Authorities were trying to determine Friday why a FedEx truck roared across the grassy median of a Northern California freeway and slammed into a charter bus, causing a fiery explosion that left 10 people dead and dozens more injured.
The National Transportation Safety Board sent an investigative "go team" from Washington to the scene on Interstate 5 near the town of Orland, about 100 miles north of Sacramento.
California Highway Patrol dispatcher Curtis Pahlka said the crash was reported at 5:41 p.m. Thursday. The crash killed the drivers of the truck and bus, five students and three chaperones.
NTSB Highway Safety Investigator Robert Accetta was leading the "multi-disciplinary" team sent to the site, the agency said.
The bus passengers were high school seniors on their way to visit the campus of Humboldt State University in Arcata, Calif. Glenn County sheriff's dispatcher Pauline Spooner said several people were airlifted to local hospitals with injuries.
"Humboldt State University is deeply saddened by a tragic accident... involving a charter bus filled with prospective students," the school said in a statement. "They were on their way to visit campus for the April 11 Spring Preview event. Our hearts go out to those who have been affected, and we are here to support them, and their families, in any way possible."
Many of the more than 40 students on board escaped through a window one of them had kicked open, running from the wreckage before the bus exploded behind them. One emergency responder said as many as 37 people needed treatment for injuries such as burns, broken bones and cuts.
"The victims were teenage kids. A lot of them were freaked out. They were shocked. They still couldn't grasp what happened,"said Jason Wyman with the Orland Volunteer Fire Department.
Steven Clavijo, 18, a student at West Ranch High School in Santa Clarita, said he was on the bus during the crash.
Clavijo said he was just getting ready to fall asleep in the back of the bus when he felt the vehicle begin to swerve.
"I just heard this loud boom," he said. "We knew we were in major trouble."
FedEx has a satisfactory safety rating, according to Federal Motor Carrier Safety Administration records. During the two-year period that ended Thursday, the company's vehicles were involved in 430 crashes in the USA. Nine of those were fatal crashes, 171 were injury crashes and 257 involved a tow truck.
FMCSA's website simply lists a motor carrier's involvement in reportable crashes with no determination as to responsibility.
The bus company involved in the crash, Silverado Stages of San Luis Obispo, also has a satisfactory safety rating. It was involved in one injury crash and one crash requiring a tow truck in the two years prior to Thursday, according to FMCSA.
Tommy Chang, the instructional superintendent for the Los Angeles School District, confirmed that students from Los Angeles schools were involved in the wreck, but he declined to provide further details.
The trip gave the students, "an amazing opportunity to see what this amazing state has to offer in terms of higher education," Chang said.
Contributing: Wiliam Cummings; The Associated Press