Even self-driving cars can cause fender-benders.

That's what Google admitted when it said one of its self-driving cars was at least partially responsible for an accident with a city bus.

Google has previously said there were 17 minor accidents involving its self-driving cars, but said none of them had been the cars' fault.

But on February 14, a Lexus 450 hybrid SUV with Google's self-driving technology had a scrape with a city bus in Mountain View, California, the company's hometown. It said no one was injured in the accident.

Google said the car was in the right lane of a city street, and was about to turn right. But after initially moving to the right side of the lane, it moved back to the center of the lane to avoid sand bags that had been placed around a storm drain. The bus, coming from behind, hit the left side of the car.

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"This type of misunderstanding happens between human drivers on the road every day. This is a classic example of the negotiation that's a normal part of driving -- we're all trying to predict each other's movements," Google said in a statement.

The company said the Google test driver who was behind the wheel thought the bus was going to yield, and the bus driver likely thought the Google car was going to yield to the bus.

"In this case, we clearly bear some responsibility, because if our car hadn't moved, there wouldn't have been a collision," Google said.

Google said its car was traveling less than 2 mph, the bus about 15 mph. Its car sustained some damage to the left side; it did not report what damage the bus sustained.

Google said it has accumulated more than 1 million miles of autonomous driving, and said it has made changes to its software to try to avoid future accidents like this.

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"From now on, our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future," said the company.