Seth Rosenblatt/CNET

If you've seen one of Google's 'chandelier' topped autonomous cars driving down the street, you may have assumed the technology is legal. But up until now, Google has been operating the cars in a gray area, as autonomous cars have not been explicitly addressed by the California Department of Motor Vehicles (DMV).

As of September 16 of this year, new regulations take effect stating the requirements for testing autonomous cars in California. Further, the DMV is developing rules for the public's use of autonomous cars, expected to be ready by January 1, 2015.

The testing rules apply to "manufacturers" of autonomous vehicles, which would not seem to apply to Google. However, the definition of manufacturer in the rules includes companies which modify existing vehicles with autonomous technology.

Nevada had previously approved the testing of autonomous vehicles on its roads, and even created a special license plate. California's rules allow vehicles registered in other states to be tested on its roads. Manufacturers testing autonomous vehicles have to apply for a permit from the state, and provide the license plate number, make and model, and vehicle identification code for each car being tested.

The rules also define what it takes to operate an autonomous vehicle. Operators must pass a special driving course and be ready to take over control of the autonomous vehicle at any time. The rules require operators to have an understanding of the technology, and to have no more than one point on their licenses for a traffic code violation.

Of vehicle manufacturers, Audi has been the most aggressive in pursuing autonomous vehicle technology. Automotive equipment supplier Continental has also been conducting tests. Nissan earlier promised self-driving cars by 2020. Tesla also said it would be developing self-driving technology for its cars, which would likely be tested in California.