Should Seattle rethink its $2B+ Second Transit Tunnel?

Seattle, Washington – As Sound Transit works toward designing the Ballard Link Extension (BLE), Seattle’s public transportation landscape is about to undergo a significant make-over.  Including nine new stations and stretching 7.7 miles, the BLE—now scheduled for a 2039 opening—is expected to improve mobility around the city.  Building a second Downtown Seattle Transit Tunnel (DSTT2), meant to serve Ballard-bound trains heading south toward Tacoma, is a major element of the concept.  But concerns continue to arise about whether this expensive tunnel section is really the best course forward.

Instead, an increasing number of urban designers and transit activists are supporting something else: an autonomous, automated rail line connecting Ballard and Westlake.  Proponents argue that this strategy might speed up building, provide more regular service, and stop the needless redundancy of expensive new tunnels that might remain underutilized for years.

The promise of Ballard Link

Promising to link Ballard, Uptown, South Lake Union (SLU), and Downtown Seattle with a fully grade-separated light rail line, the Ballard Link Extension is among the most ambitious transit developments in the region. Unlike many other metropolitan corridors, these areas are not separated by freeways, hence once the line opens planners anticipate substantial demand for riders.

Still unresolved, though, is whether the current BLE architecture maximizes efficiency or whether an autonomous automated line will best serve Ballard and its expanding population.

Travel times along the Ballard–Westlake corridor could be cut to just 11 minutes, according to the West Seattle and Ballard Link Extensions Draft Environmental Impact Statement (WSBLE Draft EIS), a notable change over current commuting options and a convincing alternative to driving at any time of day. The new light rail is predicted to thrive since Ballard and Downtown Seattle do not have a direct highway link, therefore avoiding the difficulties suburban expansions experience like navigating development restrictions near highways.

Even the own planning notes of Sound Transit highlight the great opportunities of the Ballard Link Extension. The official BLE website of the City of Seattle as of August 2024 emphasizes important project goals like smooth access to future stations, support of housing and commercial development, and preservation of neighborhood character surrounding Salmon Bay.

The City of Seattle and Sound Transit have started public workshops and street concept planning projects to match the new stations with more general community needs, so ensuring that station areas—usually one or two blocks from each stop—integrate naturally into existing urban environments and improve walkability and access.

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Courtesy of Sound Transit

The controversial second tunnel

Though the Ballard-Westlake service has clear advantages, Sound Transit’s current plans call for running the route south from Westlake through a brand-new tunnel—also known as DSTT2—which would run parallel to the current Downtown Seattle Transit Tunnel (DSTT1). Ultimately, this massive, multibillion-dollar project will link Ballard trains all the way to Tacoma. Critics argue that since most services are projected to remain running in DSTT1, DSTT2 may see limited train traffic for years.

In addition, the new tunnel demands answers about upsetting current transit lines. Riders heading between Southeast Seattle (or the airport) and Northeast Seattle, for instance, might lose their direct, one-seat journeys and have to be forced to transfer downtown.

A recent post on the Seattle Transit Blog highlighted this issue, stating:

“The latest preferred alternative doesn’t even include a stop in International District, further worsening the transfer experience.”

The absence of a significant station in the Chinatown-International District (CID) has only raised doubts regarding DSTT2’s capacity to adequately service existing communities. Critics argue that the area should critically reevaluate whether the project is really necessary if the tunnel eventually causes a deterioration in service for many current users.

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Why an Automated Line could work

Rather than building tunnels south of Westlake, some urban designers propose to convert the Ballard Link—at least in the long term—into a totally automated line finishing at Westlake. Higher frequency train operating could be made possible by automation without appreciably raising running expenses. One particularly noteworthy example is Vancouver’s SkyTrain, which runs trains as frequently as every two minutes and is entirely automated.

Advocates contend that by enhancing signals, adding more station exits, and renovating at-grade crossings, Sound Transit might relieve congestion in DSTT1 instead of building an expensive new tunnel.

As noted in the Seattle Transit Blog analysis:

“Sound Transit believes that achieving better than 3-minute frequencies will require upgrades to DSTT1, including egress improvements (stairs/elevators/escalators) and better signaling. Even if these upgrades cost several times more than the 2015 estimate of $20 million, it would still be far cheaper than a new $2+ billion tunnel.”

By focusing investment from DSTT2 on automation and modernization of DSTT1, service dependability throughout the system could improve. Opponents of DSTT2 also warn about the major construction disturbance a second tunnel may cause to downtown, stressing that any temporary annoyance should result in long-term benefits—something they fear may not come to pass if DSTT2 is kept underused for decades.

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Financial and logistical hurdles

Establishing a separate Ballard-Westlake line would not be free. It would still need new maintenance facilities even if it would cut the enormous cost of building a second tunnel. Sound Transit’s vehicle maintenance facilities are now connected with existing Link lines, hence a standalone Ballard line would either need either a dedicated facility or creative alternatives—such as keeping certain trains overnight at stops.

Additionally, separating Ballard Link from the existing system would mean that trains couldn’t be easily extended through the University of Washington or south to Sea-Tac Airport without requiring transfers at Westlake. Planners, on the contrary, say that regular service may make these movements smooth. Even if riders have to change trains, an automated line running every two to three minutes could help to keep general travel times short and reduce inconvenience.

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Courtesy of Sound Transit

Future extensions: First Hill to Mount Baker

Eventually extending the tunnel east and south will allow a Ballard-Westlake line to serve some of the densest areas of the city that now lack high-capacity transit. Under one plan, the line would run first from First Hill, Yesler Terace, the Central District, Judkins Park, and finally Mount Baker.

These sites have enormous potential for transit-oriented development free from the negative effects of freeway routes, such as traffic noise and air pollution. Stations in the Central District or close to First Hill could benefit local businesses, offer smooth connections to current Link stations, and remove the need for users to detour all the way downtown, only for a transfer.

Although building a short terminal now—while keeping future growth in mind—could streamline the process of adding new segments down the line, planners advise that extending the route to Mount Baker remains a long-term target.

Station context planning and environmental review

The City of Seattle keeps designing its Station Context for the Ballard Link Extension (BLE). The January 2022 Station Progress Report states that the city is working with Sound Transit to develop station designs, open spaces, and bus connections inside a block or two of proposed stations. Focusing on walkability, bike access, public space improvements, and possibilities for additional homes and shops, a larger Station Area planning project spans around half-mile radius.

Additional environmental study emphasizes the project’s difficulty. The West Seattle and Ballard extensions first followed the same Environmental Impact Statement (EIS) timeline. But now, since 2023 has seen improvements, the Ballard Link Extension operates on its own schedule. Early 2025 will see a revised Draft EIS; a Final EIS could arrive in 2026—almost three years following the final papers of the West Seattle project.

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Looking ahead

Clearly, the Ballard Link has enormous potential regardless of how it finally takes shape. Whether by the building of DSTT2 or the acceptance of an automated Ballard-Westlake link, both methods seek to serve areas where light rail regularly beats driving, regardless of the time of day. Strong ridership from day one could be guaranteed in Ballard, Uptown, South Lake Union, and Downtown by their current high density and walkability.

Still, opponents are wary of the political, logistical, and financial obstacles a second tunnel might create. They contend that focusing money on an autonomous automated line—and finally growing it into underprivileged central neighborhoods—may better balance cost and rider potential. As Sound Transit unveils its next round of design changes and environmental results in the following months, Seattleites will have the chance to comment on the most reasonable and cost-effective course of action.

The city is currently advancing Station Context seminars, community outreach initiatives, and street concept ideas to assist shape the Ballard Link Extension. Whether DSTT2 finally advances or not, the basic objective stays the same: building a dependable, high-frequency rail line linking Ballard’s lively neighborhood to the rest of Seattle. The idea of quick, strong urban rail keeps driving official planning efforts and grassroots activism even with changing budgets and timeframes.