Diesel multiple units (DMUs) are regional rail cars which contain both passenger accommodations and propulsion. Diesel engines, electric generators and electric motors are located below the passenger compartment.
Because they are self-propelled, no large locomotive engine is required. The train "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.
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DMU manufactuers include:
Bombardier Transportation (http://www.bombardier.com/) of Montreal, Canada
A multipleunit is a type of train where the traction is supplied by driving bogies under one or more carriages of the (usually very short) train.
Most multipleunits are powered either by a diesel engine driving the wheels through a gearbox (a dieselmultipleunit, or DMU), or by electric motors, receiving their power through a live rail or overhead wire (an electric multipleunit or EMU).
In North America, multipleunits are not common (and dieselmultipleunits almost non existent).
Multipleunits were made possible by the development of multiple-unittrain control by the American inventor (Franklin J. Sprague), to allow electrically-powered rapid transit trains to be operated from a single position without the need for a separate locomotive, as was required when such trains were hauled by steam engines.
The motors driving the train on an MU unit are typically mounted underneath the floor of the carriages, on the bogies (U.S. "trucks"), the assembly beneath the train that holds the axles and wheels.
Most MUs are powered either by a diesel engine driving the wheels through a gearbox or hydraulic transmission (a dieselmultipleunit, or DMU), or by electric motors, receiving their power through a live rail or overhead wire (an electric multipleunit or EMU).
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