A Cruise self-driving car, which is owned by General Motors Corp, is seen outside the company’s headquarters in San Francisco where it does most of its testing, in California, U.S., September 26, 2018.
A Cruise self-driving car, which is owned by General Motors Corp, is seen outside the company’s headquarters in San Francisco where it does most of its testing, in California, U.S., September 26, 2018. Reuters / HEATHER SOMERVILLE

San Francisco police were left scratching their heads after they pulled over a car earlier this month for driving without headlights at night and found no one inside.

In what otherwise would have been a great April Fools' Day joke, San Francisco police officers pulled over a driverless car operated by General Motor Co's Cruise unit on April 1 and found no one behind the wheel. The resulting video footage has gone viral online.

The two officers, who were not identified, pulled the car over and were puzzled by the lack of humans inside, according to a video posted on Instagram that has been viewed almost 80,000 times.

"Ain't nobody in it. This is crazy," said one of the officers, who tried to open the vehicle door before walking back to his cruiser. The car subsequently drove through the intersection and stopped again in the next block as bystanders laughed.

The video illustrated what Cruise Chief Executive Kyle Vogt previously said was one of the biggest challenges for autonomous vehicles - how to interact with humans.

Cruise, which blamed human error for the lack of headlights, said it works closely with the police on how to interact with its vehicles and has a dedicated phone number for police to call. Once the officer was clear of the vehicle, Cruise said the car relocated to the nearest safe location.

Cruise is operating a small number of vehicles to give full driverless rides to the public free of charge at night in San Francisco. The company is seeking the last regulatory approval required to launch commercial driverless service in the densely populated city.

Ironically, Cruise CEO Vogt last month had said a scenario where a police officer pulls over a driverless car has to go smoothly.

"You are kind of papering over all the weird stuff that can happen when there's no driver," he said at a Morgan Stanley conference.

The San Francisco police department said the officers were able to make contact with the vehicle's remote operator and a maintenance team took control. Cruise was lucky in another respect.

"No citation was issued during the traffic stop," the police department said.

Social media had fun with the incident.

"Insane that no citation was issued," Twitter user Theodectes said. "Why was this driverless car behaving as if it was completely drunk?"

"IT WAS DRIVING WITHOUT ITS HEADLIGHTS!!! Cops weren't confused, they we're probably questioning why cutting edge technology somehow can't turn its own lights on," Albino Guidedog said on YouTube.

(The story refiles to correct date.)