# 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.

## Contents

### 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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