According to a blog post by the Mountain View Police Department, the self-driving car was traveling 24 MPH in a 35 MPH zone on El Camino Real, near Rengstorff Avenue. The slow speed caught the attention of the officer, who "stopped the car and made contact with the operators to learn more about how the car was choosing speeds along certain roadways."
Google's prototype vehicles have a speed cap of 25 MPH for safety reasons, and also because Google wants them to appear "friendly and approachable, rather than zooming scarily through neighborhood streets." Under California law, they're only allowed to operate on roadways with speed limits at or under 35 MPH, so it wasn't breaking any laws (nor was Google ticketed).
Aleksandr Milewski, a photographer living in Berkeley, California, took the photo of the police officer standing next to the prototype vehicle, which promptly spread through Twitter and the web at large like wildfire. Google re-posted the picture on its Google+ page and acknowledged the incident, adding that its self-driving cars have yet to get a ticket.
Since this seems to be all over the internets, I might as well post here as well. pic.twitter.com/m7FD9pvRmi— Aleksandr Milewski (@zandr) November 13, 2015
"Like this officer, people sometimes flag us down when they want to know more about our project. 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!," Google said.
Google earlier this year revealed that its fleet of autonomous vehicles (prototypes and otherwise) have been involved just 11 accidents in 1.7 million miles of testing, all them minor ones with no injuries. Its cars were not at fault in any of the incidents.