A switcher locomotive (American English) or shunter locomotive (British English), is a small locomotive used for maneuvering railway vehicles over short distances. Switchers do not usually move trains over long distances, instead they typically assemble trains in order for another locomotive to take over. Switchers often operate in a railyard or make short transfer runs. They may serve as the primary motive power on short branch lines or switching and terminal railroads.
Switchers are optimized for their role, being relatively low-powered but with a high starting tractive effort for getting heavy cars rolling quickly. Switchers are geared to produce high torque but are restricted to low top speeds and have small diameter driving wheels. Switchers tend to be durable and to remain in service for a long time, such as the Swedish class U.
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