The accident occurred in the past week, Brin said Wednesday during a meeting of shareholders in Mountain View, California. Google's self-driving vehicles have been involved in 11 accidents in the six years they've been in testing, though none was the fault of the car, the company said last month.

"I'm very proud of the record of our cars," Brin said. "Our goal is to beat human drivers."

Google is grappling with questions about the safety and performance of driverless cars. The company's investment in such vehicles is part of its internal project, Google X, that focuses on long-term opportunities for cutting-edge technologies. Google has touted safety as an advantage for the cars that can use sensors, maps and other tools to avoid the mistakes leading to accidents caused by human drivers.

The majority of the collisions happened when the experimental cars were hit from behind, with some on the freeway and some at traffic lights, Chris Urmson, director of Google's self-driving program, said last month in a blog post.