Which is London’s hottest tube line?

Temperatures on the tube in August 2013. Image: TfL.

So which underground line is actually the hottest?

This is the sort of question that holds only idle interest for most of the year, but becomes pretty much life-and-death during a heatwave. Like, for example, the one we’re in the middle of right now.

This week, especially on Wednesday, it’s predicted to be so hot that some route re-jigging may be necessary. As noted by the Evening Standard last year, parts of TfL’s public transport network, can, in the summer months, break the temperature beyond which its illegal to transport cattle. Which is less than ideal.

But some sections, of course, are hotter than others. Using a combination of hard facts, science, intuition, and a bit of guesswork, we've ranked the tube lines from hottest to coolest – or, from those you should avoid at all costs, to those where there's a passing chance you might be able to breathe. Here they are: 

How we did it

The temperatures on board the tube rely on a lot of different factors: the size of the tunnel, its depth, the ventilation available, and the number of trains and people bustling through it. 

One factor, though, tends to override the rest: air-conditioning. Air-con is widespread across the Metropolitan, Hammersmith & City, and Circle lines, which makes them, as a rule, cooler than the Underground network (it's currently being introduced on the District Line, which makes it a little warmer than the others on average). 

All four are also "sub-surface lines", meaning they're far closer to the surface than the rest of the network, occasionally pass through above-ground stations like Barbican, and are generally just better ventilated. All four lines are also introducing walk-through trains: that, too, will improve airflow through the trains.

Air conditioning is also operational on a fair number of Overground trains. The combination of being above ground and air-conditioning puts the Overground in first place, in our opinion (though on an extremely hot day the disadvantages of being in direct contact with sunlight could outweigh the advantages of fresh air). 

The DLR is next: it, too, operates almost exclusively above ground, and stops so often that heat doesn't have much of a chance to build up. Plus, you get to feel like you're driving the train. But – no air con.

Then, we get to what are called the "deep level" lines.These are where things get really steamy, thanks to the depth of the tunnels and the thinness of both tunnels and trains.

You can't install air conditioning on these trains: there isn't enough space in the carriages, and besides, there's nowhere for the heat to actually go once the air-con tries to release it. You'd just turn the tunnel into a heating pipe.

Ranking these lines took a little more guesswork. First, here's a heat map of central London provided to us by TfL, which shows the average daytime temperatures at the end of platforms throughout August 2013: 

Image: TfL. 

The Jubliee line, despite hosting some of the deepest tunnels in the network, does best out of these lines: as you can see on the map, it manages to stay coolest, thanks in part to fans which cool the stations' ambient temperature during the night. (The fact it's a relative newcomer, a large chunk of which was built in the 1990s, probably helps.)


Next up is the Victoria line, which was actually one of the hottest lines on a 2006 version of the map shown above. Since then, TfL has managed to cool it down using "regenerative braking systems" on its trains, which convert the friction of braking back into the power supply, rather than into heat; as well as the regeneration of the line's 50-odd ventilation shafts. New trains on the Victoria line also ventilate carriages by pulling up air from the base of the tunnel into the carriage at passengers' head height. 

The Waterloo and City line is, to be honest, a bit of a mystery. TfL's map doesn't give much information on its temperature, though platforms at Waterloo and Bank are both quite cool. We suspect, though, that a calculation of average daily temperatures don't mean much on a line which used mostly at commuter times.One final clue is that it runs four-car trains, not six, which could reduce the temperature – so we've given it the benefit of the doubt and put it in fifth place. 

The Northern line was once famed for its roasting conditions, but, like the Victoria line, recent ventilation improvements and new regenerative brake systems have lowered temperatures considerably over the past five years or so. Things still get a little sticky around Charing Cross and Bank, though. 

The Piccadilly and Bakerloo lines haven't had the same cross-network cooling mechanisms put in place, so they're still hitting the high 20s or even 30°C in summer months. A TfL spokesperson told me that high speed fans have been installed at Bakerloo platforms at Lambeth North and Marylebone to tackle the heat, though we're assuming that was after this map was made:

And finally, we come to the big hitter. The Sauna line. The line where 30°C starts to feel positively breezy. Appropriately enough, the hottest line is the red-hued Central line – something you can on the map above, and which is backed up by more anecdotal evidence:

This, presumably, is thanks to the Central Line's deep, low-ceilinged trains, plus the fact that TfL hasn't introduced any coolling mechanisms on the line over the past few years. 

The Central Line's Twitter feed has this helpful advice for travellers on the sweltering trains:

We have some more: avoid the Central line at all costs. Seriously. Science says so. 

 
 
 
 

Jane Jacobs and Le Corbusier would agree on one thing: we need more social housing

Unite d’Habitation, Marseille. Image: Iantomferry/Wikimedia Commons.

Much has been written in CityMetric and beyond about the urban planning debates of the 1950s and ‘60s, that came to be characterised as a battle between master-planning and preservation. One side of the debate was personified by the father of modernist architecture, Le Corbusier, whilst the counter-argument was advanced by writer and journalist Jane Jacobs.

But when it comes to London’s housing crisis, aren’t there a few things that these two would actually agree on?

Jane Jacobs’ writing about the organic nature of self-organising communities, demonstrated, in her words, by the “intricate sidewalk ballet” of inner city neighbourhoods, should be required reading for anyone interested in how cities function. But today, Jacobs is increasingly invoked in attempts to oppose new developments of any kind. Her role in conceiving Manhattan’s West Village Houses, a low cost rented housing scheme built through New York State’s Mitchell-Lama Program, is unfortunately much less well known. It’s been suggested that if Jacobs were around today, she’d be working with New York’s housing activists. When her seminal work The Death and Life of Great American Cities was written, there were almost 2 million rent-controlled or rent-stabilised apartments in New York City; nowadays, there are fewer than half that number.

Le Corbusier, on the other hand, is too often blamed for drab high-rise blocks. But regardless of how well his followers across Europe interpreted his ideas, Le Corbusier’s vision for cities was about high quality residential blocks that also contained shops and leisure amenities and were surrounded by parkland – the original mixed use development if you like. His most famous building, Marseille’s Unite d’Habitation, consisted of 337 apartments with views of the mountains and the sea together with shops, a restaurant and a nursery school. The building was originally intended to be public housing, but the French government eventually sold off the flats to recoup costs. Alton West Estate in Roehampton and Park Hill in Sheffield are just some of the examples of Le Corbusier’s influence on the design of post-war council housing here in the UK.

Building homes for a serious business in post-war Britain. Under Attlee’s 1945 Labour Government, 700,000 new council homes were completed. In 1952, the largest architectural practice in the World was at London County Council, with 1,577 staff including 350 professional architects and trainees. These were the days of consensus, and very quickly Tory governments were actually competing with Labour governments about who could built the most council homes.

Some of the council homes built post-war have stood the test of time better than others. But what’s not in doubt is that building council homes on such a scale immeasurably changed the lives of so many families in desperate need of a decent, secure and affordable home. And so many of the post-war modernist high-rise blocks so despised by Jacobs quickly took on the organic self-organising traits that she held in such high regard and have become some of the most enduring and closely-knit communities in London.

Fast forward to 2019 and Right To Buy continues to decimate council housing stock, but perversely home ownership seems more out of reach than ever for so many. An entire generation is being forced to embrace long term private ting in a country that has some weakest protections for private tenants in Europe. Meanwhile, government spending on building new homes fell from £11.4bn in 2009 to just £5.3bn in 2015 – from 0.7 per cent to 0.2 per cent of GDP – and since then, the housing minister’s desk has been occupied by no fewer than six people.


So what would a comprehensive drive for new council and social housing on the scale of the 1945 government’s efforts look like in 2019?

Lubetkin, the architect responsible for Islington’s Spa Green Estate and Bevin Court, summed up the spirit of post-war council home building with his maxim that “nothing is too good for ordinary people”. It’s a vision that we’re trying to recreate through our own council home building programme in Islington.

One of the best opportunities for small council home building schemes is to expand upon existing communities. The vast majority of Islington’s new council housing takes the form of infill, construction on existing estates; in unloved spaces, in old garages, and in old undercrofts. These projects often involve landscaping and new amenities to enhance rather than reinvent local communities. We have built community centres and even rebuilt a library as part of council housing schemes. One Tenants’ and Residents’ Association had an idea for a new specialist over 55s block for the older residents of the estate who wanted to stay in their community.

But there’s a place for large-scale place making as well. When the Ministry of Justice closed Holloway Prison and announced that the site would be sold, Islington Council published a Supplementary Planning Document (SPD) on the site. We had one aim – to send a clear signal to the market that anyone who was looking at buying the site needed to be aware of their planning obligations. Most importantly, any development on the site needed to include at least 50 per cent genuinely affordable homes. The speculation around the site came to an end on 8 March this year when Peabody Housing Association announced that it had bought it. It has committed to going well above and beyond our planning requirements, by making 600 out of a total 1000 homes genuinely affordable homes, including 420 homes for social rent. We need to see more detail on what they are proposing but this is potentially brilliant for the borough. A local grassroots group, Community Plan for Holloway, have been instrumental in ensuring that the community’s voice is heard since the site was sold.

To recreate the scale of the massive post-war council home building programmes would require a Jane Jacobs inspired level of community activism combined with the architectural idealism of Le Corbusier. But it would also need the political will from central government to help local authorities get council housing built. And that, sadly, feels as far away as ever.

Diarmaid Ward is a Labour councillor and the executive member for housing & development at the London Borough of Islington.