We all know the feeling of stepping into London’s Tube network and feeling the unbearable wall of “disgustingly” hot air hit us in the face. But the reason why this phenomenon takes place is more bizarre than you might first think.
Hanna Fry, Professor of the Public Understanding of Mathematics at University of Cambridge, said that the London Underground is essentially a “slow cooker” which has been heating up since it was first constructed in the 1860s.
The elaborate transport system was built by digging out clay tunnels which had temperatures of around 14C at the time. Since then the clay’s temperature has been rising from the heat being added by the approximately five million people who use the system each day.
The best-selling author and podcaster said: “They’ve all been adding heat to this essentially closed system, slowly warming up that clay so that its now 26C - it is essentially saturated with the heat of over a century which means that any extra heat that gets generated inside of these tunnels just warms up the air inside.”
“Sometimes in the Summer the heat down in the London Underground gets up to 40C even when it's only 25C, 28C outside. I mean this is basically a slow cooker that has been going since Queen Victoria was on the throne.”
Professor Fry also said that it would be tricky to bring the temperature down as an air con system would just make one part of the Tube colder and the rest hotter, while the clay would always bring the heat back up.
So, the only way to effectively bring down the temperature successfully on the Tube would be to figure out how to cool down the clay, she says. But in the meantime, some Tube lines now have aircon which at least helps things feel a little more bearable.
Which London Underground lines have air con?
Only a handful of Tube lines have air conditioning. These include:
Circle
Hammersmith & City
District
Metropolitan
The following public transport services also have cooling technology:
Overground
Trams
Elizabeth line
More air conditioning is also on the way for the Piccadilly line which is set to be cooler than ever thanks to a £2.9 billion upgrade. This new fleet will replace the existing 86 trains and are expected to be in use by the end of 2025.
TfL is trying to acquire Government funding to install new trains on the Bakerloo line by 2030, which would also boast air conditioning. The Central line has also been given solar reflective material on the external train roofs and solar reducing films on windows to minimise solar gains into the carriages.
Got a story? Please get in touch at katherine.gray@reachplc.com
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