In theory autonomous care would be able to include a number of other factor to decide if they are on the road or not. Including, GPS, wifi signals, the grade of the road, the texture of the road, etc.
What about situations where lanes have been plowed off-center? Even the most accurate GPS and accelerometers aren't going to help the vehicle understand that the appropriate path has been shifted.
The car would still factor in the 3d analysis of nearby objects so assuming the use technology that works in heavy snow/rain fall they wouldn't run into anything.
