Program Spotlight

Latest updates on the Alaskan Way Viaduct Replacement Program

  • 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 reconnection of Harrison, Thomas and John streets will make walking between each side … 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

  • The story behind the north portal's signature tree

    The signs of summer are everywhere. There’s more sun in the sky and more boats in the water. There’s also more of something that most folks wouldn’t even know to look for: leaves in one of Seattle’s newest trees.

    Allow us to introduce you to the Garry Oak, the area’s only native oak species. Native Garry Oak prairies were once commonly found in Western Washington. This particular Garry Oak was planted this spring a few blocks east of the Space Needle, … more

  • What to expect from Bertha as tunneling continues

    We’ve been hearing a lot of forecasting lately from members of the public tracking Bertha’s progress. We’ve said this before, but now that Seattle Tunnel Partners crews have passed the 25 percent mark of the tunnel drive, it’s worth repeating: Trying to predict future progress is tempting, but there’s no simple equation for doing so.

    Tunneling progress depends on a number of factors, including soil conditions and the need to stop tunneling when Bertha … more