New York (AFP) - US authorities opened a preliminary investigation into General Motors’ Cruise autonomous driving program following sudden stop incidents, according to a notice seen Friday by AFP.

The National Highway Traffic Safety Administration is reviewing two types of incidents that result in Cruise vehicles “becoming unexpected roadway obstacles,” said the notice.

Cruise began offering first-in-the-nation commercial driverless taxi service to the public in part of San Francisco in June.

While there have been no fatalities from the incidents, the investigation comes on the heels of an ongoing NHTSA probe into Tesla’s “Autopilot” driver-assistance system.

The agency received three incident reports in which Cruise vehicles were struck by another auto from the rear following a “hard braking maneuver,” according to the notice.

The agency has also been alerted to “multiple” cases where unmanned Cruise vehicles became “immobilized,” stranding passengers in unsafe locations or becoming an impediment to others on the road.

“Immobilization may cause other road users to make abrupt or unsafe maneuvers to avoid colliding with the immobilized Cruise vehicle, by, for example, diverting into oncoming lanes of traffic or into bike lanes,” said the notice, which also cited the risk of delay to emergency response vehicles.

The review by NHTSA’s Office of Defects Investigation covers around 242 vehicles and aims to determine the frequency of the incidents and their safety consequences.

A Cruise statement highlighted that the service has run nearly 700,000 fully autonomous miles “in an extremely complex urban environment with zero life-threatening injuries or fatalities,” while there are more than 40,000 deaths annually on US roads, Cruise said.

“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,” Cruise said.

Cruise recalled 80 vehicles earlier this year to upgrade software following an incident in June in which one of its cars was hit from the rear by another vehicle after breaking sharply while making an unprotected left turn.

Two people were slightly injured, according to a report submitted to the California Department of Motor Vehicles.