Details about the confrontation that led to the gunfire were not immediately available.
The CHP said officers are looking for a while sedan in connection with the shooting. The car was seen on the northbound 55 Freeway sometime between 7:55 a.m. and 8:15 a.m.
A more detailed description of the car was not immediately available.
The CHP closed the northbound side of the freeway for several hours to search for clues.
Aerial video showed a line of law enforcement officers walking on the freeway in a search for evidence, possibly bullet casings.
The shooting was reported as authorities investigate a series of BB or pellet gun shootings on the 91 Freeway in Riverside and Orange counties. The CHP said the fatal shooting Friday was not related to the other shootings and stemmed from the road rage confrontation.