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29.06.18

Surviving the heatwave: are we truly the laughing stock of the world?

It’s safe to say the internet has not been kind to the rail industry for the widespread disruptions that took place this week as a result of soaring temperatures up and down the country. Passengers have taken to Twitter to call the UK rail network the “laughing stock of the world” because they’ve never heard of extreme temperatures impacting tracks in naturally hot countries.

So why have our tracks been baking under sizzling pressure, and why exactly is the UK the only one to experience this?

In a handy blog from Network Rail – perhaps partly released to deal with the cynics and engineer aspirants on the internet – the infrastructure owner explained that when we enjoy a rare summer heatwave, direct sunshine can cause rails to be as much as 20°C hotter than air temperature. Most of the network is designed to continue operating even when track temperatures reach a scorching 46°C – equivalent to an air temperature of around 30°C. But lately, they’ve been recorded at temperatures as high as 51°C.

Because they’re made from steel, they expand as they get hotter and begin to curve – or what is known as buckling.

So how does all this cause network-wide disruption? When remote monitoring systems alert engineers to the fact that a section of the track might be expanding too much and could cause problems for drivers, Network Rail introduces speed restrictions. Slower trains exert lower forces, create less heat and therefore reduce the chance of buckling.

But sometimes this isn’t enough, and rail can buckle even with speed preventions in place. This forces engineers to close down the line to repair the rails before trains can be allowed back on, which naturally can disrupt journeys as Network Rail waits for temperatures to drop down to acceptable levels before maintenance can be carried out.

And why is the UK the only country seemingly affected by this, as many have pointed out online? Well, the debate is a bit more complex than that. Naturally hotter countries will have rails stressed to cope with a much wider range of temperatures, or at least higher ones, whereas this week’s scorching climate is abnormal in Britain. The UK rail tension is set so that pre-stressed tracks only start to expand once the outside temperature hits 27°C, which is already a positive departure from the previous coping method, which involved leaving expansion joints along the line to allow rails to slide past each other as they expand (at the expense of a quiet and smooth journey).

Other countries, such as Japan and Austria, also use slab track, which means rails are laid on reinforced concrete slabs that hold them into place more rigidly (it’s the same material used in the Crossrail network). But it’s also more expensive to install than sleepers and ballast, meaning it’s hard to make a sound business case for widespread uptake.

But not all is lost without slab. To prevent tracks from getting too hot, Network Rail works closely with weather forecasters to take action ahead of time. Teams check track stability each winter in order to strengthen it before summer comes along, and they paint certain parts of the rail white so that they absorb less heat (they can be 5-10°C cooler than a section left unpainted).

Longer pieces of tracks welded together also mean there is much less chance of buckling in very hot weather because of reduced compression.

While this summer’s heatwave shows no signs of cooling off anytime soon, commuters outside of the capital can at least be thankful they don’t need to rely on the Underground – at least you won’t be exposed to the almost illegally hot temperatures of stations as a result of the London Clay.

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Image credit: Gareth Fuller, PA Wire

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