MENU
SEARCHBeginning Tuesday, Big Alma was set to be in operation 24 hours a day to build the approximately 425 feet of new tunnel beneath the Market Street tunnels.
The San Francisco Municipal Transportation Agency (SFMTA) announced the Central Subway’s second tunnel boring machine (TBM) will soon pass beneath existing Bay Area Rapid Transit District (BART) and Muni Metro tunnels, while passing under Market Street from SoMa into Union Square.
When the Central Subway opens, the new tunnels will allow T Third Line trains to cut travel times by more than half along this busy corridor.
The SFMTA has worked in close coordination with BART and an independent panel of top tunneling experts to plan and carry out this key phase of tunnel construction. To pass beneath Market Street and the existing transit tunnels, TBM Big Alma will turn slightly left beneath 4th Street just south of Market Street. The machine will then veer right to head north under Market Street and then Stockton Street. The new T Third Line tunnels will be about 10 feet below the existing BART tunnels.
Beginning Tuesday, Big Alma was set to be in operation 24 hours a day to build the approximately 425 feet of new tunnel beneath the Market Street tunnels. Late last year the first TBM, called Mom Chung, safely and successfully completed the same undercrossing, using the same techniques and interagency coordination. Mom Chung is now beginning to tunnel under Nob Hill, heading toward Chinatown.
Including both tunnels, tunneling contractor Barnard Impregilo Healy (BIH) has constructed more than 6,900 feet of tunnel under 4th Street and Stockton Street so far.
The crossing under BART may last up to six days, with the tunneling also possibly causing BART to run at slower speeds in the area.
Operation Lifesaver awarded $220,200 in grants to 12 states to support rail safety campaigns focused on grade crossing awareness and trespass prevention.
Read More →
The survey showed that commute trips still make up the majority of ridership, with most riders boarding 2 to 3 days a week, reflecting hybrid work schedules. Two-thirds of Caltrain riders have access to a car, while 37% of Caltrain riders are considered low-income.
Read More →
Advances in data and analytics are giving transit agencies new opportunities to refine maintenance practices, improve efficiency and make more informed decisions about asset performance.
Read More →
In this Consultant Roundtable, Carmen C. Cham shares insights on how agencies can create spaces that are intuitive, connected and built for long-term impact.
Read More →
The Red Line Extension Project will provide the Far South Side of Chicago with rapid rail transit for the first time by extending the Red Line by 5.5 miles from 95th Street to 130th Street, including the construction of four new Red Line stations at 103rd, 111th, Michigan, and 130th streets.
Read More →
Every year, more than 2,000 incidents and 300 fatalities occur at railroad crossings nationwide.
Read More →
The Siemens CBTC System, Trainguard MT, in compliance with New York Subway Interoperability Interface Specifications, enables trains to run as close as 90 seconds apart, using next-generation signaling and continuous communication to keep operations moving seamlessly.
Read More →
While recognizing regional economic constraints and continuing to improve service, the budget increases the jurisdictional subsidy to less than 1.8%, significantly below the inflation rate and the 3% regional target, said agency officials.
Read More →
With more than 59,400,000 boardings since the service’s debut, the A Line’s utilization surpassed that of all other RTD rail services in 2025, the agency reported.
Read More →
The plan outlines funding for transit operations, capital projects, and freight and passenger rail initiatives, as state officials seek public input on priorities shaping mobility and infrastructure across the Commonwealth.
Read More →