I still can't see, gromit, how that combination with normal humans will ever work.
No matter what the technology is (unless it literally is 100%), it is just never going to work with people. You can't give people nothing to do or be responsible for, while still expecting them to be alert at every moment. That just isn't how we work.
Surely, most people have been a passenger in a car... where they haven't had to be "in control" of it, and have drifted off in their mind at some point, because of that. If you think this is a good idea... try paying full attention every time you are a passenger im future, and see how much you really concentrate.
The worst thing is, these are the best statistics. Any of us, getting a "self-driving" car, would be really alert to begin with, naturally. But the longer drivers go without a problem, the less they will pay attention. People will get more and more blase, the longer it goes on. So, not impressed so far...