switcher

A switcher or shunter (Great Britain: shunter; Australia: shunter or yard pilot; USA: switcher or switch engine, except Pennsylvania Railroad: shifter) is a small railroad locomotive intended not for moving trains over long distances but rather for assembling trains ready for a road locomotive to take over, disassembling a train that has been brought in, and generally moving railroad cars around – a process usually known as switching (USA) or shunting (UK). They do this in classification yards (Great Britain: marshalling yards). Switchers may also make short transfer runs and even be the only motive power on branch lines and switching and terminal railroads. The term can also be used to describe the workers operating these engines or engaged in directing shunting operations.