Railways
Steel rails expand and tend to bend in the heat – regardless of the climate. According to Network Rail, railways around the world are designed to operate within a range of 45C, depending on local conditions. In the UK, steel rails are ‘prestressed’ at summer temperatures of 27C, while in countries with warmer climates, rails are prestressed at higher temperatures. The sleepers and ballast must 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 bend. A train traveling fast over rails can speed up this process through frictional heat and could be at greater risk if buckling occurs – hence the extensive speed restrictions. Overhead wires in electrical routes also expand and sag in heat and contract in cold weather. Engineers have solutions, with the tension automatically reduced by a pulley system. But eventually the counterweights hit the ground and the wires fall — making them more likely to get tangled in a pantograph, the device on top of the train that draws power from the tracks.
Roads
Motorways and strategic roads are built with modified asphalt surfaces that – so far – should not start to melt, be durable above 60 C or an equivalent air temperature of 40 C, according to the National Road. However, the basic asphalt materials used on local roads – the vast majority – can start to soften at temperatures of 50 C. At that point, Professor Xiangming Zhou, head of civil and environmental engineering at Brunel University, says: “The road it can get soft and greasy and it’s hard for cars to brake.” That’s why councils have put trucks normally used in freezing weather on standby to cover roads with sand and dust. Bitumen and asphalt are cheaper and less abrasive to tires than some materials, he says, but since they’re black they tend to heat up faster in the sun. About 4% of Britain’s roads are made of concrete, which is more popular overseas for motorways and motorways and may be more durable, but it is not immune to problems in extreme temperatures, as the closure of the A14 shows. The dual carriageway near Cambridge had been built with asphalt over old concrete slabs that expanded and buckled in the heat, creating a dent enough to close the road overnight for emergency repairs. Rick Green, of the Asphalt Industry Alliance, says getting a road to withstand all temperatures is “a significant challenge for design engineers”. At extremely high temperatures the surface “does not melt, but the asphalt it contains can soften”, “increasing the risk of deformation”.
Airport runways
Then again, some may be concrete – but Luton’s tarmac was the problem when temperatures soared into the mid-30s, says Zhou. In the airport’s words, “high surface temperatures caused a small section to lift” – a buckle on the runway that engineers repaired within hours, but still caused major disruption to passengers. While local roads are often shaded by trees and houses, runways are fully exposed and under further thermal stress from aircraft landing and taking off. Repairs and maintenance are frequent. Heathrow, which was even hotter than Luton on Monday, also had a runway problem last week when overnight repair work was not finished in time for planes to land. However, it has two runways and was not forced to stop work.
So what is the solution?
Network Rail already spends hundreds of millions of pounds a year on climate change mitigation. However, most of it is to deal with erosion or damage from rain or storms. Future infrastructure could be measured in a warmer climate – but then could be more prone to failure and cracks in a cold winter when the rails contract. Some track materials, such as concrete sleepers, are more durable over a wider range of temperatures and conditions – and significantly more expensive. The rails are already painted white in critical spots to combat the heat. Countries with extreme weather conditions make much wider seasonal adjustments for monitoring, which is time-consuming and expensive. Air conditioning was not a standard feature of the older trains still in operation. Resilience will become an economic and political choice – and a few days off for heating each year may be seen as preferable to an amendment bill. Subscribe to First Edition, our free daily newsletter – every morning at 7am. BST
