I would imagine that the initial complexity of the autonomous cars would be rather low. Something like an "enhanced cruise control" made for freeway driving. even speeds, predictable roads, plenty of "targets" to bounce range finding sensors off of, no pedestrians. It could probably even be done by sensing the flow of traffic around you paired rudimentary lane imaging/recognition and gps. perhaps in a traffic jam you could just read a book while your vehicle crawls along, starting and stopping itself.
of course the manufacturer would have some kind of interface stating that the driver is still responsible for the vehicle, all liability rests on the driver, watch the road attentively while the car drives itself ready to take control manually etc etc, much like cruise control, it would probably disengage at the slightest bump of the controls (foot on gas or brake, touch the steering wheel)
It could even have minimum parameters for engaging, such as lanes not marked brightly enough, not enough cars around to flow with, etc. its not insane to think that construction sites could put up radio beacons that warn autopilots to sound an alarm requiring the driver to take over as the site is approached. Heavy fines (like the traffic fines double) could be in place when someone is observed approaching the construction site under autopilot.
Personally i don't think we'll see automated cars in busy intersection traffic for quite some time.
If no law permits it, though, there isn't any market, and thus no R&D or products (usually), so making these laws is the first step towards innovation.
We've all heard the idea that we won't have flying cars until cars drive themselves. I think this is a huge step and really awesome!
