A California police officer made a traffic stop - but wrote no ticket as the car had no driver.

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

He noticed the car going a road-clogging 24mph in a 35mph zone and realised it was a Google Autonomous Vehicle.

The officer then stopped the car and contacted its operators to let them know it was impeding traffic.

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

The Google project responded in a blog post, saying it has never received a ticket and adding: "Driving too slowly? Bet humans don't get pulled over for that too often."

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