multipleunit

A multiple unit (MU) is a self-propelled rail vehicle or a set of rail vehicles designed to be coupled with other units and controlled from a single cab or control point. Unlike locomotives that haul trains, an MU consist contains its own propulsion equipment within one or more units, enabling operation of the train as a cohesive whole. MUs are primarily used for passenger services and encompass electric multiple units (EMUs) and diesel multiple units (DMUs).

EMUs obtain electrical power from overhead lines or third-rail systems and distribute traction to multiple carriages. DMUs carry on-board diesel engines that drive traction motors, eliminating the need for a separate locomotive. Many MU systems are bi-directional, with driving cabs at both ends, while others require converting the train to run in the opposite direction.

Each unit in an MU set can be connected via electrical and control links, allowing a single driver to operate the entire train and coordinate braking across all cars. The mechanical and electrical connections also transmit power, control signals, and pneumatic braking commands between units. Additional units can be coupled to extend capacity, a common arrangement on commuter and regional networks.

Advantages of multiple units include quicker acceleration for frequent-stop services, centralized control without a separate locomotive, and flexible train length by adding or removing units. They also simplify maintenance by distributing propulsion equipment across the train. Limitations involve higher initial cost and complexity of electrical systems, compatibility requirements across fleets and infrastructure, and potential challenges in standardizing controls and couplings across regions.

MU designs are widespread in urban transit, regional rail, and some high-capacity intercity services, encompassing a range of EMU and DMU configurations tailored to specific service patterns.