How to Prevent Another European Transport Meltdown

As if the cancellation of flights and trains due to strikes and staff shortages weren’t upsetting travelers enough this summer, the European heat wave arrived to exacerbate the travel chaos. Extreme heat can be dangerous to people’s health—even deadly—but it affects the built environment, too. It can cause metals and asphalt surfaces to expand and warp, making roads, rails, and runways difficult or dangerous to use.

This disrupted thousands of journeys this summer. The fact that rails can buckle and asphalt “melt”—or rather, soften and deform—became clear in July as temperatures climbed above 40 degrees Celsius in many European countries, setting many new records. On July 18, a small section of the runway at London Luton Airport in the United Kingdom heated up so much that it began to lift.

The runway had to be closed for two hours while engineers repaired the surface, with some flights redirected and others canceled. Across Europe, hundreds of train services were canceled because of heat distorting the rails. Due to climate change, heat waves are becoming more intense and more frequent, so transport infrastructure needs to be adapted.

There are already projects underway to keep infrastructure cooler during heat waves—many are simple concepts that involve plants, paint, or purpose-built shade. Meanwhile, materials scientists can offer more complex solutions, such as heat-resistant metals. But updating infrastructure is not easy or cheap.

Railways and roads are particularly vulnerable to heat, says Giovanni Forzieri, an assistant professor of civil and environmental engineering at the University of Florence. In 2018, Forzieri and his colleagues examined how heat waves and other climate extremes—such as flooding, wildfires, and windstorms—could damage European infrastructure in the future. Currently, Europe’s transport sector sustains 800 million euros ($820 million) of climate-related damage per year, but by the final decades of the century, the researchers estimate that that figure will have reached 11.

9 billion euros ($12. 2 billion). About 90 percent of the damage will be due to heat waves.

With railways, the difficulty is that steel rails can get 20 degrees Celsius hotter than the ambient temperature, and so are susceptible to experiencing extreme temperatures. So, before laying a new track, steel rails are heated and then cooled in a controlled manner to make them resist higher temperatures, with different treatments allowing rails to operate in different temperature windows. In the UK, rails work stress-free around summer temperatures of 27 degrees Celsius.

But if it gets too hot, the rails expand and become constrained by the anchorage that holds them in place, putting them under stress and potentially leading to buckling, where the rails bend out of shape. Slowing down trains can reduce the chance of this happening, as trains at slower speeds put less pressure on the rails. This is why network operators across Europe had to impose temporary speed limits that led to costly delays and cancellations this summer.

One solution is to paint the rails white, which reflects the sunlight off them and can keep the rails 5 to 10 degrees Celsius cooler. In the UK, Spain, and Switzerland, operators had already started doing this ahead of the heat wave. Of course, many parts of Europe regularly see temperatures above 27 degrees, and manufacture their rails to work within warmer temperature windows .

However, if rails in places like the UK are replaced with those suited to hotter climates, they may not be able to withstand the low temperatures of winter. Steel contracts and becomes brittle when exposed to the cold, meaning rails may crack if put under pressure when it’s colder than their operating window. “It’s a very tricky situation, because the temperature ranges are far wider in countries like the UK,” says Kiran Tota-Maharaj, reader in civil and environmental engineering at Aston University in Birmingham.

Some countries use solid concrete slabs to cope with temperature fluctuations, as these more firmly hold the rails in place, but these cost about four times as much as the tracks that are standard in the UK (which have rails attached to sleepers laid over the top of ballast). Network Rail, which owns and operates more than 30,000 kilometers of track, bridges, and tunnels across the UK, says it is neither practical nor cost-effective to implement such solutions—there are too few summer days with temperatures above 27 degrees Celsius. “If a heat wave does happen again later this summer, or even next year, the communities across various towns and cities will have to be prepared for transportation delays,” Tota-Maharaj says.

“It’s not an overnight fix. ” Temperature variations between summer and winter also affect the asphalt surface of roads, which is essentially a mixture of sand, gravel, crushed stone, and a sticky binder called bitumen, a semisolid form of petroleum. Because asphalt is black, it tends to heat up quickly in the sun.

As a result, the bitumen becomes softer and the asphalt surface stickier and more susceptible to being damaged by pressure from vehicles, as happened in July in Manchester in the UK and Lucerne in Switzerland . Adding polymers to the asphalt mix can raise the softening point to about 80 degrees Celsius , but this makes the material more expensive. This mix is generally used only for heavily trafficked surfaces such as highways outside of Milan and Madrid.

Increasing damage to critical infrastructure from heat waves is one thing. But the operating and maintenance (O&M) costs of roads and railways are also expected to rise, according to a 2021 study by researchers at the Joint Research Centres in Italy and Spain. With 3 degrees Celsius of global warming, they project that O&M costs for UK and EU roads and railways will increase by 4.

1 percent compared to current values, partly because maintenance work would be needed more frequently; if climate pledges are kept and warming is limited to 1. 5 or 2 degrees, costs would only increase by 1. 3 or 1.

5 percent. Prevention is of course better than a cure, and trees and vegetation can play a significant role in this, especially in cities where pavements, buildings, and other surfaces absorb and store heat. Municipalities in central Europe have planted grass between the tram tracks that cross their cities to reduce the risk of rails buckling.

Researchers in Warsaw, Poland, wrote in a 2018 study that green tram tracks not only cool the surrounding area by evaporating stored rainwater, but also dampen noise and are well-received by the public. Some cities in Germany and Switzerland even want to become so-called Schwammstädte (sponge cities) by covering the asphalt and cement on buildings, streets, and pavements with trees, grass, and wetlands. Several studies have shown that trees can cool streets and buildings as they shade windows and roofs.

Birgit Georgi, an independent expert who advises various EU projects and municipalities on climate change adaptation strategies, says adaptation should be considered when planning, maintaining, or renewing public infrastructure to minimize costs. “We don’t have to implement all the measures now, but keep them in mind,” she says. Georgi says that nature-based measures or changes in material composition could be applied outside cities, too.

These, though, may need to be phased in. Roads and runways are typically resurfaced every 10 to 15 years, depending on traffic volumes. Rails also have a lifespan of several decades, but are maintained by engineers every few years.

And yet, Georgi says, climate-proofing is progressing more slowly in transportation than in other sectors. “The problem with transportation is that there are a lot of players involved in a system. The burdens may simply be shifted back and forth,” she says.

But with heat waves likely to become more frequent, delays in mitigation now could mean many more delayed journeys in future. .