As if the Flight and train cancellations due to strikes and staff shortages didn’t anger travelers enough this summer, the European heatwave hit and exacerbated the travel chaos. Extreme heat can be hazardous to health – even deadly – but it also affects the built environment. It can cause metal and asphalt surfaces to expand and warp, making roads, rails, and runways difficult or dangerous to use. This disrupted thousands of trips this summer.
That rails can buckle and asphalt “melt” – or rather soften and deform – became clear in July, when temperatures climbed above 40 degrees Celsius in many European countries and set many new records. On July 18, a small section of the runway at London Luton Airport in the United Kingdom became so hot that it began to lift. The runway had to be closed for two hours while engineers repaired the surface, with some flights being diverted and others cancelled. Hundreds of train services were canceled across Europe because the heat deformed the rails.
Due to climate change, heat waves are becoming more intense and frequent, so transport infrastructure needs to be adapted. Projects already exist to keep infrastructure cooler during heat waves – many are simple concepts involving plants, color or custom-made shades. Materials scientists can now offer more complex solutions, such as heat-resistant metals. But upgrading infrastructure is neither easy nor 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 studied how heat waves and other climate extremes – such as floods, wildfires and storms – could damage Europe’s infrastructure in the future. Currently, Europe’s transport sector suffers 800 million euros ($820 million) in climate-related damage a year, but researchers estimate that figure increased to 11.9 billion euros ($12.2 billion) in the last decades of the century ) will have reached. About 90 percent of the damage will be due to heat waves.
The difficulty with railways is that steel rails can get 20 degrees Celsius hotter than ambient temperature and are therefore susceptible to temperature extremes. Therefore, before new track is laid, steel rails are heated and then cooled in a controlled manner to withstand higher temperatures, with different treatments allowing the rails to operate in different temperature windows. In Great Britain, rails work stress-free in summer temperatures of 27 degrees Celsius.
But when it gets too hot, the rails expand and are constrained by the anchorage holding them in place, putting stress on them and potentially causing buckling where the rails bend. Slowing down trains can reduce the likelihood of this happening, since slower-speed trains put less pressure on the rails. As a result, network operators across Europe have had to impose temporary speed limits, resulting in costly delays and cancellations this summer.
One solution is to paint the rails white, which reflects sunlight off them and allows the rails to stay 5 to 10 degrees Celsius cooler. Operators in the UK, Spain and Switzerland had already started doing this before the heat wave hit.
Of course, many parts of Europe regularly see temperatures above 27 degrees and manufacture their splints to perform in warmer temperature windows. However, when rails are replaced in places like Britain with ones suited to hotter climates, they may not be able to withstand the low temperatures of winter. Steel contracts and becomes brittle when exposed to cold, meaning rails can crack if pressurized when it’s colder than their operating window. “It’s a very tricky situation because the temperature ranges in countries like the UK are much wider,” says Kiran Tota-Maharaj, lecturer in civil and environmental engineering at Aston University in Birmingham.