San Francisco, CA

Central Subway

San Francisco Municipal Transportation Agency (SFMTA)


The Central Subway Project extends the Muni Metro T Third Line 1.7 miles (2.7 km) through the South of Market, Union Square, and Chinatown neighborhoods in San Francisco. The project cost was $1.95 billion and includes tunnels and three new underground stations for light rail service. The Central Subway Project vastly improves transportation to and from some of the city’s busiest, most densely populated areas.

Fast Facts
  • 1.7 miles (2.7 km) of twin bored soft-ground tunnels
  • Three underground stations
  • Open-cut station excavation

Scope of Work

Delve Underground was an integral part of the project management/​construction management team, providing staff at all levels, including Resident Engineers for the tunneling and station work. The firm also performed design oversight prior to construction, and we are currently supporting the SFMTA in claims resolution. The project has required tunneling and station excavation in both soil and rock through downtown San Francisco, with materials ranging from saturated alluvial soils to cemented sand and weathered to fresh bedrock.

Challenges & Innovations

Major design and construction issues include minimizing community disruption, managing tunneling risks, complex utility relocations, and extensive building protection measures.

The project is located in highly urban, congested areas surrounded by historic high-rise structures.

The tunnels passed under the existing BART tunnels without incident.