You know us by now, dear readers. You know what sort of crazy cats we are. We're the sort of party animals who love nothing more than to kick back and relax with some spreadsheets showing passenger flow data on public transport systems.
So it was that this week we decided to spend a happy hour working which is London's busiest tube line.
The data we used comes from a file with the exotic name “Performance Datastore, Period 3, 2014-15”. And, while parts of that document include figures for the 2013-14 financial year, the last sheet, which shows passenger figures on each line, only goes up to 2011-12. (Boo.)
It also, while we're explaining ourselves, bundles the statistics for the Circle and Hammersmith & City lines together into a single lump: that’s presumably because it essentially functions as a single line with two branches, making it harder to work out which line any particular passenger is travelling on.
With those caveats, though, here’s a graph showing passenger numbers across the network, between 2003 and 2012.
- The most-used lines are roughly 20 times as busy as the least-used. That's the tiny Waterloo & City (W&C) shuttle, which only has two stops (so you'd expect it to be used relatively rarely).
- Some time around 2011, the Central Line overtook the Northern line to become London's busiest.
- Traffic is growing pretty steadily across the network, but at different rates. While passenger numbers grew in the nine years shown here by an average of 30 per cent, they grew most on the W&C and Jubilee lines (up 56 per cent each), and least on the Hammersmith & Circle lines (just 7 per cent). Here's another graph:
So why would those three lines on the left be growing so fast? Our guess is that they all provide fast links to London's major employment centres: Canary Wharf in the case of the Jubilee, the City in the case of the W&C, and both the City and West End in the case of the Central. In other words, what we're looking at here is the growth of London's economy, as seen through its transport network.
The vast disparity between the most and least used lines must be explained in part by differences in size, of course. The various branches of the Central line run to 74km in length and serve 49 stations. The Waterloo & City is a 2.5km shuttle serving just two. Obviously you'd expect the former to be vastly busier than the latter.
So what happens if you control for the size of the line? Well, here's a third graph, this time dividing the traffic on the line by the number of stations it serves
...and suddenly everything changes.
Observations this time around:
- You can suddenly spot the dip in traffic on the Waterloo & City, c2006 (it’s there in the first graph, but almost invisible). There's a good reason for that dip: the line was closed for five months.
- The Central & Northern lines, which serve a lot of different stations, suddenly fall down the league table...
- ...while the Victoria line has now zoomed to the top.
Partly this is because of the way the line is structured. Not only is it fast (no, it really is), but its stations are relatively widely-spaced. In other words, there's not really anywhere along the route that is too far from a station to be served by the line; but all those passengers are being funnelled into just 16 stations.
- But much of the Victoria's high passenger traffic is no doubt a simple matter of train frequency. It's a single line with no branches to complicate things, and it doesn't share track space with any other route. Consequently, it can run a whopping 34 trains an hour, which Transport for London claims to be the most frequent train service anywhere in the UK. Perhaps not coincidentally, the next busiest is the Jubilee, which runs 30 trains an hour.
- Scraping along the bottom you'll find the “sub-surface” lines: the District, Hammersmith & Circle and Metropolitan. These are relatively infrequent, with 18, 12, and 19 trains apiece on their core sections. The District, Hammersmith and Circle lines also have relatively narrowly spaced stations.
Result: they're slow and annoying, and can only take so many passengers anyway.
- The Metropolitan may be dragging along the bottom for an entirely different reason: it barely stops in inner London, only serving a single station (Finchley Road) between the centre of town and suburbia. In many ways, despite its name, it’s more of a suburban railway than a proper metro.
That means it's serving either districts of low-density housing, or central London stations where it shares track with the Hammersmith & Circle lines. Its trains are not only infrequent, they're also serving relatively small catchment areas anyway. Hence, low traffic.
One last graph: this is what happens if we divide total passenger figures by kilometres of line served:
The Metropolitan – which runs for miles out into Buckinghamshire – is still dragging its way along the bottom. But just above it now is the ultra-long (71km) Piccadilly line.
Overall, though, the lines are more tightly bunched when we analyse the data this way– something that becomes obvious if you ignore the Met (which, as noted, is a freak). That suggests that the length of a line – and thus the area served – has more of an impact on its traffic than the exact spacing of the stations on it, at least within reason.
So, now you know: any metro planners who want the maximum bang for their buck could do worse than to look at the Victoria line for inspiration.
You should come to one of our parties, some time. They’re brilliant.