A cab unit and a carbody unit are body styles of locomotives in North American railroad terminology. While closely related, they are not exactly the same. A carbody unit may be either a cabless booster unit controlled from a linked cab unit, or a cab unit that contains its own controls. With both body styles, a 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.