That's the puzzling question faced by cops in Mountain View, CA the other day.
Mountain View, where Google...oops, Alphabet...is the most prominent corporate citizen is also one of the areas where Google's driverless cars are being tested. The cars, called GAVs for Google Autonomous Vehicles, are legally able to drive on streets where the speed limit is 35 mph or less. A Google employee sits in the car, but does not have control.
In this case, Mountain View officers noted that the car was doing 24 in a 35 zone, and traffic was piling up behind it. They pulled it over, determined that it was operating legally if annoyingly, and let it go...so we still don't know how a ticket for a (not)driver would look. USA Today has more, with quotes from the cops, HERE
Google had a word to say, too: “After 1.2 million miles of autonomous driving (that’s the human equivalent of 90 years of driving experience), we’re proud to say we’ve never been ticketed!”