California governor Jerry Brown travelled to Google headquarters in a self-driving Toyota Prius - then signed state legislation that will pave the way for driverless cars.
The bill by Democratic senator Alex Padilla will establish safety and performance regulations to test and operate autonomous vehicles on the state's roads and highways.
"Today we're looking at science fiction becoming tomorrow's reality - the self-driving car," Mr Brown said. "Anyone who gets inside a car and finds out the car is driving will be a little skittish but they'll get over it."
Google has been developing autonomous car technology and lobbying for the regulations. The company's fleet of a dozen computer-controlled vehicles has logged more than 300,000 miles of self-driving without an accident, according to the internet company.
"I think the self-driving car can really dramatically improve the quality of life for everyone," Google co-founder Sergey Brin said. Autonomous cars can make roads safer, free commuters from the drudgery of driving, reduce congestion and provide transport to people who can't drive themselves, such as the blind, disabled, elderly and intoxicated, Mr Brin said. "I expect that self-driving cars will be far safer than human-driven cars," he said.
He predicted that autonomous vehicles would be commercially available within a decade. He said Google had no plans to produce its own cars, but instead wanted to partner the industry to develop autonomous vehicles.
But the Alliance of Automobile Manufacturers expressed concern that California was moving too quickly to embrace self-driving cars and needed to first sort out liability issues. "Unfortunately this legislation lacks any provision protecting a car manufacturer whose car is converted to an autonomous operation vehicle without the consent or even knowledge of that auto manufacturer," the trade group said.
Autonomous cars use computers, sensors and other technology to operate independently, but a human driver can override the autopilot function and take control of the vehicle at any time.
With smartphone-wielding drivers more distracted than ever, backers say robotic vehicles have the potential to significantly reduce collisions and traffic fatalities, noting that nearly all car accidents are a result of human error.
The legislation requires the California Department of Motor Vehicles to draft regulations for autonomous cars by January 1 2015. Currently, state law does not mention self-driving cars because the technology is so new. The regulations would allow vehicles to operate autonomously, but a licensed driver would still need to sit behind the wheel to serve as a back-up operator in case of emergency.