The plan for West Germany in case of a sudden Soviet invasion was to destroy bridges and railways, render tunnels unusable by dropping huge concrete blocks on the entrances or – my favourite – filling them with foam so Diesel motors would suffocate while driving through; and destroying many roads.
All just to buy a little time to be able to mount an actual defence against the invasion in France.
The plan for West Germany was to use nuclear land mines in the Fulda Gap to both destroy whole divisions en route and to create massive geological barriers.
I think in Korea (not sure if the pictures I saw were taken in the North or South) there are the same type of preparations, with obstacles ready to be deployed on N-S roads, like concrete block above the road ready to be dropped.
All just to buy a little time to be able to mount an actual defence against the invasion in France.