Google Inc.'s quest to popularize cars that drive themselves seemed to hit a roadblock Friday when news emerged that one of the automated vehicles was in an accident. But in an ironic twist, the company is saying that the car was not driving itself; a human was.

Auto blog Jalopnik posted a photo apparently showing a car pulled to the side of the road after banging into another near Google's Mountain View, Calif., headquarters. In the photo, the Google car, with its telltale rack of roof electronics, is parked behind the other vehicle as a policeman and other drivers look on.

Self-driving cars must legally have a human at the wheel, ready to assume control if anything goes wrong. Google says that in this case, the human driver was operating the car in manual mode at the time of the accident.

"Safety is our top priority. One of our goals is to prevent fender-benders like this one, which occurred while a person was manually driving the car," according to a Google spokesperson, adding that the cars have now traveled more than 160,000 miles autonomously "without incident."

In June, Nevada became the first state to legalize self-driving cars, a victory for Google's driverless ambitions.

Google has been working on a project to put human drivers in the backseat, so to speak, by building cars that use radar, and lasers to navigate roads and stay safe in traffic. The company has said that eventually computer-controlled cars should drive more safely than humans - who, after all, get sleepy and distracted and can see in only one direction rather than in every direction.

That sort of mega-awareness would also help reduce traffic, explained Stanford University robotics professor Sebastian Thrun, a project leader on Google's effort, earlier this year.

"Do you realize that we could change the capacity of highways by a factor of two or three if we didn't rely on human precision on staying in the lane but on robotic precision, and thereby drive a little bit closer together on a little bit narrower lanes and do away with all traffic jams on highways?" he said in a speech at the TED 2011 conference in Long Beach, Calif., this spring.