When it opened in 1953, the much-maligned Alaskan Way Viaduct, State Route 99's route along the Seattle waterfront, offered the first route around Seattle's congested central business district. The expressway relieved traffic on city streets, eased the movement of through traffic, and improved connections between growing southwest Seattle neighborhoods, such as West Seattle, and downtown. Despite its utility, critics derided it for its lack of beauty and for its negative effect on the waterfront. Over several decades, various groups and individuals argued and planned for its demise. But the lack of a viable alternative for handling the tens of thousands of daily users stymied their efforts. The 2001 Nisqually earthquake significantly damaged the viaduct's joints and foundations and furthered the discussion. A decade of studying, planning, and public discussion passed before a viable option, a deep bore tunnel, garnered enough support to move forward. The southern end of the viaduct was demolished in October 2011 and tunnel boring began in 2013.
Early Years of the Viaduct
The southern extension, the final section of the Alaskan Way Viaduct route between Aurora Avenue and E Marginal Way opened on September 3, 1959. Other parts of the route, including the double-decked structure on the central waterfront and the Battery Street Tunnel, had opened to traffic earlier, but this last section allowed traffic to travel via an expressway from the southern end of downtown Seattle to 74th Street N, near Green Lake. It offered the only limited-access route through Seattle until the mid-1960s, when the Seattle Freeway (Interstate 5) opened.
The bypass route reduced traffic congestion on downtown streets and made it easier to move cargo through the city. In 1953, after the central waterfront section of the viaduct opened, a city traffic study found that 19,000 vehicles traveled on the viaduct. Traffic on Alaskan Way dropped by 33 percent, and 1st and 4th avenues saw about a 20 percent decrease. By the summer of 1959, 22,000 vehicles used the viaduct each day. That number increased to 37,000 vehicles when the southern extension opened that September.
A few days after the first section of the viaduct opened in 1953, The Seattle Times sent drivers through town on the viaduct and on city streets, timing them. Obviously thrilled to have a bypass, the reporter drew a sharp contrast between the two experiences, writing that the driver on city streets, "inched, started, stopped, crawled, fussed, fumed and shifted," and, "The viaduct user got back to Fourth and Vine fresh as a daffodil. The midtown traveler finished his round-trip junket just that way ... FINISHED!" (Heilman, "Viaduct Saves Drivers Time").
Truck drivers especially appreciated avoiding streets filled with trains, train tracks, passenger vehicles, other delivery trucks, and the steep hills. One of them, Henry P. Knutsen of south Seattle, wrote to the City in 1954, "I want to thank the people who help[ed] build the Battery subway [Battery Street Tunnel] it sure is wonderful. I am a truck driver [Teamsters] Local 174 and it means a lot to me. Easier driving no hills or stoplights and save[s] time and no hard pull for trucks to get on Aurora. So I want the city of Seattle to know that I appreciate the new Subway and Viaduct and will help to make it safe -- as will my fellow union members" (Knutsen).
City planning in the 1940s and 1950s, when the viaduct was designed and built, did not include environmental or design reviews. Seattle architect Paul Thiry (1904-1993) vocally objected to the idea of building an elevated roadway between downtown and the waterfront, calling it, "half-baked" and "ridiculous without study of the whole problem, to be sure that the span is the proper solution" (Heilman, "Tunnel, Not Viaduct"). Without a mechanism to review the project or a significant public outcry, little could be done to stop a project already in the works.
Legacy of an Industrial Waterfront
The existing conditions on the waterfront contributed to a lack of public concern about how an elevated structure might blight the neighborhood. Long an industrial area and transportation corridor, full of warehouses on piers and commission houses along Western Avenue, crisscrossed by railroad tracks, and full of traffic and haphazardly parked cars and trucks, it was chaotic and rundown. When federal and state government agencies conducted a traffic study in 1947, the waterfront seemed an ideal place to put a bypass route.
But as construction of the viaduct progressed, people began to realize how it would dominate the narrow central waterfront. Edward Flohr (1884-1970), of Flohr & Co. Metal Fabricators, wrote to City Engineer Ralph Finke (1901-2003) in 1952 that, "Although this structure is very well proportioned ... [a]s it now appears it presents an unfriendly and inhospitable look to visitors approaching Seattle from the Bay side." Flohr offered to donate metal piping for use as planters at the base of the columns on the viaduct's west side. Ivy planted in the pipes would grow up the side of the structure and, "take away the cold utilitarian aspect of the viaduct" (Flohr).
The structure did, in fact, dominate the waterfront. It was noisy, it cast a large shadow, and it essentially created a barrier between downtown and the waterfront, despite efforts, over the next few decades, to make connections via pedestrian corridors, a streetcar, and bus routes.
Dissatisfactions and Dreams
Despite dissatisfaction with the viaduct's effect on the waterfront, the elevated roadway remained. In the mid-1960s it carried 88,000 vehicles per day. When the Seattle Freeway opened, that number dropped to about 54,000, where it stayed for some time and then began to climb again as the region's population grew. In 1977, Stimson Bullitt (1919-2009), president of King Broadcasting, told the Seattle Post-Intelligencer, "It would be a great boon if the viaduct disappeared but I fear it is durable. One may dream, perhaps, of comets" (Smith).
In the 1970s and 1980s city planners and city activists began to look at the waterfront as a space that could be part of the revitalization of downtown Seattle. Several people suggested changes to make the viaduct less of a wall between downtown and the waterfront. In 1971, Seattle resident John McFarland suggested adding a pedestrian walkway along the length of the viaduct, with cafés and overpasses to reach sidewalks along Alaskan Way. The next year Seattle architect Donald D. Myers proposed turning the viaduct into an office building, with openings in the structure at cross streets and traffic moved to lidded tunnels below the viaduct. No one actively criticized McFarland or Myers' plans, but neither did they take them up.
One of the Forward Thrust initiatives passed in 1968 provided funds for the development of a waterfront park. The city hired the San Francisco-based architecture firm Rockrise Odermatt Mountjoy Amis (known as Rockrise) to develop a plan for the entire waterfront.
The Rockrise Plan estimated that it would cost $100 million to remove the viaduct and replace it with a tunnel, which led Seattle Times reporter Don Duncan to write: "So much for tearing it down" (Duncan). Instead, the plan recommended four options for improving the waterfront with the viaduct in place, hoping that rising property values would make it economically feasible to remove the viaduct in 10 to 15 years. Rockrise likened the anticipated effect to "throwing open a window in a dingy attic" ("Alaskan Way Viaduct Big Headache").
Also in 1972, city council member John Miller (1938-2017) asked City Engineer Robert J. Gulino to study the cost and feasibility of tearing down the viaduct. According to an article in The Seattle Times, Gulino balked at the request because there was no funding for the study or for carrying out the project, and, he told the newspaper, the viaduct was an important traffic route.
A Need to Transform
The Rockrise plan languished but other changes came to the area that set the stage for further pressure to improve the waterfront. The Pike Place Market, Pioneer Square, and the Bell Street Pier, all underwent improvements and renovations and the city approved a plan to develop a new facility for the Seattle Aquarium, which opened in 1976. Several people in city government continued with efforts to remove the viaduct, including city council members John Miller and Bruce Chapman (b. 1934) and city policy aide Phil Sherburne.
In 1976, Klaus Otto Bodenmüller, a Seattle architect, began promoting a plan to turn the entire viaduct structure into a building, creating a half million square feet of new space that could be used for a school, an art museum, offices, and retail. According to his plan, the city could move traffic to Western Avenue, where it would descend into a tunnel between Seneca and South Main streets. A "city gate" could be built into the building at Madison Street and the Toyota car company could use the southern portion for a factory (the firm had recently expressed an interest in opening its first American factory). The structure would attract rather than repel people, provide a linear connection between the Pike Place Market and Pioneer Square, and avoid demolition expenses. Bodenmüller enthusiastically presented his elaborate plan to a wide array of public and private entities. In letters reproduced in a report he compiled in 1981, many of them responded positively but noncommittally to the proposal.
In the early 1980s, as the city considered re-zoning parts of the central waterfront from manufacturing and industrial uses to retail and residential uses as part of an effort to create a longterm plan for downtown Seattle, a group of local organizations and University of Washington departments sponsored a symposium about the future of the waterfront. In their interim report, the symposium panel discussed the viaduct, writing, "The Alaskan Way Viaduct must be transformed from a liability to an asset. Wishing the Alaska Way Viaduct will go away, or underestimating its vital role in the City traffic system are likely to lead to frustration. Opportunities exist to exploit the Viaduct and should be the focus of concerted urban design efforts" (Seattle Waterfront Symposium Panel).
The Earthquake Danger
The 1989 Loma Prieta earthquake in the San Francisco Bay area grabbed Seattle's attention because an elevated, double-decked highway along the Oakland waterfront, the Cypress Viaduct, collapsed during the earthquake. Comparisons to the Alaskan Way Viaduct raised fears of a similar event happening here.
The Washington State Department of Transportation asked engineers from the Washington State Transportation Center at the University of Washington to study the viaduct's seismic vulnerability. The Center's report described differences between the Alaskan Way Viaduct and the Cypress Viaduct that might make Seattle's viaduct more resilient to earthquakes, but also sounded an alarm about the risks faced by Seattle's elevated highway.
Unlike the Cypress Viaduct, the Alaskan Way Viaduct has discrete sections, with connections that could withstand movement more easily than the types of connections on the Cypress Viaduct. The Alaskan Way Viaduct also has longitudinal girders that the Oakland viaduct did not and different underlying soil conditions. A 2001 report by engineering firm T.Y. Lin International would also note that the Seattle viaduct's thermal expansion and contraction joints between each section allow more room for movement.
However, these factors did not make the Alaskan Way Viaduct certain to survive another strong earthquake. The Transportation Center report explained that the viaduct was built before the 1971 San Fernando Earthquake, also in California, that led to changes in construction practices. The viaduct is a strong structure, but it has too little transverse reinforcement, too little overlap in the splices at joints, and is at risk of excessive stress on the column foundations because of the high likelihood that the soil around the foundations and pilings, which had been brought in to fill behind the Alaskan Way seawall in the 1930s, would be subject to destabilizing liquefaction.
Just as the state's Office of Urban Mobility began a new study of the viaduct's seismic vulnerability in early 2001, the Nisqually Earthquake, a 40-second, 6.8-magnitude quake with an epicenter near the Nisqually Delta, on the southern end of Puget Sound, struck on February 28th. The earthquake's depth, 30 miles under the surface, reduced its destructiveness, but the shaking caused significant damage to the viaduct structure and the road had to be closed intermittently for months as crews inspected it and shored it up.
The following June, T.Y. Lin International issued a structural review of the viaduct that warned that the earthquake had weakened connections between the columns and the roadway decks. Additionally, the aging concrete had cracked and the structure had shifted to the east, indicating problems with the foundations. The sections near Washington Street, in Pioneer Square, experienced the greatest damage, most likely because the viaduct curves there, placing more force on the connections between its sections.
The viaduct shifted four more times in the months following the earthquake. Near Yesler Way, the columns settled five and one-half inches by 2009. Near Seneca Street the columns settled about an inch and a half. The Washington State Department of Transportation installed reinforcements along the columns that stopped the settlement and, to reduce the pressure on the structure, instituted lane and weight restrictions for vehicles traveling on it.
In addition to structural issues, the soil around the viaduct's foundations posed a problem. The study found evidence of liquefaction in scattered areas during the 2001 earthquake, including the settlement of a 100-foot-by-10-foot section of Alaskan Way, and warned that the liquefaction could be more widespread in future earthquakes.
Concerns about the seawall compounded fears about the stability of the soil behind it. Gribbles, marine organisms that bore through wood, had caused significant deterioration in ekki wood panels that were placed in front of the seawall's metal sheet pilings during the 1980s to protect the metal from corrosive sea water and erosive tidal action. Additionally, the wooden support system for the seawall, located under Alaskan Way and subjected to daily raising and lowering of seawater, had weak spots.
Engineers feared that the seawall would collapse in a strong earthquake, possibly leading to the movement of massive amounts of soils. This would remove part of the viaduct's piling and column support and could lead to severe damage or collapse.
Options and Alternatives
As a result of the concerns about the viaduct and the seawall, the state and city departments of transportation began planning to replace both structures. An initial review of possible solutions resulted in a list of 76 options. Many were rejected outright because they would not resolve earthquake concerns, they could not be adapted to the existing Battery Street Tunnel configuration, or because they did not serve western neighborhoods such as Ballard or West Seattle.
By June 2002, the transportation departments had created a list of five options:
a rebuild of the existing configuration;
a new aerial design;
a single-level tunnel and a single-level aerial structure with two bored tunnels under Broad Street to Aurora Avenue;
a stacked cut-and-cover tunnel with ramps to downtown and a tunnel under Broad Street;
a stacked cut-and-cover tunnel with ramps to downtown and a bored tunnel under Belltown.
All the options included a new seawall along Alaskan Way. All but the rebuild and the new aerial option were rejected because they would cost too much.
Over the next two years, five new options based on the rebuild and aerial options were developed. Engineers used 10 goals to evaluate their relative merit. The first goal, which had to be met, required the alternative to meet current seismic design standards. The additional nine goals, which could be met to varying degrees, sought to find an alternative that would "maintain the current transportation functions of the Alaskan Way Viaduct Corridor," not send traffic to other transportation infrastructure components to the extent that it would reduce function, improve traffic safety, fit within the regional traffic system, include provisions for pedestrians and bicyclists, be usable by regional transit systems, be compatible with shoreline management plans and policies, improve habitat along the seawall, and involve construction methods and practices that entailed reasonable risk and a minimum of disruption to downtown residents and businesses.
In March 2004 a draft environmental impact statement presented the five options:
a six-lane, side-by-side, cut-and-cover tunnel with an aerial connection to the Battery Street Tunnel;
an aerial structure with improvements along Aurora Avenue north of the Battery Street Tunnel;
a four-lane, side-by-side, cut-and-cover tunnel with Aurora Avenue improvements;
a new waterfront street with an aerial structure connecting it with the Battery Street Tunnel;
a rebuild of the existing structure.
All these projects also included replacement of the seawall.
The No Viaduct, No Tunnel Idea
The next month, the People's Waterfront Coalition, an advocacy group started by landscape and urban designer Cary Moon, Julie Parrett, and Grant Cogswell, called for a surface streets and transit option in which the viaduct would be torn down and not replaced with either a new elevated structure or a tunnel. They argued that the city would regain its waterfront, reduce transportation impacts on the environment, and reduce suburban sprawl by making downtown more livable. In an editorial printed in The Seattle Times, Moon and Ralph J. Cipriani, an urban planner, outlined the reasons why the city could accommodate the viaduct's traffic on city streets and with improved mass transit. Primarily, they argued that many trips would not be made if the highway did not exist, improvements could be made to increase the city street grid's capacity, truck-only lanes could serve freight transportation needs, improving Interstate 5's downtown ramp configuration could improve traffic flow, and increased mass transit could draw still more travelers out of their cars.
That December the transportation agencies published an information sheet titled, "Is the Viaduct an Essential Transportation Corridor?," which reported on a study of the streets and transit option. The study found that the option would ruin neighborhood-to-neighborhood connections, result in downtown gridlock, make Alaskan Way so busy with traffic that the waterfront would not be pedestrian friendly, and the freight priority measures would be inadequate to serve cargo handling. Proponents of the streets and transit option questioned the transportation departments' study methodology.
Debating the Tunnel
Also in December, city, state, and federal officials announced that they had chosen the six-lane cut-and-cover tunnel as the preferred alternative, with the elevated option included in the environmental impact statement process as a backup plan in case funding could not be secured for the tunnel. They chose the tunnel, despite its significantly higher cost, because it "maintained the mobility provided by SR 99 and reconnected downtown with the waterfront" (Alaskan Way Viaduct Replacement Project History Report, 13). The Seattle City Council passed a resolution in January 2005 adopting the tunnel as its preferred alternative.
Numerous groups and agencies spent the next year and a half debating the relative merits of each option. The Alaskan Way Tunnel Coalition, a pro-tunnel group largely composed of business leaders, commissioned a study by economist Glenn Pascall that described the significant projected economic benefits of building a tunnel to replace the viaduct. The Congress for New Urbanism issued a report in 2006 arguing that other cities, including San Francisco and Milwaukee, had removed their elevated freeways, seen a revitalization of their waterfronts and traffic continued to move smoothly.
Representatives from the city government, the Port of Seattle, and maritime industries pointed out that Seattle's topographical situation is different from the other cities that had successfully removed their elevated highways. They cited a 2004 study, which found that the viaduct provides a key link between the Ballard/Interbay industrial area and the Duwamish River industrial area. Because Seattle's narrow center and numerous hills impeded traffic flow, industrial groups worried that workers would not be able to get to their jobs on the waterfront and that freight movement between manufacturing and port facilities and the region via the Alaskan Way Viaduct would be hindered. Other transportation agency publications described the importance of the rail link on the waterfront, which connects Seattle to a transcontinental rail line, the economic impact of cargo handling at Puget Sound ports, which was valued at $100 billion annually, and the needs of the 110,000 vehicles and 26 trains that use the waterfront corridor each day.
The Seattle Design Commission held a series of design workshops in the spring of 2005 that focused on what the waterfront could become once the viaduct was replaced. The workshops produced several recommendations, including investments in pedestrian connections to Pioneer Square, providing access to the water's edge, restoring habitat at Pier 48, making renovations to Colman Dock that would "recognize its essential role as a multimodal transportation hub as well as its potential as an iconic presence on the waterfront," and making improvements to the Pier 62/63 area to develop its connection with the Pike Place Market and create open space that could become a "great civic space" (Seattle Design Commission).
Allied Arts, an advocacy group that sought to replace the viaduct with open space, issued a report, "Waterfront for All," in 2006. In an opening letter Allied Arts members David Yeaworth, Sally Bagshaw (b. 1951), and Laine Ross wrote, "Fifty years ago, our civic leaders made a serious mistake. They cut off Seattle from its waterfront by building the Alaskan Way Viaduct. Now, the people of Seattle and the Northwest have an opportunity to correct this error and redirect the future of the region. We have the choice of giving future generations a vibrant Waterfront neighborhood, or cursing them with an even larger viaduct ripping through some of the most significant urban land in the Northwest" (Allied Arts).
The office of Seattle Mayor Greg Nickels (b. 1955) produced a brochure describing a vibrant viaduct-free waterfront neighborhood with the Seattle Art Museum's Olympic Sculpture Park at the north end, new views from Belltown and downtown, a new civic space centered on the Pike Place Market area, and a renovated Washington State Ferries terminal at the south end. According to the report, the city would gain economic and environmental benefits and a new sense of place.
In March 2006, the transportation departments issued a supplemental draft environmental impact statement with the cut-and-cover tunnel and the elevated structure alternatives and new information about improvements that would be needed north of the Battery Street Tunnel and new technical information. In September, the city council passed an ordinance identifying the tunnel as the City's preferred alternative.
Explanations and Complications
As part of a public information campaign, the Washington State Department of Transportation released a series of fact sheets in the summer of 2006 to explain some of the gamut of options that had been rejected in the early rounds of decision making. The publications explained that a tunnel under Western Avenue would have moved the project away from the piers, sparing the waterfront from the construction project, but it would not have fixed the seawall and it would have been difficult to build a useful structure in Western Avenue's far narrower right-of-way. An Elliott Bay bridge would have added a "world-class signature structure" to Seattle's waterfront, but would have required the equivalent of two 60-story buildings for underwater supports, which would have adversely affected the bay and endangered species in it. The bored tunnel posed exceptionally high risks and costs and would not have had ramps to downtown. T.Y. Lin International analyzed a retrofit option proposed by engineer Victor O. Gray (1926-2016) and the Viaduct Preservation Group in 2004 and found that even with a number of improvements, including adding shock absorbers and wrapping steel jackets around column bases, the viaduct was likely to fail in a serious earthquake.
Though the chosen alternatives cost less than a bored tunnel, they were still very costly. Estimates for the cut-and-cover tunnel ranged from $3.6 billion to $4.3 billion, while the elevated structure estimates ranged from $2.5 billion to $2.9 billion. An expert panel reviewed the costs, risks, plans, and environmental concerns for each of the alternatives and sent their findings to Governor Christine Gregoire (b. 1947) in September 2006.
According to a February 2007 memo from state Department of Transportation officials to state Secretary of Transportation Douglas B. MacDonald (b. 1945), the review panel found that the six-lane tunnel's financial plan insufficient and the discussion over it "politically gridlocked." The city then approached the state Department of Transportation with a plan for a four-lane tunnel. The state reviewed the plan and, "It became clear that the four-lane tunnel was not adequate to meet the transportation needs in the corridor, or the project's National Environmental Policy Act purpose and need statement as agreed to by the City, WSDOT and the FHWA [Federal Highway Administration]" (David L. Dye et al). Meanwhile, the city presented the four-lane tunnel to the state Senate Transportation Committee as a choice that would serve transportation needs and stay within an acceptable budget.
Governor Gregoire supported the elevated alternative and Seattle city officials supported the tunnel alternative. An impasse ensued because the city needed the state to fund and construct the project, and the state needed city permits for the project and its involvement in extensive related projects. In an effort to gauge public sentiment on the two options, the Seattle City Council passed two resolutions calling for an election, to be held on March 13, 2007, that would ask Seattle voters for a non-binding, advisory vote on the two options. Voters were asked about each option separately, not in comparison to each other. In the election, voters rejected both options, with 70 percent against the tunnel and 57 percent against the elevated structure.
Thinking and Rethinking
Faced with resounding voter disapproval of the two alternatives, city, county, and state government officials rethought their plans. Governor Gregoire, King County Executive Ron Sims (b. 1948), and Seattle Mayor Greg Nickels agreed to a series of "Moving Forward" projects that could be done to prepare for the eventual replacement of the viaduct, but would be compatible with whichever option was eventually chosen. These projects included stabilizing the viaduct's footings between Yesler Way and Columbia Street, relocating electrical lines between S Massachusetts Street and Railroad Way S, safety upgrades to the Battery Street Tunnel, transit enhancements, and the replacement of the S Holgate Street to S King Street viaduct structure with a side-by-side elevated roadway.
In order to move forward on the central waterfront project, the state, county, and city officials signed a memorandum of agreement pledging to participate in a "collaborative process." This process would, "resolve the longstanding needs of the Alaskan Way Viaduct and related projects in a manner capable of being broadly supported and implemented" ("The Alaskan Way Viaduct Collaborative Process"). The parties agreed to use six guiding principles -- focusing, as in earlier guiding principles, on finding a safe solution that improved the central waterfront for people and the environment -- to find a regional solution to replacing the viaduct. In order to assess the options in a timely and collaborative manner, a Project Oversight Committee was formed, consisting of the governor, the King County executive, the Seattle mayor, the chairs of the Senate and House transportation committees, and one member each of the King County and Seattle councils. To ensure public involvement in the process, a Stakeholder Advisory Committee, with members from advocacy groups, neighborhoods, business groups, and labor groups, was formed in December 2007. The state legislature set December 2008 as the deadline for these groups to decide upon a solution.
The city, county, and state transportation departments, along with an Interagency Working Group made up of representatives of Community Transit, the Federal Highway Administration, the Freight Mobility Strategic Investment Board, the Passenger Ferry District, Pierce Transit, the Port of Seattle, King County Public Health, the Puget Sound Clean Air Agency, the Puget Sound Regional Council, and Washington State Ferries, analyzed eight new proposed alternatives. These included three surface street plans, a four-lane elevated structure, an elevated structure with a park on the top of two roadway levels and levels with office and retail space, a four-lane bored tunnel under Western Avenue, a cut-and-cover tunnel along the waterfront connecting to an elevated structure between Stewart Street and the Battery Street Tunnel, and a four-lane lidded trench along the waterfront.
In early December 2008, the Project Oversight Committee presented two new preferred alternatives to the public. The first, the I-5, Surface, and Transit Hybrid would turn Western Avenue and Alaskan Way into a one-way street couplet, add RapidRide bus lines, other new bus service, eight trolley lines in Seattle, a streetcar line from Pioneer Square to Queen Anne, a lane to northbound Interstate 5 between Seneca Street and State Route 520, and a transit access ramp off of Interstate 5 to Industrial Way and the busway. The second alternative, an Elevated Bypass Hybrid, would utilize two two-lane, side-by-side viaducts on the waterfront with ramps at Railroad Way S and Elliott Avenue, some bus system improvements, four trolley lines, the downtown streetcar, and improvements to Interstate 5. A four-lane Tunnel Hybrid, which included transit improvements and the downtown streetcar but not mid-town ramps was also studied, but not presented to the public because the costs exceeded the targeted cost of $2.8 billion.
The Deep-Bored Tunnel Hybrid Option
In response to the Project Oversight Committee's announcement, a member of the Stakeholder Advisory Committee, Tayloe Washburn, from the Greater Seattle Chamber of Commerce, presented a tunnel hybrid option to the committee. It called for a deep-bore or lidded trench tunnel extending from S Royal Brougham Way to Harrison Street, with two or three lanes of traffic on top, and improvements to Interstate 5 and city streets to facilitate traffic flow. Washburn also suggested that the seawall be removed from the project (to be replaced by the city separately) and that regional tolling could provide the additional funds needed for the project.
Recent advances in tunneling technology made this alternative more feasible than it had been earlier. The Cascadia Center, a Discovery Institute program, had sent information about the increased size of bored tunnels, the lower costs per mile of recently completed projects, and comparisons of soil types in which the other tunnels had been bored to the Stakeholder Advisory Committee in November 2008. Twenty-two of the 25 active members of the Stakeholder Advisory Committee agreed to Washburn's proposal and sent a letter to the governor announcing their preference in December 2008.
The next month, after the departments of transportation had reviewed the proposal, Gregoire, Sims, Nickels, and Port of Seattle CEO Tay Yoshitani (b. 1946) announced the choice of the deep-bore tunnel hybrid to replace the Alaskan Way Viaduct.
The state committed to funding the construction of the tunnel and removal of the viaduct. The city agreed to pay for the seawall replacement project, the new waterfront street, and the downtown streetcar. The Port of Seattle agreed to contribute $300 million to the project and King County agreed to make transit improvements. In legislation authorizing the state's contribution, the state legislature added an amendment assigning responsibility for cost overruns exceeding $400 million to the City of Seattle. The enforceability of this amendment has been debated.
After analyzing the final environmental impact statement for the deep bore tunnel option in the summer of 2011, the Federal Highway Administration issued its Record of Decision in August, approving the Tolled Bored Tunnel Alternative. This allowed the Washington State Department of Transportation to move forward with the project.
Concerns about the benefits of the tunnel, the risks associated with building it, and its role in shaping Seattle's future continued, however. In February 2011, Seattle Mayor Mike McGinn (b. 1959), who had campaigned vigorously against the tunnel in the 2009 mayoral election, vetoed a city council-passed bill that affirmed agreements with the state for the construction of the tunnel and related work out of concern that potential cost overruns could saddle the city with debt. On February 28, 2011, the city council overrode the veto by a vote of eight to one.
In March 29, 2011, the group Protect Seattle Now filed a referendum petition calling for a vote on the ordinance. Protect Seattle Now argued against allowing the City to move forward because the tunnel was too expensive, it lacked downtown access ramps, the project did not include any transit improvement elements, a proposed Pioneer Square interchange would impede the movement of buses serving West Seattle, and tolls would divert traffic to city streets, causing gridlock. After some legal wrangling, the referendum was placed on the ballot in the August election. The measure passed, authorizing the city to move forward, with a vote of 58 percent in favor on August 16, 2011.
Tunnel boring began in the summer of 2013, but in December of that year, after completing the first 1,000 feet of tunnel, the boring machine, nicknamed Bertha, was halted due to increasing resistance at the front of the machine and concerns about unexplained overheating. Work continued on other aspects of the tunnel project as the boring-machine manufacturer, Hitachi, and Seattle Tunnel Partners, the partnership drilling the tunnel, worked to determine the cause of the problems. By March 2015, crews had completed an access pit and the damaged cutterhead was raised to the surface for inspection and repair.
The damage turned out to be extensive, and it was not until December 2015 that tunneling began again. Bertha completed boring the 9,270-foot tunnel on April 4, 2017, emerging into a previously constructed disassembly pit at the north end of the route. But by then, with years of work remaining to disassemble and remove the boring machine and build the double-decked highway within the tunnel, the new underground SR 99 was not expected to open to traffic until early 2019, more than three years later than the original schedule had called for.
Though not often beloved or celebrated, the Alaskan Way Viaduct was often appreciated for the purpose it served. The 2001 Nisqually earthquake spurred the inevitable process of deciding how to replace it, but in a very different political and social context than that in which the decision to the build the structure was made, with different assumptions about how people and goods should move through the city and what elements of the waterfront we value. Given the ambivalence many people feel about the project's cost and the risks inherent in tunnel construction, it remains to be seen if the tunnel will be celebrated.
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