Minnesota is getting still more ice/sleet/freezing rain/snow today. We will see piles of snow for a long time. Why will we see piles of snow? Because we piled it up. The snow on top acts as insulation for the snow below.
Imagine there is a winter where we get 1 meter of snow (in fact the average for Minneapolis is 1.26 m of snowfall). On the 1 m wide boulevard between the 1 m wide sidewalk and the street, we get 1.5 meters high of snow, as we transport half the snow from the sidewalk to the boulevard to "clear the sidewalk" (the other half goes into the yard maybe, if we have yards. If we have buildings, it all goes to the boulevard). (I realize this is not all at one time, which complicates the model but does not change the basic point).
If the snow melts and sublimates at 5 cm/day (this varies), (and water (liquid snow) refreezes at night), instead of 20 mornings of icy sidewalks, we have 40 hazardous mornings. We have approximately doubled the problem.
This problem in embiggened when you add the snow plows piling additional snow onto the boulevard. In this case we take a 10 m wide street and pile 5 m x 1 m of snow on the boulevard on each side. Now we have put not just 0.5 m from the sidewalk but an additional 5 m of snow on each Boulevard. So the Boulevard is responsible for storing 5.5 m of snowfall over the course of the winter. The ground absorbs very little since it is frozen.
Fortunately, cars are local urban heat islands, so the road is warmer than the sidewalk, and the snow melts back towards the roads at a faster rate than on the sidewalk. Unfortunately, sidewalks are interrupted by streets, which are now icy and slushy in the gutter in the morning. Similarly, we are fortunate that buildings are urban heat islands. Unfortunately, new buildings are well-insulated, greedily keeping their warmth rather than sharing it with the adjacent sidewalks.
For the purposes of walking, I wonder whether it might be better to not shovel or plow at all, and take the inconvenience of walking (driving) through snow, than to shovel and increase the duration over which we must traverse ice and slush. This might be a case of getting punished for doing the "right thing."
An alternatives is to actually move the snow off the sidewalk's upstream water-basin. In large cities, we might take the snow piles and put them to the side away from the walk path. This answers the questions: Surface parking lots, what are they good for?
Cartoon from AMAZING FACTS...AND BEYOND! WITH LEON BEYOND