Over the past nine years, we’ve put our vehicles through the world’s longest and toughest ongoing driving test. Each day our vehicles can be found test driving on closed courses, on public roads, and in simulation. Waymo’s testing program is a critical aspect to building a safe and capable driver: it lets us extend our vehicle’s capabilities, try out new driving skills, and introduce new vehicle platforms and hardware.

As we prepare to launch Waymo’s self-driving ride-hailing service this year, we’ve accelerated the pace of testing at every level. Last year was a record year for Waymo:

We doubled our number of autonomous miles, racking up nearly 2 million miles over a 12 month period . Today, Waymo vehicles have self-driven more than 4 million miles across 25 U.S. cities.

. Today, Waymo vehicles have self-driven more than 4 million miles across 25 U.S. cities. We put our new self-driving Chrysler Pacifica Hybrid minivans on the road, equipped with a new suite of sensors, including a Waymo-designed LiDAR, radar, and vision systems that are our most advanced to date.

We grew our database to more than 20,000 scenarios tested on our private test track, evaluating our system’s core driving skills and its ability to avoid common pre-crash scenarios.

Our vehicles continued to gain more practice with advanced driving skills, including using machine learning to better recognize and respond to emergency vehicles or mastering challenging driving situations such as unprotected left turns.

All this real-world experience is multiplied further in simulation: in 2017, we drove an additional 2.7 billion miles in our virtual world, focused on some of the most challenging situations on the road. At its peak, Waymo’s simulators complete 2,000 complex driving scenarios each second.

Altogether, our extensive testing program enables us to gather as much data as possible in order to improve our technology. Disengagements — when a test driver takes manual control of a vehicle while it is in autonomous mode — are a piece of that data.

Today, we’re publishing Waymo’s third disengagements report from our testing program in California, which shows a continued improvement year-over-year. In the reporting period ending November 2017, our fleet travelled 352,545 autonomous miles in California on public roads, safely navigating everything from city streets to local neighborhoods to freeways. Our disengagement rate fell from 0.20 to 0.18 per thousand miles travelled.

Our rigorous testing program is designed to ensure that Waymo’s vehicles never stop learning. For more information about Waymo’s testing program and how we test and validate our technology, check out our Safety Report.