Transportation Planning Casebook/Alaska Way Viaduct in Seattle


The existing Alaskan Way Viaduct (constructed in the early 1950s) is a two-tier-ed overpass that brings Washington State Highway 99 directly through the city of Seattle. The existing structure cuts off the downtown area from the waterfront of Elliot Bay of the famed Pudget Sound. Following years of material degradation and earthquakes (most notably the Nisqually earthquake of 2001), the state of Washington, in conjunction with the city of Seattle, began debating on a course of action to improve the existing structure. Years of debate were to follow which eventually resulted in the state's decision for a replacement tunnel. The tunnel would be bored directly underneath downtown and would enable traffic to freely travel through the area. Removal of the existing bridge structure could also reconnect the city to its waterfront and would have the potential to spur much real estate development. Despite its appearance as a 'slam dunk' project, the decision to tunnel was heavily political. The debate which led to the tunnel decision was an all-out drama between a variety of actors including Seattle residents, city and state governments, environmentalists, and many interest groups. Additionally, the project's total cost is tremendous and is considerably more expensive than alternatives to the tunnel. Due to Seattle's proximity to fault lines, there is concern for the safety of travelers in the tunnel during potential future seismic activity despite being told that the tunnel is being constructed to all the standards to be safe during an earthquake.

Construction of the tunnel is currently underway. The official groundbreaking took place in 2013 and the project was scheduled to be completed well within two year's time. This project has experienced its fair share of unexpected events which include the tunnel boring machine, known as Bertha, striking debris underground and needing to be repaired. Currently, the project is on hold due to repairs. This single incident has extended the project's time frame by nearly two additional years. Construction is scheduled to resume in the near future (January 2016) and the project is now scheduled to be completed in Spring 2018. Whether this will actually happen on this new time-frame remains to be seen.

Annotated List of ActorsEdit

Former Governor Christine Gregoire

Former Mayor Gregory Nickels

Port of Seattle Commissioner John Creighton

WSDOT The Washington State Department of Transportation is the primary facilitator of this construction project. The DOT was responsible for the plans, the current construction, and for future repairs and maintenance. They are also responsible for footing a large amount of the bill.

Seattle Residents Locals to the city are charged with footing some of the bill through a tax increase. This includes all residents of the city, even those that might not have traveled along the old viaduct or will not use the new tunnel.

Commuters All travelers to and through the city stand to benefit from the new tunnel. Traffic could potentially pass through the city (underneath) at a faster rate of travel.

Timeline of EventsEdit

1949 Construction of Alaskan Way Viaduct begins.

April 4, 1953 Completion of Alaskan Way Viaduct

February 28, 2001 Nisqually Earthquake badly damages viaduct and Alaskan Way Seawall. Emergency repairs cost WSDOT $14.5 million.

2003-2008 Debate on what viaduct replacement should be

January 12, 2009 Announcement of viaduct replacement tunnel

October 21, 2011 Beginning of initial demolition phase of old viaduct

July 30, 2013 Construction Commencement (estimated 14 months out from completion)

December 6, 2013 Bertha (tunnel bore-ing device) strikes old steel pipe and is badly damaged. Borer cannot move in reverse and can only be fixed by repairing from front end which requires a vertical shaft to be constructed. Project is halted for at least 12 months.


December 2015 Estimated resumption of construction.

Spring 2018 Estimated completion of tunnel

2019 Completion of waterfront area on location of old viaduct.

Maps of LocationsEdit


Policy IssuesEdit

Almost everyone can agree that the Alaskan Way Viaduct in Seattle was in need of replacement. One of the major issues initially with the Alaskan Way Viaduct replacement was that policy makers were arguing for different proposals. Each with severe implications, with both pros and cons. The three main options that were proposed include a replacement structure, a tunnel, or a street level alternative. Since the freeway on the viaduct is State Route (SR) 99, it involves the collaboration of both the state and local governments.

Replacement Options

One option that was proposed was tearing down the viaduct and replacing it with a new structure that would meet current seismic requirements, expecting that it will then be able to resist a strong earthquake. The 2001 Nisqually earthquake significantly damaged the structure and the viaduct has been growing weaker ever since. Proponents from this plan stem from those who argue the view on the structure (while in a car) is great, as you can see the waterfront of the Puget Sound to the west and downtown Seattle to the east.

Another option was to do away with the structure altogether and improve the surface streets and nearby I-5 on the east side of downtown Seattle. This plan was notably favored by King County Executive Ron Sims, as he argued that a surface street replacement would be a “success” with the creation of pedestrian-friendly neighborhoods, and more bike friendly infrastructure. He wanted to seek the opportunity to remove the existing structure.[1]

The third proposal that was ultimately selected was a bored tunnel underneath the current viaduct. This has been a generally favored choice as it addresses concerns about traffic spill over from the demolition of the current viaduct, and because of its removal, a large swath of land between downtown Seattle and the waterfront could be utilized for prime real estate development. This could potentially spur economic development in the region as these new prime condos/apartments would provide a new tax base. In addition, parks, pedestrian/bicycle areas could be created to help reconnected the previously divided sections of the city. This would be similar to the current Freeway Park over I-5.

A rendering of the surface replacement where the Alaska Way Viaduct currently runs

Oppositions and Concerns About the Tunnel Selection

Of course with any major project, funding must be present for the visions to become reality. When the replacement tunnel was selected, the initial costs of the project was expected to be around $3.1 billion according to the WSDOT.[2] However, it is currently estimated to be $4.25 billion. This has been a major reason as to why this project is subjected to controversy. Additionally, the passage of this project was signed by governor Gregoire in March of 2009 with no election or referendum on the bill. This is important to note since the Seattle tax payers according to this bill would pay for any cost overruns. Under the agreement, $2.8 billion would come from the state and $1 billion would come from the city.[3] The additional $400 million would be expected to be generated from dynamic tolling. A WSDOT analysis suggests that this would not deter a significant amount of travelers because this could provide an option with reduced congestion that people would be willing to pay.[4]

Opponents have often referenced the Boston Big Dig project as a reason why a tunnel choice should not be considered. They cite the fact the project cost an extraordinary amount over their projected budget, $14.8 billion as compared to $2.6 billion, and the technical challenges with boring a huge tunnel to accommodate multiple lanes of traffic[5]; additionally, tunneling so close to a major body of water presents an additional set of challenges from the encroachment of sea water.

Some other concerns that came as a result of the tunnel choice have only added controversy to the decision. One of which are the environmental concerns of boring a tunnel in the heart of downtown next to the Puget Sound. There are concerns about inducing demand on this new tunnel will not promote breaking the community’s “oil addiction” and there are arguments that replacing the urban freeway with surface improvements focusing on transit, bicycles, and pedestrians will benefit the environment.[6]

In additon, the interest group, Cascade Bicycle Club, opposed the tunnel selection because they believe that the project is too costly and doesn’t support a green, multi-modal transportation network. They do support the idea of removing the existing structure however. Their argument is that the project would produce too much traffic downtown and make it unsafe for bicyclists to travel there.[7]

The Allied Arts of Seattle doesn’t directly oppose the tunnel project, but they support the removal as well because it would open up a connection between downtown Seattle and the waterfront. The land could be used for activities to connect the Seattle community, whether it’s from art fairs or other festivals. [8]

Narrative of the CaseEdit


The Alaska Way Viaduct to carry Washington State Route 99 was constructed in the 1950s between downtown Seattle and its waterfront. The elevated structure allowed traffic to pass through downtown Seattle unhindered by local traffic. Unfortunately, the Nisqually earthquake of 2001 caused substantial damage to the structure and necessitated the need for costly repairs[9]. Though stability and at least temporary safety were reestablished in the structure, the inability of the structure to endure another sizeable earthquake was deemed a significant public risk and the search for replacement or removal plans began[10].

Viaduct Replacement Deliberation

Three main alternatives to the existing viaduct emerged, replacing the existing viaduct with a similar elevated structure built to withstand earthquakes, replacing the viaduct with a tunnel, and removing the route entirely but increasing local street and transit capacity. Early project meetings in 2004 showed preference on the part of citizens and local businesses (especially local restaurants) for a tunnel in an effort to improve the waterfront area. The idyllic vision fueling the tunnel argument was a pedestrian walkway in place of the current elevated structure with traffic routed below and out of sight. In addition to this, business owners in the area supported the tunnel in hopes of reduced noise pollution and incorporation of the waterfront into the downtown area. Support for a similar elevated structure came from industrial and manufacturing businesses whose primary concern was the maintenance of traffic capacity. While the tunnel would have the possibility of handling ordinary traffic previously managed on the viaduct, it would likely be closed to the transport of hazardous materials, a vital element to certain businesses in the area. Support for removing the structure altogether with improvements to existing infrastructure came from citizens accompanied by several urban planners collectively forming the People’s Waterfront Coalition. The city conducted a traffic study to investigate the effects of this plan and forcasted gridlock as a result. The results were met with skepticism by the People’s Waterfront Coalition and others[11].

The skepticism was not entirely unfounded. The city’s traffic study did not include any information regarding changes in land use or travel patterns over time due to redevelopment in its evaluation of removal or replacement options for the Alaska Way Viaduct. An independent study by Sevcikova, Raftery, and Waddell into the uncertainty surrounding large infrastructure projects with the Alaska Way Viaduct as its case study did include changes in land use and travel patterns. This second study compared two scenarios, one in which the viaduct was replaced with a structure (type unspecified) and one in which the viaduct was removed and not replaced without any improvements to transit or surrounding city streets. The second case was not a plan the city would ever implement, but rather a worst case scenario. As a part of the study, the travel times of fifteen commuter routes were evaluated. Of these, seven did not require the driver to utilize the viaduct while the other nine did. The model developed for the study found that increased (or decreased) travel times for the seven routes that did not include the viaduct were unlikely after viaduct removal while an average increase post viaduct removal of approximately six minutes was predicted for those routes initially including the viaduct[12].

To an extent, these findings contradict the findings of the city which stated replacing the viaduct with a comparable structure would decrease travel times. Sevcikova, et al. identify potential reasons for this discrepancy. While the independent study utilized a regional travel model without network details, the model of the city incorporated micro elements including intersection geometry, pedestrian traffic, and transit conflicts. However, the study done by the city did not include changes in land use or travel patterns as mentioned, nor the ability for people to adapt to changes in infrastructure such as moving to more convenient locations, getting different jobs closer to home, or utilizing transit more effectively[13].

By 2005, state and local officials openly stated they preferred the option of a replacement tunnel. The estimated cost of the tunnel project at this time was between $3.7 billion and $4.1 billion. Of this, the city of Seattle would be called upon to pay approximately $1 billion while the state would fund the remainder[14]. While the replacement of the viaduct with a similar structure would cost approximately $1 billion less, public opinion of constructing another elevated structure was marked with distrust as to safety. As a citizen was quoted, “Elevated roadways are bad in seismic areas. They had their time in history. Now, I like the vision of a pedestrian walkway."[15] Eight finalist plans for the project were announced in 2008. These included elevated roadways, surface roadways, and roadways in tunnels. During the gap in time between 2005 and 2008, the state was forced to spend some of the funds intended for the replacement of the Alaska Way Viaduct on repairs to it, thus reducing their available funds to about $1.5 billion. Because of this, the state legislature would need to become involved to assure adequate funding for the project, especially if the more costly tunnel option was to be chosen.[16]

During the decision making process, concern was raised in regard to whether or not State Route 99 would be open through downtown Seattle during the construction process. For many of the proposed designs, this would not be an option. However, in 2009, after improvements in tunnel boring technology, a tunnel design that would allow State Route 99 to be open during construction was proposed to, and accepted by, city and state officials. The plan included replacing the southern portion of the viaduct with another elevated structure designed to withstand earthquakes prior to beginning tunnel boring.[17]

Funding remained an issue within the project plan. Though the roadway runs through Seattle and directly impacts Seattle’s infrastructure, the route is maintained by the state as State Route 99. After much discussion of which entity was responsible for which costs, an agreement was reached in 2010 between Seattle and State of Washington. The state would take responsibility for cost overruns for the tunnel and road itself while the city would be responsible for the costs of replacing the seawall and utility relocation.[18]

Earth Pressure Balance Shield Tunneling

Digging a tunnel underneath Seattle would require some extraordinary engineering work. The close proximity of Elliot Bay (an offshoot of the Pudget Sound) to the proposed project (meaning an elevated water table) and the prospect of tunneling underneath the heart of Seattle posed significant challenges. Fortunately, advances in tunneling technology led to the innovation of earth pressure balance tunneling. In this tunneling technique, a tunnel boring machine utilizes soil it removes to balance the pressure being exerted on its front cutting wheel as well as to balance the support pressure of the tunnel. (A video of the process can be seen here.)

The Washington Department of transportation commissioned Japanese Hitachi Zosen Corporation to construct an earth pressure balance shield tunneling machine for the project. With a diameter of 17.45 meters, the machine was the largest of its kind in the world. The machine was completed in Japan in December of 2012, then disassembled and shipped to the United States in March of 2013. The machine was officially named Bertha, a name submitted to the official naming contest by an elementary schooler, on December 20, 2012.[19]


Bertha began boring in the summer of 2013 and continued until December 6, 2013 when she was stalled due to overheating 1000 feet into the dig. (Video to animation of how Bertha works) Initial inspections found damage to Bertha’s seal system and contamination within the main bearing.[20] To determine what had happened, the front of the machine required inspection. The loose soil and high water table in the area complicated the ability to access the front of Bertha. Wells were drilled in front of the machine in an effort lower the water table and create a safe environment to which workers could descend.[21] It was not until January that workers gained the ability to descend to identify the cause of the blockage. An 8 inch steel pipe was found lodged in Bertha’s cutterhead. The Washington Department of Transportation stated that information on the location of the pipe was included in the project contract. At this point, there was no mention of removing Bertha for repairs.[22]

By March of 2014 it was clear that continuing with the project would require substantial repairs and project delay. An estimated two months would be required to remove enough soil from in front of the machine after construction of access pit walls in order to be able to remove the machine for repairs. While the Washington Department of Transportation had originally set an opening date of November 2016, the contractor hoped to complete the project in late 2015. With the newfound delay, the contractor revised the plan to complete the project on the date initially set by the department of transportation with tunneling resuming in March of 2015.[23]

The March 2015 goal was not realized. Rather, Bertha’s cutterhead was brought to the surface at that time as she was more damaged than was originally thought. Because of Bertha’s unique nature, her manufacturer was required to identify and replace broken parts. Beyond simply repairing the broken parts of the machine, the manufacturer opted to make improvements as well. Her soil removal system gained additional mixing devices to better handle the highly muddy soil being removed and her cutting surface was reconfigured with additional blades. Substantial testing was needed in order to determine if she could be returned to the ground to continue drilling as no procedural model exists to follow.[24]

Despite the tunneling delay, other portions of the project are still underway. The roadway approaching the tunnel and the roadway within the already constructed 1000 feet of tunnel have been continued. [25]

Northbound view inside replacement tunnel. Cars will travel southbound through this section.

Discussion QuestionsEdit

Before discussion of the impact of the damaged boring machine, what is your opinion on the selection of a tunnel as a solution to the viaduct problem?

Can you think of any alternatives to building the tunnel that might have been viable options for Seattle?

Are there any other cities in the world where an expressway, such as Washington Route 99, could be replaced with a tunnel similar to Seattle's new tunnel? Why might tunneling be a good option?

What are some potential reasons cities might consider relocating expressways through re-routing or tunneling?

Complete ReferencesEdit

  1. Lindbolm, Mike. "City, County, State Agree to Replace Viaduct with Tunnel." The Seattle Times. 12 Jan. 2009. Web. 14 Nov. 2015.
  2. "SR 99 Alaskan Way Viaduct Replacement Updated Cost and Tolling Summary Report to the Washington State Legislature." Washington State Department of Transportation, January 2010. p3 Web. 8 Nov. 2015.
  3. Garber, Andrew. "Tunnel in Place of Viaduct: A Deal, but How to Pay?" The Seattle Times. 13 Jan. 2009. Web. 8 Nov. 2015.
  4. "SR 99 Alaskan Way Viaduct Replacement Updated Cost and Tolling Summary Report to the Washington State Legislature." Washington State Department of Transportation, January 2010. p5 Web. 8 Nov. 2015.
  5. LeBlanc, Steve. "Boston Finally Completes $14.8B “Big Dig”." The Seattle Times. 26 Dec. 2007. Web. 9 Nov. 2015.
  6. During, Alan. "The Environmental Case Against the Deep-bore Tunnel Six Prominent Environmentalists Argue against Seattle's Proposed Deep-bore Tunnel." Sightline Institute. 20 July 2011. Web. 13 Nov. 2015.
  7. "Alaskan Way Viaduct: Issue Identification." pp 3-4. Web. 10 Nov. 2015.
  8. "Alaskan Way Viaduct: Issue Identification." p 4. Web. 10 Nov. 2015.
  9. Ševčíková, Hana, Raftery, Adrian E., & Waddell, Paul A. (2011). Uncertain benefits: Application of Bayesian melding to the Alaskan Way Viaduct in Seattle. Transportation Research Part A, 45(6), 540-553.
  10. Building a New State Route 99 Through Seattle. WSDOT. Retrieved from
  11. Tice, C. (2004). Viaduct view. Puget Sound Business Journal, 25(23), 1. Retrieved from
  12. Ševčíková, Hana, Raftery, Adrian E., & Waddell, Paul A. (2011). Uncertain benefits: Application of Bayesian melding to the Alaskan Way Viaduct in Seattle. Transportation Research Part A, 45(6), 540-553.
  13. Ševčíková, Hana, Raftery, Adrian E., & Waddell, Paul A. (2011). Uncertain benefits: Application of Bayesian melding to the Alaskan Way Viaduct in Seattle. Transportation Research Part A, 45(6), 540-553.
  14. Staff. (2005). Tunnel Preferred For Seattle Waterfront.(damaged Alaska Way Viaduct to be replaced)(Brief Article). Pacific Builder and Engineer, 111(2), 21
  15. Tice, C. (2004). Viaduct view. Puget Sound Business Journal, 25(23), 1. Retrieved from
  16. Gilmore, Susan (2008). “New viaduct speediest option, studies show.” Seattle Times, 14 November 2008.
  17. Viaduct History.” WSDOT 2015. Web. 8 Nov. 2015.
  19. “The World’s Largest EPB Shield Tunneling Machine.” 2013. Hitachi Zosen Corporation. Web. 13 November 2015.
  20. “Seattle Tunnel Partners working to repair Bertha.” Follow Bertha. 2015. WSDOT. Web. 13 November 2015.
  21. “Tunnel crews lowering groundwater to get a closer look at what’s blocking Bertha.” News. 13 December 2013. WSDOT. 13 November 2015.
  22. “Progress made on SR 99 tunnel blockage.” News. 3 January 2014. WSDOT. 13 November 2015.
  23. “SR 99 tunneling machine to resume digging in March 2015.” News. 21 April 2014. WSDOT. 13 November 2015.
  24. Lindblom, Mike “New Bertha start date: Nov. 23.” Transportation.17 July 2015. The Seattle Times. Web. 13 November 2015.
  25. "A look inside the new-look SR 99 tunnel." News. 19 March 2015. WSDOT. Web. 13 November 2015.