In the US the last giant scale build-out was permitted before the EPA or Army Corps of Engineers had any regulatory teeth on the matter. Most projects since have been lane additions or incremental extensions. Loops have been built, but are politically easier since they only need to make one metro area happy. There's only been a handful of "new" interstates built since then (at a substantially higher cost). Much of the originally planned interstate system (that was to be a later phase) just never got built.