"Alert and aware human" is already a high standard, given how most humans drive in routine mode, which is well understood to be much worse than "alert and aware".

From what I've seen I wouldn't trust autonomous cars to "understand" all situations. I would trust Waymo cars to understand enough to avoid hitting anything (at a level better than a human), at the risk of being rear-ended more often. Everything I've seen from Tesla and Uber has given me significantly less confidence than that.