Interstate Highway System

Dwight D. Eisenhower National System of Interstate and Defense Highways

Interstate 80 marker

Interstate 80 Business marker

Eisenhower Interstate System sign
Highway shields for Interstate 80, Business Loop Interstate 80, and the Eisenhower Interstate System Map
Primary Interstate Highways in the 48 contiguous states. Alaska, Hawaii, and Puerto Rico also have Interstate Highways.
System information
Length48,756 mi[a] (78,465 km)
FormedJune 29, 1956 (1956-06-29)[1]
Highway names
InterstatesInterstate X (I-X)
System links

The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, or the Eisenhower Interstate System, is a network of controlled-access highways that forms part of the National Highway System in the United States. The system extends throughout the contiguous United States and has routes in Hawaii, Alaska, and Puerto Rico.

In the 20th century, the United States Congress began funding roadways through the Federal Aid Road Act of 1916, and started an effort to construct a national road grid with the passage of the Federal Aid Highway Act of 1921. In 1926, the United States Numbered Highway System was established, creating the first national road numbering system for cross-country travel. The roads were state-funded and maintained, and there were few national standards for road design. United States Numbered Highways ranged from two-lane country roads to multi-lane freeways. After Dwight D. Eisenhower became president in 1953, his administration developed a proposal for an interstate highway system, eventually resulting in the enactment of the Federal-Aid Highway Act of 1956.

Unlike the earlier United States Numbered Highway System, the Interstates were designed to be all freeways, with nationally unified standards for construction and signage. While some older freeways were adopted into the system, most of the routes were completely new. In dense urban areas, the choice of routing destroyed many well-established neighborhoods, often intentionally as part of a program of "urban renewal".[3] In the two decades following the 1956 Highway Act, the construction of the freeways displaced one million people,[4] and as a result of the many freeway revolts during this era, several planned Interstates were abandoned or re-routed to avoid urban cores.

Construction of the original Interstate Highway System was proclaimed complete in 1992, despite deviations from the original 1956 plan and several stretches that did not fully conform with federal standards. The construction of the Interstate Highway System cost approximately $114 billion (equivalent to $597 billion in 2023). The system has continued to expand and grow as additional federal funding has provided for new routes to be added, and many future Interstate Highways are currently either being planned or under construction.

Though heavily funded by the federal government, Interstate Highways are owned by the state in which they were built. With few exceptions, all Interstates must meet specific standards, such as having controlled access, physical barriers or median strips between lanes of oncoming traffic, breakdown lanes, avoiding at-grade intersections, no traffic lights and complying with federal traffic sign specifications. Interstate Highways use a numbering scheme in which primary Interstates are assigned one- or two-digit numbers, and shorter routes which branch off of longer ones are assigned three-digit numbers where the last two digits match the parent route. The Interstate Highway System is partially financed through the Highway Trust Fund, which itself is funded by a federal fuel tax. Though federal legislation initially banned the collection of tolls, some Interstate routes are toll roads, either because they were grandfathered into the system or because subsequent legislation has allowed for tolling of Interstates in some cases.

As of 2020, about one quarter of all vehicle miles driven in the country used the Interstate Highway System,[5] which had a total length of 48,756 miles (78,465 km).[2] In 2020 and 2021, the number of fatalities on the Interstate Highway System amounted to more than 5,000 people annually.[6]

  1. ^ Weingroff, Richard F. (Summer 1996). "Federal-Aid Highway Act of 1956, Creating the Interstate System". Public Roads. Vol. 60, no. 1. ISSN 0033-3735. Archived from the original on March 7, 2012. Retrieved March 16, 2012.
  2. ^ a b Office of Highway Policy Information (October 26, 2021). Table HM-20: Public Road Length, 2020, Miles By Functional System (Report). Federal Highway Administration. Retrieved May 13, 2022.
  3. ^ Cite error: The named reference StrombergVox was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference GamboaNBC was invoked but never defined (see the help page).
  5. ^ Office of Highway Policy Information (December 15, 2021). Table VM-1: Annual Vehicle Distance Traveled in Miles and Related Data, 2020, by Highway Category and Vehicle Type (Report). Federal Highway Administration. Retrieved May 13, 2022.
  6. ^ National Center for Statistics and Analysis (May 2022). Early Estimates of Motor Vehicle Traffic Fatalities and Fatality Rate by Sub-Categories in 2021 (Report). National Highway Traffic Safety Administration. DOT HS 813 298. Retrieved November 11, 2023.


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