A bobtail truck traveling at an unsafe speed into traffic slowing for a construction zone may have set in motion the fiery wreck that killed three people Monday on Interstate 5 in the Woodland area, the California Highway Patrol reported.

Two adults and a child died in the chain-reaction collision that sent five vehicles up in flames in the southbound lanes of the highway near County Road 102, around 12:45 p.m., authorities said.

A preliminary collision report released by the CHP on Tuesday states the bobtail truck apparently merged into the left lane of the two-lane highway just as traffic was slowing for a lane closure. The truck then "struck several slower moving and/or stopped vehicles that were traveling" in the left lane, the release states.

A 53-year-old man and 49-year-old woman, both of Oregon, died in a 2004 Chevrolet sport-utility vehicle, according to the CHP report. A 2-year-old girl, who was riding in a 1996 Acura Integra, also died at the scene, according to the report. Their names were not released.

The Yolo County Coroner's Office was still working Tuesday to determine whether the deaths were caused by the impact or ensuing fire, a spokesman said.

Authorities are in the early stages of determining the events that led up to the crash, as well as its cause, said Officer Adrian Quintero, CHP Valley Division spokesman. The Valley Division Multidisciplinary Accident Investigation Team, which is conducting the investigation, is interviewing witnesses and gathering evidence, Quintero said.

The CHP release indicates alcohol and drugs are not believed to be factors in the collision. It states the speed of the truck before the collision has not been determined.

But Sharen Vierra, 63, of Redding, who said Tuesday that she narrowly avoided being involved in the collision, said traffic had come to an abrupt stop in the southbound lanes when she looked in her rear-view mirror and saw the truck "flying at me."

"I didn't see it changing its speed or anything," she said.

Vierra said she accelerated out of the left lane into the center divide and then saw the truck hit the vehicle that had been in front of her. She said the fire ignited immediately after the collision.

"All of a sudden there's instant, huge flames and black smoke on top of it," she said.

Laurie Ward, 51, of Lower Lake, who was identified by the CHP as the driver of a 2010 Ford van that was rear-ended in the collision but did not catch fire, said the truck driver was trapped inside the toppled, flaming vehicle, nearly hanging upside down, and had to be helped out by an occupant of another vehicle involved in the crash.

Ward said she placed a sleeping bag from her van around the injured driver, then tried to restrain a young woman who was "screaming frantically" that her child was trapped in another burning car on the grassy median.

"She was running toward the flames and stopping, but she kept trying to go forward," Ward said. "I could see there was no way she could get to where she was trying to get to. It was completely engulfed."

Two adult occupants of the Acura Integra, a 21-year-old Washington woman and a 61-year-old man from Riverside, were transported to Mercy San Juan Medical Center with moderate injuries, according to the CHP news release. Calls seeking their condition were unsuccessful.

Four occupants of a 1998 Ford Expedition also involved in the collision were transported to UC Davis Medical Center with minor to moderate injuries, the CHP reported. A 39-year-old woman was still hospitalized in good condition as of Tuesday afternoon, and the others had been discharged, said Charles Casey, hospital spokesman.

The driver of the bobtail truck, a 38-year-old Elk Grove man, was hospitalized with major injuries, including a broken wrist, cuts to his head and burns, the CHP reported. His condition Tuesday was not available.

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