EL CAJON, Calif. — A truck driver died Tuesday on eastbound Interstate 8 after being impaled by an “improperly secured load” that crashed through the cab of the vehicle when he applied the brakes, according to an initial investigation by California Highway Patrol.

The incident, which happened at approximately 2:53 p.m. west of Dunbar Lane, involved a driver in a blue single cab Peterbilt truck that was towing a flatbed two-axle Fontaine trailer, CHP spokesperson Officer Travis Garrow said. It isn’t immediately clear why the driver hit the brakes, but the result of it caused the steel sheet piling to shift forward through the back of the cab and mortally wound the driver.

The driver, who has not been publicly identified, died at the scene of the crash, Garrow said. He was wearing a seatbelt at the time of the incident and it is not yet known if drugs or alcohol were a factor.

No other vehicles appear to have been involved.

As of 4:30 p.m., only the No. 2 eastbound lane is open to travelers. The No. 1 lane, where the incident occurred, is expected to be closed for approximately three hours, according to Garrow.

The incident remains under investigation.