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. 

 
 
 
 

More than 830 cities have brought essential services back under public control. Others should follow

A power station near Nottingham: not one owned by Robin Hood Energy, alas, but we couldn't find anything better. Image: Getty.

The wave of cities worldwide rejecting privatization is far bigger and more successful than anyone thought, according to a new report from the Transnational Institute, Reclaiming Public Services: How cities and citizens are turning back privatisation. Some 835 cities in 45 countries have brought essential services like water, energy and health care back under public control.

The persistent myth that public services are by nature more expensive and less efficient is losing its momentum. Citizens and users do not necessarily have to resign to paying increasingly higher tariffs for lower standard services. The decline of working conditions in public services is not an inevitability.

And the ever larger role private companies have played in public service delivery may at last be waning. The remunicipalisation movement – cities or local authorities reclaiming privatised services or developing new options – demonstrates that cities and citizens are working to protect and reinvent essential services.

The failure of austerity and privatisation to deliver promised improvements and investments is part of the reason this movement has advanced. But the real driver has been a desire to meet goals such as addressing climate change or increasing democratic participation in service provision. Lower costs and tariffs, improved conditions for workers and better service quality are frequently reported following remunicipalisation.  Meanwhile transparency and accountability have also improved.

Where remunicipalisation succeeds, it also tends to inspire other local authorities to make similar moves. Examples are plentiful. Municipalities have joined forces to push for renewable, climate-friendly energy initiatives in countries like Germany. Public water operators in France and Catalonia are sharing resources and expertise, and working together to overcome the challenges they meet.

Outside Europe, experiments in public services are gaining ground too. Delhi set up 1,000 Mohalla (community) clinics across the city in 2015 as a first step to delivering affordable primary health care. Some 110 clinics were working in some of the poorest areas of Delhi as of February 2017. The Delhi government claims that more than 2.6m of its poorest residents have received free quality health care since the clinics were set up.


Local authorities and the public are benefiting from savings too. When the Nottingham City Council found out that many low-income families in the city were struggling to pay their energy bills, they set up a new supply company. The company, Robin Hood Energy, which offers the lowest prices in the UK, has the motto: “No private shareholders. No director bonuses. Just clear transparent pricing.”

Robin Hood Energy has also formed partnerships with other major cities. In 2016, the city of Leeds set up the White Rose Energy municipal company to promote simple no-profit tariffs throughout the Yorkshire and Humberside regions. In 2017, the cities of Bradford and Doncaster agreed to join the White Rose/Robin Hood partnership.

Meanwhile, campaigners with Switched on London are pushing their city to set up a not-for-profit energy company with genuine citizen participation. The motivations in these diverse cities are similar: young municipal companies can simultaneously beat energy poverty and play a key role in achieving a just and renewable energy transition.

Remunicipalised public services often involve new forms of participation for workers and citizens. Remunicipalisation is often a first step towards creating the public services of the future: sustainable and grounded in the local economy. Inspiration can be found in the European towns and villages aiming for 'zero waste' with their remunicipalised waste service, or providing 100 per cent locally-sourced organic food in their remunicipalised school restaurants.

Public services are not good simply because they are not private. Public services must also continuously renew themselves, grow, innovate and recommit to the public they serve.

The push for remunicipalisation in Catalonia, for example, has come from a movement of citizen platforms. For them, a return to public management is not just an end in itself, but a first step towards the democratic management of public services based on ongoing civil participation.

Evidence is building that people are able to reclaim public services and usher in a new generation of public ownership. The momentum is building, as diverse movements and actors join forces to bring positive change in communities around the world.

You can read the Transnational Institute report, “Reclaiming Public Services: How cities and citizens are turning back privatisation”, on its website.