"We hope to handle situations like this more gracefully in the future," Google said in a monthly report.
"We clearly bear some responsibility, because if our car hadn't moved there wouldn't have been a collision."
The accident highlights the imperfections of the current self-driving technology, which is widely seen as a promising solution to the thousands of lives lost each year on roadways.
While many in the tech and auto industry have circled 2020 as a roll-out date for self-driving vehicles, others have warned that it will likely take longer.
Google's self-driving cars have two employees present, and they are trained to intervene to prevent crashes. Earlier this year, Google revealed that 13 times over a 14-month span, its drivers had to intervene to prevent crashes.
In the February 14 crash, Google said its test driver thought the bus would slow or stop so the Google car could go ahead of it.