Riders of the 23, 28, and 29 buses, which run through Mattapan, Dorchester, and Roxbury, will not be charged any fares starting in March, a first step, Mayor Michelle Wu hopes, toward making the T free.

After a two-month delay to work out the details, Boston and the Massachusetts Bay Transportation Authority have reached an agreement to make the three bus routes free for riders for two years, Wu and MBTA general manager Steve Poftak said Wednesday.

Wu indicated that the fare-free service is just the first step toward a larger goal of making all buses — and eventually all public transit — in Boston free, something she campaigned on and hopes to achieve through partnerships with other municipalities, the Legislature, and the federal government.

“Transportation is about connectedness at the end of the day,” Wu said. “It is the single fastest way that we can achieve our goals . . . from equity and economic mobility, to our climate justice goals, to our public health goals of reducing asthma and reducing exposure to pollution in our neighborhoods, to traffic and congestion.”

And, she added, “bus service is the best place to start.”

As Wu handed out fliers about the free service in three languages at businesses in Grove Hall on Wednesday, other cities and towns surrounding Boston were moving forward with plans to make MBTA bus lines in their areas free, too.

Brian Kane, executive director of the MBTA advisory board who also serves as chair of the Brookline transportation board, said he met with staff from Boston and Cambridge to discuss the possibility of eliminating fares on the Route 66 bus, which runs from Nubian Square to Harvard Square through Brookline. He credits Wu with pushing other municipalities toward fare-free buses.

“Nobody was taking this seriously before she put it on the agenda,” he said. “She has made this a legitimate piece of policy discussion in Massachusetts.”

In Boston, the city will reimburse the MBTA for the lost fare revenue on the 23, 28, and 29 buses for the pilot program using $8 million for COVID-19 relief the city received from the federal government. Wu said the areas served by the bus routes have been disproportionately impacted by the pandemic.

The process of determining how much to pay the T for lost fares on the 66 bus is more complicated, Kane said, because it runs through three municipalities. Kane hopes to have a methodology sorted out soon enough for fare-free service to start this summer.

“There is no road map, so we are working to put together a unified approach that we can take to the T and negotiate,” he said. “It’s not easy, but it’s not impossible.”

Cambridge Mayor Sumbul Siddiqui has formed a working group that will determine which bus lines the city plans to make free and for how long. She said they should have details sorted out in the next two to three months.

“It sets the bar for others to hopefully follow,” she said of Boston’s pilot program. “The more examples we have the better.”

Riders of the 23, 28, and 29 buses are primarily people of color who have low incomes, according to a 2019 report from LivableStreets, a public transportation advocacy group. The routes travel along or intersect with Blue Hill Avenue, where the city plans to install center-running bus lanes.

The 28 bus has been free for riders since late August, when Boston began reimbursing the T for fare revenue under former acting mayor Kim Janey, and has seen ridership skyrocket. The 28 has recovered 91 percent of its pre-COVID weekday ridership, according to the most recent data available from the state’s Department of Transportation, while the entire MBTA bus system has recovered just 60 percent.

Eliminating fares can boost ridership and also make bus service more reliable by allowing people to board through all doors and cutting down on the time buses spend at stops, transit experts say.

Peggy James, a 28 bus rider, said she has been able to move around the city more easily since it became free.

“This is one of the best things that has happened in this city,” she said at Wednesday’s news conference.

Poftak, the T’s general manager, said he is ready to work with other municipalities that want to eliminate fares and reimburse the T for lost revenue.

“We stand willing to cooperate with these partners who want to do this type of work,” he said.

Jascha Franklin-Hodge, Boston’s chief of streets, said boarding times for the 28 bus have decreased by around 20 percent since the bus became free, and the city and MBTA will be publishing a report about the findings from the pilot in the coming weeks.

Wu requested the funds for the three bus lines from the City Council on her first full day in office and intended to start free service on the routes in January. But concerns about whether the MBTA and the city needed to conduct a formal equity analysis to comply with a Federal Transit Administration rule pushed the start date to March.

Representatives from the city and the MBTA met with the FTA last month to sort out the details and got the green light, potentially paving the way for more fare-free routes in Boston and beyond.

On Wednesday, Wu indicated that replacing fares on buses in the MBTA system could cost around $30 million each year.

“It is a relatively small cost,” she said. “This [pilot] will help us understand that a bit more and think about what the most effective next steps will be.”

Some other cities and towns are waiting to see how the pilot goes in Boston before getting in on the fare-free bus trend.

Quincy Mayor Tom Koch said he’s concerned about the long term viability of fare-free buses given that the MBTA is facing a fiscal cliff in the next few years when federal COVID-19 relief funds dry up. Koch also serves on the MBTA Advisory Board, the MBTA board of directors, and the MassDOT board of directors.

“At the end of the day we do have to figure out the revenue side of things,” he said. “I’m not making any judgment on the program. We’re going to be monitoring it closely from my position as mayor to see if it’s worth looking at for any of the routes in Quincy.”

Representative Ayanna Pressley said she is working to pass a bill she introduced with Senator Edward J. Markey that would create a $5 billion competitive grant program to offset fare revenues for transit agencies.

“Public transit is a public good and it’s time we invest in it as such,” she said in a statement.

The Boston area isn’t the only place where people are already riding the bus for free. The Worcester Regional Transit Authority first eliminated fares on its bus routes in March 2020. Last year, the agency’s board voted to extend fare-free service through the end of 2022. Also last year, Merrimack Valley Regional Transit Authority’s advisory board unanimously approved eliminating fares across its fixed-route bus system for two years starting March 1 using federal COVID-19 relief funds.