Ballard Link Extension: 4th Ave Shallow is Dead, Long Live 5th Ave Diagonal

Slide from a November 14 presentation to the Sound Transit Board's System Expansion Committee.

Eight years after Sound Transit 3 was approved by voters in 2016, Sound Transit is still trying to figure out where exactly to put a new station near the Chinatown-International District as part of the Ballard Link Extension (BLE). After the agency published the Draft West Seattle and Ballard Link Extensions Draft Environmental Impact Statement in 2022, community uproar around the potential impacts of building an expanded International District-Chinatown station under 5th Avenue South drove Sound Transit to consider several alternative station locations. In late 2023, the agency determined that the amount of additional study required splitting the two projects apart, necessitating a complete restart of the environmental impact assessment process for BLE (starting with a request for comments on impact assessment scoping) and forsaking the supposed expediency of planning these projects simultaneously.

At the Board's System Expansion Committee meeting on Thursday, Sound Transit staff presented a review of another round of Further Studies" on the Ballard Link Extension, this time focused on three alternatives under serious consideration for the CID: the Preferred Alternative" of a Dearborn Street location (formerly known as the CID South" Station), a diagonal station under 5th Avenue South, and a transit hub under 4th Avenue South.

Alternatives considered in the latest round of Further Studies on BLE.

Although there are a few other alternatives under consideration for this station's location (including the original 5th Avenue location), these three locations appear to be the main contenders for the final project. Sound Transit staff presented an extensive review of the constructability of each station alternative including how long each would likely take to build and methods used to build them. They then reviewed how each alternative impacts local and regional transit connections, including differences in modeled ridership, station access, and transfers.

Construction Duration Drivers

Sound Transit's presented a slide summarizing construction duration drivers for each alternative (click to enlarge):

You might notice the duration drivers for the current Preferred Alternative (Dearborn Street") and the 5th Avenue Shallow Diagonal alternatives are downright demure in comparison to the 4th Avenue Shallow alternative. While Sound Transit estimates construction of either the Dearborn Street or 5th Avenue alternatives would take 6 to 7 years, the agency estimates construction of the 4th Avenue Shallow alternative would take 10 to 12 years. As the saying goes, time is money, and while these studies didn't present cost differences between these alternatives, in 2023 the 4th Avenue Shallow alternative was estimated to cost over $600 million more than the proposed Dearborn alternative.

4th Ave Shallow costs above representative alignment" in 2023: +$700MCID South (Dearborn Street) costs above representative alignment" in 2023: +$80M

Agency staff noted that construction of the 4th Avenue Shallower option, which would build a station practically at-grade with King Street Station (as opposed to the Shallow" option, which would be somewhat deeper below the street), would require reconstruction of the Yesler Way Bridge and demolition of the King County Administrative Building in order to build the tunnel to Westlake Station and on to South Lake Union.

Staff also considered completed closure of 4th Avenue South as a way to speed up construction but determined that while this would shave 3.5 years off the construction timeline, traffic impacts would be especially severe in the CID as 4th Avenue is a major transit and freight thoroughfare.

Regional Connections

To assess whether or not the construction difficulties are worth the cost, Sound Transit staff modeled ridership and travel times to regional destinations for each alternative.

Ridership modeling results from Sound Transit's presentation.

After acknowledging the high volume of transit choices in the Seattle core makes modeling results highly sensitive to small changes, such as station access times," the modeling of these stations (which have fairly significant differences in station access times from the street and other transit connections) resulted in nearly indistinguishable differences in travel patterns, with slight (~1%) differences in predicted weekday boardings between each alternative. Apparently, this is due to many riders simply transferring between stations at more convenient locations.

For the Dearborn and 5th Avenue Diagonal alternatives, Link-to-Link transfers would mostly happen at Westlake Station; for the 4th Avenue Shallow alternative, these transfers would mostly happen at the ID/C Station.

Similarly, Sound Transit determined that no matter the chosen station location, total boardings near new stations in Downtown would be relatively similar, but did admit the Dearborn alternative would have slightly fewer boardings.

While the ridership modeling shows significant differences in where these boardings would occur with the various alternatives, the Midtown station (either at James Street or Madison Street) is expected to garner more boardings if the CID station is at 5th or Dearborn rather than 4th Avenue. This may be to due to additional effort put requested by the Board to refine station access designs for parts of these alternatives, including assessment of two different transfer tunnel alternatives for the Midtown James Street" alternative (formerly known as CID North):

With all this work, Sound Transit is building a body of evidence which suggests the complexity of the 4th Avenue Shallow station is not worth the supposed benefits. Counter-intuitively, the agency's modeling work indicates building a new station in the center of our region's transportation hub would have a largely negligible benefit compared to placing the station blocks away.

Independent Assessment

While we may have to take Sound Transit's word regarding network benefits of building a station under 4th Avenue South, the agency commissioned an independent report from professional engineer David A. Peters regarding the construction risks there. The engineer independently identified several construction risks, most significantly the adjacency of the BNSF railway to the project site.

Construction risks related to construction next to the BNSF railway at 4th Avenue, from David A. Peters' presentation to the System Expansion Committee on November 14, 2024.

While construction at 4th Avenue would encounter typical construction issues like poor soils, hazardous materials, and underground obstructions like poorly-mapped utility lines, Mr. Peters identified a multitude of potential issues regarding construction immediately adjacent to the BNSF Railway passing King Street Station into the Great Northern Railway Tunnel under Downtown.

The greatest risk to construction is BNSF, which has near-sovereign control over its railway due to a long history of railroad rights spanning back to the 1800s. As Peters put it in his presentation, the railroad-related risks for the CID 4th Ave S alternatives, as opposed to the other alternatives, are substantial, unpredictable, unquantifiable, and cannot be mitigated".

With little quantifiable benefit to offset the immense risk and associated cost, the 4th Avenue Shallow alternative appears to be dead.

A Worthy Successor

With a station under the 4th Avenue South viaduct all but proven to be impractical, eyes are turning toward Sound Transit's 5th Avenue Shallow Diagonal Alternative, which is a refinement of the former 5th Avenue Shallow alternative which would have shut down 5th Avenue for several years during construction and kicked off a myriad of community complaints against the proposed station.

This alternative would be have fewer construction impacts to traffic (only closing half a block of King Street) and few business displacements.

Additionally, the station would be closely tied with the existing ID/C Station, albeit at a depth requiring four flights of escalators to transfer between the platforms. Although this conceptual design has room for improvement (particularly in enabling in-station transfers from the 1 Line to the southbound 2 and 3 Lines), the proposed transfers are much better than those assumed for the Dearborn station.

This station alternative has the shortest estimated construction timeline, assumes construction of a proper Midtown station near Madison (which would have easy transfers to RapidRide G) and would have similar connectivity at King Street to the original 5th Avenue alternative.

Of course, this assumes construction of BLE is affordable; as we've seen with WSLE's latest cost estimates, costs may explode well beyond affordability; such cost explosion may threaten the entire Sound Transit 3 program. Advocates have proposed some radical cost-savings measures including scrapping the second transit tunnel altogether, but it may be some time before the Board is faced with seriously considering such measures.

In the meantime, the 5th Avenue Shallow Diagonal alternative seems to be Sound Transit's only viable option to directly connect the Ballard Link Extension to our existing primary transit hub. Although the Dearborn Station is getting preferential treatment in the draft environmental impact assessment work, there is at least one more chance to convince Sound Transit to seriously consider building a Ballard Link Extension that doesn't force riders to choose between a long walk in the rain from Dearborn to King Street or a longer detour through Downtown. However, it will be up to transit advocates to work with the CID community to build a coalition of support behind the 5th Avenue Shallow Diagonal alternative, our last option for a truly integrated hub connecting all our transit modes in one place.