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Here are the possible Silver Line extension routes the MBTA is considering

"We are still developing these ideas."

A Silver Line bus stopped at the SL3 terminus in Chelsea, to which service was expanded in 2018. Lane Turner / The Boston Globe

The MBTA’s potential extension of the Silver Line is beginning to take shape.

During a meeting Tuesday evening, officials presented the preliminary routes they’ve developed as part of the project to potentially expand Silver Line bus service into Everett, Medford, Malden, Somerville, and Cambridge, as well as Charlestown and downtown Boston.

Specifically, the proposed routes would extend from the SL3‘s current end in Chelsea to Everett Square, Malden Center, Wellington, Sullivan Square, Kendall Square, and Haymarket.

The proposed routes are far from being finalized, and “in some cases, there are multiple options” for getting to the various hubs, noted MassDOT planner Doug Johnson.

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“We are still developing these ideas, so they are subject to change,” Johnson said, encouraging local residents to provide feedback on the ideas.

A draft map presented during the meeting showed six potential overlapping routes circling through Everett and then looping back to either Kendall Square or downtown Boston through East Somerville or Charlestown.

The proposed routes generally follow the alignment of the long-proposed Urban Ring transit project, providing underserved communities in Chelsea and Everett faster and more direct transit options to the area’s major employment, medical, and educational centers, in addition to Logan Airport.

Johnson also noted that the Silver Line extension wouldn’t simply be a new bus route; rather, officials would invest in a number of bus infrastructure changes to deliver “bus rapid transit-level quality of service,” he said.

“Think of the SL3 busway in Chelsea, where the Silver Line has its own dedicated space,” Johnson said.

“We’re also talking about things like shelters at bus stops; signal priority at traffic lights so that buses can glide through intersections rather than waiting for a long time at red lights; level boarding at bus stops where, when you’re standing at the bus stop, you’re at the same level as the bus, you don’t have to step up or down to get in; and other features like that that really enhance bus service and make it more like rapid transit than like traditional bus service,” he said.

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Silver Line extension stops would also be spaced farther apart than traditional bus routes.

That doesn’t necessarily mean there’d be a dedicated busway running through the entire swath of Everett, Somerville, and Cambridge.

Johnson said they’ll need to consider “tradeoffs” with general traffic, street parking, and other transit, where “constraints” exist. But “where constraints do not exist, we will assume the highest level of transit priority possible,” he said.

There are many questions still remaining, such as whether the extension would simply be a continuation of the SL3 or a new “SL6” route — and where transfers would occur if the latter option is chosen. Additionally is the question of how the routes could be combined (hypothetically, the SL3 could be extended into Everett and Malden, while a different SL6 route branches back to Somerville and Cambridge).

The entire analysis won’t be completed until next spring.

“The next phase of this study is to evaluate those full routes and compare them against each other to see which provide the most benefit to riders, as well as the potential costs, and other factors,” Johnson said Tuesday.

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