Control city

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This sign in Oklahoma City, Oklahoma lists control cities of Wichita, Kansas and Ft. Smith, Arkansas for Interstate 35 and Interstate 40 respectively.

This sign in Petersburg, Virginia aids long-distance travelers, by listing the cities of Miami, Florida (920 miles away) and Atlanta, Georgia (500 miles away).

A control city is a city or locality posted on a traffic sign indicating forward destinations on a certain route. Signs indicating such cities are usually found at highway junctions to show where the intersecting road goes, or on mileage signs on longer routes.

The determination of major destinations or control cities is important to the quality of service provided by the freeway. Control cities on freeway guide signs are selected by the States and are contained in the "List of Control Cities for Use in Guide Signs on Interstate Highways," published and available from American Association of State and Highway Transportation Officials.

—Federal Highway Administration, Manual on Uniform Traffic Control Devices, 2003 Edition, Chapter 2E

The American Association of State Highway and Transportation Officials (AASHTO) has standardized all control cities used on the Interstate highway system in the United States. The published standard is not always followed, either because major destinations have since appeared that were not on the original list, or because of state highway departments' hesitancy to sign destinations in other states. An example is a sign on eastbound Interstate 10 near Palm Springs, California, which, though Phoenix, Arizona is the nearest major forward destination, signs only the small city of Indio, California and "other Desert Cities". [1]

A control city is not always a major city. For instance, Interstate 76 heading westbound out of Philadelphia, Pennsylvania uses Valley Forge, a historic but minor locality where I-76 joins the Pennsylvania Turnpike.

Occasionally, a large city will not be a control city because a larger city is located farther along a highway. For example, highway signs in Maryland on Interstate 95 northbound between the Interstate 395 junction in Baltimore and the Mason-Dixon Line at the Delaware border use New York City as their control city, even though I-95 directly passes through the closer Philadelphia, Pennsylvania (although the branching off of the New Jersey Turnpike from northbound I-95 about 40 miles south of Philadelphia probably accounts for this).

Control cities are particularly necessary for highways that do not follow strict linear directions. Ontario's Queen Elizabeth Way, for example, wraps around the western end of Lake Ontario, with segments proceeding both east and west at different points. Compass directions are not used at all in its central sections, and the control cities of Toronto and (for the opposite direction) Hamilton/Niagara Falls/Fort Erie are the only bearings provided.