List of Interstate Highways

Interstate Highways in the 48 contiguous states. Purple routes are currently built and open freeways, blue are currently open spur routes, and green indicates proposed routes, future roads, or those currently under construction.

Primary interstates are the major interstate highways of the United States and are assigned a one or two-digit route number. Even route numbers are assigned to east/west routes, with the lower numbered routes being further south (I-10) and higher numbered routes in the north (I-90). Similarly, odd route numbers are assigned to north/south routes, with the lower numbered routes being further west (I-5) and the higher numbered routes being further east (I-95).

There are four pairs of numbers that are duplicated throughout the system; the corresponding highways are separated by large distances to prevent confusion. Below, these are differentiated from each other by West and East.

Three-digit Interstates are spur or loop interstates that usually service large cities and suburbs. The last two digits of a three-digit interstate are always the number of the parent route, the primary interstate where it originated. If the first digit is odd, the interstate is typically a spur route while if the first digit is even, the interstate is typically a loop route. Three-digit interstates are covered in their parent route's article, and those that have their own articles are linked below. (In the table below, interstates designated with an asterisk are "secret" interstates—that is, they are not signposted as interstates.)

1 Primary Interstates
2 Interstates outside of the mainland
- 2.1 Hawaiian Interstates
- 2.2 Alaska and Puerto Rico
  - 2.2.1 Alaska
  - 2.2.2 Puerto Rico
3 See also
4 References
5 External links

Primary Interstates

There are 66 Primary Interstates listed in the table below, with 43 of them having auxiliary routes. Listed lengths are as of October 31, 2002.

Interstates outside of the mainland

Interstate Highways not only reside in the contiguous 48 states of the United States, but there are also Interstates in Hawaii, Alaska, and Puerto Rico.

Hawaiian Interstates

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

Interstate Route Length (miles)[2]Interstate H-1
Kapolei, Hawaii(HI-93) to Honolulu, Hawaii(HI-72)
Associated route: H-20127.16 Interstate H-2
Pearl City, Hawaii(H-1) to Wahiawa, Hawaii(HI-99)
8.33 Interstate H-3
Halawa, Hawaii(H-1& H-201) to Marine Corps Base Hawaii
15.32

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.[3]”

Alaska

Map of the Interstates in Alaska

Alaska's "Interstates" are unsigned, though they all have state highway numbers (which don't match the Interstate numbers).[4]

Puerto Rico

Map of the Interstates in Puerto Rico

Like Alaska, Puerto Rico signs its "Interstates" as territorial routes, and the numbers do not match their official Interstate designations. However, many of the territory's routes are freeway-standard toll roads.[5]

References

^ Federal Highway Administration Route Log and Finder List - Table 1: Main Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways as of October 31, 2002
^ Federal Highway Administration Route Log and Finder List - Table 1: Main Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways as of October 31, 2002
^ Federal Highway Administration. FHWA Route Log and Finder List. Retrieved on 2007-05-24.]
^ Voss, Oscar. Alaska Roads - Interstate ends photos. Retrieved on 2007-05-24.
^ Voss, Oscar. Puerto Rico road photos. Retrieved on 2007-05-24.