Extreme temperatures have caused widespread problems and disruptions to British railways, with trains running at slow speeds and main lines closed. Airport runways and some roads have also been shown to be susceptible to heat.
Railways
Steel rails expand and tend to cling to the heat, whatever the weather. According to Network Rail, railways around the world are designed to operate within a range of 45C (113F), depending on local conditions. In the UK, steel rails are “prestressed” to summer temperatures of 27 ºC, while in countries with warmer climates, the rails are prestressed to higher temperatures.
The sleepers and ballast should keep the rails in place in the British winter and summer. When the temperature reaches 40 ° C, the rails can reach 60 ° C and expand and roll. A train traveling quickly on rails can speed up this process through the heat caused by friction and could be in more danger if a break occurs, hence the widespread speed restrictions.
The overhead cables of electrified routes also expand and sink with heat, and contract in cold weather. Engineers have solutions, with the voltage automatically mitigated by a pulley system. But eventually the counterweights hit the ground and the wires sink, making it more likely to be wrapped in a pantograph, the device at the top of the train that draws energy from the lines.
Roads
Strategic highways and roads are built with modified asphalt surfaces that, until now, should not begin to melt, being resistant beyond 60ºC, or an equivalent air temperature of 40ºC, according to National Highways. However, the basic asphalt materials used on local roads, the vast majority, can begin to soften at temperatures of 50ºC. At the time, Professor Xiangming Zhou, head of civil and environmental engineering at Brunel University, said: “The road can become smooth and greasy, and it is difficult for cars to brake.” That’s why town halls have put grenade trucks on hold, mostly used in ice time, to line sand and dust roads. Asphalt and asphalt are cheaper and less abrasive to tires than some materials, he says, but because they are black they tend to heat up faster in the sun.
About 4% of British roads are built with concrete, which is more popular abroad for motorways and expressways and may be more resistant, but is not immune to extreme temperature problems, as evidenced by the closure of the A14. The motorway near Cambridge had been built with asphalt on old concrete slabs that expanded and split with the heat, creating enough shock to close the road overnight for emergency repairs.
Rick Green, president of the Asphalt Industry Alliance, says a road facing all temperatures is “a major challenge for design engineers.” At extremely high temperatures the surface “does not melt, but the bitumen that is there can be softened,” “increasing the risk of deformation.”
Airport runways
Again, some may be concrete, but Luton asphalt was the problem once temperatures soared in the mid-1930s, Zhou says. In the words of the airport, “high surface temperatures caused a small section to rise,” a buckle on the runway that engineers fixed in a few hours, but which still caused major disruptions to passengers. While local roads are often shaded by trees and houses, runways are fully exposed and subjected to more heat stress by aircraft landing and takeoff. Repairs and maintenance are frequent.
Heathrow, which on Monday was even hotter than Luton, also had a problem on the runway last week, when overnight repair work was not completed in time for the planes to land. However, it has two runways and was not forced to stop operations.
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So what is the solution?
Network Rail already spends hundreds of millions of pounds a year on climate change mitigation. Most, however, is to counteract erosion or damage from rain or storms. Future infrastructure could be measured in warmer weather, but then it could be more likely to fail and break in the winter cold when the rails contract. Some track materials, such as concrete sleepers, are more resistant to wider temperature ranges and conditions, and are significantly more expensive.
The rails are already painted white at critical points to combat heat. Countries with extreme weather conditions make much broader seasonal adjustments for monitoring, which is time consuming and costly. Air conditioning was not a standard feature of older trains still running. Resilience will become an economic and political option, and a few days of heating interruption each year may be considered preferable to the modification bill.