The day when a car can be trusted to drive safely all by itself has moved another cautious step closer with the publication of a report on experiments by Google and others with self-driving cars.
Data released by the California Department of Motor Vehicles (DMV) measured the "disengagement" history of the vehicles being tested on its roads by seven companies. That is the number of times the driver had to take over the driving of the vehicle.
The rule defines disengagements as deactivations of the autonomous mode in either of two situations:
"When a failure of the autonomous technology is detected," or
"When the safe operation of the vehicle requires that the autonomous vehicle test driver disengage the autonomous mode and take immediate manual control of the vehicle."
Over the course of the testing -- which took place between September 2014 and December 2015 -- the vehicles covered 523, 958 miles. Google's vehicles covered the majority of that -- 424,331 -- and Google's autonomous technology handed control to the driver 272 times and a test driver felt compelled to intervene 69 times.
At the moment California has regulations that cover the testing of robot cars on the state's highways. These say that a driver who is capable of taking control must be behind the wheel all the time.
"Safety is our highest priority," said Google in its report on the testing. "Test drivers are trained to take manual control in a multitude of situations, not only when safe operation 'requires' that they do so."
Eleven companies -- Bosch, BMW, Cruise Automation, Delphi Automotive, Ford, Google, Honda, Mercedes Benz, Nissan, Tesla Motors, and Volkswagen Group of America -- have been approved to test autonomous vehicles on California roads.
Consumer group Consumer Watchdog welcomed the release of the reports as a positive step. Its privacy project director John Simpson said: "But Google should also make public any video it has of the disengagement incidents, as well as any technical data it collected so we can fully understand what went wrong as it uses our public roads as its private laboratory."