On Tuesday, the MBTA said its “most recent data available” showed that travelers took 8,300 trips into Boston on Saturdays, and 4,500 on Sundays, but they couldn’t provide how many took trips out of Boston.

But since T officials floated the idea of temporarily eliminating the service, that number hasn’t been so clear-cut.

As the MBTA explores cutting weekend commuter rail service, there is one key fact that it would seem critical to nail down: just how many riders actually use the service on weekends.

Yet on Friday afternoon, after multiple inquiries from the Globe, the agency said it now estimates that riders take 18,700 trips total on Saturdays, or almost 15 percent of its weekday ridership.


At the same time, the MBTA’s acting general manager admitted the agency needs to do a better job counting commuter rail riders — so much so that it is investing more than $300,000 to do it.

The confusion over the ridership data has rankled transportation advocates, who say that accurate numbers are crucial to making cuts that could have devastating consequences for riders.

“This is an area where we need to make sure the data is right before we make a decision that impacts thousands of riders,” said Chris Dempsey, executive director of Transportation For Massachusetts, a coalition of organizations pushing for better public transit.

Massachusetts Bay Transportation Authority officials on Monday floated the idea of cutting weekend commuter rail service for a year to save approximately $10 million, as part of a series of cost-saving ideas that could balance its budget. They’ve repeatedly said that the subsidy for weekend service is high, with the MBTA paying more than $33 for each ride on weekends, compared to $5 on weekdays.

The proposal has drawn immediate pushback, including a letter from the state’s entire congressional delegation, asking the MBTA to rethink cuts to both commuter rail service and the agency’s door-to-door van service for disabled riders.


Amid the intense outcry, Joe Pesaturo, an MBTA spokesman, has said there isn’t a “formal proposal” on the table, and the MBTA’s fiscal and management control board will have extensive discussions over the decision. And Governor Charlie Baker, during a radio segment on WGBH-FM’s Boston Public Radio Thursday, said that service cuts should be the MBTA’s “last resort.”

But agency officials have insisted that they must take a hard look at lines with low ridership, particularly the weekend commuter rail service.

The estimates given by the MBTA on Monday may have helped fuel confusion on ridership numbers. After those numbers became public, Baker proclaimed in a radio interview Thursday that the volume on the weekends was about 6 percent of the volume during the week. An aide said Friday night that Baker misspoke, but his overall point was that weekend ridership is very low.

But with the new ridership estimates that the MBTA presented on Friday, the number of trips provided on Saturday alone would actually represent about 15 percent of the estimated 123,000 trips they provide on the weekdays. The 12,100 trips on an average Sunday would represent about 10 percent of weekday service.

Data from 2013 show those percentages were even higher, but ridership was also declining. During that time, the MBTA estimated that it provided about 20 percent of its weekday ridership on Saturdays, and about 16 percent on Sundays.


Most transit agencies that provide commuter rail service have lower ridership on weekends, although some do capture a higher percentage of their weekday ridership: On the Long Island Railroad, for example, riders take about 109,000 trips on Saturdays, compared to nearly 275,000 on weekdays. The numbers are lower on Sundays, when ridership averages around 87,000 trips.

But it’s also true that the MBTA and its commuter rail operators have long acknowledged that their counts could be more accurate. On the Red Line, for instance, subway riders have to tap their CharlieCards or tickets to get onto the platform, allowing the agency to count users.

For years, the MBTA has relied on conductor counts to help form the foundation of its ridership numbers on the commuter lines. That means the same people who are busy checking tickets and opening doors are also expected to eyeball the number of riders.

The MBTA and its commuter rail contractor have frequently tried to improve counting methods: In May 2015, Keolis Commuter Services — which took over the previous summer — tried out new motion sensor technology at South Station on Platform 5, as a way to better count passengers. New fare gates at South Station, proposed by the company to help curtail fare evasion and uncollected fares, could also give a much better ridership count.

In addition, the MBTA is spending about $300,000 to put technology on 11 passenger coaches that will automatically count commuters. Officials say it uses detection “eyes” that analyze how many passengers are passing through. Right now, the technology is on five coaches, and officials will place it on six more.


Meanwhile, advocates are urging the MBTA to be as clear with the data as possible before making any big decisions.

State Senator Jason Lewis, a Democrat who represents Melrose, Wakefield, and several other communities with commuter rail service, said he already believes the cuts are moving in the wrong direction. But the shaky ridership numbers give him even more pause.

“They should not make any decisions about changes to service, never mind cutting services, based on data that’s not 100 percent reliable,” he said.

Nicole Dungca can be reached at nicole.dungca@globe.com. Follow her on Twitter @ndungca.