The I-35W Mississippi River bridge in Minneapolis, Minnesota, was well known for its black ice before it collapsed in 2007 into the Mississippi River. The I-35W Mississippi River bridge seen from below in 2006 Over 100 cars were involved in the pileup and multiple fatalities were reported. On February 11, 2021, icing in Dallas and Fort Worth, Texas, contributed to a crash on I-35W which authorities called a "mass casualty event".
DIAMOND ICE DRIVER DRIVERS
The ice formed suddenly on a long downward slope, surprising drivers coming over the crest of a hill, who could not see crashed vehicles ahead until it was too late to stop on the slick pavement.
DIAMOND ICE DRIVER SERIES
A chain reaction series of crashes resulted, involving three tractor-trailers and over 60 other vehicles. On December 1, 2013, heavy post-Thanksgiving weekend traffic encountered black ice on the westbound I-290 expressway in Worcester, Massachusetts. Black ice may form even when the ambient temperature is several degrees above the freezing point of water 0 ☌ (32 ☏), if the air warms suddenly after a prolonged cold spell that has left the surface of the roadway well below the freezing point of water. Salt's ineffectiveness at melting ice at these temperatures compounds the problem. Such conditions caused multiple accidents in Minnesota when the temperatures dipped below −18 ☌ (0 ☏) for a prolonged period of time in mid-December 2008.
Other compounds such as magnesium chloride or calcium chloride have been used for extremely cold temperatures since the freezing-point depression of their solutions is lower.Īt low temperatures (below −18 ☌ ), black ice can form on roadways when the moisture from automobile exhaust, such as motorcycles and cars, condenses on the road surface. Deicing with salt ( sodium chloride) is effective down to temperatures of about −18 ☌ (0 ☏). This condition makes driving, cycling or walking on affected surfaces extremely dangerous. In addition, it is often interleaved with wet pavement, which is nearly identical in appearance. The American Meteorological Society Glossary of Meteorology includes the definition of black ice as "a thin sheet of ice, relatively dark in appearance, may form when light rain or drizzle falls on a road surface that is at a temperature below 0 ☌ (32 ☏)." Because it represents only a thin accumulation, black ice is highly transparent and thus difficult to see compared with snow, frozen slush, or thicker ice layers. On lakes, black ice is also commonly overlain by white ice formed from refrozen snow or slush.įormation On roads and pavements Thin, new ice on freshwater or saltwater, appearing dark in color because of its transparency, a result of its columnar grain structure.It may also be formed when supercooled fog droplets are intercepted by buildings, fences, and vegetation. A thin sheet of ice, relatively dark in appearance, may form when light rain or drizzle falls on a road surface that is at a temperature below 0 ☌ or, alternatively, when water already on the road surface subsequently freezes when its temperature falls below freezing point. A popular alternative for the term "glaze".The World Meteorological Organization definitions of black ice are:
Black ice can also form when roadways are slick from rain and temperatures drop below freezing overnight." It is most prevalent during the early morning hours, especially after snowmelt on the roadways has a chance to refreeze overnight when the temperature drops below freezing. It is often clear (not white) with the black road surface visible underneath. The term "black ice" in the United States is defined by the National Weather Service as "patchy ice on roadways or other transportation surfaces that cannot easily be seen. There is, thus, a risk of slippage and subsequent accident due to the unexpected loss of traction. The typically low levels of noticeable ice pellets, snow, or sleet surrounding black ice means that areas of the ice are often practically invisible to drivers or people stepping on it. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it. Warning sign for icy pavement in Quebec, Canadaīlack ice, sometimes called clear ice, is a thin coating of glaze ice on a surface, especially on streets.
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