The death toll from a chain reaction of crashes on a Wyoming highway rose to four Friday as authorities spent the day clearing the charred wreckage from the road.

Thirty-three vehicles piled up Thursday between Cheyenne and Laramie, beginning with seven tractor-trailer rigs and a passenger car that became engulfed in flames. Other vehicles crashed as drivers stopped or swerved to avoid the first accidents.

Close to 40 people went to hospitals, and about a dozen remained there Friday.

Officials believe heavy fog, wet roads and speeding drivers were factors in the wrecks, but they do not yet know exactly what touched them off.

"It may be some time before we find out, if we ever find out," said Sgt. Steve Townsend of the Wyoming Highway Patrol (search).

Tom Throop said he encountered rain and fog as he and his wife traveled to Cheyenne on business.

"All of a sudden visibility just dropped very quickly" and his car hit the back of a semi truck, he told the Laramie Boomerang.

"We scrambled out of the car just as another car bashed into the back of our car," he said.

One body was found hours later, two more turned up overnight and the fourth was found Friday morning, Townsend said.

Traffic was diverted at Laramie while wreckage while crews cleared wreckage and repaired fire damage in a 100-foot section, state Transportation Department spokeswoman Lisa Murphy said.

Officials hoped to have the eastbound lanes of the busy highway reopened by late Friday afternoon.

The collisions occurred in a stretch through the Laramie Mountains (search) notorious for treacherous conditions, though not usually in summer. At 8,000 feet above sea level, the section is the highest along Interstate 80, which runs between San Francisco and New York.