Google's driverless cars make progress
The number of human interventions in journeys made by driverless cars from Google company Waymo in California more than halved in 2016.
There were only 124 "disengagement" incidents last year, where a driver had to take control of a test vehicle on public roads, down from 341 in 2015.
The cars drove nearly 636,000 miles last year, compared with just over 424,000 in 2015.
Other states in the US do not require such reporting.
The California Department of Motor Vehicles published the annual reports on Wednesday.
Under law, every company that has a state permit to test autonomous vehicles in California must report how many times a driver had to intervene.
"Disengagements are a natural part of the testing process that allow our engineers to expand the software' s capabilities and identify areas of improvement," Waymo said in its report.
The most common reasons for interventions in Waymo cars were "software discrepancies, unwanted manoeuvres of the vehicle and perception discrepancies", according to the company.
Of the 124 incidents, only 10 were caused by the "reckless" behaviour of another road user.
Beyond Waymo's impressive results, the news was generally good.
Cruise, the start-up leading General Motors' autonomous driving development, upped its testing in San Francisco markedly. It went from driving fewer than five miles in June 2015, to nearly 400 in June 2016.
It reported 414 disengagements in almost 10,000 miles of driving in 2016 overall.
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