The collision was reported shortly after 8:30 a.m. on the westbound side of the freeway near Lemon Street, according to a California Highway Patrol incident log.
The policeman is expected to be OK. There were no other reports of injuries.
Traffic was snarled in both directions in the aftermath of the crash, which prompted the closure of four westbound lanes. The freeway was fully reopened by 10:30 a.m., the CHP said.
The cause of the crash was under investigation. No citations or arrest was immediately announced.