Mysterious Japanese Guardrail Sabotage

Note: I lived in Saitama for three years, so it's pretty interesting to me to note that this is one of the central areas affected by this strange act: planting metal spikes in guardrails, to cut and damage those who pass too close. Note that Japan uses guardrails as a sort of vertical speedbump, too: instead of slowing to go over a bump in the road, you slow to pass through a narrow set of guardrails. If this were one of the things affected by this freakish form of sabotage, it would make getting around without badly damaging your paintjob a bit of a challenge!