Behind the scenes with MBTA data.

How the net cost of a bus route is calculated.

As part of the service planning process the MBTA analyzes bus routes for cost-efficiency. Historically this was done by calculating the net cost to operate the route. For the revised Service Delivery Policy (SDP) (adopted in January 2017), the MBTA developed a benefit-cost tool that has a more holistic definition of the benefits of a bus route. This post explains how we developed the tool and provides a graphical illustration of how each bus route scores.  

The previous version of the Service Delivery Policy (2010) included a cost-efficiency measure that compared the ridership on a bus route to the net cost to operate that route. The net cost is calculated taking into account the average fare on different types of bus services (Local, Inner Express, or Outer Express). But the benefit of the route only accounted for ridership. 

For the 2017 revision of the SDP, the MBTA developed a benefit-cost tool with a more holistic definition of the benefit a bus route. In this tool, the benefit of a bus route is comprised of three components: total ridership, transit dependent ridership, and the value of the route to the network. 

  • Total ridership measures the demand for the route using average weekday ridership.
  • Transit dependent ridership is a way to value social equity. A route provides greater benefit if it provides access to people with limited other transportation options.  Given the limited data we have available, this component is measured as the proportion of total fare payments that are done using MBTA reduced fare categories (Student, Youth, Senior, Blind or Visually Impaired, and People with Disabilities). 
  • The value of the route to the network acknowledges that each bus route doesn’t stand alone; bus services comprise a critical element of our overall transit network. This component includes three subcomponents: transfers, unique access for people, and access to destinations.
    • Transfers: The number of transfers from that route to rest of the network gives the route credit for its role as a feeder into the system.
    • Unique Access for People: The population for which that route specifically provides access to the network. People living in areas with access to multiple bus routes in a ½ mile buffer were divided so each route got a proportion of those people as its share of this measure. 
    • Access to Destinations: The number of jobs and other destinations the route serves, estimated from the Longitudinal Employer-Household Dynamics (LEHD) data.

OPMI worked with CTPS and the MassDOT GIS team to compile all of the data and conduct the analysis to build the index for each route. Because each type of data had different scales (for example, Transfers are in percentages and Access for People is in population), we scaled each dataset based on the largest value and the smallest possible value. The benefits for a single route are relative to how well the other routes perform in a given metric. The benefit of a route is the combination of the three normalized components (ridership, transit dependent riders, and value to the network).

For illustrative purposes the three components of the index were drawn as a triangle for each bus route. The triangles show how the overall value of a bus route can come from different combinations of the three components. In order to see which component contributes the most value to the total benefit, we have color-coded the components. 

 

For example, these routes have roughly the same total benefit, but the value to the network contributes the most for the 110, ridership contributes the most for the 31, transit dependent passengers contributes the most for the 42, and the components are about the same for the 120.

In order to see all of the bus routes at the same time, we created a poster using a small multiples design. 

See the poster at this link

This tool also allows us to identify different types of interventions for  low-performing routes. A route that has high transit dependent ridership but low value to the network might need to be redesigned to better serve more destinations. A route with high transit dependent ridership and good value to the network, but still low overall ridership might be a good candidate for service with smaller vehicles.

The MBTA Fiscal and Management Control Board set the weights for the importance of each of the three components in Service Delivery Policy. The weights were set at ridership 70%, transit dependent 15%, and value to the network 15%. 

Using these weights, this index calculates the benefit of each bus route. The final step is to compare the benefit to the cost. The weekday net cost for each bus route is calculated based on the number of peak and off-peak hours of service operated, the miles of service operated, and the revenue generated on that route.

Dividing the benefits by the cost provides a benefit-cost ratio for each route. In the service planning process we will examine both the bottom 10% for possible changes, but also the top 10% to identify characteristics of high performing routes.

Since this is a new tool, we will be evaluating how it works over the next round of service planning. In addition, we will update the underlying data as we get more recent data or new datasets that better represent the benefits.