You forgot to mention that all of the mountain passes and hiway overpasses are already prepared for demolition. Have been for thirty or forty years. Also the tanks aren't much good once the weather turns better and the rice paddies thaw. They will be stuck on the roads and the roads will be impassible. The NK airforce is a joke and the US and SK flyboys will have a turkey shoot that will make the "Hiway of Death" look like a sunday school picnic.
RE #10
I agree. To cite an example, there are many funny-looking gates over the road to the north of Seoul. They have two concrete slabs working as pillars on each side of a road. And the really big concrete slab on the top, too big. Once N. Korean troops invades, the pillars are to be demolished and the top part will be on the ground, blocking the advance of N. Korea columns.