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Alaskan Way Viaduct Legacy Part 3; the Alaskan Way Viaduct replacement tunnel

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Following the 2001 Nisqually Earthquake the Alaskan Way Viaduct was determined to be in need of replacement due to it not meeting seismic standards.  Ultimately a double-deck tunnel bore structure was selected as a replacement after years of debate in the many political circles in the city of Seattle.  Construction of so-called Alaskan Way Viaduct replacement tunnel began via boring operations during Summer 2013 through Spring 2017.  The completed tolled tunnel would open as the then new alignment of Washington State Route 99 during February 2019.

Part 3 of the Alaskan Way Viaduct Legacy series covers the history of the tunnel which replaced it.  The blog cover photo is from the Alaskan Way Viaduct replacement tunnel approaching the south portal near Royal Brougham Way. 


This blog is part of the larger Gribblenation US Route 99 Page.  For more information pertaining to the other various segments of US Route 99 and its three-digit child routes check out the link the below.



Part 1 of the Alaskan Way Viaduct Legacy series featured the history of Railroad Avenue:


Part 2 of the Alaskan Way Viaduct Legacy series features the history of the Alaskan Way Viaduct and alignments of US Route 99 in downtown Seattle:




Part 3A; the Alaskan Way Viaduct replacement tunnel

Following the 2001 Nisqually Earthquake five options regarding the Alaskan Way Viaduct were considered.  All options included rebuilding the seawall along Alaskan Way to mitigate potential liquefaction during a major earthquake:

1. A rebuild of the existing configuration.
2. A new aerial design.
3. A single-level tunnel and a single-level aerial structure with two bored tunnels under Broad Street to Aurora Avenue.
4. A stacked cut-and-cover tunnel with ramps to downtown and a tunnel under Broad Street.
5. A stacked cut-and-cover tunnel with ramps to downtown and a bored tunnel under Belltown.

Initially only the rebuild and aerial options remained after assessment due to being cost effective.  Ultimately five new corridor options were developed which emphasized maintaining the traffic flow of the Alaskan Way Viaduct and mitigate potential earthquake hazards.  An Environmental Impact Report conducted during March 2004 studied the following options:

1. A six-lane, side-by-side, cut-and-cover tunnel with an aerial connection to the Battery Street Tunnel.
2. An aerial structure with improvements along Aurora Avenue north of the Battery Street Tunnel.
3. A four-lane, side-by-side, cut-and-cover tunnel with Aurora Avenue improvements.
4. A new waterfront street with an aerial structure connecting it with the Battery Street Tunnel.
5. A rebuild of the existing structure. 

Following the 2004 Environmental Impact Report debate over a "no viaduct" and "no tunnel" option was considered.  This option was largely dismissed due to the negative impacts it would have on increased traffic in downtown Seattle.  Ultimately during January 2005, the Seattle city council would adopt a resolution favoring replacing the Alaskan Way Viaduct with a tunnel.  This resolution was followed up in March 2006 with a Supplemental Draft Environmental Impact Statement regarding a cut and cover tunnel. 

Debate would persist over a tunnel structure would be four or six lanes.  This led to three new projects options being proposed during December 2008:

1. Turn Alaskan Way and Western Avenue into one-way couplets.  This option included adding dedicated RapidRide bus lanes.  
2. Two two-lane elevated viaduct structures with ramps to Railroad Way and Elliott Avenue.
3. A four-lane tunnel with no exits into downtown along with transit options. 

During 2009 then Seattle Mayor Mike McGinn vetoed a city council resolution which concurred with a State of Washington decision favoring a tunnel option.  The city council was ultimately able to override the veto on February 28, 2011.  During August 2011 the Federal Highway Administration issued a record of decision approving a tolled Deep Bore Tunnel alternative. 

Work on the so-called Alaskan Way Viaduct replacement tunnel began on July 30, 2013.  A tunnel bore machine nick-named "Bertha" was sourced from Hitachi Zosen.  The machine initially only worked until December 6, 2013, due to unexpected damage caused by striking a pipe which had been missed in a survey.  The damage was severe enough that a recovery pit had to be dug to lift the cutterhead for repairs.  

Tunnel bore operations resumed on December 22, 2015.  Work halted in again during winter 2016 due to a sinkhole opening related to a shipping incident in Elliott Bay.  Tunnel boring operations were finally complete on April 4, 2017.  The tunnel bore measured at a length of 9,270 feet. 

A completed segment of the Alaskan Way Viaduct replacement tunnel wall can be seen in a Seattle city council photo dated January 4, 2017.   The boring machine was fully dissembled and removed by August 2017.  


The northbound lanes of the Alaskan Way Viaduct replacement tunnel opened at 11 PM on February 3, 2019.  The southbound lanes opened at 12:15 AM on February 4, 2019.  The project ultimately incurred approximately $223,000,000 in cost overrides.  Tolling did not begin until November 9, 2019.  The initial toll rate for two-axle vehicles was $1.20-$2.70 for Good to Go transponder users and $3.20-$4.70 for pay-by-mail users.  

This graphic depicts the two-level structure of the Alaskan Way Viaduct replacement tunnel.  To-date the tunnel has no designated name and is generally referred to as the "State Route 99 Tunnel" in Washington State Department of Transportation documents. 


Demolition of the Alaskan Way Viaduct began on February 15, 2019.  The partially demolished structure can be seen in the vicinity of Columbia Street during April 2019 (source SounderBruce). 


Demolition of the Alaskan Way Viaduct was completed on November 21, 2019.  The debris from the viaduct were used to backfill the now redundant Battery Street Tunnel.  The so-called Overlook Walk was installed as a Seattle Waterfront park above Alaskan Way during 2021. 



Part 3B; a drive through the Alaskan Way Viaduct replacement tunnel

This Washington State Department of Transportation graphic depicts the current alignment of Washington State Route 99 through the Alaskan Way Viaduct replacement tunnel.


Traffic on southbound Washington State Route 99 along Aurora Avenue is now advised of the tolled nature of the Alaskan Way Viaduct replacement tunnel.  Denny Way is signed as the last exit before tolls.  Hazardous cargo is required exit onto Denny Way and not enter the tunnel. 









There are no exits in the Alaskan Way Viaduct replacement tunnel.  Southbound traffic can exit onto Royal Brougham Way towards Lumen Field and T-Mobile Park after emerging from the tunnel.  The current toll rates are displayed upon exiting the south tunnel portal. 






















Part 3C; the Overlook Walk above Alaskan Way

These photos were taken from the Overlook Walk during July 2025 by Gribblenation's Tom.  This first photo faces south down Alaskan Way.


This view faces north along Elliott Way towards where the Alaskan Way Viaduct once entered the Battery Street Tunnel.  The Battery Street Tunnel portal is now blocked as it has been filled with debris from the viaduct structure.  


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