A 20-year-old driver was killed and two passengers were injured in a solo-vehicle crash early Saturday on Interstate 5 near Camp Pendleton, a California Highway Patrol officer said.

The man was driving north on I-5 around 5:45 a.m., just south of Las Pulgas Road, when for unknown reasons he veered his BMW coupe left into the center median guard rail. The car then veered back to the right, where it overturned and crashed into a call box and barbed wire fence, CHP Officer Hunter Gerber said in a news release.

The driver, a resident of Mount Vernon, Wash., died in the crash. His name was not released.

A 21-year-old Oceanside man who was a passenger in the car suffered major injuries not thought to be life-threatening. Another passenger, a 19-year-old woman, suffered minor injuries.

Investigators are trying to determine if drugs or alcohol played a factor in the collision, and the investigation is ongoing.

Anyone who witnessed the crash or has information about it was asked to contact the Oceanside area CHP office at (760) 643-3400.