Are London commuters treated worse than cattle in hot weather? I took the Tube to find out

Telegraph

20-06-2025

Whether you're commuting to work or simply travelling around London, on even a relatively mild summer's day it's practically a guarantee that you'll arrive at your destination drenched in sweat.
The hottest temperature ever recorded on London's Tube is a matter of some debate. During the 2006 heatwave, unsubstantiated reports of 47C made headlines. During the 2022 heatwave, Transport for London (TfL) advised customers to only travel if absolutely necessary, and reporters recorded temperatures over 40C on the Tube.
According to TfL's own stats, the highest temperature recorded in 2024 was a comparatively cool 31.1C on the Victoria line in August. Yet, for context, regulations prohibit the moving of farm animals if temperatures exceed 30C. Truly, today's commuters are treated worse than cattle.
But just how bad can it get? With the mercury already at 26C outside, and armed with a Tommee Tippee baby room thermometer, I jumped on the Tube just after the morning rush hour in central London to find out.
Which is the hottest Tube line?
Starting at Tottenham Court Road at 9.30am, I hopped straight on the Central line to Oxford Circus. It is infamous amongst Londoners for being the stickiest of all the Underground's lines, and according to TfL's data in 2024 it was in fact only the second hottest (behind the Victoria line), with stations reaching a peak of 30.6C. On the train, my thermometer beat this comfortably.
Central line: 31.7C
From Oxford Circus, I raced up to Warren Street on the TfL's 'official' hottest route: the Victoria line. It's worth emphasising that TfL only records temperatures at stations, rather than the trains themselves, with highs of 31.1C recorded. My on-train reading was much warmer.
Victoria line: 33.6C
The Northern line is considered one of the Underground's 'Deep' lines (Hampstead lies 58.5m below ground level) so consequently ventilation isn't always great. My journey avoided plumbing those depths while spiriting me from Warren Street back to Tottenham Court Road, but it was still hot, hot, hot.
Northern line: 32.4C
From the baking to the merely simmering, the journey from Tottenham Court Road to Bond Street via London's newest stretch of underground railway, the Elizabeth line, really shows the difference that air conditioning can make.
Elizabeth line: 25.8C
By the time I boarded the Jubilee line from Bond Street to Westminster I was starting to get used to the heat. Jubilee line trains are some of the smallest physically so there is very little room for ventilation or air conditioning units to be installed.
Jubilee line: 31.3C
The modern 'walk-through' District and Circle lines, like the Elizabeth line, are blessed with air conditioning. However, as they are only partially overground, they suffer from 'solar gain' where the trains and tracks heat up due to the sun when it's hot outside. On my journey from Westminster to Embankment, I could still feel the heat.
District line: 30.4C
Bakerloo line trains date back to 1972 and are therefore the oldest rolling stock still in active service on any railway line in Britain. I feared temperatures would be excessive, especially when I saw the swathe of newspapers placed over the ventilation within my carriage, but it turned out the Bakerloo was relatively cool.
Bakerloo line: 30.9C
With new air-conditioned trains coming into service on the Piccadilly line from the end of 2025, it should rapidly cool down in the coming years. Just as well, as my journey from Piccadilly Circus to Green Park saw me recording the hottest temperatures on my Tube odyssey.
Piccadilly line: 34.2C
The average temperature of my morning's travel was 31.3C, which, given that I was travelling before midday, is alarmingly hot. It's certainly warm enough for TfL to activate its hot weather plan: warnings that passengers should carry a bottle of water at all times could be heard frequently on my journey.
Why does the Tube get so hot?
A report by Rail Engineering in 2007 found that the vast majority of the heat is caused by the friction of the trains braking on the tracks.
During the 2022 heatwave, trains were ordered to run more slowly to mitigate the release of braking heat.
Once the underground gets hot, it stays hot. The clay into which the underground tunnels were dug acts as a heat sink, absorbing around 80 per cent of the heat generated.
Scientists have estimated that when the tunnels were first dug, that clay would have been about 14C, and it is now 19-26C.
Ventilation systems on the older and deeper lines such as the Piccadilly and Bakerloo were not designed to cope with the levels of heat produced by modern trains, so only around 10 per cent of heat is vented out of the network.
The size of the tunnels on the London Underground are the second smallest of any underground railways in the world (only the Glasgow Subway has smaller tunnels) making it difficult and expensive to fit extra ventilation and air conditioning systems into them.
What is TfL doing to cool down the Tube?
There are a variety of schemes underway to help reduce temperatures underground, from air cooling units to massive chillers at some stations.
Groundwater beneath Victoria station has been used for cooling; Green Park features an underground aquifer which helps cool it. Ventilation capacity and new fans are also being installed.
Some Tube trains – including the Circle, District, Hammersmith & City, Metropolitan and Elizabeth line – now feature air-conditioning within their carriages. The Piccadilly line will join this list when its new trains enter service from the end of 2025.
The Bakerloo, Waterloo and City, and Central lines will be next in line, though no firm timeline has been announced. A TfL spokesperson told The Telegraph that despite 2019 reports of new air-conditioned trains being unveiled by 2030, funding was never secured and it was unlikely the trains would be air conditioned within the next 20 years, with Bakerloo line trains being given priority before then.
Despite the Victoria line being the hottest on the underground last year (with temperatures averaging 30C between June and October) there are no plans to upgrade trains on the Victoria, Northern or Jubilee lines.
How to stay safe when travelling in hot weather
Always carry water to avoid dehydration. During hot weather, you can lose 1.5 to 2 litres of water an hour through sweat.
'If you don't replace these fluids, your blood thickens and your heart has to work harder to maintain your blood pressure and oxygen levels,' warns Dileep Lobo, a professor of gastrointestinal surgery at University of Nottingham, who researches fluid and electrolyte balance.
According to nutritional therapist Madeleine Shaw, it could also be worth adding an electrolyte sachet to your water before you travel: 'This is a great way to start the day and really important on hot sweaty days,' she says.
TfL regularly advices passengers to get off the train if they feel dizzy or unwell, as it is easier for paramedics to reach people on platforms than on the trains themselves.
Carl Eddleston, TfL's Director of Streets & Network Operations, said: 'With continuous hot weather forecast over the coming days, we are encouraging customers to carry water with them when they travel.
'We have a comprehensive hot weather plan in place to protect the network's infrastructure with resources on standby to help respond to the impact and to keep services running.
'Please look out for each other while travelling. For the latest information on how TfL services are operating, customers should use TfL's real-time travel tools, including status updates, Journey Planner and TfL Go.'