in the big smoke its not an issue of snow but more ice and slippery intersections where cars idle their hot exhaust onto the pavement where the moisture in it turns to ice and freezes (thus black ice).
Perhaps there are regional differences in how road conditions are described.
In BC, black ice is used to describe a veneer of ice that forms in patches where the micro climate has fallen below zero. The ice isn't visible - hence the name - because it's nothing more than frozen atmospheric moisture, not pooled water. It tends to form in areas that are in shadows or exposed to flowing cold air like a bridge. Road conditions go from normal to zero traction within a few feet.
In the lower mainland the ice at snow covered intersections results from the snow being compacted by passing cars. The process is very much like the ice that forms on the well travelled areas of a ski run over the course of the day.
The ice is most prevelant in the last few feet approaching the intersection where cars are either braking or accelerating. It isn't present further back where cars are idling waiting for signal changes. Out here, at least, the heat of passing cars doesn't appear to have anything to do with the formation of ice.
Vancouver is a very challenging place to drive in the snow. The coefficient of friction on snow is lowest when temperatures are hovering around zero. The coefficient goes up and stabilizes below -10C or so if memory serves me well.
When it's snowing our temperatures are usually close to zero so it's very slippery. Add to that many hills, a substantial percentage of inexperienced drivers, few winter tires, small snow removal budgets, and an already congested road system to create a nightmare.
