Federal safety investigators joined Oregon state police on Monday in trying to find out what caused a tour bus to veer off a mountain highway and plunge down a snow-covered slope, killing nine passengers and injuring 39 others.
The charter bus was carrying nearly 50 people, about two dozen of them holding foreign passports, through the Blue Mountains of northern Oregon en route from Las Vegas to Vancouver, British Columbia, when it crashed through a guard rail on Interstate 84 shortly after 10 a.m. on Sunday, authorities said.
The foreign nationals included South Koreans, Japanese, Taiwanese and Canadians along with American passengers.
The bus rolled over at least once as it careened 200 feet down the embankment before coming to rest upright in the snow at the bottom of a hill, according to the National Transportation Safety Board. Oregon State Police Lieutenant Gregg Hastings said many of the victims were ejected from the bus.
Photos of the crash scene posted by the state police showed that part of the vehicle's roof was crushed.
"This was a very horrible, tragic crash which led to many people's lives being lost and many people being injured," Hastings said. "We still want to keep that in perspective."
Authorities said they could not immediately explain what triggered the accident, which occurred near the town of Pendleton, about 200 miles east of Portland. Attention turned early on to road conditions but a full investigation was expected to take at least four weeks to complete.
Hastings said troopers arriving on the scene found icy spots along on the stretch of road where the bus hit a concrete barrier along the highway's inside median, then veered across both westbound lanes of traffic and plowed through a guard rail.
At an afternoon news conference on Monday, Hastings said investigators had yet to determine the speed of the bus at the time it crashed.
A spokesman for the state transportation department, Dave Thompson, told Reuters on Monday that the area where the crash occurred "is well known for treacherous conditions in winter."
Road surfaces there at the time were generally were "icy in spots, with some areas of packed snow, and that's absolutely typical for the area at this of the year."
Thompson said road crews had been out spreading sand in the area and that one sand truck "was just turning around after having passed the bus" on the highway shortly before the crash, but he said he did not know the condition of the highway surface where the bus veered off the interstate.
The NTSB, which has made improved motor coach transportation safety a top priority, said Monday it was sending a team to investigate the accident. A spokesman for the agency in Washington, Terry Williams said, "We'll be looking at the man, the environment and the machine."
The 49 passengers on the bus ranged in age from 7 to 70, though most of them were adults, and none of the nine killed were believed to be children, Hastings said.
In addition to nine passengers confirmed killed, 39 people were transported to area hospitals with injuries, authorities said. Of those, 29 remained hospitalized on Monday, several in serious condition.
Investigators had spoken to the driver, who was also injured, Hastings said.
According to the NTSB, more than 250 people were killed and 20,000 injured in bus-related crashes in 2009, the latest year for which data was available.
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