A truck driver died Tuesday on eastbound Interstate-8 in El Cajon after being impaled by an “improperly secured load” that crashed through the cab of the vehicle when he applied the brakes, KTLA sister station KSWB in San Diego reports.

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, California Highway Patrol 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 seat belt 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.

The incident remains under investigation.