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2nd Transbay Tube?

written by andy on

The talk in town after the construction of the Bay Bridge East Span is another transbay tube. The concept, along with another bridge, has been studied about 14 years ago. Some of the ideas that are being thrown around is to have a second BART tube reach South of Market, head up toward Union Square, extend to the west on Geary, and perhaps turn south on 19th Ave. Others have suggested that the 2nd tube should be standard gauge as an extension of Caltrain from Transbay terminal.

BART, HSR technology, or light rail

I don’t know if the 2nd tube based in HSR technology is necessarily better. Right now there’s no Caltrain (or SEPTA, NJ Transit, LIRR) equivalent in the East Bay to connect the dots with. Capitol Corridor operates on UP owned tracks which UP is notorious for its anti-passenger rail attitude. Even if you take away the UP factor, the freight rail corridor serves the Port of Oakland so the opportunity is limited, and the exist rail alignment to Sacramento is slow due to curves and such.

One of the advantage of BART technology crossing the Bay is the strong East Bay coverage. A advantage of standard gauge technology is the strong SF/West Bay coverage. It is difficult to build a new BART line in SF as supposed to a new Muni or an upgraded Muni because of the limited available corridor and complexity to tie into the existing system. It is difficult to build new standard gauge line in the East Bay because of lack of available corridors.

If the 2nd tube is to be using light rail technology, then it could tie both to the Embarcadero line and the 3rd Street line in SOMA, with direct service under Market, to Chinatown, and to Bay View. The problem with that is how to connect with BART in the East Bay, which has no such standard gauge network, but leaves a possibility of less costly surface rail which can serve the Oakland inner core better than BART.

On the other hand, BART has now somewhat “grown up” these days when it is having different rail technologies in the system. So a BART train could mean a diesel train, light rail, FRA compliant trains, or even BRT. This is something that large rail transit agencies have been doing for decades.


The problem with the plan as shown on the map above is that it cannot be implemented in phases which is the most realistic way to get it built. The Muni’s 3rd Street corridor is a 25 year project in 4 phases (MM Turnback, MMX extension down Embarcadero, 3rd Street LRT, Central Subway). Considering that there’s no possibility of track connection at Market, MMX is a required component or otherwise the 3rd Street corridor will have to be a separate system.

So a part of the discussion is how a 2nd Tube/SF expansion could be phased, and that such phase is small enough to be financed/funded, that can be tied on with the existing system (so you don’t need a separate rail yard in the Richmond District for example), and that has independent utility. Also such line should not duplicate existing rail lines. The original BART system did not have a train yard in the west side of the bay during its first 20 years, and I doubt that they want to operate a new line on the West Bay that cannot access a train yard there.

The alignment shown above partly duplicates the existing Muni Metro system. It calls into question whether it is more cost effective or useful in building a new BART line serving UCSF or SFSU versus improving Muni Metro. For less money than this, could they put N-Judah underground between Sunset Tunnel and Market Street?

“Quick and easy” alignment with no new downtown station

If the idea is to have a second tube implemented as quick as possible without having to first build a second BART subway line within SF (that first ties with the existing system), the best alignment I think is to run under South of Market and connect with the existing BART line on Mission Street. From there, East Bay trains using the new tube will run north on Market and serve the existing BART stations. Some of the East Bay trains coming off from the current tube will turn to the new line south of Civic Center and return to the East Bay via the new tube. With this alignment, only two new stations are necessary in the South of Market area. There’s no need to build new BART stations in the Market Street area.

At the current BART stations, transbay service will be available on both tracks, rather than one track as it is now. The other track still has available capacity both in terms of train slots and seats. Also there’s Muni and Caltrain which provide additional rail capacity going to and from Downtown SF in the west side of the Bay.

The problem with any new BART line in SF is that it may not be as effective as a diversion from the existing line on Market Street because of station location. If the idea is to have the 2nd tube land in South of Market, the main stations would be in the South of Market or the Union Square area, which are not as close to the financial district as the two most popular BART stations (Embarcadero and Montgomery). With this plan, trains running in the new tube will use the existing BART stations, but in the reverse direction where capacity is available.