The National Highway Transportation Safety Administration (NHTSA) has formally opened a safety probe into Cruise, General Motor's autonomous driving subsidiary. The robotaxi, a heavily modified all-electric Chevrolet Bolt, reportedly has been having issues regarding unexpected braking and sudden immobility. Per Reuters, the government agency states that the vehicles "may engage in appropriately hard braking or become immobilized." Both problems, furthermore, "result in the Cruise vehicles becoming unexpectedly roadway obstacles."

So far, the NHTSA's early investigation covers a total of 242 autonomous vehicles built by Cruise. It's possible this is the first stage before a formal recall is issued. The current situation is the direct result of three reported crashes that involved Cruise vehicles.

All were hit from behind by other vehicles when the self-driving vehicles suddenly braked hard in traffic. The incidents happened in San Francisco, California where Cruise is operating a fleet of these autonomous vehicles.

To date, Cruise's safety record has been relatively solid. Its vehicles have "driven nearly 700,000 fully autonomous miles in an extremely complex urban environment with zero life-threatening injuries or fatalities," Cruise states. "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." For now, the NHTSA said it will continue with its probe to determine any potential safety-related issues as a result of the sudden braking and immobility.

It will also begin to review "the commonality and safety logic of the hard braking incidents" and the "frequency, duration and safety consequences associated with the vehicle immobilization incidents."

The timing of the probe is not the best for Cruise. Competition is heating up with rival Waymo and, to a lesser extent, Tesla. Cruise is aiming to enter additional markets and scale up its operations to thousands of more vehicles in 2023.

However, the NHTSA is rightly concerned about the three incidents involving "a hard braking maneuver in response to another road user that was quickly approaching from the rear. In each case, the other road user subsequently struck the rear of the ADS-equipped vehicle."

Cruise confirmed police did not issue any tickets in all three crashes. The ongoing probe may delay Cruise's petition to the NHTSA, filed last February, seeking permission to deploy some self-driving vehicles that lack a steering wheel, mirrors, turn signals, and even windshield wipers.