Westbound lanes of the 60 Freeway were reopened Thursday night after a big-rig fire led authorities to shut down the busy artery in both directions in Hacienda Heights.
The California Highway Patrol said the lanes were opened shortly before 9 p.m.
The eastbound lanes could open around 11 p.m., the CHP said.
The cab of the big rig burst into flames on the eastbound side of the freeway shortly before 3 p.m. The rig was carrying tanks filled with compressed hydrogen.
The closure created a rush-hour traffic nightmare as vehicles flooded adjacent surface streets and the 10 and 210 freeways, which also run east and west across the San Gabriel Valley.
Eastbound traffic on the 60 Freeway was being diverted to the 605 Freeway, and westbound vehicles were being diverted at Azusa Avenue. The freeway is one of main arteries connecting Los Angeles to the San Gabriel Valley and Inland Empire.
After the cab fire was knocked down, firefighters continued spraying the tanks with tens of thousands of gallons of water.
The water kept the tanks cool while the compressed hydrogen was burning off through an emergency relief valve, Los Angeles County Fire Department Inspector Anthony Akins said.
"The threat of explosion is reduced when the valve works properly," he said.
The CHP said the tanks initially contained about 1500 pounds of compressed hydrogen. The woman who was driving the big rig was not injured.