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List of Interstate Highways

There are 70 primary Interstate Highways in the Interstate Highway System, a network of freeways in the United States. These primary highways are assigned one- or two-digit route numbers, whereas their associated auxiliary Interstate Highways receive three-digit route numbers. Typically, odd-numbered Interstates run south–north, with lower numbers in the west and higher numbers in the east; even-numbered Interstates run west–east, with lower numbers in the south and higher numbers in the north. Route numbers divisible by 5 usually represent major coast-to-coast or border-to-border routes (ex. I-10 connects Santa Monica, California to Jacksonville, Florida, extending between the Pacific and Atlantic oceans). Auxiliary highways have an added digit prefixing the number of the parent highway.

Five route numbers are duplicated in the system; the corresponding highways are in different regions, reducing potential confusion. In addition to primary highways in the contiguous United States, there are signed Interstates in Hawaii and unsigned Interstates in Alaska and Puerto Rico.

Contiguous United States

There are 70 primary interstate highways in the 48 contiguous United States as well as five former and two future primary interstate highways. This number does not include auxiliary Interstate Highways.

Other regions

In addition to the 48 contiguous states, Interstate Highways are found in Hawaii, Alaska, and Puerto Rico. The Federal Highway Administration funds four routes in Alaska and three routes in Puerto Rico under the same program as the rest of the Interstate Highway System. However, these routes are not required to meet the same standards as the mainland routes:

Highways on the Interstate System in Alaska and Puerto Rico shall be designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway.[4]

Hawaii

Map of Hawaii's Interstate Highways (excluding H-201)

The Interstate Highways on the island of Oʻahu, Hawaii are signed with the standard Interstate Highway shield, with the letter "H-" prefixed before the number. They are fully controlled-access routes built to the same standards as the mainland Interstate Highways.

Alaska

Map of Alaska's Interstate Highways

Alaska's Interstate Highways are unsigned as such, although they all have state highway numbers that do not match the Interstate Highway numbers.[5]

Puerto Rico

Map of the Interstates in Puerto Rico

Puerto Rico signs its Interstate Highways as territorial routes, as the numbers do not match their official Interstate Highway designations. Many of the territory's routes are freeway-standard toll roads.[10]

See also


References

  1. ^ Weingroff, Richard F. (Summer 1996). "Federal-Aid Highway Act of 1956, Creating the Interstate System". Public Roads. 60 (1). Washington, DC: Federal Highway Administration. Retrieved March 16, 2012.
  2. ^ a b c d "Table 1: Main Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways as of December 31, 2018". FHWA Route Log and Finder List. Federal Highway Administration. May 6, 2019. Retrieved April 21, 2021.
  3. ^ Nelsen, Carrie (July 9, 2015). "For Immediate Release" (PDF) (Press release). Illinois Department of Transportation. Archived from the original (PDF) on September 6, 2015.
  4. ^ Staff. "FHWA Route Log and Finder List". Federal Highway Administration. Retrieved May 24, 2007.
  5. ^ Voss, Oscar. "Alaska Roads: Interstate ends photos". Retrieved May 24, 2007.
  6. ^ a b c Witt, Jennifer W. (2010). Annual Traffic Volume Report (PDF) (Report) (2008-2009-2010 ed.). Alaska Department of Transportation & Public Facilities. Archived from the original (PDF) on March 30, 2014. Retrieved March 15, 2012.
  7. ^ a b c Birkholz, Ethan (2010). Annual Traffic Volume Report (PDF) (Report) (2008-2009-2010 ed.). Alaska Department of Transportation & Public Facilities. Archived from the original (PDF) on April 17, 2014. Retrieved May 31, 2012.
  8. ^ a b c d Staff. "Dwight D. Eisenhower Interstate Routes Statewide" (PDF). Federal Highway Administration. Retrieved May 31, 2012.
  9. ^ a b c d Staff. "Alaska Department of Transportation and Public Facilities Routes by Description: CDS Route Numbers as of 28 October 2008" (PDF). Federal Highway Administration. Retrieved May 31, 2012.
  10. ^ Voss, Oscar. "Puerto Rico road photos". Retrieved May 24, 2007.

External links