Program Spotlight

Latest updates on the Alaskan Way Viaduct Replacement Program

  • 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

  • Inside tunneling under the viaduct

    After nearly a week of tunneling under the Alaskan Way Viaduct, crews are steadily continuing Bertha’s underground drive towards downtown Seattle. This video gives you a behind-the-scenes glimpse into how the new tunnel is being built, showcasing the complex operations involved in this project. Massive concrete ring segments are transported to Bertha’s segment erector where they are lifted into place, allowing the machine to push forward while the excavated soil is transported … more

  • #99closure feature: Drone footage inside the SR 99 tunnel

    Just a few days before the SR 99 tunneling machine started tunneling under the Alaskan Way Viaduct, the Washington State Department of Transportation flew a video-equipped drone through the SR 99 tunnel to show Seattle Tunnel Partners’ construction progress. There has been continued interest in seeing what has been built below ground and this video gives a glimpse of the tunnel as well as the nooks and crannies of the complex tunneling machine.

    On an average day, the tunnel is … more

  • #99closure feature: Removing soil from the tunnel

    More than 850,000 cubic yards of soil will be removed from the ground during the course of tunneling. To put that in perspective, imagine this: If you piled that soil on the turf at nearby CenturyLink Field, the pile would be about 400 feet tall – more than 100 feet taller than the stadium’s roof.


    Excavated soil travels via conveyor belt from the front of the tunneling machine to a barge waiting at the north end of Terminal 46. When the barge is full, it travels … more