One of the iconic sensory experiences of train riding is actually the sound of ingenuity. As steel railroad tracks heat, they grow: 1,800 feet of track expands by more than an inch for every 10 degrees Fahrenheit of temperature increase. So rails were laid in sections – each between 30 and 60 feet long – with small gaps.
“The very specific railroad noise you hear— chuchat… chuchat… chuchat… chuchat… chuchat — is because there is a gap between the rails, and this gap is intended for such expansion,” says Dev Niyogi, who studies urban climate extremes at the University of Texas at Austin.
However, in a severe heat wave, the track can swell until the underlying tires can no longer contain it. Then the rail becomes visibly undulating and turns into what is known as a sunknife. This is a serious danger to trains, which can derail on wrong tracks. In extreme cases, the track can bend violently, from a straight shot to grotesque curves almost immediately. So if it’s excessively hot, rail services will slow down their trains as a precaution, providing less of the mechanical energy that can lead to buckling. Amtrak, for example, limit speed to 80 miles per hour if the rail temperature reaches 140 degrees. That was partly the reason behind Amtrak delays in the Northeast Corridor, which runs between Washington DC and Boston, during a brutal heat wave last month. (Amtrak did not respond to multiple requests for comment for this story.)
As extreme heat waves worsen, more tracks will turn into sunspots — disrupting commuter rail service that cuts carbon emissions and slows warming. In 2019, a study estimated that the US rail network could see additional delay costs totaling between $25 billion and $45 billion by the year 2100, in a scenario that assumed greenhouse gas emissions decline over the next 20 years.
Compared to a tree falling on top of a track and blocking traffic, or a switch breaking, heat is a much bigger, more difficult problem for rail operators to deal with. “Heat waves tend to be regional, so the impact can be large,” said Jacob Helman, one of the authors of that 2019 study and a senior climate consultant at Resilient Analytics, which provides infrastructure vulnerability assessments. “It could affect the entire Northeast Corridor over the course of five days.”
As climate change drives warmer and longer heat waves companies reevaluate their operations and adapt new technology. Railroads already use remote sensors to determine the temperature of their rails, but are becoming more sophisticated as heat waves increase. For example, they use computer modeling to figure out how to make tracks more resistant to buckling, among many other steps. “The industry is implementing new ways to use advanced sensors, satellite imaging and AI to continuously monitor health and respond to any potential hazards,” said Scott Cummings, assistant vice president of research and innovation at MxV Rail, a subsidiary of the Association . of American Railroads.
While those gaps in the track reduce the problem of buckling, each wheel of a train rolling over each gap results in wear and tear on both the track and the cars. In response, railroads have been deploying “continuous welded rail,” or CWR, for decades — segments of track that stretch a quarter-mile or more. CWR is held firmly in place by concrete ties (the strips under the rails that used to be made of wood), themselves held in place with ballast stones thrown in between them. “It’s all just that much more rigid,” said Daniel Pyke, a rail expert at UK-based Sensonic, which makes train safety technology. “You have so much more mass there to hold everything in place.”
Railroads even adapt tracks to a specific climate: By installing continuous welded track on a day with the right conditions, crews prepare it for the local high and low temperatures. “Tracks are laid and fixed at the ‘neutral temperature,’ which is the average temperature of the rails,” said Farshid Vahedifard, a professor of civil and environmental engineering at Tufts University who studies the impact of climate change on infrastructure. “This helps to ensure that the track remains stable through temperature fluctuations.” As regional temperatures rise, railroads may choose to lay down track on warmer days, thus preparing the track for increasingly extreme heat. (Although when the rails get cold in the winter, they contract, which can cause cracks.)
Another intervention is paint the rails white, which reflects a good amount of the sun’s energy off the steel. “It sounds crazy,” Pyke said, “but it works.” It’s labor intensive — you have to keep reapplying it because of the wear and tear on the paint and the fact that it gets dirty over time — but track-mounted machines can get the job done quickly.
A new technology known as distributed acoustic sensing uses fiber optic cables running along railway tracks to “listen” for defects. Disturbances on the track bump the optics and change how light travels through them. It is analyzed by a special device to determine if a rockfall has driven into the tracks, or if a crack has formed in the rails, as each type of disturbance has its own unique signal.
Like the track heat and expand, the optical fiber already hears “thermal pops.” Theoretically, Pyke said, Sensonic’s technology could detect the unique ground vibrations associated with buckling. They just need data—perhaps they can manually heat a test track to cause a solar nodule—to train the algorithm on what to listen for. “We’ve already produced some rockfall, landslide sensors, and they look for ground vibration,” Pyke said. “So I would think — I can’t promise — but I would think we would adapt it to be able to detect it.”
If railroads can get better data about their vulnerability to buckling — such as specific track temperatures over wide areas, instead of relying on inferences from local air temperatures — they can more accurately determine how much to slow trains as a precaution. This will avoid delays, prevent commuters from returning to their cars, save railways money and generally make trains safer. “You can make more informed decisions about rush orders,” said Helman of Resilient Analytics. “Maybe it doesn’t have to be 40 miles an hour. Maybe it should only be 10. Maybe you don’t need it at all.”
