List of primary Interstate Highways

Contiguous United States

There are 71 primary interstate highways in the 48 contiguous United States as well as five former and one future primary interstate highway. This number does not include auxiliary Interstate Highways. Associated routes: I-105, I-205, I-305, I-405, I-505, I-605, I-705, I-805; Planned: I-905 in California Associated routes: I-110, I-210, I-310, I-410, I-510, I-610, I-710, I-910 Planned associated routes: I-14N, I-14S, and I-214 in Texas Associated routes: I-115, I-215, I-315 Associated route: I-516 Uses kilometers instead of miles Associated routes: I-220, I-520, I-820 Planned associated routes: I-222 and I-422 in Alabama Associated route: I-124 Associated route: I-225 Associated routes: I-126, I-526 Associated routes: I-129, I-229 Associated routes: I-430, I-530, I-630 Replaced by a northward extension of I-29 Associated routes: I-35E, I-35W, I-135, I-235, I-335, I-435, I-535, I-635 Associated routes: I-140, I-240, I-440, I-540, I-640, I-840 Associated routes: I-244, I-344, I-444 Associated route: I-345 Associated routes: I-155, I-255, I-355, I-555 Associated routes: I-359, I-459, I-759 Associated routes: I-264, I-464, I-564, I-664 Associated routes: I-165, I-265, I-465, I-565, I-865; Planned: I-365 in Kentucky Associated routes: I-66 Spur in Kentucky The project was unpopular and ultimately cancelled without the interstate being completed; I-66 Spur eventually became I-165

• Unfinished in Texas, Mississippi, Tennessee, Kentucky, and Indiana; serves six states: Texas, Mississippi, Tennessee, Kentucky, Indiana, Michigan
• Planned/started in 2 more: Louisiana, Arkansas
• Associated routes: I-69C, I-69E, I-69W, I-169, I-269, I-369, I-469; Planned: I-569 in Kentucky Associated routes: I-170, I-270, I-370, I-470, I-670 Associated routes: I-271, I-471 Associated route: I-172 Associated routes: I-474; Planned: I-274 in North Carolina Associated routes: I-175, I-275, I-375, I-475, I-575, I-675 Associated routes: I-176, I-276, I-376, I-476, I-676 Associated route: I-277 Associated routes: I-278, I-478, I-678, I-878 Associated routes: I-279, I-579 Associated routes: I-180, I-238, I-280, I-380, I-480, I-580, I-680, I-780, I-880, I-980 Associated routes: I-381, I-481, I-581, I-781 Associated route: I-182 Was the initial designation to what is now I-380 and I-80 Redesignated as I-84 in 1968 Associated route: I-283 Associated route: I-184 Associated routes: I-384, I-684 Associated routes: I-185, I-285, I-385, I-485, I-585, I-785, I-885, I-985; Future/Planned: I-685 in both Alabama and North Carolina Redesignated as I-84 in 1984 when the I-84 Hartford-Providence corridor was cancelled Associated route: I-587 Associated routes: I-287, I-587, I-787 Associated route: I-189 Associated routes: I-190, I-290, I-390, I-490, I-590, I-690, I-790, I-890, I-990 Longest Interstate highway Associated routes: I-291, I-391, I-691 Associated routes: I-293, I-393 Associated routes: I-194, I-294, I-394, I-494, I-694, I-794, I-894 Associated routes: I-195, I-295, I-395, I-495, I-595, I-695, I-795, I-895 Longest primary north-south Interstate highway Associated routes: I-196, I-296, I-496, I-696

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:

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Hawaii

The Interstate Highways on the island of Oahu, 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

Main article: List of Interstate Highways in Alaska

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

Puerto Rico

Main article: List of highways in Puerto Rico#Interstates

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.

References

References

1. Weingroff, Richard F.. (Summer 1996). "Federal-Aid Highway Act of 1956, Creating the Interstate System". [[Federal Highway Administration]].
2. (May 6, 2019). "Table 1: Main Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways as of December 31, 2018". [[Federal Highway Administration]].
3. Public Roads Administration. (August 14, 1957). "Official Route Numbering for the National System of Interstate and Defense Highways as Adopted by the American Association of State Highway Officials". Public Roads Administration.
4. (March 22, 2024). "Text - S.992 - 118th Congress (2023-2024): I-27 Numbering Act of 2023". Library of Congress.
5. Nelsen, Carrie. (July 9, 2015). "For Immediate Release". Illinois Department of Transportation.
6. Voss, Oscar. "Alaska Roads: Interstate ends photos".
7. Witt, Jennifer W.. (2010). "Annual Traffic Volume Report". [[Alaska Department of Transportation & Public Facilities]].
8. Birkholz, Ethan. (2010). "Annual Traffic Volume Report". [[Alaska Department of Transportation & Public Facilities]].
9. Staff. "Dwight D. Eisenhower Interstate Routes Statewide". Federal Highway Administration.
10. Staff. "Alaska Department of Transportation and Public Facilities Routes by Description: CDS Route Numbers as of 28 October 2008". Federal Highway Administration.
11. Voss, Oscar. "Puerto Rico road photos".