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. 

 
 
 
 

Where actually is South London?

TFW Stephen Bush tells you that Chelsea is a South London team. Image: Getty.

To the casual observer, this may not seem like a particularly contentious question: isn’t it just everything ‘under’ the Thames when you look at the map? But despite this, some people will insist that places like Fulham, clearly north of the river, are in South London. Why?

Here are nine ways of defining South London.

The Thames

Image: Google Maps/CityMetric.

It’s a curvy river, the Thames. Hampton Court Palace, which is on the north bank of the river, is miles south of the London Eye, on the south bank. If the river forms a hard border between North and South Londons, then logically sometimes North London is going to be south of South London, which is, to be fair, confusing. But how else could we do it?

Latitude

You could just draw a horizontal line across a central point (say, Charing Cross, where the road distances are measured from). While this solves the London Eye/Hampton Court problem, this puts Thamesmead in North London, and Shepherd’s Bush in South London, which doesn’t seem right either.

Image: Google Maps/CityMetric.

And if you tried to use longitude to define West and East London on top of this, nothing would ever make sense ever again.

The Post Office

Image: Wikimedia Commons.

Some people give the Post Office the deciding vote, arguing that North and South London are defined by their postcodes. This does have some advantages, such as removing many contentious areas from the debate because they’re either in the West, East or Central postcode divisions, or ignoring Croydon.

But six of the SW postcodes are north of the river Thames, so we’re back to saying places like Fulham and Chelsea are in south London. Which is apparently fine with some people, but are we also going to concede that Big Ben and Buckingham Palace are South London landmarks?

Taken to the extreme this argument denies that South London exists at all. The South postcode region was abolished in 1868, to be merged into the SE and SW regions. The S postcode area is now Sheffield. So is Sheffield in South London, postcode truthers? Is that what you want?

Transport for London

Image: TfL.

At first glance TfL might not appear to have anything to add to the debate. The transport zones are about distance from the centre rather than compass point. And the Northern Line runs all the way through both North and South London, so maybe they’re just confused about the entire concept of directions.

 

Image: TfL.

But their website does provide bus maps that divide the city into 5 regions: North East, South East, South West, North West and the Centre. Although this unusual approach is roughly speaking achieved by drawing lines across and down the middle, then a box around the central London, there are some inconsistencies. Parts of Fulham are called for the South West region, yet the whole of the Isle of Dogs is now in North East London? Sick. It’s sick.

The Boundary Commission

One group of people who ought to know a thing or two about boundaries is the Boundary Commission for England. When coming up with proposals for reforming parliamentary constituencies in 2011, it first had to define ‘sub-regions’ for London.

Initially it suggested three – South, North East, and a combined North, West and Central region, which included Richmond (controversial!) – before merging the latter two into ‘North’ and shifting Richmond back to the South.

In the most recent proposal the regions have reverted to North Thames and South Thames (splitting Richmond), landing us right back where we started. Thanks a bunch, boundary commission.

The London Plan

Image: Greater London Authority.

What does the Mayor of London have to say? His office issues a London Plan, which divides London into five parts. Currently ‘South’ includes only Bromley, Croydon, Kingston upon Thames, Merton, Sutton, and Wandsworth, while the ‘North’ consists of just Barnet, Enfield, and Haringey. Everywhere else is divvied into East, South or Central.

While this minimalist approach does have the appeal of satisfying no-one, given the scheme has been completely revised twice since 2004 it does carry the risk of seismic upheaval. What if Sadiq gets drunk on power and declares that Islington is in East London? What then?

Wikipedia

 

Image: Wikimedia Commons/CityMetric.

The coordinates listed on the South London article lead to Brockwell Park near Herne Hill, while the coordinates on the North London article lead to a garden centre near Redbridge. I don’t know what this means, so I tried to ring the garden centre to see if they had any advice on the matter. It was closed.

Pevsner Guides

Image: Wikimedia Commons/CityMetric.

Art historian Sir Nikolaus Pevsner might seem an unlikely source of help at this juncture, but we’ve tried everything else. And the series of architectural guides that he edited, The Buildings of England, originally included 2 volumes for London: “The Cities of London and Westminster”, and “everything else”. Which is useless.

But as his successors have revised his work, London has expanded to fill 6 volumes: North, North West, East, The City, Westminster, and South. South, quite sensibly, includes every borough south of the Thames, and any borough that is partly south of the Thames (i.e. Richmond). And as a bonus: West London no longer exists.

McDonald’s

I rang a McDonald’s in Fulham and asked if they were in South London. They said no.

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