If the cars obey the posted speed limit and slow down and split-the-difference when on curves or near hazards (such as children running on the sidewalk), the hypothetical moral dilemmas shouldn't even happen. So far, I've only heard of one accident involving a Google car, and there wasn't a fatality.
Natural environment/human/animal behaviour related issues kind of throw a wrench in that idea.
Yes, in normal conditions you shouldn't ever be in a situation where the 'trolley problem' is relevant. But it's also quite easy to imagine external factors that might make it unavoidable. Like say, a car running out of power in the middle of the road, falling trees, buildings, fences or other obstacles, people or animals in the road, natural disasters or freak weather conditions.
All of these situations open up a possibility that the car won't have enough time to stop regardless of the speed limit.
