California Governor Jerry Brown on Tuesday signed a bill clearing the way for self-driving cars to jockey with human-operated vehicles to test the technology on the state's roads.

"Autonomous vehicles are another example of how California's technological leadership is turning today's science fiction into tomorrow's reality," Brown said during a signing ceremony at the Google campus in Mountain View.

"This law will allow California's pioneering engineers to safely test and implement this amazing new technology."

The legislation backed by state senator Alex Padilla lets driverless cars be operated on public roads for testing purposes as long as licensed drivers are behind the wheels to take over if needed.

Google co-founder Sergey Brin heads a stealth team working on visionary innovations such as self-driving cars and eye glasses that mesh the online world with the real world.

Brown, Brin and Padilla took a ride in a Google self-driving car before the governor signed the bill into law.

"It obviously seems the stuff of science fiction," Brin said.

"It is a fascinating area to work on but it really has the power to change people's lives, which is why I am really excited about it."

The state of Nevada in May issued a license plate giving Google's self-driving car the green light to travel along public roads there.

The modified Toyota Prius was issued a license bearing an infinity sign next to the left of number "001" after demonstrating its auto-pilot capabilities on highways, neighborhood streets and even the hectic "strip" in Las Vegas.

The Nevada Department of Motor Vehicles (DMV) proclaimed the license the first for an autonomous vehicle in the United States.

The legislation signed by Brown on Tuesday directs the California DMV to begin issuing license plates for self-driving vehicles.

Brin said the Google cars have logged more than 300,000 miles, 50,000 of which were made without human drivers taking over at "critical moments."

A video posted at Google-owned YouTube showed a blind man using a self-driving car to get about on errands.

"This can really enable huge classes of people effectively trapped or hampered to get around," Brin said while itemizing benefits of self-driving cars. "Including those too young, too old, or sometimes too intoxicated."

Padilla said he took numerous rides self-driving cars, which he contended have the potential to create jobs, reduce air pollution, and save lives by avoiding accidents.

When a news reporter asked Brown who gets the traffic citation when a driverless car ignores a red traffic signal, Brin jumped in with an emphatic "Self-driving cars do not run red lights."

Brin said Google wanted to have a broadened set of employees testing the cars by the end of this year and hoped the vehicles would be available in some form to the public in five years or less.

"You can count on one hand the number of years until ordinary people can experience this," Brin said.

Google has had "great conversations" with a variety of auto manufacturers and whatever it does with the technology would "involve partnerships with the industry."

Brown summed up the legislation signed on Tuesday essentially sets up rules and procedures for judging "when the car is ready for prime time."