List of Interstate Highways

Dwight D. Eisenhower National System of Interstate and Defense Highways
Highway shield for Interstate 90 and the Eisenhower Interstate System
Interstate Highways in the 48 contiguous states
System information
Formed:	June 29, 1956
Highway names
Interstates:	Interstate X (I-X)
System links
Interstate Highway System Main Auxiliary Suffixed Business

Primary Interstate Highways of the United States are numbered with one- or two-digit designations. Their associated auxiliary highways have three-digit numbers. Generally, odd-numbered routes run north-south, with lower numbers in the west and higher numbers in the east; even-numbered routes run east-west, with lower numbers in the south and higher numbers in the north. Routes divisible by "5" (for example, I-40 or I-75) are major routes, often running coast-to-coast or border-to-border.

Five pairs of numbers are duplicated throughout the system; the corresponding highways are separated by large distances which prevent confusion. Below, these are differentiated from each other by "West" and "East". The main list is followed by sections listing the primary Interstate highways in Alaska, Hawaii, and Puerto Rico.

There are 68 primary Interstate Highways listed in the table below, and 43 of them have auxiliary routes.

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:

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

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

The title of interactive fiction I-0 refers to the fictional "Interstate Zero".