London's Tube has been running so long it's literally raising the temperature of the earth around it

Londoners swelter on the Central line during the heat wave of 2003. Image: Getty.

“Why is the tube so hot?” is one of those questions Londoners find themselves asking a lot during the three or four days a year when the city’s weather isn’t completely bloody miserable. But it’s not something to which I’ve ever given much thought. Lot of people, enclosed space – the reasons are obvious, surely?

Except, not every underground railway in the world has this problem. And once upon a time, London didn’t either: when the Bakerloo line first opened, posters suggested it was a good place to keep cool on a hot day, an idea that’s clearly nonsensical in 2017.

And then, from the Twitter feed of occasional CityMetric contributor @LeftOutside earlier*, I learned something genuinely amazing:

My mind, as the kids say, is blown.

And it’s true. In 1900, according to this fascinating article in Rail magazine, the ambient heat of the earth surrounding the tunnels – clay, mostly – was around 14°C. In the height of summer, the tunnels were indeed colder than the air above, so it made sense to travel by tube to cool down.

The problem is – trains full of people tend to give off heat. According to this article from a 2007 edition of Plant Engineering magazine, the vast majority (89 per cent) of that heat comes from the train itself (the friction during braking is the big one), 7 per cent from passengers and 4 per cent from “Tunnel support systems”.

What happens to this heat? On the sub-surface lines – basically, those which share tracks with the Circle – it’s not too big a problem. The tunnels are close to the surface, so often emerge into the light for brief periods (Barbican, South Kensington and Edgware Road are all above ground). They also have plenty of ventilation shafts. The heat has somewhere to go.

The deep tubes, though – the ones which are literally tunnels bored through the ground – are more problematic. Most of them are old, so were built before anyone realised heat would be a problem, and don’t come with enough ventilation shafts to solve it. The air is trapped. And so, the heat is absorbed by the walls, and the earth behind them.

In 1900, as noted above, the average ambient temperature was 14°C. Some 117 years and millions of trains later, it can be anywhere between 20°C and 25°C.


 Let’s just say that again: London has been running tube trains so long that the ground beneath parts of the city is now as much as 10°C hotter than it was in 1900.

One result of this is that the earth has become much less effective at absorbing the excess heat. That means the tunnels themselves have heated up, too. A lot: air inside them can often reach as high as 30°C. You’ve probably noticed this is you’ve been on the tube recently.

For the last decade or so, Transport for London has been looking for solutions to this. Some of them involve increasing the capacity of existing ventilation systems (lack of space above ground means it’s extremely difficult to build new ones). Others involve adding systems which circulate water to cool the air. Yet other options involve things like more efficient braking systems, on the grounds that if you put less heat in, you have less to take out.

Experimental air coolers on the Victoria line. Image: Oxyman/Wikipedia Commons.

It’s clear that there’s no easy solution, however: in 2003, then London mayor Ken Livingstone offered a prize of £100,000 to anyone who could come up with fresh ideas. Nobody could think of anything TfL wasn’t already trying, and the prize went unclaimed.

The upside to this story is that other cities have learned from London’s mistakes, and ensured that ventilation systems are an integral part of new metro systems.

The downside is you’re likely to boil every time you get the Central line in summer for the foreseeable future.

*LeftOutside has since been in touch to tell me he was summarising another article, from the Ian Visits blog. I haven’t read that one – the above article is drawn from the two articles I reference, plus some bits from TfL. But in the name of politeness and an easy life I'm acknowledging its existence and adding a link. Read that too, if you like. 

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason. 

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Treating towns as bastions of Brexit ignores the reasons for the referendum result – and how to address them

Newcastle: not all cities are booming. Image: Getty.

The EU Referendum result has often been characterised as a revolt of Britain’s “left-behind” towns and rural areas against the “metropolitan elite”. But this view diverts attention from the underlying issues which drove the Brexit vote – and ironically has diverted policy attention away from addressing them too.

It’s true that a number of big urban authorities, led by London, voted to stay. And overall people living in cities were less likely to vote leave than towns. Setting aside Scottish cities and towns, which both voted very strongly for remain, Leave polled 51 per cent of the vote in English and Welsh cities, compared to 56 per cent in local authorities that include towns. (Consistent data isn’t available below local authority level.)

Yet there is a lot of variation underlying this average across towns. In Boston, 75 per cent voted Leave, and in Hartlepool and Grimsby it was 70 per cent. But at the other end of the scale, there were a number of towns that voted to stay. For example, Leave polled at 49 per cent in Horsham and Harrogate, and 46 per cent in Windsor and Hitchin. In places such as Winchester, Leamington Spa and Bath, the Leave voted amounted to less than 42 per cent of the vote.

What drives this variation across towns? Data from the Centre for Cities’ recent report Talk of the Town shows economic outcomes were the biggest factor – with towns that voted Remain also having stronger economies.

For a start, pro-Remain towns generally have smaller shares of people who were either unemployed or claiming long-term benefit. (This is based on 2011 data, the latest available.)

Towns which voted Remain also had a higher share of jobs in high-skilled exporting businesses – an indication of how successful they have been at attracting and retaining high-paid job opportunities.

And both measures will have been influenced by the skills of the residents in each town: the higher the share of residents with a degree, the stronger the Remain vote.

So the Brexit vote was reflective of the varying economic outcomes for people in different parts of the country. Places which have responded well to changes in the national economy voted to Remain in the EU, and those that have been ‘left behind’ – be they towns or cities – were more likely to have voted to Leave.

This sends a clear message to politicians about the need to improve the economic outcomes of the people that live in these towns and cities. But the irony is that the fallout from the Brexit has left no room for domestic policy, and little progress has been made on addressing the problem that, in part, is likely to have been responsible for the referendum outcome in the first place.

Indeed, politicians of all stripes have seemed more concerned about jostling for position within their parties, than setting out ideas for domestic policy agenda. Most worryingly, progress on devolution – a crucial way of giving areas a greater political voice – has stalled.


There was talk earlier this year of Theresa May relaunching her premiership next summer focusing on domestic policy. One of her biggest concerns should be that so many cities perform below the national average on a range of measures, and so do not make the contribution that they should to the national economy.

But addressing this problem wouldn’t ignore towns – quite the opposite. What Talk of the Town shows is that the underperformance of a number of cities is bad not just for their residents or the national economy, but also for the residents in surrounding towns too. A poorly performing neighbouring city limits both the job opportunities open to its residents and impacts on nearby towns’ ability to attract-in business investment and create higher paid jobs.

This isn’t the only factor – as the last chart above suggests, addressing poor skills should be central to any serious domestic policy agenda. But place has an influence on economic outcomes for people too, and policy needs recognise that different places play different roles. It also needs to reflect the importance of the relationships between places to improve the access that people across the country have to job opportunities and higher wages.

The Brexit vote didn’t result from a split between cities and towns. And if we are to address the reasons for it, we need to better understand the relationship between them, rather than seeing them as opposing entities.

Paul Swinney is head of policy & research at the Centre for Cities, on whose blog this article first appeared.

Read the Centre’s Talk of the Town report to find out more about the relationship between cities and towns, and what this means for policy.