That's only one lane that is enforced to a varying degree (hardly in CA), and subject to cheating. I think in order for cars to become safer we need to force the human out of the driver's seat. Even if we had a hybrid system, self-driving is still subject to other human drivers. Try taking away the keys of Americans. I ride a motorcycle and I would miss riding if it came to forcing people to adopt self-driving, but that's how we reduce highway deaths.
Edit: now that I think about it, cheating could be enforced by camera. Assuming the road had a computer network (like a much more reliable Bluetooth), I am sure cars could identify an unauthorized manually-driven vehicle and alert authorities.
I suspect there'd be a strong selection bias where the only people who'd continue to drive manually would be the better (or at least more attentive) drivers.
To enforce that, you could make the licensing regime more like an FAA private pilot rating and less like a token ritual for access to your God-given right to drive no matter how incompetent.
