Bodycam shows a driverless Waymo car pulled over by Phoenix police officer

The police officer hits their lights, pulling over the vehicle in front of them, walks up to the driver's window, and ... there's no one inside.

It prompts a question that can only be asked in the handful of U.S. cities that allow autonomous vehicles: What happens when an officer stops a car and there's no driver?

That question, accompanied by a photograph of a Waymo autonomous vehicle that had been pulled over in central Phoenix on June 19, was posted on the social media website Reddit last month. Phoenix police and Waymo officials confirmed the vehicle was driving in an oncoming traffic lane near 7th Avenue and Osborn Road. There was no passenger, and no other cars involved.

Just after 11 a.m. on June 19, a Phoenix police officer initiated a traffic stop on the Waymo, according to police dispatch records. The vehicle drove into oncoming traffic, ran a red light and "FREAKED OUT," said the dispatch records, which are typed in all capital letters.

A spokesperson for Waymo initially declined to comment for this story. After The Arizona Republic confirmed it would still report on the traffic stop, Waymo provided a statement saying it wanted to offer more context than was posted on Reddit.

The vehicle "encountered inconsistent construction signage" and went into an oncoming lane of traffic, according to Waymo. That's consistent with the Reddit post, too.

The driverless car "was blocked from navigating back into the correct lane" for approximately 30 seconds, according to the company. That's when the officer pulled in behind the car.

"In an effort to clear the intersection, the Waymo vehicle proceeded forward a short distance and pulled into the next available parking lot," Waymo said, describing the traffic incident as lasting "approximately one minute."

The situation was cleared without further action. "UNABLE TO ISSUE CITATION TO COMPUTER," the police dispatch records say.

Phoenix police and Waymo confirmed the autonomous vehicles have equipment that senses emergency vehicles, so they should know when to pull over. Waymo's training guide for first responders says the cars can detect emergency vehicles, their lights and sirens.

When a vehicle is stopped, a Waymo can unlock its doors and roll down the windows, according to the guide.

Officers can use an intercom in the car to speak to an operator in real time or call a dedicated phone number, according to Phoenix police spokesperson Sgt. Brian Bower. The cars can also be put into a manual override so first responders can move them if necessary, Bower said.

The vehicle's in-car audio system allows first responders to communicate with Waymo Rider Support, which can provide insurance information and further instructions. If necessary, Waymo will dispatch support staff, the company's law enforcement guidance says.