Viaduct questions

  • + 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 then 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.


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

    Before we demolished the southern mile of the viaduct in October 2011, it carried approximately 110,000 vehicles per day just south of the mid-town ramps. Of this amount, approximately 17,000 vehicles entered or exited downtown at Columbia and Seneca streets, and 33,000 exited or entered at Elliott and Western avenues toward Belltown, Uptown, and neighborhoods along the 15th Avenue and Elliott Avenue corridor. The remaining 60,000 vehicles continued 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 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.


  • + 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.


SR 99 tunnel questions

  • + 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.


  • + 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.


  • + Why has tunneling stopped?

    Tunneling began in summer 2013, just west of the stadiums. In December 2013, Seattle Tunnel Partners stopped tunneling approximately 1,000 feet into the tunnel drive after experiencing increased temperatures in the machine. While investigating the cause of the high temperature readings, Seattle Tunnel Partners discovered damage to the machine’s seal system and contamination within the main bearing. Seattle Tunnel Partners plans to make repairs and enhancements to the machine that will allow crews to resume tunneling. The latest schedule is available here.


  • + How will the tunneling machine be repaired?

    Seattle Tunnel Partners is building a 120-foot-deep circular pit (pdf 2.5 Mb) in front of the machine, which is located about 60 feet below the surface in a fenced off construction zone between South Jackson and South Main streets. When the pit is complete, the machine will tunnel forward into it. Crews will then partially disassemble the machine and make repairs and enhancements. Seattle Tunnel Partners' work plan (pdf 4.8 Mb), which is illustrated in an animation (view on YouTube or download WMV file), contains four major repair and enhancement elements:

    • Replacing the damaged seal system with a more robust system
    • Replacing the main bearing
    • Installing enhanced monitoring systems
    • Adding steel to strengthen the machine and accommodate the new seal system

    You can watch crews work via our construction cameras.


  • + What work is happening while tunneling is on hold?

    Construction is taking place at the north and south end of the SR 99 tunnel. The north portal is taking shape near the Space Needle, including construction of the pit where the SR 99 tunneling machine will emerge at the end of tunneling. Crews are also building the cut-and-cover tunnel that will connect the bored section of the tunnel to SR 99/Aurora Avenue North.

    Crews at the south portal are continuing to work on the south portal operations building, which will control safety features, lighting and ventilation within the future tunnel. Work is also focused on the south cut-and-cover tunnel that will connect the new south-end SR 99 roadway with the bored section of the tunnel.

    Crews in Frederickson, Wash. continue to produce the concrete tunnel segments that are pieced together to form the exterior walls of the SR 99 tunnel.


  • + Who will pay for the cost associated with the tunneling machine stoppage?

    WSDOT does not believe the state or taxpayers will be responsible for costs associated with the current delay. Earlier this year, Seattle Tunnel Partners requested $125 million in additional compensation. WSDOT denied that request after determining it had no contractual merit. The process for resolving disputes within the tunnel contract is prescriptive. It requires multiple steps by both parties. Should Seattle Tunnel Partners continue to pursue entitlement related to the stoppage, it will take time to resolve.


  • + When will the viaduct be closed?

    For the most part, SR 99 remains open during construction thanks in part to a construction bypass roadway that connects SR 99 in SODO to the viaduct along the waterfront. The viaduct is closed for two weekends a year – generally in the spring and fall - for inspection and maintenance. We also have a few planned closures due to construction activities such as when the tunneling machine tunnels beneath the viaduct. For any type of planned closure, we provide advance notice to the public so they can plan their trips accordingly.


  • + 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 a magnitude 9.0 earthquake) 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.


  • + 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.


  • + 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.


  • + 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.


  • + How many lanes will the tunnel have?

    The tunnel will have two 11-foot travel lanes with an eight-foot safety shoulder and a two-foot shoulder in each direction that will ensure enough space for all vehicles and legal size trucks.


  • + 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, 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 Seattle Tunnel Partners' 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 the SR 99 tunnel be tolled?

    In 2013, WSDOT was directed by the Washington State Legislature to raise $200 million from tolls for the SR 99 Tunnel Project. The Advisory Committee on Tolling and Traffic Management studied ways to refine tolling of the SR 99 tunnel to minimize traffic diversion and meet funding goals, and investigate strategies to reduce or mitigate diversion. The committee submitted recommendations in 2014 (pdf 1.8 Mb).

    Tolling is anticipated to start when the tunnel opens to traffic.


  • + 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.


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.