Not only that. As a general rule road markings are hidden beneath the snow, and often signs will be covered as well. You have to make an educated guess what they say. E.g. speed limit is based on contextual clues like road width, distance to treeline etc).

Really any technology that relies on signs and markings being visible will fail. There is little indication of where the road is. Often a fork in the road is not apparent because the plow has pushed up a snow bank that you must push through (but be careful not to get stuck in it if it’s too dense).

Combine this with heavy snow in the wind, road salt that picks up dirt that sticks to sensors, fog, and other cars that overtake you while spraying snow across your windshield. It’s honestly crazy that humans manage so well in these conditions.

Human eyes are way better at this than any camera based self driving system. No self driving system is anywhere close to driving in Swedish winter with bad weather and no sun, yet us Swedes do it routinely by the millions every day.