I’m not super convinced by Maggie’s interpretation of the Discover blog’s explanation. If it’s from the exhaust condensate that “dribbl[es]” onto the roadway (presumably from the tailpipe), then you would expect black ice to be highly localized and appear primarily below tailpipes. Maybe condensation from exhaust fumes coming into contact with the ground causes black ice, but I’m not buying that it’s mainly dribblings.
I’ve experienced black ice on roads with relatively little traffic, and given the speed at which cars travel, the amount of exhaust moisture emitted per car per meter, and the dissipation patterns of vehicle exhaust, I would be very surprised if the black ice I’ve experienced comes primarily from car exhaust as opposed to fog or other meteorological phenomenon. Maybe on heavily trafficked roads cars could be a real contributor, but I’m having problems buying this as the predominant contributor to black ice: if it was true, black ice would be very predictable based on temperature and traffic, but this isn’t the case at all.
The Discover blog’s statement that “salt is also not as effective at freezing temperatures” is pretty ridiculous. Salt is really unnecessary in the absence of freezing temperatures, and is only effective after the temperature has dropped below freezing. And it’s only when it’s well below freezing (-21°C) that regular NaCl salt becomes ineffective.
