Hood unit

In contrast, a cab unit has a full-width carbody for the length of the locomotive and walkways inside.

Also, the locomotive frame is the main load-bearing member, allowing the hood to be non-structural and easily opened or even removed for maintenance.

The long hood of a locomotive is usually about as tall as the cab roof in order to fit the large prime mover and its related subsystems.

The visibility and access advantages mean that the hood unit is overwhelmingly the most popular style of locomotive in North America, as well as many other regions.

This was usually done to offer greater protection to the crew in the event of a collision and to give better visibility of trackside signs and objects.

In North America, all locomotives are required to have the letter F printed on the side sill at the end which is normally operated as its front.