The California Department of Motor Vehicles has released its annual autonomous vehicle disengagement report.

The report includes data from all companies that are actively testing self-driving cars on roadways in California, and those companies are required to disclose the number of times human drivers have to intervene while testing a self-driving car. Waymo, Google’s new self-driving car company, reported a major drop in disengagements last year while driving significantly more miles. That means even though Waymo is testing its cars more frequently, its human drivers are having to take control less than before.

According to Waymo, its rate of safety-related disengages fell from 0.8 per thousand miles to 0.2 per thousand miles in 2016. Last year, it increased its driving by 50 percent in California to 635,668 miles and only had to take over 124 times, compared to 341 in 2015.

Head of Waymo’s self-driving technology, Dmitri Dolgov, shared more details in a recent blog post: “This four-fold improvement reflects the significant work we’ve been doing to make our software and hardware more capable and mature. And because we’re creating a self-driving car that can take you from door to door, almost all our time has been spent on complex urban or suburban streets. This has given us valuable experience sharing the road safely with pedestrians and cyclists, and practicing advanced maneuvers such as making unprotected left turns and traversing multi-lane intersections.”

As for the actual disengagements, Waymo said they were caused by “software glitches,” “unwanted maneuvers,” “perception discrepancies” and “recklessly behaving road user.” The company had no reports of crashes or accidents.

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