A Google driverless car was involved in the fleet’s first collision to result in injury.

One of Google’s vehicles braked during a green light because of congestion, and the car behind hit it at 17 mph and lost its bumper, Google said. The most-recent incident occurred during evening rush hour on July 1 in Mountain View, California, where the search giant is based.

“Everyone in both vehicles was okay, except for a bit of minor whiplash,” Chris Urmson, Google’s director for self- driving cars, wrote in a blog item posted Thursday.

Google last month said it would issue monthly reports about its self-driving automobiles after a shareholder asked the company to be more transparent about accidents involving the technology.

The company says robotic vehicles drive better than humans do and will reduce deaths caused by cars driven by people.

Google’s hands-free cars have been hit by other drivers 14 times since the project began in 2009, according to the company.

“Our self-driving cars are being hit surprisingly often by other drivers who are distracted and not paying attention to the road,” Urmson wrote.

–With assistance from Brian Womack in San Francisco.