All lanes on the northbound 5 Freeway in Castaic were back open after a spill and hazardous materials investigation shut down the roadway for several hours, authorities said.
The California Highway Patrol issued a SigAlert at around 3 p.m. for the northbound 5 Freeway, south of Templin Highway. All lanes were blocked for an unknown duration of time, the CHP said.
Hydrogen peroxide was the hazardous material identified by the CHP.
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Monday of Memorial Day weekend is one of the busiest travel days of the year, so the closure was affecting traffic and causing serious delays for holiday travelers. Traffic was backed up at least as far back as Valencia as of 3:55 p.m.
All lanes were back open as of 6:10 p.m., the CHP said.