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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What do new business rates pilots tell us about government’s appetite for devolution?

Sheffield Town Hall, 1897. Image: Hulton Archive/Getty.

There have been big question marks about any future devolution of business rates ever since the last general election stopped the legislation in its tracks.

Not only did it not make its way to the statute book before the pre-election cut off, it was nowhere to be seen in the Queen’s Speech, suggesting the Government had gone cold on the idea. (This scenario was complicated further recently by the introduction of a private members’ bill on business rates by Conservative MP Peter Bone, details of which remain scarce.)

However, regardless of the situation with legislation, the government’s announcement in recent days of a pilot phase of reforms suggests that business rates devolution will go ahead after all. DCLG has invited local authorities to take part in a pilot scheme which will allow volunteer authorities to retain 100 per cent of the business rates growth they generate locally. (It also notes that a further three pilots are currently in operation as they were set up under the last government.)

There are two interesting things in this announcement that give some insight on how the government would like to push the reform forward.

The first is that only authorities that come forward with their neighbours with a proposal to pool all business rates raised into one pot across a wider geography will be considered. This suggests that pooling is likely to be strongly encouraged under the new system, even more considering that the initial position was to give power to the Secretary of State to form pools unilaterally.

The second is that pooled authorities are given free rein to propose their own local arrangements. This includes determining, where applicable, a tier split (i.e. rates distribution between districts and counties), a plan for distributing additional growth across the pool, and how this will be managed between authorities.

It’s the second which is most interesting. Although current pools already have the ability to decide for some of their arrangements, it’s fair to say that the Theresa May-led government has been much less bullish on devolution than George Osborne in particular was, with policies having a much greater ‘top down’ feel to them (for example, the Industrial Strategy) rather than a move towards giving places the tools they need to support economic growth in their areas. So the decision to allow local authorities to come up with proposed arrangements feels like a change in approach from the centre.


Of course, the point of a pilot is to test different arrangements, and the outcomes of this experiment will be used to shape any future reform of the business rates system. Given the complexity of the system and the multitude of options for reform, this seems like a sensible approach to take. But it remains to be seen whether the complex reform of a national system can be led from the bottom up. In effect, making sure this local governance is driven by common growth objectives, rather than individual authorities’ interests, will be essential.

Nonetheless, the government’s reaffirmation of its commitment to business rates to devolution and its willingness to test new approaches is welcome. Given that the UK is one of the most centralised countries in the western world, moves to allow local authorities to keep at least some of the tax revenue that is generated in their area is a step forward in giving places more autonomy over how they spend their money. That interest in changing this appears to have been whetted once more is encouraging.

There are, however, a number of other issues with the current business rates system which need to be ironed out. Centre for Cities is currently working on a briefing of the business rates system, building on our previous work in this area, and we’ll be making suggestions as to how the system can be improved.

Hugo Bessis is a researcher for the Centre for Cities, on whose blog this article originally appeared.

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