Waymo reported that its fleet drove itself more than 635,000 miles with 124 safety-related “disengagements,” which must be reported when the technology fails or the backup driver takes control out of concern the car is malfunctioning. The Google project’s disengagement rate was the equivalent of two incidents every 10,000 miles, a notable decrease over the prior year, when there were eight disengagements per 10,000 miles.

“This four-fold improvement reflects the significant work we’ve been doing to make our software and hardware more capable and mature,” Dmitri Dolgov, Waymo’s head of self-driving technology,Dmitri Dolgov, Waymo’s head of self-driving technology wrote in a blog post.