Why is London’s Central line so hot? Science has the answer

Bank station on the Central Line

This has little or nothing to do with the weather. Ingenious engineers needed to find ways to take some of the heat off London’s perspiring Central Line travellers.

The London Underground is hot. But nowhere is hotter than the Central line, which is routinely so hot that it exceeds the EU limit at which it is legal to transport cows, sheep and pigs, says Wired UK.
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Cooling the Central line in particular presents an almost impossible puzzle for TfL [Transport for London] to solve.

In the late 1800s and early 1900s, when many of London’s tube tunnels were carved out of its subterranean clay, engineers didn’t leave a lot of extra space. In fact, they left none.

That makes installing air-con units on trains that run through deep level tunnels impossible. The tunnels are too small to allow the heat to escape, effectively turning the Tube into a giant underground oven.

Gaze absent-mindedly out of the window on the Central line and you’ll see cables and panelling whizzing past just inches from the train itself. Above them, London’s cloying clay keeps all that heat locked in.

And that clay has been heating up. When much of central London’s Tube network opened in the early 1900s, temperatures in tunnels and at stations were recorded at around 14C.

But with nearly 80 per cent of energy dissipated by trains, people and related infrastructure seeping out into London’s clay, it’s been slowly heating up. So much so that the ambient temperature of the clay is now between 20C and 25C.

Unlike the Victoria and Jubilee lines, London’s oldest tube lines, and the Central line in particular, suffer from having very few ventilation shafts. And with the Central line cutting a path through some of London’s most densely-populated and expensive post codes, there are few options for introducing shafts now.
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So while other parts of the London Underground benefit either from investment in cooling technology or the luxury of not being surrounded by rapidly-heating clay with nowhere for hot air to escape, the Central Line keeps on cooking.

It’s the perfect, sweaty storm and one that TfL is nowhere close to solving.

Full report here.