Program Spotlight

Latest updates on the Alaskan Way Viaduct Replacement Program

  • #99closure prep: Analyzing traffic patterns on the Alaskan Way Viaduct

    Measuring traffic on the SR 99 Alaskan Way Viaduct isn’t as simple as you might think. Traffic volumes vary along the structure. For example, more vehicles drive the section south of downtown than the section near the Battery Street Tunnel.

    But no matter how you add things up, the end result is the same: thousands of vehicles will be forced to find other routes when the viaduct temporarily closes on April 29. And that will equal congestion and frustration, especially for … more

  • Ordinary maintenance, extraordinary conditions

    With Bertha, the SR 99 tunneling machine, having safely reached her planned maintenance stop, Seattle Tunnel Partners is preparing to complete up to one month of planned maintenance. While the maintenance is routine, some of the methods crews will use to complete it are anything but. That’s because they’ll be performing some work in hyperbaric conditions as they get Bertha ready to tunnel beneath the Alaskan Way Viaduct and downtown.


    Hyperbaric conditions are those … more

  • Tunnels and earthquakes

    Seattle is prone to earthquakes, so it’s not surprising that one of the most common questions we receive is this: Will the tunnel be safe in an earthquake? 

    All modern structures in the area – including bridges and highways – must be designed with earthquake safety in mind. But geotechnical and structural engineers agree that tunnels are among the safest places to be during an earthquake. 

    Some folks find this counterintuitive. How is it safe to be … more

  • Good news for SR 99 commuters: first phase of lane closures wrapping up early

    Last week we reported that crews were making good progress as they worked to install sign foundations on SR 99/Aurora Avenue North in Seattle. Turns out good progress leads to good news: the first phase of sign foundation work is finishing ahead of schedule. By Friday afternoon, median lane closures should be removed and the southbound bus-only lane will be restored to normal operations.

    It may be tough to tell, but the new foundations for each sign on SR 99 extend 14 to 18 feet … more

  • Sign foundation work progressing well on SR 99 in Seattle

    If you’re a regular user of SR 99/Aurora Avenue North between the Aurora Bridge and just north of Mercer Street, we’d like to thank you for doing your part to help keep traffic delays to a minimum during the past two weeks.


    Crews are around the halfway mark for the first phase of sign foundation installation work happening on this stretch of SR 99 and are pleased with the progress they’ve made. Work is continuing on schedule and crews expect to move into the … more

  • The story behind the Aurora Avenue lane closures

    We’re quickly nearing some major lane closures in both directions of SR 99/Aurora Avenue heading into and out of downtown Seattle. Starting Jan. 18 and continuing for several weeks, drivers and bus riders should expect slower commutes and some challenging traffic, which is never welcome news. Why these particular closures now? Please read on.

    What is closing?


    The inside lane in each direction  of Aurora Avenue North between the Aurora Bridge and just north of … more

  • Milepost 31 marks four years, 50,000 visitors

    For being Seattle’s “most boring” exhibit, Milepost 31 sure is popular. December marks the four-year anniversary of the information center, which blends information about the SR 99 Tunnel Project with the history of Seattle’s Pioneer Square neighborhood. In addition to recently welcoming the center’s 50,000th visitor, Milepost 31 staff have led hundreds of tours to see SR 99 tunnel construction, and hosted educational programs for school groups and youth … more

  • Exterior walls for operations buildings prioritize transparency

    As walls are installed at the north and south portal operations buildings in the coming weeks, drivers may be surprised by how little their view inside the buildings changes. The exterior walls of the large fan rooms will be made of glass, providing passersby with a glimpse of the everyday activities that will occur inside these important operation centers.

    The decision to use glass walls arose out of the guiding principles for the operations buildings: to reflect their function and … more

  • Understanding project insurance

    Protecting taxpayers is a top priority as we replace the Alaskan Way Viaduct. An important tool in this effort is our design-build contract with Seattle Tunnel Partners, which places a greater share of project risk on the contractor by requiring them to design and build the tunnel.

    Another protective measure is insurance, which the contract requires STP to have. Both STP and WSDOT are named on the project’s insurance policy, and both entities have the right to make insurance … more

  • Another underground connection at the south portal

    Future connections between the SR 99 tunnel and city streets are continuing to take shape at the south portal, even if they're only partially visible from the surface. Drivers passing overhead didn't know it, but Seattle Tunnel Partners recently demolished a temporary wall separating the future mainline section of the tunnel from the on-ramp that will one day allow travelers to access northbound SR 99 from the stadiums.

    The first photo shows the view from inside the cut-and-cover … more