Researchers for decades have tried to figure out how to keep steel railroad tracks from warping in high temperatures, the so-called sun kink that may have caused this week's derailment that injured more than 100 people.
Experts said the number of accidents blamed on heat-twisted track has dropped over the years, but no technology exists to stop it.
"It just happens out of the blue," said Andrew Kish, a researcher for the Transportation Department at the Volpe Center in Cambridge, Mass., who has studied the problem. "You can't really forecast it."
The buckling happens on welded rails that don't have joints, such as the CSX Corp. track the Amtrak train was on at the time of Monday's accident in Kensington, Md.
When heat expands the rail, there are no joints to create any extra room, creating pressure on the steel. When the pressure becomes too much, the track can buckle or bulge out more than a foot.
The problem arose in the 1950s, when rails became welded instead of jointed, Kish said. Welded tracks made for a smoother ride and reduced maintenance costs, but the change indirectly raised the potential for rail accidents.
To prevent buckling, railroads often heat existing track in an effort to condition it to high temperatures. In the South, tracks are typically heated to 100 degrees, while a 90-degree temperature is used in the North.
Improvements in track-laying technology and stronger alloys are also credited with dropping the number of sun-kink accidents over the years. But the problem has not gone away.
In 1980, there were 174 accidents resulting from buckled tracks, according to Federal Railroad Administration statistics. In 2001, 44 accidents were reported.
"I don't think anyone has found a way to totally prevent it, but they are relatively rare and there are a lot fewer now than there used to be," said Tom White, a spokesman with the Association of American Railroads.
"There's no such thing, that I'm aware of, where you can continuously inspect every inch of your track," he said.
Preventing buckling depends largely on how the tracks are installed. The rail must be laid at a temperature that will accommodate expansion and contraction causedby fluctuations in the temperature.
Crews can return and make adjustments to the track to accommodate different temperatures, a process that isparticularly important on heavily used tracks. Railroads often send crews out on hot days to look for buckling.
Montana Rail Link sends out crews whenever the temperature gets above 90 degrees and it slows down its trains.
Despite the precautions, one of the railroad's freight trains derailed this month near St. Regis, Mont. Railroad spokeswoman Lynda Frost said the accident was attributed to a sun kink.
Today, CSX said Amtrak and commuter rail services that use its lines will have to slow down on hot days.