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.