With sub-zero temperatures predicted for this weekend, the Minnesota Department of Transportation is urging drivers to be alert for "black ice," which can rapidly develop during extremely cold temperatures.
Black ice forms when the air temperature is just slightly warmer than the pavement, which causes moisture to rapidly freeze and create a thin and almost transparent layer of ice on the roadway, according to a Mn/DOT news release.
It forms on heavily traveled highways from auto exhaust emissions and moisture vapors from nearby buildings. Black ice also forms on roadways in shaded areas, near lakes and rivers, in tunnels and on overpasses, according to Mn/DOT.
Road salt begins to lose its effectiveness against black ice at temperatures lower than 15 degrees.
