The SigAlert was finally lifted around 6 p.m., some three hours after the closure. It was expected to take some time before traffic would clear.
The CHP initially shut down all lanes northbound in the Castaic area after the spill, reported just after 3 p.m.
The truck was carrying about 4,500 gallons of hydrogen peroxide, but it wasn't clear how much of it spilled onto the road.
People were seen getting out of their parked cars on the freeway, walking around and even skateboarding as they waited.