SPUR’s report Critical Cooling recommends 42 options for reducing local carbon emissions. This is one of them. To learn about all 42 ideas, read the full report

Build the Central Subway

Urbanist Article
Annual savings potential:
Annual public cost:
Public cost per ton:
Implementing agency:
Horizon year:
500 tons
Municipal Transportation Agency


  • Implementation of the Central Subway will add an estimated 4,754 new daily Muni Trips in the corridor, resulting in a reduction of 495 metric tons per year in CO2 emissions
  • Capital cost of implementation will be $1.2 billion1
  • Our analysis excludes the emissions associated with construction, which can be significant in the case of large infrastructure projects


Building the Central Subway would improve transit connectivity between the newly completed Third Street light rail, the South of Market Area, downtown, and Chinatown. In so doing, it would attract some new passengers to Muni. However, the project has an extremely high capital cost — the current supplemental environmental impact report estimates the capital cost at more than $1.2 billion. While the project will enhance transit connections for many existing riders, the project’s environmental document estimates that it will add just 14,840 daily riders to Muni ridership, of which a minority will be diverted from driving private autos. The Central Subway is therefore not a cost-effective way to reduce CO2 emissions, and must be justified on other grounds.

What we do now
Several Muni bus routes provide service in the subway corridor, including the 9X-San Bruno Express (A and B), the 30-Stockton andthe 45-Union/Stockton. The Central Subway SEIR estimates ridership in the corridor at 147,450.

What we could do
The Central Subway is a planned 1.7 mile extension of Muni metro rail service that will complete the second phase of the Third Street Light Rail Project by providing light rail transit service from the terminus of the T-Third Line at Fourth and King streets through the South of Market Area, downtown and Chinatown.

Trains will travel north on Fourth Street, stop at an above-ground station at Fourth and Brannan streets, and enter a new subway through at Fourth between Bryant and Harrison streets. The route will then continue under Fourth Street through the South of Market Area. North of Market Street, the subway will continue under Stockton to a station in Chinatown at Stockton and Jackson streets. The timeline for the project envisions completion in 2016.

The project SEIR estimates the capital cost of the central subway project at $1.24 billion. Financed at 5 percent interest over 50 years, the annualized capital cost of the project would be $68 million. Muni could also expect that the 14,840 new daily riders would generate about $2.2 million per year in new fare revenue. The total annual cost of the project is therefore an estimated $65,423,000.

Carbon savings potential
The Central Subway SEIR estimates that the service will generate an additional 14,840 transit trips per day and reduce VMT by 1,730. It further estimates that the project will reduce emissions by 1.65 metric tons per day, or 495.6 metric tons per year. This relatively small decrease in emissions, combined with the project’s extremely high capital cost yields a very high cost per ton of emissions abatement: nearly $132,000 per ton.

1 Central Subway Draft SEIR.