Editing Cab unit (section)

==Characteristics==
With both body styles, a [[Truss|bridge-truss]] [[design]] framework is used to make the body a structural element of the locomotive. The body extends the full width and length of the locomotive. The service walkways are inside the body.

Carbody units, gaining rigidity from the body trusswork, require less structural weight to achieve rigidity than do locomotives with non-structural bodies.  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. Recent years have seen carbody construction [[GE Genesis|revived]] in the quest for greater [[fuel efficiency]] with passenger locomotives.

The full-width body gives a carbody cab unit poor rear visibility compared with a [[hood unit]].  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 train]]s.  Cab and carbody units are also more aerodynamic than hood units, and pulled many of the [[streamliner]] trains.