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Nick Ut, Associated Press
Firefighters aim a stream of foam at a burning double-tanker truck gasoline fire in Montebello, Calif, Wednesday, Dec. 14, 2011. Thousands of motorists were stuck on a 10-mile stretch of freeway near Los Angeles after the big-rig tanker truck burst into flames Wednesday. No one was injured.

LOS ANGELES — After three days of frustration for both Southern California motorists and construction crews, officials hoped to have the fire-damaged Pomona Freeway reopened on Saturday.

Test showed that the part of the bridge spanning the freeway's westbound lanes was safe and would not need to be demolished, which would have taken longer, delaying the reopening of the busy artery.

Southern Californians endured another nightmarish commute Friday after crews discovered telephone lines nestled in asbestos inside a bridge in suburban Montebello that was weakened when a fuel tanker caught fire beneath it on Wednesday.

Crews that had expected to quickly tear down part of the bridge and reopen a 10-mile section of freeway providing a key link between Los Angeles and its eastern suburbs suddenly realized the work would last into the weekend. And that meant the hours-long rush-hour delays commuters have been enduring since the freeway was closed would continue until then.

Rather than just knock down the damaged section of bridge, workers must gingerly dismantle it, taking care not to release cancer-causing asbestos into the air or cut off telephone communications to thousands of people.

"It's pretty complicated," said Scott J. Brandenberg, an associate professor of engineering at University of California, Los Angeles. "Bridges are designed to be built to last and stay in place. They're not like interchangeable pieces where you pop out a bridge and put a new one in place."

Repair crews had to stop working on the 36-foot wide, 125-foot long bridge Thursday night when they uncovered the tangle of telephone wires buried under a sidewalk.

"In construction anything is normal," said Caltrans spokeswoman Judy Gish, adding that crews have been working around the clock. "With these types of structures you just don't know what you're going to find until you go in there."

The phone lines were not damaged by the fire but the asbestos posed a health threat, so hazardous materials crews and phone company officials were called in. After unearthing all the lines, crews were working to build an I-beam to drape the lines across to keep from disrupting telephone service.

Meanwhile, the cause of the tanker fire remained under investigation. There was no crash, so investigators planned to look at other factors, such as possible brake or other mechanical failure.

The truck was hauling 9,000 gallons of gasoline when it burst into flames Wednesday afternoon just under the Paramount Boulevard Bridge in Montebello, about 12 miles east of downtown Los Angeles.

The driver was not hurt, but the intense flames and heat melted the truck, cratered the road beneath it and cracked the concrete on the overpass so that chunks crashed onto the pavement below.

Tens of thousands of drivers use the freeway daily to commute from communities in eastern Los Angeles County and adjoining Riverside and San Bernardino counties. It also is a main route for trucks delivering vast streams of goods from the ports of Los Angeles and Long Beach to inland warehouses.