Google self-driving cars in 11 accidents

The Google cars have been rear-ended seven times, often when stopped "but also on the freeway", Urmson wrote. In other collisions, the cars were side-swiped or "hit by a car rolling through a stop sign". Eight of the 11 collisions were on city streets.

He also described instances in which Google's cars avoided hitting other cars or bicyclists as they drove on streets near the company's Silicon Valley headquarters.

Nevada, Michigan and Florida have passed laws welcoming tests of self-driving cars onto their roads. Their regulators told AP they weren't aware of any reports.

California's regulators provided the total－four accidents since September－but would not comment about their nature or severity, citing a longstanding state law making collision reports confidential.

Some details, however, were revealed to the AP by a person familiar with these reports: Two of the accidents happened while the cars were in self-driving mode. In the other two, the person required to be behind the wheel was in control.

All four happened when the test car was moving at speeds of less than 16 kph, said the person, who spoke on condition of anonymity for lack of authorization to discuss the reports publicly.

Selling point

A chief selling point for self-driving cars is safety.

Their cameras, radar and laser sensors provide a far more detailed understanding of their surroundings than humans have. Reaction times should be faster. Cars could be programmed to adjust if they sense a crash coming－move a few feet, tighten seat belts, honk the horn or flash lights at a distracted driver.

The top priority so far is not avoiding fender benders, but teaching them to avoid causing a serious accident that could set back acceptance of the technology for years, said Raj Rajkumar, a pioneer of the technology with Carnegie Mellon University.

The national rate for reported "property-damage-only crashes" is about 0.3 per 160,000 kilometers driven, according to the National Highway Traffic Safety Administration.

Google's 11 accidents over 2.8 million kilometers would work out to 0.4 per 100,000, but as company officials noted, as many as 5 million minor accidents are not reported to authorities each year－so it is hard to gauge how typical this is.

"Even when our software and sensors can detect a sticky situation and take action earlier and faster than an alert human driver, sometimes we won't be able to overcome the realities of speed and distance," Google's Urmson wrote. "Sometimes we'll get hit just waiting for a light to change."