An autonomous driving AI doesn't need to perform like a professional racing driver in order to improve safety.
The causes of most crashes are human fallibilities that AI doesn't suffer from:
An AI isn't tempted to drive drunk. It isn't distracted by incoming text messages. It doesn't get fatigued after driving for hours late at night. It doesn't suffer from road rage, and it isn't tempted to drive aggressively and take risks because it's running late for work. Just by avoiding these issues you've made driving a lot safer!
An AI also has reaction times that no human can match, has no blind spots and can track other vehicles in 360 degrees at once, and "see" through fog and rain using radar to detect obstacles.
Conversely, some of the things that are easy for humans are also the most difficult for AI to grasp: the social cues that we use to resolve pathing conflicts (eye contact, a wave, a blink of the headlights, etc), or our ability to intuitively predict the behaviour of other road users.
So while we may be some way yet from true, socially-accepted Level 5 autonomy, we're not far at all from semi-autonomous, driver-assistance technologies that significantly improve safety.