"black ice" vs. "glare ice" vs. "glaze" in NAmEng

What's the difference between those varieties of ice forming on paved surfaces during the cold season?

black ice

sometimes called clear ice: a thin, nearly invisible coating of ice that forms on paved surfaces. AHD

glare ice

: a thin coating of ice (as from freezing mist) on a road or sidewalk; nearly invisible but very hazardous Memidex

glare

n A sheet or surface of glassy and very slippery ice. AHD

adj (US and Canadian) smooth and glassy: glare ice. CED

glaze

: a thin glassy coating of ice. AHD

: a smooth slippery coating of thin ice M-W

: (US: ice) verglas (Collins-Robert French and English Dictionary, Ed. 1985)

The differences between black, glare and glaze ice on paved surfaces are colloquial, regional and attributive. The terms are often used interchangably, and the sense of each overlaps with the others. So, without accounting for regionalism and localism, the distinctions I know from personal experience with the use of the terms in cold climates are these:

black ice on paved surfaces may or may not appear black. It is effectively invisible while traveling, even at pedestrian speeds, but the term is applied when water freezes on a paved surface in such a way as to compromise traction. I first encountered the term black ice used with this sense in Washington State (> 1990). In my prior experience with the term black ice in Minnesota (1970-1990), it was applied exclusively to lake ice frozen without many air bubbles. In that case, the ice appears black. With that reference, such ice was highly prized by ice skaters and ice boaters, for its smooth surface and transparency, and by others for its outstanding scenic properties.

glare and glaze ice on paved surfaces, unlike black ice, reflects light, as suggested by the names, and so is sometimes visible. The two terms are used interchangably, but my observations indicate that glare is sometimes used to distinguish a thinner ice layer from the thicker layer formed by glaze ice. These observations are supported by my observations of the use of glaze ice in, for example, Oklahoma (< 1970), to describe the coating of surfaces and structures, including the twigs and branches of trees and shrubs, etc., with a layer of ice more than one quarter inch thick. While glare ice might be used with the same reference, the use of glaze as the descriptor was more common.

As mentioned, with reference to ice on pavement, black, glare and glaze are often used interchangably by individual speakers in all regions where I've encountered the terms. With reference to ice on surfaces other than pavement, the choice of term is more likely to be specific to the most notable attribute of the ice, that is, whether it appears black, reflects glare, or glazes surfaces and structures.

Here in Minnesota the most significant term of the above is "black ice". This term describes what you get when a thin layer of ice coats a relatively smooth asphalt or concrete roadway, so thin that the ice doesn't quite fill in all the voids in the paving material. That is, there are still some bits of paving material projecting above the ice.

One might think that so long as there is SOME paving material projecting above the ice surface then the ice would not be a problem, but this is not the case. The surface may seem sound from a traction standpoint, but as soon as one makes, say, a slight directional adjustment to center the car in the lane traction may suddenly be lost, sending the car into a violent skid.

The problem with "black ice" is that it's so deceptive. Because the ice is down inside the little indentations of the road surface it behaves in a way that very little light from the headlights can be reflected back to the driver -- the roadway appears black, as if it were simply wet. You also don't get, eg, the glare from the headlights of the car ahead that you would get from "glare" ice. And, because there is SOME traction, it's easy to become over-confident and drive at a speed that is inappropriate for the actual roadway conditions.

My husband uses "glare ice" but I thought he made it up because I've never heard anyone else refer to it this way. I would say a glaze of ice, personally. A lot of news media use black ice.