A bill to bring driverless cars to roads in California has been signed.
State Governor Jerry Brown backed legislation on Tuesday, and said: "Today we're looking at science-fiction becoming tomorrow's reality".
The bill was signed at the headquarters of Google, which has been testing a fleet of 12 autonomous computer-controlled vehicles for several years.
Google co-founder Sergey Brin said self-driving cars would be "far safer" than those driven by humans.
Other manufacturers, including Audi, Ford and Volvo have also been experimenting with the technology.
The bill, drawn up by Senator Alex Padilla, will establish safety and performance regulations to test and operate the vehicles on roads across the state.
It requires the California Department of Motor Vehicles to draft the regulations by 2015.
A licensed driver would still be required to sit behind the wheel, however, in order to provide back-up in an emergency.
Google has said that it has logged more than 300,000 miles in its cars without an accident - although one of its vehicles was involved in a minor crash in summer 2011. The company said it was being driven manually at the time.
"I think the self-driving car can really dramatically improve the quality of life for everyone," Google co-founder Sergey Brin said, adding that he thought the vehicles would be commercially available within the decade.
Governor Brown said self-driving cars would at first make passengers feel uneasy.
"Anyone who gets inside a car and finds out the car is driving will be a little skittish," he said. "But they'll get over it."
'Darn driverless cars'
The cars are powered and controlled using a combination of sensors, location tracking and on-board computing power to drive the vehicle safely.
Other less ambitious autonomous driving functions are already in use across the car industry - such as guided parking and adaptive cruise control.
However, speaking after the signing of the Californian bill, one motoring trade group voiced concern.
"Unfortunately this legislation lacks any provision protecting an automaker whose car is converted to an autonomous operation vehicle without the consent or even knowledge of that auto manufacturer," the Alliance of Automobile Manufacturers said.
Governor Brown's backing follows new regulations in Nevada, where a law was passed earlier this year to allow driverless cars on the state's roads.
In Florida, similar moves have been made - but have ended up the subject of political debate. An advert which criticised a local Senate candidate was entitled "Those darn driverless cars", and raised questions about the technology's safety.
One motoring news website described the advert as being "so misinformed, it may cross the line into libel".