Report filed to California outlines 272 occurrences over a 14-month period

Autonomous cars tested by Alphabet Inc. ’s Google X division are getting better, but they still have to hand over control to human test engineers on rare occasions.

Google filed a report with the state of California on Tuesday that outlined 272 occurrences during a 14-month period where the software on its vehicles detected a problem that required an immediate handover to the human test driver. Of those, Google analyzed that if a human hadn’t taken over, there likely would have been 13 “contacts” with other vehicles or objects.

The report also showed that the number of disengagements declined significantly during the period, going from once every 785 miles in the first quarter of testing to once every 5,318 miles in the most recent.

Each auto maker or supplier testing autonomous vehicles in California is required to make these disclosures. Google has, by far, the most extensive fleet of autonomous vehicles driving on public roads.

The results show that despite big improvements, the vehicles aren’t able to navigate all circumstances without a driver ready to jump into the situation.

On Tuesday, John Krafcik, the chief of Google’s self-driving car program, said the company is firmly committed to making vehicles that require no human backup.

Other suppliers and auto makers, including Robert Bosch GmbH and Delphi Automotive PLC, made similar reports with a higher frequency of interventions. Delphi’s report detailed the causes of the disengagements, which frequently involved poor roadway lane markings, bright sunlight blinding cameras, construction zones and erratic behavior from other drivers.

The Google report served as fuel for safety advocates who don’t want to allow cars like Google’s to be introduced on public roads without a driver in command. Google’s vision is to build vehicles that don’t require humans to be involved.

Last month, California released proposed regulations for autonomous cars that require specially licensed drivers, which essentially would undermine the company’s efforts.

“The [Department of Motor Vehicles] got it exactly right and is putting our safety first,” John M. Simpson, Consumer Watchdog’s Privacy Project director said in a statement. “Release of the disengagement report was a positive step, but Google should also make public any video it has of the disengagement incidents.”

Write to Mike Ramsey at [email protected]