I Guess I don’t see anything wrong with what happen, I do believe it is a illegal to plow snow across a public road way.
If this is truly the case, don’t you think we have let our local/county governments have a bit too much power? This probably happened because someone pushed their snow across a road and left huge piles of it on the road, which someone hit and maybe got hurt. So the answer is now nobody can plow across the road.
I would keep doing what you are doing. Make certain to clean it up 100% after you are done. Snap a few pictures when done and wait for the ticket in the mail. When you go to court, you now have all of the evidence you need to fight the ticket. Ask the judge, respectfully of course, what you are to do with the 20 cy of snow that was deposited by the plow truck at the end of your driveway. Chances are, the ticket gets thrown out, which will set the future precedence for local law enforcement to act. Eventually, if enough people do this, the law will be called into question and likely ignored or possibly removed from the legal books.
This is a great example of when we as the people can stand up and fight overreaching laws of the local government.