Also remember that driving outside of the US presents other challenges. Roundabouts are everywhere in many countries. Sometimes you'll come across a gyratory, which is a bunch of mini roundabouts around a larger one, and you can opt to go one way or another. In the UK, and I assume many other countries, if a pedestrian is waiting at a 'zebra crossing', it's the law to stop. Road construction is marked differently everywhere. Fortunately in the UK there's no such thing as a 4 way stop, but even the logic needed there is complicated. It's bad enough with humans, but I can see a time when 4 Tesla's roll up, and they all try to stutter their way though because each keeps yielding to the other. Solving 80% of the problem is relatively within grasp. The other 20% required for full autonomy is incredibly complicated.