Silver Line (MBTA)


The Silver Line is a system of bus routes in Boston and Chelsea, Massachusetts, operated by the Massachusetts Bay Transportation Authority. It is operated as part of the MBTA bus system, but branded as bus rapid transit as part of the MBTA subway system. Six routes are operated as part of two disconnected corridors., weekday ridership on the Silver Line was 39,000.
The four Waterfront routes operate out of an underground terminal at and run through the South Boston Piers Transitway – a dedicated bus tunnel through the Seaport District with stations at and. At, they fan out on the surface: the SL1 to Logan International Airport, the SL2 to Design Center, and the SL3 to via East Boston. An additional short turn route, SLW, runs only at peak hours between South Station and Silver Line Way. The Waterfront routes use articulated dual-mode buses that operate as electric trolleybuses in the Transitway and conventional diesel buses on the surface. Two routes operate on Washington Street between Nubian station and Downtown Boston. The SL5 terminates at and the SL4 on the surface at. The Washington Street routes use articulated diesel hybrid buses.
The Washington Street corridor was built to replace the Washington Street Elevated, which was used by the Orange Line rapid transit line until 1987. Initial plans called for a light rail branch of the Green Line, but trolleybuses and later CNG buses were substituted. Planning began in 1987 for mass transit to serve the growing Seaport; a new transit tunnel called the South Boston Piers Transitway was chosen in 1989. It was to run from to World Trade Center via and South Station, though the Boylston–South Station section was later deferred as a separate phase. In 1999, the MBTA designated the Washington Street and Transitway projects as the Silver Line, and planned for the Boylston tunnel extension to include a portal to Washington Street for through-running. Service improvements on Washington Street began in 2001. After years of delays, service through the $624 million Transitway began on December 17, 2004.
The connecting tunnel was cancelled in 2010 due to rising costs; a surface route was introduced the previous year. The original SL3 route to was discontinued on March 20, 2009. A separate SL3 route to Chelsea – originally planned as part of the cancelled Urban Ring Project – began service on April 21, 2018. Several other Silver Line extensions have been proposed, as has a conversion of the Washington Street corridor to light rail, but most have not been pursued. The Silver Line has been the target of criticism by riders and transportation planners. Much of the system is missing BRT Standard features such as enforced dedicated lanes, off-vehicle fare collection, sheltered stations, and transit signal priority.

Routes

Waterfront: SL1, SL2, SL3

Three Silver Line services operate from in a dedicated tunnel, the South Boston Piers Transitway, serving the underground and stations in the Seaport District then splitting at the surface station:
During rush hours, additional short turns are run between South Station and Silver Line Way to increase frequency in the Transitway.
Route SL2 runs on Northern Avenue, then on a one-way loop on Drydock Avenue and Black Falcon Avenue with multiple stops serving the Innovation and Design Building and the Flynn Cruiseport Boston. Buses run clockwise around the loop, with a layover at Design Center Place in the morning and 23 Dry Dock Avenue in the afternoon. From Silver Line Way, route SL1 and SL3 buses loop backwards on Haul Road, then cross under Boston Harbor in the Ted Williams Tunnel to East Boston. Route SL1 loops around the Logan International Airport terminals, with stops at the arrivals level of each terminal. Route SL3 serves station, follows the Coughlin Bypass Road, and crosses Chelsea Creek on the Chelsea Street Bridge. It then follows a dedicated busway to, with intermediate stops at,, and. The three Transitway stops are full rapid transit stations; the Chelsea busway stations have large concrete shelters, while most other surface stops have small shelters.
The Waterfront routes have regular rapid transit fares. Passengers enter through faregates at the three Transitway stations, and pay at the on-board farebox at all other stops. Fares are free when boarding at the Logan Airport stops. Transfer is possible to the Red Line within fare control at South Station. Normal transfers to other routes are available with a CharlieCard; transfers to/from the Blue Line at Airport and the Washington Street routes are available with a CharlieTicket.
The Waterfront routes primarily use articulated buses with three doors, which provide greater capacity than standard transit buses. The dual-mode buses operate as electric trolleybuses between South Station and Silver Line Way, and as conventional diesel buses on the surface branches. The buses are low-floor and fully accessible, with kneeling bus technology and a wheelchair ramp at the front door. The 32 dual-mode buses, built by Neoplan USA, were delivered in 2004–05 and overhauled from 2014 to 2018. Eight of the buses were funded by Massport and include luggage racks for airport passengers. All Silver Line buses are maintained at Southampton Street Garage.
The existing dual-mode service pattern requires difficult-to-maintain dual-mode buses, and buses must make a time-consuming switch between modes at Silver Line Way. Additionally, the overhead lines in the Transitway are difficult to maintain. The MBTA has obtained several buses to test alternate options for Waterfront service. A single New Flyer diesel hybrid bus with extended battery range – sufficient to run through the Transitway on battery power – was obtained as an option on a separate order; it entered testing in September 2018 and revenue service in December. If that bus is deemed successful, the MBTA could order up to 45 similar buses. On July 31, 2019, the MBTA began using five New Flyer battery electric buses on both Waterfront and Washington Street routes.

Station listing

Former stops

Washington Street: SL4 and SL5

Two Silver Line routes run between Nubian station and Downtown Boston along Washington Street:
These two routes share most of their routing on Washington Street between Nubian Square and, with dedicated lanes for most of the corridor and eight intermediate stops. North of Kneeland Street, the routes run on separate one-way loops. The SL5 runs north on Washington Street to Template Place to a surface stop at. It returns south on Surface Road and Kneeland Street. Most stops have a canopy shelter with seating, maps, and a real-time arrival information display.
The two routes have the same fare as local bus services, with normal transfers with a CharlieCard. In recognition of their role as replacement for the Orange Line, transfers are also available with a paper CharlieTicket. This was inherited from the previous route 49 bus, which had free transfers to and from the Orange Line only at.
The Washington Street routes use diesel hybrid articulated buses with three doors. The buses are low-floor and fully accessible, with kneeling bus technology and a wheelchair ramp at the front door. The routes use 21 New Flyer buses delivered in 2016–17, which replaced the original compressed natural gas buses, plus three similar hybrid buses delivered in 2010. All Silver Line buses are maintained at Southampton Street Garage.

Station listing

History

Washington Street development

The 1947 state act that created the Metropolitan Transit Authority from the Boston Elevated Railway established four immediate projects for the new agency: extension of rapid transit to, expansion of the Tremont Street Subway to four tracks, replacement of the existing elevated lines with subways, and an extension of the Cambridge-Dorchester Line northwest from. In 1948, the legislature authorized the city to issue $19 million in bonds to construct an extension of the Washington Street Tunnel under Shawmut Street, connecting with the existing elevated south of Dudley Square. Although none of the proposals were built immediately, it established a precedent of replacing the elevated lines. In 1972, protests led to cancellation of the planned Southwest Expressway. Instead, the alignment was used for a combined corridor for intercity rail, commuter rail, and the Orange Line – replacing the Washington Street Elevated of the latter.
The northern part of the new corridor was about west of Washington Street, so the MBTA began planning in 1978 for a replacement service between Dudley Square and Downtown Boston. By 1985, the MBTA favored bus or light rail service on Washington Street; the latter would have been a branch of the Green Line, operated through the 1962-abandoned southern branch. The Orange Line was rerouted in 1987; that year, the Urban Mass Transportation Administration rejected the MBTA's funding request to create a light rail line on the corridor. Local opinion favored the temporary retention of the northern portion of the Elevated until a permanent replacement could be built. However, the MBTA closed the Elevated and instead upgraded the route 49 bus from a feeder route to a more frequent trunk route.
In 1989, the MBTA announced that trolleybuses would be used on Washington Street, operating on 4-minute headways at peak hours. By 1990, the MBTA expected service to begin in 1993, with an underground connection to Boylston station and the proposed South Boston Piers tunnel in a future phase. After several more years of studies, the MBTA decided in 1996–97 to build the route as a bus rapid transit line using compressed natural gas buses to avoid the visual impact of overhead wires. Environmental documentation was filed in 1998, and construction began in 2001. The project cost $27.3 million, with major elements including $10.9 million for the 17 new buses, $10.9 million for road work, and $2.6 million for shelters. Planning and construction were combined with a necessary repaving of Washington Street, reducing costs. Intended for the route to equal the service quality of light rail, the MBTA branded it as the "Silver Line" and designated it equally to the existing MBTA subway lines on maps.
The Silver Line followed largely the same route between Dudley Square and Downtown Boston as route 49; the primary change was the consolidation of stops. Although the MBTA considered other stop locations, most of the final stops were at existing route 49 stops. The conversion to the Silver Line occurred in several steps. In December 2001, the MBTA opened a contraflow bus-only lane on Washington Street between Marginal Street and East Berkeley Street, allowing southbound buses to use Washington Street. This eliminated a longer outbound routing via Surface Road, and allowed an extension to a new downtown terminal at Temple Place. Service frequency was also increased at that time. On July 20, 2002, new Silver Line-branded CNG buses began operation – the first low-floor buses to operate in Boston – and the 20 stops were reduced to 11. In November 2002, a twelfth stop at was restored. The were replaced by buses in August 2003, and service frequency was again increased. On January 31, 2005, the route was the first MBTA bus route to receive new automated fare collection equipment. By 2005, ridership was double that of route 49, but early decreases in travel time were cancelled out by longer dwell times. In February 2020, the MBTA agreed to change the name of Dudley Square station to Nubian, following the December 2019 renaming of the square itself. The station renaming took effect in June 2020.

Waterfront development

For most of the 20th century, the Seaport District was an industrial area occupied by rail yards and wharves; the South Boston Army Base and South Boston Naval Annex were served by short bus routes that connected with the Red Line at. After the military bases closed in 1974 and the rail yards were no longer needed, the Seaport was designated for commercial development, with accompanying need for expanded transit. The MBTA conducted a feasibility study in 1987 and released a Draft Environmental Impact Report in 1989. The DEIR selected an underground "transitway" over alternatives including a surface light rail line, an elevated people mover, a commuter rail shuttle, and a relocation of the Red Line. The transitway was to use trolleybuses or dual-mode buses, rather than the light rail and people mover possibilities considered; it would connect with the Red Line at South Station, the Orange Line at, and the Green Line at. Costs could be reduced by combining its construction with the upcoming Central Artery/Tunnel Project. Service from the transitway could be extended to serve Logan International Airport, to form part of a proposed circumferential transit line, and to connect with the planned Washington Street service.
The South Boston Piers Transitway alignment was refined by the Draft Environmental Impact Statement in 1992. The Final Environmental Impact Statement/Final Environmental Impact Report was approved in December 1993. The South Station–Seaport segment was to open in 2000, with the Boylston segment opening in 2006. The stations at,, South Station, Chinatown, and Boylston would each have island platforms, and the tunnel could be later converted to light rail as a Green Line branch if needed. Daily ridership was expected to be between 24,200 and 37,200 for the first phase, and between 34,800 and 69,800 for the full build, depending on the rate of commercial development. In November 1994, the Federal Transit Administration agreed to fund $331 million of the $413 million first phase, which was to be completed in December 2000. The environmental approval process was completed in April 1995.
In 1997, with construction on the transitway already under way, Massport cancelled a planned people mover at Logan Airport in favor of dual-mode buses operating from the transitway and through the newly-opened Ted Williams Tunnel. A connector road was to extend the transitway from D Street to Haul Road. These changes were approved in February 1998. In May 1999, the MBTA indicated plans to through-route the transitway with the planned Washington Street service as the "Silver Line", with the Washington Street service as Phase I, the initial Transitway build as Phase II, and the Boylston extension as [|Phase III].
Initial construction of the Transitway was divided into four main sections: South Station and turnaround loop plus of tunnel, Russia Wharf and Fort Point Channel tunnel, Courthouse station plus of tunnel, and World Trade Center station plus of tunnel. The Russia Wharf section, using the New Austrian tunnelling method, was the most technically complex; ground freezing was required to support the historic Russia Wharf Buildings. It also included an immersed tube under the Fort Point Channel. The discovery of a massive boulder under the Channel delayed the project by a year. By late 2000, the project was three years behind schedule and almost $200 million over budget; the MBTA diverted $150 million of other federal grants and $50 million of contingency funds to cover the costs. The Transitway was ultimately completed in 2004, with a final cost to the MBTA of $624 million. Although some projects like the new federal courthouse and the new convention center had been built, commercial development had lagged early plans; the MBTA adjusted its 2006 daily ridership projections from 45,000 to 14,000 shortly before opening.
The Transitway opened on December 17, 2004, with the Waterfront shuttle route between South Station and Silver Line operated by a mix of new dual-mode buses and trolleybuses borrowed from the Harvard-based routes. It was only the third "urban trolleybus subway" in the world, after the Harvard bus tunnel and the Downtown Seattle Transit Tunnel. On December 31, 2004, service began on routes SL2 to the Boston Marine Industrial Park and route SL3 to. Two days later, a Sunday-only Silver Line Way-Logan Airport shuttle service called "Silver Line Connector" began operation to meet a legal commitment to begin airport service that month. The existing surface routes in the Seaport were discontinued or rerouted in January. Due to a lack of available dual-mode buses, CNG shuttles operated on the surface sections of the SL2 and SL3 routes from January 5 to March 14, 2005. On March 26, the two routes were combined on nights and weekends. On April 9, weekday SL3 service was extended from City Point to a loop on Farragut Road.
On May 28, 2005, the two routes were combined at all times as the SL2/3. This freed up buses for SL1 service to Logan Airport, which began on June 1. As more buses entered service, the SL2 and SL3 were resplit into separate routes on August 20, and the Farragut Road loop was cut due to noise complaints from residents. On October 15, City Point service was cut on nights and weekends. An SL4 route from South Station to Andrew station via the Boston Convention and Exhibition Center and D Street was planned to open in 2005, but was never implemented. As enough dual-mode buses became available, the borrewed 40-foot trolleybuses were phased out; they were last used on February 12, 2006. By 2006, the Silver Line had doubled transit ridership to the Seaport, and increased transit ridership to Logan by 24%. The SL3 service was never successful, as the parallel route had a more direct routing, lower fares, and better downtown connections. By 2008, the SL3 averaged less than one passenger per trip on the segment not shared with the SL2. On March 20, 2009, SL3 service was cut, with SL2 service increased in its stead. In October 2009, the SL2 terminus was renamed "Design Center" with no changes in service.
Until 2019, SL2 buses served the Design Center loop in two different patterns. Before noon, outbound buses proceeded around the whole loop, laid over at the Design Center stop, then proceeded inbound. After noon, outbound buses made a shorter western loop, laid over at Design Center, then proceeded inbound via the main loop. On December 22, 2019, the route was changed so that buses proceeded around the whole loop before the layover at all times. On March 15, 2020, afternoon service began laying over at 23 Dry Dock Avenue before making the loop.

Phase III plans

The Boylston extension, as planned in 1993, would have run west from South Station under Essex Street, Avenue de Lafayette, and Avery Street. The Chinatown platform would have been under Hayward Place east of Washington Street, and the Boylston platform under the existing Green Line station, with a turnaround loop under Boylston Street and the Central Burying Ground. The 1999 decision to combine the Waterfront and Washington Street projects as the Silver Line resulted in the addition of a southern segment, likely using the same abandoned streetcar tunnel as had been proposed a decade before. A new underground station would have been built under Tremont Street, connecting to the existing station, with a portal to Washington Street just north of Oak Street. In April 2000, the MBTA adjusted the alignment to use Boylston Street instead of Avenue de Lafayette and Avery Street, with side platforms at the stations. The new alignment would conflict less with development, provide a straighter route, avoid the need for a pedestrian crossing and a lengthy pedestrian tunnel at Chinatown, and move the Boylston loop away from the Burying Ground.
In January 2002, the MBTA began seeking federal funding for 60% of the project cost. The FTA approved the project for further planning that July. The Boston Regional Metropolitan Planning Organization rated the project as "high priority" in its May 2003 Program for Mass Transportation, citing its high estimated ridership, low operating cost and service to environmental justice neighborhoods. In 2003, the preferred portal location was moved slightly north to avoid the need to demolish the YMCA building, and the NEMC station was removed. A proposal to consolidate the Chinatown and Boylsyon stations was rejected due to steep grades required and lack of cost savings, and a proposal to eliminate the loop was rejected because of the need to short turn most buses at Boylston. Further changes in 2003–04 were caused by the need to add a second platform at Boylston due to high expected ridership, and to reduce impacts to the historic Boston Common from the loop. One alternative placed the station and loop under Tremont Street south of Boylston Street; the other enlarged them under the Common.
Continued concerns about the Common, concerns from Bay Village residents about impacts to Eliot Norton Park, and desires to add Back Bay service resulted in further changes in 2004–05. The platforms at Boylston were to be aligned east–west under Boylston Street west of Tremont Street, with the loop further to the west at Charles Street. New portal alignments were considered, including one on Columbus Avenue to the southwest. Capital cost was originally estimated at $768–812 million depending on the portal location; completion was moved from 2010 to 2013. Daily ridership for the completed Silver Line system was estimated to reach 160,000 by 2025. In August 2005, the MBTA put the Phase III project "on hold" in order to build community consensus on a locally preferred routing.
In February 2006, State Transportation Secretary John Cogliano proposed a $94 million plan that would eliminate most of the tunneling and cost of the original proposal while still connecting the two phases of the service. Under Cogliano's plan, the Silver Line would run on the surface via Kneeland Street and Surface Road to a new tunnel portal on Essex Street near South Station. A fare-controlled shelter would be added at Downtown Crossing for routes still terminating there. The plan also included expansion of surface Silver Line service, with a new branch running from Copley Square into the Essex Street portal to provide a one-seat ride from the Back Bay area. The southern branch would be extended from Dudley to the Red Line stations at via Blue Hill Avenue and via Washington Street The plan was popular with Bay Village residents who had been worried about the full-length tunnel, but attracted criticism because it would not substantially speed travel times to downtown.
for route SL4
A revised tunnel plan was put forward in March 2006, with support from most transportation leaders including Cogliano. The plan involved a variation of the Charles Street tunnel alignment, with the portal moved southwest onto Tremont Street near Marginal Road. This "Charles Street Modified" alignment remained the preferred alternative for the remainder of the project. Contra-flow dedicated bus lanes, already in place on Washington Street, were to be extended onto Marginal Road and Herald Street to allow buses to reach the portal from the surface section. On December 12, 2006, the FTA approved the project to re-enter its funding process. By mid-2008, environmental review and preliminary engineering were expected to be completed by the end of the year, with federal funding sought in 2010 and construction lasting from 2011 to a 2016 opening.
However, the estimated price of the tunnel plan, dubbed the "Little Dig", had risen to $2.1 billion by May 2009. The FTA assigned it a Medium Low overall rating, making it ineligible to move into the final design phase for federal New Starts funding. The Boston Region Metropolitan Planning Organization removed Phase III from the list of recommended projects in its long range plan because of funding limitations. Concluding that it could not successfully compete for more than one New Starts grant, the Massachusetts Department of Transportation informed the FTA that it was no longer seeking New Starts money for Phase III. All New Starts funds available would instead be directed to the legally mandated Green Line Extension project. In a July 2010 report, the MBTA declared that Phase III was on indefinite hold and no further funds would be spent on the project.
A partial solution that did not require a new tunnel opened on October 13, 2009, after expedited construction using federal stimulus money. The new route, SL4, covered much of the same alignment as the proposed Phase III, with a dedicated bus lane on Essex Street and a South Station stop west of Atlantic Avenue. The existing Downtown Crossing-Dudley route was renamed SL5 at that time.

Extension to Chelsea

The Urban Ring Project was a planned circumferential surface BRT line. It would have shared the Silver Line berths at Dudley Square, and have had a surface stop outside World Trade Center station, but otherwise would have been separate from the Silver Line. The project was cancelled in 2010 due to high cost, but planning for several smaller sections continued. The Chelsea–South Boston section was given high priority because Chelsea was densely populated yet underserved by transit. MassDOT had also purchased the Grand Junction Branch – including abandoned sections in Chelsea and East Boston – from CSX Transportation in 2009, meaning that a potential right-of-way was available. A state study in 2011 analyzed potential Chelsea services, including a Silver Line branch or improvements to the route bus.
In 2013, MassDOT began public planning of the Silver Line Gateway. In addition to serving Chelsea, the proposed line would provide Blue Line riders a direct connection to the Seaport and South Station. Three possible alignments were studied. All used the Transitway and the Ted Williams Tunnel to reach station, then the 2012-opened Coughlin Bypass Road to the Chelsea Street Bridge. The first alignment was to run entirely on a new busway on the Grand Junction right-of-way in Chelsea, with stops at,, at the Chelsea commuter rail station, and Mystic Mall. The second alignment option would have followed the Grand Junction to just short of the commuter rail station, then diverge onto surface roads to Bellingham Square, while the third alignment would have run entirely on surface streets, serving two stops on Central Avenue and four stops along a loop serving Chelsea station and the MGH Chelsea healthcare center.
In September 2013, the MBTA indicated that it would pursue the first alternative, with an estimated daily ridership of 8,700, despite potential issues with bridge clearances and rebuilding the commuter rail station. On October 30, 2013, MassDOT announced $82.5 million in state funding for the new Silver Line route to Chelsea, with completion expected in 2015. The announcement also included the relocation of the commuter rail station to and a $3 million, multi-use path from Eastern Avenue to Washington Street. MassDOT awarded a $33.8 construction contract for the first phase of the project on September 17, 2014. That phase included the -long busway, the four Silver Line stations, replacement of the Washington Street bridge, and the Chelsea Greenway.
Silver Line service to Chelsea began on April 21, 2018. By October, daily ridership reached 6,200. The second phase of the project includes the relocated Chelsea commuter rail station plus transit signal priority upgrades for the SL3. Construction began in August 2019, with completion planned for late 2021.

Proposed future corridors

Several other bus rapid transit and express bus projects have been proposed in Boston, many under the Silver Line banner. The first two phases of the 2010-cancelled Urban Ring Project were to be BRT, with light or heavy rail for the final phase. The Urban Ring was considered a separate project, although it would have shared the SL1 route between Silver Line Way and Logan Airport.
A number of Silver Line expansion corridors were considered in the 2003 Program for Mass Transportation ; most were given brief consideration but not acted upon. One, a BRT express overlay for the route 28 bus, was revived in 2006 as part of the Phase III plans. In 2009, the state proposed to replace the 28 bus entirely with a BRT route called 28X, including the installation of dedicated bus lanes, bus signal priority, and on-platform fare collection. However, the proposal was withdrawn in 2010 due to local opposition, both to the design of the route and because the plan had been made without consulting local officials. In 2012, the Roxbury-Dorcester-Mattapan Transit Needs Study recommended the 28X bus to be implemented with no new infrastructure as an express bus adding additional trips to the corridor.
Several other corridors were considered in the 2003 PMT. These included a Dudley–Ashmont route replacing the route 23 bus, as well as a new BRT tunnel to Kenmore with surface branches to the Longwood Medical Area via Brookline Avenue and Allston via Commonwealth Avenue, the Mass Pike, and Cambridge Street. The City of Boston proposed an alternate western Silver Line branch using buses along the Mass Pike without a new tunnel, similar to existing express buses.
The 2003 PMT included the possibility of converting the Washington Street section of the Silver Line to light rail using the abandoned southern section of the Tremont Street Subway. The project was estimated to cost $374 million; ridership was estimated to be 34,000 daily riders almost entirely diverted from the Silver Line service. The project was given low priority, with the Phase III tunnel recommended instead. In 2012, the Roxbury–Dorcester–Mattapan Transit Needs Study recommended the conversion to light rail as a long-term project, with the additional possibility of extending the line down Blue Hill Avenue to Mattapan along the route 28 bus corridor.
In March 2019, state and local officials indicated plans to extend service from Chelsea on two routes to Kendall Square and to North Station, both via Sullivan Square. The routes would primarily use dedicated busways and bus lanes, although they may not be part of the Silver Line brand. In February 2020, the cities of Everett and Somerville submitted an application for $425,000 in Massachusetts Gaming Commission funds to design the extension.

Service

Frequency and ridership

The Silver Line routes are among the most frequent MBTA bus routes. All routes run at least every 15 minutes during all service hours, except for late evening service on the SL4. At peak hours, combined frequency on the trunk sections is about 30 buses per hour in each direction in the Transitway, and 12–14 buses per hour on Washington Street. The routes have high ridership and low costs per rider compared to other bus routes in the MBTA system. In 2012, three routes were the only MBTA bus routes to show a profit; the median net cost on all MBTA bus routes was $2.13 per passenger. In 2019, combined weekday ridership on Silver Line routes was 39,000.
In addition to the public route name, the Silver Line and crosstown routes have internal route numbers in the 700 series. The SL5 is designated 749 after the 49 bus it replaced, while the other routes have similar numbers.
Route#Rush hour headwaysMidday headwaysWeekend headwaysWeekday ridership
SL17418–10 minutes8 minutes8–12 minutes8,132
SL27425 minutes10 minutes15 minutes6,420
SL374310–12 minutes15 minutes12–15 minutes6,200
SLW74610 minutes——
SL47519 minutes15 minutes15 minutes5,800
SL57498 minutes10 minutes7–8 minutes10,300

Criticism

Mode choice

When the Washington Street Elevated was replaced with the Southwest Corridor, MBTA promised "equal or better" surface transit on Washington Street to replace the Elevated. Riders supported light rail; the decision to instead run buses was viewed as a broken promise and intentional disinvestment. The Silver Line is substantially slower than the Elevated, with travel time from Nubian Square to Downtown Boston increased from 8 minutes to 20 minutes. The Washington Street corridor population is poorer and less educated than the Southwest Corridor, and has a larger Black population; advocates including state representative Gloria Fox have called the poor service on the Silver Line "discrimination against people of color". Because of the poor service and the perception that the bus service was an inferior substitute for the originally-planned light rail line, advocates nicknamed the Washington Street service as the "Silver Lie".
Two theoretical advantages of BRT compared to light rail are low cost and speedy implementation. However, Silver Line service did not begin Washington Street until 15 years after the Elevated came down; the first phase of the Transitway opened 15 years after the DEIR, and the second phase was never completed. The Transitway was built at "enormous cost"; it was the most expensive single BRT project in the world by a 2007 report. Like the Downtown Seattle Transit Tunnel, the Transitway had comparable construction cost to light rail, but a lower level of service. At the time of its cancellation, Phase III was expected to cost $2.1 billion - more than three times that of the Transitway. Although transit ridership in the Seaport doubled after the introduction of the Silver Line, that growth is due partially to commercial development rather than the service quality.

BRT quality

Key features of bus rapid transit include dedicated lanes, frequent service, off-vehicle fare collection, sheltered stations, and intelligent transportation systems features such as transit signal priority. A 2011 study by the Institute for Transportation and Development Policy determined that the Silver Line was best classified as "Not BRT" because it lacked many of these BRT Standard features.
Off-board fare collection is only present at the three underground stops. A significant portion of delays on the surface sections are caused by long dwell times, as passengers only board through the front door to pay at the single farebox. On June 6, 2012, Massport began funding a three-month pilot of free fares from the five Logan Airport stops as an effort to decrease traffic congestion at the airport terminals. Within the first month, average dwell time dropped by 20 seconds per stop. Massport later extended the pilot until January 2013, then made free fares from Logan permanent. Stops on the Washington Street routes with more than fifteen passengers have an average dwell time of over one minute, which affects both running time and reliability. A two-week pilot program in 2017 tested all-door boarding on these routes, with free fares funded by a nonprofit. The pilot halved dwell times at busy stops, reduced overall average dwell time from 24 to 19 seconds, and increased reliability. All-door boarding will be permanently implemented on all routes in the early 2020s as part of the AFC 2.0 fare system.
The Washington Street routes have dedicated bus lanes between and, as well as on Essex Street. However, these lanes are not physically separated from general traffic lanes and are designated as right-turn lanes at many intersections. A lack of loading zones causes many vehicles to double-park in the bus lanes, and violations of the exclusive lanes are rarely prosecuted. In the most congested parts of the corridor – Nubian Square and Downtown Crossing – no dedicated lanes are present. Transit signal priority was only planned for four locations on Washington Street. Due to conflicts between the MBTA, the contractors, and the city, the TSP equipment was not activated until 2006. Due to the lack of BRT elements, running times on the corridor show significant variability. Peak-hour times were as much as 1.7 times that of uncontested periods in 2006, indicating that the limited BRT elements on Washington Street were ineffective at actually speeding travel during congested periods. Headway reliability is poor, largely due to operators failing to depart Nubian on time. Additional enforced downtown bus lanes, plus traffic restrictions on Temple Place and new loading zones in Chinatown, were added by the city in 2020.
Although the Transitway is a dedicated bus tunnel without interference from automobile traffic, Waterfront service is no faster than the on-street buses it replaced. The tunnel was built for a maximum speed of ; the narrow lanes without guided buses limit actual speeds to. Water leakage and poor drainage has damaged the concrete floor of the tunnel, leading to "poor ride quality". The switch between electric and diesel power at Silver Line Way also represents a "significant delay". Because the original Transitway design ended at D Street, buses must cross the street at a traffic light. A 2003 study indicated extending the Transitway tunnel under D Street for grade separation was feasible, with a cost around $75 million. The light has attracted criticism from riders due to the delays it causes. A 2013 study found a median delay of 1.5 minutes per round trip at the light. In early 2016, the Boston Transportation Department modified the traffic light to use a fixed cycle, rather than relying on the detection of buses to give a green light for the Transitway. However, the BTD's modifications did not modify the unusually-long 100-second cycle length nor actively prioritize buses, leading to criticism from transportation planners that the solution was inadequate. Proposed air rights development over the station is required not to preclude later grade separation of D Street. A gate and movable bollard near the light, which are used to prevent private vehicles from entering the Transitway, also cause delays to buses.
Although stop spacing varies widely between BRT systems, distances from to are typically recommended. Even after dropping half the stops, the Washington Street corridor averages only between stops, with several stop spacings as low as. The Washington Street stops were built with open canopies; protected shelters were not added until 2010. A small traditional glass shelter is available at Temple Place; Boylston, Chinatown, and Tufts Medical Center have no shelters at all. Silver Line Way and the SL2 surface stops have glass shelters or none at all; the SL3 surface stops have canopies without shelters.

Indirect routing

Because the Transitway was not originally designed for service to Logan Airport or Chelsea, it does not have a direct connection to the Ted Williams Tunnel. Outbound SL1 and SL3 buses must travel west on Haul Road from Silver Line to access an eastbound ramp west of B Street, then travel east on a frequently-congested section of I-90. Inbound buses must exit I-90 at B Street and travel east on Congress Street to reach Silver Line Way. An eastbound entrance ramp near Silver Line Way, normally restricted for use by Massachusetts State Police vehicles and MassDOT maintenance vehicles from an adjacent operations center, can shorten the outbound routing by about. MassDOT claims the ramp was not designed for buses, though Big Dig planner Fred Salvucci has claimed it was. Outbound buses were temporarily allowed to use the ramp in 2006 after the Big Dig ceiling collapse, when there was no regular eastbound traffic through the tunnel. The Urban Ring was also proposed to use the ramp. A 2010 study indicated that the ramp was safe for use by the Silver Line.
Transit advocates have since pushed to allow use of the ramp by Silver Line buses, though MassDOT claims the ramp is not safe to use when highway traffic is freely flowing. The MBTA hired a consultant in 2018 to study potential use of the ramp. In May 2019, MassDOT agreed to a limited test of ramp use, though advocates criticized MassDOT for limiting the test to only the evening peak hour, and only when highway speeds did not exceed. The three-day test in August 2019 resulting in average time savings of 3–8 minutes per bus, with significantly larger time savings at the most congested times. After these results, MassDOT agreed to make modifications to the ramp entrance to eventually allow use of the ramp whenever traffic speeds are below 30 mph.

Other issues

The SL3 route is subject to frequent delays due to the opening of the Chelsea Street Bridge – as many as ten times per day – for ships serving the upstream oil terminals. Each bridge opening causes a delay of up to 20 minutes, and the only alternate route involves a lengthy detour on Route 1A. Federal regulations give priority to marine traffic. In December 2018, MassDOT officials sought to create a six-month pilot program to reduce peak-hour openings of the bridge, as well as the nearby Meridian Street Bridge used by the busy and bus routes.
The CNG buses bought for the Washington Street service caused disruptive 35 Hz vibrations in nearby residential buildings. It took a year to retrofit the fleet with new mufflers; during that time, older buses which did not have that problem were used at night.