So, here’s a thing:

The short version: Transport for London (TfL) is trialling a new colour-coding system for bus routes. Each bus will get its own colour, which will be used on the “spider maps” showing bus routes around a particular area, as well as on signs at stops, and in big numbers on the side of each bus.

At the moment this is only a pilot. Initially, it’s been trialled on seven bus routes around Barkingside, out in the far east; in the summer, it’ll spread to Hayes in the west. But if it works, it could be rolled out further.

So – will it work? Some thoughts.

There aren’t that many colours

London has a lot of bus routes. A lot. Even excluding special services like night buses, school buses and so on, there are over 500 routes.

There are of course an infinite number of colours, so this wouldn’t be a problem – except that there’s a limit to the number the human eye can instantly distinguish. You can get away with a light blue and a dark blue; but throw in any more blues than that, and users have to consciously try to follow a line rather than simply see it at a glance.

One result of this is that no metro map in the world contains more than 15 shades; only a dozen use more than 10. (Lots more analysis on this stuff here.) So the implication that each bus will get an identifying colour like each tube line does is very clearly nonsense.

And buses cross each others’ paths

Not every bus needs a unique colour, of course: you can have multiple buses numbered in violet, providing they don’t go anywhere near each other.

The difficulty is they probably will – and TfL has started with an easy bit of town. There are only seven buses in Barkingside. It’s easy enough, then, to give them all a unique colour:

The Barkingside spider map: click to expand Image: TfL.

But five of those routes go to Ilford, where they cross paths with 12 more. Two of them go to Romford, from where they meet another 19 buses.

And the Romford one: click to expand. Image: TfL.

Even thinking about the maths does my head in – but it seems unlikely to me that every bus in London can be given a colour different from that of every bus it ever shares a stop with. At some bus stops, there’ll be two buses in violet.

The problem is the maps

That’s not necessarily a critical flaw: the big colourful numbers on the side of each bus will still help you when identifying buses from a distance. If a violet 25 and a violet 101 happen to share a stop at some point, well, those numbers look different enough that nobody’s going to confuse them. The colour coding will still be useful.

Except – those numbers aren’t just for the sides of buses, or the stop signs. They’re also meant to match those shown on spider maps, like those above.

I am unconvinced it will be possible to do this in such a way that no map needs to use the same colour for multiple different routes. In fact, I suspect it’ll happen rather a lot.

And I’m not sure a world in which three buses are shown on a single map in the same colour is one in which buses are more accessible than the world we’re living in now.

What about service flexibility?

There’s another issue. The whole point of rotating bus blinds is that the same bus can be used on several different routes. Historically, you’d turn a handle, and both the destination and the number shown on the front of the bus would change.

Old London bus blinds in the London Transport Museum. Image: Leif Jørgensen/Wikimedia.

This meant a degree of flexibility: if a bus broke down, another could be swapped over from a different route to plug the gap. Even today, when London’s bus services are provided by a dozen different companies, each of them generally runs enough routes to retain these advantages.

One quick way to remove this flexibility, though, is to paint the route number on the side of the bus in big colourful numbers, so that a 150 is a 150 is a 150.

I don’t want to be down on this idea. I think it sounds lovely: you’ll be able to spot your bus from further away, and giving bus routes colours should give them a stronger identity, something for people to latch onto. All this should make the bus network more usable to those who find it a bit intimidating.

But – I just can’t see how it’s going to work in practice. I’m sure it’ll work in Barkingside and Hayes. But how can it work in a network of over 500 buses?

I fear this may be one of those ideas where the theory is better than the reality.

You can read more on public transport map colour schemes here, if you so wish.

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

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