An SL3 bus waits for passengers at the MBTA's Box District station in Chelsea in this undated photo. Photo courtesy of the MBTA

The MBTA wants to extend the SL3 service on its Silver Line bus rapid transit network from Chelsea to Everett and Boston’s Sullivan Square. But a timeline for doing so is still unclear.

The line currently connects Boston’s South Station and Seaport District with Chelsea via East Boston and Logan Airport.

In a report released Friday morning, the agency said a public process that took place between 2021 and 2022 settled on a conceptual route that connects the current SL3 terminus by Chelsea’s Mystic Mall with Everett’s Commercial Triangle development hot-spot, Everett Square, the Encore Boston Harbor Casino and a planned entertainment and industrial district centered on a proposed New England Revolution soccer stadium across the street and the Sullivan Square MBTA bus and Orange Line subway station.

The Boston Globe reports a key piece of enabling legislation for the soccer stadium is likely to get a hearing on Beacon Hill this month.

“The importance of the Silver Line’s ability to increase access to jobs and educational opportunities for all Everett residents cannot be understated and I am proud to endorse this commitment from the MBTA,” Everett Mayor Carlo DeMaria said in a statement released by the T. “The Silver Line will also provide critical transit access that will support Everett’s growth while reducing reliance on private vehicles.”

Other routes evaluated included connecting Everett Square and Chelsea to the MBTA’s Wellington and Malden Center stations in Medford and Malden, respectively.

“We are beyond excited to be advancing plans to extend Silver Line service between Chelsea, Everett and Sullivan Square in Boston’s Charlestown neighborhood,” Transportation Secretary Monica Tibbits-Nutt said in a statement released by the T. “This extension of service is exactly what we are talking about when we say the administration is prioritizing public transportation investments which fill gaps in our system, increase access for residents in underserved communities and make our transportation network more equitable.”

The Silver Line serves neighborhoods that are seeing significant new or planned development, as in Everett’s Commercial Triangle and casino areas, and which have largely been ignored by subway networks built by the MBTA and its predecessors over the last 120 years.

The proposed conceptual route for an SL3 Silver Line extension. Image courtesy of the MBTA

“Public transportation provides enormous economic opportunity for residents of all income backgrounds and our economy, but still so many of my community’s residents lack access to any convenient public transit options,” state Sen. Sal DiDomenico, assistant Senate majority leader and the state senator for Chelsea and Everett, said in a statement provided by the T. “These proposed investments in Silver Line expansions will reduce traffic, cut greenhouse gas emissions, and drastically improve lives and livelihoods for countless people throughout Chelsea, Everett and beyond. I have advocated for these changes for years alongside municipal leaders and community members and am thrilled to see these proposed developments. I want to thank Governor Healey, MassDOT and the MBTA for their leadership on expanding public transportation for people who have lived without it for far too long.”

The report says that this lack of subway service means the areas buses are “not competitive with driving for many types of trips being made to and from Chelsea and Everett” despite the bus lanes both cities have added to speed trips on their most heavily trafficked bus routes. In addition, both cities’ transit ridership has remained high despite a work-from-home-driven fall-off seen in other, richer communities. And the study predicts that, by 2040, the area served by the extended Silver Line would house 321,510 people, an 11 percent increase from today, and 320,700 jobs, a nearly 7 percent jump over today.

The extension would put 345,000 jobs in reach of Chelsea, East Boston and and Everett residents assuming a 45-minute commute, the T said, and add around 15,000 daily riders to the SL3. The report also explored an additional Silver Line service, temporarily dubbed the “SL6,” that would connect northern Everett and Kendall Square via Sullivan Square, but shelved that idea pending the purchase of more Silver Line buses.

“Extending the SL3 to Sullivan Square will have a profound impact on thousands of riders, expanding access to our rapid transit system and a dozen more bus routes, amplifying more opportunities for jobs, education and recreational activities,” MBTA General Manager and CEO Phillip Eng said in a statement. “We appreciate the efforts of the MBTA team and our partners at MassDOT for their work on the Silver Line Extension Alternatives Analysis and look forward to reviewing the upcoming design.”

With congestion in Everett and Chelsea already bad, the T’s ability to keep SL3 buses separate from car traffic will bey key. The report says around 80 percent of the proposed route would be run in a dedicated busway on Lower Broadway in Everett alongside other bus lines that currently serve Everett, an extended Silver Line busway in Chelsea, curbside bus lanes on Second Street in Everett to be added as new housing development proposals make it possible to widen the road to accommodate them, and existing bus lanes in Everett Square and the Sweetster Circle rotary.

The extension will cost around $95 million, the T said. MBTA spokesperson Lisa Battiston said in an email that the the agency has already filed a $22.4 million grant application with the federal Department of Transit’s RAISE program to pay for building the Lower Broadway busway, and that an announcement about whether it lands the grant is expected this summer. Battiston said the T is also on the hunt for other dollars that could pay for preliminary design work on other parts of the route, but that more money is needed to pay for the full engineering work for the project. Other pieces of bus priority infrastructure along the route are also being worked on as part of the T’s sweeping Bus Network Redesign project.

“While the critical segment to enable SL3 is the busway extension along Commuter Rail right-of-way, the MBTA is simultaneously considering roadway improvements – some which may be done prior to SL3 implementation,” Battiston said.

Editor’s Note: 4:10 p.m. March 8, 2024: This story has been updated with additional comments from an MBTA spokesperson.