UK heatwave: Why can't roads and rail cope with the extreme heat?

Warnings that the country's infrastructure would not be able to cope with extreme weather became reality during the UK's historic heatwave - with roads melting, airport runways damaged and rails buckling as temperatures hit 40C.

Transport Secretary Grant Shapps conceded the UK’s transport network could not cope with the record heat, saying that the Victorian-era infrastructure “just wasn’t built to withstand this type of temperature”.

But why do extreme temperatures wreak such havoc with the UK's transport network?

Across the country, damage to road surfaces has been reported because of the heat, while Luton Airport was forced to close its runway on Monday after a defect was found in the asphalt.

On Tuesday, the A14 in Cambridgeshire - a major transport artery to Britain's biggest container port - was the latest road to succumb.

Police tweeted an image of a sunken road saying: "No, the A14 is not being turned into a skatepark… unfortunately the road surface isn’t coping well in this heat."

Why are our roads melting in the heat?

British roads are made from asphalt, but some are built from concrete.

The Road Surface Treatments Association said the surface can begin to melt as it hits 50C.

This can happen even when the air temperature drops as low as 20C at the end of a day, because the road surface absorbs heat during the heat of the day.

Why can't the railways cope with extreme heat?

Forecasters said the temperatures of road surfaces could reach 60C or higher, due to their prolonged exposure to the sun.

That was certainly true on the rail network on Monday, with Network Rail revealing that its hottest rail recorded hit 62C (144F), in Suffolk.

Network Rail says Britain’s rails are pre-stressed to help them resist high temperatures.

British tracks have a stress-free temperature of 27 degrees – the UK average summer rail temperature. Countries with traditionally hotter climates will "set" rails to higher temperatures.

When the air temperature reaches 30 degrees, the temperature on the rail can actually be up to 20 degrees higher.

When steel rails get hot, they expand, which can cause a buckled rail - and raises the risk of derailment.

Network Rail also pointed out that the rails do get just as hot in Europe - but the key difference is that they have been designed to cope.

The rail body wrote on Twitter that in countries typically hotter than the UK, rails are stressed to withstand higher temperatures.The unprecedented extreme weather caused by climate change is already hotter than the UK's rail infrastructure was designed to cope with, Network Rail said.

Why can't we make adjustments to cope?

Stressing the tracks to prepare for increasingly hot summers brought its own challenges, said Network Rail.

It explained some countries regularly have extremes in temperature that affect their railway and may adjust their rails between summer and winter, or have other measures in place to manage the effects over the long term.

But it said it would not be "practical or cost-effective" to adjust rails to manage the effects of temperature.

Network Rail said if it stressed the UK's rails for exceptionally hot weather "they wouldn’t be safe for the winter and we’d have broken rail because it’s too cold."

"That’s why other countries choose different temperature ranges depending on their climate," it tweeted.

"More than three-quarters of our track is modern on concrete sleepers, which can help rail withstand very hot weather.

"But sometimes, steel rails get so hot they expand and bend or break. In fact, we expect [Tuesday's] temperatures to expand each kilometre of rail by 30cm.

"We have about 30,000km of rail on a normal day but the network is 9km longer [on Tuesday]!"

Why are emergency speed restrictions in place during hot weather periods?

Network Rail said the emergency speed restrictions ensure slower trains - which mean less pressure on the rails.

This means the rail is less likely to buckle, helping avoid derailments.

Speed restrictions also help avoid damage from overhead line equipment that have expanded and sagged.

In hotter countries rails have likely already been stressed for higher temperatures because they typically have long, very hot summers, while UK summers tend to be "much less predictable", it said.

But on hotter days than their infrastructure is designed for, even the hottest countries have to respond in the same way the UK does.

Network Rail tweeted: "That’s why you may have heard about rails in Spain, Italy and Switzerland being painted white to keep the steel cool. And slower trains to prevent buckling.

"At the end of the day, we and other European countries are all dealing with the impact of climate change. And our priority is to do everything we can to keep you safe.

"We may need to consider changing our standards and engineering for more severe summers and less severe winters for the decades to come but for now, it’s still too early to make such an enormous decision."

What causes buckling?

Metal can expand or contract depending on temperature. This generates forces that try to push and pull the railway out of shape.

Rail engineers try to prevent this using sleepers and ballast.

Network Rail said measures used in other countries include using a solid concrete slab to contain the higher forces - but warns that "slab tracks costs approximately four times as much to install as standard ballasted track".

It said: "The movement of trains also generates forces in the track. The higher the speed, the greater the force of a train.

"When heat expansion forces are high, trains deliberately slow down to reduce the additional forces they apply to the railway."

When will UK infrastructure improve to cope?

Mr Shapps said issues on the rails and roads would continue for decades during extreme heatwaves.

Asked how long it will take to upgrade existing rail infrastructure to be more resilient, he told Sky News: “Decades, actually, to replace it all. Ditto with Tarmac on the roads."

He told BBC Breakfast: “We’ve seen a considerable amount of travel disruption, we’re probably going to see the hottest day ever in the UK recorded today and infrastructure, much of it built in Victorian times, just wasn’t built to withstand this type of temperature – and it will be many years before we can replace infrastructure with the kind of infrastructure that could, because the temperatures are so extreme.”

Asked if the transport system can cope with the weather, he said: “The simple answer at the moment is no."

On Monday Luton Airport had to divert flights after soaring temperatures melted the surface of its runway.

The airport said it had discovered a defect in the surface which was being repaired, and apologised to passengers.

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