AI will need to be better than a good human driver, so these kinds of comparisons are not helpful. A good human driver would back up out of the way of the truck and/or sound the horn. If this is too hard for AI, then it is not ready.
AI needs to be better than the average human driver to drastically reduce accidents and deaths. We agree on the horn though, it should know when to honk at things.
A SDC needs to be better than humans on average to be a safer choice. It doesn't need to be perfect. Now, getting humans to acknowledge that and embrace that is the real problem.
Particularly since most drivers think they're above average. A car which is just better than the average driver might be a tough sell for them.
Practically it needs to be perfect, because whoever makes the self-driving car will be liable every time it kills someone. And there's going to be millions of these things.