Humans are not a "reliable backup" for the self-driving system.

Unfortunately, Teller and his team quickly learned that people are too quick to trust that the car will simply take care of everything. The car had to be driven to and from the freeway before the self-driving could be engaged and in between, passengers needed to closely monitor how the vehicle behaved. Instead, they would immediately check out and engage in what we can only assume is questionable behavior. Teller pointed out that people do "really stupid stuff" when actually driving, like texting. So imagine what they would do when able to put their trust fully in the car itself. Teller didn't get specific; he only said it "wasn't pretty."

So now the challenge is to master city driving and completely remove people from the equation.

He also answered a few other burning questions about Google's self-driving prototype. Specifically why, if the goal is to have no steering, no brakes and no way for a person to take control of the vehicle are there mirrors and a windshield wiper. Well, it turns out that's just the law. Regulations require mirrors and a windshield wiper, even if they don't benefit the actual driver. Go figure.