The performance of a human is inherently limited by biology, and the road rules are written with this in mind. Machines don't have this inherent limitation, so the rules for machines should be much stronger.

I think there is an argument for incentivising the technology to be pushed to its absolute limits by making the machine 100% liable. It's not to say the accident rate has to be zero in practice, but it has to be so low that any remaining accidents can be economically covered by insurance.