There's a lot of private plow operators doing driveways and parking lots in their pickups, for many of them it's a chance for a second paycheck and they put in as much time as they can, often after working a full-time job. I wouldn't trust them to be seeing straight after a night of plowing. I also don't think that there is much regulation for the private plow operators.
City and especially highway plows can be very large with not only big plows on the front, but wings on the side. MassDOT announced a super-plow this fall with a side mounted plow designed to clear two lanes at once; I they said during the announcement that it would be limited to highway work. Headlights get covered with snow and if its somewhat warm salted slush that dries on the headlamps making visibility even worse.
Pay attention to what is coming up behind you - you can often hear road plows as they scrape along. If one comes up behind you, get off the road and let them do their job.