Transportation safety officials say it could be weeks before they know the cause of the collision between a FedEx tractor-trailer and a bus that took 10 lives, half of them Los Angeles-area high school students on their way to visit the college in northern California where they hoped to continue their education.
Even then, why the FedEx truck – which was hauling two heavy trailers – crossed a grassy median as it traveled south along I-5, slamming head-on into the bus and bursting into flames, may remain unclear.
"We don't know whether the FedEx driver had fallen asleep, whether he experienced a mechanical failure with his vehicle or whether there was a separate collision on the southbound side that caused him to lose control," said Lieutenant Scott Fredrick, lead investigator for the California Highway Patrol.
Witnesses report seeing the truck clip an automobile before careening across the median. One eye witness said the truck already was in flames before it smashed into the bus, which was headed north along California’s main north-south interstate highway midway between Sacramento and the Oregon border.
"It was in flames as it came through the median," Bonnie Duran told NBC News. "It was already in flames. It wasn’t coming from the front engine, it was more from behind the cab."
Both vehicles had devices that could shed light on the accident.
“There’s an electronic module on the bus that could tell us information about the speed, any hard braking that might have happened,” National Transportation Safety Board (NTSB) investigator Mark Rosekind told NBC. However, he added, any similar technology on the truck was most likely destroyed in the intense fire that raged through both vehicles.
"The big rig and the bus were both engulfed in flames,” said California Highway Patrol spokeswoman Tracy Hoover. “You are talking about two vehicles that are destroyed. There is hardly anything left of the truck.”
Those killed include the drivers of both vehicles and three high school chaperones, including a couple who had recently become engaged. The twin sister of one of the five students killed was riding on another bus headed toward Humboldt State University in redwood country on the northern California coast. More than 30 other passengers were injured, some of them seriously.
The trip from southern California was part of a program to help low-income and first-generation college hopefuls.
This week’s accident raises questions in two controversial areas:
Allowing double- and even triple-trailer tractors onto roads and highways. Such vehicles are harder to maneuver, especially in situations where stopping quickly can prevent deadly accidents.
And mandating the retrofitting of buses used by schools and tour operators with seat belts and other safety devices.
“While preventing accidents is always the goal, saving lives and reducing injuries in the event of an accident is also critical,” the NTSB states in its “most wanted” list for 2014. “Increasing the use of available occupant protection systems and improving crashworthiness to preserve survivable space can mean the difference between life and death.”
As the investigation continues, says the NTSB’s Mr. Rosekind, “The most important thing we can do is issue recommendations so that these kinds of accidents don't happen again.”
This report includes material from Reuters.