One of Google's self-driving cars was causing a traffic jam in Mountain View, CA on Thursday — but it wasn't in an accident. A police officer pulled over the driverless vehicle because it was driving too slow (24mph in a 35mph zone, to be exact). But, unlike so many senior citizens and driving students in similar scenarios, Google's car didn't get a ticket.The company explained what happened in a post on Google+ : "We’ve capped the speed of our prototype vehicles at 25mph for safety reasons. We want them to feel friendly and approachable, rather than zooming scarily through neighborhood streets," the post says. Yeah, the world isn't quite ready for zooming robo-cars yet.And, as it turns out, the car wasn't breaking any laws by traveling on the road it was on, as the Mountan View PD explained in a blog post of its own. Here's the officer's account:As the officer approached the slow moving car he realized it was a Google Autonomous Vehicle. The officer stopped the car and made contact with the operators to learn more about how the car was choosing speeds along certain roadways and to educate the operators about impeding traffic... The Google self-driving cars operate under the Neighborhood Electric Vehicle Definition per 385.5 of the California Vehicle Code and can only be operated on roadways with speed limits at or under 35 mph. In this case, it was lawful for the car to be traveling on the street as El Camino Real is rated at 35 mph.