An EMU or Electric Multiple Unit is a type of train consisting of self-propelled carriages that use electricity as the motive power. Unlike traditional trains, an EMU does not require a separate locomotive, as electric traction motors are incorporated within one or a number of the carriages. EMUs are popular on commuter and suburban rail networks around the world due to their fast acceleration and pollution-free operation. They are usually formed of two or more semi-permanently coupled carriages, but electrically powered single-unit railcars are also generally classed as EMUs. EMUs are quieter than diesel multiple units (DMUs) and locomotive-hauled trains, which allows them to operate later at night and more frequently without disturbing nearby residents. The maximum number of coaches in an EMU train is 12.