Having been involved in a lot of moves in the 200 to 400 tonne range, I would say there are TWO significant shortcomings: the overpasses (but almost every overpass has a ramp off/ramp on provision) but the 80k bridge design limit. When General Ike and his merry band of strategists conceived the system, it was hard to imagine ANYTHING going down a highway over 40 tons. You simply gave it to the rail oligopolies to handle.The biggest flaw in the interstate system is that we allow anything to cross over them at all.
For just a few dollars more we could have had a nationwide system where NOTHING passed over the highways..
Interstate highways are the one place that I believe roundabouts are justified.
Now: have you ever watched North American drivers use a roundabout????? Would need a sea change in discipline, attitude and skills to be workable. Also, they would be a huge deterrent to use of LCVs. When we learn to run transportation better, you should expect to see "B" train triples and double 53s (we have them on some routes now) that should go forward to something approaching Ozzy road trains. Something NO BEV will ever be able to do unless half of their load is batteries. Yes, there IS an aviation tie-in here.
I am not sure how many people appreciate that one the THE keys to the post-war economy of USA is the Interstate system and the trucking business that uses it. Converseley: the death of it will come from the lawyers, regulators and financiers.