Google has confirmed it is road-testing cars that steer, stop and start without a human driver.
The company is hoping the experiment will "help prevent traffic accidents, free up people's time and reduce carbon emissions" through ride sharing and "the new 'highway trains of tomorrow,'" said project leader Sebastian Thrun.
The cars are never taken out without someone in the vehicle ready to take control, Thrun wrote in a blog. He said a backup driver is always behind the wheel to monitor the software.
The move is the latest signal that Google is determined to change how cars are driven. In a speech on 29 September, Google CEO Eric Schmidt said "your car should drive itself. It just makes sense."
"It's a bug that cars were invented before computers," Schmidt said.
The cars have traveled a total of 140,000 miles on major California roads without much human intervention, according to Google's corporate blog.
The New York Times reported that the technology company has sent seven test cars a total of 1,000 miles without a driver touching the controls at all.
The software on board the cars is able to recognise speed limits, traffic patterns and maps. They use a combination of radar, video cameras, and laser technology to detect other cars.
The cars have navigated Los Angeles' Hollywood Boulevard, San Francisco's curvy Lombard Street, and the cliff-hugging Pacific Coast Highway.