The suspect was arrested after the multi-vehicle crash, which resulted in a partial closure of the interstate, authorities said.
The officer and his partner had pulled over a motorist on the right shoulder of the 405, near Santa Monica Boulevard, when the collision pinned the officer between two vehicles.
The policeman suffered a leg injury and was transported to a hospital where he underwent surgery. He is expected to survive.
California Highway Patrol officers happened to be driving near the scene shortly after the incident.
"They said it could have been maybe even a minute right after it happened," said Officer Vance Perreira, a CHP spokesman. "They passed by, were first on scene, rendered aid, possibly saving his life."
The driver of the vehicle that struck the officer was arrested after officers administered a field sobriety test, Perreira said.
Following an hourslong closure of the northbound side of the freeway all lanes except one were reopened by 7:30 a.m. Tuesday, according to the CHP.
An investigation into the crash is ongoing.
SIGALERT UPDATE: NB I-405 SOUTH OF SANTA MONICA BLVD, ONLY #5 LANE IS STILL BLOCKED DUE TO A TRAFFIC COLLISION UNTIL FURTHER NOTICE— CHP PIO - LA County (@CHPsouthern) December 12, 2017