Opinion

2nd Transbay Tube needed to help keep BART on track

April 28, 1968: A section of the BART tube is towed down the Napa River after being fitted with a flexible seismic protection joint at Kaiser Steel's Napa plant. April 28, 1968: A section of the BART tube is towed down the Napa River after being fitted with a flexible seismic protection joint at Kaiser Steel's Napa plant. Photo: Courtesy Kaiser Graphic Arts Photo: Courtesy Kaiser Graphic Arts Image 1 of / 9 Caption Close 2nd Transbay Tube needed to help keep BART on track 1 / 9 Back to Gallery

It typically takes but a single mechanical or track problem in West Oakland, in the Transbay Tube or along BART’s San Francisco corridor to shut down the entire BART transit system. Even without such problems, BART is at capacity for running trains under the bay during commute periods. The system can barely meet existing travel demand, let alone serve future transbay demand. That’s why the Bay Area must invest in a second Transbay Tube and why BART, in partnership with other agencies, is expected to commission in the coming several months a study that looks at increasing transbay transit capacity.

It’s also why, in my view, a second tube must duplicate service through the heart of the BART system.

A fundamental purpose of a second Transbay Tube is to increase the number of trains that can cross the bay. Trains already are crossing the bay just 2.5 minutes behind each other during commute hours, and very limited potential exists to reduce that spacing with just one set of tracks. Only a second Transbay Tube would allow BART to as much as double the number of trains it pushes across the bay. This would require constructing a new set of tracks to separate some BART routes from the existing tracks before the Oakland Wye (the junction point between the downtown Oakland and Lake Merritt stations and the West Oakland station, where all routes converge into one main line). It would also require a second BART alignment through San Francisco so that trains using the new Transbay Tube could remain separated from the existing tracks.

The most frequently referenced alignment option for a second tube is one that would serve Alameda, San Francisco’s South of Market area via Mission or Third streets, and the western districts via Geary Boulevard. I have reservations about this concept.

While San Francisco has prioritized development in its SoMa and South Beach neighborhoods, and some interests would like to use a second BART alignment to further spur that development, that’s not what BART is for. Furthermore, regardless of whether economic activity increases to the degree envisioned, for the foreseeable future, transbay travel demand will continue to be primarily concentrated near the Market Street corridor. Today, two-thirds of all BART trips begin or end in downtown San Francisco, and there aren’t frequent-enough trains to comfortably accommodate these riders now. Why serve a new area when BART doesn’t have the capacity and flexibility to meet existing demand?

The reservation I have with a SoMa alignment is that it skews BART service south of the Market Street corridor, San Francisco’s center of economic activity. While a SoMa alignment would serve new neighborhoods, it would do little to alleviate the crushing passenger loads at the existing BART stations along Market Street.

Proponents of the SoMa alignments point out that other subway systems have multiple service lines to the metropolitan center; not just one. This is true.

But that’s because in most cities, the multiple subway routes collectively circle around the metropolitan center. Riders can take a variety of routes to get to their destination without transferring because the destinations are concentrated between the various routes.

BART, on the other hand, has several routes that converge into one line that spurs through the metropolitan center. Any alignment north or south of Market Street would take service away from San Francisco’s center of economic activity and encourage or even require riders to transfer to get to their final destinations.

An alternative is to duplicate existing downtown San Francisco service with a second bore of tracks. A second level of tracks would be constructed from points near the Oakland Wye and follow BART’s existing service to a point south of the Powell Street Station. Here, this second set of tracks would diverge — perhaps following Fulton Street, with stations at Van Ness Avenue, the University of San Francisco and Golden Gate Park, then following 19th Avenue out to the Sunset District, San Francisco State University and a remodeled, four-platform, Daly City Station.

Between the West Oakland and Powell Street stations, traffic on the upper- and lower-level platforms would be organized by destination. For example, northern East Bay and Mission District routes could use the upper-level platform, while southern East Bay and western loop routes could use the lower-level platform. Junctions would be constructed so that trains could be rerouted to other tracks as needed.

This alternative protects the need to serve existing travel demand by providing additional throughput capacity along the Market Street corridor and not due-south of Market Street. Also, by serving regional points of interest along the western extension, it better maintains BART as a regional service rather than a local service alternative, as a Geary Boulevard alignment would.

Ultimately, a comprehensive study that competitively evaluates all options will help decide which option is best.

Zakhary Mallett is a member of the BART board of directors, representing District 7 (which includes portions of West Contra Costa, Albany, Berkeley, Emeryville, Oakland, and San Francisco). To comment, submit your letter to the editor at www.sfgate.com/submissions/#1.