LOS ANGELES—A Tesla involved in a fatal crash on a Southern California freeway last week was operating on Autopilot at the time, authorities said. The May 5 crash in Fontana, a city 50 miles east of Los Angeles, is under investigation by the National Highway Traffic Safety Administration. The probe is the 29th case involving a Tesla that the agency has responded to. A 35-year-old man was killed when his Tesla Model 3 struck an overturned semi on a freeway at about 2:30 a.m. The driver’s name has not yet been made public. Another man was seriously injured when the electric vehicle hit him as he was helping the semi’s driver out of the wreck. The California Highway Patrol, or CHP, announced on Thursday that the car had been operating Tesla’s partially automated driving system called Autopilot, which has been involved in multiple crashes. The Fontana crash marks at least …