Interstate highways are supposed to go from one state to the next.
That fact is in the very name: “inter” meaning between and “state” meaning. . . uh. . . state. So interstate highways should go between states. Sure, Texas drivers can drive on the interstate for hours without hitting a state border, but they’re original purpose was to make it possible for people to go from one state to another.
So this question comes up from time to time:
Why are there interstate highways in Hawaii?
And usually it seems to be asked by some smart aleck who thinks he’s just thought of something really clever and original. (You know who you are.)
In truth, Hawaii does have three interstate highways — H1, H2, and H3 — all of which were built to connect important military facilities on the island of Oahu. So not only do they not connect to other states, they don’t even connect to the other eight major islands.
And that mention of military facilities is a big part of the explanation of why they’re called “interstate highways” even when they’re obviously not inter-state highways.
Following World War II and during the Cold War, the US government had been concerned about the ability to rapidly move military personnel and equipment rapidly across the country. President Eisenhower in particular had returned from Germany very impressed by the Autobahn system that Hitler’s National Socialist had created to move their army around. So a movement was begun to build a similar system in the USA, which led eventually to the Federal Aid Highway Act of 1956. This act called for the construction of an enormous highway infrastructure to connect major cities and military facilities, even the three in Hawaii.
And that’s why Hawaii has three interstate highways, even if they’re not for travelling inter-state.