Not a complete list but I believe these all must exist before broad general acceptance.
1 Autonomous driving becomes better than human driving, including "edge cases" (e.g., junk falling from a truck, ball rolling out in front of car, etc).
2 Some way to deal with the inevitable liabilities. Cars will still kill people. Maybe something built into all car insurance and/or into the price of cars to fund liability payments.
3 Some way to deal with all the insane people in non-automated cars.