How good are they so far?

The important point is how often do the emergency drivers have to take over, and in what circumstances? That eight year figure implies there's still a lot of problems.

The really difficult bit will come when they are better than humans in most circumstances. You might find that they would reduce accidents overall, but fail in a few rare circumstances where a human could have coped. Do you then deploy them? And what is the legal position for the victims of those rare accidents? It could get very messy, especially with US lawyers involved.