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. 

 
 
 
 

How do North Koreans get to work? A guide to transport in the DPRK

Buhung station, on the Pyongyang Metro. Image: Jodie Hill.

Like so much else in North Korea, the country’s transport can be divided into categories: Pyongyang and not Pyongyang.

In the capital, centrally-run transportation is, compared to other extremely poor countries, efficient, cheap and well maintained. Outside Pyongyang, by contrast, the state has withered away – albeit not quite as Marx imagined it would. The near total collapse of state run transport infrastructure has left room for a wide range of enterprising North Koreans to make their living in the transport sector – provided, of course, a chunk of those proceeds makes its way back to the party.

So how do North Koreans get around Pyongyang?  

Here’s a homemade map of the city’s transport section:

A homemade map of the Pyongyang transport sector. Image: Michael Hill.

Some notes on all this. The names for Subway stations are translations of the Korean names, but bear no relation to their location. I filled in the (unnamed) trolley bus and tram stop names myself, with reference local landmarks; in fact, those systems both stop way more than my map implies.

What’s more, the Gwangmyeong/Bright Future station is closed, and has been for years – out of respect for Kim Jeong Il and Kim Il Sung who are in a nearby mausoleum, which used to be Kim Il Sung’s Pyongyang pad. The tramline to Gwangmyeong/Bright Future is also not really part of the public transport network, but is just for visitors to the mausoleum.

Getting about

A subway ticket costs just 5 North Korean Won (9,500 won to the dollar at black market rates). If you need to transfer you will have to buy another ticket, there are no travelcards or season tickets. You can check the best way to get where you are going at most stations (possibly all) contain interactive maps.

Pyongyang subway interactive map. Image: Jodie Hill.

Just press the name of the station you wish to travel to from the list along the bottom, and the route from your current station to your destination lights up. This may or may not be overkill for a network with just two lines and 16 stations.

Incidentally, the logo has the word 지 (ji) which is the first syllable of 지하 (jiha) which means underground. The title just means “Information board”, and the question is, ‘Where are you going?’

Some stations are 360ft (110m) deep, double the depth of the deepest station (Hampstead) on the London Underground.

The escalators at Buhung/Revival station escalator. Image: Jodie Hill.

While this bomb shelter might be useful one day, for now it just means Pyongyangites add ten minutes to their planned journey time – which encourages many people to take the tram or trolley bus instead. When you finally get down to the platform you won’t have long to wait – at most 5 minutes during peak times, 10 minutes off peak.

The North Korean government never misses a chance to propagandise: every station has a theme. For example the station name Gaeson means “Triumphant Return”; it’s situated near where Kim Il-Sung gave his first speech as ruler. Inside the murals depict crowds attentively listening to him. The style is not dissimilar to the grandeur of subways in the former Soviet Union, but with much less emphasis on the workers and modernist art and a lot more on the rulers.

The trains themselves were made in West Germany in the 1950s and 60s. There are allegedly some new trains – but they look suspiciously like their older counterparts given a lick of paint and an electronic information board. The old East German stock has been moved onto the national rail network. While these days powercuts are much rarer than in the 1990s (when, for long periods of the day, the subway didn’t operate at all), a torch and something to read might be advised just in case you get stuck.

The central figure is Kim Il-Sung. Image: Jodie Hill.

The ‘showcase’ station is Buhung (“Revival”):

Images: Jodie Hill.

The others are much the same only without the chandeliers and with much dimmer lights.

Above ground

While electricity is hardly plentiful in North Korea, compared to oil it is pretty abundant. Therefore, buses have gradually been phased out: now trolley buses and trams then form the backbone of the transit network in Pyongyang. As regular as the subway, but with a bigger network and not requiring a long escalator ride – or walk, as the escalators often break down – this is the most popular way to travel around Pyongyang.

The ticket price is again just 5 won (about 0.4p). The trolley bus vehicles were mostly manufactured domestically, while the trams are second hand from communist era Prague. Power cuts are much more frequent on the trolley buses and trams than on the subway: passengers on an affected service are expected to push.

The rail network is rarely used for commuting. Even for those way out in the plush satellite town of Ryeongsong (at the far north of the map, and home of Kim Jong-Un and many other top party cadres), those not high enough ranked for a car take the trolleybus rather than the train to commute to work.

Venturing out of the capital, the official transport network shows signs of near collapse. As far as I am aware, the only other city with a tram network is Chongjin, but it’s hardly extensive – a one line system, eight miles long. It suffers from much more regular power cuts than its Pyongyang counterpart, and relies on hand me down trains from the capital. Many cities have a trolley bus service on paper – but most have no service at all or, at best, a skeleton peak hours service only.

The national rail network is worse. Before you can even get a ticket you must apply for permission – a process that can take days – though nowadays this can be circumvented with a bribe. Tickets are cheap, usually just a few hundred won (a few pence), but with frequent power cuts, journeys take even longer than the 12mph average speed suggests they will. While Kim Jong-Un’s travel habits are unknown, both his father and grandfather liked to travel by private train, and this would lead delays of 24 hours for people travelling in the same area. Freight takes priority over passenger rail, and virtually the entire network is single track and with no sophisticated signalling equipment, meaning trains often have to wait for a long time to let others pass.

A map of the network. Image: Voland77/Wikimedia Commons.

As a result of these problems lot of passenger traffic has moved onto the roads. Enterprising Koreans who have obtained licenses, as well as state operated enterprises (particularly people associated with the police), have bought second hand buses from China and now use them for inter-city transport.

Reports vary about whether travel permits are required for bus travel, and about how hard they are to obtain. Prices fluctuate due to changes in the oil price and vary wildly by region. A journey from Nampo to Pyongyang (about 30 miles) costs $5. A journey of similar length between two cities in the north east costs around $15, while in the north west just $2.

Journeys are not comfortable. North Korean roads are often unpaved, always potholed, and the buses were not in great condition even when they left China. Nevertheless they link the emerging market economy together.  

North Korea road map:

A map of the network. Blue routes are all paved, others mostly unpaved or paved a very long time ago. Image: Voland77/Wikimedia Commons.

For shorter journeys, taxis are now an option in most medium sized cities and even in some rural areas. There are at least four taxi companies operating these days in Pyongyang.

North Korean won won’t get you very far though: taxi drivers want dollars (two of them), to take you anywhere plus another 50 cents for every kilometer you travel, about three times the cost as in North East China. The only network outside Pyongyang I know in detail is one run by a state-owned enterprise in Chongjin, which recently imported dozens of almost new taxis from China. Payment is accepted in North Korean won, Chinese RMB and US dollars; a 10 minute journey costs 1 dollar.

Taxis are beyond the means of most North Koreans, though. The backbone of North Korea’s transport infrastructure is formed by bikes.


Bicycles were illegal in Pyongyang until 1992, and this ban was strictly enforced – but since it was lifted, bike use has really taken off. In smaller towns they often serve as a status symbol as much as transport, much as cars do for many in the west. The wealthiest now ride electric assisted bikes imported from China, though the Ford of North Korea is the Pyongjin bike company, which has cornered 70% of the market according to the leading North Korea scholar Andrei Lankov.

It is still technically illegal for a woman to ride a bike, but this ban is not strictly enforced. (I know of one woman who used to ride her technically illegal bike to her technically illegal small business, a bicycle repair shop.) Legally, every bike needs a license plate, and each rider needs take a test and get a license – but this too is mostly unenforced.

It is illegal to ride on North Korea’s mostly empty roads. This ban is not enforced in most cities, but is in Pyongyang, where the government has started creating cycle paths on the pavements as well as a bike hire scheme. If you can’t afford a bike yourself, a ‘bicycle carrier’ will give you a lift for about five US cents per kilometre – although, like a land based Ryanair, you have to pay more for bags. Both customers and workers in this sector tend to be very poor.

North Korea’s transport mirrors the North Korean economy. Pyongyang just about manages to present itself as a communist city. Outside the capital, though, secret policeman, state-operated enterprises and sole traders make a living – and sometimes a fortune – keeping the country moving among the remains of a communist economy which never delivered.

With thanks to Michael Spavor of Paektu Cultural Exchange and Rowan Beard of Young Pioneer Tours for helpful conversations.  

Michael Hill wants you to be his third twitter follower so you can see more versions of the Pyongyang transport map.