California law had previously not recognized or prohibited autonomous self-driving cars, but that changed with the signing ceremony held at the Googleplex in Mountain View, Calif., on Tuesday (Sept. 25). Brown took a ride in one of Google's self-driving vehicles before signing Senate Bill 1298 — legislation that officially approves test driving of autonomous cars on public roads and paves the way for the U.S. public to legally drive such cars in several years.

"Autonomous vehicles are another example of how California’s technological leadership is turning today's science fiction into tomorrow's reality," Brown said. "This law will allow California’s pioneering engineers to safely test and implement this amazing new technology."

Self-driving cars operated by Google have already spent months prowling the San Francisco Bay Area, and automakers such as Ford and Cadillac have also begun developing their own versions. Experts have welcomed the idea of self-driving cars as vehicles that could reduce traffic congestion, make roads safer and give improved road access to people such as the elderly or disabled.