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

 
 
 
 

“A story of incompetence, arrogance, privilege and power”: A brief history of the Garden Bridge

Ewwww. Image: Heatherwick.

Labour assembly member Tom Copley on a an ignominious history.

The publication last week of the final bill for Boris Johnson’s failed Garden Bridge has once again pushed this fiasco into the headlines.

As well as an eye-watering £43m bill for taxpayers for this Johnsonian indulgence, what has been revealed this week is astonishing profligacy by the arms-length vehicle established to deliver it: the Garden Bridge Trust. The line by line account of their spending reveals £161,000 spent on their website and £400,000 on a gala fundraising event, amongst many other eyebrow raising numbers. 

Bear in mind that back in 2012, Johnson promised that the bridge would be entirely privately funded. The bridge’s most ardent advocate, Joanna Lumley, called it a “tiara for the Thames” and “a gift for London”. Today, the project would seem the very opposite of a “gift”.

The London Assembly has been scrutinising this project since its inception, and I now chair a working group tasked with continuing our investigation. We are indebted to the work of local campaigners around Waterloo as well as Will Hurst of the Architects Journal, who has brought many of the scandals surrounding the project into the open, and who was the subject of an extraordinary public attack by Johnson for doing so.

Yet every revelation about this cursed project has thrown up more questions than it has answers, and it’s worth reminding ourselves just how shady and rotten the story of this project has been.

There was Johnson’s £10,000 taxpayer funded trip to San Francisco to drum up sponsorship for the Thomas Heatherwick garden bridge design, despite the fact that TfL had not at that point even tendered for a designer for the project.

The design contest itself was a sham, with one of the two other architects TfL begged to enter in an attempt to create the illusion of due process later saying they felt “used”. Heatherwick Studios was awarded the contract and made a total of £2.7m from taxpayers from the failed project.


Soon after the bridge’s engineering contract had been awarded to Arup, it was announced that TfL’s then managing director of planning, Richard de Cani, was departing TfL for a new job – at Arup. He continued to make key decisions relating to the project while working his notice period, a flagrant conflict of interest that wouldn’t have been allowed in the civil service. Arup received more than £13m of taxpayer cash from the failed project.

The tendering process attracted such concern that the then Transport Commissioner, Peter Hendy, ordered an internal audit of it. The resulting report was a whitewash, and a far more critical earlier draft was leaked to the London Assembly.

As concerns about the project grew, so did the interventions by the bridge’s powerful advocates to keep it on track. Boris Johnson signed a mayoral direction which watered down the conditions the Garden Bridge Trust had to meet in order to gain access to further public money, exposing taxpayers to further risk. When he was hauled in front of the London Assembly to explain this decision, after blustering for while he finally told me that he couldn’t remember.

David Cameron overruled the advice of senior civil servants in order to extend the project’s government credit line. And George Osborne was at one point even more keen on the Garden Bridge than Johnson himself. The then chancellor was criticised by the National Audit Office for bypassing usual channels in order to commit funding to it. Strangely, none of the project’s travails have made it onto the pages of the London Evening Standard, a paper he now edits. Nor did they under his predecessor Sarah Sands, now editor of the Today Programme, another firm advocate for the Garden Bridge.

By 2016 the project appeared to be in real trouble. Yet the Garden Bridge Trust ploughed ahead in the face of mounting risks. In February 2016, despite having not secured the land on the south bank to actually build the bridge on, nor satisfied all their planning consents, the Trust signed an engineering contract. That decision alone has cost the taxpayer £21m.

Minutes of the Trust’s board meetings that I secured from TfL (after much wailing and gnashing of teeth from the Trust itself) reveal that weeks beforehand Thomas Heatherwick had urged the trustees to sign the contract in order to demonstrate “momentum”.

Meanwhile TfL, which was represented at board meetings by Richard de Cani and so should’ve been well aware of the mounting risks to the project, astonishingly failed to act in interests of taxpayers by shutting the project down.

Indeed, TfL allowed further public money to be released for the project despite the Trust not having satisfied at least two of the six conditions that had been set by TfL in order to protect the public purse. The decision to approve funding was personally approved by Transport Commissioner Mike Brown, who has never provided an adequate explanation for his decision.

The story of the Garden Bridge project is one of incompetence, arrogance and recklessness, but also of privilege and power. This was “the great and the good” trying to rig the system to force upon London a plaything for themselves wrapped up as a gift.

The London Assembly is determined to hold those responsible to account, and we will particularly focus on TfL’s role in this mess. However, this is not just a London issue, but a national scandal. There is a growing case for a Parliamentary inquiry into the project, and I would urge the Public Accounts Committee to launch an investigation. 

The Garden Bridge may seem like small beer compared to Brexit. But there is a common thread: Boris Johnson. It should appal and outrage us that this man is still being talked about as a potential future Prime Minister. His most expensive vanity project, now dead in the water, perhaps serves as an unwelcome prophecy for what may be to come should he ever enter Number 10.

Tom Copley is a Labour member of the London Assembly.