During road tests of Google's autonomous vehicles, human drivers had to take manual control on 341 occasions in 14 months.
Data that Google submitted recently to the California Department of Motor Vehicles shows that during road tests over a 14-month period, the company's autonomous cars had to hand over control to a human driver on 272 occasions because of potential safety issues.
The second category of disengagement in Google's book is when the driver proactively takes manual control of the vehicle because of doubts over its ability to safely navigate a particular situation in autonomous mode.
According to Google, disengagement rates on its autonomous vehicles dropped sharply as the tests progressed. The number of immediate manual control disengagements, for instance, dropped from 785 miles per disengagement in the fourth quarter of 2014 to 5,318 miles per disengagement last November.
technology, but it did not offer any details on how many vehicles were tested or for how many miles.