Ric Francis, Associated Press
Structural engineers with the California Department of Transportation examine damaged walls of I-5 tunnel Sunday.

SANTA CLARITA, Calif. — With the work week fast approaching, authorities scrambled Sunday to move traffic around a major artery out of Los Angeles that was shut down by a fiery interstate tunnel pileup.

The main southbound lanes of Interstate 5 were to reopen this morning, authorities said, helping to alleviate some of the problem.

But on Sunday, Interstate 5 was still shut down in both directions, snarling traffic on surrounding roads, where drivers looked for alternative routes after Friday night's pileup crash left more than two dozen trucks and other vehicles in flames.

Commuters who depe nd on the stretch of freeway, which carries about 225,000 vehicles a day, faced the prospect of a nightmare getting to and from work.

"We're doing everything we can ... and we'll continue to re-evaluate our alternate traffic routes," said Warren Stanley, California Highway Patrol assistant chief.

Investigators determined that 31 vehicles — including big rigs and one passenger vehicle — were involved in the crash 30 miles north of Los Angeles that killed two men and an infant and injured at least 10 people, authorities said.

The fire spread from vehicle to vehicle, sent flames shooting nearly 100 feet in the air outside the tunnel and reached temperatures as high as 1,400 degrees.

The tunnel is a truck bypass that runs beneath eight lanes of I-5, the main West Coast interstate, linking Mexico and Canada. It is also a major route from Los Angeles to the city's northern suburbs.

The southbound lanes of I-5 were closed for 2 1/2 miles; the northbound side was closed for about a mile.

Two northbound truck-bypass lanes around the crash site, which cars would be permitted to use, could reopen as early as Sunday night, said Deborah Harris, California Department of Transportation spokeswoman.

Officials hoped to reopen the southbound lanes today with detours around the tunnel area, said Doug Failing, Transportation Department district director. Other northbound lanes could reopen 24 hours later.

Metrolink, which operates commuter trains throughout Southern California, planned to start running nonstop service with extra cars between downtown Los Angeles and Santa Clarita today, spokeswoman Denise Tyrrell said.

Gov. Arnold Schwarzenegger declared a state of emergency in Los Angeles County, which will allow the state to deploy emergency workers and equipment and give aid to local government.

Stanley refused to speculate on the cause of the crash. He did not know when findings would be released.

The pileup in the southbound truck tunnel began about 11 p.m. Friday. According to early reports, two big rigs collided on the rain-slickened highway.

It was remarkable that 10 people were able to escape on their own, given the extent of the crash and the intensity of the blaze, fueled for hours by truck cargo, said Los Angeles County Deputy Fire Chief John Tripp.

"When we look at tunnel fires ... it's pretty miraculous those people were able to get out," Tripp said.

The acrid smell of burned oil and rubber lingered Sunday at the 550-foot tunnel. The roadbed and walls where charred black, and concrete had fallen away in places, exposing the structure's steel skeleton.

The bodies of one man and a child were in the cab of a truck hauling cantaloupe, which appeared to have hit a pillar outside the tunnel, a fire official told The Associated Press on condition of anonymity because he was not authorized to speak about the incident.

The other body was found in a truck about 12 feet short of the tunnel's exit, said the official. All the bodies were burned beyond recognition, he said.

The tunnel, built in the 1970s, and its mix of curves and darkness has long been regarded by truckers as one of the most dangerous areas of the freeway.

Truck driver Fausto Angelino said he has been driving that stretch of road for 23 years.

"I hold my breath every time," he said.

But Failing insisted that the tunnel was safe if motorists drove with care.

Trucks use the road to haul produce from the Central Valley into Southern California and to move goods from the ports of Los Angeles and Long Beach into the state's north.

But Stephen Levy of the Center for Continuing Study of the California Economy said the shutdown would not cause much damage to the state's economy.

"Usually these things are a much smaller hit on the economy than people anticipate," he said. "Usually what happens is the goods that are hit get delayed for a bit, but it's not like they're actual losses."

The road would have to be closed two weeks or longer in order for it to seriously hurt the economy, although companies that sell perishable items may suffer during shorter delays, he said.