some places are ploughed, some places are not.
Why? I don't know.
One thing is for sure, I like the unploughed sections, because the winter tires roll better on that, than bare pavement.
Problem with unploughed sections is that you can be rolling through on some light snow, then hit a major drift and stop suddenly in your tracks. This is more of a problem if you are riding at night when it's hard to gauge snow depth.