“Black ice” was originally used to describe a thin layer of new ice on fresh or salt water. Its transparency made it appear dark or “black” in color. The term was also used by mariners to describe a form of icing that was sometimes sufficiently heavy to capsize small ships. As modes of transportation changed however, so did the words’ most common meaning. In the United States today, “black ice” typically refers to a thin layer of ice on a road or sidewalk. Often left by freezing mist or fog, it is nearly invisible. But it is also extremely hazardous. This is due not only to its transparent nature, but also to the unexpected slickness it produces. You can be driving along, see no change in the surface of the highway, but suddenly find your car’s tires have lost all traction.
Mary Knapp, Weather Data Library