Is TfL losing the battle against heat on the Victoria line?

Why the Victoria Line Is So Hot

• Several commenters note that deep-level tunnels were once cooled by surrounding wet clay, but decades of operation have “heat soaked” the ground. Clay is a good insulator, so heat now accumulates rather than dissipates.
• Main heat sources identified: train traction power, braking (even with some regenerative braking, resistors still dump heat), densely spaced stations causing frequent acceleration/deceleration, and passenger body heat.
• The pandemic dip in temperatures is cited as evidence that fewer trains and passengers quickly reduce tunnel temperatures, but the ground then slowly reheats.

Cooling Constraints and Ideas

• Ventilation: Large fans and shafts already exist where possible; further expansion is limited by lack of surface space, noise complaints, and the depth/route of tunnels under dense buildings.
• Water/ice concepts: Ideas like rehydrating clay, ice trains, or liquid air are discussed, with consensus that clay is hard to re-wet, enormous thermal loads make “obvious” water/ice fixes impractical, and humidity risks are high.
• Air conditioning on trains: AC is attractive for passenger comfort but would dump even more heat into the same insulated system unless there’s robust heat rejection to the surface; some argue this can worsen the long‑term problem.
• District heating / heat pumps: Multiple comments suggest using tunnel heat for nearby buildings or hot water preheating. Technically possible but challenged by cost, plumbing complexity, weak gradients, and London’s dense subsurface environment.

Statistics and Temperature Scales

• A long subthread criticizes the article’s use of percentage changes on Celsius values (e.g., “30% hotter”) as mathematically misleading; Kelvin would be correct but yields unimpressive numbers, so it’s seen as sensationalism.
• Debate spills into Fahrenheit vs Celsius vs Kelvin for everyday use, with no consensus beyond “don’t use percentages on arbitrary scales.”

Comparisons and Human Factors

• Some argue 31°C isn’t extreme compared to New York or hotter countries; others counter that lack of AC, humidity, overcrowding, and unaccustomed populations make such temperatures dangerous in London.
• Safety concerns include heatstroke, fainting, and legal/health limits for working conditions underground.