Viaduct questions

  • + Is most of the traffic using the viaduct today going to downtown or through downtown?

    The viaduct carries approximately 110,000 vehicles per day just south of the mid-town ramps (based on 2011 traffic information). Of this amount, approximately 17,000 vehicles enter or exit downtown at Columbia and Seneca streets, and 33,000 exit or enter at Elliott and Western avenues toward Belltown, Uptown, and neighborhoods along the 15th Avenue and Elliott Avenue corridor. The remaining 60,000 vehicles continue north through the Battery Street Tunnel, either exiting in the South Lake Union/Queen Anne area or continuing further north.


  • + Is the viaduct still a safe structure on which to drive?

    Routine safety inspections and maintenance keep the viaduct safe for public use. In 2008, crews strengthened four column footings where the viaduct had settled approximately five-and-a-half inches into the ground since the 2001 Nisqually earthquake. The column safety project limits settlement in this area of the viaduct and prevents further damage to the structure.

    We also installed a system designed to close the viaduct automatically in the event of a moderate to severe earthquake in the greater Seattle area. The new automated closure system consists of traffic gates at all viaduct access points controlled by an earthquake detection system. If the earthquake monitoring system detects significant ground movement, it will simultaneously lower all nine traffic gates and safely close the viaduct in two minutes.

    In 2011, crews demolished nearly half of the vulnerable viaduct near Seattle’s port and stadiums. Drivers now use a construction bypass connected to new side-by-side bridges built to current safety standards.


  • + Why is the viaduct a safety issue?

    The 1950s-era viaduct was already showing signs of age and deterioration before the 2001 Nisqually earthquake further weakened the structure, but the earthquake heightened the need for its replacement. The major risk facing the viaduct is its seismic vulnerability. The viaduct stands on fill soil bounded by the seawall. Marine organisms have slowly eaten away parts of the seawall and weakened it. In an earthquake, the fill soil is subject to liquefaction, where a shaking motion causes the soils to turn into a quicksand-like condition. Another major earthquake could collapse the seawall and liquefy the soil, damaging the viaduct beyond repair.

    View a simulation (YouTube) of what could happen to the viaduct if a strong earthquake were to shake the Puget Sound region (or watch a non-YouTube version - requires Windows Media Player). Visit the Elliott Bay Seawall Project website for information on the plans to replace the seawall.


  • + Is viaduct replacement construction being coordinated with other nearby projects?

    WSDOT coordinates with partner agencies on nearly every aspect of the program including overall strategy and management, project schedules, construction and public involvement. Project coordination extends beyond the SR 99 viaduct replacement - coordination with the Elliott Bay Seawall Project, Mercer Corridor Project, Waterfront Seattle and many more are vital to keeping traffic moving and all projects on schedule.


  • + How are you managing parking during construction?

    WSDOT and program partners meet regularly with a group of Pioneer Square and central waterfront stakeholders to identify and implement parking mitigation strategies. A plan to address short- and long-term parking concerns in these neighborhoods was completed in 2012. Example strategies include: adding temporary on-street parking spaces on Alaskan Way, implementing wayfinding signs and implementing a parking marketing program to let customers, visitors and the general public know that parking is available in Pioneer Square and on the waterfront during SR 99 tunnel construction.


  • + When will the viaduct be demolished?

    In 2011, crews demolished the southern mile of the viaduct, which accounted for nearly half the structure. The remaining portion of the viaduct will be demolished after the SR 99 tunnel opens to traffic, and a new Alaskan Way street will be built in its place. The new Alaskan Way, which will connect over the railroad tracks to Elliott and Western avenues and to SR 99 near the stadiums, will provide several east-west connections to downtown.


  • + What will happen to the Battery Street Tunnel?

    The Battery Street Tunnel was constructed in the 1950s and has not been upgraded since. Its electrical and mechanical systems are difficult to maintain and do not meet modern safety requirements. WSDOT conducts regular safety inspections of the tunnel. It will be closed and filled in after the SR 99 tunnel opens to traffic in 2016.


SR 99 tunnel questions

  • + Will the tunnel work for freight?

    The SR 99 tunnel will maintain freight routes through Seattle and preserve I-5 for regional and state freight trips. It will also provide a route through the city for vehicles that would otherwise use city streets.

    Some freight trips destined for Ballard and the Interbay industrial area will likely use the new Alaskan Way street along the waterfront, with its crossing over the railroad tracks to Elliott and Western avenues. Traffic signals along the waterfront will be operated to ensure through trips move efficiently.

    Freight trips leaving Port of Seattle terminals will also have improved access to I-5 and I-90 as a result of SR 519 and Spokane Street improvements and a new overpass at South Atlantic Street, which is included in our south-end viaduct replacement project.


  • + Where will the tunnel be located?

    The tunnel route begins on Alaskan Way South south of South King Street, then moves toward First Avenue near Yesler Way, turns north near Stewart Street and ends at Sixth Avenue North and Thomas Street.


  • + Will there be restrictions on freight using the tunnel?

    Most freight will be able to use the SR 99 tunnel. Vehicles hauling hazardous or combustible materials will be prohibited from the tunnel, similar to current restrictions in the Battery Street Tunnel and on the viaduct during peak hours. These vehicles will take I-5 or Alaskan Way along the waterfront, as they do today.


  • + Will the tunnel be safe?

    Structural engineers agree that tunnels can be one of the safest places to be during an earthquake. The SR 99 tunnel is being designed to withstand an earthquake that only happens every 2,500 years on average (in the range of 9.0 on the Richter scale) without collapsing.

    The tunnel will have emergency passages to safe refuge areas, and state-of-the-art ventilation, fire detection and suppression, security and lighting systems. It will be monitored 24 hours a day by WSDOT, similar to the I-90 tunnel today.


  • + How will northwest Seattle residents get to SR 99?

    Residents from northwest Seattle will have two options to get to or through downtown Seattle. They could travel along Elliott Avenue, as they do today, and drive down a new bridge over the railroad tracks near Pike Place Market to a new Alaskan Way street along the waterfront. Alaskan Way will connect directly to SR 99 near South Royal Brougham Way.

    If northwest Seattle residents want to use the SR 99 tunnel, they could take the new two-way Mercer Street to Sixth Avenue North and enter the tunnel at Republican Street. They could also use any of the existing connections to Aurora Avenue north of Mercer Street.


  • + Why is the tunneling machine named Bertha?

    Naming tunneling machines is a long-running tradition within the tunneling industry. Brenda, Togo, Balto, Rainier and Elizabeth are all names of tunneling machines that are currently or have recently completed tunneling in the Puget Sound region.

    Like most ships, tunneling machines are traditionally named after females and WSDOT chose to follow in that tradition. Bertha’s name was chosen as part of a contest for kindergarten through 12th-grade students. Proposed names had to be female and have significance to Washington state heritage, life, nature, transportation or engineering. Elected mayor of Seattle in 1926, Bertha Knight Landes was the first woman to lead a major American city.


  • + Will the tunnel have mid-town exits?

    The SR 99 tunnel will not have mid-town exits. The tunnel and a new Alaskan Way street are designed to work together to replace the functionality of the viaduct. The tunnel will have the capacity to accommodate trips through downtown, while the rest of today’s viaduct users will access downtown using ramps at either end of the tunnel. Along the waterfront, a new Alaskan Way street will provide several east-west connections to downtown, replacing the function of today’s midtown viaduct on-ramp and off-ramp.


  • + How many local jobs are created through the SR 99 Tunnel Project?

    Construction to replace the Alaskan Way Viaduct is boosting our local economy in many ways. Seattle Tunnel Partners (STP), the joint venture that is building the SR 99 tunnel, includes several local firms, such as Frank Coluccio Construction, HNTB Corp and Malcolm Drilling Company. Seventy-five percent of STP’s subcontracts – including contractors, consultants and suppliers – are with firms located in Washington state. At the height of construction, the viaduct replacement will sustain nearly 3,900 jobs.


  • + Will there be cost overruns on the tunnel?

    We signed a design-build contract with Seattle Tunnel Partners in January 2011. Design-build combines project design and construction in a single contract.

    More than 90 percent of the design-build work will be performed for a fixed price. The remaining amount includes work such as building repairs along the tunnel route, unplanned repairs to the tunneling machine and work stoppages due to differing site conditions. For these items, we established risk sharing with the design-builder.

    We have set aside $205 million for known and unknown risks during tunnel construction. This amounts to 15 percent of the design-build contract, which falls well within industry standards.


  • + Where will the dirt from tunneling go?

    During tunneling, crews will remove 850,000 cubic yards of soil. Clean tunnel spoils will be barged to CalPortland’s Mats Mats reclamation facility at Port Ludlow where they will help fill a gravel quarry.


  • + How does the tunneling machine operate?

    The SR 99 tunneling machine was built specifically for the ground conditions beneath Seattle. The machine’s cutterhead will chip away the ground as it rotates and carry excavated soil back through the machine using a spiral screw conveyor. Curved concrete panels are installed behind the machine’s front end to form rings that serve as the machine’s exterior walls. Ring by ring, the machine pushes forward while the tunnel takes shape in its wake. The machine will dig an average of 35 feet per day. A conveyor belt, that will eventually reach 9,000 feet in length, will move excavated soil from the front of the machine out of the tunnel to barges waiting at nearby Terminal 46.

    The tunneling machine uses a laser as a reference as it moves forward through the earth. Projected from a fixed point behind the machine, the laser is received by a guidance system at the front of the machine that is precisely calibrated to the tunnel’s predetermined path. The guidance system is referenced by the machine’s operator to ensure the machine remains on course. The operator steers the machine by making slight adjustments with each push forward. To learn more about how the machine operates watch the tunneling machine video.


  • + Why was the tunneling machine built in Japan?

    Based in Osaka, Japan, Hitachi Zosen has successfully built more than 1,300 tunneling machines, a number of them for large-diameter tunnel projects such as ours. It is critical that we ensure the manufacturer of the SR 99 tunneling machine, which is the world’s largest boring machine to date, is at the leading edge of the industry, with expertise in producing similar large-scale machines. Hitachi Zosen Corp. was selected as the SR 99 tunneling machine manufacturer ahead of three other American and international firms based on overall technical requirements, support capabilities, price and schedule.


Temporary winter viaduct closure questions

  • + Why is it necessary to close the viaduct while the machine passes beneath?

    Keeping SR 99 open to traffic while we replace the viaduct is a top priority. Temporarily removing traffic from the viaduct while we tunnel beneath it will enable crews to monitor the structure more closely and act quickly to mitigate any settlement that may occur during this section of the tunnel drive. The short-term inconvenience of closing the viaduct will help us preserve it until we shift SR 99 traffic to the tunnel.


  • + How long will the closure last?

    The closure will start on a Friday following the evening commute and remain closed for one to two weeks. Tunneling crews will work around the clock to complete this portion of the tunnel drive and reopen the viaduct as quickly as possible.


  • + How do you know it’s safe to tunnel beneath the viaduct?

    Our team has extensive experience tunneling in dense urban areas. Some of our crew members successfully built a nearly 40-foot diameter tunnel six feet beneath the famed La Sagrada Familia cathedral in Barcelona. The mitigation techniques that were used successfully during that project, including building angled walls beneath the structure’s foundation, are being used during SR 99 tunnel construction. Sound Transit has successfully tunneled through similar ground conditions and beneath a number of major roadways in the area, including I-5 and SR 520.


  • + How will you protect buildings and other structures above the tunnel route?

    While we do not anticipate significant levels of settlement, as a precaution, we are implementing a comprehensive program to monitor and mitigate any effects of tunneling. As the tunneling machine pushes forward through the earth, crews will measure the soil it removes while also tracking any ground movement above its path.

    Buildings, utilities and streets located above and near the tunnel route will be monitored before, during and after construction. Each building will be surveyed prior to construction to document its interior and exterior condition. Monitors installed on the buildings by our crews will be checked against data from before construction, as well as data from monitors installed outside the monitoring area (pdf 2.9 Mb). If damage does occur to buildings, utilities or streets as a result of tunnel construction, we will be responsible for costs associated with repairs.


  • + What will WSDOT do to keep traffic moving during the closure?

    We will work with the Seattle Department of Transportation, King County, the Port of Seattle, Seattle Center and the stadiums to keep traffic moving during the closure. Alternate routes will be available. We will have WSDOT Incident Response Teams available to help clear blocking incidents or stalls. WSDOT, in partnership with King County Metro and the City of Seattle, recognized the potential effects of traffic closures during viaduct replacement construction and invested $125 million in projects designed to keep traffic moving. These investments include:


    • Phase 2 of the SR 519 project – a new I-5/I-90 westbound off-ramp to South Atlantic Street/Edgar Martinez Drive South which improved access to the waterfront and Port of Seattle.


    • $32 million to fund additional bus service with 41 new bus trips on key routes connecting downtown Seattle to West Seattle, White Center and Burien and strategies to encourage use of transit, carpools and vanpools.



  • + Are you doing anything to protect the viaduct from settlement?

    Like most other structures, the viaduct was designed to withstand some settlement. We have taken a number of steps  (pdf 913 kb) to reinforce the viaduct and strengthen the soil beneath it. In 2012, crews installed angled underground walls around the viaduct’s footings to create a barrier between the machine and the structure. They also wrapped portions of the viaduct in carbon fiber to provide additional strength.


  • + When will the viaduct be closed?

    Seattle Tunnel Partners, our contractor for the tunnel project, is developing a plan to address an issue with the machine’s seal system that halted tunneling in December 2013. The closure will occur after tunneling resumes. We will provide notice in advance and conduct extensive outreach to help travelers prepare.


Alaskan Way Viaduct looking north from SODO district.

Alaskan Way Viaduct looking north from SODO district. The southern mile of the viaduct was demolished in 2011.


Alaskan Way Viaduct looking south from Victor Steinbrueck Park, Pike Place Market.

Alaskan Way Viaduct looking south from Victor Steinbrueck Park, Pike Place Market.