In my neck of the woods when you see a sign like that - Road Closed from Nov 1 to April 1, or some such, it means it is a seasonal road and they do not maintain the road (plow or otherwise) during the period specified. They (local municipalities) probably plow up an embankment to keep people out so they won't have to try and go in after them if they get stuck or go off the road.
My own road becomes 'seasonal' just down a bit. Once in November we had 3 local police cars, two tow trucks and a pickup all off the road - seems it snowed, then melted but froze up just enough to make the entire downslop pure ice. It was an incredible scene, it was also a major piece of work trying to get all of those vehicles out of there. Mikey.