A twin unit, twinset, or double unit is a set of two
railroad
Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
cars
A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people rather than cargo. There are around one billio ...
or
locomotive
A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pull train, push–pull operation has become common, and in the pursuit for ...
s which are permanently coupled and treated as if they were a single unit. A twinset of cars or coaches can also be called a twin car. In
US passenger railroad parlance, twin units are also known as married pairs.
On passenger railroads,
light rail
Light rail (or light rail transit, abbreviated to LRT) is a form of passenger urban rail transit that uses rolling stock derived from tram technology National Conference of the Transportation Research Board while also having some features from ...
, and
monorail
A monorail is a Rail transport, railway in which the track consists of a single rail or beam. Colloquially, the term "monorail" is often used to describe any form of elevated rail or people mover. More accurately, the term refers to the style ...
services, married pairs may have machinery necessary for full operation of the cars split between them. Items that are typically shared include
transformer
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
s,
motor controller
A motor controller is a device or group of devices that can coordinate in a predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forw ...
s,
dynamic braking
Dynamic braking is the use of an electric traction motor as a generator when slowing a vehicle such as an electric or diesel-electric locomotive. It is termed " rheostatic" if the generated electrical power is dissipated as heat in brake grid re ...
grids, cabs,
current collector
A current collector (often called a "pickup") is a device used in trolleybuses, trams, electric locomotives and EMUs to carry electric power ( current) from overhead lines, electric third rails, or ground-level power supplies to the electrical ...
s, batteries, and
air compressor
An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a Pneumatics, pneumatic device that energy conversion, converts mechanical power (from ...
s. This provides significant savings in both cost of equipment and weight, which increases performance and decreases energy consumption. The
cost of operating such a pair may be slightly higher when the extra car in such a pair is not needed to meet level-of-service demands at a particular time.
See also
*
Cow–calf
*
Multiple unit
A multiple-unit train (or multiple unit (MU)) is a self-propelled train composed of one or more Coach (rail), carriages joined, and where one or more of the carriages have the means of propulsion built in. By contrast, a locomotive-hauled ...
References
Rolling stock
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