SLW (MBTA bus)

Silver Line

Company type	Public transit service
Industry	Public transportation
Founded	2001
Founder	Massachusetts Bay Transportation Authority (MBTA)
Headquarters	Boston, Massachusetts , United States
Area served	Boston and Chelsea, Massachusetts
Key people	Massachusetts Bay Transportation Authority (MBTA)
Products	Bus rapid transit service
Owner	Massachusetts Bay Transportation Authority (MBTA)
Parent	Massachusetts Bay Transportation Authority (MBTA)
Website	www.mbta.com/silver-line

The Silver Line constitutes a bus transit network serving Boston and Chelsea, Massachusetts, managed by the Massachusetts Bay Transportation Authority (MBTA). Although it forms part of the MBTA bus system, it is distinctly marketed as bus rapid transit (BRT) within the MBTA subway infrastructure. The system comprises six routes spread over two separate corridors. In 2023, its average weekday ridership reached approximately 27,000 passengers.

The four routes operating in the Waterfront area depart from an underground terminal at , utilizing the South Boston Piers Transitway—a dedicated bus tunnel featuring stations at and . At the surface station , the lines diverge: SL1 proceeds to Logan International Airport, SL2 serves Dry Dock Avenue, and SL3 travels to via East Boston. Additionally, the SLW provides peak-hour short-turn service between South Station and Silver Line Way. These Waterfront services primarily employ articulated diesel hybrid buses equipped with extended battery capabilities.

Two other routes run along Washington Street, connecting Nubian station in Roxbury with Downtown Boston. Route SL5 terminates at , while SL4 ends at . Both utilize articulated diesel hybrid buses.

The Washington Street corridor replaced the former Washington Street Elevated, which was part of the Orange Line until its closure in 1987. Initially, a branch of the Green Line light rail was considered for this corridor; however, trolleybuses and later compressed natural gas (CNG) buses were implemented instead. Transit planning for the Seaport district commenced in 1987, and by 1989, the South Boston Piers Transitway was chosen to connect to World Trade Center through and South Station, although the segment between Boylston and South Station was postponed. In 1999, MBTA consolidated these projects under the Silver Line name, including intentions for a tunnel extension from Boylston to Washington Street. Service enhancements on Washington Street started in 2001; 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 route (SL4) was launched in 2009. The initial SL3 route to ceased operations on March 20, 2009. A new SL3 service to Chelsea—originally part of the discontinued Urban Ring Project—was inaugurated on April 21, 2018, with future plans for extension to . Other suggested expansions for the Silver Line and conversion of Washington Street to light rail have largely not progressed.

Criticism has been directed at the Silver Line for lacking several fundamental BRT characteristics such as exclusive lanes, off-board fare collection systems, sheltered stations, and transit signal priority.

Waterfront: SL1, SL2, SL3

Operating from , three Silver Line routes utilize a dedicated tunnel known as the South Boston Piers Transitway, serving underground stations at and within the Seaport District. At the surface stop , these lines separate:

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

During peak periods, additional short-turn trips designated SLW operate between South Station and Silver Line Way to enhance service frequency on the Transitway.

Route SL2 travels along Northern Avenue before completing a one-way loop on Drydock and Black Falcon Avenues, servicing both the Raymond L. Flynn Marine Park and Flynn Cruiseport Boston. From Silver Line Way, buses on SL1 and SL3 reverse direction on Haul Road and then traverse beneath Boston Harbor via the Ted Williams Tunnel toward East Boston. The SL1 route circulates around terminals at Logan International Airport, stopping at arrivals levels. The SL3 line stops at station , follows Coughlin Bypass Road, crosses over Chelsea Creek via the Chelsea Street Bridge, then utilizes a dedicated busway to reach , making stops at , , and . Transitway stations are constructed as full rapid transit facilities; Chelsea busway stops feature substantial shelters; most other surface-level stops provide smaller shelter structures.

Standard rapid transit fares apply on Waterfront routes. Passengers enter through faregates located at Transitway stations but pay onboard when boarding at other stops. Boarding is free at Logan Airport stops. Transfers within fare control to the Red Line are available at South Station; transfers involving other routes require a CharlieCard. Transfers between Waterfront routes and the Blue Line or Washington Street services use a CharlieTicket.

The Waterfront fleet consists of articulated buses with three doors designed to offer higher capacity compared to standard length buses. These low-floor vehicles are fully accessible with kneeling capability and wheelchair ramps. The principal fleet includes 45 diesel hybrid buses featuring extended battery range that allows battery-only operation through the Transitway; these were delivered between 2022 and 2023. Additionally, a comparable hybrid model introduced in 2018 and five battery electric buses from 2019 are also in service. All Silver Line vehicles are housed at Southampton Street Garage.

Previously, Waterfront services operated with 32 dual-mode buses manufactured by Neoplan USA during 2004–05; these underwent overhauls from 2014 to 2018. These buses functioned as electric trolleybuses within the Transitway and switched to diesel mode on surface segments. Eight of these dual-mode vehicles were funded by Massport and equipped with luggage racks for airport travelers. However, maintaining this dual-mode fleet along with overhead wires proved costly and required time-consuming mode changes at Silver Line Way.

Between 2018 and 2019, MBTA trialed alternatives including New Flyer diesel hybrid buses with extended battery capacity entering service in late 2018. On July 31, 2019, five New Flyer battery electric buses were introduced across Waterfront and Washington Street routes. In November 2020, MBTA placed an order for an additional forty-five sixty-foot hybrid buses with extended battery range aimed at replacing the dual-mode fleet. The last dual-mode buses were retired in July 2023, marking an end to trolleybus operations in Boston.

Station directory

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Discontinued stops

Location	Station	Service lines				Inauguration date	Connections and remarks
		SL1	SL2	SL3	SLW
Financial District		●	●	●	●	December 17, 2004	: , , : Fairmount Line, Fall River/New Bedford Line, Framingham/Worcester Line, Franklin/Foxboro Line, Greenbush Line, Kingston Line, Needham Line, Providence/Stoughton Line, CapeFLYER (seasonal) : , () : Intercity buses at South Station Bus Terminal
Seaport District		●	●	●	●		MBTA bus:
		●	●	●	●
	●	●	●	●
East Boston		●				June 1, 2005	: Massport:
		●					: Massport:
		●					: Massport:
		●					: Massport:
		●					: Massport:
				●		rowspan=5 April 21, 2018   |   : : Massport:

Neighborhood	Station name	Served by line(s)	Start of service	End of service	Comments
South Boston	88 Black Falcon Avenue	SL2	December 31, 2004	April 2019	Closed temporarily in April 2019 for pier maintenance; permanently shut down March 13, 2022. The planned reopening on June 19, 2022 was cancelled.
	Black Falcon Avenue & Design Center Place	SL2		2014
	Summer Street & Powerhouse Street	SL3		March 20, 2009	Service ended due to insufficient ridership.
	East 1st Street & M Street	SL3			Service ended due to insufficient ridership.
	REDIRECT Template:Boston transportation system	SL3			Service ended due to insufficient ridership.
	Farragut Road	SL3	April 9, 2005	August 20, 2005	Route altered as a result of noise complaints.

Washington Street routes: SL4 and SL5

Two Silver Line services run along Washington Street connecting Nubian station in Roxbury with central Boston:

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

The majority of the corridor between Nubian Square and features shared dedicated bus lanes with eight stops in between. Beyond Kneeland Street, the SL4 and SL5 operate distinct one-way loops. The SL5 heads north on Washington Street up to Temple Place (located between and ), making a stop at , then proceeds southbound on Tremont Street with a stop at . Conversely, the SL4 travels north on Washington Street to Chinatown, then east along Essex Street—equipped with dedicated lanes—to a surface stop at , returning south via Surface Road and Kneeland Street. Most stations offer covered shelters furnished with seating, route maps, and real-time arrival information.

Fare for these lines matches local bus pricing—lower than rapid transit fares—and standard CharlieCard transfers apply. Given their role as substitutes for the Orange Line, paper CharlieTicket holders also receive transfers (normally unavailable), continuing the policy from former route 49 that provided free transfers to the Orange Line at .

Washington Street routes utilize 60-foot diesel hybrid articulated buses featuring three doors. These low-floor vehicles are fully accessible with kneeling capabilities and wheelchair ramps. The fleet includes 21 New Flyer buses delivered during 2016–17 (part of a larger order of 44 buses also serving routes and ), which replaced earlier compressed natural gas (CNG) models, along with three similar hybrids from 2010. All Silver Line vehicles are housed at Southampton Street Garage.

Station Overview

Area	Stop	Routes		Inauguration Date	Connections and Remarks
		SL4	SL5
Roxbury	REDIRECT Template:Boston transportation system	●	●	July 20, 2002	Template:Ric: Template:MBTA bus links
	REDIRECT Template:Boston transportation system	●	●		Template:Ric: Template:MBTA bus links
South End	REDIRECT Template:Boston transportation system	●	●		Template:Ric: Template:MBTA bus links
	REDIRECT Template:Boston transportation system	●	●		Template:Ric: Template:MBTA bus links
	REDIRECT Template:Boston transportation system	●	●	November 30, 2002	Template:Ric: Template:MBTA bus links
	REDIRECT Template:Boston transportation system	●	●	July 20, 2002	Template:Ric: Template:MBTA bus links

Area	Stop	SL4	SL5	Start Date	- South End, Boston || || align=center | ● || align=center | ● || July 20, 2002 || : |- South End, Boston || || align=center | ● || align=center | ● || July 20, 2002 || : |- South End, Boston || || align=center | ● || align=center | ● || July 20, 2002 || : |- Chinatown, Boston || || align=center | ● || align=center | ● || July 20, 2002 || : : |- Chinatown, Boston || || align=center | ● || align=center | ● || July 20, 2002 || : : |- Downtown Boston || || || align=center | ● || July 20, 2002 || : Green, Orange, Red lines : Park Street routes |- Downtown Boston || || || align=center | ● || July 20, 2002 || Green line Boylston |- Downtown Boston || || align=center  ●||   || October 13, 2009|| Amtrak (Acela, Lake Shore Limited, Northeast Regional) MBTA Commuter Rail (various lines) Red and Silver subway lines Bus connections Intercity buses at South Station Bus Terminal |- Chinatown, Boston|| Chinatown Gate|| align=center  ●|| || August 19, 2022|| Bus connections at Chinatown Gate | } Washington Street development The 1947 legislation that established the Metropolitan Transit Authority (MTA) as the successor to the Boston Elevated Railway outlined four key initiatives: extending rapid transit service to , expanding the Tremont Street Subway to a four-track configuration, replacing the elevated lines (Charlestown Elevated, Causeway Street Elevated, and Washington Street Elevated) with underground subways, and extending the Cambridge–Dorchester line northwest from . In 1948, the city received authorization to issue $19 million in bonds for constructing an extension of the Washington Street Tunnel beneath Shawmut Street, linking to the elevated line south of Dudley Square. Although this project was not immediately realized, it set a precedent for substituting elevated lines with subways. In 1972, public opposition halted plans for the Southwest Expressway, leading to the corridor's conversion into a route for intercity rail, commuter rail, and the Orange Line, which replaced the Washington Street Elevated. Since the northern corridor lay approximately west of Washington Street, by 1978 the MBTA—successor to MTA since 1964—proposed replacement transit options connecting Dudley Square and Downtown Boston. By 1985, preference was given to either bus or light rail service along Washington Street; a light rail option would have extended a Green Line branch through the disused Pleasant Street Portal. The Orange Line was rerouted in 1987; however, funding requests for a light rail extension were denied by the Urban Mass Transportation Administration. While local sentiment favored maintaining a portion of the Elevated until a replacement was ready, the MBTA ultimately closed it and enhanced route 49 bus service with increased frequency. In 1989, MBTA announced plans to introduce trolleybuses on Washington Street with peak intervals of four minutes. By 1990, service commencement was projected for 1993 alongside future plans for underground connections. Following further evaluation, MBTA decided between 1996 and 1997 to develop a bus rapid transit corridor employing compressed natural gas buses to avoid installing overhead wires. Environmental reviews were submitted in 1998, and construction began in 2001. The $27.3 million initiative included $10.9 million allocated for acquiring 17 new buses, $10.9 million dedicated to roadway improvements, and $2.6 million for passenger shelters. Coordinating construction with street repaving helped contain costs. The service was branded as the "Silver Line" starting in 1996 and was depicted on maps alongside existing subway lines. The Silver Line primarily traced route 49 between Dudley Square and Downtown Boston, consolidating stops mainly at existing locations. Implementation occurred in stages: in December 2001, a contraflow bus lane was introduced on Washington Street permitting southbound buses direct routing and extending service to Temple Place downtown terminal; service frequency also increased. On July 20, 2002, new Silver Line-branded low-floor CNG buses entered operation while stops were reduced from twenty to eleven; later that year a twelfth stop at was reinstated. In August 2003, larger buses replaced previous models with increased service frequency. On January 31, 2005, it became the MBTA's first bus route equipped with automated fare collection. By 2005, ridership had doubled relative to route 49, although travel time gains were partially offset by longer boarding times. In February 2020, following the renaming of Dudley Square itself, MBTA agreed to rename Dudley Square station as Nubian; this change took effect in June 2020. In May 2022, MBTA proposed merging SL4 and SL5 into a single Nubian–South Station route to simplify downtown operations; this proposal remained in place as of November 2022 planning documents. Additionally, an SL4 stop at Chinatown Gate on Surface Artery was introduced on August 19, 2022 during Orange Line maintenance and retained permanently after that work concluded. Waterfront development Following the 1974 closure of military installations, the Seaport District evolved from a predominantly industrial zone—characterized by rail yards and military facilities—into a commercial development area, necessitating expanded transit options. The MBTA conducted a feasibility study in 1987 and released a Draft Environmental Impact Report (DEIR) in 1989, which supported an underground "transitway" utilizing trolleybuses or dual-mode buses. This transitway was designed to connect with the Red, Orange, and Green Lines within downtown Boston. The initiative was intended to coordinate with the Central Artery/Tunnel Project ("Big Dig") in order to optimize expenses and included envisioned extensions reaching Logan Airport as well as other transit corridors. A supplemental DEIR issued in 1992 refined the plan, leading to approval in 1993 for the South Boston Piers Transitway. This plan featured stations at , , South Station, Chinatown, and Boylston, with provisions for future light rail conversion. Initial ridership estimates ranged from 24,200 to 37,200 passengers per day, with projections rising to nearly 69,800 upon full implementation. In 1994, the Federal Transit Administration (FTA) committed $331 million—covering 80% of the $413 million first phase—with a completion target set for the year 2000. By 1997, Massport abandoned its earlier proposal for a Logan Airport people mover in favor of dual-mode bus operations through the transitway and Ted Williams Tunnel. The MBTA incorporated this transitway into the planned Washington Street service under the "Silver Line" brand, dividing construction into four principal segments with a combined budget exceeding $377 million. Technical difficulties arose during construction due to complex tunneling beneath historic buildings and an immersed tube crossing Fort Point Channel; progress was further delayed by an unexpected large boulder that caused a one-year setback. As of late 2000, the project lagged three years behind schedule and faced cost overruns nearing $200 million, prompting the MBTA to reassign federal grants along with contingency funds. When completed in 2004, total MBTA expenditures reached $624 million—partly attributable to higher costs associated with dual-mode buses. The Transitway commenced service amid slower-than-expected commercial growth in the area, which led to revised daily ridership forecasts dropping from an anticipated 45,000 to approximately 14,000 prior to opening. The Transitway officially began operations on December 17, 2004, launching Waterfront shuttle service between South Station and Silver Line using newly acquired dual-mode buses supplemented by leased 40-foot trolleybuses. Due to local parking concerns, initial routes were divided: one running to via D Street and another reaching City Point via E 1st Street. Although lettered route designations were initially considered by the MBTA, numeric identifiers were ultimately adopted. On December 31, 2004, service commenced on routes SL2 (Boston Marine Industrial Park) and SL3 (City Point), followed shortly by a Sunday-only airport shuttle known as the "Silver Line Connector" to satisfy legal obligations. By January 2005, surface routes were either rerouted or discontinued. Early that year, limited dual-mode bus availability necessitated temporary use of CNG shuttles on surface sections. On May 28, SL2 and SL3 merged during all operating hours as SL2/3 to allocate more buses for the SL1 airport route launched June 1. Subsequent modifications included separating routes again in August and shortening loops in response to noise complaints; notably, plans for an SL4 route never materialized. As more dual-mode buses became accessible, borrowed trolleybuses were phased out by February 2006. By that time, Silver Line service had doubled transit ridership in the Seaport area and increased Logan Airport transit usage by 24%. However, SL3 faced stiff competition from parallel route , which offered more direct travel paths and superior downtown connections; unique segments of SL3 averaged fewer than one passenger per trip by 2008. Consequently, SL3 service was discontinued on March 20, 2009, while SL2 frequency was increased; later that year in October, the SL2 terminus was renamed "Design Center" without altering service patterns. Until 2019, SL2 operated two loop patterns at Design Center depending on time of day; beginning December 22, 2019, all trips completed the entire loop before layover periods. Afternoon layover locations were adjusted again in March 2020 due to operational considerations. In January 2021, Massport approved a ground lease enabling air rights development above Silver Line Way station along with station improvements. On March 13, 2022, all SL2 buses began terminating at 23 Dry Dock Avenue following permanent closure of the nearby stop at 88 Black Falcon Avenue due to pier repairs. Redevelopment plans include upgrading the Black Falcon Avenue stop by 2025. The draft network plan released in May 2022 proposed routing SL1 and SL3 via D Street for direct access through Ted Williams Tunnel while dedicating SL2 and shuttle services exclusively to Silver Line Way. A revised proposal published in November 2022 maintained this configuration and called for increased SL2 frequency throughout all days of operation. Phase III proposals The 1993 plan for the Boylston extension envisioned a westward route from South Station beneath Essex Street and nearby corridors, featuring stations at Chinatown and Boylston. This included a turnaround loop beneath Boylston Street and the Central Burying Ground. In 1999, the decision to combine the Waterfront and Washington Street initiatives into the Silver Line introduced a southern segment likely utilizing a previously suggested abandoned streetcar tunnel. An underground station was planned to connect with New England Medical Center (NEMC), with a portal positioned near Oak Street. By 2000, the MBTA revised the route to follow Boylston Street instead of Avenue de Lafayette and Avery Street, aiming to enhance operational efficiency and reduce conflicts with development projects. In January 2002, the MBTA requested federal support covering 60% of project expenses; by July, the FTA had approved continued planning efforts. The Boston Regional Metropolitan Planning Organization designated the project as a "high priority" in 2003, citing anticipated high ridership, low operational costs, and service to environmental justice communities. That same year, the preferred portal location shifted northward to avoid demolishing a YMCA building, resulting in removal of the NEMC station from the plans. Suggestions to merge stations or remove the loop were dismissed due to financial and operational concerns. Further modifications during 2003–04 introduced an additional platform at Boylston to accommodate expected increases in ridership while lessening impacts on Boston Common. Community feedback between 2004 and 2005 prompted additional refinements: platforms at Boylston were realigned east–west beneath Boylston Street west of Tremont Street, and the loop was relocated westward to Charles Street; alternative portal sites including Columbus Avenue were evaluated. Initial capital cost estimates ranged from $768 million to $812 million depending on portal placement, with project completion pushed back from 2010 to 2013. Daily ridership projections anticipated approximately 160,000 passengers by 2025. In August 2005, MBTA paused Phase III development to foster community consensus regarding routing options. In February 2006, State Transportation Secretary John Cogliano proposed a $94 million scheme that would eliminate most tunneling expenses by routing Silver Line surface service along Kneeland Street and Surface Road to a new tunnel portal near South Station. This concept also involved expanding surface service with an additional branch from Copley Square into the Essex Street portal, enabling a one-seat ride from Back Bay, alongside southern extensions replacing existing bus routes. Although this plan was well received by Bay Village residents, it drew criticism for offering limited improvements in downtown travel times. A revised tunnel proposal introduced in March 2006 gained endorsement from transportation authorities; it featured a variation of the Charles Street tunnel alignment with the portal relocated southwest onto Tremont Street near Marginal Road. This "Charles Street Modified" alignment became the preferred option. Plans included dedicated contra-flow bus lanes on Washington Street extending onto Marginal Road and Herald Street to provide access to the portal. On December 12, 2006, the FTA approved re-entry into funding processes. By mid-2008, environmental assessments and preliminary engineering were anticipated to conclude by year-end; federal funding was sought in 2010 with construction slated for commencement in 2011 and an opening targeted for 2016. However, by May 2009 projected costs had escalated to $2.1 billion for the "Little Dig" tunnel plan. The FTA assigned it a Medium Low rating, which disqualified it from receiving final design phase funding through New Starts. Consequently, the Boston Region Metropolitan Planning Organization removed Phase III from its long-range strategy due to budgetary limitations. MassDOT redirected New Starts funds exclusively toward the Green Line Extension project. In July 2010, MBTA placed Phase III on indefinite hold without allocating further funding. As a partial alternative, on October 13, 2009, a new route opened using federal stimulus funds: route SL4 covered much of Phase III's proposed path with dedicated bus lanes along Essex Street and included a South Station stop west of Atlantic Avenue; meanwhile, the existing Downtown Crossing-Dudley route was redesignated as SL5. Extension toward Chelsea The Urban Ring Project was envisioned as a circumferential BRT route that would utilize Silver Line platforms at Dudley Square and feature a surface stop near World Trade Center station, though it would otherwise operate independently. Due to prohibitive expenses, the initiative was terminated in 2010; however, planning efforts for smaller segments persisted. Priority was given to the Chelsea–South Boston corridor because Chelsea had a high population density but limited transit options. In 2010, MassDOT acquired the Grand Junction Branch from CSX Transportation, securing a potential corridor for development. A 2011 state evaluation examined alternatives such as extending a Silver Line branch to Bellingham Square or the Chelsea commuter rail station, along with enhancements to bus route . In 2013, MassDOT launched public engagement for the Silver Line Gateway project aimed at connecting Chelsea and offering Blue Line users direct access to the Seaport District and South Station. Three route options were assessed, all utilizing the Transitway and Ted Williams Tunnel to reach station, followed by the Coughlin Bypass Road to the Chelsea Street Bridge. The first option proposed constructing a new busway along the Grand Junction right-of-way in Chelsea with stops at , , (Chelsea commuter rail), and Mystic Mall. The second option would divert onto surface streets near the commuter rail stop, while the third would operate entirely on surface roads serving Central Avenue and forming a loop around Chelsea station and MGH Chelsea healthcare facility. By September 2013, MBTA selected the first alternative despite difficulties related to bridge height clearances and reconstructing the commuter rail station, estimating daily ridership at approximately 8,700. On October 30 of that year, MassDOT announced an $82.5 million state investment for the Silver Line extension to Chelsea with an anticipated completion date in 2015. Plans included relocating the commuter rail station to (Mystic Mall) and allocating $3 million toward a multi-use pathway connecting Eastern Avenue to Washington Street. The Environmental Impact Report was released in March 2014. In September 2014, a $33.8 million construction contract was awarded for phase one, which encompassed building a 1.3-mile busway, four Silver Line stations, replacing the Washington Street bridge, and developing the Chelsea Greenway. Service on Silver Line route SL3 to Chelsea commenced on April 21, 2018. By October of that year, average daily ridership had reached about 6,200. The second phase involves relocating the Chelsea commuter rail station and implementing transit signal priority improvements for SL3. Construction began in August 2019; the new station opened on November 15, 2021. As of January 2024, plans by MBTA and Boston officials aim to redesign Day Square in East Boston by late that year. This project includes dedicated bus lanes on Chelsea Street and establishing a bus-only corridor through Day Square with a new station serving SL3 along with local bus routes. Sullivan Square extension In March 2019, authorities revealed intentions to expand service from on two lines reaching Kendall Square and North Station, both routed through Sullivan Square. These lines would primarily travel along dedicated busways and lanes, though it was undecided whether they would carry the Silver Line branding. By January 2021, the MBTA and MassDOT initiated the Silver Line Extension (SLX) study, evaluating route possibilities extending from Chelsea into Everett, Somerville, Cambridge, and Boston. By September 2021, six potential corridors had been outlined: to , Sullivan, , downtown Boston via Sullivan, Kendall Square via Sullivan, and Kendall Square via Wellington. Some of these could function as independent routes apart from SL3, terminating at Chelsea or Airport instead of South Station. By September 2022, proposed options included three SL3 extensions heading to Malden Center, Wellington, or Sullivan—each passing through Everett Square with varying levels of dedicated lane infrastructure. Four SL6 routes were suggested: 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 mainly operating within dedicated lanes. In March 2024, the preferred choice was an SL3 extension to Sullivan; however, planning for SL6 was postponed pending additional analysis of Sullivan Square, Rutherford Avenue, Gilmore Bridge, Kendall Square, and the overall bus network redesign. The proposed SL3 extension would travel off-street westward to 2nd Street, then continue mixed with traffic along 2nd Street and Spring Street (with potential future dedicated lanes), followed by dedicated lanes on Chelsea Street and most of Broadway. South of Sweetser Circle, a dedicated busway is planned along Lower Broadway. New stops would be added at 2nd Street (Boston Street and Spring Street), Broadway (Chelsea Street/Everett Square, Beacham Street, Horizon Way), and Sullivan Square station. This extension introduces round trips—approximately 80% within dedicated lanes—and is expected to boost SL3 ridership by 15,000 daily boardings by 2040. The capital expenditure is estimated at $95 million. In June 2024, the MBTA received a $22.4 million federal grant to rebuild Lower Broadway to accommodate existing bus routes alongside future Silver Line service. Other proposed corridors Multiple bus rapid transit (BRT) and express bus initiatives have been suggested in Boston, many under the Silver Line designation. The initial two phases of the discontinued 2010 Urban Ring Project were designed as BRT corridors, with light or heavy rail planned for its final phase. Although separate systems, it would have shared the SL1 route segment between Silver Line Way and Logan Airport. The 2003 Program for Mass Transportation (PMT) evaluated several Silver Line expansion corridors but dismissed most except for a BRT overlay on the route 28 bus connecting Ruggles station and Mattapan via Nubian. This concept was revived in 2006 under Phase III plans when the state proposed fully replacing route 28 with a BRT service named 28X in 2009. This service would have featured dedicated lanes, signal priority systems, and on-platform fare collection. However, due to local opposition concerning route design and insufficient community engagement, the proposal was withdrawn in 2010. Subsequent improvements on Blue Hill Avenue buses have proceeded without adopting Silver Line branding. Additional corridors considered in the 2003 PMT included a Dudley–Ashmont line intended to replace the route 23 bus, which was also revisited during Phase III planning but remained unconnected with the 28X proposal. There was also consideration of a new BRT tunnel leading to Kenmore, with surface branches extending to the Longwood Medical Area via Brookline Avenue and to Allston along Commonwealth Avenue, crossing the Mass Pike, and continuing on Cambridge Street. The City of Boston suggested an alternative western Silver Line branch utilizing buses along the Mass Pike without constructing new tunnels—similar in operation to existing express services. The PMT further explored converting the Washington Street Silver Line segment into light rail by repurposing the abandoned southern section of the Tremont Street subway. Estimated at $374 million with projected daily ridership of approximately 34,000—mostly transferring from Silver Line buses—this project was ranked lower in priority compared to Phase III tunnel developments. In 2012, the Roxbury–Dorchester–Mattapan Transit Needs Study recommended this light rail conversion as a long-term objective that could potentially extend down Blue Hill Avenue to Mattapan following the route 28 corridor. Frequency and ridership Silver Line routes are among the MBTA bus services with the highest frequency. Apart from the SLW shuttle, all lines operate at intervals of 15 minutes or less during most hours of operation, with somewhat reduced service during late evenings and weekends on the SL4. During peak periods, combined service frequency reaches approximately 30 buses per hour (headways of about 2 minutes) in each direction along the Transitway, and 12 buses per hour (5-minute intervals) on Washington Street. These routes attract substantial ridership and exhibit lower cost per passenger compared to many other MBTA bus lines. In 2012, only the SL1, SL5, and SLW routes were financially self-sustaining; at that time, the median net expense per rider for all MBTA bus routes stood at $2.13. By 2023, the combined weekday ridership for Silver Line services was recorded at 27,000 passengers. Silver Line and crosstown routes are internally designated with 700-series numbers; for instance, SL5 carries the number 749, a continuation from the former route 49 it replaced. Route # Rush hour headways Midday headways Weekend headways Weekday ridership (2018) SL1 741 10–12 minutes 12 minutes 8–12 minutes 8,132 SL2 742 5–8 minutes 15 minutes 15 minutes 6,420 SL3 743 10 minutes 15 minutes 12–15 minutes 6,200 SLW 746 8 minutes — Limited service (not available) SL4 751 12 minutes 14 minutes 16–17 minutes 5,800 SL5 749 8–9 minutes 8–11 minutes 8–9 minutes 10,300 Mode choice Following the removal of the Washington Street Elevated as part of the Southwest Corridor project, the MBTA committed to providing surface transit that was "equal or better" along Washington Street. Instead of implementing light rail preferred by many riders, bus service was introduced—a decision perceived as a broken promise and a form of disinvestment. Travel time on the Silver Line between Nubian Square and Downtown Boston increased from 8 to 20 minutes. Advocates—including state representative Gloria Fox—have criticized this corridor’s service as discriminatory toward its predominantly Black and lower-income communities. Due to poor performance and its reputation as an inadequate replacement for light rail, the Washington Street Silver Line has earned the nickname "Silver Lie." Although Bus Rapid Transit offers cost savings and quicker deployment compared to light rail, Silver Line service on Washington Street commenced 15 years after the Elevated’s removal; similarly, the Transitway opened 15 years after its Draft Environmental Impact Report was issued, with its second phase never realized. The Transitway’s construction incurred "enormous cost," making it the world’s most expensive single BRT project by 2007. Its building expenses rivaled those of light rail but delivered lower service levels. The cancellation of Phase III was projected to cost $2.1 billion—more than three times the Transitway’s expenditure. Increases in ridership in the Seaport following Silver Line introduction are attributed more to commercial development than improvements in service quality. BRT quality Essential components of bus rapid transit encompass dedicated busways, frequent scheduling, fare payment conducted off the vehicle, covered stations, and intelligent transportation systems like transit signal priority. According to a 2011 evaluation by the Institute for Transportation and Development Policy (ITDP), the Silver Line was designated as "Not BRT" due to the absence of numerous BRT Standard criteria. Off-vehicle fare payment is limited to the three underground stations. Surface-level delays frequently arise from extended dwell times because passengers board solely through the front door to pay at a single farebox. On June 6, 2012, Massport initiated a three-month pilot program offering free rides from Logan Airport stops to alleviate terminal congestion. This initiative reduced average dwell times by 20 seconds per stop during its first month. Following this success, Massport prolonged the pilot until January 2013 before making free fares permanent. At Washington Street stops with more than fifteen passengers, average dwell times surpass one minute, negatively affecting service dependability. A two-week 2017 pilot featuring all-door boarding combined with nonprofit-funded free fares cut dwell times at busy stops in half and enhanced reliability. Full implementation of all-door boarding across routes is planned for the 2020s as part of the AFC 2.0 fare system rollout. Dedicated bus lanes exist on Washington Street between and , as well as along Essex Street. However, these lanes lack physical separation and frequently serve as right-turn lanes at intersections. The absence of designated loading zones results in frequent double-parking within bus lanes, with enforcement being infrequent. No exclusive lanes are present in heavily congested areas such as Nubian Square and Downtown Crossing. Deployment of transit signal priority (TSP) was postponed until 2006 due to coordination challenges. Travel times vary widely; during peak hours in 2006, trips took up to 1.7 times longer than during uncongested periods, indicating that limited BRT features on Washington Street do not effectively reduce delays caused by congestion. Headway consistency is poor, primarily due to late departures at Nubian Square. In 2020, the city introduced enforced bus lanes downtown, imposed traffic restrictions on Temple Place, and established new loading zones in Chinatown. While the Transitway is a dedicated bus tunnel free from automobile traffic, Waterfront service operates at speeds comparable to the surface buses it replaced. Although the tunnel is designed for speeds up to , narrow lanes without guided bus technology restrict speeds to roughly . Water infiltration has damaged the concrete floor, leading to subpar ride comfort. The transition between electric and diesel propulsion at Silver Line Way results in notable delays. Since the Transitway terminates at D Street, buses must cross an intersection controlled by a traffic light, causing median delays of approximately 1.5 minutes per round trip according to a 2013 study. In early 2016, Boston Transportation Department altered this light to operate on a fixed cycle without implementing active bus prioritization or reducing its unusually long duration, drawing criticism from transit planners. Proposed air rights development above the station must accommodate future grade separation beneath D Street. Additionally, a gate and movable bollard near this intersection delay buses by restricting private vehicle access onto the Transitway. Typical spacing between BRT stops ranges from to ; however, even after reducing stop numbers by half, Washington Street averages only about between stops with some stops located as close as . Initial stations featured open canopies; enclosed shelters were added starting in 2010. Temple Place includes a small glass shelter; Boylston, Chinatown, and Tufts Medical Center stops lack any shelter structures entirely. Silver Line Way and SL2 surface stops have either glass shelters or none at all; SL3 surface stops provide canopies but no enclosed shelters. Indirect routing The Transitway was not initially planned to provide service to Logan Airport or Chelsea and does not have a direct link to the Ted Williams Tunnel. Outbound SL1 and SL3 buses head west along Haul Road from Silver Line Way to reach an eastbound ramp located just west of B Street, then continue eastbound on a heavily congested segment of I-90. For inbound trips, buses leave I-90 at B Street and proceed east on Congress Street before arriving at Silver Line Way. There is an eastbound entrance ramp near Silver Line Way, generally reserved for Massachusetts State Police and MassDOT maintenance vehicles, which could potentially reduce outbound travel distance by approximately . While MassDOT maintains that this ramp was not designed for bus traffic, Big Dig planner Fred Salvucci holds a contrary view. In fact, outbound buses made use of this ramp temporarily in 2006 following the Big Dig ceiling collapse. The Urban Ring initiative also suggested utilizing this ramp, and a 2010 study confirmed its safety for Silver Line operations. Transit advocates have long pushed to open this ramp for Silver Line buses under the slogan "Free the ramp," but MassDOT raises safety concerns related to merging with high-speed highway traffic. In 2018, the MBTA engaged a consultant to evaluate the feasibility of using the ramp. By May 2019, MassDOT authorized a limited trial during evening rush hours when highway speeds dropped below ; this restriction drew criticism from supporters. During a three-day test in August 2019, buses saved an average of 3–8 minutes per trip, with larger time reductions observed during peak congestion periods. Based on these findings, MassDOT planned adjustments to permit ramp access whenever traffic speeds fall under 30 mph. During a 2023 closure of the Sumner Tunnel, Silver Line buses were once again allowed to utilize this ramp. Other issues Delays on the SL3 route are common due to frequent openings of the Chelsea Street Bridge—up to ten times daily—to allow ships servicing upstream oil terminals passage. Each bridge opening can cause service interruptions lasting as long as 20 minutes. The only alternative route involves a significant detour via Route 1A. Federal regulations give priority to marine traffic in these situations. To address this, in December 2018 MassDOT proposed a six-month pilot program aimed at restricting bridge openings during peak travel hours; this plan also included nearby Meridian Street Bridge, which serves the heavily used 116 and 117 bus routes. The introduction of CNG buses on the Washington Street line generated disruptive vibrations at a frequency of 35 Hz in adjacent homes. It required a year to retrofit the fleet with improved mufflers; meanwhile, older buses without this issue were deployed during nighttime hours. See also Trolleybuses in Greater Boston External links MBTA: SL1, SL2, SL3, SL4, SL5 Silver Line Extension (SLX) Alternatives Analysis