I heard this question the other day and I'm still trying to answer it... Why does Hawaii have interstate highways?? -- Judo

Dictionary.com defines “interstate” as “One of a system of highways extending between the major cities of the 48 contiguous United States.” So what’s the deal? Hawaii isn’t one of the 48 contiguous states… Could the internet be wrong… Hath Al Gore forsaken us? It can’t be, the father of the internet wouldn’t think of such things… So our analysis goes deeper… and when you can’t go any deeper where do you end up??? That’s right, the Federal Government!!!!

And here in the bowels of Washington DC, we find our answer… Although not interstates in the traditional sense, the four Hawaiian interstates (H-1, H-2, H-3, and H-201) are considered interstates in order to qualify for federal funds subsidization

And if you read further, you will see how we can once again blame the Democrats in Maryland

A little background

As the first outspoken proponent of a Federal Highway system, President Dwight D. Eisenhower said in his Feb. 22, 1955 State of the Union Address, “Together, the united forces of our communication and transportation systems are dynamic elements in the very name we bear - United States. Without them, we would be a mere alliance of many separate parts.” And thus the story begins.

The genesis of the Interstate Highway System can be traced to “The Federal-Aid Highway Act of 1952” Although this Act never passed into Law, it ignited the national debate. Through a variet of political wranglings and various legislative permutations, the Highway Revenue Act of 1956 was born. The act was proposed by Rep. Hale Boggs of Louisiana and Rep. George H. Fallon (Represenative from the 4th Congressional District of MD and chairman of the Subcommittee on Roads ) and introduced on April 21 of that year.. it was passed on April 27 by a House vote of 388 to 19. And although Hawaii was not yet a member of the Union in 1956, it’s was included in this legislation upon joining the United States of America in 1959.

Side Note Rep. George Fallon, chairman of the Subcommittee on Roads in the Committee on Public Works, was sometimes called "The Big Man From Baltimore" partially because he stood 1.88 meters (6 feet 2 inches) tall. Even while serving in Congress, he lived in Baltimore, commuting daily to Capitol Hill via the Pennsylvania Railroad. Although he played a pivotal role in creation of the interstate highway system, he disliked driving, especially freeway driving.

Other Exceptions

However, Hawaii isn’t the only anomaly that fits into this category… Upon further investigation, one will find public roads in Alaska and various interstates that never pass over state lines…such as INTERSTATE 238 which traverses the two miles between San Lorenzo and Hayward California

Note from Puddin:

These non-interstate roads have two sources of genesis. One is political, the nature of which depends on the particular jurisdiction where the roadway is being categorized. For Alaska and Hawaii, it was argued as a matter of fairness. Basically, they claimed that due to their geographic alignment (or lack thereof), they were incapable of accessing this category of federal funds. As such, the federal government worked to provide that equity by allowing them to label roads as "interstates". For the contiguous states, it was largely a function of particular lobbying by congressional representatives. Now, as to why these others could be seen as rational to be included in the interstate system, the purpose of creating the system was two-fold.

One) Provide for greater interstate commerce.

Two) Provide for ease of movement for defense armaments.

As such, it was determined that since the roads in question were used for interstate commerce and would likely be used for military ordinance movement in case of war, they were candidates for those federal funds.

For more info
CREATING THE INTERSTATE SYSTEMFederal-Aid Highway Act of 1956: Creating the Interstate System Sidebars
Federal-Aid Highway Act of 1956: Creating the Interstate System Sidebars