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Most Googled: why is the tube so hot?

Written by
Matt Breen

The arrival of summer is always a cause for celebration in London, but there is one downside: the Underground turns into a grim subterranean sauna of clammy brows, seeping armpits and more fainting than the average One Direction gig. But why is it so damn hot down there?

We put this to London blogger and transport expert Ian Visits, and he threw this curveball our way: since it was built, the tube has in fact been getting hotter. ‘When they were dug, the deep-level tube tunnels were actually cold, and were advertised as the coolest way to commute,’ Ian explains. ‘But over the past 120 years, the London clay that the tunnels pass through has slowly absorbed the heat from the trains braking and accelerating. What was once the coolest place to be is now one of the hottest.’

Yep, you read that right: the tube itself is to blame for the soaring temperatures. But Ian is keen to add that, in TfL’s defence, lots of work has gone into upgrading the ventilation in the tunnels in the past decade. So hopefully the temperature won’t keep on getting hotter as more trains run faster and closer together during peak hours. Still, don’t even think about going underground this time of year without a bottle of water.

And if you want to know which tube lines are the hottest, we made this handy map.

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