Google is racing ahead of its rivals in testing self-driving cars, clocking-up over one million kilometres in 12 months as data reveals human backup drivers needed to intervene less.
The data, released on Wednesday, reflects safety-related incidents reported by 11 companies that have been testing more than 100 vehicles on public roads, primarily in the Silicon Valley neighbourhoods where the technology has grown up.
Waymo, Google's self-driving car project, did far more testing than the other 10 companies combined.
Waymo reported that its fleet drove itself more than one million kilometres 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 to two incidents every 16,093 km a notable decrease over the prior year, when there were eight disengagements per 16,093 km.
"This four-fold improvement reflects the significant work we've been doing to make our software and hardware more capable and mature," Waymo head of self-driving technology Dmitri Dolgov wrote in a blog post.
But John Simpson of the nonprofit Consumer Watchdog said the number of disengagements shows the cars still "simply aren't ready to be released to roam our roads" without human backup drivers.
General Motors, with its self-driving wing Cruise Automation, reported driving the second most test miles with 181 disengagements over 15,733 km or 185 per 16,093 km.
Though imperfect, the data represent the best peek the public gets into the secretive and fiercely competitive world of self-driving cars and how the prototypes are performing.
California required the disengagement reports as part of regulations governing testing on public roads. Separately, the state also requires companies to report any collisions involving its cars.
While Tesla's Elon Musk has been bullish, talking about months rather than years, companies such as Waymo have suggested 2017 or 2018 is more realistic.
Tesla's disengagement report said four prototypes drove a total of 885.1 km last autumn, experiencing 182 disengagements - the equivalent of 3,309 disengagements every 16,093 km.
Tesla has began shipping cars with advanced sensors that will be activated in the future.
The company already is gathering tens of millions of miles of real-world data when owners engage the current Autopilot feature, which can control steering and speed but is not sophisticated enough to make the cars self-driving from the regulatory perspective.
