We can start by putting the autonomous vehicles to the driver license test to see if they can just pass the lowest standard of driving, ie the quality of a novice driver. If they can't do that without instructor needing to step in then just like the novice they shouldn't be allowed on the roads without a licensed driver to oversee them.
That is the bar that autonomous vehicles need to reach. Crash rate of zero is not required, through if it is higher than the average driver then it might be worth to make the license requirements higher.
This doesn't seem like a very high bar to pass. Around here a drivers test involves a short stint on a low speed closed course with a few intersections and then a parallel parking test. Our current self driving systems should have no trouble with that once they are informed what you expect.
I guess every country has their own set of expectations and rules for what qualify for operating a car in a safe manner.
Where I live the practical part of the driver exam is 30m of driving in mixed environment, usually involving a number of environments (based on what the driver inspector can find that day). Those involve city driving, country driving and on-off to the highway, with a number of events such as driving in areas where there are pedestrians/cyclists/children, crossing railway, lane changes, roundabouts, passing construction work, and so on. Just like with a driver instructor the car has double controls, but if the inspector has to take control of the car to prevent an accident then its an automatic fail and the person has to retake the test at a later date. Minor failures can be accepted, through the basic concept is that a person who can't drive around for 30 minutes without causing an accident shouldn't be on the road.
That is the bar that autonomous vehicles need to reach. Crash rate of zero is not required, through if it is higher than the average driver then it might be worth to make the license requirements higher.