You've seen the signs, "Bridge May Be Icy." Those are the roadways most likely to develop black ice. Black ice is also identified as glare or clear ice. The American Meteorological Society defines it as a thin sheet of ice, relatively dark in appearance due to the black asphalt/macadam roadway color.
While the air temperature may be above freezing, the surface temperature is lower. Combine these cold temperatures with light rain, drizzle or fog and you have dangerous conditions especially over raised surfaces like bridges and overpasses.
Not only can this be an almost invisible headache for drivers, but can cause you to lose your footing while walking on the sidewalk or in the parking lot. Similar thin layers of ice forming on a ship can cause a problem with balance. Mountain climbers call the same conditions verglas.
