For years, even decades, I've heard this cited as if it's a legal can of worms that makes the whole notion of automated driving a political impossibility, so to speak, in the foreseeable future. Sure, it would save a lot of lives, the argument goes, but the rare failures would bring down a deluge of lawsuits that would crush any manufacturer foolish enough to try to mass-produce something like this.
I don't think that's the case, even taking as a given America's disgusting obsession with lawsuits. There's an obvious answer to the liability question, and one that I think Google is already depending on in allowing their robot cars to drive all over California: The person in the driver's seat is responsible as always. That person can choose to press the autopilot button but it's not fundamentally different than cruise control. Touching the brakes (or the steering wheel) immediately transfers control back to the driver. The car is doing what it does, as always, strictly as the driver's proxy.
Now of course it will happen that some driver sues the manufacturer because there was an accident they believe wouldn't have happened if they'd never gone on autopilot. Just like there have been (I blithely presume) lawsuits over cruise control. But the manufacturer will weather those lawsuits and reasonable legal precedent will be established soon enough.
But now suppose you press autopilot, go to sleep, and wake up to find you've committed vehicular homicide. That's a scary thought, but is it a potential dealbreaker in bringing this to the mass market? I think the answer is no, because we've already established the liability question: You were, officially and legally speaking, criminally negligent to go to sleep. Unofficially it might well have been a perfectly reasonable risk to have taken, if the probability of it ending in tragegy is sufficiently low. Logically, you could argue, citing statistics on human and robot drivers, that going to sleep with the car on autopilot was markedly less negligent than not putting the car on autopilot at all. I don't know if that would fly in court. But as far as legal obstacles to adoption of robot cars, I don't see it as much of an issue.
PS: I'm not a lawyer.