California Highway Patrol officers are investigating a fatal collision late Wednesday evening that left a Central Valley man dead in a big rig truck and a passenger in the truck with major injuries.

The crash happened around 11:40 p.m. Wednesday, when a 2009 Peterbilt tractor trailer heading southbound on Interstate 5, north of the 210 Freeway, “drifted to the left off the roadway for an unknown reason and collided with four attenuator barrels,” according to a CHP collision report. The truck “then struck a guard rail and subsequently collided with a concrete bridge pillar.”

The cause of this traffic collision is under investigation, according to CHP officers.

While the crash happened before midnight, the investigation took several hours and impacted the morning commute because the damage was so extensive that officers weren’t initially aware the collision was fatal, according to Josh Greengard, spokesman for the CHP-Newhall Area office. The cab of the big rig truck was so badly damaged the driver was not found in his seat.

“Those big rig cabs are fairly big, so he got pushed to the back of the passenger compartment,” Greengard said of the deceased. Once the CHP officers on scene learned the crash involved a fatality, which was at approximately 1:05 a.m., the investigation then required additional measures to be taken, he said.

“There was quite a backup (for early-morning commuters). It’s cleared now,” he said around 9:15 a.m. Thursday.

The passenger in the truck, a Porterville man, was left unconscious from major injuries sustained in the collision and was transported to Providence Holy Cross Medical Center for treatment.

The name of the deceased was not released by CHP officers pending the next-of-kin notification from the Coroner’s Office.