Many commuters will know too well that the London Underground has been unbearably hot in recent weeks.
And if you’ve got the feeling your journey is getting hotter by the year, you might just be right.
MailOnline’s interactive chart reveals the average summer temperatures on seven popular tube lines over the past decade.
Based on data from Transport for London (TfL), it shows the Victoria line is hotter than any other, with the summer average pushing past 30°C (86°F) – breaking the legal maximum to transport cattle.
Passengers are also sweltering on the Central, Bakerloo and Northern lines, with the deepest lines among the balmiest – so, how does your commute stack up?
For each year, the graph presents temperatures as an average for July and August – generally the two hottest months of the year.
Over the past decade, they’ve mostly fluctuated between 25°C and 30°C, but the Victoria line in particular shows a concerning increase.
The average for July and August 2014 was 26.5°C, but this climbed to 31°C in July-August 2022 and 30.6°C in July-August 2023.
In 2023, the Victoria line was the hottest line, not just in the summer but overall for the whole year – just like it was in 2022.
The Victoria line – which runs between Brixton and Walthamstow Central – may be so hot because the entire line is underground, meaning heat gets trapped in the tunnel.
It is also one of the deepest lines – and the deeper a line the less ventilation it receives from the world above.
According to one expert, tube temperatures above 30°C not only feel uncomfortable but can get ‘difficult for the body’.
The Victoria line – which runs between Brixton and Walthamstow Central – was the hottest line on the London Underground in summer 2023
In 2023, the Victoria line was the hottest line, not just in the summer but overall for the whole year – just like in 2022. Pictured, a woman cools off in front of a giant fan on the Victoria line, 2023
Lewis Halsey, a professor of health sciences at the University of Roehampton, said dangerous conditions depend on both temperature and humidity – how much water vapour is in the surrounding air.
When both humidity and temperature are high, the body finds it difficult to keep cool.
That’s because it’s harder to remove heat via evaporation of sweat into the air, potentially leading to dangerous levels of overheating.
A busier tube will make it worse because there are more people breathing and sweating – meaning more humidity.
‘People measure temperature and people less commonly measure humidity, but it’s the two combined that affect how well we deal with the heat,’ Professor Halsey told MailOnline.
How dangerous a trip on the tube could be depends on both temperature and humidity. Pictured, a woman cools down on the London Underground, July 2018
‘Over 30 degrees – we all know its not the most pleasant temperature but it’s not going to kill us off unless we’re incredibly frail.
‘But if it gets humid, which of course it can get it London, temperatures above 30°C can get difficult for the body to “dump” heat as quickly as we’re taking it on.
‘If the body can’t lose heat as quickly as it’s taking it on, you’re going to get a net gain of heat into the body and body temperature will rise.
‘And if body temperature rises too much then you’ve had it.’
If temperatures increase on the tube – pushing up towards the 40°C mark – the most vulnerable people could potentially ‘keel over’ if there’s high humidity, Professor Halsey warned.
‘Some people will be fine with that, some people won’t and of course it tends to hit the elderly and frail,’ he told MailOnline.
Fortunately, TfL is working on rolling out cooling and ventilation technologies to tube lines, especially the likes of Victoria, Northern and Central.
These include installing air conditioning in carriages, adding more ventilation shafts and using a more efficient braking system that doesn’t generate heat.
