A Canadian man has been charged with dangerous driving for allegedly taking a nap while his self-driving Tesla car clocked up more than 90mph (150km/h).
Police said both front seats were fully reclined, and the driver and passenger were apparently asleep when they were alerted to the incident in Alberta.
When police turned on emergency lights and other vehicles moved out of the way, the Tesla Model S sped up.
The 20-year-old driver from British Columbia is due in court in December.
He had initially been charged with speeding and handed a 24-hour licence suspension for fatigue, but was subsequently charged with dangerous driving.
The incident happened near Ponoka, some 100km south of Edmonton, in July.
"Nobody was looking out the windshield to see where the car was going," Police Sgt Darri Turnbull told CBC News.
He said that when they put on their emergency lights the Tesla accelerated, with vehicles ahead of it moving out of the way.
"Nobody appeared to be in the car, but the vehicle sped up because the line was clear in front."
He added: "I've been in policing for over 23 years, and the majority of that in traffic law enforcement, and I'm speechless. I've never, ever seen anything like this before but of course the technology wasn't there."
Tesla cars currently operate at a level-two Autopilot, which requires the driver to remain alert and ready to act, with hands on the wheel.
Tesla founder Elon Musk has said he expects his vehicles to be completely autonomous, with little driver input needed, by the end of the year.
However, he added that there were "many small problems" that would need solving through real-world testing.