A JURY has awarded more than $US150 million ($A156 million) in damages to a 13-year-old girl who watched her family burn to death in a fiery crash on a southern California freeway.

"It's hard for her to comprehend'' the scope of the verdict reached last week in Los Angeles Superior Court, attorney Brian Brandt said Monday about his young client.

The jury found a California trucking company and one of its drivers liable.

Kylie Asam was nine when she and her 11-year-old brother, Blaine, managed to escape from their family's mangled SUV after it struck and got caught under a big rig parked on the shoulder of Interstate 210 nearly four years ago.

They saw their parents and older brother get burned alive after the vehicle they were trapped in caught fire.

The verdict included $US8.75 million the jury awarded to Blaine, who committed suicide on his mother's birthday, before the trial began, Brandt said. That money will go to Kylie as her brother's successor-in-interest, but all of the award will be placed in a trust until she is 18, he said.

A jury deliberated for about three days before finding Friday that the truck driver, Rudolph Ortiz, was negligent for parking on the side of the freeway in the early morning darkness without leaving on any light or emergency reflector.

Ortiz and his employer, Watsonville-based Bhandal Bros. Trucking, were found jointly liable.

Asam's wrongful death lawsuit alleged Ortiz pulled over to sleep, ignoring written warnings that stopping there was allowed only in emergencies.

The suit said Ortiz parked on the same shoulder Asam's father tried to reach after he struck debris on the freeway and tried to stop. The Riverside family was headed to Oregon to visit relatives for Thanksgiving when the crash occurred on November 22, 2009.

During the trial, defence attorneys countered that Ortiz stopped to take medication for a severe headache, which constituted an emergency. Attorney Raymond McElfish also contended the truck driver broke no law because he was parked on the dirt to the right of the shoulder.

Although California Highway Patrol officers found no debris on the road, Mr Brandt said a dent in the rim of one of the SUV's tires was proof that the SUV hit something.

He said the children flagged down a driver who used a fire extinguisher and shovelled dirt to try to put out the growing fire. The driver said Ortiz came out of the truck after a second 911 call was made to authorities.

The jury agreed that Asam's father also was negligent, but determined his actions were not a substantial factor in causing his family's deaths.

Kylie Asam now lives with her aunt and uncle in Orange County, California.