Washington ? Google Inc. is road-testing cars that steer, stop and start without a human driver, the company says.

The goal is to “help prevent traffic accidents, free up people’s time and reduce carbon emissions” through ride sharing and “the new ‘highway trains of tomorrow,'” project leader Sebastian Thrun wrote Saturday on Google’s corporate blog.

The cars are never unmanned, Thrun wrote. He said a backup driver is always behind the wheel to monitor the software.

It’s not the first signal that Google wants to change how people get from place to place. In a speech Sept. 29 at the TechCrunch “Disrupt” conference, 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 Mountain View, Calif.-based technology giant has sent seven test cars a total of 1,000 miles without a human touching the controls at all, the New York Times reported. The newspaper published a report on the cars earlier Sunday.

The cars know speed limits, traffic patterns and road maps, Thrun’s posting says. They use video cameras, radar sensors and lasers to detect other cars.