Alternative Link Alignments Into Downtown Tacoma: A Mapped Review

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November 20, 2021 by seradt

Critical Note: Additional alignment investigation for a Central Tacoma Link Extension has resulted in a preferred alternative that has been formally proposed by Sound Transit since 1996: the integration of the Tacoma Link “starter line” with the Central Link system, a project approved by voters and constructed in the early 2000s. Integrating this existing infrastructure would deliver trains to the Commerce Street Hub in an efficient and incredibly cost effective manner. The alignment is represented here and will be elaborated upon in a future post.

The publishing of the Central Tacoma Link Extension (CTLE) surface alignment proposal has stirred a large debate regarding how Link should properly serve the city of Tacoma over a decade from now. There was broad agreement that terminating services at Tacoma Dome Station was deeply unsatisfactory, with most commenters agreeing that a natural terminus for the regional metro system is, indeed, Downtown Tacoma.

However, among the many proponents of such an extension, there were legitimate concerns of how it would be accomplished. Where the surface CTLE came under routine fire was on two fronts: its interaction with the existing streetcar system, and the location of the Central Tacoma Station. Although these points are addressed extensively, they are real concerns that warrant further investigation. The CTLE surface option remains the cheapest and most cost effective manner of delivering trains into Central Tacoma. That station, even without extensive bus connections, has independent utility as a rail station in an urban core. Still, it is worthy to consider alternative alignments into Tacoma that, one, have no impacts on the existing streetcar system, two, more finely integrate Link with the existing Downtown transit hub at Commerce Street, and, three, furthers the conversation of getting trains into the city center. 

A preliminary review of alternative alignments into Downtown Tacoma produced three additional alignments, whose components could be mixed to produce a larger variety of routing options. Of course, the first option is the original surface alignment. The three new alignments include moderate tunneling or aerial segments. Worthy of note, the impacted areas are predominantly surface parking lots, a wide avenue, or the margins of a freeway, all of which should dramatically reduce construction costs relative to other large rail projects through a developed urban quarter.

TUNNEL: Pacific Avenue is a wide thoroughfare and should be a prime candidate for shallow cut-and-cover tunneling. This manner of tunneling is disruptive, but only a small segment of tunneling is required for the project, which would mitigate its most deleterious impacts (see pages 10 & 11). Additionally, such tunneling is substantially less expensive than deep bore tunneling and quicker to construct (with the surface impacted for a one to two-year period). Disruption to surface streets could be reduced with the minimization of trench width and via the use of the Milan method of cut-and-cover tunneling. As far as tunneling in an urban area goes, it could not be more straightforward than the options presented within the ArcGIS review map. A deep bore tunnel is simply not required. With a thorough survey of underground utilities, the trenching and utility relocation could be done swiftly and inexpensively compared to similar projects in more densely developed cities. Tacoma is “fortunate” in that regard; it long ago demolished the neighborhoods in the right-of-way under the guise of urban renewal. Of course, TBMs should remain on the table if it is determined that their method of construction could deliver a better product for the city, but they would likely represent major scope creep for the project.

1. A surface and tunneling hybrid. This proposal preserves the Union Station-area track sharing arrangement of the CTLE surface alignment. However, just north of S. 17th Street, the trains are sent straight into a shallow tunnel under Pacific Avenue. With only the wide avenue above, the construction method favors cut-and-cover tunneling.
2. An aerial and tunneling hybrid. This proposal abandons in its entirety the alignment of the surface CTLE and has no track sharing with the existing streetcar system. Instead, an easterly and largely aerial alignment hugs the west side of I-705, curving around freeway facilities both horizontally and vertically, to provide a new approach into Downtown. Union Station / UWT would be served by a new rail station to the east of the History Museum, requiring a rebuild of the Bridge of Glass that fully integrates into the platform system. At 109 South 15th Street, presently a lone building surrounded by a sunken surface parking lot, the tracks would eventually rest underneath future development here before beginning a shallow tunnel alignment that curves toward Pacific Avenue. With only surface parking lots and a wide avenue above, the construction method again favors cut-and-cover tunneling.
3. Pacific Avenue stations. Directly under Pacific Avenue, a new station could be constructed just south of the intersection of 9th and Pacific; or, preferably, trains could be diverted westerly into the large property now hosting the multi-story parking garage owned by Commencement Plaza, LLC, at 923 Commerce Street. This property would be purchased by Sound Transit and would accommodate a seamless Link/bus transfer facility, along with affordable and market-rate housing and commercial businesses. The City Center Station would be a game-changer for the city of Tacoma and the regional transit system. 

Determination: both tunneling alignments, along with a City Center Station under 923 Commerce Street, appear to be more preferable alignments than the surface option (and they are represented by the diagram accompanying this post). Option #2 delivers Link trains to Central Tacoma without impacting the streetcar system, a very appealing attribute for a transit system that avoids mixing rail technologies. In fact, the merits of Option #2 are so pronounced that they may render the cheaper surface proposal a penny-wise and pound-foolish option for serving Central Tacoma and knitting together the regional transportation system.

AERIAL: An aerial alternative exists that is not represented within the plans. They were removed from consideration as being too complex, too visually obstructive, and for making only marginal improvements to local transit system integration over the proposed Central Tacoma Station of the surface alignment.

1. A largely aerial alignment. This proposal abandons in its entirety the alignment of the surface CTLE and has no track sharing with the existing streetcar system. Instead, an easterly and largely aerial alignment hugs the west side of I-705, curving around freeway facilities both horizontally and vertically, to provide a new approach into Downtown. Union Station / UWT would be served by a new rail station to the east of the History Museum, requiring a rebuild of the Bridge of Glass that fully integrates into the platform system. Near the I-705 ramps at East 15th Street, both the at-grade and aerial approach to access A Street may require impacts to the ramps. Any significant impact would necessitate intensive coordination with the State and the federal government. Once on the A Street viaduct, trains would either terminate on A Street somewhere between East 10th and 12th Street, or the trains could swing sharply via a reverse curve on 12th Street into the alley. There, a station could be sited at 110 South 10th Street. This building, now a multi-story parking garage, would be replaced by an aerial station facility along with affordable and market-rate housing.

COSTS

A rudimentary evaluation of the costs for any of these CTLE alternative alignments should be compared against the $1.1-billion dollar Tacoma Mall extension (in 2015-dollars) that would presumably be completed under an ST4 program. For this cursory review, Option #2, the Aerial & Tunnel Hybrid alignment above, with a terminal station at 923 Commerce Street, will be held as the preferred alternative to the original surface proposal. Even with tunneling segments, this city center extension is far less expensive than the suburban mall extension. There would also be the added benefit of centralizing the regional transit system in Downtown, with all the positive qualities such an urban core hub would entail.

Holding Federal Way Link Extension costs per mile that include frequently elevated rail infrastructure, and using rough estimates for the cost of cut-and-cover tunneling, we get the following breakdown between an aerial-and-tunnel CTLE hybrid and a Tacoma Mall Extension within a hypothetical ST4 initiative (in today’s dollars):

TUNNELING LENGTH

CTLE: 0.43 miles; Tacoma Mall: some required, unclear length

AERIAL LENGTH

CTLE: 0.88 miles; Tacoma Mall: some required, unclear length

ROUGH BREAKDOWNS

Federal Way Link Extension cost per mile (overall): $400,000,000 per mile

Cut-and-cover tunneling cost per mile (estimate): $245,000,000 per mile

Station construction at 923 Commerce Street: $150,000,000 (to be compared with the cost of the new Traxx Apartment Building: $41-million. Overall costs could potentially be offset through sale of real estate)

TOTAL PROJECT LENGTH

CTLE: 1.31 miles; Tacoma Mall: 3.55 miles

TOTAL PROJECT COST

CTLE: $610-million (employing a very conservative estimation)

Tacoma Mall: $1.2-billion (but consider the track record of recent ST cost estimates. Note: holding Federal Way Link Extension costs, which is a dramatically less complex project to execute than the mall extension, the costs for the mall extension would be $1.42-billion, an almost certain cost underestimation).

SUMMARY

Any of the four CTLE alignments would directly serve Downtown Tacoma and properly interface with the local transit system, if not at Union Station then at a Downtown station. As Pierce Transit advances plans to redirect bus services toward Tacoma Dome Station, mandating transfers there at the expense of quality services to the urban core of the city, the CTLE promises to restore the proper dominance of Central Tacoma. This is the logical path forward for the South Sound and the Link spine. Crucially, the first step to ensuring its realization is securing a TDLE Puyallup Avenue alignment.

Central Tacoma Link Extension (CTLE) Alternative Alignments Map

ArcGIS Interactive Map, detailing the CTLE alternative alignments on a viewer-friendly map.

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