This allows manufacturers to cheaply and easily create full-width locomotives from their hood unit designs by simply adding cowling. All structural support on a cowl unit is provided by the frame of the locomotive, rather than in the body as with a cab unit. Despite some visual similarities, cowl units are actually very different from cab units.
By contrast, a carbody unit can be either an A unit, or a B unit (a locomotive without a cab).Ī cowl unit is an adaptation of the hood unit design with a full-width body. Thus, a cab unit is also always an A unit (a locomotive with a cab). Cab and carbody units are also more aerodynamic than hood units, and pulled many of the streamliner trains.Ī cab unit is a carbody unit with a driving cab (or crew compartment). For that reason, cab or carbody units are mostly used in situations where rear visibility is not important, such as power for through freight and passenger trains. The full-width body gives a carbody cab unit poor rear visibility compared with a hood unit. Recent years have seen carbody construction revived in the quest for greater fuel efficiency with passenger locomotives. For that reason, carbody construction was favored to increase the power-to-weight ratio for early diesel locomotives, before the power available with diesel technology was increased. The service walkways are inside the body.Ĭarbody units, gaining rigidity from the body trusswork, require less structural weight to achieve rigidity than do locomotives with non-structural bodies. The body extends the full width and length of the locomotive. With both body styles, a bridge-truss design framework is used to make the body a structural element of the locomotive.
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