Governor Jerry Brown has signed state legislature to officially legalise automated cars in California.
The modified Toyota Priuses, designed and operated by Google, have already been made legal in Nevada, and have so far clocked up more than 300,000 miles of automated driving.
"We are looking at science fiction becoming reality in a self-driving car" said Gov. Jerry Brown, who assumed office winning last year's election ahead of Arnold Schwarzenegger.
According to the Los Angeles Times, Arizona, Hawaii, Florida and Oklahoma states are now also considering introducing autonomous cars.
Speaking at the signing, Google co-founder Sergey Brin said: "These vehicles have the potential to avoid accidents - we can save lives, create jobs, and reduce congestion...I expect that self-driving cars will be far safer than human-driven cars."
But despite positive preliminary tests of the 'robot' cars, scholars and safety officials are still not convinced they are 100 percent safe.
In a blog post earlier this year, reported by Ars Technica, Bryan Walker Smith, a fellow of Stanford University's Centre for Automotive Research, explained that automated cars still need to drive several hundred thousand more miles before they can be certified safer than human driven cars:
"Google's cars would need to drive themselves (by themselves) more than 725,000 representative miles without incident for us to say with 99 percent confidence that they crash less frequently than conventional cars.
"If we look only at fatal crashes, this minimum skyrockets to 300 million miles. To my knowledge, Google has yet to reach these milestones."
In May 2012, when Nevada permitted Google to test the cars, regulations determined that the company would have to pay a $1 million dollar insurance bond, and ensure that the cars were 'driven' by two people, who would both have the ability to take manual control of the vehicle if necessary.
Under the new bill, official state regulations for the use of automated cars in California will need to be drafted by 1 January, 2015.