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. 

 
 
 
 

Does it matter that TfL are renaming White Hart Lane station Tottenham Hotspur?

New White Hart Lane. Image: Getty.

Pretend for a moment that you’re travelling in the London of 1932. You’re taking the Piccadilly Line northbound and alight at Gillespie Road station. The name should be obvious: it’s inscribed in bespoke brown tiling on the platform.

But that 31 October, following an intense campaign by the eponymous football club, the London County Council changed the station’s name to Arsenal (Highbury Hill). The area’s growing association with the name “Arsenal” ended in a lengthy negotiation that changed maps, signs and train tickets alike. Football had acquired so much power that it changed the name of not just a Tube station but an entire suburb, even before the era of Wenger or the Emirates.

Now the spectre of name changes is on the horizon once again. As Tottenham Hotspur FC inches closer to completing its new stadium, the club is clamouring for a renamed Overground station. Despite the fact the new stadium is located on almost exactly the same site as the old just off White Hart Lane, and fans have long been calling the scaffolding-laden mess “New White Hart Lane”, the club’s executive director is adamant that the station’s existing name cannot stand. White Hart Lane station, on the Overground line leaving Liverpool Street, is set to be renamed “Tottenham Hotspur”, at a cost to the club of £14.7m.

Little has been made of the fact that this peculiar PR kerfuffle is tied to Spurs’ failure to convince Nike to sponsor the venue. Some sources have even claimed that the sponsorship is yet to be finalised because it is somehow contingent on the renaming of the Overground station; beyond the ridiculous Johnson-era vanity project that was the Emirates Air Line, it seems improbable that TfL will allow any more corporate-flavoured information pollution. There will be no “Nike Stadium” station on the way to Enfield, much as there is no “Emirates” on the way to Cockfosters, especially if public consultation gets a look in.

The scene of the crime. Image: TfL.

But there’s a problem with the new name, all the same. “White Hart Lane” already means “football stadium”, in the same way Loftus Road or Stamford Bridge do. Changing it to “Tottenham Hotspur” risks opening the floodgates to an “O2 North Greenwich” or a “Virgin Euston” at some point in future, names as banal as there are dystopian. The Greater London Authority has promised to spend the £14.7m fee on community programmes in the local area – but that’s not much money to set the precedent that a private company can mess about with the Tube map.


What’s more, as CityMetric has often observed, there are plenty of station names across London that could do with a tidy up. Picking one that’s perfect already and asking for £14.7m to change it is adding insult to injury. How much would it cost a community group if they asked to change the name of Goodge Street to Fitzrovia? Why does a vast corporate entity backed by international sponsors and thousands of season ticket holders get to set the standard?

Back in Arsenal’s day, changing names on the Tube must have been easy; changes could be accommodated gradually without bothering the every day traveller. But in our world of online information, maps and apps, name changes are rather more complicated.

The question is – if TfL can bring itself to balefully accept this particular proposition, why can’t it accept ours? Why sort out a single non-issue on the Tube Map when you can catch lots of real ones in one go? A day’s pandemonium might just be a price worth paying to fix the Bethnal Greens problem once and for all.