Twin Peaks Tunnel#Rail replacement project

File:Twin Peaks Tunnel and Observatory, Aug 1910 (SF Call) +curves.png

File:MUNI 1149 East Portal Feb 1967xRP - Flickr - drewj1946.jpg

Plans for a tunnel extending from Market Street under Twin Peaks were first presented at the Merchants' Association banquet in May 1909. A. W. Scott Jr. spoke on the need for the tunnel to open up the western part of San Francisco to development, as "40,000 San Franciscans lived across the bay or in San Mateo county because of the lack of proper transportation in this city."{{Cite news |date=May 28, 1909 |title=Mayor's tactful speech blasts Redding's hopes |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19090528.2.5 |access-date=July 23, 2018}} In April 1910, a committee, named the Twin Peaks Convention, was formed to plan the project, which would open the development of approximately one quarter of San Francisco's land area.{{Cite news |date=August 6, 1910 |title=Twin Peaks' Tunnel Convention's Work |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19100806.2.74 |access-date=July 23, 2018}}

In July 1910, an architectural rendering was released of the eastern portal; the tunnel was initially envisioned as a two-story bore {{convert|1.5|mi|km}} long, carrying road traffic on the upper deck and rail traffic on the lower deck. Market Street would be extended southwest in a straight line across private property to connect to the eastern portal, to be located at the intersection of 19th and Douglass.{{Cite news |date=July 9, 1910 |title=Plans being made for building of big tube |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19100709.2.64.2 |access-date=July 23, 2018}} Initial estimates for the cost of the tunnel ranged from {{USD|1500000|1909|round=-6}} in 1909 to {{USD|3000000|1910|round=-6}} in 1910.

The Twin Peaks Tunnel and Improvement Convention released their report in August 1910 recommending a municipal bond to pay for the tunnel, whose costs would be recouped by the additional taxation of the land that would then be opened for development. Other options were considered and rejected, including a special assessment district or a long-term railroad lease.{{Cite news |date=August 20, 1910 |title=Convention solves engineering problem |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19100820.2.58.2 |access-date=July 23, 2018}}

The San Francisco Board of Supervisors approved a competing plan to build a longer tunnel under Twin Peaks in March 1912, continuing under Market to Valencia, which was seen as the foundation for a rapid transit system connecting the downtown Financial District with western San Francisco and the Peninsula.{{Cite news |date=March 23, 1912 |title=Building of Twin Peaks Tunnel assured by action of Supervisors |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19120323.2.113.2 |access-date=July 23, 2018}} This action was taken on the recommendation of noted tunnel expert, Bion J. Arnold, who had submitted two preliminary reports in 1912, following up with a final report in March 1913. The 1913 report studied several alternative alignments and configurations, recommending construction of both the Twin Peaks Tunnel and what would become the Sunset Tunnel.{{Cite report |url=https://archive.org/details/reportonimprovem1913arno |title=Report on the Improvement and Development of the Transportation Facilities of San Francisco |last=Arnold, Bion J. |date=March 1913 |pages=225–270 |access-date=April 17, 2018 |chapter=11. Market Street extension tunnel under Twin Peaks}}

In the 1913 report, Arnold primarily considered proposals No. 2 and No. 5B, concluding "I can recommend unqualifiedly {{sic}} the construction of a Twin Peaks Rapid Transit tunnel at the earliest possible date. In so doing, there will be brought within 30 minutes' running time of the business district, approximately 10,000 acres of new territory, 75% of which is suitable for residence land, that has been practically useless heretofore by reason of lack of adequate transportation thereto." One of the key elements of proposal No. 5B was the creation of a new station along the tunnel, which is now present-day Forest Hill station (then called Laguna Honda station, at the intersection of Laguna Honda and Dewey Boulevard). The San Francisco Call speculated the presence of a station at Laguna Honda meant the Geary line could be extended through Golden Gate Park.{{Cite news |date=July 27, 1912 |title=Geary Car Line may be extended |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19120727.2.143.9 |access-date=July 24, 2018}} A 1912 report, by Arnold, proposed that Laguna Honda would be a transfer point, enabling passengers to move from Third and Market to Ocean Beach within 25 minutes on an express car, assuming a Seventh Avenue surface line was built.{{Cite news |date=October 8, 1912 |title=Subway Express Under Twin Peaks for 25 Minute Dash to Beach: Arnold Devises Clever Project to Solve 1915 Traffic Problem |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19121008.2.97 |access-date=July 27, 2018}}

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At a proposed {{convert|16000|ft}} in length, Arnold's proposed tunnel would not be suitable for road traffic for lack of adequate ventilation. He also believed the straight extension of Market to 19th and Douglass was impractical, as it would require extensive earth moving and exceed 3% maximum grade. It was on this basis that the Twin Peaks Association of Improvement voiced their opposition to Arnold's plans, in May 1912.{{Cite news |date=May 8, 1912 |title=Arnold's Twin Peaks Tunnel plan opposed |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19120508.2.59 |access-date=July 24, 2018}} City Engineer M.M. O'Shaughnessy recommended terminating the tunnel at 17th and Market in February 1913, as he thought the Market Street subway may need to be extended past Valencia, potentially to Third.{{Cite news |date=February 25, 1913 |title=Twin Peaks Tunnel to start on 17th Street |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19130225.2.35 |access-date=July 24, 2018}} O'Shaughnessy's report, endorsing Arnold's plan,{{Cite report |url=https://catalog.hathitrust.org/Record/100154822 |title=Specifications for the construction of a tunnel and appurtenances under Twin Peaks |last=O'Shaughnessy, M.M. |date=July 1913 |publisher=Department of Public Works, City and County of San Francisco, California |access-date=July 24, 2018}} was unanimously adopted by the Board of Supervisors in October 1913.{{Cite news |date=October 25, 1913 |title=Twin Peaks $4,000,000 Tunnel means a great forward step for city |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19131025.2.84 |access-date=July 24, 2018}}{{Cite news |date=October 22, 1913 |title=City in Position To Proceed With Twin Peaks Tunnel |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19131022.2.60 |access-date=July 24, 2018}} With the addition of {{convert|15000|acre}} of "the best residence property on the peninsula within 15 minutes of the business center of the city", the Call estimated the population of San Francisco would add 100,000 within three years and 200,000 within five.{{Cite news |date=September 27, 1913 |title=Population to be increased by tunnel |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19130927.2.121 |access-date=July 24, 2018}}

Carl Larsen, a prominent resident of the rural western side of San Francisco, recommended shortening the tunnel proposed by Arnold by moving the western portal to Laguna Honda station, but O'Shaughnessy stated the resulting grade would be too steep.{{Cite news |date=November 6, 1913 |title=Shorter Twin Peaks Tunnel Investigated |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19131106.2.43 |access-date=July 24, 2018}}{{Cite news |date=September 20, 1913 |title=Twin Peaks Tunnel, Says City Engineer, Can Not Be Reduced |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19130920.2.52 |access-date=July 24, 2018}} Mayor James Rolph signed the Twin Peaks Tunnel Act in November 1913, rejecting the proposal for a shorter tunnel.{{Cite news |date=November 7, 1913 |title=Mayor Signs Twin Peaks Tunnel Act |work=San Francisco Call |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SFC19131107.2.170 |access-date=July 24, 2018}}

File:B&EN v16 no 24 fig02 pg05 (1916-06-24) General Plan and Profile.jpg

The contract for tunnel construction was awarded on November 2, 1914, to the R.C. Storrie Company for {{US$|3372000|1914|round=-4}}{{Cite journal |last=Glick, L. |date=June 21, 1916 |title=Method and Progress of Construction of the Twin Peaks Tunnel In San Francisco, Cal. |url=https://archive.org/stream/buildingengineer1616cont#page/n868/mode/1up |journal=Building and Engineering News |volume=16 |pages=5–13 |access-date=July 24, 2018 |number=24}}{{rp|5;7}} and work began on the Twin Peaks Tunnel in December 1914, with an estimated three-year construction schedule for the twin-track bore.{{Cite news |date=December 29, 1914 |title=Frisco tunnel has begun |work=Riverside Daily Press |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=RDP19141229.2.50 |access-date=July 24, 2018}} Construction was completed thirty-three months later.{{Cite news |date=September 1, 1918 |title=Log of a Motor Truck Tells Story of Great Performance on Long, Hard Drive |work=Sacramento Union |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SU19180901.2.219 |access-date=July 26, 2018}} Funding for the tunnel came from special assessment districts established at the eastern and western ends; the undeveloped western area, approximately {{convert|4000|acre}}, was responsible for 85% of tunnel costs.{{rp|5}}

{{multiple image

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|caption2="Soft Ground"

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| footer = Profile sections of Twin Peaks Tunnel. Most of the structure uses the "Soft Ground" arched profile, with the exception of the eastern end of the tunnel, which uses the "Double Tube Flat Top" section.}}

The eastern approach to the tunnel was built along a parcel purchased by the city approximately {{convert|1800|ft}} long and {{convert|90|ft}} wide at the end of Market. This right-of-way was also later paved to connect Market with Portola.{{rp|5}} As originally constructed, the total length of the tunnel is {{convert|11675|ft}} (including approaches) and the highest point of the tunnel is near Laguna Honda station. Sloping down from the peak at Laguna Honda, the tunnel has a maximum grade of 3% from west to east and 1.15% from east to west.{{rp|5}} Excluding approaches, the tunnel is {{convert|8800|ft}} long.{{Cite news |date=February 9, 1918 |title=New Car Speeds Through Picturesque Tunnel With the Mayor and President of Board of Public Works as Crew |work=Sausalito News |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SN19180209.2.103 |access-date=July 26, 2018}}

The eastern {{convert|1665|ft|adj=on}} portion (with the exception of the {{convert|300|ft|adj=on}} long Eureka Valley station) of the tunnel uses a double-tube subway structure, and the remainder adopts an arched tube profile.{{rp|5–6}} As designed, both sections provide {{convert|15|ft}} of vertical clearance above the top of the rail; each tube in the double-tube section is {{convert|14|ft}} wide, and the arched tube is {{convert|25|ft}} wide at its maximum.{{rp|6}} The lunette space between the arched roof and flat ceiling of the tube was used as a duct to convey fresh air into the tunnel. One blower was mounted at the west end of the double-tube structure, and the other was at a ventilating shaft {{convert|110|ft}} deep, located {{convert|4600|ft}} east of the western portal. Excavation of the ventilating shaft required pumping {{convert|300000|gal|kl}} of water per day after a horizontal drift at the bottom of the shaft struck water-bearing sand.{{rp|7}}

Laguna Honda, West Portal, and Eureka Valley stations were constructed using cut-and-cover methods. Laguna Honda station is approximately {{convert|70|ft|-1}} below grade.{{rp|7}} The tunnel was excavated simultaneously from the open cuts at each end; initial excavation sank three drifts (one at each side along the springline, and one at the crown of the tunnel). A fourth drift was added at the centerline bottom of the tunnel to facilitate drainage of the ground at the western end.{{rp|7–8}} The two crews first "holed through" and connected their excavations near Laguna Honda station on April 5, 1917, {{convert|6100|ft}} from the east portal and {{convert|5900|ft}} from the west.

Several notable accidents occurred during the construction of the tunnel:

• A cave-in at the west portal trapped several men in April 1915, killing one{{Cite news |date=April 10, 1915 |title=8 Men Buried in Tunnel Collapse |work=Los Angeles Herald |agency=Pacific News Service |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=LAH19150410.2.86 |access-date=July 26, 2018}}{{Cite news |date=April 11, 1915 |title=One Killed, a Dozen Injured When Street Tunnel Caves In |work=San Bernardino Sun |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SBS19150411.1.1 |access-date=July 26, 2018}}
• A fire broke out in November 1915{{Cite news |date=November 29, 1915 |title=Twin Peaks Tunnel fire |work=Riverside Daily Press |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=RDP19151129.2.17 |access-date=July 26, 2018}}
• Four were killed and several injured while investigating a blasting charge that did not go off when planned in February 1917{{Cite news |date=February 16, 1917 |title=Delayed blast kills four |work=Riverside Daily Press |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=RDP19170216.2.43 |access-date=July 26, 2018}}
• A woman's house was nearly blown off its foundation by a blasting charge.{{Cite news |date=February 28, 1917 |title=Damage settlement was surely easy |work=Riverside Daily Press |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=RDP19170228.2.9 |access-date=July 26, 2018}}

Dedication ceremonies were held at each portal on July 14, 1917. Mayor Rolph and several other dignitaries, including former Mayor P. H. McCarthy spoke at the east portal, beginning at 2:00 p.m.; after the remarks, hundreds of people walked through the tunnel to the west portal, and Judge E. P. Shortall was the first of the pedestrians to arrive. At the west portal, Mayor Rolph spoke again and a ceremonial silver spike was driven by O'Shaughnessy and Rolph to mark the start of construction of the Twin Peaks Railway.{{Cite news |date=July 21, 1917 |title=Crowd applauds mayor as he declares two-mile bore open |work=Mariposa Gazette |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=MG19170721.2.22 |access-date=July 26, 2018}} The inaugural trip through the tunnel occurred on December 31, 1917.{{Cite journal |date=January 19, 1918 |title=First Car Through Twin Peaks Tunnel |url=https://library.si.edu/digital-library/book/electricrailway511918newy |journal=Electric Railway Journal|volume=51 |page=151 |access-date=July 23, 2018}} The tunnel was opened to revenue service on February 3, 1918,{{Cite news |last=Wallace |first=Kevin |date=March 27, 1949 |title=San Francisco History - City's Tunnels |work=San Francisco Chronicle |url=http://www.sfgenealogy.com/sf/history/hgtun.htm |access-date=July 14, 2008}} and was the world's longest tunnel for street railway traffic at the time.{{Cite news |date=February 4, 2009 |title=Twin Peaks tunnel opens |work=San Francisco Chronicle |url=http://www.sfgate.com/bayarea/article/Twin-Peaks-tunnel-opens-3252492.php |access-date=February 1, 2018}}{{Cite news |date=February 2, 1918 |title=Cars run through Twin Peaks |work=Sausalito News |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SN19180202.2.19 |access-date=July 26, 2018}} Mayor Rolph served as the motorman for the first revenue trip, and most of the paying passengers were City Supervisors, wives, and invited guests. The trip through the tunnel took seven minutes.

File:B&EN v16 no 24 fig01 pg05 (1916-06-24) General Plan and Profile.jpg

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| image1=B&EN v16 no 24 fig06 pg08 (1916-06-24) Arch Section West Portal.jpg

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| footer = West Portal station, the western tunnel entrance, in 1916 (during construction), 1967 (before the conversion to light rail), and present-day (2017)}}

The tunnel was built sloping downwards at the east end, anticipating future expansion to a tunnel under Market Street per Arnold's plan.{{Cite web |last=Callwell |first=Robert |title=Transit in San Francisco A Selected Chronology, 1850 - 1995 |url=https://archives.sfmta.com/cms/rhome/documents/TransitinSanFrancisco-CallwellChronologyweb.pdf |access-date=July 24, 2018 |website=SFMTA.com |publisher=San Francisco Municipal Railway}} A technical report was commissioned by the city in 1960 to study possible rapid transit routes. This recommended that the initial line linking BART from a transbay tunnel to Daly City be routed through Twin Peaks Tunnel.{{Cite book |last=De Leuw, Cather & Company |date=May 19, 1960 |title=A Plan for Rapid Transit in San Francisco Consonant with the Bay Area Rapid Transit System |url=https://catalog.hathitrust.org/Record/003502850 |access-date=January 10, 2018 |publisher=The Transportation Technical Committee of the Mayor's Transportation Council, City of San Francisco}} BART's 1961 plan did not include the tunnel connection on Market Street.{{Cite web |title=Rapid Transit for the San Francisco Bay Area |url=http://libraryarchives.metro.net/DPGTL/bart/1961-parsons-engineering-report-to-sf-bart-district.pdf |access-date=July 21, 2018 |website=LA Metro Library |publisher=Parsons Brinckerhoff / Tudor / Bechtel}}

When the Market Street subway was built in the early 1970s, it was connected to the Twin Peaks Tunnel to be used by the K Ingleside, L Taraval and M Ocean View lines. These services were spared from conversion to trolleybus by virtue of their use of Twin Peaks Tunnel. The Eureka Valley station was closed and was functionally replaced by Castro Street Station. This combined subway line was the impetus for transitioning the system to light rail and served as the basis of Muni Metro.

The original eastern entrance to the tunnel in the middle of Market Street at Castro was removed and new entrances and ramps were constructed on the sides of the street further up the block. These were connected to track on 17th Street, and in December 1972 the K, L and M lines were diverted via the new East Portal ramps (and via 17th, Church Street and Duboce Avenue, removed from Upper Market) to allow construction of the Muni Metro subway under Upper Market to begin.{{Cite book |last1=McKane |first1=John |title=Inside Muni: The Properties and Operations of the Municipal Railway of San Francisco |last2=Perles |first2=Anthony |publisher=Interurban Press |year=1982 |isbn=0-916374-49-1 |location=Glendale, CA (US) |pages=192, 195, 198}} These newer portals and ramps remained in use by all K-L-M service until 1980.

File:PCC 1125 leaving Twin Peaks Tunnel at East Portal in Sep. 1982.jpg

After the Muni Metro subway section between Van Ness station and the Twin Peaks Tunnel opened for use, in December 1980, weekday trains on lines K, L, and M were converted to Boeing LRVs, and trains continued directly from the Market Street subway into the tunnel without going above ground. Weekend service initially remained operated by the old PCC cars and routed along the surface of Market Street, and the subway was closed on weekends. Regular weekend use of the east portal ramps to 17th and Castro finally ended on September 19, 1982, with the conversion of weekend K-L-M service to light rail and the closure of the surface tracks on Market Street—a closure that was planned at the time to be permanent.{{Cite book |last=Ehrlich |first=Peter |title=San Francisco's F-Line |publisher=Trafford Publishing |year=2012 |isbn=978-1-4669-3739-0}}{{rp|43}} However, the surface tracks – and the 1972-built Castro portals – came back into use the following summer for the first Historic Trolley Festival, in 1983. Trolley Festival service gradually expanded from being summer-only and five days a week to running May to October and daily for part of the year, and all streetcars on that service reached Market Street from Muni's Metro Rail Center via the Twin Peaks Tunnel and the 1972 portals. The last Trolley Festival took place in 1987, and by the time its replacement, the F Market line, opened in 1995, its streetcars were able to use the J Church for "pull-in" and "pull-out" trips (to and from the carhouse){{rp|86}} because the 1991-opened extension of the J line from 30th Street to Balboa Park BART station had provided an alternative routing for streetcars traveling between Metro Rail Center (and the nearby Cameron Beach Yard) and Castro. As a result, there was no need to bring the 1972 portals back into regular use when the F line reopened as a full-time service in 1995. Light rail service briefly used the 1972 portals for two weeks in 1991 (August 19 to September 2), when K-L-M service was diverted via 17th and Church Streets, and entering and leaving the Muni Metro subway via the portal on Duboce Avenue, to permit track work near Castro station.{{Cite magazine |date=December 1991 |title=World News [regular news section] |magazine=Modern Tramway |location=UK |publisher=Ian Allan Publishing |page=430 |issn=0144-1655}}

Forest Hill and Eureka Valley stations were originally constructed with low platforms, as streetcars of that era had steps to load passengers from street level. However, the six new Market Street subway stations were built with high-level platforms for speedier level boarding onto the new Boeing LRVs. West Portal station, which was originally a surface stop outside of the tunnel's western entrance, was rebuilt as a high-platform station located just inside of the entrance. With Eureka Valley station permanently closed, Forest Hill was left as the only low-platform station on the Muni Metro subway. Muni soon modified the station with high-level platforms, completing that project in 1985.{{Cite book |chapter-url=https://archive.org/stream/munimetroturnaro1989unit#page/n63/mode/2up |title=Muni Metro Turnaround Project: Final Environmental Impact Statement |date=August 1989 |publisher=United States Department of Transportation Urban Mass Transportation Administration |pages=1–2 |chapter=Chapter 1 |via=Internet Archive}}

On March 30, 2020, Muni Metro service, including trains through the Twin Peaks Tunnel, were replaced with buses due to the pandemic.{{Cite press release |title=Starting March 30: New Muni Service Changes |date=March 26, 2020 |publisher=San Francisco Municipal Transportation Agency |url=https://www.sfmta.com/blog/starting-march-30-new-muni-service-changes |last1=Fowler |first1=Amy}}

Light rail service returned on August 22, with the routes reconfigured to improve reliability in the tunnel and at West Portal.{{Cite press release|title=Major Muni Service Expansion August 22|date=August 18, 2020|publisher=San Francisco Municipal Transportation Agency|url=https://www.sfmta.com/blog/major-muni-service-expansion-august-22|first1=Mariana|last1=Maguire|access-date=December 23, 2021}} K Ingleside and L Taraval services were interlined, running between {{Munis|SF Zoo}} and {{Munis|Balboa Park}} and not entering the tunnel, with passengers transferring at West Portal station. M Ocean View and T Third Street services were interlined, running between {{Munis|Sunnydale}} and Balboa Park station. Longer S Shuttle services operated in the tunnel.{{Cite press release |title=Big Changes Ahead when Muni Rail Returns in August |date=June 18, 2020 |publisher=San Francisco Municipal Transportation Agency |url=https://www.sfmta.com/blog/big-changes-ahead-when-muni-rail-returns-august |last1=Maguire |first1=Mariana}} The forced transfers at West Portal were criticized by disability advocates.{{Cite news|last=Graf|first=Carly|date=August 18, 2020|title=Muni 'improvements' could make things harder for seniors, disabled|work=San Francisco Examiner|url=https://www.sfexaminer.com/news/muni-improvements-could-make-things-harder-for-seniors-disabled/|access-date=December 23, 2021}}

Service was stopped and substituted with buses just three days later due to a malfunctioning overhead wire splice in the subway and the need to quarantine a control center staff after a COVID-19 case.{{Cite press release|title=Effective August 25 Buses Serve Muni Metro Routes|date=August 25, 2020|publisher=San Francisco Municipal Transportation Agency|url=https://www.sfmta.com/blog/effective-august-25-buses-serve-muni-metro-routes|first1=Bradley|last1=Dunn|access-date=November 27, 2021}}

On May 15, 2021, Muni Metro rail service resumed the K Ingleside, T Third Street, and S Shuttle lines. K Ingleside and T Third Street services were again interlined (as before the August changes).{{Cite press release|title=Welcome Back to the Westside, K Ingleside Trains!|date=April 16, 2021|publisher=San Francisco Municipal Transportation Agency|url=https://www.sfmta.com/blog/welcome-back-westside-k-ingleside-trains|access-date=November 27, 2021}} At that time, some stations were converted to new wayfinding signage based on international standards, with compass directions like "westbound" replacing older "inbound"/"outbound" directions.{{Cite press release|title=Muni Metro Debuts New International Wayfinding Standards|date=July 22, 2021|publisher=San Francisco Municipal Transportation Agency|url=https://www.sfmta.com/blog/muni-metro-debuts-new-international-wayfinding-standards|first1=Mariana|last1=Maguire|access-date=December 23, 2021}} M Ocean View service resumed on August 14. The L Taraval remained as a bus shuttle due to work on the line.{{Cite press release|title=Welcoming Back the M Ocean View and 31 Balboa|url=https://www.sfmta.com/blog/welcoming-back-m-ocean-view-and-31-balboa|date=July 15, 2021|publisher=San Francisco Municipal Transportation Agency|last1=McCarthy|first1=Kate|access-date=November 27, 2021}} Light rail service through the tunnel ended at 9 p.m. until October 2, when it was extended to 10 p.m. on Sundays and midnight on other days to better align with BART's late night service.{{Cite press release|title=Late Night Metro and More J Church Service Starts October 2, 2021|url=https://www.sfmta.com/blog/late-night-metro-and-more-j-church-service-starts-october-2-2021|date=September 30, 2021|publisher=San Francisco Municipal Transportation Agency|access-date=November 27, 2021|first1=Mariana|last1=Maguire}}

File:Muni shuttle buses at Castro station, July 2018.JPG

Around 2014, with the tunnel nearing a century of continuous use, Muni began planning a major track replacement project in the tunnel.{{Cite press release |title=Twin Peaks Tunnel Contract Awarded |date=April 28, 2016 |publisher=San Francisco Municipal Transportation Agency |url=https://www.sfmta.com/news/project-updates/twin-peaks-tunnel-contract-awarded}} The project would include the replacement of all rails and ties in the tunnel with new rails directly fixed to concrete pads, the installation of two pairs of crossovers (one near West Portal, the other just east of Forest Hill), replacement of existing switches to the unused eastern portals, a structural refit in the area of the former Eureka Valley station, replacement of the overhead wires, and a number of other repairs and improvements.{{Cite web |last=San Francisco Planning Department |date=February 13, 2015 |title=CEQA Categorical Exemption Determination |url=https://www.sfmta.com/sites/default/files/projects/2015/2015-008803ENV%20-%20SFMTA%20-%20Twin%20Peaks%20Tunnel%20Project_CatEx.pdf |publisher=San Francisco Municipal Transportation Agency |pages=5–6}} The work would lift speed restriction that limited trains to {{convert|25|mph}} through the tunnel and would allow for the use of two-car trains on the K/T lines.{{Cite press release |title=Two-Car Trains Now Permanent on K/T Line |date=August 24, 2018 |publisher=San Francisco Municipal Transportation Agency |url=https://www.sfmta.com/blog/two-car-trains-now-permanent-kt-line |last1=von Krogh |first1=Bonnie Jean}}

The construction contract was awarded on April 5, 2016. The project was originally planned to begin in late 2016, but suffered a series of delays. The start date was first pushed to April 2017, then in March 2017 it was pushed to mid-2017 to allow for "additional technical analysis" of the tunnel.{{Cite press release |title=Twin Peaks Tunnel Construction Held Until Summer |date=March 16, 2017 |publisher=San Francisco Municipal Transportation Agency |url=https://www.sfmta.com/news/project-updates/twin-peaks-tunnel-construction-held-until-summer}} In June 2017, the project was indefinitely delayed after the construction contract was terminated.{{Cite press release |title=Twin Peaks Tunnel Construction Delayed |date=June 6, 2017 |publisher=San Francisco Municipal Transportation Agency |url=https://www.sfmta.com/news/project-updates/twin-peaks-tunnel-construction-delayed}} Muni and the contractor could not agree on a new schedule and costs to minimize disruptions to riders; and the project duration increased from 460 days to 807 days and the cost to $48 million.{{Cite news |last=Chinn |first=Jerold |date=January 16, 2018 |title=Years of delay haunt Muni tunnel projects |work=SFBay |url=https://sfbay.ca/2018/01/16/years-of-delay-haunt-muni-tunnel-projects/}} The SFMTA released a Request for Qualifications in October 2017, and bidding opened for the $35.5 million project in November.{{Cite web |date=October 17, 2017 |title=Bid Document |url=http://mission.sfgov.org/OCABidPublication/BidDetail.aspx?K=12415 |publisher=City and County of San Francisco}}{{Cite web |date=November 2017 |title=Bid Document |url=http://mission.sfgov.org/OCABidPublication/BidDetail.aspx?K=12516 |publisher=City and County of San Francisco}}

Work began on June 25, 2018, and lasted until August 24.{{Cite news |last=Hernández |first=Lauren |date=August 25, 2018 |title=Muni's Twin Peaks Tunnel reopens to the relief of frustrated passengers |work=San Francisco Chronicle |url=https://www.sfchronicle.com/bayarea/article/Muni-s-Twin-Peaks-Tunnel-reopens-to-the-relief-13182708.php |access-date=August 25, 2018}} During the closure, Muni Metro trains were short turned at Castro station; the surface section of the K Ingleside was through-routed with the J Church, while the L Taraval and M Ocean View were replaced by buses.{{Cite web |date=June 25, 2018 |title=Twin Peaks Tunnel Improvements |url=https://www.sfmta.com/projects/twin-peaks-tunnel-improvements-0 |archive-url=https://web.archive.org/web/20180626232234/https://www.sfmta.com/projects/twin-peaks-tunnel-improvements-0 |archive-date=June 26, 2018 |publisher=San Francisco Municipal Transportation Agency}}

Systemwide delays during the summer of 2018 resulted from a combination of the tunnel shutdown and decreased qualified driver availability, which in turn was attributed to the rollout of LRV4s (requiring driver training), and contract issues.{{Cite news |last=Rodriguez |first=Joe Fitzgerald |date=July 26, 2018 |title=Muni suffering major citywide service gaps due to operator shortage |work=San Francisco Examiner |url=http://www.sfexaminer.com/muni-suffering-major-citywide-service-gaps-due-operator-shortage/ |access-date=August 27, 2018}} Refurbishment work was temporarily suspended after a signal technician was fatally crushed by a steel beam on August 10.{{Cite news |last=Barba |first=Michael |date=August 12, 2018 |title=Twin Peaks Tunnel construction resumes after accidental death of worker |work=San Francisco Examiner |url=http://www.sfexaminer.com/sf-twin-peaks-tunnel-construction-resume-accidental-death-worker/ |access-date=August 27, 2018}}{{Cite news |last=Barba |first=Michael |date=August 13, 2018 |title=Technician killed by beam in Twin Peaks Tunnel was working with stepson |work=San Francisco Examiner |url=http://www.sfexaminer.com/worker-fatally-struck-steel-beam-muni-tunnel-idd/ |access-date=August 27, 2018}} The technician was an employee of Shimmick Construction, the firm contracted to handle the refurbishment; Shimmick had been cited for serious and willful safety violations on an unrelated job in 2011 by Cal/OSHA but neglected to disclose those violations during the bidding for the Twin Peaks Tunnel job.{{Cite news |last=Barba |first=Michael |date=August 21, 2018 |title=SFMTA head defends choice of contractor in Twin Peaks tunnel death |work=San Francisco Examiner |url=http://www.sfexaminer.com/sfmta-head-defends-decision-hire-company-muni-tunnel-worker-death/ |access-date=August 27, 2018}} Muni was also criticized for inadequate notice of service degradation to bus lines during the closure, since buses were pulled off regular routes to substitute for trains,{{Cite web |last=Eskenazi |first=Joe |date=August 6, 2018 |title=Muni meltdown 2018: Our transit service failed to plan — and, thereby, planned to fail |url=https://missionlocal.org/2018/08/muni-meltdown-2018-our-transit-service-failed-to-plan-and-thereby-planned-to-fail/ |access-date=August 27, 2018 |website=Mission Local}} and for the death during the project.{{Cite news |last=Swan |first=Rachel |date=August 20, 2018 |title=SF mayor Breed blasts Muni chief over delays, background checks and scooter permitting |work=San Francisco Chronicle |url=https://www.sfgate.com/bayarea/article/Breed-blasts-Muni-chief-over-delays-background-13169518.php |access-date=August 25, 2018}}

During the project, it was discovered that the track ballast was contaminated with toxic heavy metals. Muni had planned to replace the ballast, which degrades over time, creating a dust called fines, which can turn to mud when water enters the tunnel. In an effort to save time and avoid the cost of disposal, Muni ordered the ballast to instead be reused, but did not ensure that the contractor followed the proper procedure to thoroughly wash and filter the ballast before it was reused. By November 2020, Muni acknowledged that it had made an "oversight" during the 2018 project and that the ballast was likely to create track stability issues in the Eureka Curve just west of Castro station. Taking advantage of an unscheduled closure of the Muni Metro due to the COVID-19 pandemic, the agency replaced the ballast between November 2020 and February 2021.{{Cite news |last=Brekke |first=Dan |date=Nov 18, 2020 |title=Muni Forced to Redo Part of $52 Million Tunnel Project – Just 2 Years After Finishing It |language=en-us |work=KQED |url=https://www.kqed.org/news/11847897/sfmta-muni-forced-to-redo-portion-of-52-million-twin-peaks-tunnel-project |access-date=2020-11-20}}{{cite press release |url=https://www.sfmta.com/blog/twin-peaks-tunnel-work-start-november-30 |title=Twin Peaks Tunnel Work to Start November 30 |date=November 20, 2020 |publisher=San Francisco Municipal Transportation Authority}}

{{reflist|30em}}

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{{Attached KML |display=title,inline}}

• [https://www.oldmapsonline.org/map/harvard/10219759 Twin Peaks Tunnel Map] by O'Shaughnessy, Michael Maurice, 1864-1934
• [https://archive.org/details/TwinPeaksTunnel1917 Silent film by SF real estate company of construction of tunnel (1914-17)]
• {{Cite web |last=Menzies |first=Jeremy |date=January 25, 2018 |title=Twin Peaks Tunnel: A Portal to the West |url=https://www.sfmta.com/blog/twin-peaks-tunnel-portal-west |access-date=July 25, 2018 |publisher=SFMTA}}
• {{Cite web |last=Woods |first=Arnold |date=February 2018 |title=Westward the Course of Empire Takes its Way |url=https://www.outsidelands.org/twin-peaks-tunnel.php |access-date=August 3, 2018 |publisher=Outside Lands}}
• {{Cite web |last=Laubscher |first=Rick |author-link=Rick Laubscher |date=February 2, 2018 |title=Tunnel Vision |url=https://www.streetcar.org/tunnel-vision/ |access-date=August 3, 2018 |publisher=Market Street Railway}}
• {{Cite web |date=2018 |title=Twin Peaks Tunnel from 1915 to Today |url=https://sfmta.photoshelter.com/portfolio/G0000T2A03WNbG54 |access-date=August 3, 2018 |publisher=SFMTA}}

{{Muni}}

{{Castro District, San Francisco}}

{{Bay Area tunnels}}

Category:Muni Metro

Category:Railroad tunnels in California

Category:Tunnels in San Francisco

Category:Tunnels completed in 1918

Category:1918 establishments in California

Category:Castro District, San Francisco

Category:Underground rapid transit in the United States