Not the most dangerous, but the strangest event I've encountered while driving. One cool morning I left Austin heading south to San Antonio on I35. All the windows were rolled up and the AC was not on. Apparently I drove through a warm front about twenty miles down the road. I was cruising at about 75 with little or no traffic. Apparently I crossed into a warm (humid) front because every window instantly and completely fogged up. I was suddenly blind at 75mph. The highway was straight so I was able to pull the car over and wait for the AC to clear the windows. I understand the chemistry involved, but that doesn't help when you're in the middle of it all.
