but they already have a far better safety record than the average human driver.
I want you to realize that the only source we have for this is Google. It's not from a scientific journal, or an independent research team, or an auditor, it is from the same people who want you to eventually buy their product.
Furthermore, I want you to realize that the Google team is very careful in what information they reveal. All the information they present is shaped in a way that makes them look good, and to increase demand for the car. Now, maybe they've built the perfect driverless car, and it somehow got off the ground running with a near-perfect driver record, but the information they've given us isn't enough to determine that.