With the recent daytime melting and the below freezing temperatures at night, black ice has been forming on area roadways. The ice that forms isn't really black, it's exceptionally clear. This allows the color of the roadway to shine through. Roads are often made of black asphalt so we call it "black ice".
The reason for it's transparency is the lack of air bubbles trapped in the ice. The more air trapped inside, the higher the reflectivity of the ice. This lack of bubbles makes it difficult to see and exceptionally slippery. Especially if the pavement is wet to begin with. You may be driving along on a wet roadway and not even realize the road surface has turned to ice until it's too late.
Black Ice will often form on bridges and overpasses first. Cold air can circulate under these structures and cool more quickly than surrounding roads.
When humidity is high and temperature are below freezing be careful and slow down.

Mike Wankum
Meteorologist
WCVB-TV