A row of Google self-driving cars outside the Computer History Museum in Mountain View, Calif. AP Photo/Eric Risberg Google's self-driving car project was started in 2009 on one premise: build an autonomous vehicle by 2020.

Now, it's seven years later, and Google's test cars have driven two million miles in four cities around the nation and have learned everything from how to honk politely to how to sense cyclists and pedestrians.

But Google has also failed to commercialize its cars so far — falling behind competitors like Uber and Tesla, despite being the first company to put the cars on the road — and has lost some of its best talent to other companies in the industry.

As Google prepares to spin out the project as its own company under the Alphabet umbrella, here's a look back at the company's progress in building the world's first fully autonomous vehicle.