Discrepancies in 2023 MBTA Ridership Data - Seeking Clarifications

I wanted to bring up some discrepancies we've noticed in MBTA's open data portal regarding ridership numbers across different datasets. Specifically, the Fall 2023 MBTA Rail Ridership Data by Route and Stop  and the MBTA Monthly Ridership By Mode and Line  show significant differences for the Blue Line (and to a lesser extent Green Line), while the Red and Orange Lines are more consistent.

Here are the numbers we found, along with their percentage differences:

    Red Line:
        Fall Season Stop Ridership Average: 129,171
        Monthly Route Ridership Average: 119,664
        Difference: -7.4%

    Orange Line:
        Fall Season Stop Ridership Average: 102,362
        Monthly Route Ridership Average: 107,639
        Difference: +5.2%

    Blue Line:
        Fall Season Stop Ridership Average: 63,193
        Monthly Route Ridership Average: 48,385
        Difference: -23.4%

    Green Line:
        Fall Season Stop Ridership Average: 102,947
        Monthly Route Ridership Average: 86,332
        Difference: -16.1%

The two data sources can be found on the open data portal as follows:

Fall Season Stop Ridership: https://mbta-massdot.opendata.arcgis.com/datasets/80a379ebaa374cfd836ca4d3880ceda4_0/explore

Monthly Route Ridership Average: https://mbta-massdot.opendata.arcgis.com/datasets/2048258a18354256a650d41f8fe4532c_0/explore

One possible explanation we’ve considered is that the Blue Line discrepancy (-23.4%) could stem from differences in data collection methods - perhaps related to AFC (Automated Fare Collection) tap counts versus ODX generated boarding counts, which may include both station-level entries and transfers. Given that the Blue Line operates on a regular schedule with minimal external disruptions, we wouldn't expect major ridership fluctuations beyond normal variance.

Chandler Jong

Thanks for reaching out. I'm with the Office of Performance Management & Innovation (OPMI) at the T, and our team manages these datasets. The discrepancies can be attributed, as you hypothesized, to the different underlying data sources. Namely, the factors used for scaling. The ODX algorithm gets very specific, with each passenger trip being modeled where available, so things like which route gets boarded at a transfer station and how many passengers transfer behind-the-gate (i.e., without tapping again) are specific to the time of day and service date. The ODX dataset also uses entries recorded by the faregate laser passenger counters to account for non-interaction (passengers who board without validating a fare).

Conversely, the Monthly dataset is based on validations scaled up using single factors for non-interaction, station split, and behind-the-gate transfers to estimate ridership. In particular I think that the station split for Blue Line transfer stations has changed in recent years with all the development that has happened in East Boston, which the ODX model will have captured but not the Monthly factor. We are doing work over here to shore up the two datasets so as to not have conflicting data out there, but that's a work in progress.

Please feel free to reach out (either here or to my email mwillis...@mbta.com ) with any additional questions/follow-up, we're happy to chat!

Thanks,