electrically powered, with a locomotive at each end.
The TGV runs at 300 kilometres per hour - half as fast again as most express trains - and holds the world-record speed of 515 kilometres per hour. It runs on a purpose-built track, which has few bends, and uses computerized signaling.
The TGV can climb steeper slopes than other trains, allowing its purpose-built track to go straight over hills instead of around them.
Many high-speed expresses run on similar tracks, including the Japanese shinkansen or “bullet” trains, which began operating in 1965. 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. Other special trains include magnetic levitation (maglev) trains, which are both supported above their tracks and propelled by magnets. Maglev trains can reach very high speeds because there is no friction between the train and the track.
Picture Credit : Google