The highways, railways and bridges that keep economies and communities thriving were not built to withstand rising temperatures. How can we stop them from melting down?
The extreme weather markingten consecutive years of record heatglobally have tested the resilience of the paved roads, steel rail lines and bridges that facilitate mass transport, trade and everyday travel.
Transport infrastructure has the highest worldwide exposure to climate risks, according to global consultancy the Boston Consulting Group (BCG). From coastal freeways to mountain rail lines and air traffic,extreme heatis having an impact. It reduces road and airport runway traction, deforms and buckles rail tracks, expands the joints that hold bridges together, ages infrastructure and increases the need for maintenance — including on personal vehicles.
One prominent example of infrastructure failure was a New York bridge connecting Manhattan to the Bronx. When it was opened to let ships through during a mid-2024heatwave, high air temperatures caused the metal of the structure to expand. As a result, it got stuck, reducing rush hour traffic to a long standstill.
As the world continues to get hotter, it will be vital to findsolutionsand climate-proof the infrastructure that keep the wheels in motion.
When temperatures remain very high, standard asphalt road surfaces tend to rut, and the bitumen holding it together can crack and bleed. As the binder loosens, asphalt roads not built forextreme heatcan literally melt, and heavy traffic can cause the surface to permanently deform.
One remedy, as suggested by experts including the BCG, includes heat-reflective coatings and so-called cool pavements that absorb less energy from the sun — and are also permeable to offset flooding damage.
Unlike solar-absorbing asphalt made with petroleum-based binding elements, cool pavements comprised of clear, tree-based resins have a more reflective surface. A mix of colored asphalt and light-colored concrete also helps.
Bitumen used on highways and runways can also be enhanced with modifiers that lessen thermal or heat stress and make roads more durable.
Even concrete, despiteits high carbon footprint, has a higher temperature resistance and will last longer in a hotter world.
Traditional roads and pathways can also be made more flexible and stress-resistant by adding paving fabrics, geotextiles, or stress absorbing membrane layers to the asphalt, as illustrated by products like Sealmac Green.
When railway tracks suffer "sun kinks," or buckling under extreme heat, it results in long train delays, and in extreme cases derailments — as happened last year with a mining freight train in Australia.
Experts have cautioned that if trains, which are critical for economies and communities, are to be a successful low-carbon transport of the future, they have to be able to stand up the impacts of extreme weather connected to rising temperatures.
In the UK, the Network Rail train operator is building resilience to high temperature fluctuations by painting parts of the rail white so it absorbs less heat and expands less. A white rail can stay up to 50 degrees Fahrenheit (10 degrees Celsius) cooler.
Another way to prevent buckling is to substitute any outdated timber sleepers with reinforced concrete slabs.
Meanwhile, the operators of Washington, D.C.'s Metro train system avoided derailment by reducing the maximum speed to 35 mph (56 km/h) when rail temperatures reached above 135 degrees Fahrenheit in summer 2024.
This is according to Suyun Paul Ham, Associate Professor of Civil Engineering at the University of Texas. The engineer notes that rail expansion risk can also be reduced by using heat-resistant materials such as hard martensite rail steel.
Stretching railway tracks with hydraulic "tensor" machines as they are laid is another way to prevent the line from expanding, and hence buckling, as it heats up.
Constructed largely of steel, bridges that carry roads and trains across rivers and harbors are especially vulnerable to thermal expansion that causes structural deterioration.
According to a Colorado State University study from 2019, a quarter of the 600,000-odd bridges in the US could suffer asection collapseby 2040 due to rising temperatures that increase stress on the joints holding them up.
Expansion joints, or spaced gaps, along the length of a bridge allow flexibility in the superstructure as temperatures fluctuate. However, these gaps easily become clogged with debris, which prevents the bridge from expanding with rising heat, causing the joints to deteriorate.
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Most bridges have been built without accounting forclimate changeextremes. But researchers at Rutgers University in New Jersey are simulatingbridge deteriorationby imposing environmental stresses, including rapid temperature fluctuations between 0 and 104 degrees Fahrenheit.
The goal is for bridges to be designed with bearings that help take the load and can absorb larger movements without malfunctioning. Regular mandatory on-site inspections during and after extreme temperature events can also help to prevent severe structural stresses.
The researchers note that major bridges in the US are being rebuilt and climate-proofed for the future. Completed in 2018, the Goethals Bridge replacement project, a dual cable-strayed structure linking New Jersey and New York that substitutes the original 1928 bridge, is designed to withstand extreme heat — and to stay upright for at least a century.Edited by Sarah Steffen
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