G.M. Unit’s Self-Driving Taxis Are Subject of U.S. Safety Investigation

The main federal auto safety agency disclosed on Friday that it has begun a preliminary investigation into cars that a division of General Motors has been testing as driverless taxis in San Francisco.

The agency, the National Highway Traffic Safety Administration, said in a filing posted on its website that it had received reports that autonomous taxis operated by G.M.’s Cruise division had become immobilized on roadways, creating obstacles for other vehicles. The agency also said G.M. reported three incidents in which Cruise vehicles slowed suddenly and were hit from behind.

The agency said its Office of Defects Investigation would try to determine the scope and severity of the two types of incidents.

Regulators are increasingly scrutinizing autonomous and semiautonomous cars, and the claims automakers have made about them. The auto safety agency’s most high profile investigation in this area involves Tesla’s self-driving technology. Regulators are looking into at least 14 crashes involving Tesla cars driving on Autopilot that resulted in 19 deaths.

No fatalities or serious injuries have been reported in Cruise cars, but the auto safety agency said the vehicles could potentially put people at risk. When Cruise taxis stop unexpectedly, they “may strand vehicle passengers in unsafe locations, such as lanes of travel or intersections, and become an unexpected obstacle to other road users,” the agency said in its filing. “These immobilizations may increase the risk to exiting passengers. Further, immobilization may cause other road users to make abrupt or unsafe maneuvers to avoid colliding with the immobilized Cruise vehicle.”

The investigation covers 242 vehicles and is the first step before the agency could force G.M. to recall vehicles.

This year, Cruise began offering autonomous taxi rides in part of San Francisco and during low-traffic nighttime hours. It recently was cleared to expand the service to the city’s downtown area and to operate 24 hours a day. The division has been preparing to expand its operations to Austin, Texas, and Phoenix.

G.M. and other auto and technology companies have spent billions of dollars developing autonomous driving systems with hopes of offering taxi rides, deliveries and trucking services to consumers and other businesses. Waymo, which is owned by Google’s parent company, has been working on the technology for more than a decade and is offering driverless taxis in and around Phoenix. The company said on Friday it had started offering driverless taxi rides in San Francisco after receiving approval from California regulators.

In a daylong investor presentation last month, G.M.’s chief financial officer, Paul Jacobson, said the company believed Cruise could become a $50 billion business by 2030. “Cruise is an integral part of this and will expand to other cities,” he said. “They’re making really good progress.”

But progress has come much more slowly than originally expected, and some auto companies and investors have grown wary of putting more money into the technology because it may not produce significant sales or profits for years to come. In October, Ford Motor and Volkswagen said they would wind down Argo AI, the autonomous-car company they had invested in.

Cade Metz contributed reporting.