The temporary viaduct closure ended on May 8, 2016. These FAQs have not been updated since then and may no longer reflect the current status of the program or project. They are kept here for reference purposes and will be taken down at a future date.

Viaduct Tunneling Closure FAQs  

Have additional questions?

View the closure overview folio (PDF). Email viaduct@wsdot.wa.gov or call 1-888-AWV-LINE (298-5463).


Closure details

  • + Why is the viaduct being closed?

    The viaduct is being closed while Bertha tunnels beneath the structure. This temporary closure of the viaduct is precautionary. Removing vehicles from the structure will give crews better access to the structure to allow for better monitoring while the tunneling machine passes beneath. This also allows crews to more quickly respond to any movement in the structure that might occur.

    Additionally, WSDOT recognizes that advertising a planned closure ahead of time, instead of conducting an unexpected and last-minute closure, will give the travelling public time to plan their trips accordingly.


  • + What portion of SR 99 will be closed?

    The Alaskan Way Viaduct will be closed from South Spokane Street (aka the West Seattle Bridge) to the south end of the Battery Street Tunnel. The Battery Street Tunnel southbound off-ramp and northbound on-ramp at Western Ave will remain open, but all of the other on and off-ramps to the viaduct within this stretch of SR 99 will be closed.

    You can see a map of the closure here.


  • + Why are you starting the closure on a Friday?

    There is no good day to begin a closure of a major highway. The exact start date of the closure was dependent upon the contractor Seattle Tunnel Partners completing maintenance work on the tunneling machine. At the same time, we committed to providing the public with two weeks’ notice of the closure so drivers could hear about the closure and make plans.

    Every day on this contract counts. Beginning the closure on a Friday is the result of our desire to provide the public with two weeks’ notice, while not losing any additional time on the project. Traffic volumes are typically lower on Fridays, and beginning on a Friday allows the closure to take full advantage of lower traffic volumes on weekends.

    WSDOT recognizes that closing the viaduct will have a substantial effect upon local and regional traffic patterns. WSDOT is working with agency partners to keep people moving through a variety of measures (PDF), while asking drivers to make a plan and change traditional commuting patterns if possible to help keep traffic moving.


  • + Why aren’t you closing surface streets in the area?

    • This temporary closure is all about monitoring the viaduct and giving the public time to plan ahead. Closing the viaduct will give crews better access to the structure for monitoring while Bertha tunnels beneath it.
    • We have ways to monitor ground movement on surface streets without closing them, but the best way to keep a close eye on the viaduct is to remove traffic.
    • It’s safe for drivers and pedestrians to be under and near the viaduct during tunneling. If it weren’t safe, we would restrict access.
    • STP’s structural engineers don’t expect the tunneling operation to significantly affect the viaduct or the ground beneath it.
    • That being said, we will be monitoring conditions around the clock and have planned for many contingencies – WSDOT, SDOT and Washington State Ferries have plans in place if we need to close a portion of the surface street.


Keeping people moving during the closure

  • + What is WSDOT doing to keep traffic moving during the closure?

    WSDOT, the city of Seattle, the Port of Seattle and King County Metro have developed a coordinated plan to minimize congestion during the closure. This plan involves a variety of efforts to provide alternative routes, maximize traffic and transit flow, and encourage people to find alternative routes or travel times. During the closure the agencies will coordinate daily to minimize congestion through mitigation measures and proactive public outreach and media relations.

    Efforts and strategies include:

    More buses: King County Metro will alter bus routes that use the viaduct and deploy stand-by coaches to give commuters more transit options and to maintain schedules.

    Real-time traffic monitoring: WSDOT and SDOT will monitor highway and street traffic and use portable electronic message signs (VMS) to inform drivers about delays and provide other information.

    Police traffic control: Seattle Police Department officers will be on hand as needed to do manual intersection control at key chokepoint intersections and ferry dock entrances.

    More water taxi capacity: King County Water Taxi will increase service to Vashon and take advantage of its new larger boats for increased capacity between West Seattle and downtown.


  • + Will there be dedicated detour routes?

    The 12 King County Metro buses that take the viaduct will be detoured to surface streets (PDF map of detours). The King County Metro website has additional information.

    For individual drivers WSDOT has created a commute alternatives checklist (PDF) that provides travel options. WSDOT recognizes that closing a major highway will have substantial traffic impacts in the region, and is requesting employers and the public’s help in planning ahead.

    Designated freight routes can be found here.


  • + How will this affect surface streets in the area?

    We expect to see increased congestion on surface streets during the closure as vehicles find alternate routes. At this time we do not anticipate any closures of surface streets due to the tunneling process. WSDOT,  SDOT and Washington State Ferries are coordinating for contingency plans should any unanticipated surface street closures become necessary .


  • + How can I stay informed during the closure?

    WSDOT will be sharing information constantly with the public and with partner agencies to help drivers make informed travel choices. Agency Twitter accounts will share information and real-time traffic updates, this website will be updated frequently and WSDOT, SDOT and King County Metro offer free apps that provide real-time travel information.

    Twitter accounts to follow before and during the closure:

    • @BerthaDigsSR99
    • @WSDOT
    • @WSDOT_traffic
    • @kcmetrobus
    • @seattledot
    • Monitor the hashtag #99Closure


  • + What local streets will have temporary parking restrictions?

    In order to improve transit and keep traffic flowing during the closure, SDOT will be restricting parking at locations along key corridors. Some restrictions will be in place during the weekday commute periods, while others will be 24 hours, seven days a week (24/7). Certain turn lanes will also be affected.

    Parking restrictions during the closure

    Downtown/Belltown/South Lake Union

    This PDF map shows temporary transit priority lanes in the Belltown/South Lake Union neighborhoods to help keep buses moving. Additional restrictions listed below:

    • South side of Blanchard between 3rd Ave and Westlake Ave (3 p.m. - 7 p.m., for transit, weekdays)
    • North side of Blanchard between 5th Ave and 6th Ave (3 p.m. - 7 p.m., for transit, weekdays)
    • North side of Lenora between Westlake and 3rd Ave (6 a.m. - 10 a.m., for transit, weekdays)
    • North side of Olive Way between 4th Ave and 6th Ave (24/7, for transit)
    • South side of Wall St between 6th Ave and 5th Ave (24/7, to facilitate double left turn to 5th Ave)
    • South side of Battery St between 4th Ave and 5th Ave (3 p.m. - 7 p.m. for right turns from 4th to Battery, weekdays)
    • South side of John St. between 6th Ave N and Aurora Ave N (24/7, for trucks turning)
    • North side of John St. between 9th Ave N and Dexter Ave N (24/7, for transit)
    • South side of Valley St between Fairview Ave N and Minor Ave N (24/7, for transit)
    • East side of Minor Ave N south of Valley St (24/7, for transit)


    Pioneer Square/SoDo

    • Both sides of 1st Ave S between S King St and Cherry St (6 a.m. - 10 a.m. and 3 p.m. - 7 p.m., weekdays)
    • Both sides of 4th Ave S between S Spokane St and S Massachusetts St (6 a.m. - 10 a.m. and 3 p.m. - 7 p.m., for transit, weekdays)
    • West side of 5th Ave S. between S. Jackson St and Seattle Blvd S. (24/7, for transit)


    West Seattle

    • East side of Harbor Ave SW between Fairmount Ave SW and SW Maryland Pl (2 a.m. - 5 a.m., for Water Taxi parking, weekdays)
    • East side of Delridge Way SW between SW Edmunds and SW Oregon St (6 a.m. - 10 a.m., for transit, weekdays)

    North Seattle

    • East side of 8th Ave NW between NW 97th and NW 98th (24/7, for transit)


    Travel lane and pedestrian restrictions during the closure

    • Aurora southbound left turn lane onto Denny Way: closed (posted signs will direct to eastbound Denny via John and 6th Ave)
    • Battery Street Tunnel: one southbound lane open to Western Ave off-ramp
    • Pedestrian crossing on south leg of 5th Ave at Wall St: closed 6 a.m. - 10 a.m. and 3 p.m. - 7 p.m., weekdays


Tunneling and protecting structures

  • + How is WSDOT protecting and monitoring the viaduct during Bertha’s time underneath it?

    The viaduct can withstand some settlement, and WSDOT has implemented a comprehensive program to monitor and mitigate settlement. You can learn more about these efforts in this video

    Sections of the viaduct have been reinforced with fiber wrap, and monitoring instruments on the viaduct and surrounding ground can detect movement in real time. Additionally, underground support walls hold soil in place between the viaduct foundation and Bertha’s path.


  • + How will WSDOT know if the viaduct begins to settle during tunneling?

    Removing vehicles from the viaduct will allow for easier access to the structure, so crews can better monitor for any structural movement that might occur. The viaduct is monitored in real time by automated sensors and WSDOT will be conducting manual surveys of the structure twice a day. WSDOT bridge inspectors will also conduct pre-tunneling and post-tunneling inspections of the viaduct before reopening the structure to traffic.


  • + Why is WSDOT taking these precautions with the viaduct but not with other buildings along the tunnel route?

    Bertha and the top of the future SR 99 tunnel will come within 14 vertical feet of the bottom of one of the viaduct’s foundations. By contrast, the closest Bertha will travel to any other building foundation or structure is 40 feet. This proximity, combined with the sands and gravels of the soil in this area, make tunneling under the Alaskan Way Viaduct some of the most challenging mining conditions of the tunnel alignment.


  • + Is WSDOT monitoring nearby buildings?

    WSDOT implemented a comprehensive monitoring program before construction began and expanded its ground monitoring efforts in Pioneer Square in early 2015. Monitoring equipment installed on buildings along the tunnel route detects movement, and laser imaging technology is used to detect change over a broad area in Pioneer Square.


  • + What would WSDOT do if Bertha stopped while beneath the viaduct?

    WSDOT would first ensure that the viaduct was safe for daily use. The viaduct is being monitored 24/7 by a high-tech system that watches for any motion or settlement in the structure (this video provides an overview of that system). Once inspectors determined that the viaduct was safe, WSDOT would work to reopen the structure until the contractor, Seattle Tunnel Partners, was able to resume mining. WSDOT would continue to work with partner agencies to keep people moving while the viaduct was closed.


  • + How far will Bertha tunnel beneath the viaduct each day?

    Mining rates will vary throughout the #99closure. The contractor Seattle Tunnel Partners expects to start slowly as crews mine out of the block of concrete near Yesler Way in which the tunneling machine has been stopped for its planned maintenance. The machine must dig through approximately 10 feet of concrete to exit the maintenance stop and enter the soil near the intersection of Yesler and Alaskan Way. Crews intend to proceed deliberately throughout the first weekend and then pick up speed further into the closure. While STP will be working 24/7 during the closure, the machine will not be tunneling constantly. Crews will have to stop tunneling to build tunnel rings and do machine maintenance.