First, air temperature is just a critical as ground temperature in the formation of ice. Seldom will the ground be cold enough to form ice if the air blanketing it is above the freezing point of water...mostly because the water in the air is above the freezing point of water. Any water deposited on a cold surface is going to give up its heat to the surface warming the very top layers enough that surface where freezing can occur will quickly warm above the freezing point.

Well the "exhaust" from an internal combustion engine is composed of water and carbon dioxide. If the engine is running poorly, it may have a bit of unburned hydrocarbon in it...not likely in the age of catalytic converters...and, if it is starved for air, a bit of carbon monoxide...again not likely in the catalytic converter age. It will also have some oxides of nitrogen in it, although, again, that is handled by modern catalytic converters. Of the possible components of car exhaust...carbon dioxide, carbon monoxide, nitrogen oxides, unburned hydrocarbons and water...only water has any possible chance of condensing at temperatures experienced on the inhabited bits of Earth. Unburned hydrocarbons might condense out of the air if they were there quantities several fold higher than possible with even a poorly tuned IC engine and if the temperature was extremely cold. Even then, it is unlikely that hydrocarbons would form a visible cloud that water vapor does when it condenses.

The only component of a car's exhaust that can condense is the water vapor and, due to the properties of water and hydrogen bonding, form "clouds" that are visible. But, as I pointed out post 156 above, even if every last drop of water could be wrung out of a car's exhaust...which is impossible...there isn't enough water in car's exhaust (or even hundreds of car's exhausts) to cause icing. Yes, the water condenses out of the exhaust and some of it reaches the ground but most of it is going to be mixed with other air. If there is sufficient water in the air over the pavement or ground, it can condense out an form black ice (which is really just clear and colorless) on the road surface but the water vapor in car exhaust is going to be an insignificant contribution to the process.

I have little problem with the formation of "black ice" nor explanations on how it forms (with the exception of the idea that car exhaust contributes much to the issue). However to state that "there's no warning before you're on it" is just wrong. Americans over use the term. "I was just driving along when all of a sudden I hit a patch of black ice! No one could have predicted that it was there," is a very common statement...or I should say a very common excuse. "Black ice" doesn't magically appear. The conditions for its formation are very well known. Fog, drizzle, freezing drizzle, etc. all can form "black ice". People who claim they never saw it just aren't being very observant. Every time I've crashed on ice...and I've crashed on a lot of "black ice", I knew it was there or, at least, should have known it was there. It forms from melt water or from freezing drizzle or from a municipality not fixing a water main leak for around 15 years but it always comes with a warning. If I see water on the ground and the air temperature is below freezing and the ground has been cold for a few days, that's a "warning". Or if I'm driving my car and the temperature is below freezing and the road looks wet, that's a warning. Anything else is just an excuse for being unobservant.

I disagree...big surprise. In many decades of observing weather, I seen "black ice" on roads when the roads are warm (very common for Denver) and the air temperatures drop suddenly during a cold front. I've seen "black ice" during freezing drizzle storms in the spring when the roads are warmer here. I've seen "black ice" form during a snowstorm when the roads are still warm but the snow is melting and freezing. I've seen "black ice" following snow storms when the snow melts and runs across the road and refreezes at night when the air temperature drops. Sometimes it forms when the pavement is cold but, from my experience, it's just a likely to form when the roads are warm but are being cooled by an atmospheric event.