Originally Posted by Torrilin

Black ice doesn't actually sparkle when illuminated. That's the problem. It doesn't look wet, even in glaringly bright sunlight. At worst, the road surface looks clean. That's your tip-off, since the ground has to be very cold in order to get water to freeze so invisibly... so odds are there was a road salt layer everywhere. If it looks like the roads are pristine all of a sudden, get really suspicious. The change can happen very fast, even at a walking pace.