Cecil wrote in October of 1988 (republished in February 2012):
I don’t know if that was accurate in 1988, but it isn’t accurate now. The Federal Highway Administration reports here and here that Alaska has 1,082.22 miles of interstate highways, over twenty times as much as Hawaii’s paltry 50.81 miles.
Personally, I see no conflict at all in referring to the highway system as being “interstate” even if some of the individual highways themselves do not cross state lines. For example, I-45 is entirely within the state of Texas, running from Galveston to Dallas.
(Note that, although certain Alaskan and Puerto Rican highways are on the books as part of the Interstate system, and receive funding as such, none of them have Interstate signage, and you will not find them labeled as Interstate highways on roadmaps.)
Turns out there are quite a few Intrastate Interstates, including A1-A4 in Alaska. Oddly, I can’t find any cites that say when the Alaska roads got their Interstate designations. Hopefully somebody who knows more than I will come along.
It is true that the definition of “Interstate” has been somewhat fluid over the years. I remember when Illinois Route 5 became I-88 back in the '80s. As I recall, the assumption was that because it was a limited access highway that connected other Interstates, it could be considered part of the overall Interstate system. Made sense to me. Turns out, though, it was because the Feds wanted to impose the National Speed Limit, which it couldn’t do for a state route.
The state wanted to take advantage of a new modification to the national speed limit, where interstates could be signed as 65. The sensible thing now would be to extend I-88 to downtown instead of or with I-290 rather than have it end abruptly out in the suburbs.