A diesel multiple unit (DMU) can be:

• a multiple unit powered by a diesel engine. (A multiple unit car contains both passenger accommodations and propulsion systems.)
• a combination of diesel powered locomotives operating under the control of one engine-driver, coupled together consecutively, usually at the head end of the train, which further consists of wagons or carriages.

It 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 overboard or underslung. When underslung, it is also referred to as Railcar.

A regional rail train composed of DMU cars "scales" well (I.e. adding additional cars automatically adds power). Distribution of the propulsion among the cars also results in a system that is less vulnerable to single-point-of-failure outtages. 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 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. In the USA, Federal Railway Administration rules effectively prohibit the type of lightweight DMU's used elsewhere in the world.

See also:

• Railways

• DMU manufactuers include:
  • Bombardier Transportation of Montreal, Canada
  • Colorado Railcar
  • Rotem Company of Seoul, South Korea
  • Siemens Desiro DMU
  • Colorado Railcar
  • Integral Coach Factory of Chennai, India