For this week’s Skylines, I dragged Stephen Bush down into our podcasting catacombs to rank London tube lines. We’re both London natives, we’re both professional nerds, the podcast was running short – this seemed like it might be a good way of plugging the gap.

Except we swiftly ran into a problem: before we even started the ranking, we fell into a heated argument about exactly how many tube lines there are. Both Stephen and I, it turned out, have strong feelings that the official number is wrong, albeit for entirely different reasons. His arguments were mostly about how you define the Tube; mine about how you define a line.

We’ll get into that in a moment. First, though, let’s deal with the easy stuff. 

The official stance

According to Transport for London, who let’s be honest, should know these things, there are 11 tube lines. Here they all are:

Purists will tell you that only seven of these actually count as tube lines. The word, they’ll say, should refer strictly to deep-level tube lines: routes through tunnels bored deep into the ground. Four others lines (the Circle, District, Hammersmith & City, and Metropolitan) are technically sub-surface lines, which were excavated using “cut and cover” methods – I’m not going to explain that, because it’s exactly what it sounds like.

The trains are different sizes, too. Look:

A sub-surface Metropolitan line train next to its smaller tube brethren on the Piccadilly line. Image: Chris McKenna/Wikipedia.

This feels like one of those battles that’s long been lost, however: even TfL itself refers to the whole network as the Tube. And so, I feel, the purists should give up and find something more important to argue about. 

Like, for example, how many lines the District line is. 

What’s in a line?

Three of the lines are a simple business. The Bakerloo, Jubilee and Victoria are very definitely individual lines, in the most literal sense that they have one destination apiece at each end. (They’re also, as it happens, all deep tube lines.)

The Piccadilly and Central lines (two more deep lines) are slightly more complicated because they involve branches and multiple destinations. But that seems fine, really: each has a single route through inner London that just happens to branch in the suburbs. For most Central line passengers, the fact their train is going to Hainault rather than Epping doesn’t really matter.

Then things get more complicated. Why are the Circle and Hammersmith & City lines two different lines? They’re managed as a unit, served by the same trains, and share a route for 18 stops over 15km, only splitting east of Liverpool Street.  Why not treat them as a single line, too?

Except of course we don’t, because that would obviously be ridiculous.

Firstly, they’ve always been treated as separate lines: until 2009, when the Circle line stopped being a Circle, their routes were much less alike.

But it’s also obviously silly to consider them as a single line because they diverge in central London, rather than somewhere out in the wilds of zone 3: it matters to enough passengers which of the two routes they’re on that it makes sense treat them as separate. 

So: where trains take different routes through central London, it’s logical to treat them as separate lines, right? Makes sense.

Now explain the District or Northen line to me.

Shades of green

The District line is a complicated beast. It has a single branch to the east of London (Upminster), but splits three ways in the West (Wimbledon, Richmond, Ealing Broadway). It’s also in charge of the weird little part time shuttle service from High Street Kensington to Kensington Olympia, a route it is often, quite genuinely, quicker to walk.

The real problem, though, is that it has two routes through central London: the main one, following the south side of the Circle line from Earl’s Court to Aldgate East; and another, served almost exclusively by trains from Wimbledon, following the west side up to Edgware Road. Not so long ago, these were served by separate trains, too.

Click to expand, should you wish. Image: Wikipedia. 

This seems to violate the “only have one route in central London” principle: more sensible, surely, to brand the Wimbledon-Edgware Road services as a seperate line. It even has a name of sorts: it’s unofficially known on the nerd-web as the Wimbleware.

So why doesn’t TfL split it up? Partly I assume it’s because of the tiny number of trains that do, say, run from Richmond to Edgware Road, but mostly I suspect the answer is history. We treat it as a single line because we always have.

That said, until the 1990s, the Hammersmith & City line was part of the Metropolitan line, so things can change if we grump enough.

North and south

The Northern line is, if anything, even stupider. On no sensible definition is this a line:

Click to expand, should you wish. Image: Wikipedia. 

And giving two separate branches that go through completely different bits of central London the same name seems to be asking for trouble.

In the long term, TfL’s ambition is to split the line. One route will run from Edgware to Camden Town, down through the West End, then turn west at Kennington to terminate at the new Battersea station. The other will go from High Barnet or Mill Hill East, to Camden Town, Bank, and all the way to Morden. 

Doing this would reduce the number of points at which trains get in each other’s way, and so allow slightly higher frequencies. But it is, counter-intuitively, dependent on entirely rebuilding Camden Town station, because so many people will need to change trains there and at the moment it can’t cope. 

Anyway, when it does, if TfL have any sense of humour at all they’ll rename the Edgware-West End-Battersea branch the “Southern line” just to confuse everyone. And in the mean time, the Northern line is two lines and I refuse to countenance any other point of view.

The leftovers

There are two other lines on the Tube, whose tube-iness I’m not entirely convinced by.

One is the Metropolitan, which acts like a suburban mainline railway that just happens to use the north side of the Circle line. Some of its trains even terminate at the bit of Baker Street that looks like a rail terminal. I don’t really want to revoke its tube status because it was the first one; I’m just saying it’s on thin ice, that’s all.

The other is the Waterloo & City which was treated as part of British Rail until 1994. Also, it’s not really much of a line, is it? In other cities they treat these little stubs as half-lines. In New York they’re called “shuttles” and don’t get proper brand identities; in Paris they don’t get numbers of their own, and are instead referred to as 3 Bis or 7 Bis (roughly the equivalent of numbering them 3a or 7a in English). 

I don’t want to say the W&C isn’t a tube line either, really. I’m just pointing out that this whole thing is arbitrary and in another world we could have anything between 8 and 13 tube lines without things being noticeably weirder or less logically consistent than they already are.

Things that are definitely not tube lines

On the podcast, Stephen argued that we should count the DLR and London Overground as tube lines. Which we very obviously shouldn’t, because it’s a really stupid idea, but okay, let’s run with it. 

His main, though wrong, argument seems to be that they involve trains and are on the tube map, and that he quite likes them. I would have had more time for this if he hadn’t scoffed at the idea Tramlink should also count on the same basis. Honestly, there’s no consistency to this position at all is there?

At any rate, if we’re going to start counting things as tube lines just because they appear on the tube map, we might as well count the River Thames and that would be stupid.

In defence of the Overground, it did swallow a tube line – the East London line, from Whitechapel to New Cross, is now part of a much longer route from Highbury down to darkest south London. And yes, it is aggravating that the tube should have lost a line, albeit in a way that made it better and much more useful.

Nonetheless: neither of these things are tube lines. The DLR is a form of light rail; the Overground is more like mainline heavy rail, an S-Bahn rather than a U-Bahn. What’s more, both are also networks of their own rather than individual lines: as ever, it depends how you count, but Wikipedia gives them seven and nine different routes respectively.

So, no, Stephen, they’re not tube lines. Stick to politics in future, eh? Amateur.

In conclusion though: there are 11 tube lines. But only because we choose to count them as 11. Could be more, could be less.

Anyway, it’s nearly the weekend, why are you still reading this? Be off with you. To a pub, right now.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason. 

Want more of this stuff? Follow CityMetric on Twitter or Facebook.