The historic 70-year-old trolleys used on the high-speed line that runs through Dorchester, Milton, and Mattapan will ride the tracks until at least the early 2020s, after the Massachusetts Bay Transportation Authority pledged $7.9 million to give the aging streetcars an overhaul.
On Monday, MBTA officials announced plans to equip the trolleys with new propulsion, brakes, and power supply systems, and spend $1.1 million to study the future of the Mattapan line.
Supporters have feared that the MBTA will phase out the beloved trolleys, which have become more costly to maintain with each passing year, and welcomed the upgrade.
“They’re essential to the character of our communities,’’ state Representative Dan Cullinane, a Democrat who represents several neighborhoods served by the line, said at the MBTA’s fiscal and management control board’s weekly meeting. “This is a big win for all those who rely on and support the Mattapan high-speed line.’’
The high-speed line — so named because its route is intersected only twice by city streets — opened in 1929. Its 10 trolleys, which rolled out of the factory in 1945 and 1946, are the last of their kind, and MBTA machinists must often make replacement parts, or contact museums for spares.
“With this investment, we feel relatively confident that this will get us out to the early 2020s, and give us enough time to do the due diligence study to make the right decision on the future of the line,’’ said Jeffrey Gonneville, the MBTA’s chief operating officer.
The line runs 2.6 miles through eight stations in Dorchester, Milton, and Mattapan, providing more than 4,600 rides on weekdays and running about every five minutes during rush hour.
In December, the MBTA awarded a $1.1 million contract to CH2M Hill to study the line’s future. The engineering consulting firm is expected to lay out options for future vehicles and infrastructure on the line within the year.
Also on Monday, the Massachusetts Department of Transportation provided a cost estimate for daily commuter rail service from South Station to Foxborough. The yearlong pilot program would include at least three trips during both the morning and evening rush hours, as well as midday service.
The program would cost about $950,000, officials said, while raising about $411,000 in revenue based on roughly 190 passengers a day. The tracks would require about $10 million in upgrades before service could begin next year.
The service could be a boon to Robert Kraft, the owner of the New England Patriots. Trains would drop off passengers near Gillette Stadium, the team’s home, and could spur more development near Patriot Place, an entertainment complex near the stadium.
Kraft Group, the business founded by Kraft, has pledged to subsidize the trial program by up to $200,000 and provide 500 parking spaces for use near Foxboro station.
Currently, trains run only on game days.
The pilot program has generated a good deal of disagreement. While Foxborough’s selectmen have endorsed the plan, Walpole’s board has withheld its support.
State Senator James Timilty, a Walpole Democrat, testified against the program Monday, calling it “ill-conceived.’’
“When I see an expansion project in areas where there is already service, I have great, grave concerns,’’ he said.
But the plan picked up an important endorsement: Governor Charlie Baker’s economic development and housing chief, Jay Ash.
Ash called it an opportunity to unlock economic development along Route 1 and said the investment wouldn’t affect current service.
“I don’t believe it takes away from the investment in the core system,’’ he said.
This is a relatively modest number. We’re talking about millions of dollars, not hundreds of millions of dollars.’’
Nicole Dungca can be reached at nicole.dungca@globe.com. Follow her on Twitter @ndungca.
