The California Department of Motor Vehicles today started issuing permits for self-driving cars. The main requirement is that they have a person capable of stopping the car if anything bad happens.

Audi has signed on, though Google will have the highest number of self-driving cars on the road at 25.

Additional requirements include extensive identification of the autonomous vehicle, as well as proof that the "driver" is on the company's payroll and has met all state-required qualifications—including passing the training program.

Audi was the first car maker to receive one of the red autonomous vehicle license plates issues by Nevada, which approved self-driving car rules in 2012.