An overturned semi-trailer Wednesday night caused a major traffic backup on northbound I-5 north of Parker Road in Castaic.
All lanes were blocked for several hours, according to the California Highway Patrol. Traffic was being diverted off at Parker Road.
All but one lane was reopened by 6 a.m. Thurday.
The crash was reported at about 9:42 p.m. Further details were not immediately released.