Cover Story: Railroad tracks "sun kinks"

By Jeff Atkinson - bio l email

CHARLOTTE, NC (WBTV) - Charlotte, a city on the tracks.  And in this heat that could be a scary thought.  Scorching temperatures pose a threat to our trains and your safety.

There are thousands of miles of train tracks crossing the Carolinas.  And in extreme temperatures those tracks can come under assault by mother nature.

The heat may be to blame for a train derailment in Waxhaw on Thursday.  A freight train hauling grain and other goods jumped the tracks and spilled some of its load.

Fortunately, no one was hurt.  But the crash cut off one of the main roads in and out of the Union county town.  And luckily, the train wasn't hauling anything hazardous.

For many it's hard to imagine the extreme heat could cause something like this.  But it can happen when we have triple-digit temperatures like the east coast has experienced this week.

What happens to the tracks is known as "sun kink."  It's when the track buckles - becomes warped.  And if a train goes through the area too fast, it can cause a derailment.

Researchers have tried for decades to figure out how to keep it from happening.  But no technology exists to stop it.

"Whrrrrr."  The sound is familiar we hear it all the time.

Railroad tracks warping in high temperatures - what's believed to have caused the derailment in Waxhaw - we're not so familiar with.  But it does happen.

"The rail as it heats needs room to expand."

Larry Neal, chief of museum operations and education at the North Carolina Transportation Museum in Spencer and himself a certified brake man showed us how tracks can become buckled.

"You see there's four bolts that hold them in place."

Before 1950 he says rail came in 39-foot sections.  And there was room left where the track comes together to give the steel room to expand in the extreme heat.

These days to make for a smoother ride and less maintenance track comes in quarter-mile strips and is welded together - without the expansion joints.

Get an extremely hot day and steel expands.  Says Neal, "The rail heats up.. it gets to a point where the ties and everything can no longer hold it and the rail has nowhere else to go lineally so it'll pop out to the sides."

And with hot weather we've had recently, it's happening more frequently.

Problems with "sun kinks" also known as "heat kinks" have turned up in Greater Boston's public transportation system.  And in Philadelphia. Baltimore and on Washington, DC's METRO system.  All of them are cities who've been hit in the record heat wave.

In one of the most dramatic scenes, in July 2002, an Amtrak train derailed outside Washington, injuring more than 100 people.  The derailment linked in part to sun kink.

"In hot weather we increase our inspections of lines that could be affected," says Norfolk Southern Corp. spokesman Robin Chapman.

He said they if they do find a problem track a so-called "heat order" goes out notifying train crews to go slowly in that area until the track can be fixed or until it goes back in place on its own when the temperature drops.

"There were a lot more occurrences of this in year's past," says the NC Transportation Museum's Larry Neil.  "But because of better technology better understanding of metallurgy of rail they're improving the sun kink occurrences."

To prevent buckling railroads often heat existing track in an effort to condition it to high temperatures.  In the South tracks are typically treated to withstand up to 100-degrees.  While a 90-degree temperature is used in North.

Does this usually happen where the track comes together?  It can happen anywhere along the line.

Often the problem is caught before a train passes through but if the track bends too much we can see derailments.

The number of accidents resulting from buckled tracks have gone down over the years.  From 174 in 1980 to about 40 in 2001.  But nothing can prevent it from happening.

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