How do we prepare for rare and odd situations on the road? By following these 3 steps.

September 2015

Our vehicles have self-driven the equivalent of over 90 years of typical US adult human driving, and over that time, we’ve seen a lot of crazy stuff on the road. We want our cars to be capable of handling odd or rare scenarios, but even over a million miles or more of testing, we can’t expect to see everything that might be possible. So we’ve had to figure out our own methods for pushing our software’s capabilities. That’s why we created a special team to dream up rare and diabolical situations and run tests on our test track.

Step 1: Coming up with ideas for different situations.

We see lots of challenging things out on the roads — both as test drivers and during our own commutes to work. We take these ideas and brainstorm some more to make them even weirder and harder. Our software benefits in two ways: we can validate that the software works as expected in extreme versions of common situations, and we can prepare for truly rare or odd occurrences

Step 2: Creating a field test.

Specially trained members of the team recreate each situation on our private test track, including multiple variations of each scenario — almost as if they were shooting a Hollywood movie — and we run through several variations of each test. For example, we recently tested how the car would respond to a person coming out of a “porta potty” on the side of the road. We had people pop out slowly, or spring out quickly as it from a birthday cake. We put the car in different positions, distances and speeds. If the vehicle does what we expect, great. If it does something different, our engineers can take a closer look and make adjustments to the software.

Step 3: Building on what we’ve learned by testing some more.

One of the beautiful things about our self-driving software is that it can get practice without ever leaving the garage. Using our simulator software, we can take any of the individual scenarios we practiced on our test track (as well as ones we encounter on the roads) and subtly change the variations to get even more practice. What if that pedestrian were taller, or shorter? If they darted out into traffic at different angles? We can very quickly get virtual practice on hundreds or thousands of variations on a single on-the-street scenario, adding to the 10,000 to 15,000 miles of real-world driving experience we gain every week.