LOS ANGELES — Federal safety regulators are sending a team to California to investigate a fatal freeway crash involving a Tesla, just after authorities near Oakland arrested a man in another Tesla rolling down a freeway with no one behind the steering wheel.

Experts say both cases raise pressure on the National Highway Traffic Safety Administration to take action on Tesla’s partially automated driving system called Autopilot, which has been involved in multiple crashes that have resulted in at least three U.S. deaths.

The probe of the May 5 crash in Fontana, California, east of Los Angeles, is the 29th case involving a Tesla that the agency has responded to.

“The details of whether the Tesla was in autonomous mode are still under investigation,” Officer Stephen Rawls, a spokesperson for the California Highway Patrol, said in an email Wednesday.

The Tesla driver, a 35-year-old man whose name has not been released, was killed and another man was seriously injured when the electric car struck an overturned semi on a freeway. The injured man, a 30-year-old passing motorist, was struck by the Tesla as he was helping the semi’s driver out of the wreck.

“We have launched a Special Crash Investigation for this crash. NHTSA remains vigilant in overseeing the safety of all motor vehicles and equipment, including automated technologies,” the agency said in a statement Wednesday.

The investigation comes just after the California Highway Patrol arrested another man who authorities say was in the back seat of a Tesla that was riding down Interstate 80 with no one behind the wheel.

Param Sharma, 25, is accused of reckless driving and disobeying a peace officer, the CHP said in a statement Tuesday.

Tesla, which has disbanded its public relations department, did not respond to messages seeking comment Wednesday.