Thursday, December 29, 2011
When ice forms unexpectedly on roadways it often is called black ice because it is so difficult to detect and it is often unexpected.
Black ice frequently is obscured because it typically is a thin layer of ice. Black asphalt or concrete frequently is still visible through the thin layer of clear ice, making it even more difficult to detect.
The thin ice forms on bridges and overpasses before the rest of the roadway. Cold air can circulate both above and below the surfaces of elevated roadways, causing bridge and overpass temperatures to drop more rapidly and freeze quicker than the rest of the roadway.