The 'wrong problem' might include trying to achieve everything with smart-as-an-ant cars on dumb roads. It may be possible to make any important road smarter inexpensively, so that the car's sensors could 'read' the road. Then the car has external, deterministic 'input'.

By reading the road, pinging dumb targets, the car has input to help it decide if it can drive safely. If the targets go missing, it quits safely. The dumb targets should ping thru snow. At certain intervals, the road is smarter, with powered, networked targets that can update the car about 'danger, Will Robinson' conditions in real-time.