List of Interstate Highways

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Primary Interstate Highways 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 five 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.


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.

Routes ending in 0 or 5 are highlighted in green.

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.

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