The company disclosed the accident on Thursday. Three employees complained of minor whiplash and checked into a hospital. The driver of another car involved in the accident complained of neck and back pain.
According to the accident report filed by Google with the California Department of Motor Vehicles, the self-driving SUV was traveling behind two other cars at about 15 miles per hour as it approached an intersection with a green light, reported the Associated Press.
The first car stopped at the intersection because traffic on the far side was not moving. Then both the Google car and the car just in front of it stopped as well.
About a second later, a fourth vehicle smashed into Google’s car at 17 mph, resulting in minor whiplash to passengers in both cars and causing the offending car’s front bumper to fall off. On-board sensors showed the other car had not braked. The Google SUV’s bumper was slightly damaged.
The three Google employees riding in the car at the time complained of minor whiplash and were checked into a hospital, but were soon cleared and allowed to go back to work. The driver of the second car complained of neck and back pain.
In a blog post, the head of Google’s self-driving car program, Chris Urmson, wrote that his SUVs “are being hit surprisingly often” by distracted drivers, perhaps by people looking at their phones.
“The clear theme is human error and inattention,” Urmson wrote. “We’ll take all this as a signal that we’re starting to compare favorably with human drivers.”
Urmson included a video showing a computer readout of the accident.
Google has been testing 20 self-driving prototypes in Mountain View. It has invested heavily in the technology as it believes their cars will be safer and more efficient than those driven by human.
Under California law, self-driving cars being tested on public roads must have a person behind the wheel who can take control in case of an emergency situation.
This was the 14th accident in six years and about 1.9 million miles of testing, according to the company. In 11 of the 14 accidents, Google said its car had been rear-ended.
Google said that its cars have not caused any of the collisions, though in 2011 an employee who took a car to run an errand rear-ended another vehicle while the Google car was out of self-driving mode.