black ice 
noun [mass noun]
A transparent coating of ice, especially on a road surface.The A127 and A13 were particularly badly hit after several centimetres of snow fell overnight, compounded by black ice and a frost which hardened the snow into a virtual skating rink....
- Road conditions were bad after Wednesday night's rain led to areas of black ice on both roads and footpaths making driving conditions difficult for both drivers and pedestrians.
- The Longfield Road, which leads to Dundalk, is completely out of bounds because of the amount of black ice on the road.