There are almost no cars in North Korea, yet the country has a meticulously maintained road system. Part of this is because of the fact that it can be used for military purposes. It can also be used by other invading militaries, however — and the way North Korea deals with that proves just how little interest Pyongyang has in peace.
If you go to the demilitarized zone between North and South Korea, you’re going to see some very odd structures on the side of the road when you pass on over to the North’s side of things.
According to a June, 2010, article in Stars and Stripes, they’re known as “North Korean speed bumps,” rock drops or tank traps. Basically, it’s part of a surprise strategy: In the event of an invasion, the North Koreans would topple them over into the road and make it impossible for tanks to quickly navigate through the mess.