Google has been working on its self-driving cars for years now, with the latest update being that the prototypes of the cars have been seen on the roads of Mountain View.

The cars are the same prototypes that Google first showed off in December, and they were completely built by Google with autonomous driving being the goal.

Of course, the cars being spotted aren't empty, and they have "safety drivers" in the driver's seat to take control if need be. These drivers are required to be there during this phase of testing and have a removable steering wheel, an accelerator and a brake pedal. The cars also cannot go past 25 mph when they're in self-driving mode and are run using the same software behind the Lexus-built self-driving cars Google has tested in the past.

Google's self-driving cars have been the subjects of public scrutiny, especially when it was revealed that they had been involved in a number of accidents. Despite this, Google has said that none of the accidents were the self-driving car's fault, instead being the fault of the other drivers in the accidents.

Google's self-driving cars are also set to get a little more glamorous in the near future, with the company announcing an initiative that will see self-driving cars being decorated by artists around California.

"As our prototype vehicles start to cruise the streets of Mountain View, California, we want you to make these cars your own," said Google on the website for the project. "We're inviting artists in California to submit art to be featured on our self-driving prototype vehicles for a month or more later this year. Imagine spotting your art on one of the world's first self-driving cars!"

The art must adhere to certain guidelines, with Google not accepting submissions with obscene images, logos, branding or text.

Of course, this project isn't just to make the cars pretty. Anything that the company can do to make the cars more approachable is a good thing for Google, with public opinion being a very important factor in the testing of the cars and the safety of other drivers on the road.

Google isn't the only company working on self-driving cars, with multiple car manufacturers working on cars of their own. Even ride-sharing company Uber is working on autonomous vehicles and is expected by many to become a major player in the market over the next few years, with Bill Gates hailing the company as having the best shot at self-driving cars.