Commuter Alert in the Nation’s Capital: “It’s March but…unseasonable heat forces trains to slow down during the afternoon commute.”
Train Tracks Strain under High Temperatures
On the Ides of March, I was stopped in my tracks as this following alert came over my cell phone.
The US Global Change Research Program (USGCRP) 2009 National Climate Assessment report notes that unusually hot days can deform tracks. To prevent derailment trains have to slow down, causing delays in shipping or, in this case, afternoon commutes. Temperatures above 90 degrees Fahrenheit can start creating consequences to transportation infrastructure, according to a 2008 USGCRP report known as “Synthesis and Assessment Product (SAP) 4.7” The National Research Council 2008 Transportation Research Board report lists equipment failure above 110°F air temperature. For rail transportation it is not only a matter of air temperature—the type of track design is also a critical factor that can slow trains on hot days.
“Sun kinks” – rail buckling
According to the SAP 4.7, on very hot days “sun kinks” can occur when the rail expands beyond what the constrained track can withstand, leading to lateral displacement or buckling of the track. Some have reached 30 inches or more displacement. The report also notes that tracks appropriately designed for hot summer temperatures such as in Galveston or New Orleans have expansion joints that can handle the extreme heat, but other cities have “continuously welded track” that is more prone to sun kinks. Improved track replacement can help as can concrete crossties with improved fasteners, which are less prone to buckling than wooden ties with spikes.
Another adaptation option reported in SAP 4.7 is to issue “blanket slow orders” with air temperatures above 95 °F to reduce all train speeds and help prevent derailments caused by buckling. Although it may be counterintuitive, SAP 4.7 highlights the critical period for such risks – the isolated hot day in springtime or early summer.This is in contrast to a lower risk of sun kinks, ironically, during the high summer when consecutive days are consistently hot.
Ides of March in the Nation’s Capital
On March 15, 2012, according to the National Weather Service, the high temperature recorded at National Airport was 80 °F. It was an unusually hot day for the region at this time of year and many commuters riding those rails returned home later than typical to their families. Until today, I have resisted using what some have called climate change—“global weirding”—but on the Ides of March the term global weirding kept ringing in my ears all day long.
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