Roadswitcher

A road switcher is a type of railroad locomotive which was originally employed for delivering or picking up railcars outside of a railroad yard. Both type and term are North American in origin, although similar types have been used elsewhere. Since the road switcher must work some distance away from a yard, it must be able to operate at road speeds, it must also have high-visibility while it is switching, and it must have the ability to run in both directions. Additionally, a road switcher must have the power rating and cooling capacity of a traditional road engine, and a road switcher must have high-speed (i.e., road) trucks, not low-speed (i.e., switcher) trucks. Modern road trucks are always equipped with (frictionless) roller bearings; switcher trucks were almost always equipped with (friction) plain bearings, until such bearings were outlawed in interchange service on railcars and locomotives.

For the reasons given above, road switchers are generally hood units. The set-back cab of a hood unit provides more safety in the event of a collision at speed than most switcher designs, and the rear visibility is much better than that of a cab unit. Due to their ability to both run at road speeds for long distances and to switch cars, road switchers, as their name implies, are often used for road (heavy-haul) duties, in addition to their yard (switching) duties. Since the 1960s, road switchers have completely displaced cab units in heavy-haul freight service (but cab-type units, adapted from certain road switcher prototypes, have been employed for contemporary passenger service, in selected cases). Some road switchers were provided with twin control stands, so that the units could operate conventionally (locomotive engineer and conductor/switchman facing the direction of travel) in either "long hood forward" or "short hood forward" directions. However, twin control engineer positions have fallen into disuse as almost all operations are now run "short hood forward". For obvious reasons, the short hood is labeled "F" (meaning "front").

Alco's RS-1 was the first successful example of the type, and virtually all modern hood units are laid out in a similar fashion (long hood for all propulsion equipment, short hood for crew accommodations including a toilet). The RS-1, being the first example of a road switcher, and having been initially developed when plain bearings were still common (although not on cab-type road units), often were equipped with plain bearings. Subsequently, roller bearing conversions were implemented, and new units were generally ordered with roller bearings. The RS-1 had a very long manufacturing history, so most 1940s units might be initially ordered with plain bearings (and subsequently converted to roller bearings), but most 1960s units might be ordered with roller bearings.

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Wikipedia