I decided to dig deeper into the existing regulations currently in place in the United States. At this point, there are only four states (and D.C.!) that have approved legislation regarding the testing of driverless cars: Nevada, California, Washington, D.C., Florida, and Michigan. This site provides a nice summary of all of the status of all states’ driverless car bills, including which ones have passed, failed, or are under consideration.
All of these states have different variations on the following general concepts:
There are at least 10 states who have legislation under consideration and at least 10 that have had legislation fail. That being said, most driving laws do not actually prohibit driverless cars. The four states listed above have just formally allowed for driverless car testing (and put specific requirements around the testing).
Despite all of these regulatory actions, Google still believes its own safety processes are adequate and “that the technology behind autonomous vehicles is too intricate for state government representatives to fully grasp — and therefore regulate.” (source)