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Why is it called Interstate 40? How are interstate highway numbers selected?

Merton Vance

After passage of the Federal  Highway Act of 1956 to pay for construction of the interstate highway system, the American Association of State Highway Officials was given the responsibility for applying numbers to interstate highways, as it had done previously for other federal highways, according to the Federal Highway Administration.

The numbering plan adopted for interstates was a mirror image of the numbering plan previously used for non-interstate federal highways.

For example, U.S. 1 is on the east coast, while Interstate 5 is on the west coast. U.S. 10 is in the north, while I-10 is in the south.

Even numbers were given to east-west interstate routes and odd numbers to north-south routes.

U.S. 40, by the way, runs from Atlantic  City, N.J. to Silver Creek Junction, Utah. It once went all the way to San Francisco, put parts of it were decommissioned after the interstate system came along. The very first  stretch of interstate highway ever built with federal money was begun on April 13,  1956 along U.S. 40 in Missouri . It became Interstate 70 .

(In Kansas, the state had begun work on a stretch of Interstate 70 near Topeka before federal funding passed, allowing it to put up a sign proclaiming it was the first to start an interstate .)

Incidentally, that’s why there is no Interstate 50. The numbering plan was arranged to prevent having an interstate and another federal highway with the same number in the same state, to avoid confusion.

Under the numbering plan, an Interstate 50 would have run through some of the same states that are crossed by U.S. 50, which runs from Ocean City, Md. To Sacramento, Calif. So the number 50 wasn’t used for an interstate route.


Why are there several large signs for the Castle Hayne exit off I-40 while there is nothing prominently marking the Rocky Point exit? http://www.myreporter.com/?p=3242

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