Power cars are a highly specialized type of railroad locomotive. The purpose of a typical locomotive is to move the attached train cars and to provide electricity to any passenger compartments. A power car also performs these functions but may have cargo or passenger compartments integrated into its body. Locomotives are usually very interchangeable, while power cars are more integrated into the entire train unit. Power cars are usually used for passenger service due to an overall lack of versatility that stems from their configurations.
There are a number of advantages of using power cars instead of traditional locomotives. Placing a power car on each end of the train set can save on time and energy when compared to turning a traditional locomotive. The use of multiple power cars throughout the configuration can also create versatility, since a single train can be broken into multiple smaller units at any time. These trains may also have a lighter axle load as well, allowing them to operate on tracks that conventional locomotives can not.
Train sets that use power cars often give the visual impression of being long, continuous units due to the styling and lines. The most common application of power cars is in high speed passenger service. A typical configuration is to have a power car at each end and a number of passenger compartments in between. The power cars typically also contain space for passengers or cargo. These trains will sometimes haul small amounts of cargo, though they typically can not accept the containers commonly used in railway cargo transport.
In the United States, Amtrak operates a number of power car locomotives on the eastern seaboard. British Rail has also operated high speed passenger trains using power car configurations since the 1970s. In Japan, the shinkansen, or bullet trains, use electric power cars to move passengers around the country at speeds exceeding 275 mph (443 kph).
Light rail often makes use of power cars as well, particularly in the form of multiple units (MUs). These self-propelled train cars are commonly powered by either electricity or diesel and are marked by the inclusion of multiple sets of powered and non-powered passenger cars. Multiple units may consist of a single powered train car, a powered unit, and several non-powered units, or virtually any other configuration. It is usually possible to mate two multiple units together to create one larger train that consists of several power cars and passenger compartments.