Another thing I haven't seen discussed anywhere is how easy these cars are to fool.
eg. What happens if a bunch of youtube idiots make some fake "Stop" signs and goes out to the autobahn to hold them up?
A human driver will easily ignore them but what will a robot car do? Emergency braking?
Rumor says that if you place a beautiful naked woman beside a busy street, it won't be long before there are multiple crashes. (How will the Mythbusters test that in a safe and ethical way?) The self driving cars will probably recognize her as just another person.
I've also heard that billboards with ads for underwear increase the probability for crashes!
How easy it is to fool an autonomous car is an interesting question. I don't think anyone can answer that except people who actually work with it since I assume it's not something the companies divulge freely.
I think someone mentioned that in the early days the google cars would think a life-size cutout of a person (i.e. ads) next to the road were real pedestrians, and if they were standing next to a zebra crossing, it would cause the car to think they were about to cross and slow down/stop. But these days they can tell the difference apparently.
There was also a demo of a facial recognition program in the tv-segment about Chinese surveillance technology that was posted above. In that example the software was able to tell that a life size printed image of a face was not a real face of a living person. What it takes to fool that system wasn't clear though. But if it was not a problem that some facial recognition systems are easy to fool with just a picture they would not have featured that technology I guess.
It will probably be possible to fool robot cars to some extent, but I assume they prioritise safety over traffic rules at least. So if following a law would cause a crash, or conversely if breaking a law means it can avoid an almost certain crash, the car would choose to break the law. But to program such behaviour into the software sounds a lot like the developers are planning to break the law. That kind of issues are probably giving them and their lawyers a headache.
I've heard that they have to bend the rules a little just to be able to drive normally. For example if a traffic sign just turned yellow you should stop if possible, but when they did that other cars behind them often did not keep enough distance and would sometimes crash into them because they wouldn't expect anyone to stop suddenly in that situation. Another problem was getting onto a busy freeway or traversing a busy intersection, if they followed the rules perfectly they would have to wait forever which is not what human drivers do.
If it meant avoiding a serious accident I think most would agree it is acceptable to break the law (sometimes even the law itself says so). But what about less serious accidents, or when both actions could cause an accident but breaking the law is less likely to do so. etc. It's not an easy problem to solve.