A charter bus run by Royal American of Glendale, Calif., skidded 100 feet down Interstate 40 Saturday morning when the driver flipped his vehicle following an unexplained drift into the median, the Los Angeles Times said Sunday.

A 31-year-old Los Angeles woman died at the scene when she was thrown from the bus, California Highway Patrol officer Taj Johnson said. Eight people suffered severe injuries and 13 others sustained minor injuries from the accident.

"We don't know why he allowed it to drift," Johnson said. "The driver himself didn't know why it drifted."

The crashed occurred at 70 mph shortly before 11 a.m., Johnson said, adding the temperature already reached 101 degrees by that time.

A Royal American charter bus burst into flames in December 2005 on its way to a casino in California, though there were no injuries in that incident, the newspaper said.