San Francisco Municipal Transportation Agency (SFMTA)

CA: Introducing Big Alma and Mom Chung, the Central Subway’s Tunnel Boring Machines

The San Francisco Municipal Transportation Agency (SFMTA) , which manages transportation in the city, including the Municipal Railway (Muni), today announced the names of the tunnel boring machines (TBMs) that will excavate and construct the Central Subway tunnels. The two tunneling machines will be named Big Alma, after “Big Alma” de Bretteville Spreckels, and Mom Chung, after Dr. Margaret “Mom” Chung.

The first of the machines, Mom Chung, is expected to arrive in San Francisco in April. The 300-foot-long machine will be assembled within an excavation on 4th Street between Harrison and Bryant streets and will start building the tunnel for southbound trains about two months later. Big Alma will arrive soon after Mom Chung to construct the northbound tunnel.

As tunneling proceeds, updates about the TBMs, including photos of the machines and the tunnels, will be posted on Twitter. The public may follow the TBMs’ tweets at the usernames @BigAlmatheTBM and @MomChungtheTBM.

“With these two state-of-the-art machines, we will connect some of the most populous, fastest growing and highly traveled areas of San Francisco. From South of Market to Chinatown, the Central Subway will bridge our vibrant communities and vastly improve transportation options for residents and visitors alike,” said Mayor Edwin M. Lee.

“These machines will help build the San Francisco of the future, just as their namesakes helped build the dynamic San Francisco of today,” said SFMTA Board Chairman Tom Nolan. “The Central Subway will provide efficient, convenient transportation for tens of thousands of Muni customers daily.”

The names were selected by the public in an online poll held in January. Participants could select up to two names, one for each TBM. Of the 1,453 responses, Big Alma was the top vote-getter at 682 votes. Mom Chung took second place with 487 votes, closely followed by Firebelle Lil (451 votes), Mary Ellen (437 votes) and Juana (148 votes).

In tunneling tradition, the custom of naming TBMs is believed to bring good luck to tunneling projects. The names will remain in official use by the SFMTA and the tunneling contractor throughout the duration of the project.

“Big Alma and Mom Chung will construct San Francisco’s first new subway tunnel in decades, bringing together neighborhoods of our city that have long been in need of improved public transit,” said Ed Reiskin, SFMTA director of transportation. “We are happy to have included the public in this exciting part of tunneling tradition. We thank everyone who voted for contributing to this important project.”

Each TBM consists of a rotating cutter wheel (the cutter head), a cylindrical steel shell (the shield) and a 300-foot train of tunnel-building mechanisms (the trailing gear). The TBMs will arrive in several parts, to be assembled at the site on 4th Street between Harrison and Bryant streets where tunneling will begin.