One metric to rank self-driving technology and advancement is by looking at the rate of disengagements. California mandates that companies testing in the state report this figure every year and Waymo shows a marked decrease in 2018 while driving more miles.

A lower rate of disengagements shows that our cars are getting better at recognizing and handling a wide variety of driving situations, including “edge cases” across the cities we’ve been testing in: those unusual situations that a human driver might see only once (or never) in a lifetime of driving.

Disengagement is when a human safety driver has to take over the autonomous vehicle due to errors or when avoiding a dangerous situation that the car is not yet equipped to handle. The California Department of Motor Vehicles (DMV) today published the Alphabet division’s fourth annual results:

Across the millions of urban miles we’ve driven on California roads, our disengagement rate dropped to 0.09 per 1,000 self-driven miles in 2018 (or 1 disengage per 11,017 miles self-driven). It’s a 50% reduction in the rate and a 96% increase in the average miles traveled between disengagements from the previous year (which had a rate of 0.18 disengages per 1,000 miles, equating to 1 disengage per 5,595 miles self-driven).

At one disengagement per 11,017 miles, Waymo’s closest competitor is GM-owned Cruise Automation at 5,205 miles. Apple’s effort is last at a disengagement every 1.1 miles, though the company disagrees with the metric.

This 50% reduction comes amid Waymo driving 1.26 million miles in 2018 versus just 352,000 miles in 2017. Meanwhile, the company touts the actual importance of disengagements as vehicles expand to new environments and acquire more skills.

Disengagements in these cases are actually a good thing because they are the equivalent to discovering and solving an issue with our car’s capability. As we continue to expand our test fleet, we actively seek places that present challenges to give our fleet the opportunity to learn.

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