More than a dozen of Cruise’s robotaxis blocked off a street in San Francisco last week after randomly gathering together.

Images first shared to Reddit show a fleet of Cruise robotaxis stopped at and around the intersection of Gough and Fulton Streets. While Cruise has been testing its self-driving technology in San Francisco for a few years now, it only recently launched its commercial robotaxi service where there is no human safety driver behind the wheel.

The photos were snapped at approximately midnight and show the vehicles stopped randomly in the middle of the road. It is understood that employees from Cruise arrived on the scene in roughly 20 minutes but that it took a long time before all of the cars could be moved and the street cleared.

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In a statement issued to Tech Crunch, a Cruise spokesperson didn’t reveal what had caused the incident.

“We had an issue earlier this week that caused some of our vehicles to cluster together,” the spokesperson said. “While it was resolved and no passengers were impacted, we apologize to anyone who was inconvenienced.”

Cruise is rolling out as many as 30 robotaxis as part of its commercial service in San Francisco. The vehicles are limited to a maximum speed of 30 mph (48 km/h), can only operate between 6 a.m. and 10 p.m., cannot go to downtown or onto highways, and are prevented from driving at times of heavy fog, rain, or smoke.

The introduction of the robotaxi service comes just a couple of weeks after a Cruise test vehicle blocked a fire truck responding to an emergency. Cruise asserts that its test vehicle behaved as designed and yielded to the fire truck after blocking it for 25 seconds.