View source for Silver Line (MBTA)

{{short description|Bus rapid transit system in Massachusetts, US}}
{{good article}}
{{Use mdy dates|date=June 2020}}
{{Infobox Bus transit
| name            = MBTA Silver Line
| image           = MBTA New Flyer XDE60 1315 at South Station, March 2023.jpg
| image_size      = 320px
| image_caption   = A Silver Line bus at {{bts|South Station Under}} in 2023
| alt             = A silver-colored bus at an underground bus stations
| parent          = [[Massachusetts Bay Transportation Authority]]
| founded         = July 20, 2002 (Washington Street)<br />December 17, 2004 (Waterfront)
| locale          = [[Boston]] and [[Chelsea, Massachusetts|Chelsea]], [[Massachusetts]], US
| service_type    = [[Bus rapid transit]] ([[#BRT quality|disputed]])
| routes          = 6
| stops           = 15 (Washington Street)<br />20 (Waterfront)
| hubs            = {{bts|South Station Under}}, {{bts|Nubian}}
| fleet           = 21 (Washington Street)<br />50 (Waterfront)
| ridership       = 27,000 (2023)<ref name=ridership>{{cite web |url=https://cdn.mbta.com/sites/default/files/2024-08/7.%20History%20of%20Funding%20Updated%20V16%208.21.24.pdf |date=August 22, 2024 |first1=Mary Ann |last1=O'Hara |first2=Pat |last2=Turners |publisher=Massachusetts Bay Transportation Authority |page=2 |title=History of Funding Update}}</ref>
| fuel_type       = [[Hybrid electric bus|Diesel hybrid]]
| website         = [http://www.mbta.com/schedules/bus MBTA – Bus]
| map             = {{switcher
|{{maplink-road
|from1=Silver Line 1 (MBTA).map
|from2=Silver Line 2 (MBTA).map
|from3=Silver Line 3 (MBTA).map
|from4=Silver Line 4 (MBTA).map
|from5=Silver Line 5 (MBTA).map
}}
|Show interactive map
|[[File:MBTA Silver Line Geographic Map (2022).svg|300px]]
|Show static map
}}
| map_state       = 
}}

The '''Silver Line''' is a system of bus routes 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. {{As of|2023}}, weekday ridership on the Silver Line was 27,000.

The four Waterfront routes operate out of an underground terminal at {{bts|South Station Under}} and run through the South Boston Piers Transitway – a dedicated bus tunnel through the [[Seaport District]] with stations at {{bts|Courthouse}} and {{bts|World Trade Center}}. At {{bts|Silver Line Way}}, they fan out on the surface: the SL1 to [[Logan International Airport]], the SL2 to [[Raymond L. Flynn Marine Park|Dry Dock Avenue]], and the SL3 to {{bts|Chelsea}} 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 buses|articulated]] diesel hybrid buses with extended battery range. Two routes operate on [[Washington Street (Boston)|Washington Street]] between [[Nubian station]] (at [[Nubian Square]] in [[Roxbury (Boston)|Roxbury]]) and [[Downtown Boston]]. The SL5 terminates at {{bts|Downtown Crossing}} and the SL4 on the surface at {{bts|South Station Under}}. 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 (MBTA)|Orange Line]] [[rapid transit]] line until 1987. Initial plans called for a [[light rail]] branch of the [[Green Line (MBTA)|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 {{bts|Boylston}} to World Trade Center via {{bts|Chinatown}} 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&nbsp;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 {{bts|City Point}} was discontinued on March 20, 2009. A separate SL3 route to Chelsea – originally planned as part of the cancelled [[Urban Ring Project (MBTA)|Urban Ring Project]] – began service on April 21, 2018. Extension of the SL3 route to {{bts|Sullivan Square}} 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==
{{anchor|Waterfront|SL1|SL2|SL3|SLW}}

===Waterfront: SL1, SL2, SL3===
{{MBTA Silver Line Waterfront}}
Three Silver Line services operate from {{bts|South Station Under}} in a dedicated tunnel, the South Boston Piers Transitway, serving the underground {{bts|Courthouse}} and {{bts|World Trade Center}} stations in the [[Seaport District]] then splitting at the {{bts|Silver Line Way}} surface station:<ref name=busmap />
* '''SL1''' Logan Airport–South Station
* '''SL2''' Drydock–South Station
* '''SL3''' Chelsea–South Station
During rush hours, additional [[short turn]]s (designated SLW) are run between South Station and Silver Line Way to increase frequency in the Transitway.<ref name=busmap />

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 {{bts|Airport}} station, follows the Coughlin Bypass Road, and crosses [[Chelsea Creek]] on the [[Chelsea Street Bridge (Boston)|Chelsea Street Bridge]]. It then follows a dedicated busway to {{bts|Chelsea}}, with intermediate stops at {{bts|Eastern Avenue}}, {{bts|Box District}}, and {{bts|Bellingham Square}}.<ref name=busmap /><ref name=netransit /> 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.<ref name=2007report />{{rp|10}}

The Waterfront routes have regular rapid transit fares.<ref name=tariff />{{rp|13}} Passengers enter through faregates at the three Transitway stations, and pay at the on-board farebox at all other stops.<ref name=2007report />{{rp|12}} Fares are free when boarding at the Logan Airport stops.<ref name=tariff />{{rp|31}} 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 (MBTA)|Blue Line]] at Airport and the Washington Street routes are available with a CharlieTicket.<ref name=tariff />{{rp|27}}

The Waterfront routes use {{convert|60|ft|adj=on}} [[articulated bus]]es with three doors, which provide greater capacity than standard {{convert|40|ft|adj=on}} transit buses.<ref name=roster /> 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 [[hybrid electric bus|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 bus]]es built in 2019 are also used. All Silver Line buses are maintained at Southampton Street Garage.<ref name=roster>{{cite web |url=http://www.transithistory.org/roster/ |title=The MBTA Vehicle Inventory Page |publisher=NETransit |access-date=July 8, 2023}}</ref><ref name=2005report />{{rp|2.8}}

The Waterfront routes previously used [[dual-mode bus]]es which operated as electric [[trolleybus]]es 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.<ref name=2007report />{{rp|11}}<ref>{{cite news |url=https://bangordailynews.com/2018/0/28/news/aroostock/mma-completes-mbta-bus-contract-releases-more-than-50-employees-2/ |newspaper=Bangor Daily News |title=MMA completes MBTA bus contract, releases more than 50 employees |date=August 28, 2018 |first=Christopher |last=Bouchard}}</ref> Eight of the buses were funded by [[Massport]] and included luggage racks for airport passengers.<ref name=2007report />{{rp|11}} 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.<ref name=ITDP /><ref name=stateofthesystem>{{cite web |url=https://www.mbtafocus40.com/s/Bus-SoS-Report-Final-Accessible_121815.pdf |title=State of the System: Bus |publisher=Massachusetts Bay Transportation Authority |date=December 2015 |pages=28, 39–40}}</ref> In 2018–19, the MBTA obtained several buses to test alternate options for Waterfront service. A single [[New Flyer]] [[hybrid electric bus|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.<ref>{{cite press release |url=https://www.mbta.com/news/2018-09-26/first-extended-range-hybrid-bus-joins-mbta-silver-line-fleet |title=First Extended-range Hybrid Bus Joins MBTA Silver Line Fleet |date=September 26, 2018 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref>{{cite magazine |title=MBTA Vehicle Inventory as of February 28, 2019 |first=Jonathan |last=Belcher |date=January–February 2019 |magazine=Rollsign |volume=56 |issue=1/2 |page=19}}</ref> On July 31, 2019, the MBTA began using five New Flyer battery electric buses on both Waterfront and Washington Street routes.<ref>{{cite press release |url=https://www.mbta.com/news/2019-07-31/first-zero-emission-battery-electric-buses-join-the-mbta-silver-line-fleet |title=First Zero-emission, Battery-electric Buses Join the MBTA Silver Line Fleet |date=July 31, 2019 |publisher=Massachusetts Bay Transportation Authority}}</ref> 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.<ref>{{cite web |url=https://cdn.mbta.com/sites/default/files/2020-11/2020-11-23-fmcb-19-silver-line-bus-fleet-replacements-accessible.pdf |title=Silver Line Bus Fleet Replacement |date=November 23, 2020 |first=Bill |last=Wolfgang |publisher=Massachusetts Bay Transportation Authority}}</ref> The final dual-mode buses were retired in July 2023, ending [[Trolleybuses in Greater Boston|trolleybus operations in the Boston area]].<ref name=roster />
{{clear right}}
{{anchor|Waterfront stops|Waterfront stop listing}}

====Station listing====
[[File:Power changeover at Silver Line Way inbound, March 2016.JPG|thumb|right|The power changeover at Silver Line Way in 2016; the wires have since been dismantled|alt=Two silver-painted trolleybuses at a bus stop. Rewiring pans are visible on the overhead lines.]]
[[File:MBTA route SL1 bus at Terminal E, October 2016.jpg|thumb|right|An SL1 bus at Logan Airport Terminal E|alt=A silver-painted bus curbside at an airport]]
[[File:MBTA route SL2 bus on Black Falcon Avenue, June 2017.JPG|thumb|right|An SL2 bus on Black Falcon Avenue|alt=A silver-painted bus in an industrial area]]
[[File:World Trade Center Inbound MBTA Silver Line Platform, June 2024.jpg|thumb|right|An SLW bus at World Trade Center station|alt=A silver-painted bus at an underground station]]
{| class=wikitable
|-
!rowspan=2|Location
!rowspan=2|Station
!colspan=4|Services
!rowspan=2|Service began
!rowspan=2|Transfers and notes
|-
!SL1
!SL2
!SL3
!SLW
|-
|[[Financial District (Boston)|Financial<br/>District]]
|{{bts|South Station Under}}
|align=center|●
|align=center|●
|align=center|●
|align=center|●
|rowspan=4|December 17, 2004
|{{ric|Amtrak|name=y}}: {{lnl|Amtrak|Acela}}, {{lnl|Amtrak|Lake Shore Limited}}, {{lnl|Amtrak|Northeast Regional}}<br />{{ric|MBTA|Commuter Rail|name=y}}: [[Fairmount Line]], [[Fall River/New Bedford Line]], [[Framingham/Worcester Line]], [[Franklin/Foxboro Line]], [[Greenbush Line]], [[Kingston Line]], [[Needham Line]], [[Providence/Stoughton Line]], ''[[CapeFLYER]]'' (seasonal)<br />{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|Red|name=y}}, {{ric|MBTA|Silver|link=SL4 (MBTA bus)|name=y}} ({{MBTABus|SL4}})<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|South Station}}<br />{{bus icon}} Intercity buses at [[South Station Bus Terminal]]
|-
|rowspan=3|[[Seaport District|Seaport<br/>District]]
|{{bts|Courthouse}}
|align=center|●
|align=center|●
|align=center|●
|align=center|●
|{{bus icon}} MBTA bus: {{MBTA bus links|Courthouse}}
|-
|{{bts|World Trade Center}}
|align=center|●
|align=center|●
|align=center|●
|align=center|●
|
|-
|{{bts|Silver Line Way}}
|align=center|●
|align=center|●
|align=center|●
|align=center|●
|
|-
|rowspan=6|[[East Boston|East<br/>Boston]]
|{{bts|Terminal A}}
|align=center|●
|
|
|
|rowspan=5|June 1, 2005
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Terminal A}}<br />{{bus icon}} [[Massachusetts Port Authority#Massport Shuttle|Massport]]: {{MBTA other buses|Terminal A Massport}}<br />{{bus icon}} {{MBTA other buses|Logan terminals intercity simple}}
|-
|{{bts|Terminal B Stop 1}}
|align=center|●
|
|
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Terminal B1}}<br />{{bus icon}} Massport: {{MBTA other buses|Terminal B1 Massport}}<br />{{bus icon}} {{MBTA other buses|Logan terminals intercity simple}}
|-
|{{bts|Terminal B Stop 2}}
|align=center|●
|
|
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Terminal B2}}<br />{{bus icon}} Massport: {{MBTA other buses|Terminal B2 Massport}}<br />{{bus icon}} {{MBTA other buses|Logan terminals intercity simple}}
|-
|{{bts|Terminal C}}
|align=center|●
|
|
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Terminal C}}<br />{{bus icon}} Massport: {{MBTA other buses|Terminal C Massport}}<br />{{bus icon}} {{MBTA other buses|Logan terminals intercity simple}}
|-
|{{bts|Terminal E}}
|align=center|●
|
|
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Terminal E}}<br />{{bus icon}} Massport: {{MBTA other buses|Terminal E Massport}}<br />{{bus icon}} {{MBTA other buses|Logan terminals intercity simple}}
|-
|{{bts|Airport}}
|
|
|align=center|●
|
|rowspan=5|April 21, 2018
|{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|Blue|name=y}}<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Airport}}<br />{{bus icon}} Massport: {{MBTA other buses|Airport Massport}}
|-
|rowspan=4|[[Chelsea, Massachusetts|Chelsea]]
|{{bts|Eastern Avenue}}
|
|
|align=center|●
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Eastern Avenue}}
|-
|{{bts|Box District}}
|
|
|align=center|●
|
|
|-
|{{bts|Bellingham Square}}
|
|
|align=center|●
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Bellingham Square}}
|-
|{{bts|Chelsea}}
|
|
|align=center|●
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Chelsea}}<br />{{ric|MBTA|Commuter Rail|name=y}}: [[Newburyport/Rockport Line]]
|-
|rowspan=6|South<br/>Boston
|Northern Avenue & Harbor Street
|
|align=center|●
|
|
|rowspan=2|December 31, 2004
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Harbor Street}}
|-
|Northern Avenue & Tide Street
|
|align=center|●
|
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Tide Street}}
|-
|23 Drydock Avenue
|
|align=center|●
|
|
|{{circa|2006}}<ref>{{cite web |archive-url=https://web.archive.org/web/20060110200931/http://www.mbta.com/traveling_t/pdf/system/dt3_southboston.pdf |archive-date=January 10, 2006 |url=http://www.mbta.com:80/traveling_t/pdf/system/dt3_southboston.pdf |title=MBTA Downtown Map [Downtown Boston quadrant] |publisher=Massachusetts Bay Transportation Authority |first=Kenneth A. |last=Dumas |year=2005 |access-date=November 19, 2021 |url-status=dead}}</ref><ref>{{cite web |archive-url=https://web.archive.org/web/20060221110856/http://www.mbta.com/traveling_t/pdf/system/dt3_southboston.pdf |archive-date=February 21, 2006 |url=http://www.mbta.com:80/traveling_t/pdf/system/dt3_southboston.pdf |title=MBTA Downtown Map [Downtown Boston quadrant] |publisher=Massachusetts Bay Transportation Authority |first=Kenneth A. |last=Dumas |year=2006 |access-date=November 19, 2021 |url-status=dead}}</ref><!-- https://web.archive.org/web/20051230130902/http://www.mbta.com/traveling_t/schedules_pdfmaps_downtown.asp# -->
|Relocated from 21 Drydock Avenue in 2016<ref>{{cite web |archive-url=https://web.archive.org/web/20160522171604/http://www.mbta.com/rider_tools/transit_updates/?ttype=bus&atype=alert&route=SL2&detail=SL2 |archive-date=May 22, 2016 |url=http://www.mbta.com/rider_tools/transit_updates/?ttype=bus&atype=alert&route=SL2&detail=SL2 |date=April 27, 2016 |title=Bus Service Alerts: SL2 |publisher=Massachusetts Bay Transportation Authority}}</ref>
|-
|27 Drydock Avenue
|
|align=center|●
|
|
|rowspan=3|December 31, 2004
|Former stop at 25 Drydock Avenue closed in January 2016, relocated stop opened 2018<!--first source has relocated to 27DD in 2016, but that was actually the DD&BF corner stop. GTFS says September 2018; maps say December.--><ref>{{cite web |archive-url=https://web.archive.org/web/20160423091718/http://www.mbta.com/rider_tools/transit_updates/?ttype=bus&atype=alert&route=SL2&detail=SL2 |archive-date=April 23, 2016 |url=http://www.mbta.com/rider_tools/transit_updates/?ttype=bus&atype=alert&route=SL2&detail=SL2 |date=January 3, 2016 |title=Bus Service Alerts: SL2 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=sept2018map>{{cite web |title=Silver Line SL1•SL2•SL3 Effective September 2, 2018 |url=https://cdn.mbta.com/sites/default/files/route_pdfs/2018-fall/rtSilver1-3.pdf |archive-url=https://web.archive.org/web/20180818121347/https://cdn.mbta.com/sites/default/files/route_pdfs/2018-fall/rtSilver1-3.pdf |archive-date=August 18, 2018 |publisher=Massachusetts Bay Transportation Authority |date=September 2, 2018}}</ref><ref name=dec2018map>{{cite web |title=Silver Line SL1•SL2•SL3 Effective December 23, 2018 |url=https://cdn.mbta.com/sites/default/files/route_pdfs/2019-winter/rtSilver1-3.pdf |date=December 23, 2018 |publisher=Massachusetts Bay Transportation Authority}}</ref>
|-
|Drydock Avenue & Black Falcon Avenue
|
|align=center|●
|
|
|Replacement stop for 88 Black Falcon Avenue during nights and poor weather until January 2016; official stop since 2018<ref name=sept2018map /><ref name=dec2018map /><!--GTFS has it as a full-time stop beginning September 3, 2016; however, it appears it was used beginning in January when 25DD was closed.-->
|-
|Design Center
|
|align=center|●
|
|
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Design Center}}

|}

====Former stops====
{|class="wikitable"
!Neighborhood
!Station
!Served by
!Service began
!Service ended
!Notes
|-
|rowspan=6|South Boston
|88 Black Falcon Avenue
|SL2
|rowspan=5|December 31, 2004
|April 2019
|Temporarily closed in April 2019 due to pier repair; permanent closure effective March 13, 2022.<ref name=88bf>{{cite web |archive-url=https://web.archive.org/web/20191001191212/https://mbta.com/alerts/bus |archive-date=October 1, 2019 |url=https://mbta.com/alerts/bus |date=April 27, 2019 |title=SL2 Design Center–South Station |work=Alerts |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=netransit /><ref name=march132022 /> Service was planned to resume on June 19, 2022, but this was cancelled.<ref>{{cite web |url=https://mbta.com/sites/default/files/route_pdfs/2022-summer/SL123_3.pdf |title=Silver Line |date=June 19, 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref>{{cite web |url=https://www.mbta.com/schedules/742/alerts |archiveurl=https://web.archive.org/web/20220622185619/https://www.mbta.com/schedules/742/alerts |archivedate=June 22, 2022 |title=Alerts: SL2 |date=June 16, 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref>
|-
|Black Falcon Avenue & Design Center Place
|SL2
|2014
|
|-
|Summer Street & Powerhouse Street
|SL3
|rowspan=3|March 20, 2009
|Discontinued due to low ridership<ref name=netransit />
|-
|East 1st Street & M Street
|SL3
|Discontinued due to low ridership<ref name=netransit />
|-
|{{bts|City Point}}
|SL3
|Discontinued due to low ridership<ref name=netransit />
|-
|Farragut Road
|SL3
|April 9, 2005<ref name=netransit />
|August 20, 2005
|Rerouted due to noise complaints<ref name=2008serviceplan />
|}

{{anchor|Washington Street|SL4|SL5}}

===Washington Street: SL4 and SL5===
{{MBTA Silver Line Washington Street}}
Two Silver Line routes run between [[Nubian station]] (at [[Nubian Square]] in [[Roxbury (Boston)|Roxbury]]) and [[Downtown Boston]] along [[Washington Street (Boston)|Washington Street]]:<ref name=busmap />
* '''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 {{bts|Tufts Medical Center}}, 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 {{bts|Downtown Crossing}} and {{bts|Park Street}}, with an intermediate stop at {{bts|Chinatown}}. It returns south on [[Tremont Street]], with a southbound stop at {{bts|Boylston}}. The SL4 runs north on Washington Street to Chinatown, then east on Essex Street (with a dedicated lane) to a surface stop at {{bts|South Station Under}}. It returns south on Surface Road and Kneeland Street.<ref name=busmap>{{cite web |url=https://mbta.com/bus-map |title=System Map |publisher=Massachusetts Bay Transportation Authority |access-date=May 12, 2020}}</ref> Most stops have a canopy shelter with seating, maps, and a real-time arrival information display.<ref name=2005report />{{rp|2.5}}

The two routes have the [[MBTA#fares|same fare]] as local bus services (lower than rapid transit), with normal transfers with a CharlieCard.<ref name=tariff>{{cite web |url=https://cdn.mbta.com/sites/default/files/fares/2019-06-28-mbta-and-cr-tariff-effective-20190701.pdf |title=MBTA Tariff and Statement of Fare and Transfer Rules |date=July 1, 2019 |publisher=Massachusetts Bay Transportation Authority}}</ref>{{rp|14}} 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).<ref name=tariff />{{rp|27}} This was inherited from the previous route 49 bus, which had free transfers (with the flat [[token coin|token]] fare) to and from the Orange Line only at {{bts|New England Medical Center}}.<ref name=2005report />{{rp|2.9}}

The Washington Street routes use {{convert|60|ft|adj=on}} [[Hybrid electric bus|diesel hybrid]] [[articulated bus]]es with three doors.<ref name=roster /> 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 {{MBTABus|28}} and {{MBTABus|39}}), which replaced the original [[compressed natural gas]] (CNG) buses, plus three similar hybrid buses delivered in 2010.<ref name=roster /><ref>{{cite press release |url=https://www.mbta.com/news/2015-10-06/mbta-purchases-dozens-new-high-capacity-buses |title=MBTA Purchases Dozens of New, High Capacity Buses |date=October 6, 2015 |publisher=Massachusetts Bay Transportation Authority}}</ref> All Silver Line buses are maintained at Southampton Street Garage.<ref name=roster /><ref name=2005report />{{rp|2.8}}

{{anchor|Washington Street stop listing|Washington Street stops}}

====Station listing====
[[File:MBTA Silver Line SL5 and SL4 buses on Washington St.jpg|thumb|right|Route SL5 and SL4 buses on Washington Street|alt=Two silver-painted buses on an urban street]]
[[File:Southbound shelter at Melnea Cass Boulevard station, July 2019.JPG|thumb|right|Melnea Cass Boulevard, a typical Washington Street stop|alt=A large bus stop shelter made of silver metal and glass]]
{| class="wikitable"
!rowspan=2|Neighborhood
!rowspan=2|Station
!colspan=2|Services
!rowspan=2|Service began
!rowspan=2|Transfers and notes
|-
!SL4
!SL5
|-
|rowspan=2|[[Roxbury, Boston|Roxbury]]
|{{bts|Nubian}}
|align=center|●
|align=center|●
|rowspan=4|July 20, 2002<ref name=netransit/>
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Nubian}}
|-
|{{bts|Melnea Cass Boulevard}}
|align=center|●
|align=center|●
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Melnea Cass Boulevard}}
|-
|rowspan=7|[[South End, Boston|South End]]
|{{bts|Lenox Street}}
|align=center|●
|align=center|●
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Lenox Street}}
|-
|{{bts|Massachusetts Avenue|Silver}}
|align=center|●
|align=center|●
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Massachusetts Avenue SL}}
|-
|{{bts|Worcester Square}}
|align=center|●
|align=center|●
|November 30, 2002<ref name=bluebook2004>{{cite book |url=https://archive.org/details/ridershipservice2003mass |title=Ridership and Service Statistics |publisher=Massachusetts Bay Transportation Authority |page=3A{{hyphen}}3 |chapter=Silver Line |edition=9 |year=2003–2004 |via=Internet Archive}}</ref>
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Worcester Square}}
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|rowspan=8|July 20, 2002<ref name=netransit/>
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Newton Street}}
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|{{bts|Union Park Street}}
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|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Union Park Street}}
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|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|East Berkeley Street}}
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|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Herald Street}}
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|rowspan=2|[[Chinatown, Boston|Chinatown]]
|{{bts|Tufts Medical Center}}
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|{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|ORange|name=y}}<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Tufts Medical Center}}
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|{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|Orange|name=y}}<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Chinatown}}
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|rowspan=3|[[Downtown Boston]]
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|{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|Green|name=y}}, {{ric|MBTA|Orange|name=y}}, {{ric|MBTA|Red|name=y}}<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Park Street}}
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|{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|Green|name=y}}<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Boylston}}
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|October 13, 2009<ref name=netransit/>
|{{ric|Amtrak|name=y}}: {{lnl|Amtrak|Acela}}, {{lnl|Amtrak|Lake Shore Limited}}, {{lnl|Amtrak|Northeast Regional}}<br />{{ric|MBTA|Commuter Rail|name=y}}: [[Fairmount Line]], [[Fall River/New Bedford Line]], [[Framingham/Worcester Line]], [[Franklin/Foxboro Line]], [[Greenbush Line]], [[Kingston Line]], [[Needham Line]],[[Providence/Stoughton Line]], ''[[CapeFLYER]]'' (seasonal)<br />{{ric|MBTA|Subway|name=y}}: {{ric|MBTA|Red|name=y}}, {{ric|MBTA|Silver|name=y}} ([[#Waterfront: SL1, SL2, SL3|SL1, SL2, SL3, SLW]])<br />{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|South Station}}<br />{{bus icon}} Intercity buses at [[South Station Bus Terminal]]
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|Chinatown
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|August 19, 2022<ref name=ctgate /><ref name=afterOL />
|{{ric|MBTA|Bus|name=y}}: {{MBTA bus links|Chinatown Gate}}
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==History==
===Washington Street development===
[[File:Removal of Northampton station headhouse, 1987.jpg|thumb|right|Removal of the Elevated in 1987|alt=A elevated rapid transit station being disassembled with a cran]]
The 1947 state act that created the [[Metropolitan Transit Authority (Boston)|Metropolitan Transit Authority]] (MTA) from the [[Boston Elevated Railway]] established four immediate projects for the new agency: extension of rapid transit to {{bts|Braintree}}, 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 {{bts|Harvard}}.<ref>{{cite book |chapter-url=https://archive.org/details/actsresolvespass1947mass/page/538 |title=Acts and Resolves passed by the General Court of Massachusetts in the year 1947 |chapter=Chapter 544: An act providing for the creation of the Metropolitan Transit Authority and the acquisition and operation by it of the entire assets, property and franchises of the Boston Elevated Railway Company |pages=539–556 |date=June 19, 1947 |publisher=Secretary of the Commonwealth |via=Internet Archive}}</ref> In 1948, the legislature authorized the city to issue $19&nbsp;million in bonds (equivalent to ${{format price|{{Inflation|US-GDP|19000000|1948}}}} in {{Inflation/year|US}}) to construct an extension of the [[Washington Street Tunnel (Boston)|Washington Street Tunnel]] under Shawmut Street, connecting with the existing elevated south of Dudley Square.<ref>{{cite book |chapter-url=https://archive.org/details/actsresolvespass1948mass/page/692 |title=Acts and Resolves passed by the General Court of Massachusetts in the year 1948 |chapter=Chapter 622: An act providing for certain rapid transit improvements in the City of Boston |pages=693–702 |date=June 15, 1948 |publisher=Secretary of the Commonwealth |via=Internet Archive}}</ref> Although none of the proposals were built immediately, it established a precedent of replacing the elevated lines. In 1972, [[Highway revolts in the United States#Massachusetts|protests]] led to cancellation of the planned [[Southwest Corridor (Boston)|Southwest Expressway]]. Instead, the alignment was used for [[Southwest Corridor (Boston)|a combined corridor]] for intercity rail, commuter rail, and the [[Orange Line (MBTA)|Orange Line]] – replacing the Washington Street Elevated of the latter.<ref name=2005report />{{rp|3.1}}

The northern part of the new corridor was about {{convert|1/2|mile}} west of Washington Street, so the MBTA (which had replaced the MTA in 1964) began planning in 1978 for a replacement service between Dudley Square and Downtown Boston.<ref name=2005report />{{rp|3.1}}<ref>{{cite report |url=https://archive.org/details/replacementtrans1978mass |title=Replacement / transit improvement study: South End / Roxbury / Dorchester / Mattapan: Phase I Feasibility Report |year=1978 |publisher=Massachusetts Bay Transportation Authority |via=Internet Archive}}</ref> By 1985, the MBTA favored bus or [[light rail]] service on Washington Street; the latter would have been a branch of the [[Green Line (MBTA)|Green Line]], operated through [[Pleasant Street Portal|the 1962-abandoned southern branch]].<ref>{{cite report |url=https://archive.org/details/replacementtrans00cbtc |title=Replacement / transit improvement study: South End / Roxbury / Dorchester / Mattapan: What's happened... and what's happening next? |year=1985 |publisher=Massachusetts Bay Transportation Authority |via=Internet Archive}}</ref> The Orange Line was rerouted in 1987; that year, the [[Federal Transit Administration|Urban Mass Transportation Administration]] rejected the MBTA's funding request to create a [[light rail]] line on the corridor.<ref name=2005report />{{rp|3.1}} Local opinion favored the temporary retention of the northern portion of the Elevated until a permanent replacement could be built.<ref name=orangelinebook>{{cite book |title=When Boston Rode The El |last1=Cheney |first1=Frank |last2=Sammarco |first2=Anthony M. |year=2000 |publisher=Arcadia Publishing |isbn=9780738504629 |page=9}}</ref> However, the MBTA closed the Elevated and instead upgraded the route 49 bus from a feeder route to a more frequent trunk route.<ref name=2005report />{{rp|3.1}}
[[File:MBTA Silver Line logo.png|thumb|left|The MBTA used this logo to advertise the Silver Line|alt=A logo reading "SILVERLINE" over a graphic of wings]]
In 1989, the MBTA announced that [[trolleybuses]] would be used on Washington Street, operating on 4-minute headways at peak hours.<ref name=2005report />{{rp|3.1}} 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.<ref>{{cite web |url=https://archive.org/details/trolleybusesonwa00mass |title=Trolley buses on Washington Street! |date=October 1990 |publisher=Massachusetts Bay Transportation Authority |via=Internet Archive}}</ref> 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]] (CNG) buses to avoid the visual impact of overhead wires.<ref name=2005report />{{rp|3.2}} Environmental documentation was filed in 1998, and construction began in 2001.<ref name=2005report />{{rp|3.2}} The project cost $27.3&nbsp;million, with major elements including $10.9&nbsp;million for the 17 new buses, $10.9&nbsp;million for road work, and $2.6&nbsp;million for shelters.<ref name=2005report />{{rp|2.14}} Planning and construction were combined with a necessary repaving of Washington Street, reducing costs.<ref name=2005report />{{rp|5.8}} 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.<ref name=2005report />{{rp|4.11}} The Silver Line name was introduced in 1996.<ref>{{cite news |url=https://www.newspapers.com/article/the-boston-globe/129238504/ |title=T opens up back-door policy |newspaper=Boston Globe |date=October 17, 1996 |pages=B1, [https://www.newspapers.com/article/the-boston-globe/129238520/ B3] |via=Newspapers.com |first=Thomas |last=Palmer}}</ref><ref>{{cite news |url=https://www.newspapers.com/article/the-boston-globe/129240145/ |title=A slow, costly ride to downtown |newspaper=Boston Globe City Weekly |date=October 27, 1996 |pages=1, [https://www.newspapers.com/article/the-boston-globe/129240199/ 12] |via=Newspapers.com |first=Joe |last=Yonan}}</ref>

The Silver Line followed largely the same route between [[Nubian station|Dudley Square]] and Downtown Boston as route 49; the primary change was the consolidation of stops.<ref name=netransit /> Although the MBTA considered other stop locations, most of the final stops were at existing route 49 stops.<ref name=2005report />{{rp|3.3}} The conversion to the Silver Line occurred in several steps. In December 2001, the MBTA opened a [[contraflow lane|contraflow]] bus-only lane on Washington Street between Marginal Road 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 (between {{bts|Park Street}} and {{bts|Downtown Crossing}} stations). Service frequency was also increased at that time.<ref name=2005report>{{cite report |url=https://nbrti.org/wp-content/uploads/2017/05/Boston_Silver_Line_final_report.pdf |title=Boston Silver Line Washington Street Bus Rapid Transit (BRT): Demonstration Project Evaluation |first1=Paul |last1=Schimek |first2=Georges |last2=Darido |first3=Donald |last3=Schneck |date=September 2005 |publisher=Federal Transit Administration}}</ref>{{rp|1.2}} 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.<ref name=2005report />{{rp|1.2, 4.11}} In November 2002, a twelfth stop at {{bts|Worcester Square}} was restored.<ref name=2005report />{{rp|2.5}} The {{convert|40|ft|adj=on}} were replaced by {{convert|60|ft|adj=on}} buses in August 2003, and service frequency was again increased.<ref name=2005report />{{rp|1.2}} On January 31, 2005, the route was the first MBTA bus route to receive new [[automated fare collection]] equipment.<ref name=2005report />{{rp|2.9}} By 2005, ridership was double that of route 49, but early decreases in travel time were cancelled out by longer dwell times.<ref name=2005report />{{rp|4.4, 5.1}} 

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.<ref>{{Cite news |url=https://www.wbur.org/news/2020/02/16/mbta-dudley-nubian-station-roxbury |title=Roxbury's Dudley Station To Be Renamed Nubian Station |last=Menard |first=Fausto |date=February 16, 2020 |website=[[WBUR-FM|WBUR]] |access-date=February 16, 2020}}</ref> The station renaming took effect in June 2020.<ref name=netransit /> In May 2022, the MBTA released a draft plan for a systemwide network redesign. The draft called for the SL4 and SL5 to be combined into a single Nubian–South Station route to provide simpler and more consistent downtown service.<ref>{{cite web |url=https://cdn.mbta.com/sites/default/files/Bus%20Network%20Redesign/4_Back%20Bay.pdf |title=A better bus network: new connections, more service, more frequency. See what this means in Back Bay, Beacon Hill, Downtown Boston, North End, South End, and West End. |date=May 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=draftmap>{{cite web |url=https://cdn.mbta.com/sites/default/files/2022-05/2022-05-12-bnrd-proposed-regional-map.pdf|title=Draft Bus Network Redesign Map |date=May 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref> The November 2022 draft network plan kept the same proposal.<ref name=nov2022changes /><ref name=nov2022map /> An additional SL4 stop (Chinatown Gate) on Surface Artery at Kneeland Street in Chinatown was added on August 19, 2022, while the Orange Line was closed for maintenance work; it was retained after the closure.<ref name=ctgate>{{cite press release |url=https://www.mbta.com/news/2022-08-18/mbta-announces-additional-sl4-stop-during-orange-line-shutdown-supplemental-shuttle |title=MBTA Announces Additional SL4 Stop during Orange Line Shutdown; Supplemental Shuttle to Serve Tufts Medical Community |date=August 18, 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=afterOL>{{cite press release |url=https://www.boston.gov/news/city-boston-announces-permanent-street-changes-following-orange-line-shutdown |title=City of Boston Announces Permanent Street Changes Following Orange Line Shutdown |publisher=City of Boston |date=September 20, 2022}}</ref>

===Waterfront development===
[[File:World Trade Center station construction, circa 2002.jpg|thumb|right|World Trade Center station under construction around 2002|alt=Concrete walls of a partially-below-ground station under construction]]
[[File:Outbound MBTA Silver Line buses at Courthouse station.jpg|thumb|right|A 40-foot Silver Line [[trolleybus]] at Courthouse station in 2005. These buses were briefly used until the dual-mode buses entered service.|alt=A silver-painted trolleybus at an underground station]]
For most of the 20th century, the [[Seaport District]] was an industrial area occupied by [[Track 61 (Boston)|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 (MBTA)|Red Line]] at {{bts|South Station}}.<ref>{{cite map |title-link=:commons:File:1965 MBTA system map.png |year=1965 |first=Richard F. |last=Lufkin |title=System Route Map |publisher=Massachusetts Bay Transportation Authority |via=Wikimedia Commons}}</ref> 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.<ref name=feis />{{rp|1.1}} The MBTA conducted a feasibility study in 1987 and released a Draft [[Environmental Impact Report]] (DEIR) in 1989.<ref name=2007report />{{rp|23}}<ref>{{cite book |chapter-url=https://archive.org/details/southbostonpiers00mass/ |chapter=Public scoping session |title=South Boston Piers/Fort Point Channel Area Transportation Alternatives Environmental Impact Report |date=December 10, 1987 |publisher=Massachusetts Bay Transportation Authority |via=Internet Archive}}</ref> 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 [[trolleybus]]es or [[dual-mode bus]]es, rather than the [[light rail]] and people mover possibilities considered; it would connect with the Red Line at South Station, the [[Orange Line (MBTA)|Orange Line]] at {{bts|Chinatown}}, and the [[Green Line (MBTA)|Green Line]] at {{bts|Boylston}}. Costs could be reduced by combining its construction with the upcoming [[Central Artery/Tunnel Project]] ("Big Dig"). Service from the transitway could be extended to serve [[Logan International Airport]], to form part of [[Urban Ring (MBTA)|a proposed circumferential transit line]], and to connect with the planned Washington Street service.<ref name=feis>{{cite book |url=https://archive.org/details/southbostonpiers00usde |title=South Boston Piers / Fort Point Channel transit project, Boston, Massachusetts: Final Environmental Impact Statement / Final Environmental Impact Report |date=December 1993 |publisher=Federal Transit Administration and Massachusetts Bay Transportation Authority |via=Internet Archive}}</ref>{{rp|iii}}

The South Boston Piers Transitway alignment was refined by a supplemental DEIR in 1992.<ref name=feis />{{rp|V}} The Final Environmental Impact Statement/Final Environmental Impact Report (FEIS/FEIR) was approved in December 1993.<ref name=2007report />{{rp|24}} The South Station–Seaport segment was to open in 2000, with the Boylston segment opening in 2006.<ref name=feis />{{rp|2.81}} The stations at {{bts|World Trade Center}}, {{bts|Courthouse}}, South Station, Chinatown, and Boylston would each have [[island platform]]s, and the tunnel could be later converted to light rail as a Green Line branch if needed.<ref>{{cite book |url=https://books.google.com/books?id=Nhw3AQAAMAAJ |chapter=Design Drawings Appendix |title=South Boston Piers / Fort Point Channel transit project, Boston, Massachusetts: Final Environmental Impact Statement / Final Environmental Impact Report |date=December 1993 |publisher=Federal Transit Administration and Massachusetts Bay Transportation Authority |via=Google Books |pages=Figures A16 to A33 |no-pp=yes}}</ref><ref>{{cite book |chapter-url=https://books.google.com/books?id=Phw3AQAAMAAJ&pg=PA14 |chapter=Response to Comments Appendix |title=South Boston Piers / Fort Point Channel transit project, Boston, Massachusetts: Final Environmental Impact Statement / Final Environmental Impact Report |date=December 1993 |publisher=Federal Transit Administration and Massachusetts Bay Transportation Authority |page=14 |via=Google Books}}</ref> 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.<ref name=feis />{{rp|4.26}} In November 1994, the [[Federal Transit Administration]] (FTA) agreed to fund $331&nbsp;million (80%) of the $413&nbsp;million first phase, which was to be completed in December 2000.<ref name=gao2000>{{cite report |url=https://www.gao.gov/assets/100/90177.pdf |title=Mass Transit: Review of the South Boston Piers Transitway Finance Plan |publisher=General Accounting Office |date=November 9, 2000}}</ref>{{rp|1}} The environmental approval process was completed in April 1995.<ref name=2007report />{{rp|24}}

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]].<ref name=2007report />{{rp|24–25}}<ref name=phase3 />{{rp|2.1}}{{refn|group=note|Such use of the third harbor tunnel to run express bus service to the airport had been proposed as early as 1968.<ref>{{cite book |url=https://archive.org/details/studyofimprovedh00mass/page/n97 |title=A study of improved high speed public transportation between Logan International Airport and downtown Boston |page=98 |publisher=Massachusetts Bay Transportation Authority and Massachusetts Port Authority |date=December 18, 1968 |via=Internet Archive}}</ref>}} A connector road was to extend the transitway from D Street to Haul Road. These changes were approved in February 1998.<ref name=2007report />{{rp|25}} 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 plans|Phase III]].<ref name=2007report />{{rp|25}}

Initial construction of the Transitway was divided into four main sections: South Station and turnaround loop plus {{convert|1550|feet}} of tunnel ($96&nbsp;million), Russia Wharf and Fort Point Channel tunnel ($128&nbsp;million), Courthouse station plus {{convert|1450|feet}} of tunnel ($110&nbsp;million), and World Trade Center station plus {{convert|1200|feet}} of tunnel ($43&nbsp;million).<ref name=2007report />{{rp|15}} 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]].<ref name=gao2000 />{{rp|5}}<ref name=grout /> It also included an [[immersed tube]] under the Fort Point Channel.<ref name=grout>{{cite book |chapter-url=https://books.google.com/books?id=JCJnZLCuOUEC&pg=PA265 |chapter=Jet grout bottom seal for cut and cover tunnel |first=Thomas M. |last=Hurley |title=North American Tunneling 2004: Proceedings of the North American Tunneling Conference 2004 |editor=Levent Ozdemir |year=2004 |publisher=CRC Press |isbn=9781439833759 |pages=265–270 |via=Google Books}}</ref> The discovery of a massive boulder under the Channel delayed the project by a year.<ref name=2007report />{{rp|15}} By late 2000, the project was three years behind schedule and almost $200&nbsp;million over budget; the MBTA diverted $150&nbsp;million of other federal grants and $50&nbsp;million of contingency funds to cover the costs.<ref name=gao2000 />{{rp|4}} The Transitway was ultimately completed in 2004, with a final cost to the MBTA of $624&nbsp;million.<ref name=2007report />{{rp|16}}{{refn|group=note|That figure includes the higher-than-expected cost of dual-mode buses, and part of the cost of the Southampton maintenance facility, but subtracts reimbursements from other projects.<ref name=2007report />{{rp|16}}}} Although some projects like the [[John Joseph Moakley United States Courthouse|new federal courthouse]] and the [[Boston Convention and Exhibition Center|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.<ref>{{cite news |url=http://archive.boston.com/news/local/articles/2004/11/22/bus_tunnel_to_open_but_waterfront_boom_lags?pg=full |title=Bus tunnel to open, but waterfront boom lags |date=November 22, 2004 |first=Anthony |last=Flint |newspaper=Boston Globe |archive-url=https://web.archive.org/web/20211214215823/http://archive.boston.com/news/local/articles/2004/11/22/bus_tunnel_to_open_but_waterfront_boom_lags?pg=full |archive-date=December 14, 2021}}</ref>
[[File:Silver Line service plan map, 2005.jpg|thumb|right|Silver Line service plans as of 2005, showing the SL3 (discontinued in 2009) and the original SL4 and Phase III (never implemented)|alt=See caption.]]
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 {{convert|40|ft|adj=on}} trolleybuses borrowed from the [[Trolleybuses in Greater Boston|Harvard-based routes]].<ref name="netransit">{{NETransit}}</ref><ref name=2007report />{{rp|26}} It was only the third "urban trolleybus subway" (tunnel with stations) in the world, after the [[Harvard station|Harvard bus tunnel]] and the [[Downtown Seattle Transit Tunnel]] (in which trolleybus service ended in 2005).<ref name=tm2006>{{cite magazine |magazine=Trolleybus Magazine |title=Trolleynews |page=70 |editor-first=Peter |editor-last=Haseldine |volume=42 |issue=267 |date=May–June 2006|publisher=National Trolleybus Association|location=UK|issn=0266-7452}}</ref> Original plans called for a single South Boston route running to {{bts|City Point}} via D Street, Broadway, Summer Street, and E 1st Street. After concerns from residents over reduction of legal parking spaces and impacts to the "local custom" of double parking, this was split into two routes: one running to {{bts|Andrew}} via D Street, and one to City Point via E 1st Street.<ref>{{cite news |url=https://www.newspapers.com/clip/83245654/the-boston-globe/ |title=S. Boston split on route shift for Silver Line |first=Anthony |last=Flint |newspaper=Boston Globe |date=December 17, 2004 |pages=B1, [https://www.newspapers.com/clip/83245654/the-boston-globe/ B4] |via=Newspapers.com}}</ref> Until shortly before the routes opened, the MBTA planned to distinguish them with letters like the Green Line branches, rather than the numbers that were ultimately used.<ref>{{cite web |url=http://www.allaboutsilverline.com/waterfront.asp |archive-url=https://web.archive.org/web/20041124151454/http://www.allaboutsilverline.com/waterfront.asp |archive-date=November 24, 2004 |date=2004 |publisher=Massachusetts Bay Transportation Authority |title=Silver Line Waterfront - Opening December 2004}}</ref>

On December 31, 2004, service began on routes SL2 to the [[Boston Marine Industrial Park]] and route SL3 to City Point – the latter running via Northern Avenue, Drydock Avenue, and Summer Street. 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.<ref name=netransit /> The existing surface routes in the Seaport were discontinued or rerouted in January.<ref name=2007report />{{rp|5–7}} 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.<ref name=netransit /> On April 9, weekday SL3 service was extended from City Point to a loop on Farragut Road.<ref name=netransit /> 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.<ref name=netransit /> As more buses entered service, the SL2 and SL3 were re-split into separate routes (except nights and weekends) on August 20, and the Farragut Road loop was cut due to noise complaints from residents.<ref name=2008serviceplan /> On October 15, City Point service was cut on nights and weekends.<ref name=netransit /> The planned SL4 route to Andrew, expected to begin service in 2005, was never implemented.<ref>{{cite journal |url=http://archives.lib.state.ma.us/bitstream/handle/2452/37411/ocm10561343-2005-01.pdf |journal=TRANSreport |date=January 2005 |publisher=Boston Region Metropolitan Planning Organization |title=The Silver Line Waterfront Line Opens for Service |page=1}}</ref><ref name=netransit />

As enough dual-mode buses became available, the borrowed 40-foot trolleybuses were phased out; they were last used on February 12, 2006.<ref name=tm2006 /> By 2006, the Silver Line had doubled transit ridership to the Seaport, and increased transit ridership to Logan by 24%.<ref name=2007report>{{cite report |url=https://www.transit.dot.gov/sites/fta.dot.gov/files/FINALBOSTONBRTREPORT062507.pdf |title=Silver Line Waterfront Bus Rapid Transit (BRT): 2007 Evaluation |date=June 1, 2007 |first1=Paul |last1=Schimek |first2=Kari |last2=Watkins |first3=David |last3=Chase |first4=Karl |last4=Smith |first5=Stephen |last5=Gazillo |publisher=Federal Transit Administration}}</ref>{{rp|42, 44}} The SL3 service was never successful, as the parallel route {{MBTABus|7}} 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.<ref name=2008serviceplan>{{cite report |url=http://www.mbta.com/uploadedFiles/About_the_T/T_Projects/T_Projects_List/ServicePlan08.pdf |archive-url=https://web.archive.org/web/20080908100943/http://www.mbta.com/uploadedFiles/About_the_T/T_Projects/T_Projects_List/ServicePlan08.pdf |archive-date=September 8, 2008 |title=Preliminary 2008 Service Plan: Bus, Rapid Transit, and Boat Service Changes and Service Delivery Policy Modifications |page=45 |date=Fall 2008 |publisher=Massachusetts Bay Transportation Authority}}</ref> On March 20, 2009, SL3 service was cut, with SL2 service increased in its stead.<ref name=netransit /> In October 2009, the SL2 terminus was renamed "Design Center" with no changes in service.<ref name=netransit />

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.<ref>{{cite web |url=https://cdn.mbta.com/sites/default/files/projects/betterbus/route-profiles/SL2.pdf |title=Route SL2: Design Center–South Station |work=Better Bus Project |date=December 2018 |publisher=Massachusetts Bay Transportation Authority}}</ref> On December 22, 2019, the route was changed so that buses proceeded around the whole loop before the layover at all times.<ref>{{cite press release |url=https://www.mbta.com/news/2019-12-18/bus-schedule-changes-winter-2020 |title=Bus Schedule Changes for Winter 2020 |date=December 7, 2019 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=netransit /> On March 15, 2020, afternoon service began laying over at 23 Dry Dock Avenue before making the loop.<ref>{{cite press release |url=https://mbta.com/news/2020-02-29/bus-schedule-changes-spring-2020 |title=Bus Schedule Changes for Spring 2020 |date=February 29, 2020|publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=netransit />

In January 2021, Massport approved a ground lease agreement for [[air rights]] development over Silver Line Way station, which will include improvements to the stop.<ref name=mpajan2021>{{cite web |url=https://www.massport.com/media/dnlcn5sb/massport-january-board-meeting-deck_1-21-21.pdf |title=Massachusetts Port Authority Board Meeting |date=January 21, 2021 |publisher=Massachusetts Port Authority}}</ref>{{rp|99}} On March 13, 2022, all SL2 buses began laying over at 23 Dry Dock Avenue. The stop at 88 Black Falcon Avenue, closed since April 2019 due to pier repairs, was permanently cut at that time.<ref name=88bf /><ref name=netransit /><ref name=march132022>{{cite web |url=https://cdn.mbta.com/sites/default/files/route_pdfs/2022-spring/SL123_4.pdf |title=SL1 SL2 SL3 |publisher=Massachusetts Bay Transportation Authority |date=March 13, 2022}}</ref> An improved stop on the east side of 27 Drydock Avenue (at Black Falcon Avenue) is planned by 2025 as part of redevelopment of 88 Black Falcon Avenue.<ref name=mpajan2021 />{{rp|73}} The May 2022 draft network plan called for routes SL1 and SL3 to use D Street to more directly access the Ted Williams Tunnel, with only route SL2 plus SLW shuttles serving Silver Line Way.<ref name=draftmap /><ref>{{cite web |url=https://cdn.mbta.com/sites/default/files/Bus%20Network%20Redesign/33_Seaport.pdf |title=A better bus network: new connections, more service, more frequency. See what this means in the Seaport and South Boston. |date=May 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref> The November 2022 revised proposal kept this change, with SL2 enhanced to higher frequency service all days.<ref name=nov2022changes>{{cite web |url=https://cdn.mbta.com/sites/default/files/2022-11/2022-11-7-bnrd-summary-of-changes-english-accessible.pdf |title=What we changed from the May 2022 Proposal |date=November 7, 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=nov2022map>{{cite web |url=https://cdn.mbta.com/sites/default/files/2022-11/2022-11-3-bnrd-revised-bus-network-map-7-mb.pdf |title=Revised Bus Network Fall 2022 |date=November 3, 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref>
{{Anchor|Phase III}}

=== Phase III plans ===
[[File:Silver Line Phase III alternatives labelled.svg|thumb|right|Silver Line Phase III alternatives, showing the original 4 alignments plus the Charles Street Modified (CSM) alignment. The preferred route at the time of the project's cancellation was the CSM alignment (pink) feeding into the core tunnel (green).|alt=Map of the southern portion of downtown Boston with rail lines and the Silver Line marked. The core alignment of Phase III runs south from South Station, then west along Essex Street and Boylston Street to Charles Street, with intermediate stations at Chinatown and Boylston. Five potential alignments for the southern section are shown; the first four begin at the intersection of Charles Street and Boylston Street. The Columbus Avenue alignment follows Columbus Avenue from Charles Street to Berkeley Street. The Charles Street modified alignment follows Charles Street and a short section of Tremont Street. The Charles Street alignment follows Charles Street and turns east across Eliot Norton Park to Tremont Street. The Stuart Street alignment follows Charles Street and Stuart Street to Tremont Street. The Tremont Street alignment begins at Boylston station; it follows Tremont Street south and turns east to Washington Street.]]
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, Boston|Central Burying Ground]].<ref name=phase3>{{cite book |url=https://books.google.com/books?id=-ho3AQAAMAAJ |title=Silver Line Phase III: Supplemental Draft Environmental Impact Statement / Supplemental Environmental Impact Report |publisher=Federal Transit Administration and Massachusetts Bay Transportation Authority |date=June 2005 |volume=1 |via=Google Books}}</ref>{{rp|2.5–6}} 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 {{bts|New England Medical Center}} (NEMC) station, with a portal to Washington Street just north of Oak Street.<ref name=phase3 />{{rp|2.5–7}} 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.<ref name=phase3 />{{rp|2.8}}

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.<ref name=2007report />{{rp|27}} 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.<ref name=PMT3>{{cite web |archive-url=https://web.archive.org/web/20120206131017/http://www.bostonmpo.org/bostonmpo/pmt-old/PMT-3.pdf |archive-date=February 6, 2012 |url=http://www.bostonmpo.org/bostonmpo/pmt-old/PMT-3.pdf |title=Chapter 5C: System Expansion |work=Program of Mass Transportation |date=May 2003 |publisher=Boston Regional Metropolitan Planning Organization |access-date=May 6, 2013 |page=5C-6,8,10,12,16}}</ref> 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.<ref name=phase3 />{{rp|2.10–15}} A proposal to consolidate the Chinatown and Boylston 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.<ref name=phase3 />{{rp|2.15–22}} 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.<ref name=phase3 />{{rp|2.22–25}}

Continued concerns about the Common, concerns from [[Bay Village, Boston|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 (Boston)|Columbus Avenue]] to the southwest.<ref name=phase3 />{{rp|2.23–28}} Capital cost was originally estimated at $768–812&nbsp;million depending on the portal location; completion was moved from 2010 to 2013.<ref name=phase3 />{{rp|3.38, 6.1}} Daily ridership for the completed Silver Line system was estimated to reach 160,000 by 2025.<ref name=phase3 />{{rp|3.33}} In August 2005, the MBTA put the Phase III project "on hold" in order to build community consensus on a locally preferred routing.<ref name=3dphase>{{cite news |archive-url=https://web.archive.org/web/20060115180758/http://www.boston.com/news/local/massachusetts/articles/2005/08/18/mbta_puts_hold_on_3d_final_phase_of_its_silver_line/ |archive-date=January 15, 2006 |url=http://www.boston.com/news/local/massachusetts/articles/2005/08/18/mbta_puts_hold_on_3d_final_phase_of_its_silver_line/ |newspaper=The Boston Globe |title=MBTA puts hold on 3d, final phase of its Silver Line |first=Mac |last=Daniel |date=August 18, 2005}}</ref>

In February 2006, State Transportation Secretary John Cogliano proposed a $94&nbsp;million plan that would eliminate most of the tunneling and cost of the original proposal while still connecting the two phases of the service.<ref name=essex /> 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 (MBTA)|Red Line]] stations at {{bts|Mattapan}} via Blue Hill Avenue (replacing route {{MBTABus|28}}) and {{bts|Ashmont}} via Washington Street (replacing route {{MBTABus|23}})<ref name=essex>{{cite news |url=http://archive.boston.com/news/local/massachusetts/articles/2006/02/10/new_silver_line_plan_offered_stirring_critics/?page=full |title=New Silver Line plan offered, stirring critics |newspaper=Boston Globe |date=February 10, 2006 |author=Daniel, Mac |access-date=May 6, 2013}}</ref> 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.<ref name=essex />
[[File:SouthStationSL4shelter.agr.jpg|thumb|Shelter at [[South Station]] for route SL4|alt=A large bus shelter on an urban street]]
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.<ref>{{cite web |archive-url=https://web.archive.org/web/20100102104009/http://mbta.com/uploadedFiles/About_the_T/T_Projects/T_Projects_List/Silver%20Line%20-%20Four%20Alternative%20Alignments.pdf |title=Alternatives Studied |url=http://mbta.com/uploadedFiles/About_the_T/T_Projects/T_Projects_List/Silver%20Line%20-%20Four%20Alternative%20Alignments.pdf |publisher=Massachusetts Bay Transportation Authority |author=URS / DMJM Harris |access-date=May 6, 2013 |archive-date=January 2, 2010}}</ref><ref>{{Cite news |archive-url=https://web.archive.org/web/20060615023507/http://boston.com/news/local/articles/2006/03/10/officials_endorse_silver_line_tunnel/ |archive-date=June 15, 2006 |url=http://www.boston.com/news/local/articles/2006/03/10/officials_endorse_silver_line_tunnel |title=Officials endorse Silver Line tunnel |author=Daniel, Mac |newspaper=Boston Globe |date=March 10, 2010 |access-date=April 22, 2011}}</ref><ref>{{cite web |archive-url=https://web.archive.org/web/20091229163124/http://www.mbta.com/uploadedFiles/About_the_T/T_Projects/T_Projects_List/Silver%20Line%20Phase%20III%20--%20Charles%20Modified%20Alignment.pdf |url=http://www.mbta.com/uploadedFiles/About_the_T/T_Projects/T_Projects_List/Silver%20Line%20Phase%20III%20--%20Charles%20Modified%20Alignment.pdf |title=Charles Street Modified (CSM) alignment |publisher=Massachusetts Bay Transportation Authority |author=URS / DMJM Harris |access-date=May 6, 2013 |archive-date=December 29, 2009}}</ref> 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.<ref>{{cite web |archive-url=https://web.archive.org/web/20100102104056/http://mbta.com/uploadedFiles/documents/CSM_portal_graphic.pdf |url=http://mbta.com/uploadedFiles/documents/CSM_portal_graphic.pdf |title=Tremont Two-way Portal Contra Flow Alternative |work=Silver Line Phase III: Tunnel and System Wide Elements |publisher=Massachusetts Bay Transportation Authority |author=URS / DMJM Harris |access-date=May 6, 2013 |archive-date=January 2, 2010}}</ref> On December 12, 2006, the FTA approved the project to re-enter its funding process.<ref name=2007report />{{rp|27}} 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.<ref name="all_about">{{cite web |url=http://www.mbta.com/about_the_mbta/t_projects/?id=1072 |title=MBTA Transit Projects: Silver Line Phase 3 |publisher=Massachusetts Bay Transportation Authority |archive-url=https://web.archive.org/web/20081206090354/http://www.mbta.com/about_the_mbta/t_projects/?id=1072 |archive-date=December 6, 2008 |access-date=June 22, 2012}}</ref><ref>{{cite news |url=http://www.mysouthend.com/index.php?ch=news&sc=&sc2=news&sc3=&id=78529 |title=Silver Line Phase III moving forward |author=Kearnan, Scott |date=August 7, 2008 |archive-url=https://web.archive.org/web/20110714144532/http://www.mysouthend.com/index.php?ch=news&sc=&sc2=news&sc3=&id=78529 |archive-date=July 14, 2011 |newspaper=My South End}}</ref>

However, the estimated price of the tunnel plan, dubbed the "Little Dig", had risen to $2.1&nbsp;billion by May 2009.<ref name=littledig>{{cite news |url=http://archive.boston.com/news/local/massachusetts/articles/2009/05/10/little_dig_in_danger/ |title=Little Dig in Danger |newspaper=Boston Globe |date=May 10, 2009 |access-date=April 22, 2011}}</ref> 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]] (MassDOT) 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.<ref>{{cite web |url=https://old.mbta.com/uploadedfiles/About_the_T/Environment/2010%20Annual%20Report.pdf |title=Annual Status Report |date=July 9, 2010 |author=Mohler, David J. |publisher=Massachusetts Bay Transportation Authority}}</ref>

A partial solution that did not require a new tunnel opened on October 13, 2009, after expedited construction using [[American Recovery and Reinvestment Act of 2009|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.<ref name=directconnect>{{cite press release |url=https://www.mbta.com/news/2009-10-13/patrick-murray-administration-mayor-menino-launch-silver-line-direct-connect |title=PATRICK-MURRAY ADMINISTRATION, MAYOR MENINO LAUNCH SILVER LINE DIRECT CONNECT SERVICE TO SOUTH STATION |date=October 13, 2009 |publisher=Massachusetts Bay Transportation Authority}}</ref>

{{anchor|Extension to Chelsea|Chelsea|Silver Line Gateway}}

===Extension to Chelsea===
[[File:Chelsea Station.agr.jpg|thumb|left|Chelsea station in July 2018|alt=A bus rapid transit station with a loop]]
The [[Urban Ring Project (MBTA)|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.<ref>{{cite web |archive-url=https://web.archive.org/web/20110708181035/https://www.commentmgr.com/projects/1169/docs/URnews0105c.pdf |archive-date=July 8, 2011 |url=https://www.commentmgr.com/projects/1169/docs/URnews0105c.pdf |title=Urban Ring Phase 2 FACT SHEET |date=January 2009}}</ref><ref name=urplans>{{cite web |archive-url=https://web.archive.org/web/20170227011401/http://www.massdot.state.ma.us/theurbanring/downloads/Plan_Profile_Drawings.pdf |archive-date=February 27, 2017 |url=http://www.massdot.state.ma.us/theurbanring/downloads/Plan_Profile_Drawings.pdf |title=The Urban Ring Phase 2: Revised Draft Environmental Impact Report/Statement |publisher=Massachusetts Executive Office of Transportation |date=November 2008}}</ref> The project was cancelled in 2010 due to high cost, but planning for several smaller sections continued.<ref name=ctps2012 >{{cite web |url=https://www.ctps.org/data/calendar/pdfs/2012/10.31_SilverLine.pdf |title=Work Program for: MBTA Silver Line to Chelsea: Alternatives Analysis, Phase 2 |first=Karl H. |last=Quackenbush |date=November 1, 2012 |publisher=Central Transportation Planning Staff}}</ref> The [[Chelsea, Massachusetts|Chelsea]]–South Boston section was given high priority because Chelsea was densely populated yet underserved by transit.<ref name=ctps2012 /> MassDOT had also purchased the [[Grand Junction Railroad|Grand Junction Branch]] – including abandoned sections in Chelsea and East Boston – from [[CSX Transportation]] in 2010, meaning that a potential right-of-way (which the Urban Ring had proposed to use) was available.<ref name=ctps2012 /> A state study in 2011 analyzed potential Chelsea services, including a Silver Line branch to Bellingham Square or the Chelsea commuter rail station, or improvements to the route {{MBTABus|112}} bus.<ref name=ctps2012 /><ref>{{cite web |archive-url=https://web.archive.org/web/20150820232458/http://www.massdot.state.ma.us/Portals/31/Docs/Sl-toAirportandChelsea_CTPS.pdf |archive-date=August 20, 2015 |url=http://www.massdot.state.ma.us/Portals/31/Docs/Sl-toAirportandChelsea_CTPS.pdf |title=Analysis of Silver Line Service to Airport Station and Chelsea |first=Scott |last=Peterson |publisher=Central Transportation Planning Staff}}</ref>

In 2013, MassDOT began public planning of the ''Silver Line Gateway'' project. In addition to serving Chelsea, the proposed line would provide [[Blue Line (MBTA)|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 {{bts|Airport}} station, then the 2012-opened Coughlin Bypass Road to the [[Chelsea Street Bridge (Boston)|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 {{bts|Eastern Avenue}}, {{bts|Box District}}, {{bts|Bellingham Square}} at the Chelsea commuter rail station, and [[Chelsea station (MBTA)|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.<ref>{{cite web |url=http://www.massdot.state.ma.us/Portals/31/Docs/SL_Gateway_June_19_2013_English_Accessible.pdf |title=Silver Line Gateway Alternatives Analysis |publisher=Massachusetts Department of Transportation |date=June 19, 2013 |archive-url=https://web.archive.org/web/20131105011820/http://www.massdot.state.ma.us/Portals/31/Docs/SL_Gateway_June_19_2013_English_Accessible.pdf |archive-date=November 5, 2013}}</ref>

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.<ref>{{cite web |url=http://www.massdot.state.ma.us/Portals/31/Docs/SLG_092413_English.pdf |title=Silver Line Gateway Alternatives Analysis: Public Meeting – September 18, 2013 |date=September 18, 2013 |author=Hamwey, Scott |publisher=Massachusetts Department of Transportation |archive-url=https://web.archive.org/web/20131105012200/http://www.massdot.state.ma.us/Portals/31/Docs/SLG_092413_English.pdf |archive-date=November 5, 2013}}</ref> On October 30, 2013, MassDOT announced $82.5&nbsp;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 {{bts|Chelsea}} (Mystic Mall) and a $3&nbsp;million, {{convert|3/4|mile|adj=on}} multi-use path from Eastern Avenue to Washington Street.<ref name=stateannouncement>{{cite press release |url=https://www.mbta.com/news/2013-10-30/gov-patrick-announces-expansion-silver-line |title=Governor Patrick Announces MBTA Silver Line Expansion |publisher=Massachusetts Bay Transportation Authority |date=October 30, 2013}}</ref> The Environmental Impact Report was issued in March 2014.<ref>{{cite book |archive-url=https://web.archive.org/web/20141023132443/http://www.massdot.state.ma.us/Portals/31/Docs/SLGateway_SEIR_Final_03-31-14.pdf |archive-date=October 23, 2014 |url=http://www.massdot.state.ma.us/Portals/31/Docs/SLGateway_SEIR_Final_03-31-14.pdf |title=Silver Line Gateway Service to Chelsea, East Boston & the Blue Line: Single Environmental Impact Report (Single EIR): EEA # 15124 |date=March 31, 2014 |publisher=Massachusetts Department of Transportation}}</ref> MassDOT awarded a $33.8&nbsp;million construction contract for the first phase of the project on September 17, 2014. That phase included the {{convert|1.3|mile|adj=on}}-long busway, the four Silver Line stations, replacement of the Washington Street bridge, and the [[Chelsea Greenway]].<ref>{{cite press release |url=http://blog.mass.gov/transportation/mbta/mbta-silver-line-to-chelsea-approved/ |title=MBTA Silver Line to Chelsea Approved |date=September 17, 2014 |publisher=Massachusetts Department of Transportation |access-date=October 11, 2019 |archive-date=March 26, 2018 |archive-url=https://web.archive.org/web/20180326023346/http://blog.mass.gov/transportation/mbta/mbta-silver-line-to-chelsea-approved/ |url-status=dead }}</ref>

Silver Line service to Chelsea (route SL3) began on April 21, 2018.<ref>{{Cite press release |url=https://www.mbta.com/news/2018-03-12/new-silver-line-3-chelsea-service-between-chelsea-and-south-station |title=New Silver Line 3-Chelsea Service between Chelsea and South Station |publisher=Massachusetts Bay Transportation Authority |date=March 12, 2018}}</ref> By October, daily ridership reached 6,200.<ref name=chelseaupdate /> 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; the new station opened on November 15, 2021.<ref name=chelsea-commuter>{{cite web |url=https://www.mbta.com/projects/chelsea-commuter-rail-station |title=Chelsea Commuter Rail Station |publisher=Massachusetts Bay Transportation Authority |access-date=September 13, 2019}}</ref><ref>{{cite press release |url=https://www.mbta.com/projects/chelsea-commuter-rail-station/update/new-chelsea-commuter-rail-station-opens-november-15 |title=New Chelsea Commuter Rail Station Opens November 15 |date=November 1, 2021 |publisher=Massachusetts Bay Transportation Authority}}</ref> {{As of|January 2024}}, the MBTA and the City of Boston plan to reconfigure Day Square in East Boston in late 2024. The project would include bus lanes on Chelsea Street and a bus-only street through Day Square, with a Day Square station for use by the SL3 and local bus routes.<ref>{{cite report |url=https://www.bostonplans.org/getattachment/ce2b7495-6808-4a4d-8bdc-74a5c20664fd |pages=108, 109 |title=PLAN: East Boston |publisher=Boston Planning & Development Agency |date=January 10, 2024<!--document incorrectly says 2023-->}}</ref><ref>{{cite press release |url=https://www.bostonplans.org/news-calendar/news-updates/2024/01/18/bpda-board-adopts-east-boston-tomorrow-plan-east-b |title=BPDA Board adopts East Boston Tomorrow: PLAN: East Boston planning initiative |date=January 18, 2024 |publisher=Boston Planning & Development Agency}}</ref>
{{anchor|Future development}}

===Sullivan Square extension===
[[File:Sullivan Square Busway August 2024.jpg|thumb|right|Sullivan Square station, the proposed terminal of the extension|alt=A two-level busway under an urban highway viaduct]]
In March 2019, state and local officials indicated plans to extend service from {{bts|Chelsea}} on two routes to [[Kendall Square]] and to [[North Station]], both via [[Sullivan Square station|Sullivan Square]]. The routes would primarily use dedicated busways and bus lanes, although it was not decided whether they would be under the Silver Line brand.<ref>{{cite news |url=https://www.bostonglobe.com/metro/2019/03/16/silver-line-route-extending-sullivan-square-north-station-and-kendall/4OMXe8E66YRjdULWNDjRWL/story.html |title=Silver Line-style bus could serve Sullivan Square, North Station and Kendall |newspaper=Boston Globe |date=March 16, 2019 |first=Adam |last=Vaccaro}}</ref> In January 2021, the MBTA and MassDOT began work on the Silver Line Extension (SLX), which would look into route alternatives from Chelsea into Everett, Somerville, Cambridge, and Boston.<ref>{{cite press release |url=https://www.mbta.com/news/2021-01-25/mbta-and-massdot-announce-launch-study-extending-silver-line-service-everett |title=MBTA and MassDOT Announce Launch of Study Extending Silver Line Service to Everett, Somerville, Cambridge, and Boston |date=January 25, 2021 |publisher=Massachusetts Bay Transportation Authority}}</ref> Six potential corridors were identified by September 2021: to {{bts|Wellington}}, to Sullivan, to {{bts|Malden Center}}, to downtown Boston via Sullivan, to Kendall Square via Sullivan, and to Kendall Square via Wellington. Some corridors could be operated as new routes independent from the SL3, with Chelsea or Airport as potential termini rather than South Station.<ref>{{cite web |url=https://cdn.mbta.com/sites/default/files/2021-10/2021-10-05-slx-public-meeting-2-presentation.pdf |page=26 |title=SL – Extension: Public Meeting #2 |date=September 28, 2021 |publisher=Massachusetts Bay Transportation Authority}}</ref>

Alternatives were presented in September 2022. Three potential SL3 extensions would run to Malden Center, Wellington, or Sullivan – all via Everett Square, with varying amounts of dedicated bus lanes on the western portion. Four potential SL6 routes were identified: Everett (Glendale Square)–Kendall via [[McGrath Highway]], Everett–Kendall via the Gilmore Bridge, Everett–Haymarket via [[Massachusetts Route 99|Rutherford Avenue]], and Eastern Avenue–Kendall via Everett Square. All of the potential SL6 routes would operate primarily in dedicated lanes.<ref>{{cite web |url=https://cdn.mbta.com/sites/default/files/2022-09/2022-09-21-english-slx-alternatives-analysis.pdf |title=SL – Extension Alternatives Analysis |date=September 21, 2022 |publisher=Massachusetts Bay Transportation Authority}}</ref> A SL3 extension to Sullivan was announced as the preferred alternative in March 2024; the study recommended that SL6 planning be deferred pending related planning efforts for Sullivan Square, Rutherford Avenue, the Gilmore Bridge, and Kendall Square, as well as implementation of the planned bus network redesign.<ref name=sl3march2024 /><ref name=slxaa />

The proposed SL3 extension would run in an off-street busway west to 2nd Street, mixed traffic (possibly later dedicated lanes) on 2nd Street and Spring Street, and dedicated lanes on Chelsea Street and most of [[Massachusetts Route 99|Broadway]]. South of Sweetser Circle, a dedicated busway would be built on Lower Broadway. New stops would be located on 2nd Street at Boston Street and Spring Street; on Broadway at Chelsea Street (Everett Square), Beacham Street, and Horizon Way; and at Sullivan Square station. The extension would add {{convert|6.36|miles}} of round trip distance, with {{convert|5.18|miles}} – 80% – in dedicated bus lanes. It was estimated to increase SL3 ridership by 15,000 daily boardings by 2040, with a capital cost of $95 million.<ref name=sl3march2024>{{cite press release |url=https://www.mbta.com/news/2024-03-08/mbta-and-massdot-recommend-extending-silver-line-3-chelsea-orange-lines-sullivan |title=MBTA and MassDOT Recommend Extending Silver Line 3 from Chelsea to Orange Line's Sullivan Square Station |date=March 8, 2024 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref name=slxaa>{{cite book |url=https://cdn.mbta.com/sites/default/files/2024-03/2024-02-mbta-silver-line-extension-alternatives-analysis-report.pdf |title=Silver Line Extension Alternatives Analysis: Final Report |date=February 2024 |publisher=Massachusetts Department of Transportation and Massachusetts Bay Transportation Authority}}</ref> In June 2024, the MBTA was awarded a $22.4 million federal grant for reconstruction of the Lower Broadway segment for existing bus routes and eventual Silver Line service.<ref>{{cite press release |url=https://www.markey.senate.gov/news/press-releases/sens-markey-warren-gov-maura-healey-rep-pressley-celebrate-224-million-for-everett-and-boston-mbta-project-funded-by-bipartisan-infrastructure-law |title=Sens. Markey, Warren, Gov. Maura Healey, Rep. Pressley Celebrate $22.4 Million for Everett and Boston MBTA Project Funded by Bipartisan Infrastructure Law |date=June 25, 2024 |publisher=Office of Senator Ed Markey}}</ref>

===Other proposed corridors===
[[File:Pleasant Street Branch.png|thumb|right|Southern branch of the [[Tremont Street subway]] near the former [[Pleasant Street portal]]. This tunnel was briefly considered for use in the Phase III tunnel and is the likely connecting route for a proposed conversion of the Washington Street section of the Silver Line to a branch of the Green Line.|alt=View through a two-track railway tunnel]]
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 (MBTA)|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.<ref name=PMT3 />

A number of Silver Line expansion corridors were considered in the 2003 Program for Mass Transportation (PMT); most were given brief consideration but not acted upon. One, a BRT express overlay for the [[28 (MBTA bus)|route 28 bus]] (which runs between [[Ruggles station]] and Mattapan via Nubian), 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.<ref>{{cite web |url=http://www.eot.state.ma.us/downloads/direct_connect/BRT-Brochure.pdf |title=Mattapan Bus Rapid Transit and South Station Direct Connect Project |publisher=Massachusetts Executive Office of Transportation |date=May 2009 |archive-url=https://web.archive.org/web/20110108004614/http://www.eot.state.ma.us/downloads/direct_connect/BRT-Brochure.pdf |archive-date=January 8, 2011}}</ref> 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.<ref>{{cite news |url=http://www.bostonmagazine.com/news/2011/08/31/28x-debacle-missed-opportunities/ |title=The MBTA's 28X Debacle, aka, Missed Opportunity |newspaper=Boston Magazine |date=August 31, 2011 |first=Steve |last=Poftak}}</ref> Subsequent planning for bus improvements on Blue Hill Avenue has occurred without Silver Line branding.<ref>{{cite news |url=https://www.bostonglobe.com/2024/02/28/metro/blue-hill-avenue-getting-center-bus-lanes/ |archive-date=February 28, 2024 |archive-url=https://web.archive.org/web/20240228194154/https://www.bostonglobe.com/2024/02/28/metro/blue-hill-avenue-getting-center-bus-lanes/ |date=February 28, 2024 |newspaper=The Boston Globe |first=Taylor |last=Dolven |title='Transformational' bus system is coming to traffic-choked Blue Hill Avenue, city says}}</ref><ref>{{cite press release |url=https://www.boston.gov/news/mayor-wu-announces-44-million-investment-transform-blue-hill-avenue |title=Mayor Wu Announces $44 Million Investment to Transform Blue Hill Avenue |publisher=City of Boston |date=February 28, 2024}}</ref>

Several other corridors were considered in the 2003 PMT. These included a Dudley–Ashmont route replacing the [[23 (MBTA bus)|route 23 bus]] (also revived in 2006 in Phase III planning, but not during the 28X proposal), as well as a new BRT tunnel to [[Kenmore station|Kenmore]] with surface branches to the [[Longwood Medical Area]] via [[Brookline Avenue]] and [[Allston, Massachusetts|Allston]] via [[Commonwealth Avenue (Boston)|Commonwealth Avenue]], the [[Mass Pike]], and Cambridge Street.<ref name=PMT3 /><ref name=PMT4 /> The City of Boston proposed an alternate western Silver Line branch using buses along the Mass Pike without a new tunnel, similar to existing [[List of MBTA bus routes#501-599|express buses]].<ref name=PMT4>{{cite web |archive-url=https://web.archive.org/web/20120206131017/http://www.bostonmpo.org/bostonmpo/pmt-old/PMT-4.pdf |archive-date=February 6, 2012 |url=http://www.bostonmpo.org/bostonmpo/pmt-old/PMT-4.pdf |title=Chapter 5C: System Expansion |work=Program of Mass Transportation |date=January 2004 |publisher=Boston Regional Metropolitan Planning Organization |page=5C–42,76}}</ref>

The 2003 PMT included the possibility of converting the Washington Street section of the Silver Line to light rail (as had originally been promised) using the abandoned southern section of the [[Tremont Street subway|Tremont Street Subway]]. The project was estimated to cost $374&nbsp;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.<ref name=PMT4 /> In 2012, the Roxbury–Dorchester–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.<ref name=RDM>{{cite web |url=https://www.mass.gov/files/documents/2018/03/02/RDMreport.pdf |title=Roxbury–Dorchester–Mattapan Transit Needs Study |date=September 2012 |page=53 |publisher=Massachusetts Department of Transportation<!-- https://archives.lib.state.ma.us/handle/2452/783909 -->}}</ref>

==Service==
===Frequency and ridership===
[[File:MBTA route SLW bus at Courthouse station, March 2017.JPG|thumb|right|The SLW was one of three MBTA bus routes to show a net profit in a 2012 study.|alt=A trolleybus at an underground station]]
The Silver Line routes are among the most frequent MBTA bus routes. All routes (except for the SLW shuttle) run at least every 15 minutes during all service hours, save for late evening and weekend service on the SL4. At peak hours, combined frequency on the trunk sections is about 30 buses per hour (2 minute headways) in each direction in the Transitway, and 12 buses per hour (5 minute headways) on Washington Street.<ref name=feb2022 /> The routes have high ridership (though lower than many [[MBTA key bus routes|key bus routes]]) and low costs per rider compared to other bus routes in the MBTA system. In 2012, three routes (SL1, SL5, SLW) were the only MBTA bus routes to show a profit; the median net cost (after fares) on all MBTA bus routes was $2.13 per passenger.<ref name="RPI2012">{{cite web |url=https://old.mbta.com/uploadedfiles/Fares_and_Passes_v2/Route%20Performance%20Indicators%207-6%20Fixed.pdf |title=MBTA Route Performance Indicators |year=2012 |publisher=Massachusetts Bay Transportation Authority |author=Office of Transportation Planning staff |access-date=May 7, 2013}}</ref> In 2023, combined weekday ridership on Silver Line routes was 27,000.<ref name=ridership />

In addition to the [[MBTA nomenclature|public route name]], the Silver Line and [[MBTA crosstown bus routes|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.<ref name=bluebook>{{MBTA Bluebook 2014}}</ref>

{| class="wikitable"
|-
!Route
!#
!Rush hour headways<ref name=feb2022 />
!Midday headways<ref name=feb2022 />
!Weekend headways<ref name=feb2022>{{cite magazine |magazine=Rollsign |publisher=[[Boston Street Railway Association]] |date=January–February 2022 |issue=1–2 |volume=59 |title=MBTA Vehicle Inventory as of February 28, 2022 |first=Jonathan |last=Belcher |page=27}}</ref>
!Weekday ridership (2018)<ref name=profiles>{{cite web |url=https://www.mbta.com/projects/better-bus-project/update/bus-route-profiles-now-available |title=Bus Route Profiles Now Available |date=December 10, 2018 |publisher=Massachusetts Bay Transportation Authority}}</ref>
|-
|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<ref name=chelseaupdate />
|-
|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
|}

===Criticism===
====Mode choice====
{{Quote box
 |quote = This is not bus rapid transit. All they did was take a diesel bus, change the engine, paint it silver and run it down the street through traffic.
 |author = Roxbury activist Bob Terrell<ref name=localdiversity />
 |width = 300px
 |quoted=1
}}

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.<ref name=essex /> Riders supported light rail; the decision to instead run buses was viewed as a broken promise and intentional disinvestment.<ref name=ITDP /><ref name=localdiversity /> 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.<ref name=essex /> 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".<ref name=localdiversity /><ref>{{cite thesis |type=MST |title=Moving forward equitably? : Analyzing the impact of transportation changes on Boston's neighborhoods |pages=6–7 |last=Techagumthorn |first=Yanisa |publisher=Massachusetts Institute of Technology |year=2019|hdl = 1721.1/121751}}</ref> 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".<ref name=localdiversity>{{cite book |chapter-url=https://books.google.com/books?id=HpasAgAAQBAJ&pg=PA97 |title=Place-Based Education in the Global Age: Local Diversity |first1=David A. |last1=Gruenewald |first2=Gregory A. |last2=Smith |publisher=Routledge |year=2014 |isbn=9781317670636 |via=Google Books |chapter=A Bill, A "Silver Lie," Budget Cuts, and Bioweapons: 2000–2005 |pages=95–101}}</ref><ref name=anson>{{cite thesis |type=MST |title=Visualizing urban accessibility metrics for incremental bus rapid transit projects |first=Anson Forest |last=Stewart |publisher=Massachusetts Institute of Technology |year=2014 |pages=92–94|hdl = 1721.1/92057}}</ref>

Two theoretical advantages of BRT compared to light rail are low cost and speedy implementation.<ref name=ITDP />{{rp|6}} However, Silver Line service did not begin on 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.<ref name=ITDP /><ref>{{cite report |url=http://www.reconnectingamerica.org/assets/Uploads/bestpractice246.pdf |page=8 |title=Funding Bus Rapid Transit in the U.S. |first=Lisa |last=Callaghan |year=2007 |publisher=Transportation Research Board}}</ref> Like the [[Downtown Seattle Transit Tunnel]] (which was later converted to light rail), the Transitway had comparable construction cost to light rail, but a lower level of service.<ref>{{cite book |url=https://books.google.com/books?id=MKipDAAAQBAJ&pg=PA501 |page=501 |title=Transportation Planning Handbook |first=Michael D. |last=Meyer |year=2016 |publisher=John Wiley & Sons |isbn=9781118762400 |via=Google Books}}</ref> At the time of its cancellation, Phase III was expected to cost $2.1&nbsp;billion - more than three times that of the Transitway.<ref name=littledig /> 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.<ref name=ITDP /><ref name=anson />

====BRT quality====
[[File:Washington Street with bus lanes, August 2016.JPG|thumb|right|Red-painted bus lanes on an uncongested section of Washington Street|alt=A urban street with parallel parking, a red bus lane, and a genera travel lane in each direction]]
[[File:MBTA route SL2 bus waiting at D Street (3), September 2024.JPG|thumb|An SL2 bus waiting at the D Street light|alt=A bus waiting at a traffic signal at a tunnel portal]]
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]].<ref name=cham>{{cite thesis |type=MST |title=Understanding bus service reliability : a practical framework using AVL/APC data |last=Cham |first=Laura Cecilia |year=2006 |publisher=Massachusetts Institute of Technology|hdl = 1721.1/34381}}</ref>{{rp|99}} A 2011 study by the [[Institute for Transportation and Development Policy]] (ITDP) determined that the Silver Line was best classified as "Not BRT" because it lacked many of these [[BRT Standard]] features.<ref name=ITDP>{{cite web |last1=Weinstock |first1=Annie |last2=Hook |first2=Walter |last3=Replogle |first3=Michael |last4=Cruz |first4=Ramon |title=Recapturing Global Leadership in Bus Rapid Transit |url=https://www.itdp.org/wp-content/uploads/2014/07/20110526ITDP_USBRT_Report-HR.pdf |publisher=[[Institute for Transportation and Development Policy]] |date=May 2011 |url-status=live |archive-url=https://web.archive.org/web/20170125041845/https://www.itdp.org/wp-content/uploads/2014/07/20110526ITDP_USBRT_Report-HR.pdf |archive-date=January 25, 2017 |pages=45–46}}</ref>

Off-board fare collection is only present at the three underground stops.<ref name=2007report />{{rp|12}} A significant portion of delays on the surface sections are caused by long [[dwell time (transportation)|dwell time]]s, 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.<ref>{{cite news |url=https://www.bostonglobe.com/metro/2012/06/05/mbta-give-free-rides-from-airport/4ELdEe4yNLcqakFkZt5LmJ/story.html |title=MBTA to give free rides from airport |newspaper=Boston Globe |date=June 5, 2012 |first=Eric |last=Moskowitz}}</ref><ref>{{cite press release |url=https://www.massport.com/massport/media/newsroom/logan-passengers-ride-fare-free-on-the-silver-line/ |title=Pilot Program Offers Logan Passengers Free Silver Line Ride from Logan Airport to South Station |date=June 5, 2012 |publisher=Massachusetts Port Authority}}</ref> Within the first month, average dwell time dropped by 20 seconds per stop.<ref>{{cite press release |url=http://www.massport.com/massport/media/newsroom/free-silver-line-from-logan-airport-to-continue/ |title=Free Silver Line Rides from Logan to Continue Through September Program Shaves Almost Two Minutes off 10 minute Route; More Ridership Data Needed |date=July 19, 2012 |publisher=Massachusetts Port Authority}}</ref> Massport later extended the pilot until January 2013, then made free fares from Logan permanent.<ref name=tariff />{{rp|31}}<ref>{{cite press release |url=https://www.massport.com/massport/media/newsroom/free-silver-line-service-continues-through-new-year/ |title=Massport Holds the Line on Boston Logan Rates and Charges; Free Silver Line Service to Continue through New Year |date=September 20, 2012 |publisher=Massachusetts Port Authority}}</ref><ref>{{cite report |chapter-url=https://www.massport.com/media/2279/2014_edr_web_version_file1.pdf |title=2014 Environmental Data Report |pages=5–26 |chapter=Ground Access to and from Logan Airport |date=September 2015 |publisher=Massachusetts Port Authority}}</ref> 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.<ref name=alldoorpilot /> 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.<ref name=alldoorpilot>{{cite web |url=https://www.mbtabackontrack.com/blog/74-all-door-boarding-pilot-on-the-silver-line |title=ALL-DOOR BOARDING PILOT ON THE SILVER LINE |date=October 10, 2017 |publisher=Massachusetts Bay Transportation Authority |work=Data Blog}}</ref><ref>{{cite news |last1=Vaccaro |first1=Adam |title=All-door boarding made Silver Line buses move a little quicker |url=https://www.bostonglobe.com/metro/2017/10/07/all-door-boarding-made-silver-line-buses-move-little-quicker/tZp7E2VY6MGsWbfKv3Ku8I/story.html |access-date=February 7, 2018 |newspaper=Boston Globe |date=October 7, 2017}}</ref> All-door boarding will be permanently implemented on all routes in the 2020s as part of the [[AFC 2.0]] fare system.<ref>{{cite web |url=https://www.mass.gov/files/documents/2019/05/06/dot_glx_AFC_2-0_overview_20190402.pdf |title=AFC 2.0 Next generation MBTA fare system |date=April 2, 2019 |first=David |last=Sikorski |page=4 |publisher=Massachusetts Bay Transportation Authority}}</ref>

The Washington Street routes have dedicated bus lanes between {{bts|Herald Street}} and {{bts|Melnea Cass Boulevard}}, as well as on Essex Street.<ref name=2005report />{{rp|2.1}}<ref name=directconnect /> However, these lanes are not physically separated from general traffic lanes and are designated as right-turn lanes at many intersections.<ref name=anson /><ref name=nacto /> A lack of loading zones causes many vehicles to double-park in the bus lanes, and violations of the exclusive lanes are rarely prosecuted.<ref name=ITDP /><ref name=nacto>{{cite report |url=https://nacto.org/wp-content/uploads/2015/04/brt_report_panero.pdf |title=Peer-to-Peer Information Exchange on Bus Rapid Transit (BRT) and Bus Priority Best Practices |pages=41–44 |first=Marta |last=Panero |display-authors=et al |date=May 2012 |publisher=Federal Transit Administration |chapter=Appendix A: New York Workshop Summary}}</ref> In the most congested parts of the corridor – Nubian Square and Downtown Crossing – no dedicated lanes are present.<ref name=anson /> Transit signal priority (TSP) 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.<ref name=2005report />{{rp|2.10}}<ref>{{cite report |url=https://www.abettercity.org/docs/Surface%20Transportation%20Optimization%20and%20Bus%20Priority%20Measures%20Final.pdf |title=Surface Transportation Optimization and Bus Priority Measures: The City of Boston Context |page=23 |date=March 2013 |publisher=A Better City}}</ref> 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.<ref name=anson /> Headway reliability is poor, largely due to operators failing to depart Nubian on time.<ref name=cham />{{rp|136}} Additional enforced downtown bus lanes, plus traffic restrictions on Temple Place and new loading zones in Chinatown, were added by the city in 2020.<ref>{{cite press release |url=https://www.mbta.com/news/2020-07-06/new-bus-and-bike-lanes-established-washington-street-downtown-boston-and-chinatown |title=New Bus and Bike Lanes Established on Washington Street in Downtown Boston and Chinatown To Improve Silver Line and Traffic Safety |publisher=Massachusetts Bay Transportation Authority |date=July 6, 2020}}</ref>

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.<ref name=ITDP /> The tunnel was built for a maximum speed of {{convert|25|mph}}; the narrow lanes without [[guided bus]]es limit actual speeds to {{convert|15|mph}}.<ref name=2007report />{{rp|31}}<ref>{{cite news |url=https://commonwealthmagazine.org/transportation/forget-gondolas-turn-silver-line-green/ |title=Forget gondolas, turn Silver Line Green |first1=Ari |last1=Ofsevit |first2=Ethan |last2=Kensky |date=March 10, 2018 |newspaper=Commonwealth Magazine}}</ref> Water leakage and poor drainage has damaged the concrete floor of the tunnel, leading to "poor ride quality".<ref name=stateofthesystem /> The switch between electric and diesel power at Silver Line Way also represents a "significant delay".<ref name=ITDP /> 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 ("T under D") for [[grade separation]] was feasible, with a cost around $75&nbsp;million.<ref>{{cite report |url=https://books.google.com/books?id=Mhs3AQAAMAAJ&pg=PA9-IA99 |title=MBTA Silver Line Under D Street Feasibility Study |date=January 31, 2003 |publisher=Massachusetts Bay Transportation Authority |author=HDR |via=Google Books}}</ref> 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.<ref name=anson /><ref name=cao />{{rp|136}} In early 2016, the Boston Transportation Department modified the traffic light to use a fixed cycle, rather than relying on the detection of buses (only done during part of the cycle) 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.<ref>{{cite news |url=https://www.bostonglobe.com/metro/2016/02/20/what-going-with-silver-line-traffic-signal-street/EGyrgj2gV5Y6Cy3yQUyIOM/story.html |title=What's going on with the Silver Line traffic signal on D Street? |first=Nicole |last=Dungca |date=February 20, 2016 |newspaper=Boston Globe |access-date=February 22, 2016}}</ref> Proposed [[air rights]] development over the station is required not to preclude later grade separation of D Street.<ref>{{cite web |url=http://www.massport.com/rfpattachments/770cd19a-83ef-4341-b141-2bbf3664a505/01%20-%20Parcel%20H%20RFP%2006-27-2019.pdf |title=Request for Proposals For the PARCEL H DEVELOPMENT PROJECT |no-pp=yes |page=Figure 12 |publisher=Massachusetts Port Authority |date=June 27, 2019 |archive-url=https://web.archive.org/web/20201115005857/http://www.massport.com/rfpattachments/770cd19a-83ef-4341-b141-2bbf3664a505/01%20-%20Parcel%20H%20RFP%2006-27-2019.pdf |archive-date=November 15, 2020}}</ref> A gate and movable bollard near the light, which are used to prevent private vehicles from entering the Transitway, also cause delays to buses.<ref name=cao>{{cite thesis |type=MST |title=Improving public transportation to Boston Logan International Airport |last1=Cao |first1=Siyuan |last2=O'Connor |first2=Andrew |last3=Were |first3=Brenda |year=2013 |publisher=Massachusetts Institute of Technology|hdl = 1721.1/82806}}</ref>{{rp|141}}<ref>{{cite news |url=https://www.mbta.com/news/2007-04-16/high-tech-keep-out |title=A High-tech Keep Out |newspaper=Boston Globe |date=April 14, 2007 |first=Megan |last=Tench |via=Massachusetts Institute of Technology}}</ref>

Although stop spacing varies widely between BRT systems, distances from {{convert|0.5|miles}} to {{convert|1.0|miles}} are typically recommended.<ref>{{cite report |url=https://www.apta.com/wp-content/uploads/Standards_Documents/APTA-BTS-BRT-RP-004-10.pdf |title=Bus Rapid Transit Service Design |pages=11–12 |publisher=American Public Transportation Association |date=October 2010 |first1=Dave |last1=Roberts |display-authors=et al}}</ref> Even after dropping half the stops, the Washington Street corridor averages only {{convert|0.25|miles}} between stops, with several stop spacings as low as {{convert|0.10|miles}}.<ref name=2005report />{{rp|2.5}}<ref name=cham />{{rp|102}} The Washington Street stops were built with open canopies; protected shelters were not added until 2010.<ref name=2005report />{{rp|5.8}}<ref>{{cite press release |title=MBTA Silver Line Upgrades Coming |url=https://blog.mass.gov/transportation/mbta/mbta-silver-line-upgrades-coming/ |date=November 3, 2010 |publisher=Massachusetts Department of Transportation |archive-url=https://web.archive.org/web/20130722212942/https://blog.mass.gov/transportation/mbta/mbta-silver-line-upgrades-coming/ |archive-date=July 22, 2013}}</ref> A small traditional glass shelter is available at Temple Place; Boylston, Chinatown, and Tufts Medical Center have no shelters at all.<ref name=2005report />{{rp|3.2}} Silver Line Way and the SL2 surface stops have glass shelters or none at all; the SL3 surface stops have canopies without shelters.<ref name=2007report />{{rp|10}}
{{anchor|ramp}}

====Indirect routing====
[[File:State Police ramp near Ted Williams Tunnel, June 2017.JPG|thumb|right|The disputed ramp in 2017|alt=An entrance ramp to a below-grade urban expressway]]
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 {{convert|0.5|miles}} west on Haul Road from Silver Line Way 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 {{convert|0.3|miles}} east on Congress Street to reach Silver Line Way.<ref name=busmap /> 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 {{convert|0.7|miles}}. MassDOT claims the ramp was not designed for buses, though Big Dig planner [[Fred Salvucci]] has claimed it was.<ref name=couldget>{{cite news |url=https://www.bostonglobe.com/metro/2018/07/31/silver-line-commutes-could-get-quicker-with-opening-small-highway-ramp/lCVZH3TDH77k1KvRZ9vhbO/story.html |title=Silver Line commutes could get quicker, with the opening of a small highway on-ramp |first=Adam |last=Vaccaro |newspaper=Boston Globe |date=July 31, 2018}}</ref> 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.<ref>{{cite news |url=http://archive.boston.com/news/globe/editorial_opinion/editorials/articles/2006/07/19/mbta_to_the_rescue/ |title=MBTA to the Rescue |newspaper=Boston Globe |date=July 19, 2006}}</ref><ref name=2007report />{{rp|14}} The Urban Ring was also proposed to use the ramp.<ref name=urplans /> A 2010 study indicated that the ramp was safe for use by the Silver Line.<ref name=cao />{{rp|163}}

Transit advocates have since pushed to allow use of the ramp by Silver Line buses ("Free the ramp"), though MassDOT claims the ramp is not safe to use when highway traffic is freely flowing.<ref name=rampresults /> The MBTA hired a consultant in 2018 to study potential use of the ramp.<ref name=couldget /> 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 {{convert|30|mph}}.<ref>{{cite news |url=https://www.boston.com/news/local-news/2019/05/21/silver-line-ramp |title=The MBTA is freeing the most controversial ramp in Boston. Sort of. |first=Nik| last=DeCosta-Klipa |date=May 21, 2019 |newspaper=Boston Globe}}</ref> 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&nbsp;mph.<ref name=rampresults>{{cite web |url=https://www.mass.gov/files/documents/2019/09/17/dot_Silver%20Line%20_EmergencyAccess_091619.pdf |title=South Boston Waterfront – Emergency Access Ramp: Silver Line |date=September 16, 2019 |publisher=Massachusetts Department of Transportation}}</ref>

Silver Line buses were again allowed to use the ramp during a 2023 closure of the [[Sumner Tunnel]].<ref>{{cite press release |url=https://www.mass.gov/news/massachusetts-department-of-transportation-announces-alternative-travel-options-ahead-of-sumner-tunnel-closure |title=Massachusetts Department of Transportation Announces Alternative Travel Options Ahead of Sumner Tunnel Closure |date=June 9, 2023 |publisher=Massachusetts Department of Transportation}}</ref>

====Other issues====
The SL3 route is subject to frequent delays due to the opening of the [[Chelsea Street Bridge (Boston)|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 [[Massachusetts Route 1A|Route 1A]]. Federal regulations give priority to marine traffic.<ref>{{cite news |url=https://www.bostonglobe.com/metro/2018/06/29/new-chelsea-silver-line-hits-bridge-delays/JEmI2Fzu1DCdcn0G0R7roJ/story.html |title=New Chelsea Silver Line hits bridge delays |first=Adam |last=Vaccaro |date=June 29, 2018 |newspaper=Boston Globe}}</ref> 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 [[Andrew P. McArdle Memorial Bridge|Meridian Street Bridge]] used by the busy {{MBTABus|116}} and {{MBTABus|117}} bus routes.<ref name=chelseaupdate>{{cite web |url=https://cdn.mbta.com/sites/default/files/fmcb-meeting-docs/2018/december/2018-12-17-fmcb-chelsea-task-force-update-original-accessible.pdf |title=Chelsea Update |date=December 17, 2018 |publisher=Massachusetts Bay Transportation Authority}}</ref><ref>{{cite news |url=https://chelsearecord.com/2018/12/22/mbta-massport-seek-pilot-for-chelsea-street-bridge-restrictions/ |title=MBTA, MassPort Seek Pilot for Chelsea Street Bridge Restrictions |newspaper=Chelsea Record |date=December 22, 2018 |first=Seth |last=Daniel}}</ref>

The CNG buses bought for the Washington Street service caused disruptive 35&nbsp;Hz vibrations in nearby residential buildings.<ref>{{cite journal |url=https://trid.trb.org/view/813733 |title=Low-Frequency Noise Effects in Residential Buildings Along a Bus Rapid Transit (BRT) Route |journal=Noise-Con 04: The 2004 National Conference on Noise Control Engineering |year=2004 |last1=Towers |first1=David A. |last2=Ross |first2=Jason C. |last3=McDowell |first3=Jim}}</ref> 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.<ref name=2005report />{{rp|3.5}}
{{clear}}

==See also==
*[[Trolleybuses in Greater Boston]]

==References==
{{Reflist}}

===Notes===
{{reflist|group=note}}

==External links==
{{Attached KML}}
{{Commons category-inline}}
*MBTA: [https://www.mbta.com/schedules/741/line SL1], [https://www.mbta.com/schedules/742/line SL2], [https://www.mbta.com/schedules/743/line SL3], [https://www.mbta.com/schedules/751/line SL4], [https://www.mbta.com/schedules/749/line SL5]
*[https://www.mbta.com/projects/silver-line-extension-slx-alternatives-analysis Silver Line Extension (SLX) Alternatives Analysis]

{{MBTA}}
{{Massport}}
{{Massachusetts-Rhode Island transit agencies}}
{{USBRT}}
{{Crossings navbox
|structure        = Crossings
|place            = [[Fort Point Channel]]
|bridge           = Silver Line Way (tunnel)
|bridge signs     = {{rint|boston|silver|icon}}
|upstream         = [[Congress Street Bridge (Boston)|Congress Street Bridge]]
|upstream signs   = 
|downstream       = [[Evelyn Moakley Bridge]]
|downstream signs = 
}}

[[Category:Silver Line (MBTA)| ]]
[[Category:Trolleybus transport in the United States]]
[[Category:2002 establishments in Massachusetts]]
[[Category:MBTA bus]]