Bad weather and unexpected obstacles like pedestrians are actually trivial to handle. Remember that an autopilot's "visual" perception isn't limited to the visible-light range like ours is.

Poorly-maintained roads are the problem that would give me nightmares if I worked on these. Lane markers that might have been perfectly usable when the database was compiled may be too worn out or obscured by snow, leaves, or who-knows-what else to be usable later. How can you design a system to fail safely when every input source is independently fallible? And how can we redesign the auto insurance industry to make it possible to try?