The National Highway Transportation Safety Administration announced Thursday that it is opening an investigation into the self-driving technology behind General Motors’ robotaxi fleet. This announcement follows three reported accidents allegedly caused by Cruise vehicles braking hard or otherwise becoming immobilized in traffic, creating unannounced obstacles for other vehicles and resulting in rear-end collisions with other motorists.

“With respect to the incidents of hard braking, NHTSA has received three reports of the ADS initiating a hard braking maneuver in response to another road user that was quickly approaching from the rear,” the agency reports, noting that human supervisors were aboard for each incident. “In each case, the other road user subsequently struck the rear of the ADS-equipped vehicle.”

“With respect to the incidents of vehicle immobilization, NHTSA has been notified of multiple reports involving Cruise ADS equipped vehicles, operating without onboard human supervision, becoming immobilized,” the report continues. “When this occurs, the vehicle may strand vehicle passengers in unsafe locations, such as lanes of travel or intersections, and become an unexpected obstacle to other road users.”

In response the company touted its technology’s history of safe operations. “Cruise’s safety record is publicly reported and includes having driven nearly 700,000 fully autonomous miles in an extremely complex urban environment with zero life-threatening injuries or fatalities,” Hannah Lindow, Cruise spokesperson, told Engadget via email. “This is against the backdrop of over 40,000 deaths each year on American roads. There’s always a balance between healthy regulatory scrutiny and the innovation we desperately need to save lives, which is why we’ll continue to fully cooperate with NHTSA or any regulator in achieving that shared goal.”

The company goes on to argue that in the cases of hard braking, the vehicles were reacting to the actions of other drivers, had a human operator onboard (though the ADS was in control at the time), and has already met with the NHTSA regarding each incident. Cruise frames the immobilization events as equivalent to a flat tire, wherein the ADS encounters an unexpected and potentially dangerous situation, turns on the vehicle’s hazards and pulls off to the side of the road.

Cruise LLC is headquartered in San Francisco and was founded in 2013 by Kyle Vogt and Dan Kan. GM acquired the autonomous driving technology company three years later. Since then, General Motors has lavished its subsidiary with funding, facilities and staffing, even going so far as to develop its own processor chips for the Origin autonomous shuttle bus. The company began testing ADS rides in San Francisco in June, 2021 and earlier this year earned regulatory approval to charge for driverless taxi services within the city. 

The company has also suffered setbacks in its pursuit of self-driving taxis. Division CEO Dan Ammann stepped down from his position in June, replaced for the interim by CTO and founder Kyle Vogt. Cruise made headlines in April when a police officer tried and failed to pull one over during a traffic stop and again in June when seemingly all of them decided that the corner of Gough and Fulton would make for a perfect impromptu parking lot.   

As the NHTSA is sure it’s aware of every braking/immobilization incident to date, the agency is opening a preliminary evaluation,”to determine the scope and severity of the potential problem and fully assess the potential safety-related issues posed by these two types of incidents.” It has not announced a timeline for publication of the PE’s findings.