Ridership vs coverage: The transport planner’s dilemma

Berlin. Image: Getty.

Is your transit agency succeeding? It depends on what it’s trying to do – and most transit agencies haven’t been given clear direction about what they should be trying to do.  Worse, they’re told to do contradictory things.  It’s as if you told your taxi driver to turned left and right at the same time, and then criticised them for turning the wrong direction.

On the one hand, we expect transit agencies to pursue a goal of ridership.  Yet we also demand that provide a little service to everyone, which is called a coverage goal.  The coverage goal requires an agency to run predictably low-ridership services, for non-ridership reasons, so it’s the opposite of a ridership goal

In the fictional town below, the little dots indicate dwellings and commercial buildings and other land uses. The lines indicate roads, and the 18 buses indicate the resources the town has to run transit. Most of the activity in the town is concentrated around a few roads, as in most towns.

A transit agency pursuing only a ridership goal would focus service on the streets where there are large numbers of people – where walking to transit stops is easy, and where the straight routes feel direct and fast to customers. Because service is concentrated into fewer routes, frequency is high and a bus is always coming soon.

This would result in a network like the one below.

All 18 buses are focused on the busiest areas. Waits for service are short but walks to service are longer for people in less populated areas. Frequency and ridership are high, but some places have no service.

Why is this the maximum ridership alternative? It has to do with the non-linear payoff of both high density and high frequency, as explained more fully here.

If the town were pursuing only a coverage goal, on the other hand, the transit agency would spread out services so that every street had a bus route, as in the network at below. Spreading it out sounds great – but it also means spreading it thin.

The 18 buses are spread around so that there is a route on every street. Everyone lives near a stop – but every route is infrequent, even those on main roads, and waits for service are long. Only a few people can bear to wait so long, so ridership is low.

In these two scenarios, the town is using the same number of buses. These two networks cost the same amount to operate, but they deliver very different outcomes.

Ridership-oriented networks serve several popular goals for transit, including:

  • Reducing environmental impact through lower Vehicle Miles Travelled;
  • Achieving low public subsidy per rider, through serving the more riders with the same resources, and through fares collected from more passengers;
  • Supporting continued urban development, at higher densities, without being constrained by traffic congestion;
  • Reducing the cost of for cities to build and maintain road and bridges by replacing automobile trips with transit trips, and by enabling car-free living for some people living near dense, walkable transit corridors.

On the other hand, coverage-oriented networks serve a different set of goals, including:

  • Ensuring that everyone has access to some transit service, no matter where they live;
  • Providing lifeline access to critical services for those who cannot drive;
  • Providing access for people with severe needs;
  • Providing a sense of political equity, by providing service to every municipality or electoral district.

Ridership and coverage goals are both laudable, but they lead us in opposite directions. Within a fixed budget, if a transit agency wants to do more of one, it must do less of the other.

Because of that, cities and transit agencies need to make a clear choice regarding the Ridership-Coverage trade off. In fact, we encourage cities to develop consensus on a Service Allocation Policy, which takes the form of a percentage split of resources between the different goals.


For example, an agency might decide to allocate 60 percent of its service towards the Ridership Goal and 40 percent towards the Coverage Goal.

Major network redesigns often shift this balance, intentionally and consciously.  When we led a redesign of the bus network in Houston, we led a discussion with the elected leaders about their priorities, and they decided to shift the focus of their network from 80 per cent coverage to 5per cent coverage. They knew in advance what the result would be: a more useful network, with the potential to grow more ridership, but also many angry people in areas no longer served.

What about your city? What do you think should be the split between ridership and coverage? The answer will depend on your preferences and values.  For cities, it should be up to elected officials, informed by the public, to decide.

Jarrett Walker is an international consultant in public transit network design and policy, based in Portland, Oregon. Christopher Yuen is an associate at Jarrett Walker+Associates.

Walker is also the author of “Human Transit: How clearer thinking about public transit can enrich our communities and our lives". This article was originally written for his blog, 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.