At the heart of the service cut debate is a murky outlook on transit ridership in a post-pandemic world

The MBTA’s oversight board will consider a package of service cuts at its final meeting of the year Monday, though the scale of the reductions was unclear as officials scrambled to finalize the proposal into the weekend.

After months of reduced ridership and fare revenue due to the coronavirus pandemic, the Massachusetts Bay Transportation Authority plans to reduce transit service in the first half of 2021.

But the process has been complicated by a challenge not unique to public transportation: Nobody knows what to expect next year.Among the many questions: How optimistic should the MBTA be about ridership, especially if a vaccine is widely available in the coming months? Will work habits that dramatically changed during the pandemic have long-lasting impacts on commuting? Will Congress approve aid to fill transit agencies’ budget gaps? And would the very act of reducing service ultimately stunt ridership long-term?

“Trying to predict human behavior is very difficult, particularly when it involves a very high degree of uncertainty,” said Kurt Forsgren, a managing director at S&P Global who focuses on transportation. “I think it’s been compounded by uncertainties about safety.”

In November, the MBTA proposed a package that would reduce frequency on trains and most bus routes; eliminate weekend commuter rail, ferry service, and a handful of bus lines; shorten part of the Green Line; and close the system earlier at night.

After weeks of pushback, the MBTA last week said it would likely scale back its plan, acknowledging it has enough room in its budget to stave off some of the proposed changes. Frequencies may still be reduced, but the T indicated it would try to avoid closing services altogether. The details of the new proposal have still not been made public, and were not finalized until the weekend. Further service decisions may also come next year.

As Congress continues to debate a stimulus package that could include more money for transit agencies, US Senator Edward Markey and Representatives Ayanna Pressley and Stephen Lynch are scheduled to hold a press conference opposing the cuts on Monday.But state officials have said that even with federal help, they may still cut some service to better match frequencies to ridership. That seems to be a priority of Governor Charlie Baker, who has lamented “running empty buses and trains” as poor public policy. System wide ridership is currently about 25 percent of its pre-pandemic rate, though with significant differences among routes.

Baker’s comments perturbed transit advocates, who say riders on little-used routes still rely on them. They’ve also argued the cuts are poorly timed, set to mostlytake effect next spring and summer —which may closely align with vaccine distribution.

Stacy Thompson, director of the Livable Streets Alliance, warned thatt he T should not cut buses and trains now, because it may need them as more riders return.

“It’s about having a boatload of flexibility for the next six months. And yes, that may cost some more money,“ she said. “If for some reason there is a mythical bus the governor has found that is empty, you can move it somewhere else in the system.

”Future ridership will not just depend solely on the end of the coronavirus crisis. Some passengers may remain fearful of crowds. Others may take to driving or biking.