Long hood

The long hood of a hood unit-style diesel locomotive is, as the name implies, the longer of the two hoods (narrower sections of the locomotive body in front and behind of the cab) on a locomotive. The long hood normally contains the diesel engine (prime mover), the main generator or alternator, the locomotive's cooling radiators, the dynamic brake resistor grids if fitted, and most of the locomotive's ancillary equipment. Head-end power equipment, if fitted, is normally in the long hood; steam generators for heating older passenger cars may be either in the long or short hoods.

Normally, the long hood is the rear of the locomotive. For early hood unit models, this was not the case; railroads preferred to have the long hood at the front and the cab at the rear, as in a steam locomotive; this followed crew preference for greater protection in a collision. Later, preferences changed to having the short hood at the front and the long hood at the rear, for better visibility, especially when more powerful engines required larger, visibility-obscuring radiator units. The railroads that held out the longest for long-hood leading were the Norfolk & Western Railway and the Southern Railway (later merged into the Norfolk Southern).