Google said in mid-May that its fleet of autonomous cars has been involved in 11 accidents over the past six years. The vehicles have traveled nearly 1.7 million miles during that time.

Chris Urmson, director of the Google Self-Driving Car program, says that “not once was the self-driving car the cause of the accident.”

(Read “Google’s Autonomous Cars Face Risk from Human Drivers.”)

Urmson says in a post on Backchannel that the Google cars were rear-ended seven times by other cars, sideswiped twice and hit once by a car that ran a stop sign. He says the majority of accidents were on city streets rather than highways.

Comparing the Google car with human drivers, based on data from the National Highway Traffic Safety Administration, the rate of accidents with "property damage only" in 2012 was around 0.38 per 100,000 miles driven. Google has had 0.64 accidents per 100,000 miles driven, reports say.

"Our safety drivers routinely see people weaving in and out of their lanes; we’ve spotted people reading books, and even one playing a trumpet," says Urmson.

The cars also encountered trouble at intersections, encountering some drivers that were driving the wrong way down a divided street, others changing lines mid-way through a turn and still others who changed their mind about what direction to turn and swerved in front of the Google car.

"We’ll continue to drive thousands of miles so we can all better understand the all-too-common incidents that cause many of us to dislike day to day driving— and we’ll continue to work hard on developing a self-driving car that can shoulder this burden for us," he says.