Google's self-driving cars have travelled 1.2 million miles in full autonomy on public roads, the company announced on Tuesday afternoon.

Because all of its vehicles share their driving data, that means that each car has accrued approximately 90 years of driving experience.

While the cars have encountered some unusual real-life situations — like a woman in a wheelchair chasing a goose in the road — Google also sets up its own "diabololical testing areas" to test their smarts.

Jaime Waydo, who heads up engineering for Google's self-driving cars initiative, says that her team is constantly coming up with new scenarios to try to teach the vehicles safety abilities.

For example, it has placed a porta-potty on the side of the road, which the car will recognize as a stationary object. But then, as the car approaches, a person will step out of it.

Then, there was another test where Google made someone leap out of a truck-bed while it was moving in front of the self-driving car.

Both times, the car managed to avoid hitting the person. In those tests, and in every other one, the cars send their data from the interaction to a "scenario database." Google can run its self-driving car software through all its real-life scenarios using that data.

Seperately, Google also tests the hardware of its cars by sending them through hot chambers, cold chambers, and rain booths, to make sure that the hardware can withstand real-world conditions.

Waydo also shared a story about how recently one of her friends who lives in Mountain View, where Google has been testing its cars on public roads, thanked her profusely after watching the car seemlessly stop as a child ran out in front of it.

"He told me, 'The presence of your car in my neighborhood makes my neighborhood safer,'" Waydo says. "Things like that are why we come to work every day. It's amazing."