Multiple-unit train control
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Multiple-unit train control sometimes referred to simply as multiple-unit or MU, is a method of simultaneously controlling all the electric motors in a train including a number of self-powered cars from a single operating location.
The system was designed by Frank Sprague and tested on the Chicago 'L' in 1897. Sprague also designed the first practical trolley car in the United States of America.
MU operation solved a problem in the control of street cars and rapid transit cars, where trains were made up of individually self-powered cars, or a combination of self-powered and unpowered cars. The problem involved not only the issue of transmitting control signals between cars, but also of making certain that the motors in all the cars operated in the same fashion and responded simultaneously to changes in the control signals issuing from the operator's position.
Sprague's system was adopted for the first mass-produced diesel-electric locomotives produced by General Motors Electro-Motive Division, and subsequently almost all North American diesel locomotives have been equipped for MU operation.
The invention of MU by Sprague made modern rapid transit (metro) and other commuter railway systems using self-propelled equipment possible.
