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SL3 (MBTA bus)

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Silver Line
Company typePublic transit service
IndustryPublic transportation
Founded2001
FounderMassachusetts Bay Transportation Authority (MBTA)
Headquarters
Boston, Massachusetts
,
United States
Area served
Boston and Chelsea, Massachusetts
Key people
Massachusetts Bay Transportation Authority (MBTA)
ProductsBus rapid transit services (routes SL1, SL2, SL3, SL4, SL5, SLW)
OwnerMassachusetts Bay Transportation Authority (MBTA)
Websitewww.mbta.com/schedules/silver-line

The Silver Line comprises a collection of bus routes serving Boston and Chelsea, Massachusetts, managed by the Massachusetts Bay Transportation Authority (MBTA). Although it operates within the broader MBTA bus network, it is marketed as a bus rapid transit (BRT) system under the umbrella of the MBTA subway. The system includes six routes distributed between two distinct corridors. As of , weekday ridership reached approximately 27,000 passengers.

Four routes, collectively known as the Waterfront lines, depart from an underground terminal at , utilizing the South Boston Piers Transitway—a dedicated bus tunnel traversing the Seaport District, with stops at and . Beyond , the routes branch out: SL1 heads to Logan International Airport, SL2 serves Dry Dock Avenue, and SL3 travels to via East Boston. During peak periods, the SLW short-turn service operates between South Station and Silver Line Way. These Waterfront routes mainly employ articulated diesel hybrid buses equipped with extended battery capabilities.

The other two routes operate along Washington Street, connecting Nubian station in Roxbury with Downtown Boston: SL5 terminates at , while SL4 concludes at . Both routes utilize articulated diesel hybrid buses.

The Washington Street corridor replaced the former Washington Street Elevated segment of the Orange Line, which ceased operation in 1987. While initial proposals favored extending a light rail branch of the Green Line, trolleybuses followed by compressed natural gas (CNG) buses were ultimately selected. Transit planning for the Seaport area began in 1987, culminating in approval for the South Boston Piers Transitway in 1989. This transitway was designed to connect to World Trade Center via and South Station; however, the Boylston–South Station section was postponed. In 1999, the MBTA consolidated the Washington Street and Transitway projects under the Silver Line designation, including plans for a tunnel extension with a portal to enable through-routing. Service enhancements on Washington Street commenced in 2001, and despite delays, the $624 million Transitway officially opened on December 17, 2004.

The proposed connecting tunnel (Phase III) was canceled in 2010 due to budget overruns; instead, a surface-level SL4 route was introduced in 2009. The original SL3 service to ended on March 20, 2009. A new SL3 route to Chelsea—initially part of the discontinued Urban Ring Project—was launched on April 21, 2018, with future plans to extend it to . Various other expansions and proposals for converting Washington Street service to light rail have been suggested but largely not pursued. The Silver Line has faced criticism for lacking several essential BRT elements such as exclusive lanes, off-board fare collection, fully sheltered stations, and transit signal priority.

Waterfront: SL1, SL2, SL3

Three Silver Line services operate from , running through the South Boston Piers Transitway and serving underground stations at and within the Seaport District. After reaching , these routes split:[1]

  • SL1 Logan Airport–South Station
  • SL2 Drydock–South Station
  • SL3 Chelsea–South Station

During peak hours, supplemental short-turn trips designated as SLW run between South Station and Silver Line Way to increase service frequency.[1]

Route SL2 navigates Northern Avenue and a one-way loop encompassing Drydock and Black Falcon Avenues, servicing the Raymond L. Flynn Marine Park and Flynn Cruiseport Boston. Both SL1 and SL3 loop back along Haul Road before crossing under Boston Harbor via the Ted Williams Tunnel into East Boston. SL1 stops at all Logan Airport terminals at their arrivals levels; meanwhile, SL3 serves station, crosses Chelsea Creek on the Chelsea Street Bridge, then continues along a dedicated busway to , making stops at , , and .[1][2] Stations along the Transitway provide full rapid transit amenities; Chelsea busway stops feature large shelters; most other stops have smaller shelters.[3]

Standard rapid transit fares apply on Waterfront routes.[4] Riders enter through faregates at Transitway stations but pay onboard when boarding elsewhere.[3] Boarding is free at Logan Airport stops.[4] Transfers are available to the Red Line within fare-controlled areas at South Station; transfers to other lines require a CharlieCard, with CharlieTicket transfers available for connections to/from the Blue Line at Airport and Washington Street services.[4]

The Waterfront fleet consists of articulated buses equipped with three doors to accommodate higher passenger volumes compared to standard 40-foot buses.[5] These low-floor diesel hybrid vehicles are fully accessible, featuring kneeling capabilities and wheelchair ramps. The primary fleet includes 45 extended battery range diesel hybrids delivered between 2022 and 2023 that can operate through the Transitway using battery power alone. Additional vehicles include one extended-range hybrid from 2018 and five battery electric buses introduced in 2019. All vehicles are maintained at Southampton Street Garage.[5]

Historically, dual-mode buses operated as electric trolleybuses within the Transitway and switched to diesel mode on surface segments. The fleet comprised 32 Neoplan USA dual-mode vehicles delivered during 2004–05 and refurbished between 2014–18; eight of these were funded by Massport and equipped with luggage racks for airport travelers.[3] However, these buses were challenging to maintain due to complications switching modes at Silver Line Way.[6][7]

Between 2018 and 2019, MBTA trialed alternatives including a New Flyer extended-range hybrid bus that entered service in December 2018. On July 31, 2019, five New Flyer battery electric buses were introduced on both Waterfront and Washington Street routes.[8] In November 2020, MBTA placed an order for an additional 45 sixty-foot extended battery range hybrid buses intended to replace the dual-mode fleet.[9] The final dual-mode buses were retired in July 2023, marking the end of trolleybus operations in Greater Boston.[5]

Station directory

Area Stop Routes served In service since Connections and remarks
SL1 SL2 SL3 SLW
Financial
District
  1. REDIRECT Template:Boston transportation system
 ● ● ● ● December 17, 2004 Template:Ric: Template:Lnl, Template:Lnl, Template:Lnl
Template:Ric: Fairmount Line, Fall River/New Bedford Line, Framingham/Worcester Line, Franklin/Foxboro Line, Greenbush Line, Kingston Line, Needham Line, Providence/Stoughton Line, CapeFLYER (seasonal)
Template:Ric: Template:Ric, Template:Ric (Template:MBTABus)
Template:Ric: Template:MBTA bus links
Intercity buses at South Station Bus Terminal
Seaport District
  1. REDIRECT Template:Boston transportation system
 ● ● ● ● Template:Ric: Template:MBTA bus links
  1. REDIRECT Template:Boston transportation system
 ● ● ● ●
  1. REDIRECT Template:Boston transportation system
 ● ● ● ●
East Boston
  1. REDIRECT Template:Boston transportation system
 ● June 1, 2005 \nTemplate:Ric: Template:MBTA bus links
Massport shuttles and Logan terminals intercity buses
\nTemplate:Bts\ Terminal B Stop 1 \nalign=center\ ● \nTemplate:Ric\ MBTA Bus: Template:MBTA bus links\ Terminal B1
Massport shuttles and Logan terminals intercity buses
\nTemplate:Bts\ Terminal B Stop 2 \nalign=center\ ● \nTemplate:Ric\ MBTA Bus: Template:MBTA bus links\ Terminal B2
Massport shuttles and Logan terminals intercity buses
\nTemplate:Bts\ Terminal C \nalign=center\ ● \nTemplate:Ric\ MBTA Bus: Template:MBTA bus links\ Terminal C
Massport shuttles and Logan terminals intercity buses
\nTemplate:Bts\ Terminal E \nalign=center\ ● \nTemplate:Ric\ MBTA Bus: Template:MBTA bus links\ Terminal E
Massport shuttles and Logan terminals intercity buses
\nTemplate:Bts\ Airport \nalign=center\ ● \nrowspan=5 April 21, 2018 \nTemplate:Ric MBTA Subway: Template:Ric MBTA Blue
Template:Ric MBTA Bus: Template:MBTA bus links Airport
Massport shuttles
\nrowspan=4 Chelsea, Massachusetts] \nTemplate:Bts Eastern Avenue \nalign=center ● \nTemplate:Ric MBTA Bus: Template:MBTA bus links Eastern Avenue
\nTemplate:Bts Box District \nalign=center ●
\nTemplate:Bts Bellingham Square \nalign=center ● \nTemplate:Ric MBTA Bus: Template:MBTA bus links Bellingham Square
\nTemplate:Bts Chelsea \nalign=center ● \nTemplate:Ric MBTA Bus: Template:MBTA bus links Chelsea
Commuter Rail: Newburyport/Rockport Line
\nrowspan=6 South Boston] Northern Avenue & Harbor Street align=center ● rowspan=2 December 31, 2004

Template:Ric MBTA Bus: Template:MBTA bus links Harbor Street

Northern Avenue & Tide Street align=center ● Template:Ric MBTA Bus: Template:MBTA bus links Tide Street
23 Drydock Avenue align=center ● Relocated from 21 Drydock Avenue in 2016
27 Drydock Avenue align=center ● rowspan=3 December 31, 2004

Former stop at 25 Drydock Avenue closed in January 2016; relocated stop opened in 2018

Drydock Avenue & Black Falcon Avenue align=center ● Replacement stop for 88 Black Falcon Avenue during nights and poor weather until January 2016; official stop since 2018
Design Center align=center ● Template:Ric MBTA Bus: Template:MBTA bus links Design Center


Discontinued Stops

Neighborhood Stop Served by Service started Service terminated Remarks
South Boston 88 Black Falcon Avenue SL2 December 31, 2004 April 2019 Closed temporarily in April 2019 for pier maintenance; permanently shut down on March 13, 2022. The anticipated reopening in June 2022 was cancelled.
Black Falcon Avenue & Design Center Place SL2 2014
Summer Street & Powerhouse Street SL3 March 20, 2009 Service discontinued due to insufficient ridership
East 1st Street & M Street SL3 Discontinued due to low passenger numbers
  1. REDIRECT Template:Boston transportation system
 SL3 Discontinued because of low usage
Farragut Road SL3 April 9, 2005 August 20, 2005 Route altered following complaints about noise


Washington Street: SL4 and SL5

Two Silver Line services run between Nubian station (Nubian Square, Roxbury) and Downtown Boston via Washington Street:[1]

  • SL4 connecting Nubian station to South Station
  • SL5 connecting Nubian station to Downtown Crossing

The majority of their route along Washington Street between Nubian Square and share dedicated bus lanes and eight stops. Beyond Kneeland Street, the routes split into separate one-way loops: SL5 heads north to Temple Place (located between and ), stopping at , then returns southbound along Tremont Street with a stop at . SL4 travels north toward Chinatown, continues east on Essex Street (with exclusive lanes) to a surface-level stop at , and returns south via Surface Road and Kneeland Street.[1] Most stations are equipped with shelters that include seating, route maps, and real-time arrival information.[10]

Fare prices are equivalent to local bus fares—lower than those for rapid transit—and standard CharlieCard transfers are accepted.[4] Paper CharlieTickets also allow transfers, as these routes serve as replacements for the Orange Line; this fare policy continues the previous practice from route 49 bus of free transfers to the Orange Line at .[10]

The Washington Street Silver Line routes utilize 60-foot diesel hybrid articulated buses featuring three doors.[5] These accessible vehicles have low floors, kneeling capability, and wheelchair ramps. The fleet includes 21 New Flyer buses delivered in 2016–17 (part of a larger 44-bus order also servicing routes and ), which replaced earlier compressed natural gas (CNG) buses, along with three similar hybrid buses from 2010.[5][11] All Silver Line vehicles are housed at Southampton Street Garage.[5][10]


List of Stations

Neighborhood Station Name Services Available Service Commenced Transfers and Additional Information
SL4 SL5
Roxbury
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South End
  1. REDIRECT Template:Boston transportation system
 ● ● Template:Ric: Template:MBTA bus links
  1. REDIRECT Template:Boston transportation system
 ● ● Template:Ric: Template:MBTA bus links
  1. REDIRECT Template:Boston transportation system
 ● ● November 30, 2002 Template:Ric: Template:MBTA bus links
  1. REDIRECT Template:Boston transportation system
 ● ● July 20, 2002 Template:Ric: Template:MBTA bus links

Washington Street development

The 1947 legislation that established the Metropolitan Transit Authority (MTA) as the successor to the Boston Elevated Railway initiated four key projects: extending rapid transit to , expanding the Tremont Street Subway to a four-track configuration, substituting elevated lines (Charlestown Elevated, Causeway Street Elevated, and Washington Street Elevated) with underground tunnels, and lengthening the Cambridge–Dorchester line northwest from . In 1948, the city received authorization to issue $19 million in bonds aimed at extending the Washington Street Tunnel beneath Shawmut Street, linking it to the existing elevated structure south of Dudley Square. Although these projects were not immediately realized, they established a framework for replacing elevated transit lines. In 1972, community opposition resulted in the cancellation of the proposed Southwest Expressway, with the corridor later repurposed for combined use by intercity rail, commuter rail, and the Orange Line, ultimately supplanting the Washington Street Elevated.

Since the northern segment of this corridor was situated roughly west of Washington Street, the MBTA (which succeeded the MTA in 1964) devised plans in 1978 to provide substitute service between Dudley Square and Downtown Boston. By 1985, options favored either bus or light rail transit along Washington Street; light rail would have operated as a Green Line extension via the disused southern branch through Pleasant Street Portal. The Orange Line was rerouted in 1987; however, funding for light rail on this corridor was denied by the Urban Mass Transportation Administration. Public sentiment leaned toward maintaining part of the Elevated until a permanent replacement could be established. Consequently, the MBTA discontinued the Elevated and upgraded route 49 bus service from a feeder to a frequent trunk line.

In 1989, the MBTA announced plans for trolleybus operations on Washington Street with peak intervals of four minutes. By 1990, service commencement was anticipated by 1993, including proposals for an underground link to Boylston station and a future tunnel connecting South Boston Piers. Following additional evaluation, in 1996–97 the MBTA opted to develop a bus rapid transit corridor utilizing compressed natural gas (CNG) buses to avoid overhead electrical infrastructure. Environmental assessments were submitted in 1998, with construction commencing in 2001. The $27.3 million project budget allocated $10.9 million for acquiring 17 new buses, another $10.9 million for roadway improvements, and $2.6 million for passenger shelters. Coordinated with repaving of Washington Street, these efforts helped reduce costs. Marketed as the "Silver Line"—a brand introduced in 1996—the service sought to deliver quality comparable to light rail and was presented on maps alongside existing subway lines.

The Silver Line primarily traced route 49 between Dudley Square and Downtown Boston but reduced stops from twenty to eleven by July 2002, largely preserving existing stop locations. In December 2001, a southbound contraflow bus-only lane opened on Washington Street between Marginal Road and East Berkeley Street, facilitating direct access for buses and extending service to a new downtown terminal at Temple Place near and stations. Service frequency was increased concurrently. On July 20, 2002, Silver Line-branded low-floor CNG buses began operation—the first of their kind in Boston—and a twelfth stop at was introduced in November that year. In August 2003, articulated buses replaced standard vehicles and further frequency enhancements were implemented. On January 31, 2005, this route became the first MBTA bus line equipped with automated fare collection technology. By that year, ridership had doubled compared to route 49 despite some operational difficulties.

Following the renaming of Dudley Square itself in December 2019, the MBTA agreed in February 2020 to rename Dudley Square station as Nubian; this change took effect in June 2020. In May 2022, a draft systemwide network redesign proposed merging SL4 and SL5 into a single Nubian–South Station route to simplify downtown service; this proposal remained present in drafts released in November 2022. Additionally, an SL4 stop at Chinatown Gate on Surface Artery at Kneeland Street was introduced on August 19, 2022 during Orange Line maintenance and retained thereafter.

Waterfront Development

Throughout much of the 20th century, the Seaport District functioned primarily as an industrial area, characterized by extensive rail yards and wharves. The South Boston Army Base and South Boston Naval Annex were linked to the Red Line at via brief bus routes. Following the closure of these military installations in 1974 and the subsequent shutdown of rail yards, the Seaport area was earmarked for commercial redevelopment, which in turn increased the need for enhanced transit options.[12] In response, the MBTA undertook a feasibility study in 1987 and released a Draft Environmental Impact Report (DEIR) by 1989.[3] The report recommended an underground "transitway" utilizing trolleybuses or dual-mode buses instead of surface light rail, elevated people movers, commuter rail shuttles, or relocating the Red Line. This transitway was designed to connect with the Red Line at South Station, the Orange Line at , and the Green Line at . Cost efficiencies were anticipated by coordinating construction with the Central Artery/Tunnel Project ("Big Dig"). Plans also included future extensions to Logan International Airport and links to proposed circumferential transit lines.[12]

The alignment for the South Boston Piers Transitway was further refined in a supplemental DEIR issued in 1992,[12] with final approval granted in December 1993.[3] The segment connecting South Station to the Seaport was scheduled for completion in 2000, followed by an extension to Boylston planned for 2006.[12] Stations at , , South Station, Chinatown, and Boylston were designed with island platforms; additionally, the tunnel was engineered to allow future conversion into a Green Line light rail branch.[13] Initial projections estimated daily ridership between 24,200 and 37,200 during phase one, increasing to between 34,800 and 69,800 upon full development depending on commercial expansion.[12] In November 1994, the Federal Transit Administration (FTA) agreed to finance $331 million (80%) of the $413 million first phase budget, aiming for a December 2000 completion.[14] Environmental clearances were finalized by April 1995.[3]

By 1997, as construction progressed on the transitway, Massport opted to cancel a previously planned Logan Airport people mover system in favor of dual-mode buses operating through the transitway and Ted Williams Tunnel.[3] A new connector road linking D Street to Haul Road was included in these revisions and received approval in February 1998.[3] By May 1999, MBTA intended to brand this transitway as part of the "Silver Line," integrating it with Washington Street service as Phase I; initial Transitway construction as Phase II; and Boylston extension as Phase III.[3]

The construction effort for the Transitway was segmented into four principal parts: South Station along with a turnaround loop plus of tunnel costing $96 million; Russia Wharf and Fort Point Channel tunnel at $128 million; Courthouse station plus of tunnel budgeted at $110 million; and World Trade Center station with of tunnel at $43 million.[3] The Russia Wharf section presented technical challenges due to required ground freezing techniques needed to safeguard historic structures and included an immersed tube beneath Fort Point Channel.[14]</ref> The discovery of a large boulder beneath the channel caused a delay of approximately one year.[3] By late 2000, the project was running three years behind schedule and exceeded its budget by nearly $200 million; MBTA reallocated $150 million from other federal grants along with $50 million in contingency funds to address these overruns.[14] The Transitway ultimately reached completion in 2004 with a final MBTA expenditure of $624 million,[3] which encompassed higher-than-anticipated costs for dual-mode buses as well as partial expenses related to the Southampton maintenance facility.[3] Although new facilities such as a federal courthouse and convention center were established nearby, commercial development did not meet early expectations; consequently, daily ridership estimates were revised downward from an anticipated 45,000 to just 14,000 prior to opening.[15]

The Transitway officially began operations on December 17, 2004, featuring a Waterfront shuttle running between South Station and Silver Line using newly acquired dual-mode buses alongside borrowed trolleybuses from Harvard-based routes.[2][3] This made it only the third "urban trolleybus subway" globally after Harvard's bus tunnel and Seattle's Downtown Transit Tunnel (which ceased trolleybus service in 2005).[16] Initial service plans included a single route serving City Point through several streets; however, community concerns regarding parking led to splitting this into two separate routes—one terminating at , and another serving City Point.[17] Although MBTA initially considered letter designations similar to Green Line branches, they ultimately adopted numerical route identifiers.[18]

On December 31, 2004, SL2 commenced service to Boston Marine Industrial Park while SL3 operated toward City Point via Northern Avenue. Two days later, a Sunday-only "Silver Line Connector" shuttle started airport service fulfilling legal requirements.[2] Surface routes were modified or discontinued by January.[3] Due to limited availability of dual-mode buses, compressed natural gas (CNG) shuttles operated surface segments from January through March 14, 2005; SL2 and SL3 services merged during nights and weekends starting March 26. Weekday SL3 service was extended on April 9; by May 28 full combination as SL2/3 occurred to allocate buses for SL1 airport service launched June 1.[2] The split between SL2/3 resumed on August 20 except during nights and weekends; noise complaints led to cutting Farragut Road loop; night/weekend City Point service ended October 15. A proposed SL4 route to Andrew never materialized.[19][2]

As more dual-mode buses became available, borrowed trolleybuses were phased out by February 12, 2006.[16] By that time, Silver Line had doubled transit ridership within the Seaport area and increased Logan Airport ridership by approximately 24%.[3] However, SL3 struggled against competing parallel route , which provided more direct routing and better downtown connections; by 2008 SL3 averaged fewer than one passenger per trip along its unique segment. Consequently, SL3 service ended on March 20, 2009; frequency on SL2 increased accordingly.[2][20] The SL2 terminus was renamed "Design Center" in October without altering service patterns.[2]

Up until 2019, SL2 buses operated two layover patterns at Design Center loop: a full loop before layover prior to noon; and a shorter western loop after noon. On December 22, 2019, all trips adopted the full loop layover pattern. Later on March 15, 2020 afternoon layovers shifted to a stop at 23 Dry Dock Avenue before completing the loop.[21][2]

In January 2021 Massport approved leasing air rights over Silver Line Way station for development including station improvements.[22] Beginning March 13, 2022 all SL2 buses began layovers at Dry Dock Avenue; concurrently Black Falcon Avenue stop closed permanently following pier repairs ongoing since April 2019.[23][24][2] An upgraded stop near Black Falcon Avenue is planned by 2025 as part of broader redevelopment efforts.[22] The May 2022 draft network plan proposed routing SL1 and SL3 via D Street directly accessing Ted Williams Tunnel while assigning SL2 plus shuttles exclusively to Silver Line Way,[25][26] a modification retained in November’s updated proposal alongside enhanced all-day frequency on SL2.[27][28]

Phase III proposals

The 1993 plan for the Boylston extension envisioned a westward route from South Station beneath Essex Street, Avenue de Lafayette, and Avery Street, featuring stations at Chinatown and Boylston situated below current structures. In 1999, the decision to integrate the Waterfront and Washington Street initiatives into the Silver Line introduced a southern segment utilizing a disused streetcar tunnel. A new subterranean station was suggested beneath Tremont Street, linking to the New England Medical Center (NEMC) station, with a portal positioned near Oak Street. By April 2000, the MBTA adjusted the alignment toward Boylston Street to reduce conflicts with ongoing development, create a more direct route, and eliminate pedestrian tunnels.

By January 2002, the MBTA pursued federal funding covering 60% of project expenses; the Federal Transit Administration (FTA) approved continued planning that July. In 2003, the Boston Regional Metropolitan Planning Organization designated it as a "high priority" project due to anticipated ridership levels, low operational expenses, and service to environmental justice communities. Preferred portal locations were slightly modified in 2003 to avoid demolishing buildings, while suggestions to combine stations or remove loops were dismissed because of operational difficulties. Further refinements in 2003–04 introduced a second platform at Boylston to accommodate increased passenger volumes and to lessen effects on Boston Common.

Community feedback from Bay Village residents expressing concerns about Eliot Norton Park and requests for Back Bay service prompted additional revisions during 2004–05. The Boylston platforms were reoriented east–west with the loop relocated westward near Charles Street; new portal possibilities on Columbus Avenue were explored. Initial capital cost estimates ranged from $768 million to $812 million, with completion timelines extended from 2010 to 2013. Projections indicated daily ridership could reach 160,000 by 2025. In August 2005, the MBTA temporarily halted Phase III development to foster community agreement on routing decisions.

In February 2006, State Transportation Secretary John Cogliano introduced a $94 million proposal that eliminated most tunneling while maintaining connectivity between phases. This plan routed Silver Line surface service via Kneeland Street and Surface Road to a new portal on Essex Street close to South Station, with expanded surface branches serving Copley Square and extending southward to replace bus routes 23 and 28. While this approach gained favor among Bay Village residents, it faced criticism for not substantially decreasing downtown travel times.

A revised tunnel concept surfaced in March 2006 with widespread support, featuring a modified Charles Street tunnel alignment with a portal near Tremont Street adjacent to Marginal Road. This "Charles Street Modified" (CSM) alignment continued as the preferred option. Plans included dedicated contra-flow bus lanes on Washington Street extending onto Marginal Road and Herald Street to facilitate portal access. On December 12, 2006, the FTA approved re-entry into funding procedures. By mid-2008, environmental assessments and preliminary engineering were anticipated to finish by year-end; federal funding applications targeted 2010 with construction scheduled from 2011 aiming for a 2016 launch.

However, by May 2009 estimated expenses had escalated to $2.1 billion for the "Little Dig" tunnel plan. The FTA assigned it a Medium Low rating, rendering it ineligible for final design phase funding through New Starts grants. Consequently, the Boston Region Metropolitan Planning Organization removed Phase III from its long-term plan due to financial limitations. MassDOT ceased pursuing New Starts funds for Phase III, reallocating available resources toward the Green Line Extension project. In July 2010, MBTA announced Phase III was indefinitely suspended with no further expenditures planned.

As a partial substitute, route SL4 commenced operations on October 13, 2009 using federal stimulus funds; it covered much of Phase III’s intended corridor with dedicated bus lanes along Essex Street and included a South Station stop west of Atlantic Avenue. Simultaneously, the existing Downtown Crossing-Dudley route was redesignated as SL5.

Extension toward Chelsea

The Urban Ring Project was envisioned as a circumferential surface BRT corridor, sharing Silver Line platforms at Dudley Square and a surface stop near the World Trade Center station, yet operating separately from the Silver Line otherwise. Although cancelled in 2010 due to excessive expenses, planning efforts persisted for smaller segments. Priority was given to the Chelsea–South Boston section because of Chelsea's high population density and limited transit access. In 2010, MassDOT acquired the Grand Junction Branch from CSX Transportation, including unused stretches in Chelsea and East Boston, offering a potential transit right-of-way. A 2011 state report evaluated transit options for Chelsea, considering a Silver Line branch serving Bellingham Square or the Chelsea commuter rail station, alongside enhancements to bus route .

In 2013, MassDOT initiated public planning for the Silver Line Gateway project aimed at improving service to Chelsea and providing Blue Line passengers with a direct connection to the Seaport District and South Station. Three route alignments were examined, all utilizing the Transitway and Ted Williams Tunnel to reach station, then proceeding via the Coughlin Bypass Road to the Chelsea Street Bridge. The preferred route followed a new busway entirely on the Grand Junction corridor through Chelsea, featuring stops at , , (Chelsea commuter rail station), and Mystic Mall. Other options included partial or fully surface street alignments serving multiple stops.

By September 2013, the MBTA favored the first option despite challenges related to bridge clearance and rebuilding the commuter rail station. On October 30, 2013, MassDOT announced an $82.5 million state investment for extending the Silver Line to Chelsea with a target completion in 2015. Plans included relocating the commuter rail station to (Mystic Mall) and constructing a $3 million multi-use path connecting Eastern Avenue to Washington Street. The Environmental Impact Report was published in March 2014. In September 2014, MassDOT awarded a $33.8 million contract for phase one construction: building a 1.3-mile busway, four Silver Line stations, replacing the Washington Street bridge, and developing the Chelsea Greenway.

Silver Line service on route SL3 began serving Chelsea on April 21, 2018; daily ridership reached approximately 6,200 by October of that year. Phase two comprised relocating the Chelsea commuter rail station and implementing transit signal priority improvements for SL3. Construction commenced in August 2019; the new station opened on November 15, 2021. As of January 2024, plans by MBTA and Boston include reconfiguring Day Square in East Boston later in 2024 by adding bus lanes along Chelsea Street and creating a bus-only corridor through Day Square with a new station servicing SL3 and local routes.

Sullivan Square extension

In March 2019, officials revealed intentions to extend service from on two routes toward Kendall Square and North Station, both passing through Sullivan Square. These routes would primarily operate on dedicated busways and lanes, although branding under the Silver Line remained undecided at that time. In January 2021, MBTA and MassDOT launched a study for the Silver Line Extension (SLX), exploring various routing options from Chelsea into Everett, Somerville, Cambridge, and Boston. By September 2021, six corridors had been identified: routes to , Sullivan, , downtown Boston via Sullivan Square, Kendall via Sullivan Square, and Kendall via Wellington. Some might function as new lines separate from SL3 with termini possibly at Chelsea or Airport instead of South Station.

By September 2022, proposed alternatives included three SL3 extensions reaching Malden Center, Wellington, or Sullivan—all passing through Everett Square—with varying degrees of dedicated bus lanes on their western segments. Additionally, four SL6 routes were proposed: Everett (Glendale Square)–Kendall via McGrath Highway; Everett–Kendall via Gilmore Bridge; Everett–Haymarket via Rutherford Avenue; and Eastern Avenue–Kendall via Everett Square. All SL6 variants would predominantly operate within dedicated lanes. In March 2024, an SL3 extension to Sullivan was selected as the preferred alternative; further planning for SL6 was postponed pending additional studies related to Sullivan Square improvements and other corridors alongside ongoing bus network redesign efforts.

The SL3 extension would utilize an off-street busway westward up to 2nd Street; then run in mixed traffic—potentially upgraded later with dedicated lanes—along 2nd Street and Spring Street; followed by dedicated lanes along Chelsea Street and most of Broadway. South of Sweetser Circle, construction of a dedicated busway on Lower Broadway is planned. New stops are proposed at 2nd Street (Boston Street and Spring Street), Broadway (Chelsea Street/Everett Square, Beacham Street, Horizon Way), and Sullivan Square station. The extension adds round trips—with approximately 80% () operating in dedicated lanes—and is projected to boost daily SL3 ridership by 15,000 boardings by 2040 at an estimated capital cost of $95 million. In June 2024, MBTA received a $22.4 million federal grant designated for reconstructing Lower Broadway to accommodate current bus services as well as future Silver Line operations.

Additional proposed corridors

Numerous bus rapid transit (BRT) and express bus initiatives have been suggested for Boston, many operating under the Silver Line designation. The initial two phases of the discontinued 2010 Urban Ring Project were planned as BRT, with the final phase intended to incorporate either light or heavy rail. Although distinct projects, the Urban Ring shared the SL1 segment between Silver Line Way and Logan Airport.

The 2003 Program for Mass Transportation (PMT) evaluated several potential Silver Line expansion routes, most of which did not advance. One concept involved a BRT express overlay on the route 28 bus, connecting Ruggles station to Mattapan via Nubian, which was revisited in 2006 as part of Phase III. In 2009, the state proposed fully replacing route 28 with a BRT service labeled 28X, featuring dedicated lanes, signal priority, and fare collection at platforms. This plan was withdrawn in 2010 due to local opposition concerning route alignment and insufficient community engagement. Subsequent enhancements to bus service along Blue Hill Avenue have continued without adopting Silver Line branding.

Other corridors from the PMT included a Dudley–Ashmont BRT to substitute route 23, also reconsidered during Phase III planning, and a new BRT tunnel leading to Kenmore station with surface branches extending to the Longwood Medical Area via Brookline Avenue and to Allston along Commonwealth Avenue, the Mass Pike, and Cambridge Street. The City of Boston suggested an alternative western Silver Line branch utilizing buses on the Mass Pike without constructing new tunnels, resembling current express bus services.

The PMT also explored converting the Washington Street portion of the Silver Line into light rail by repurposing the abandoned southern segment of the Tremont Street subway. Estimated at $374 million with an anticipated daily ridership of 34,000—primarily redirected from existing Silver Line passengers—this project was deemed lower priority compared to the Phase III tunnel development. In 2012, the Roxbury–Dorchester–Mattapan Transit Needs Study recommended this conversion as a long-term objective, potentially extending light rail service along Blue Hill Avenue to Mattapan following the route 28 corridor.

Frequency and ridership

Silver Line routes rank among the MBTA’s most frequent bus services. Except for the SLW shuttle, all routes operate at intervals no longer than 15 minutes during service hours. Combined peak frequencies reach approximately 30 buses per hour (headways of about two minutes) within the Transitway and around 12 buses per hour (five-minute headways) along Washington Street. While ridership is substantial, it remains lower than many major MBTA bus routes; however, operating costs per passenger are comparatively less than other MBTA bus lines. In 2012, only SL1, SL5, and SLW generated profits; across all MBTA bus routes, the median net cost per rider was $2.13. By 2023, weekday ridership across all Silver Line services had grown to approximately 27,000 passengers.

Silver Line routes and crosstown services utilize internal 700-series route numbers; for instance, SL5 is designated as route 749, reflecting its role as a successor to the former 49 bus.

Route # Peak hour frequency Midday frequency Weekend frequency Weekday ridership (2018)
SL1 741 Every 10–12 minutes Every 12 minutes Every 8–12 minutes 8,132
SL2 742 Every 5–8 minutes Every 15 minutes Every 15 minutes 6,420
SL3 743 Every 10 minutes Every 15 minutes Every 12–15 minutes 6,200
SLW 746 Every 8 minutes — Limited service (not available)
SL4 751 Every 12 minutes Every 14 minutes Every 16–17 minutes 5,800
SL5 749 Every 8–9 minutes Every 8–11 minutes Every 8–9 minutes 10,300

Mode choice

When the Southwest Corridor project replaced the Washington Street Elevated, the MBTA committed to providing surface transit that was "equal or superior" to the previous service along Washington Street. Passengers preferred light rail, and the substitution with buses was widely viewed as a broken commitment and a form of disinvestment. The Silver Line operates considerably slower than the Elevated did; for example, travel time from Nubian Square to Downtown Boston increased from 8 minutes to 20 minutes. This corridor primarily serves a community with lower income and education levels and a higher percentage of Black residents. Advocates, including state representative Gloria Fox, have criticized the transit disparity as "discrimination against people of color." Due to substandard service and its inferiority compared to the originally planned light rail, the Washington Street Silver Line earned the disparaging nickname "Silver Lie."

While bus rapid transit offers benefits such as reduced costs and quicker deployment, Silver Line service along Washington Street commenced 15 years after the Elevated was dismantled. The first segment of the Transitway opened 15 years following its Draft Environmental Impact Report (DEIR), and its second phase remains unfinished. The construction expenses were substantial—by 2007, it was cited as the most costly BRT project globally—comparable to light rail costs but delivering lower quality service. Phase III was estimated at $2.1 billion before it was canceled, which is more than triple the Transitway’s expenditure. Although ridership in the Seaport area doubled after introducing the Silver Line, this increase partially reflects commercial growth rather than improvements in transit quality.

BRT quality

Essential elements of bus rapid transit include exclusive lanes, frequent headways, off-board fare payment, sheltered stops, and intelligent transportation systems like transit signal priority. A 2011 assessment by the Institute for Transportation and Development Policy (ITDP) categorized the Silver Line as "Not BRT" because it lacks many features outlined in the BRT Standard.

Off-board fare collection is limited to only three underground stations. Surface service experiences delays primarily due to extended dwell times caused by front-door boarding and single fareboxes. On June 6, 2012, Massport initiated a three-month trial offering free rides from five Logan Airport stops to alleviate terminal congestion. Within one month, average dwell times decreased by 20 seconds per stop. This pilot was extended through January 2013 and subsequently made permanent for rides originating at Logan. Stops along Washington Street with more than fifteen passengers frequently see dwell times exceeding one minute, negatively impacting reliability. A two-week pilot in 2017 testing all-door boarding on these routes cut dwell times at busy stops by half, reduced average dwell time from 24 to 19 seconds, and enhanced schedule adherence. Full implementation of all-door boarding is planned for the 2020s with the rollout of the AFC 2.0 fare system.

Washington Street routes include dedicated bus lanes between and , as well as on Essex Street; however, these lanes are not physically separated from general traffic and often function as right-turn lanes at intersections. Double parking is common due to a lack of designated loading zones, and enforcement of bus-only lanes is infrequent. Congested areas such as Nubian Square and Downtown Crossing lack any dedicated lanes. Although transit signal priority (TSP) was planned for four locations along Washington Street, activation was delayed until 2006 due to coordination challenges. As a result, travel times vary widely; during peak hours in 2006, trips could be up to 1.7 times longer than during uncongested periods. Poor headway reliability mainly stems from operators departing Nubian behind schedule. In 2020, improvements including enforced downtown bus lanes, traffic restrictions on Temple Place, and new loading zones in Chinatown were introduced to enhance Silver Line performance.

The Transitway itself is a dedicated bus tunnel free from automobile traffic; however, Waterfront service operates at speeds comparable to former on-street buses. Although designed for higher speeds up to , narrow lanes without guided bus technology restrict actual speeds to roughly . Water intrusion and inadequate drainage have damaged the tunnel floor surface, resulting in uncomfortable rides. The transition point between electric and diesel propulsion at Silver Line Way causes notable delays. Because the Transitway terminates at D Street, buses must navigate a traffic signal that adds an average delay of 1.5 minutes per round trip. A feasibility study conducted in 2003 estimated $75 million would be required to extend the tunnel beneath D Street for grade separation. In early 2016, Boston Transportation Department altered this traffic signal to operate on a fixed cycle without active bus prioritization or shortening its lengthy 100-second duration—a decision criticized by planners. Proposed air rights development above this station must accommodate potential future grade separation enhancements. Additionally, a gate and movable bollard near this intersection delay buses by limiting private vehicle access onto the Transitway.

Standard BRT stop spacing typically ranges from 0.5 to 1 mile; however, along Washington Street stops are spaced much closer—averaging only about half a mile after their number was halved—with some stops situated less than three blocks apart. Initial stops featured open canopies; enclosed shelters were added only starting in 2010. Temple Place has a small glass shelter; Boylston, Chinatown, and Tufts Medical Center stops lack any shelter structures entirely. Surface stops on Silver Line Way and SL2 have either glass shelters or none at all; SL3 surface stops are equipped with canopies but no enclosed shelters.

Indirect routing

The Transitway was not constructed to provide direct access to Logan Airport or Chelsea and does not have a direct link to the Ted Williams Tunnel. Outbound SL1 and SL3 services head west along Haul Road from Silver Line Way to an eastbound ramp located west of B Street, then continue eastward on a heavily congested segment of I-90. For inbound trips, buses exit I-90 at B Street and proceed east on Congress Street before reaching Silver Line Way. There is an eastbound entrance ramp near Silver Line Way, usually reserved for Massachusetts State Police and MassDOT vehicles, which could reduce outbound travel distance by approximately . Although MassDOT contends that this ramp was not intended for bus use, Big Dig planner Fred Salvucci challenges this assertion. In 2006, after the Big Dig ceiling collapse, outbound buses temporarily utilized this ramp due to the suspension of eastbound tunnel traffic. The Urban Ring initiative also suggested employing this ramp, and a 2010 evaluation deemed it safe for Silver Line operations.

Transit advocates have campaigned to allow Silver Line buses access to this ramp under the slogan "Free the ramp," but MassDOT raises safety concerns related to high-speed highway traffic. The MBTA commissioned a study in 2018 to assess the feasibility of using the ramp. By May 2019, MassDOT authorized a limited trial during evening peak periods when traffic speeds were below , though transit supporters criticized these constraints. A three-day test conducted in August 2019 resulted in average time savings of 3–8 minutes per bus, with more significant reductions during heavy congestion. Following these results, MassDOT agreed to alter the ramp entrance to permit regular use whenever traffic speeds remain under 30 mph.

Silver Line buses resumed using the ramp during a 2023 closure of the Sumner Tunnel.

Other issues

The SL3 route often faces delays caused by frequent openings—up to ten times daily—of the Chelsea Street Bridge to allow ships servicing upstream oil terminals to pass. Each bridge opening can cause delays as long as 20 minutes, with the only alternative involving a lengthy detour via Route 1A. Federal regulations give priority to marine traffic in such cases. In December 2018, MassDOT proposed a six-month pilot program aimed at reducing bridge openings during peak hours; this plan also targeted the nearby Meridian Street Bridge, which serves heavily used bus routes 116 and 117.

The introduction of CNG buses on the Washington Street line generated disruptive vibrations at 35 Hz in adjacent residences. It took approximately one year to retrofit these vehicles with improved mufflers; during this period, older buses without this vibration issue operated during nighttime hours.


See also

External links

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Cite error: Invalid <ref> tag; no text was provided for refs named busmap
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Cite error: Invalid <ref> tag; no text was provided for refs named netransit
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 Cite error: Invalid <ref> tag; no text was provided for refs named 2007report
  4. ↑ 4.0 4.1 4.2 4.3 Cite error: Invalid <ref> tag; no text was provided for refs named tariff
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Cite error: Invalid <ref> tag; no text was provided for refs named roster
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named ITDP
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named stateofthesystem
  8. ↑ First Zero-emission, Battery-electric Buses Join the MBTA Silver Line Fleet (July 31, 2019)
  9. ↑ Silver Line Bus Fleet Replacement (November 23, 2020)
  10. ↑ 10.0 10.1 10.2 Cite error: Invalid <ref> tag; no text was provided for refs named 2005report
  11. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  12. ↑ 12.0 12.1 12.2 12.3 12.4 Cite error: Invalid <ref> tag; no text was provided for refs named feis
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  14. ↑ 14.0 14.1 14.2 Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  15. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  16. ↑ 16.0 16.1 Cite error: Invalid <ref> tag; no text was provided for refs named tm2006
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  19. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  20. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named 2008serviceplan
  21. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  22. ↑ 22.0 22.1 Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  23. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named march132022
  24. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named 88bf
  25. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named draftmap
  26. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  27. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nov2022changes
  28. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named nov2022map
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