I agree that it probably makes sense and it's certainly true that many other countries consciously used their highways as airstrips. But as far as I'm aware, there is no published specification or contingency plan that uses sections of the Interstates for that purpose.

Does anyone know of a stretch of Interstate that could actually be used as a military airstrip, even by WWII standards? I would suggest the minimum requirement would be: approximately 1 mile in length, completely straight, and as flat as possible - no more than a 1 degree rise (approximately 95 feet per mile). (I'm just guessing here, but a normal ILS approach is 3 degrees, it wouldn't make sense for the runway gradient to be as steep as the approach path itself.) Yeah, there are a couple of much steeper runways - there's one in the Himalayas that you could hold soap-box races on - but they're only usable by highly specialised aircraft, I believe.

I suspect that in the midwest, the whole Interstate could meet that description, whereas in Wyoming or Montana, it might be a bit more difficult.

Of course, at least until recently, Montana had no speed limit and there were a lot of Canadian yahoos who got stopped doing 120 mph. So the roads can't be all that bendy. (They didn't realise that Montana State Troopers had the power to ticket anyone who was driving at an unsafe speed, regardless of whether there was a posted limit or not. At least, I think that was the story - I've never been to Montana and I doubt if my car would do 120, even with a tailwind. <img src="images/graemlins/smile.gif" alt="" /> )