On June 29, 1956, President Dwight Eisenhower signed the Federal-Aid Highway Act of 1956, which created a 41,000-mile "National System of Interstate and Defense Highways" that would become America's most important transportation infrastructure—and one of the world's modern wonders.
Designed to reach every city with a population of more than 100,000, the system significantly changed American landscapes and lives, increasing ease of travel and affecting the way business is conducted.
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Major Interstate routes are designated by one- or two-digit numbers. Routes with odd numbers run north and south, while even numbered run east and west. All but four state capitals are directly served by the Interstate System. Those not directly served are Juneau, Alaska; Dover, Del.; Jefferson City, Mo.; and Pierre, S.D.
The oldest Interstate segments actually predate the establishment of the Interstate system, according to the US Department of Transportation's Federal Highway Administration. Early examples include a portion of the Grand Central Parkway in Queens, New York, was opened to traffic in July 1936 and later was incorporated into the Interstate System as I-278. The Pennsylvania Turnpike between Irwin (southeast of Pittsburgh) and Carlisle (west of Harrisburg) was officially opened in October 1940 and is now designated as I-76 and I-70.
View the slideshow above to see the country's 10 longest interstate highways, their length, states served and termini.
- I-90: 3,101.77 mi
- I-80: 2,899.54 mi
- I-40: 2,555.10 mi
- I-10: 2,460.34 mi
- I-70: 2,153.13 mi
- I-95: 1,925.74 mi
- I-75: 1,786.47 mi
- I-94: 1,585.20 mi
- I-35: 1,568.38 mi
- I-20: 1,539.38 mi
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