The Silver Line is a bus route system in Boston and Chelsea, Massachusetts, operated by the Massachusetts Bay Transportation Authority (MBTA). It is operated as part of the MBTA bus system, but branded as bus rapid transit (BRT) as part of the MBTA subway system. Six routes are operated as part of two disconnected corridors. , weekday ridership on the Silver Line was 37,905
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 Dry Dock Avenue, 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 mostly articulated diesel hybrid buses with extended battery range. Two routes operate on Washington Street between Nubian station (at Nubian Square in Roxbury) 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 (Phase III) was cancelled in 2010 due to rising costs; a surface route (SL4) 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. Extension of the SL3 route to is planned. 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: SL1 Logan Airport–South Station SL2 Drydock–South Station SL3 Chelsea–South Station During rush hours, additional short turns (designated SLW) 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 Raymond L. Flynn Marine Park and the Flynn Cruiseport Boston. Buses run clockwise around the loop, with a layover at 23 Drydock Avenue. 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 (including two separate stops at lengthy Terminal B). 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 use articulated buses with three doors, which provide greater capacity than standard transit buses. The buses are low-floor and fully accessible, with kneeling bus technology and a wheelchair ramp at the front door. The main Waterfront fleet consists of 45 diesel hybrid buses with extended battery range – sufficient to run through the Transitway on battery power – which were delivered in 2022–2023. A similar extended-battery-range hybrid bus built in 2018 and five battery electric buses built in 2019 are also used. All Silver Line buses are maintained at Southampton Street Garage.
The Waterfront routes previously used dual-mode buses which operated as electric trolleybuses between South Station and Silver Line Way, and as conventional diesel buses on the surface branches. 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 included luggage racks for airport passengers. The dual-mode buses (and overhead lines in the Transitway) proved difficult to maintain and required a time-consuming switch between modes at Silver Line Way. In 2018–19, the MBTA obtained several buses to test alternate options for Waterfront service. A single New Flyer diesel hybrid bus with extended battery range was obtained as an option on a separate order; it entered testing in September 2018 and revenue service in December. On July 31, 2019, the MBTA began using five New Flyer battery electric buses on both Waterfront and Washington Street routes. In November 2020, the MBTA exercised a contract option for 45 additional 60-foot hybrid buses with extended battery range similar to the 2018 test bus to replace the dual-mode Silver Line fleet. The final dual-mode buses were retired in July 2023, ending trolleybus operations in the Boston area.
Station listing
LocationStationServicesService beganTransfers and notesSL1SL2SL3SLWFinancialDistrict●●●●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 TerminalSeaportDistrict●●●● MBTA bus: ●●●●●●●●EastBoston●June 1, 2005: Massport: ●: Massport: ●: Massport: ●: Massport: ●: Massport: ●April 21, 2018: : Massport: Chelsea●: ●●: ●SouthBostonNorthern Avenue & Harbor Street●December 31, 2004: Northern Avenue & Tide Street●: 23 Drydock Avenue●Relocated from 21 Drydock Avenue in 201627 Drydock Avenue●December 31, 2004Former stop at 25 Drydock Avenue closed in January 2016, relocated stop opened 2018Drydock Avenue & Black Falcon Avenue●Replacement stop for 88 Black Falcon Avenue during nights and poor weather until January 2016; official stop since 2018Design Center●:
Former stops NeighborhoodStationServed byService beganService endedNotesSouth Boston88 Black Falcon AvenueSL2December 31, 2004April 2019Temporarily closed in April 2019 due to pier repair; permanent closure effective March 13, 2022. Service was planned to resume on June 19, 2022, but this was cancelled.Black Falcon Avenue & Design Center PlaceSL22014Summer Street & Powerhouse StreetSL3March 20, 2009Discontinued due to low ridershipEast 1st Street & M StreetSL3Discontinued due to low ridershipSL3Discontinued due to low ridershipFarragut RoadSL3April 9, 2005August 20, 2005Rerouted due to noise complaints
Washington Street: SL4 and SL5
Two Silver Line routes run between Nubian station (at Nubian Square in Roxbury) and Downtown Boston along Washington Street: SL4 Nubian station–South Station SL5 Nubian station–Downtown Crossing
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 Temple Place (between and , with an intermediate stop at . It returns south on Tremont Street, with a southbound stop at . The SL4 runs north on Washington Street to Chinatown, then east on Essex Street (with a dedicated lane) 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 (lower than rapid transit), 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 (which normally does not allow transfers). This was inherited from the previous route 49 bus, which had free transfers (with the flat token fare) 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 (part of a 44-bus order also used on routes and ), which replaced the original compressed natural gas (CNG) buses, plus three similar hybrid buses delivered in 2010. All Silver Line buses are maintained at Southampton Street Garage.
Station listing
NeighborhoodStationServicesService beganTransfers and notesSL4SL5Roxbury●●July 20, 2002: ●●: South End●●: ●●: ●●November 30, 2002: ●●July 20, 2002: ●●: ●●: ●●: Chinatown●●: : ●●: : Downtown Boston●: , , : ●: : ●October 13, 2009: , , : Fairmount Line, Fall River/New Bedford Line, Framingham/Worcester Line, Franklin/Foxboro Line, Greenbush Line, Kingston Line, Needham Line, Providence/Stoughton Line, CapeFLYER (seasonal): , (SL1, SL2, SL3, SLW): Intercity buses at South Station Bus TerminalChinatownChinatown Gate●August 19, 2022:
History Washington Street development
The 1947 state act that created the Metropolitan Transit Authority (MTA) 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 (Charlestown Elevated, Causeway Street Elevated, and Washington Street Elevated) 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 (equivalent to $ in ) 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.