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.
This post revisits a basic topic at the core of transit planning decisions that everyone engaged in conversation about transit should understand.
In the fictional town below, the little dots indicate dwellings, jobs, and other destinations. The lines indicate roads. Most of the activity in the town is concentrated around a few roads, as in most towns.
Designing for Ridership
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.
Why is this the maximum ridership alternative? It has to do with the non-linear payoff of both high density and high frequency, as we explain more fully here.
Designing for Coverage
A network designed for ridership would not go to many parts of the city. In the map above, someone who lived in the southeast part of town would not like this network at all. That person is likely to want a network designed for coverage, not ridership.
In a network designed for coverage, the transit agency would spread out services so that there would be a bus stop near everyone. Spreading it out sounds great, but it also means spreading it thin. The resources would be divided among so many routes that it wouldn’t be possible to offer much service on any of them. As a result, all routes would be infrequent, even those on the main roads. Infrequent service isn’t very useful, so not many people would ride.
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.
Both Goals are Important
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.
- Allowing continued urban development, even 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 that lack adequate resources need to make a clear choice regarding the Ridership-Coverage tradeoff. 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. Our firm has helped many transit agencies think through this question.
What about your city? How do you think your city should balance the goals of ridership and coverage? There is no technical answer. Your answer will depend on your values.
Jarrett Walker’s Journal of Transport Geography Paper, which first introduced this concept, is here.