SANTA CLARITA, Calif. — Investigators picked through scorched tire rims, truck axles, and other wreckage yesterday hoping to pinpoint what triggered a fiery interstate tunnel pileup that killed three, while police and commuters braced for a traffic nightmare at the start of the work week.

Interstate 5 was shut down in both directions around the crash site, snarling traffic on surrounding roads, where drivers looked for alternative routes after Friday night’s pileup engulfed more than two dozen trucks and other vehicles in flames.

Warren Stanley, California Highway Patrol assistant chief, refused to speculate on the cause of the crash but said authorities would finish their on-scene investigation Sunday. He did not know when findings would be released.

Investigators determined that 28 commercial vehicles — including many big rigs — and one passenger vehicle were involved in the crash, which killed two men and an infant and injured at least 10 people, said John Tripp, Los Angeles County deputy fire chief. 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, Tripp said. 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, the deputy chief said.