Something I never understood is why the highways would be so clogged up with cars. Captain Tripps wasn't exactly a fast moving virus. I wouldn't think most people would get stuck in their cars dying on the road so that things would be so clogged up. MAYBE around the cities a bit, but I would think the superful would keep most people in bed instead of driving.
Also, I read "Earth Abides" by George Stewart after hearing that it was an influence on King's work for The Stand. GREAT book, highly recommend it.