A passenger train[?] may consist of one or several locomotives, and one or more cars or carriages. Alternatively, a train may consist entirely of passenger carrying coaches, some or all of which are powered (multiple unit). Freight trains comprise wagons or trucks rather than carriages.
For more than a century almost all trains were powered by steam engines, but most countries had phased steam trains out by the 1970s. A few countries, most notably China and India still use steam trains, but this is being gradually phased out.
Modern locomotives and powered coaches may have a diesel engine and/or electric motors. On the most common form of diesel train, the diesel engine drives a generator which provides power for electric motors which turn the wheels (diesel-electric), or in some cases the power from the diesel engine is transferred to the wheels by hydraulic means (diesel-hydraulic).
However diesel powered trains are expensive to run. Where a railway line has sufficient traffic to justify the expense, it may be electrified[?], to allow the running of electric powered trains, which are cheap to run, and have higher performance than diesel trains.
For straight electric trains the power to run the electric motors is generated at a power station and supplied to the train by some form of distribution system. There are two means of doing this, current may be supplied to the train by overhead wires, or by a third rail system. Funiculars do not have an engine within the vehicle, but in the station.
Passenger trains travel between stations; the distance between stations may vary from 1 km to much more.
Long-distance trains, sometimes crossing several countries, may have a dining car; they may also have sleeping cars, but not in the case of high speed rail, these arrive at their destination before the night falls and itīs competing with airplanes in speed (very long distance trains such as those on the Trans-Siberian railway are not high speed).
For trains connecting cities we can distinguish intercity trains, which do not halt at small stations, and trains that serve all stations, usually known as local trains[?] (and sometimes an intermediate kind, see also limited-stop).
For shorter distances many cities have networks of commuter trains, serving the city and its suburbs. Some carriages may be laid out to have more standing room than seats or to facilitate the carrying of prams, cycles or wheelchairs. Some countries have some double-decked passenger trains for use in conurbations. Double deck high speed and sleeper trains are becoming more common in Europe.
Large cities often have a metro system, also called underground, subway or tube. The trains are electrically powered, usually by third rail, and their railroads are separate from other traffic, without level crossings. Usually they run in tunnels in the center and on elevated structures in the outer parts of the city. They can accelerate and decelerate faster than long-distance trains.
A light one- or two-car rail vehicle running through the streets is not called a train but a tram or streetcar, but the distinction is not strict.
The term light rail is sometimes used for a modern tram, but it may also mean an intermediate form between a tram and a train, similar to metro except that it may have level crossings. These are often protected with crossing gates.
The term rapid transit is used for public transport such as commuter trains, metro and light-rail.
Much of the world's freight is transported by train. In countries such as the USA the rail system is used mostly for transporting freight.
Under the right circumstances, transporting freight by train is highly economic, and also more energy efficient than transporting freight by road.
Rail freight is most economic, when freight is being carried in bulk and over long distances. But is less suited to short distances and small loads.
The main disadvantage of rail freight is its lack of flexibillity, for this reason, rail has lost much of the freight business to road competition. Many governments are now trying to encourage more freight onto trains, because of the enviromental benefits that it would bring.
There are many different types of freight train, which are used to carry many different kinds of freight, with many different types of wagon[?]. One of the most common types on modern railways are container trains, whereby the containers can be lifted on and off the train by cranes and loaded off or onto trucks or ships.
This type of freight train has largely superseded the traditional "box wagon" type of freight train, whereby the cargo had to be loaded or unloaded manually.
In some countries "piggy back" trains are used whereby trucks can drive straight onto the the train, and drive off again when the end destination is reached. A system like this is used on the Channel Tunnel between England and France.
There are also many other types of wagon[?], such as "low loader" wagons for transporting road vehicles. There are refrigerator wagons for transporting food. There are simple types of open-topped wagons for transporting minerals such as coal.
Model railways Toy trains have been popular with children since railroads were first built. In the 20th century, the hobby of model railroading, which attempts a more accurate depiction of railroad equipment and operation, gained popularity. Toy train[?] collecting is also popular.
According to the Oxford English Dictionary, the word train comes from French roots that mean "to drag or draw". Thus, the word also refers to the trailing part of a bride's dress, as well as to a powder train leading to an explosive. The verb to train, meaning "to educate", embodies the idea of drawing the student along.