When it snows we have the problem with areas that are cleared turning to black ice at night when the temperatures drop. Snow melt runoff runs right across our driveway and the driveway doesn't dry during the day so it becomes a skating rink in the dark. Sometimes it's safer to leave the icy snow patches, at least you can see where it's actually slippery.
Ah ... Yah, I've observed that phenomenon before. Nasty. But not something that usually happens on my block (because of which way things slope and the limits on where snow can pile up, I guess) -- when I've seen it at all here it's been a stripe a few inches wide, easy to step over if you can see it; and my block is well lit (enough so to make it easy to forget to turn on one's headlights at 2AM, and the sidewalks are as brightly lit as the street), making the shiny patches easy to see on the rare occasions when a thin layer of melt freezes like that.
So I agree that in some places it is safer to leave the snow there, and have seen such, but that's not the case here. (Also, it's not going to get too cold for salt to keep thin layers from freezing for a while yet down here.) The sections that have been cleared are dry. (Actually, what you described is more likely to be a problem over on the sunny side of the street, now that I stop to think of where I've seen those shiny patches nearby.)
BTW, I never used to think much of using salt until I moved into Baltimore, but ice formation patterns in the city seem different than in the suburbs. The likely nasty surprises here are footprints made before you get out there with the shovel, making stuck-to-the-pavement spots that Really Don't Want To Come Up with the shovel (and are sometimes too thin for whacking them with the end of a heavy pole to work). Small enough to be easily overlooked, and usually not shiny, but slick; land a foot just wrong ... between those and freezing rain / sleet, and of course stone front steps, salt seems pretty important here.
One of the problems with using rocksalt on the driveway is that the water running across the driveway washes it away before it can do any good. And you really do need that water for it to work properly. Once it starts to melt the ice, the water just runs off taking the rest of the salt with it.
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So I agree that in some places it is safer to leave the snow there, and have seen such, but that's not the case here. (Also, it's not going to get too cold for salt to keep thin layers from freezing for a while yet down here.) The sections that have been cleared are dry. (Actually, what you described is more likely to be a problem over on the sunny side of the street, now that I stop to think of where I've seen those shiny patches nearby.)
BTW, I never used to think much of using salt until I moved into Baltimore, but ice formation patterns in the city seem different than in the suburbs. The likely nasty surprises here are footprints made before you get out there with the shovel, making stuck-to-the-pavement spots that Really Don't Want To Come Up with the shovel (and are sometimes too thin for whacking them with the end of a heavy pole to work). Small enough to be easily overlooked, and usually not shiny, but slick; land a foot just wrong ... between those and freezing rain / sleet, and of course stone front steps, salt seems pretty important here.
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