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|United States Numbered Highway System|
Types of special routes in the U.S.
|US Highways||U.S. Highway nn (US nn)|
U.S. Route nn (US nn)
A special route of the United States Numbered Highway System is a route that branches off a U.S. Highway in order to divert traffic from the main highway. Special routes are distinguished from main routes by, in most cases, the addition of an auxiliary plate that describes what type of route it is, while the main highway carries no such sign. In some locations, a single letter is placed after the route number to denote the special route type in lieu of the auxiliary plate. Among members of the roadgeek community, these routes are often called auxiliary or bannered U.S. Highways.
There are four main types of special routes -- alternate, business, bypass, and temporary; though other route types exist.
A unique type of route in the U.S. Route system uses directional letter suffixes following the route number. These are known as divided U.S. Routes and are generally not considered to be special routes.
The following U.S. Highway special routes have existed: