Thanks, came here to say the same thing.
Having survived at least three accidents from black ice, all of them nowhere near city streets, I find that it’s generally caused by snow melt in mild weather or rain, followed by cold air.
[Edited to add:] Water dripping from tail pipes give you pebbly, rough ice - akin to curling ice. While slippery, it’s not as slick as black ice, and can provide good grip.
For one, a kilometer-long patch was the result of rain which turned to very slick ice when the sun set.
The second was a short stretch of less-traveled very cold (around -32degC) road that was almost perpetually in shadow from the tall trees lining it and had acquired a thin veneer of ice from the air moisture, akin to the article’s car exhaust claim. And I just barely missed being flattened into a paste by the logging truck coming the other way.
The third time was the highway between Montreal and Ottawa - very cold day, short patch of black ice. Nope, not car exhaust.
And ditto: salt is pointless above zero and useless when very cold. In this case, you need grit, not salt. The salt isn’t supposed to ‘melt’ the ice. It’s meant to break the ice up, by melting holes in it, so the plows can, er, plow it off the road.
An alternative to road salt is brine, sprayed on the road before the crappy weather, which makes it difficult for the snow/ice to stick to the road.
Black ice is treacherous, nasty, stuff.
