Sure, hitting someone stopped is almost always the legal fault of the person rear-ending.

But that doesn't mean that Google is somehow off the hook. Google could invent a car that never causes crashes, but yet is still more dangerous than a human driver based on the inability to avoid crashes that humans easily avoid.

And, really it isn't hard to envision such a car being built. If it randomly hits the breaks to avoid phantom sensor readings, then the cars might be stopping in unexpected places an order of magnitude worse than a normal driver.

I'm sure driverless cars will eventually be safer than human, but I'm not convinced they will be.