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Multiple unit
A multiple unit is a type of train where the traction is supplied by driving bogies under one or more carriages of the (usually very short) train. The driver's cab is usually truncated to a short room at both ends. The quicker turnaround time that results, and the reduced size compared with large locomotive-hauled trains, has made the multiple unit a major part of suburban commuter rail services in many countries.
Often, but not always, a series of multiple units can be connected together to form a larger train. Sometimes passage is available between the units, either for passengers, or just for train crew.
Most multiple units are powered either by a diesel engine driving the wheels through a gearbox (a diesel multiple unit, or DMU), or by electric motors,
receiving their power through a live rail or overhead wire (an electric multiple unit or EMU). However, diesel electric multiple units (DEMUS) also exist: these have a diesel engine which drives a generator producing electricity to drive electric motors.
In North America, multiple units are not common (and diesel multiple units
almost non existent). However, large fleets of electric multiple units are found in some of the urban centres on the East coast of the US. North American railroaders also refer to a combination of locomotives, at the head of a train, as a multiple unit.
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