Almost five years ago, Michelle Wu, then a city councilor, proposed in the pages of The Boston Globe a far-fetched idea: eliminate fares on the MBTA. Dozens of cities around the world had abandoned user fees, and — she argued — it was time for Boston to try it.

After she became mayor, Wu used federal COVID money in 2022 to fund a pilot program making the 23, 28, and 29 MBTA buses through Mattapan, Dorchester, and Roxbury free to ride for two years. It was meant to prove that without fares, more people would ride the bus, save money, travel faster, and reduce greenhouse gas emissions. And a city study said it mostly did that.

The mayor hoped the results would spur the MBTA to fund and expand fare-free service. But that’s not happening. On March 1, the city funds that cover the cost of the three lines run out and the T is scheduled to start charging riders again.

On paper, the mayor, some transit advocates, and Governor Maura Healey appear aligned: Buses should be fare-free. And the MBTA’s reduced-fare subway, commuter rail, ferry, paratransit, and bus program for many students, poor young adults, people with disabilities, and all elderly people should be expanded to low-income adults aged 26-64.

But as the end of the existing fare-free bus program in Boston approaches, the T is moving forward with only the low-income fare for its entire system, something advocates and the mayor have been pushing for for years.

The mayor, however, has pledged to come up with the funding to keep the fare-free bus program on the three MBTA lines going for another two years past the March 1 expiration date, effectively setting T policy on her own.

At its core is a debate about whether to fund the cash-strapped MBTA by charging poor people for bus service, and whether fare-free buses can deliver the sweeping benefits advocates promise.

“We are not about to pull out the rug from under our residents and commuters and we’ll continue advocating and fighting for the MBTA and the state to recognize the benefits that [fare-free service] would be able to have across an even broader part of our system,” Wu said.

MBTA general manager Phillip Eng said fare-free bus service would be discussed by a new task force Healey has put together to look at the “total revenue streams that are needed.”

“Free bus service, or any of those — somehow that revenue needs to be accommodated for and not only for a one-year period, but it needs to be accommodated for going forward,” he said Thursday. “The low-income fare is a key piece right now.”

In a statement, state Transportation Secretary Monica Tibbits-Nutt said the low-income fare program “will increase access for tens of thousands of riders.”

Fares from subway, ferry, commuter rail, paratransit, and bus customers are expected to total $418 million this fiscal year, covering less than 20 percent of the T’s operating budget, according to the agency.

Last fiscal year, fares from bus riders totaled about $79 million, according to T spokesperson Joe Pesaturo.

MBTA expenses are expected to exceed revenue by around $182 million come this summer and at least $620 million the following year, a funding gap the T’s chief financial officer called a “fiscal cliff.”

If there is conflict between the Boston-area transit agency and its biggest municipality, there seems to be none among riders of the fare-free buses.

They say they’ve been able to take transit more often without the burden of re-loading their Charlie Cards.

For Northeastern University junior Claire Danyluk, the free service has become an indispensable part of her morning routine. A member of the track team, Danyluk takes the 23 or 28 between Ruggles and the Reggie Lewis Track & Athletic Center for her daily practice.

”It’s super beneficial for me, especially as a student,” she said, sitting on the bench at Ruggles around 8:25 a.m. “It’s nice that I don’t have to pay. You can just hop on and hop off.”

Terminating the service, Danyluk said, “would be such a huge access issue for people that maybe don’t have the fare money.” She said she never realized the free service was a temporary program at all.

Jacori Jones, 25, stood on the curb at Ruggles Station with her son, 6-year-old Jai, around 8:15 a.m. Tuesday, waiting for the Route 28 bus.

The West Roxbury resident said she usually buys a weekly pass so she has more flexibility with her route, but she often ends up on the fare-free 23 or 28 anyway. Though she does not benefit from the free service, Jones said the free buses tend to feel quicker and more reliable than other routes, since riders can board any door and don’t have to line up to pay.

”You can hop right back on it, no problem,” she said.

Boston provided the MBTA with $8 million of its federal pandemic relief money to fund the two-year pilot program, which also includes fare-free paratransit service on the MBTA’s The Ride for trips that start and stop within three-fourths of a mile from the free routes.

A city analysis released last March after the first year of fare-free service showed ridership on the 23, 28, and 29 bus routes had inched closer to prepandemic levels faster than the T bus system as a whole. It also showed 42 percent of riders were saving money because of the program, but many still had to purchase monthly passes or transfer to other MBTA bus lines or trains that were not free. About 4 percent of riders interviewed would have taken a car instead, the study showed, and about 13 percent would have walked or biked.

The city’s study found that boarding time per passenger decreased, and travel times remained about the same even with more people riding. Riders said they were frustrated with the T’s reduced service schedules, the report said. This winter, the MBTA scheduled 14 percent fewer trips across its bus system than in the winter of 2020, before the pandemic, according to data provided by Pesaturo. An MBTA project to increase bus service by 25 percent is years behind schedule.

Given the results of the fare-free bus program, transit advocates hoped by now the T would be funding fare-free routes and planning to make all bus service free.

During her campaign for governor, Healey vowed to create a reduced T fare for adults with low incomes across all modes of travel, something the MBTA’s previous oversight board approved in 2019, and create a “pathway” for fare-free bus service statewide.

“Based on the governor’s public commitments, I thought that after municipalities used their own funds to prove this was viable, we would see this kind of leadership from the governor,” said Stacy Thompson, executive director of LivableStreets Alliance, a transportation advocacy organization.

Critics of fare-free transit say improved service, not eliminating fares, is what will get more people to take transit, especially those who have access to a car.

“My question with fare-free transit is what problem is it attempting to solve?” said David Zipper, a senior fellow at the MIT Mobility Initiative and transportation writer. “If the goal is to reduce emissions from cars and leverage transit as a tool to do so, that’s a worthy goal. But the way to attract people who could otherwise drive to ride transit more often is to provide service that is fast, frequent, and reliable.”

Wu has defended the city’s choice to invest in fare-free service, calling the criticism “cynical” and “shortsighted.” If it were up to her, buses would be reliable and free to ride citywide.

At least one other transit agency in Massachusetts has proved it can do both.

The Merrimack Valley Regional Transit Authority, recently rebranded as MeVa Transit, first made three bus lines free to ride in 2019 with funding from the city of Lawrence.

Then, in 2021, the agency faced a choice: spend to upgrade its fare collection system, or scrap fares all together. Transit leaders did the math and found the agency was only going to get back 8 cents for each dollar it collected, MeVa Transit administrator Noah Berger said at the time.

The agency eliminated fares for all of its bus lines and paratransit service across 16 municipalities in northeastern Massachusetts in March 2022 and hasn’t looked back.

Since then, MeVa has doubled bus service on Lawrence-based routes, added later evening service, and started operating service on Sundays using new state funding for regional transit authorities from the tax on incomes over $1 million a year. Bus ridership through November 2023 more than tripled, the agency said, and now exceeds prepandemic levels by more than 50 percent. Seven of the 15 regional transit authorities in Massachusetts are currently offering some kind of fare-free service, according to their websites, made possible with the tax on high incomes funds Healey and the Legislature designated.

Berger said the results at MeVa were achieved because the agency made all bus lines fare-free, not just the original three lines.

“I think that free lousy service doesn’t do anyone any good,” said Berger. “Fare-free service was part of the whole family of improvements to make our service more responsive to the needs of our community and more welcoming and useful.”

The MBTA is in charge of a much larger transit system.

A T analysis in 2022 weighing whether to make buses fare-free or implement a low-income fare found that eliminating fares on T bus and paratransit service could cost as much as about $150 million, including lost fare revenue, increased service to meet demand, and fleet expansion.

The MBTA has not analyzed how much it would cost to eliminate fares on all of its buses and paratransit service and provide a low-income fare for the other modes, Pesaturo said.

Pesaturo said the T spends about $37.9 million each year on its current fare collection system across the subway, bus, and the rest of its system. So far, he said the T has spent about $21 million on its nearly $1 billion new fare collection system, which is over budget and years behind schedule.

Thompson, the transit advocate, said she hoped the fare-free bus pilot would push the T to reexamine its planned investment in the new fare collection system.

“The T is moving forward with hiring dozens of people to do fare validation on buses instead of stepping back to say, ‘What makes sense?’” she said. “We haven’t actually answered the question of: ‘If we stop fare collection, how much money do we save?’”

The T is moving toward half-priced fare for people ages 26 to 64 with low incomes this spring, which it already provides to students, young adults, people with disabilities, and elderly people. Most large transit agencies in the United States already offer a low-income fare. The governor is proposing $45 million of new high earner tax funds for the program. If approved at a March 28 board meeting, the program would cost about $25 million in the fiscal year that begins July 1 and up to about $58 million annually by 2028, the T said.

Boston’s representative on the board, Mary Skelton Roberts, has expressed skepticism about creating a low-income fare instead of just eliminating fares. Requiring people with low incomes to prove they are poor to access the reduced fare “feels very undignified,” she said at a board meeting Thursday.

“I don’t understand how we could subsidize people that don’t need money to get Teslas and electric vehicles and we’re nickel and diming the low-income residents,” she said at a board meeting in December, referring to the state’s electric vehicle rebate program that offers drivers up to $6,000. “I want to push us to come up with a really different funding mechanism that enables us to fund our transit and not on the back of low-income people, or students, or disabled people, or elderly.”

Daniel Kool of the Boston Globe staff contributed to this report.