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A diesel multiple unit (DMU) is a train whose carriages have their own motors powered by a diesel engine.
Basics
DMU classification is subdivided into the form of the transmission: Diesel Mechanical Multiple Unit has a mechanical transmission; Diesel Hydraulic Multiple Unit has a hydraulic transmission; Diesel Electrical Multiple Unit has an electrical transmission.
The diesel engine may be overhead (very rare) or underslung. When underslung, it is also referred to as Railcar or, in North America, a Rail Diesel Car (RDC). The RDC was a single passenger car with two diesel engines and two sets of controls. Any number of cars could be connected together and all the propulsion systems controlled from a single operators station or cab. The other design places two or three cars together in a set. There are control systems at each end of the set and multiple sets can be connected together.
A regional rail train composed of DMU cars "scales" well (I.e. adding additional car sets automatically adds power). Distribution of the propulsion among the cars also results in a system that is less vulnerable to single-point-of-failure outages. Because they operate on diesel, there is no need to run overhead electric lines or electrified track, which can result in lower system construction costs.
More rugged than units strictly designed for operation on light rail, DMU systems can be safely operated within freight rail corridors, though safety regulations in the U.S., and scheduling concerns, require that they be operated on separate tracks.
Situation in the USA
In the USA, Federal Railway Administration rules effectively prohibit the type of lightweight DMUs used elsewhere in the world. However, on July 5, 2006 the Los Angeles County Metropolitan Transit Authority approved an allocation of $250,000 for a feasibility study of DMUs for "future transportation options for the region" (Ara Najarian, Metro Board Member).
When the phrase is used in conjunction with individual diesel locomotives, the connections typically consist of seven air hoses and one electrical cable. The largest hose, located next to the coupler is the main air brake line or "train line". Outboard of this are two smaller hoses which link the air compressors on the locomotives. Further out are two hoses which control the brakes on the locomotives independently of the rest of the train. The two outermost hoses control the application of sand to the rails. An electrical cable above the coupler transmits throttle information from one locomotive to the next. Locomotives set up to use slugs have extra connections for transmitting electricity from the diesel electric generator on the "mother" unit to the traction motors on the slug.
Chicago's commuter rail line, Metra, is studying the use of DMU's on its newly proposed lines. They claim these DMUs will have better acceleration, be more fuel efficient, and seat more customers than the current diesel engine cab and double decker rail cars that are currently in use.
Elsewhere in the world
Cityrail sydney
Manufacturers
DMU manufacturers include:
- Bombardier Transportation of Montreal, Canada
- Colorado Railcar
- Rotem of Seoul, South Korea
- Siemens Desiro DMU
- Integral Coach Factory of Chennai, India
See also
קרונוע | 気動車 | Szynobus | Рельсовый_автобус
"Diesel multiple unit"