Most often, a derailment is caused by speeding around a turn, as was the case in fatal Amtrak crashes in Washington and Philadelphia in recent years. Since those crashes, Amtrak has installed a braking system that prevents trains from exceeding certain speeds and that applies brakes to avoid collisions with other trains or railroad equipment.
“The single largest cause of derailments and accidents are what are called human factors,” said Allan Zarembski, director of the Railroad Engineering and Safety Program at the University of Delaware.
But in this case, he said, the human factors that might cause an accident like this didn’t appear to be present. “More than likely, something broke.”
Excluding human error, he said, most wrecks are caused by faulty equipment — maybe a wheel or an axle, or the track itself.
The train derailed on tracks owned and maintained by BNSF Railway Company, a freight railroad. Most of Amtrak’s national network runs on tracks that belong to freight railroads, meaning Amtrak is not responsible for track upkeep. A BNSF spokesman, Matt Brown, said Sunday that the section of track where the train derailed was last inspected on Sept. 23.
Some passengers reported that the train ride felt bumpy for many miles, which might signal a problem with the train’s suspension system. But even if a train’s crew takes note of a problem like that, its source could be difficult to identify while the train is running between cities, Mr. Zarembski said.
If the turbulence was more sudden, Saturday’s heat could also be to blame, said Russell Quimby, a retired accident investigator for the National Transportation Safety Board.
Mr. Quimby said he suspects the train may have hit a section of the track that had buckled from overheating.
“When that happens, the train can’t negotiate that tight little change in the curvature of the track, and it will run up over the rail and derail and fall over the side like you see in the pictures,” he said.
Around the time of the accident, the temperature in Joplin peaked at 84 degrees. Railroad tracks are usually about 20 to 30 degrees hotter than the outside temperature, Mr. Quimby said, which “could be well above” what the tracks were designed to withstand (emphasis added).