Tag Archives | coverage

Basics: The Ridership – Coverage Tradeoff

By Christopher Yuen

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 and commercial buildings and other land uses. The lines indicate roads. Most of the activity in the town is concentrated around a few roads, as in most towns.

Imagine you are the transit planner for this fictional town. The dots scattered around the map are people and jobs. The 18 buses are the resources the town has to run transit. Before you can plan transit routes you must first decide: What is the purpose of your transit system?

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 we explain 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.  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.

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, so 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.
  • 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 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?  What do you think should be the split between ridership and coverage?  The answer will depend on your preferences and values.  No two cities are the same.

 

Christopher Yuen is an associate at Jarrett Walker+Associates and will be regularly contributing to this blog.