On Monday evening I was stuck for three hours on the main dual carriageway from the M1 down to the "Magic Roundabout" in Hemel Hempstead. There were two miles of black ice. It was so slippery that even when stationary with the hand brake on my car started to slide down the not very steep slope. Luckily braking all four wheels with the footbrake was okay. I'm glad to say there didn't seem to have been any collisions.