The incident occurred on the northbound 405 Freeway between the 110 Freeway and Normandie Avenue at about 12:30 a.m.
CHP says the woman and a man were pushing his 1995 Toyota that had run out of gas to the side of the freeway, when she was fatally struck by a passing BMW. going about 75 mph.
The victim, later identified as Stephanie Hernandez Valerio, 21, of Lawndale, was thrown from the far right lane of the five-lane freeway into the No. 2 lane. She was then struck by a 2003 Audi.
The 405 Freeway was shut down for several hours following the incident, but has since reopened. No arrests have been made.
The investigation is ongoing. Anyone who may have witnessed the traffic collision was asked to contact CHP Officer D. Weeda at (310) 516-3355.