Google's self-driving cars have been busy driving around the company's headquarters and mapping roads.

Recently, two Google cars were involved in minor accidents that were the fault of other drivers, USA Today reports. 

Google says in its latest monthly report that its specially designed self-driving Lexus SUVs were rear-ended by other vehicles while stopped at a stoplight.

One of the vehicles was hit by a car traveling at about five miles per hour. This caused damage to the Google Lexus' rear bumper. The other vehicle was hit by a car traveling even slower than that and no damage was reported.

Google had reported all accidents to the California Department of Vehicles for years. That accident's data was not publicly disclosed, though. When Google was pressured by activist organizations to make the data public, the company decided to change their mind and created a website that reports updates on its self-driving cars, including accident reports.

Self-driving cars are the current popular project for tech and automotive companies. Joining Google in trying to create a self-driving car are Uber, Ford and several other companies.

Besides the modified Lexus SUVs, Google is also using cars designed in-house that offer seating for just two and no trunk space.

Google blames the last three accidents on inattentive humans. The self-driving vehicles must be accompanied by a human for safety reasons. The human would take over if an unfamiliar traffic situation causes the self-driving car to become confused.

"Given the time we're spending on busy streets, we'll inevitably be involved in collisions (because) sometimes it's impossible to overcome the realities of speed and distance," the report says. "In the six years of our project, we've been involved in 14 minor accidents during more than 1.8 million miles of autonomous and manual driving combined. Not once was the self-driving car the cause of the accident."