It doesn't require government action. Insurance will see computers causing fewer accidents, requiring lower payouts and adjusting rates accordingly. Penalties for drunk drivers might become harsher because they now have an alternative. Ditto for old people. Commuters will like having their hands and eyes free. Robo taxis will also make a dent in the market. Over time the number of human-driven vehicles will decrease on its own and it'll make less sense to get a driving permit in the first place.
My understanding is that that is a punishable offense in most states, so that's a matter of consistently enforcing existing laws rather than introducing any new ones.
Anyway, the mechanisms I have listed can still drive adoption of self-driving cars and reduce the number of human-driven cars on the road which also reduces the number of fatalities if the self-driving ones outperform humans. And if we look at QALYs instead of fatalities there may be additional benefits.
Unless the government is taking everyone else except the imaginary future perfect robots off the road, its all a moot point.