If all the AI did was decide you're unfit to drive, that it take over for a few minutes to get to the next stop and pull over and call the cops on you, we might save more lives by that alone.
For stopping people from driving, you'd have to solve the social issues there first somehow. "Our car stops you from driving if it thinks you're incompetent" isn't something that sells more cars. Maybe the government could mandate it, and that's the government's responsibility.
I could see something like that as part of a “supervised driver” safety feature. Like maybe you enable it when your kids use the car or if you rent the car out to strangers.
Why not just install the existing breathalyzers in every car right now?
Hit by a human, decent chance they flee and if you track them down, it’ll probably be some uninsured drunk with a negative net worth.