Tunnels, deep stations for West Seattle-Ballard line could add $2B

The Level 3 end-to-end alternatives. Click to enlarge. Credit: Sound Transit

At a Stakeholder Advisory Group meeting last night, Sound Transit released its first cost estimates and evaluations for the three proposed Level 3 alignments of the West Seattle-Ballard Link extension. Agency staff presented cost estimates and "mix and match" opportunities, both of which advisory group members and elected officials requested in earlier meetings.

Sound Transit project lead Cathal Ridge took pains to emphasize the cost estimates are very preliminary.

"This is a very high level evaluation that I'm giving to you," Ridge told the stakeholder group. "I'm not trying to capture everything that's in the analysis, I'm just trying to give you some high points to think about."

Below, all the figures amount to estimates of the cost that an additional funding source would have to account for in addition to existing ST3 funds. Individual items add up to the total cost of the end-to-end alignments.

The Yellow/Brown alignment, which would elevate the guideway in West Seattle and Ballard, with a bored 5th Avenue South Chinatown/International District (CID) station would cost at least $400 million above the ST3 representative project. The costs for individual big ticket items are:

• A controversial cut-and-cover tunnel in the CID on 5th could save $200 million.
• A fixed bridge over Salmon Bay on 14th Avenue Northwest would cost an additional $100 million
• A Smith Cove/Expedia station at West Galer Street would add $100 million
• A South Lake Union station at 6th and Mercer would add $300 million

The Blue/Purple alignment, which builds popular tunnels in West Seattle and Ballard, would add at least $1.9 billion for the entire line with tunnels in both neighborhoods, with a CID station on 5th. The same alignment with a mined CID station on 4th would cost $2.1 billion. The costs for individual big ticket items are:

• A West Seattle tunnel would individually cost $700 million, with an additional $300 million for a light rail bridge north of the West Seattle Bridge
• A 4th Avenue CID station would individually cost $300 million to cut and cover, or $400 million to mine
• A tunnel under Salmon Bay, with a station at either 14th of 15th Avenues NW, would cost $350 million
• A Smith Cove/Expedia station at West Prospect Street would add $200 million

Ridge presented "mix and match" opportunities-i.e. places where stakeholders and elected officials could tinker with a Level 3 alignment in a specific area.

In the Yellow/Brown alignment, stakeholders could recommend making any or all of the following changes:

• Crossing the Duwamish River either north or south of the West Seattle Bridge
• Routing the Downtown and South Lake Union segments on either 5th Avenue and Harrison Street or 6th Avenue and Mercer Street
• Placing the Smith Cove Station on West Galer Street, or closer to the Helix Pedestrian Bridge on West Prospect Street

In the Blue/Purple Alignment, stakeholders could suggest:

• Tunneling or elevating the West Seattle segment
• Building the CID station on 4th or 5th Avenues South
• Tunneling under or high bridging over Salmon Bay, with the bridged Ballard Station on 14th Avenue NW

Ridge also presented the agency's analysis of the tradeoffs in those mix and match selections, some of which is a rehash. The following table shows some of those tradeoffs, and some of the cost estimates.

Click to enlarge. Credit: Sound Transit

Elevating the West Seattle segment would cause "more displacements"-both residential and commercial-in the Junction, Avalon, and Delridge station areas, and create the "greatest disruption" near the Junction. The tunnelled West Seattle stations would "require 3rd party funding."

The bridge over the Duwamish would be a more challenging engineering project if it crossed south of the West Seattle Bridge, but a Duwamish bridge north of the existing bridge "affects freight, port terminal facilities especially during construction." In a separate conversation earlier this week, Port of Seattle Commissioner Stephanie Bowman said that the Port's analysis suggests that mitigation and construction of a new trucking right of way account for the higher cost of the north crossing.

In Sodo, the choice is between elevated track, or at-grade track. The at-grade track would separate pedestrian and car traffic from grade, probably via an overpass, at South Lander and Holgate Streets. The E3 Busway would close permanently if the at-grade alignments were chosen. Buses would also be displaced for construction of the elevated line. In both cases, buses would likely run on either 4th or 6th Avenues South, according to Sound Transit's Ron Endlich.

In the CID, the 5th Avenue South alignments would be much less costly, but more significantly impact business and residents in the neighborhood. The 4th Avenue South alignment would cost about four times more than on 5th, and displace an estimated 33,000 weekday vehicles and bus lines. Both alignments would limit either expansion or existing operations of the Central or Ryerson Metro bases.

The main tradeoffs in the new downtown station are between its location on either 5th or 6th Avenues. A station on 6th would have "limited entrance options," according to the deck, but the Seattle Center station would have "wider right-of-way" than a 5th Avenue alignment. Also, both of those tunnels' north portals would be located in landslide areas, while the ST3 representative alignment would not. The 6th Avenue alignment's South Lake Union stop on Mercer would add significant cost.

The Salmon Bay crossing still has three options. The agency says the movable bridge "has potential service interruptions and [the] most in-water effects." A fixed bridge "reduces in-water effects and avoids Fishermen's Terminal but has other potential maritime effects." The bridge would have to be very high for "navigational clearances"; Ridge said that the bridge would need to be "140 feet, plus or minus." A tunnel would avoid the impacts on maritime businesses, but, as the slide deck points out, "tunnel crossings add costs; require 3rd Party funding."

Ridge's comments on the Ballard station on 14th or 15th Avenues Northwest revisited the familiar arguments about each station's walkshed. A new wrinkle is the analysis of the elevated line, which would require "more acquisitions and displacements with elevated guideway, station and tail tracks on 15th Ave NW."

The advisory group will make its recommendations in April. Elected officials will be briefed on the alignments on Friday, and will also make recommendations in April. Both sets of recommendations are non-binding; final alignments will be selected by the Sound Transit board.

After the April meetings, Sound Transit hopes to have two alignments to enter into environmental review: one that would be funded with the ST3 package's existing funding, and one that would draw on an yet-undefined third party funding source.

At publication, the stakeholder advisory group deck was not available. The deck that Sound Transit will present to elected officials, which is based on the same estimates, is available here. The above images are drawn from that deck. We will update this post when the advisory group deck is available. Stakeholders saw this deck.