A-unit

Type of locomotive An EMD SD40 A-unit owned by BNSF Railway An A-unit, in railroad terminology, is a diesel locomotive (or more rarely an electric locomotive) equipped with a driving cab and a control system to control other locomotives in a multiple unit, and therefore able to be the lead unit in a consist of several locomotives controlled from a single position. This terminology is generally used in North America, since only there was it commonplace to build B-units—cabless locomotive units which normally could not lead a train. Typical features Typical driving cab features, and therefore A-unit features, include windshields, rectangular side windows, crew seats, heating, and sometimes, radios, air conditioning and toilets. B-units always lack all of these features, except that some EMD F-units have an extra porthole-style side window(s) for a hostler (an employee permitted to move a locomotive in a yard only, not on the road). Terminology This terminology has fallen out of use for newer locomotives, since it only really applied to the cab unit style of locomotive. Thus, the term cab unit is used only when an A-unit has a carbody design. Hood unit "road switcher" types were gen