The question of responsibility, while philosophically interesting wrt. increasingly autonomous machines, is not going to be an issue in practice. We'll end up dealing with it like we always do with multi-party responsibility in complex systems: regulators setting safety standards and outlining types and structures of liabiliy, contracts shifting the liability around, and lots and lots of insurance.

In fact, if you substitute "company providing self-driving solution (integrated software + hardware)" for "company renting out commercial drivers" (or machine operators), then self-driving cars already fit well into existing legal framework. The way I see it, the only change self-driving cars introduce here is that there is no individual operator we could blame for the accident, no specific human we could heavily fine or jail, and then feel good about ourselves because we've issued retributive justice and everything is whole now. Everything else has already long been worked out.