Program Spotlight

Latest updates on the Alaskan Way Viaduct Replacement Program

  • A full summer for Milepost 31 before closing in November

    Milepost 31 in Pioneer Square is gearing up for a busy summer of programming. Our information center continues to offer free public viewing platform tours to see the SR 99 tunnel’s south portal construction site. Bike tours have also resumed, which follow Bertha’s tunnel route and provide a unique way of understanding the historical and engineering aspects of this megaproject. You can sign up for tours online or in person at the center.

    Our First Thursday speaker series … more

  • Life after Bertha: Focus shifts from mining to other tunnel work

    Bertha, the SR 99 tunneling machine, has completed her 9,270-foot journey beneath Seattle. Although tunnel boring has come to end, crews have significant work to do before the tunnel can open to traffic in 2019.


    Construction of the SR 99 tunnel can be broken down into five activities: 


    Mining (completed in April 2017)

    Disassembly and removal of the tunneling machine

    Interior roadway construction

    Installation of mechanical, electrical … more

  • Getting to know the SR 99 tunnel's biggest fans

    Clean air is a critical element of a safe and well-functioning tunnel. In the new SR 99 tunnel, a complex system of fans will push and pull air into and out of the tunnel to ensure fresh air during routine operations and in emergencies.

    The first element of the tunnel’s ventilation system is the very traffic that uses it. Vehicles traveling through the tunnel will act like pistons, pushing fresh air into the tunnel. But when that piston effect needs a boost, the tunnel will turn to … more

  • A new place to stroll above the SR 99 tunnel

    Frequent observers of the project’s construction cameras may have noticed some white blocks being placed next to the north operations building at the corner of Sixth Avenue North and Harrison Street.






    ‹ ›

    Crews are building a public plaza that will be a centerpiece of the landscaping at the project's future north portal. The … more

  • Coming to the south portal: A “flexible bridge” to stand up to Seattle’s next big earthquake

    When the SR 99 tunnel opens to traffic, drivers on northbound SR 99 will use a new off-ramp near the stadiums to reach downtown Seattle. In addition to linking travelers to their destination, engineers and researchers hope the new ramp will provide a link to something else: earthquake-resistant bridges.

    By combining memory-retaining metal rods and a bendable concrete composite, the future off-ramp will become the first bridge in the world built to sway with a strong earthquake and … more

  • There's more than one way to change a cutterhead tool

    Performing regular maintenance on Bertha, the SR 99 tunneling machine, is critical to the success of the tunnel drive. During each of Seattle Tunnel Partners’ three planned maintenance stops in 2016, crews have spent time checking and maintaining various systems throughout the machine. Specific maintenance needs vary with each stop, but one maintenance item is always on STP’s to-do list: inspection and replacement of cutterhead tools.

    Bertha’s rotating cutterhead has … more

  • Taking stock at the tunnel’s halfway point

    Bertha has reached the halfway point in her journey beneath downtown, but tunneling crews aren't the only ones making progress on the Alaskan Way Viaduct Replacement Program. Here's a round-up of all the work that's happening along the SR 99 corridor. 

    Interior structures

    There's more to building a tunnel than simply digging through the earth. A separate crew is hard at work building the double-deck highway inside the concrete tube built by Bertha.

    The … more

  • New tour lets you "Bike above Bertha"

    The public may not be able join Bertha as she tunnels beneath downtown, but that doesn’t mean you can’t track her journey at street level. We recently launched a bicycle tour that leads attendees along Bertha’s tunnel route.

    The approximately two-hour tours depart from Milepost 31, our information center in Pioneer Square. Attendees pedal with a guide from the south portal to the north portal, learning about the historical, archaeological and engineering aspects of the … more

  • Kids discover engineering at Milepost 31

    What do you get when you combine an engineer, a group of curious young students and a table full of craft supplies? The answer, we hope, is inspiration.

    For the past two years, Milepost 31, the SR 99 Tunnel Project’s information center in Pioneer Square, has hosted engineering activity days for numerous youth groups. These events are designed to teach the kids in attendance about different fields of engineering through a variety of hands-on activities. In addition to having fun, we … more

  • Building the highway inside the tunnel

    Seattle Tunnel Partners is performing routine maintenance on Bertha, but important work is ongoing inside the tunnel. As the video below illustrates, a massive highway-building operation is trailing not far behind the tunneling machine.

    This is no ordinary highway project. It requires a complex choreography to complete this work even as crews mine beneath Seattle. Check out the video to learn how it works.




      … more