Originally Posted by
StraightLevel
apparantly over there they are built in such a way as to have a certain proportion of them straight, and the central reservation is supposed to be wide enough to take a light aircraft, specifically incase an aircraft has an engine failure.
I was told that it's nothing to do with an aircraft engine failure - it's for civil defense reasons. In times of civil unrest, the interstates can be used as landing/takeoff facilities for the military.
Same idea as in Blighty where last century there was a habit of building subterranean public conveniences at major intersections (at least in scotland) to be used by the police as bunkers/control points if there was ever a riot/civil war etc.