Self-driving cars are legal in the United States because they have never been explicitly outlawed in the United State. (A basic legal principle in the U.S. is that anything that is not explicitly illegal is legal.)
However, as automakers and others prepare to introduce self-driving cars on a large scale both federal and state legislators and regulators are racing to prepare new laws and regulations. in September 2016 National Highway Traffic Safety Administration (NHTSA) issued Federal Automated Vehicles Policy
guidelines for the testing and deployment of autonomous vehicles. Also in September 2016, California’s department of motor vehicles released a revision of draft regulations
that opened a pathway for the public to access self-driving cars, prototypes of which automakers and tech companies are testing.