MOUNTAIN VIEW, Calif. — A California police officer made a traffic stop, but wrote no ticket. There was no driver to give it to anyway.

Mountain View police said in a statement that an officer pulled over a Google self-driving car that was being tested on local roads Thursday.

The officer noticed the car going a road-clogging 24 mph in a 35 mph zone and realized it was a Google Autonomous Vehicle. He stopped the car and contacted its operators to let them know it was impeding traffic, but no citation was given.

A person is required to sit behind the wheel of self-driving cars.

The Google project responded in a blog post, saying it’s never received a ticket and adding, “Driving too slowly? Bet humans don’t get pulled over for that too often.”