The MBTA will begin construction on the Mattapan station of the Fairmount Line in early spring of next year, working weekends and evenings to avoid disruptions in service on the commuter rail line, which runs through Hyde Park, Mattapan, Dorchester and Roxbury.

At the end of the two-year construction project, riders from Mattapan Square will be able cut their travel time to downtown Boston in half, according to Desiree Patrice, a project manager with the MBTA.

“When you get on at Blue Hill Ave., your travel time will be 20 minutes to South Station,” she told the gathering of about 50 people at the Mattapan branch of the Boston Public Library last week. “This will open up a lot more access to the jobs we need.”

A long time coming

For decades, the Fairmount Line ran through Dorchester and Mattapan with stops only at Morton Street and Dudley Street. The new stations along the route, including those at Geneva Avenue and the South Bay Mall, were built as the result of a 2003 Conservation Law Foundation lawsuit targeting the MBTA for its failure to fund transit projects in Roxbury, Dorchester and Mattapan as part of its Big Dig mitigation — projects undertaken to lessen the environmental impact of the increased traffic brought about by the $24 billion road project.

The MBTA agreed to convert the Fairmount commuter rail line into a rapid transit line, with free transfers to the Red Line at South Station and service that closely matches the six-minute intervals subway trains maintain.

While former Gov. Deval Patrick ordered the MBTA to purchase smaller, self-powered diesel train cars that could run faster than the five-car trains currently running on the route — a move that would allow greater frequency on the line — the Baker administration has pulled away from that commitment, citing a $200 million cost to purchase the cars.

Currently, the line runs trains every 45 minutes during morning and afternoon commute times and at one-hour intervals at other times. Weekend service was added in 2014. Riders cannot pay with Charlie Cards and, therefore, are not given free transfers to the Red Line or buses at South Station, but riders with weekly or monthly passes can use them on the line.

The Mattapan station, which will run more than a quarter mile between Blue Hill Avenue and Cummings Highway, encountered stiff resistance from abutters, some of whom complained that the foundations of their homes were damaged when the MBTA drilled exploratory holes in the rock ledge along the train tracks. Those concerns and others, including potential traffic and parking problems, derailed the construction of the station, which the MBTA has been planning since 2009.

MBTA officials have settled on a plan to construct the passenger platform between the inbound and outbound tracks, with access from the bridges over the right of way on Cummings Highway and Blue Hill Avenue.

A faster commute?

Dorchester activist Mela Miles said that even without special self-powered diesel trains the MBTA could run shorter trains on the tracks, dropping the length from five cars to two. The reduced weight would allow the trains to accelerate and brake more quickly, shortening the times between stations. While ridership is often low on the line, the need for reliable, affordable transit is acute in the neighborhoods the rail line bisects.

“This goes through communities of color with the least cars per-capita anywhere in the city,” she said. “People here are more transit dependent.”

Patrice, who uses the Fairmount Line to get to South Station on weekdays, said the agency is seeing some growth in ridership.

“Hopefully, with the improvement in ridership, frequency of service will increase too,” she said.

Miles said the MBTA hasn’t done enough work to market the line.

“The way to get ridership up is to have a plan to market it to the entire community,” she said.