The Federal Transit Administration (FTA) has a model for ridership estimation for public transit lines, called STOPS. It’s designed to be simplified enough that transit agencies can compute rough projections with it without having a large permanent in-house team dedicated to it (the MTA has a team of about 12). At the Transit Costs Project, we’ve taken to using it to do estimates for potential extensions under various assumptions on speed, frequency, and service pattern. For example, the Effective Transit Alliance’s statement in support of QueensLink for the budget vote later today quotes a figure of 105,000 expected daily riders, with 75,000 of them new and 30,000 existing at the Rockaway stations. I’d like to both go over this figure in this post and explain why at the same time, STOPS must be used with caution, especially in New York.

The QueensLink ridership estimate

At the program, Franklin Tang is responsible for the use of STOPS. Using the tools of the model, he computed that under our assumptions of QueensLink service, total northbound boardings at all stations south of Rego Park-63rd Avenue, the branch point from the Queens Boulevard Line, are 52,634 per weekday. Every trip must be paired between north- and southbound travel, so this means a total of 105,268 trips using QueensLink. These numbers include stations that already have service on the A train, including Howard Beach and the Rockaways; one of the points of QueensLink is to give these areas faster service to Midtown than they get on the A, which takes the long way around via Downtown Brooklyn and Lower Manhattan. In a No Build scenario, we expect these preexisting stations to have about 30,000 total trips, taking into account some expected redevelopment around the Aqueduct.

The business case released by QueensLink, released using the same analysis, gives a total of 75,000 riders/day. This is not the net figure – the similarity is coincidental. Rather, it includes things it shouldn’t (namely, boardings at Rego Park, nearly all preexisting) and excludes things it should (namely, the southbound alightings), as it imitates MTA methodology, which for reasons I don’t quite get counted the Rego Park boardings in its estimate for QueensLink ridership.

The figure people should use in subsequent analysis is the higher one, which is the most comparable to how transit ridership of new projects is usually computed. Riders diverted from other lines still benefit from the project, especially in a case like QueensLink, where the diverted riders would enjoy an improvement in trip time to Midtown of about 10-15 minutes each way. Second Avenue Subway’s ridership, which we compare QueensLink’s favorably with in the ETA analysis, is based on estimates for total ridership, not just new trips, and includes diversions from the 4/5/6 and from crosstown buses in addition to new trips.

The problem of STOPS

STOPS is designed for quick-and-dirty calculations and is known to choke on New York. FTA intends for it to be used elsewhere in the United States, where I am told it gives more accurate numbers; the MTA’s in-house team can do more precise calculations by itself, without STOPS.

Case in point: we tried estimating the ridership of a Utica Avenue subway extension with STOPS, and got bad numbers. “Bad” here does not mean the numbers were low and I’d like them to be higher, but that the model gave nonsensical results. Total northbound boardings on the new stations amounted to 58,000; total southbound alightings only amounted to 25,000. In effect, the model thinks that if a Utica Avenue line opens, then 33,000 people will permanently emigrate from Southeast Brooklyn every day. We’ve rerun the numbers and at this point I don’t believe we made an error; rather, STOPS has some errors, perhaps with stations close to one another, that lead to random results that don’t quite average out correctly. Thus, I recommend caution when using it as it is still only good enough for a first-order estimate.