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." 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.
Competing proposals In July 1910, an architectural rendering was released of the eastern portal; the tunnel was initially envisioned as a two-story bore 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. Initial estimates for the cost of the tunnel ranged from in 1909 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. This action was taken on the recommendation of noted tunnel expert
Bion J. Arnold, who had submitted two preliminary reports in 1912 and followed 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. In the 1913 report, Arnold primarily considered proposals No. 2 and No. 5B, concluding "I can recommend unqualifiedly 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." 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. At a proposed 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. In February 1913 City Engineer
M.M. O'Shaughnessy recommended terminating the tunnel at 17th and Market, as he thought the Market Street subway may need to be extended past Valencia, potentially to Third. O'Shaughnessy's report, endorsing Arnold's plan, was unanimously adopted by the Board of Supervisors in October 1913. With the addition of 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. 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. Mayor
James Rolph signed the Twin Peaks Tunnel Act in November 1913, rejecting the proposal for a shorter tunnel.
Construction and opening The contract for tunnel construction was awarded on November 2, 1914, to the R.C. Storrie Company, for , and work began on the Twin Peaks Tunnel in December 1914, with an estimated three-year construction schedule for the twin-track bore. Construction was completed thirty-three months later. Funding for the tunnel came from special assessment districts established at the eastern and western ends; the undeveloped western area, approximately , was responsible for 85% of tunnel costs. The eastern portion (with the exception of the long Eureka Valley station) of the tunnel uses a double-tube subway structure, and the remainder adopts an arched tube profile. • A fire broke out in November 1915. • Four were killed and several injured while investigating a blasting charge that did not go off when planned in February 1917. • A woman's house was nearly blown off its foundation by a blasting charge. 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. The inaugural trip through the tunnel occurred on December 31, 1917. The tunnel was opened to revenue service on February 3, 1918, and was the world's longest tunnel for street railway traffic at the time. 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. 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 the Twin Peaks Tunnel. BART's 1961 plan did not include the tunnel connection on Market Street. 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. These newer portals and ramps remained in use by all K-L-M service until
1980. 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. However, the surface tracksand the 1972-built Castro portalscame 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) 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.
COVID-19 impact and attempted restart On March 30, 2020, Muni Metro service, including trains through the Twin Peaks Tunnel, were replaced with buses due to the
pandemic. Light rail service returned on August 22, with the routes reconfigured to improve reliability in the tunnel and at West Portal. K Ingleside and L Taraval services were interlined, running between and and not entering the tunnel, with passengers transferring at West Portal station. M Ocean View and T Third Street services were interlined, running between and Balboa Park station. Longer S Shuttle services operated in the tunnel. The forced transfers at West Portal were criticized by disability advocates. 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. 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). 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. M Ocean View service resumed on August 14. The L Taraval remained as a bus shuttle due to work on the line. 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.
Rail replacement project Around 2014, with the tunnel nearing a century of continuous use, Muni began planning a major track replacement project in the tunnel. 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. The work would lift speed restriction that limited trains to through the tunnel and would allow for the use of two-car trains on the K/T lines. The construction contract was awarded on April 5, 2016. In June 2017, the project was indefinitely delayed after the construction contract was terminated. 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. The SFMTA released a Request for Qualifications in October 2017, and bidding opened for the $35.5 million project in November. Work began on June 25, 2018, and lasted until August 24. 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. 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. Refurbishment work was temporarily suspended after a signal technician was fatally crushed by a steel beam on August 10. 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. 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, and for the death during the project. 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. ==References==