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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Ottawa-Gatineau, the national capital which language differences nearly split into two countries

The Canadian parliament, Ottawa.

There are many single urban areas with multiple, competing local identities: from the rivalry of Newcastle and Sunderland in Tyne & Wear, to the Wolverhampton residents who resolutely deny that they are part of Birmingham, despite being in the same urban conurbation and sharing a mayor.

However, no division is quite as stark as that of the Ottawa-Gatineau metropolitan area in Canada. Often referred to as the National Capital Region, Ottawa and Gatineau lie directly opposite each other on either side of the Ottawa River, a hundred miles from Montreal, the nearest other significant population centre. Because the conurbation straddles a provincial boundary, the two cities literally speak a different language, with Ottawa in predominantly Anglophone Ontario and Gatineau in Francophone Quebec.

This is reflected in their populations. According to the 2011 census, French was the mother tongue of 77 per cent of those in Gatineau, a percentage maintained by policies intended to keep French as Quebec’s dominant language. Similarly, although Ottawa provides some bilingual services, 68 per cent of its residents are predominantly Anglophone; Franco-Ontarians frequently complain that the city is not officially bilingual.

Although there are similar divided cities, such as the Cypriot capital of Nicosia, Ottawa-Gatineau is unique in that the city was not divided by a war or major political event: its two halves have been part of the same political territory since the British defeated the French in the Battle of the Plains of Abraham in 1759, before either of the cities were even established. Indeed, the oldest part of Gatineau is actually an Anglophone settlement with the name of Hull (it was merged into the Gatineau municipality in 2002).


Today, the two cities facing each other across the Ottawa river have separate services, and elect difference mayors to run them: OC Transpo serves Ottawa, the Société de Transport de l’Outaouais (STO) serves  Gatineau, and few tickets are transferrable between the two systems.

OC Transpo is currently constructing a light rail system to many parts of Ottawa; but proposals to expand the route into Gatineau, or to merge the two transport systems have been fraught with obstacles. The City of Ottawa owns a disused railway bridge, connecting the two cities, but arguments about funding and political differences have so far prevented it from being used as part of the light rail extension project.

The divisions between Ottawa and Gatineau are made all the more unusual by the fact that Ottawa is the federal capital of Canada – a country where bilingualism is entrenched in the Charter of Rights & Freedom as a bedrock principle of the Canadian constitution. As a result, while all proceedings within the Canadian legislature are bilingual, this principle of bilingualism is not reflected on the streets surrounding the building.

The inevitable map. Image: Google.

These linguistic, as well as political, differences have been a long-running theme in Canadian politics. Quebec held independence referendums in both 1980 and 1995; in the latter, the separatists were defeated by a margin of less than 0.6 per cent. Quebecois independence would be made all the more humiliating for Canada by the fact it would be losing the Canadian Museum of History in Gatineau, while its parliament was forced to look out across the river at its new neighbours.

While Quebec as a whole only narrowly rejected independence in 1995, 72 per cent of Gatineau residents voted against the separatist proposal. The presence of many federal employees living in the city, who commute to Ottawa, meant that the city was rather unenthusiastic about the prospect of independence.

So, with Quebec nationalism currently at a low ebb, Gatineau seems set to remain a part of Canada – albeit while retaining its independent from the other half of its conurbation, across the river. While recent challenges such as flooding may have been better tackled by a unitary authority, the National Capital Region seems set to remain a tale of two cities.

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