What rivers teach us about transport networks

The sun sets over the Mississippi. Image: Getty.

Cartographer and artist Daniel Huffman has drawn river systems as subway maps.  He insists it's just for fun, but these maps push an important button for me.

Image: Daniel Huffman.

Really, these fanciful maps are a bit reminiscent of some real transit maps, aren't they?

Image: Metlink.

Metlink's map of the Melbourne train network has important things in common with a river system map.  First, both networks are radial, which means that all lines converge to flow to a single point (New Orleans for the Mississippi River, the City Loop for Melbourne's trains).  And necessarily, both maps are full of branching:

But branching always divides frequency.  The Melbourne map gives a superficial impression that Lilydale, Boronia and Ringwood all have the same kind of transit service.  They certainly all have train stations – but the branching means that Ringwood has to have more frequent service than either branch. And that may be the difference between a service that can be used spontaneously and one that requires you to build your life around a timetable. 

It's interesting to speculate how transit policy might change if everybody was trained to be suspicious whenever they see this...

... because this always means one of three things.  Either

(a) points beyond the branching point have less frequent service, or

(b) one of the branches operates as a shuttle, requiring a connection, or in a few rare cases

(c) the train itself comes apart, with some cars proceeding along one branch and some along the other. 

Geometrically, it has to mean one of those things.  And before you decide whether the service is useful to you, or whether you support a proposed transit project whose map looks like this, you should ask which of those it is.

I've always been partial to mapping styles where a branch is rendered as a wide line splitting into two narrow lines, such that the width of the two narrow lines adds up to the width of the main line.  In this presentation, "A Field Guide to Transit Quarrels," I used that approach to clarify one of the possible branching patterns of BART's San Francisco Airport line (though this is not the pattern that runs today).

In that respect, transit lines really are like rivers: just as two converging rivers combine their volume of flow, two converging transit branches combine their frequency.

Jarrett Walker is an international consultant in public transit network design and policy, based in Portland, Oregon. He is also the author of  “Human Transit: How clearer thinking about public transit can enrich our communities and our lives”, which you can buy here.

This article was originally written for his blog in 2011, and is reposted here with permission.


What's actually in the UK government’s bailout package for Transport for London?

Wood Green Underground station, north London. Image: Getty.

On 14 May, hours before London’s transport authority ran out of money, the British government agreed to a financial rescue package. Many details of that bailout – its size, the fact it was roughly two-thirds cash and one-third loan, many conditions attached – have been known about for weeks. 

But the information was filtered through spokespeople, because the exact terms of the deal had not been published. This was clearly a source of frustration for London’s mayor Sadiq Khan, who stood to take the political heat for some of the ensuing cuts (to free travel for the old or young, say), but had no way of backing up his contention that the British government made him do it.

That changed Tuesday when Transport for London published this month's board papers, which include a copy of the letter in which transport secretary Grant Shapps sets out the exact terms of the bailout deal. You can read the whole thing here, if you’re so minded, but here are the three big things revealed in the new disclosure.

Firstly, there’s some flexibility in the size of the deal. The bailout was reported to be worth £1.6 billion, significantly less than the £1.9 billion that TfL wanted. In his letter, Shapps spells it out: “To the extent that the actual funding shortfall is greater or lesser than £1.6bn then the amount of Extraordinary Grant and TfL borrowing will increase pro rata, up to a maximum of £1.9bn in aggregate or reduce pro rata accordingly”. 

To put that in English, London’s transport network will not be grinding to a halt because the government didn’t believe TfL about how much money it would need. Up to a point, the money will be available without further negotiations.

The second big takeaway from these board papers is that negotiations will be going on anyway. This bail out is meant to keep TfL rolling until 17 October; but because the agency gets around three-quarters of its revenues from fares, and because the pandemic means fares are likely to be depressed for the foreseeable future, it’s not clear what is meant to happen after that. Social distancing, the board papers note, means that the network will only be able to handle 13 to 20% of normal passenger numbers, even when every service is running.

Shapps’ letter doesn’t answer this question, but it does at least give a sense of when an answer may be forthcoming. It promises “an immediate and broad ranging government-led review of TfL’s future financial position and future financial structure”, which will publish detailed recommendations by the end of August. That will take in fares, operating efficiencies, capital expenditure, “the current fiscal devolution arrangements” – basically, everything. 

The third thing we leaned from that letter is that, to the first approximation, every change to London’s transport policy that is now being rushed through was an explicit condition of this deal. Segregated cycle lanes, pavement extensions and road closures? All in there. So are the suspension of free travel for people under 18, or free peak-hours travel for those over 60. So are increases in the level of the congestion charge.

Many of these changes may be unpopular, but we now know they are not being embraced by London’s mayor entirely on their own merit: They’re being pushed by the Department of Transport as a condition of receiving the bailout. No wonder Khan was miffed that the latter hadn’t been published.

Jonn Elledge was founding editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.