So every time there's oncoming traffic (or a person on a sidewalk nearby) you'd have to stop until they were past, just in case they decide to turn/step in fron

So every time there's oncoming traffic (or a person on a sidewalk nearby) you'd have to stop until they were past, just in case they decide to turn/step in front of you. As long as there are other actors in the world who may behave irrationally I don't think you have to work too hard to come up with either/or scenarios for the AI to deal with. And even if the irrationality is removed there's still a chance of mechanical failure (e.g. tire blowout causes loss of control) which other AIs may need to make decisions on how to avoid.