Of the 50 self-driving cars owned by Google, at least four of these have been in 11 car accidents around California as of September 2014, the Associated Press reported. 

The cars involved included the Lexus SUV and the Delphie Automotive car, which were fitted with sensors and a computer operating system. The technology was developed to help with autonomous driving, and it has been Google's goal to work on improving car manufacturers' safety standards, minimize human error while driving on the road and reduce insurance costs.

Now, the tech giant says the accidents are largely caused by humans and not the machines, as reported by Time Magazine. One of Google's self-driving car proponents, Chris Urmson, the head of the program, confirmed via a blog post that its fleet has had 11 minor accidents since it was first introduced on the road.

"Over the 6 years since we started the project, we've been involved in 11 minor accidents (light damage, no injuries) during those 1.7 million miles of autonomous and manual driving with our safety drivers behind the wheel, and not once was the self-driving car the cause of the accident," Urmson wrote.

Seven of the accidents were apparently due to the car being rear-ended, while two have been side-swipes. A collision while the car was coming through a stop sign also took place. All these happened in the city streets.

A source in the AP report, meanwhile, said that two of the accidents had a person taking control of the car or had been in self-driving mode. In both instances, the speed of the car was below 10 mph.

"Even when our software and sensors can detect a sticky situation and take action earlier and faster than an alert human driver, sometimes we won't be able to overcome the realities of speed and distance; sometimes we'll get hit just waiting for a light to change," Urmson wrote.