The next time you drive in California, be on the lookout for cars with what look like mini-radars spinning on the roof. The state is quickly become a hotbed for testing self-driving cars.

Seven companies have been issued permits letting them take their experimental vehicles out for a spin on the state’s public roads.

The latest to get permits in the nearly two-month old program are Tesla, Nissan, Delphi Automotive, and Bosch, according to Bernard Soriano, a deputy director with California’s Department of Motor Vehicles. They join Google, Daimler’s Mercedes-Benz unit, and Volkswagen’s Audi unit, all of which received permits when the program first kicked off.

The growing list of companies with state approval to test autonomous vehicles on city streets and highways highlights the race to turn the sci-fi technology into reality. It also shows how California has become an important hub for innovation in the auto industry, which was once almost entirely centered in Detroit and Japan.

In general, the companies given permits have already publicly revealed their plans to develop self-driving car technology. In some cases, they have shown off early versions at auto shows and in online videos.

For example, Elon Musk, Tesla’s chief executive, made a splash last month when he said his company would install autopilot in his company’s electric sports cars that will help with parking, cruise control and crash avoidance. Fully autonomous vehicles, he predicted, would be available by 2023.

Tesla TSLA did not respond to requests for comment about its California testing permit, which authorizes two test drivers to drive an autonomous 2014 Model S sedan.

Delphi Automotive, an auto technology supplier, received state approval for eight drivers to test two Audi SQ5. Like many auto companies, Delphi DLPH has a Silicon Valley innovation lab that is working on autonomous car technology.

Meanwhile, Bosch, a German auto parts supplier and home appliance maker, has a permit authorizing two drivers to test a self-driving BMW 325d sedan and a Tesla Model S. Nissan, which hopes to develop a “commercially viable” self-driving car by 2020, has eight drivers experimenting with two Nissan Leaf electric cars.

“This demonstrates our commitment to bring various autonomous technologies to market and allows Nissan to continue our efforts toward zero fatalities and zero emissions,” Maarten Sierhuis, director of Nissan’s Silicon Valley research lab, said in a statement.

Companies are not required to disclose in their applications where they plan to do their testing. Nor must they reveal any details about their technology. But they must report any accidents or instances when drivers had to unexpectedly turn off the autonomous technology within 10 days to the state’s DMV. Only one company has filed such a report.

Delphi told the agency that another car crashed into its Audi test vehicle on the evening of Oct. 14 in Palo Alto, Calif. The test car was stopped while waiting to merge with traffic when a Honda traveling in the opposite direction crossed an elevated center median and struck Delphi’s car. The accident left Delphi’s vehicle with a dented front end and right fender. No one was injured in the crash.

The crash doesn’t appear to have anything to do with Delphi’s autonomous technology. At the time of the crash, the car’s self-driving mode was turned off. Instead, a human driver was in control. Furthermore, in their report, the police laid blame on the Honda’s driver, who they said caused the crash by making an unsafe turn.

In September, California officials started requiring companies testing autonomous vehicles on public roads to get permits. Until then, the state had no specific regulations related to the technology, and companies could test-drive without having to jump through any bureaucratic hoops. A number of them did so including Google GOOG , which logged hundreds of thousands of miles in its self-driving cars as part of its plan to bring the technology to the masses.

The new regulations are intended to address the inevitable safety and liability concerns without crippling the development of autonomous vehicles. Under the rules, all test drivers must have clean driving records and get training in operating autonomous cars. Companies must also have at least $5 million in insurance or post a bond.

Still, many car makers with permits are testing on private or federal land, where state regulations don’t necessarily apply. Mercedes, for instance, is using the sprawling Concord Naval Weapons Station, near San Francisco, to experiment. Installing traffic signals that communicate with cars—presumably to get them to differentiate between a red light from a green one—is among the experiments. The company is also subjecting cars to potentially dangerous situations, which would be unwise to do on city streets.

“Taken in conjunction with the results of our test drives on public roads,” said Axel Gern, head of autonomous driving at Mercedes-Benz Research and Development for North America, in a statement, “these tests will help us with the ongoing development of our autonomous cars.”

Next, read:Will we need a learner’s permit for self-driving cars?” by Verne Kopytoff.