OXNARD, Calif. — Federal investigators are trying to determine why a pickup truck driver drove on to tracks and abandoned his truck, leading to a train crash that left three cars derailed and dozens injured in Southern California.

“It was not stuck, it was not bottomed out on the track or something like that,” National Transportation Safety Board member Robert Sumwalt said at a media briefing Tuesday at the crash site in Oxnard. Officials had said immediately after the crash the driver got stuck on the tracks.

“We’re very concerned about that, we’re very interested in it,” he said.

The badly wrecked truck’s emergency brake was in the on position and its headlight switch was in the high-beams position after the pre-dawn crash, Sumwalt said.

Eight people were admitted to the hospital of the 30 people who were originally examined, officials said. Four were in critical condition, including the train’s engineer.

The driver, Jose Alejandro Sanchez-Ramirez, 54, of Yuma, Ariz., was found 1.6 miles away and 45 minutes later, said Jason Benites, an assistant chief of the Oxnard Police Department.

Police said they tested Sanchez-Ramirez for drugs and alcohol but they would not discuss the results.

He was briefly hospitalized then arrested Tuesday afternoon on suspicion of felony hit-and-run, Benites said.

His Ford F-450 pickup was pushed some 300 feet down the tracks and ended up on the other side of the rail crossing, Sumwalt said.

The truck was badly wrecked, but investigators said the engine was intact, which may give clues as to what happened.

Sumwalt said his team had already recovered video and data recorders from the train and were sending them to Washington for analysis.

The federal agency doesn’t always investigate grade crossings, especially those with no fatalities, but this one was unusual enough to warrant it, Sumwalt said.

“It’s not your typical grade crossing accident,” he said.

Passenger Joel Bingham, a railroad aficionado and frequent passenger, said many of those aboard the train were asleep and shocked awake when the loud boom first happened.