I had a similar thought from my time living in Alaska. half the year there aren't any lines on the road other than the occasional tracks from the previous car that drove on it, and that's if the wind is low. It's not unusual to have half the road covered in a foot or two of snow from a drift. Humans can see them and usually avoid them, but it involves strategically using the oncoming lane. Would be interesting to see the nav system deal with that!