Hidden route

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In the United States, a hidden route (sometimes called unsigned) is a highway which has been designated a route number by a state department of transportation, but does not use that route number on signage, usually because the highway also acts as a U.S. highway or interstate highway over its entire length.

U.S. highways are nothing more than state roads that enter an adjoining state. Contrary to popular belief, individual states control U.S. highways, and usually assign them a state route number that is not announced to the driving public. State routes are only signed as such if the road is contained entirely within a single state and is not designated as a U.S. highway. Therefore, because the AASHTO has already assigned a route number to a particular road (which was done before the development of the Interstate system to help drivers find their way across the nation), the state number is rendered useless to drivers, and there is no need to post signs announcing it.

Some states organize state routes geographically and numerically, others use a sporadic system.

One example of a hidden route is Tennessee State Route 24, which is known as U.S. Route 70 and U.S. Route 70N over its entire route, thereby eliminating the need to confuse drivers by using signage for the state route number.