Trains run on big metal rails made out of steel. These rails are simple, tough, and fit for purpose. With no surface treatment, they stand up to the elements and the punishment from hundreds of trains passing by every day. They’ve changed little in recent decades. But then certain railways decided to start painting their tracks – and not just to be fashionable. Let’s examine why.
Today’s railways face a new challenge: excessive heat. As the global warming narrative finally makes good on its dreadful promise, daily temperatures are hitting exceptional highs in some areas. These temperatures often exceed what were once considered reasonable design limits for conventional railways.
The result? The rails expand too far on hot days, and all hell breaks loose. The British call it “buckling.” The Americans, inexplicably, call it “sun kink.” No matter what it’s called, the solution to this problem might be exceptionally simple: white paint.
We've certainly been feeling the heat– but we're not the only ones.
Did you know extreme heat can also affect train tracks?
Check out our blog to learn how: https://t.co/OzsJIAYrjL pic.twitter.com/0FXh7N4wPz
— CapMetro (@CapMetroATX) August 17, 2023
Paint It White
Hot summer days are becoming too much for infrastructure around the globe. Whether you’re dealing with a bridge in New York or a railway in Britain, the root cause of your problems is likely the same: Heat makes metal expand. Engineers account for this when designing infrastructure, but they can only do so much. Eventually, if things get too hot, they expand too far, and you get problems.
As rails grow longer in the heat, they tend to buckle, typically pushing out laterally and breaking free of their sleepers or ties. This can be a great danger, as buckled rails no longer maintain the correct orientation, support, or separation distance to support passing trains. Derailments are common on buckled track if the problem isn’t identified before a train reaches the deformed rails.
Modern railways use continuously welded steel rails, where each length of rail is welded onto the previous one to create a continuous run. In extreme cold, the steel rails may contract so much that they snap, and in extreme heat, they may expand so far that they buckle or kink.
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The temperature range a railway can operate in is set during the construction process through a process called “rail stressing.” The track is installed in a stressed state, such that at a given “stress-free temperature” (SFT) there is no tension or compression caused by thermal effects. In the United Kingdom, for example, rail is typically installed so that it sits in an unstressed state at 80.6 °F (27 °C), the mean temperature in summer. In the US, rail is usually set for a stress-free temperature of 95 to 109 °F.
However, exceed this temperature by too much, and the rail may buckle. With an SFT of 80.6 °F, much of the British rail network is safe up to a track temperature of 114 °F (46 °C) before it buckles. This corresponds with an ambient temperature of around 86 °F (30 °C). However, as ambient temperatures continue to rise, rails are at times exceeding 123 °F (51 °C). The hotter the temperature, the more likely the rails will buckle.
Numerous mitigation methods exist to avoid buckling. On hotter days, railways may choose to run trains more slowly, in an effort to reduce forces on the rails and lessen any destabilizing disturbances. Services may be canceled entirely to avoid the risk of derailment.
Rails can also be installed with higher stress-free temperatures, allowing them to withstand hotter conditions. However, this makes them more susceptible to fractures in cooler temperatures. This is often unacceptable for areas with cooler climates.
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🛤️ If we stressed our rails for exceptionally hot weather, they wouldn’t be safe for the winter and we’d have broken rail because it’s too cold. ❄️🌏 That’s why other countries choose different temperature ranges depending on their climate. pic.twitter.com/VVCLbPT5NB
— Network Rail (@networkrail) July 19, 2022
Cooling the rails is becoming an altogether more popular solution, however. It’s remarkably simple to achieve, too. Simply by covering the rails with white paint, their temperature can be reduced by anywhere from 9-18 °F. In many cases, this is enough to bring the rails back down to a reasonable temperature where buckling isn’t an issue.
Only the sides of the rails are painted. There’d be no value in painting the top, as paint would quickly wear away under the weight of a locomotive. Besides, the shiny top surface is relatively reflective already.
Spotted white rails while looking our your train window? We paint these so they absorb less heat – and expand less. Typically, a rail painted white is 5°C to 10°C cooler than one left unpainted. pic.twitter.com/KRs7Zndkmm
— Network Rail Scotland (@NetworkRailSCOT) July 16, 2022
The mechanism behind this is simple. The dark surface of a railway track will absorb a great deal of heat energy from the sun. Cover the track in white paint, however, and a great deal of that solar energy will instead be reflected rather than absorbed. Having absorbed less energy from the sun, the track will remain cooler. The same technique works for buildings, too, and has been considered a useful technique to help keep homes cooler.
Paint can be applied simply by hand, or with specialist equipment. In Britain, rail workers are stuck trudging along with brush and bucket. Indian railways appear to have developed push carts to do the job more easily. Italian railways use dedicated service vehicles to spray the rails. In certain areas, the paint is applied each summer to keep temperatures in check.
https://www.facebook.com/watch/?v=850471592005436
Brits paint by hand.
Indian crews use push carts to spray the rails.
Italian operators have a spray vehicle built especially for this purpose.
Painting the rails might seem odd at first glance. Under normal circumstances, it would seem like a fool’s errand. “Go and paint the rails to keep the sun off!” you’d tell the apprentice. And yet, white paint is instead proving a crucial tool for railways to keep their operations running under hotter summer temperatures. It’s a strange world we live in, but as it changes, we’ll find ourselves turning to strange solutions like these more often than you might think.
Image credits: Network Rail, Network Rail via Facebook screenshot, Ferrovie.info via YouTube, US DOT