Train
A train is a connected series of vehicles
for rail transport that move along a track (permanent
way) to transport cargo or passengers from one place
to another place. The track usually consists of
two rails, but might also be a monorail or maglev
guideway.
Propulsion for the train is provided by a separate
locomotive, or from individual motors in self-propelled
multiple units. Most modern trains are powered by
diesel locomotives or by electricity supplied by
overhead wires or additional rails, although historically
(from the early 19th century to the mid-20th century)
the steam locomotive was the dominant form of locomotive
power. Other sources of power (such as horses, rope
or wire, gravity, pneumatics, batteries, and gas
turbines) are possible.
The word 'train' comes from the Old French trahiner,
itself from the Latin trahere 'pull, draw'.
There are various types of trains that are designed
for particular purposes. A train can consist of
a combination of one or more locomotives and attached
railroad cars, or a self-propelled multiple unit
(or occasionally a single or articulated powered
coach, called a railcar). Trains can also be hauled
by horses, pulled by a cable, or run downhill by
gravity.
Special kinds of trains running on corresponding
special 'railways' are atmospheric railways, monorails,
high-speed railways, maglev, rubber-tired underground,
funicular and cog railways.
A passenger train may consist of one or several
locomotives and coaches. Alternatively, a train
may consist entirely of passenger carrying coaches,
some or all of which are powered as a "multiple
unit". In many parts of the world, particularly
the Far East and Europe, high-speed rail is used
extensively for passenger travel.
Freight trains comprise of wagons or trucks rather
than carriages, though some parcel and mail trains
(especially Travelling Post Offices) are outwardly
more like passenger trains.
Trains can also be 'mixed', comprising both passenger
accommodation and freight vehicles. Such mixed trains
are most likely to occur where services are infrequent,
and running separate passenger and freight trains
is not cost-effective, though the differing needs
of passengers and freight usually means this is
avoided where possible.
Special trains are also used for track maintenance;
in some places, this is called maintenance of way.
In the United Kingdom, a train hauled by two locomotives
is said to be "double-headed", and in
Canada and the United States it is quite common
for a long freight train to be headed by three or
more locomotives. A train with a locomotive attached
at each end is described as 'top and tailed', this
practice typically being used when there are no
reversing facilities available. Where a second locomotive
is attached temporarily to assist a train up steep
banks or grades (or down them by providing braking
power) it is referred to as 'banking' in the UK,
or 'helper service' in North America. Recently,
many loaded trains in the US have been made up with
one or more locomotives in the middle or at the
rear of the train, operated remotely from the lead
cab. This is referred to as "DP" or "Distributed
Power."
(Source: Wikipedia.org)
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