Two million miles closer to a fully autonomous future

By Dmitri Dolgov, Head of Google’s self-driving technology

September 2016

When I first learned to drive, every mile I spent on the road was crucial. It was only through practice that I learned how to move with the flow of traffic, anticipate people’s behavior, and react to unexpected situations. Developing a truly self-driving car is no different. A self-driving car that can get you safely from door to door has to understand the nuances of the road, which only comes with experience.

That’s why our team has been focused on gaining real-world experience, and this month, we’ve reached a major milestone: we’ve now driven more than 2 million fully-autonomous miles on public roads. Put another way, if you consider the hours we’ve spent on the road, our cars now have the equivalent of 300 years of human driving experience.

What takes a self-driving car from concept, to demonstration, and finally to reality is this accumulated experience. Even in the early days of our project, it didn’t take long before we could give a good demo ride in our self-driving car. That’s because it’s relatively easy to master the first 90% of driving where you’re traveling on freeways, navigating light city-street traffic, or making your way through simple intersections.

But to create a truly self-driving car that can do all the driving, we knew we’d need experience in more challenging and interesting situations. That’s why we now spend the vast majority of our time on complex city streets, rather than simpler environments like highways. It takes much more time to accumulate miles if you’re focused on suburban roads; still, we’re gaining experience at a rapid pace: our first million miles took six years to drive, but our next million took just 16 months. Today, we’re taking a look at how our last million miles has brought us closer to making a truly self-driving car a reality.

We’ve taught our cars a collection of advanced driving skills.

In the last few years, we’ve been focusing on the harder tasks of driving — the final 10% — that take much more time and experience to master. Our cars have gotten much better at detecting and responding to everything from crossing guards to emergency vehicles to construction zones. With these advanced driving skills, we can adjust to things like sudden changes in road conditions, such as closed lanes.

The ability to navigate smoothly on the road, while subtle, is also an important advanced driving skill that helps people feel comfortable whether they’re inside or outside of the car. With each mile we drive, our test drivers provide feedback on the car’s movements — things like how quickly we accelerate and brake, the distance we keep from other cars and pedestrians, or the speed and angle we turn. With each piece of feedback, our engineers tweak our software and calibrate our driving behavior, making our self-driving car feel more natural on the road.

We have a better understanding of the social side of driving.

Ultimately, being a good driver is about understanding other people — pedestrians, bikers and fellow drivers. Over the last year, we’ve learned that being a good driver is more than just knowing how to safely navigating around people, but also knowing how to interact with them.

In a delicate social dance, people signal their intentions in a number of ways. For example, merging into traffic during rush hour is an exercise in negotiation: I’d like to cut in. May I cut in? If I speed up a little and move into the lane, will you slow down and leave me room, or will you speed up? So much of driving relies on these silent conversations conducted via gentle nudge-and-response. Because we’ve observed or interacted with hundreds of millions of vehicles, pedestrians and cyclists, our software is much better at reliably predicting the trajectory, speed, and intention of other road users. Our cars can often mimic these social behaviors and communicate our intentions to other drivers, while reading many cues that tell us if we’re able to pass, cut in or merge.

We’ve gained experience with rare and unexpected situations.

After 2 million miles of testing, our cars are more prepared to handle rare and unusual situations that human drivers may come across only once in a lifetime. In the last few months, we’ve seen everything from a horseback rider in the middle of the road, to a man wielding a chainsaw in the street (don’t worry, he was trimming trees!), to a couple riding unicycles side-by-side. Today, our cars can confidently handle unusual situations like seeing a car (or three!) driving the wrong way down a road.

When we first started the project 7.5 years ago, we saw the potential of this technology to help millions of people, making roads safer and improving quality of life. Today, our team is more confident than ever of a fully self-driving future. With every passing milestone — driving the curves of Lombard Street, navigating rain and dust in four U.S. cities, building three generations of self-driving cars (with a fourth on the way) — we’re even more committed to building that future.

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