A California officer stopped the prototype because it was travelling 24mph in a 35mph zone, causing a back-up in traffic.

The officer stopped the prototype vehicle in Mountain View, California, on Thursday as it travelled 24mph in a 35mph zone, causing a back-up of traffic.

The police department said in a blog post: “As the officer approached the slow moving car he realised 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.”

“We want them to feel friendly and approachable, rather than zooming scarily through neighbourhood streets,” it said in a blog post.

Google added: “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!”