The collision occurred shortly before 4 a.m. near San Gabriel Boulevard, according to the California Highway Patrol.
One person was pronounced dead inside his vehicle, the CHP said. The Los Angeles County medical examiner's office later identified him as Seroj Anjelian.
The incident prompted the brief closure of all westbound lanes at the scene. The HOV lane was later reopened, but commuter traffic remained backed up for miles. All lanes were reopened after crews removed the vehicle wreckage.
Initial reports that the crash was a head-on collision involving a wrong-way driver were not confirmed.
The cause of the collision is under investigation.