With temperatures soaring beyond 40°C (100°F) in the United Kingdom and in the United States, civil engineers and transit authorities say the heat is threatening rail networks across both countries. 

Officials with London’s subway mandated temporary speed limits and preemptively canceled services on parts of the city’s tube system earlier this week over fears that the rails could bend or buckle. Across the pond, Amtrak imposed “heat-related” speed restrictions within its Northeast Corridor service between New York and Philadelphia earlier this month. 

Heat restrictions on railways are not unusual, and the U.S. Department of Transportation maintains that the country’s railroads are well equipped to address the ways that extreme heat impacts their overall operations. But researchers say that climate change will make service disruptions more commonplace with more scalding heatwaves to come. 

“The U.S. is not prepared,” said Paul Chinowsky, a professor of civil engineering at the University of Colorado Boulder. “While the rail system is incrementally being improved, there is significant work to do and what is being done is not being done fast enough.” 

In Concord, California last month, triple-digit temperatures were the culprit behind a curve that emerged in a rail line that ultimately derailed a train, according to  the Bay Area Rapid Transit Authority. And in Portland, Oregon, last year, temperatures that reached over 100°F wreaked havoc on the city’s public transport, MAX Light Rail, melting the overhead cables that power its trains. City officials had to suspend all train services for almost two days. 

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“Extreme heat will continue to present challenges for BART and all transit agencies,” according to Alicia Trost, spokesperson for the Bay Area Rapid Transit Authority. 

The weight and speed of passenger or freight trains are a deadly combination for railroads baking in sweltering heat. The United States’ railways are mostly made of steel, and with higher temperatures, steel expands and softens. That’s especially true in the Northeast and Southwest, where tracks were not built to withstand or adjust to triple digit temperatures given the more mild climates, said Chinowsky.

 “When it gets significantly hotter, like it is now, it gets soft, and you run a rail car over that, you get what are called sun kinks,” he said. “It's essentially a deformation [and] the rails just buckle.”

“You can even think of it as a person standing on sand,” Chinowsky said. “When you run on sand, or you put something really heavy on sand, it pushes that sand away from you; the same thing is happening to the rail.”

For American passenger and freight rail, heat-induced delays could incur costs anywhere between $25 and $60 billion, according to a 2017 report from the “Transport Policy Journal.”

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The U.S. needs to come up with an adaptation plan, said Fernando Moreu, professor of civil engineering at the University of New Mexico. “We need to keep what we have, look at what we've been using, and retrofit,” he said.

Determining the point at which rail systems might succumb to heat is a big topic of current research, said Francesco Lanza Di Scalea, a professor of structural engineering at the University of California San Diego. “What I'm calling a blood pressure monitor for the rail is actually a big challenge,” he said. “I've worked on it for about 10 years, and it's still known as the holy grail of railroad maintenance.”