The bullets hit a dark-colored Ford minivan. The driver pulled the van off the freeway in the Santa Fe Springs area, and then flagged down an ambulance.
Officials said three people were shot and taken to the hospital. One person died. The two other victims were in stable condition as of early Thursday morning.
No suspect information was released, and the motive for the shooting remained under investigation.
Anyone with information was urged to call the Los Angeles County Sheriff's Homicide Department at (323) 890-5500.