This weekend, crews will shift State Route 99/Aurora Avenue traffic onto new lanes through the construction zone at the SR 99 tunnel's future north portal. For drivers, a traffic shift is a change in the route one takes to get to work, events or a game. For road builders, a traffic shift is a way to mark the next step toward project completion.
In this latest traffic shift, the progress is significant – 750 feet of new roadway that will be part of the permanent ramp and roadway connections to the SR 99 tunnel. But many of the accomplishments at the north portal aren't visible to drivers. Some are literally buried underground. Fortunately, we have the photos to show how much this area has changed since construction began.
The new SR 99
Crews completed the last SR 99 traffic shift less than a year ago after demolishing the bridge over Broad Street
(links to YouTube). The first photo below shows traffic on SR 99 after lanes reopened on Aug. 27, 2014. Behind the green fence, you can see the north portal starting to take shape. But much of the landscape is still dirt, including the footprint of what used to be Broad Street running diagonally alongside the Gates Foundation on the right.
August 2014 – Starting to build connections at the tunnel's north portal.
The Broad Street demolition allowed crews to start building that new section of SR 99 you'll be riding on soon. By mid-August 2015, the new lanes on a new bridge are nearly done, ready for crews to make the connections to the existing lanes during this weekend's SR 99 closure.
August 2015 – New and old SR 99 side-by-side.
The north end of the tunnel
This photo from August 2013 shows the beginnings of the massive 450-foot-long trench where crews will build a cut-and-cover section of the SR 99 tunnel at the north portal. Cut-and-cover tunnel at both portals will connect the SR 99 roadway at the surface to the bored section of the tunnel. Here, crews will also build the foundations and lower levels of the north portal operations building.
August 2013 – Trench for north portal cut-and-cover tunnel.
Two years later, the trench has disappeared and the operations building with its bright yellow ventilation stacks is starting to take shape on top of the concrete slab that makes up the tunnel’s lid, or top deck. Part of the lid, at lower left in the photo, will also serve as part of the future Harrison Street.
August 2015 – North portal operations building on top of tunnel lid.
The lid hides the 350-foot-long section of cut-and-cover tunnel that crews have built inside the trench. The photo below provides a look inside at the future northbound lanes rising up to the surface.
July 2015 – Northbound roadway heading out of the tunnel.
You may have noticed a small discrepancy between the length of the trench (450 feet) and the length of completed tunnel (350 feet).That missing 100 feet is where Bertha, the SR 99 tunneling machine, will break through after building the bored section of the tunnel under downtown Seattle. The photo below from July 2015 shows construction progress on Bertha's receiving pit. Crews working for Seattle Tunnel Partners will complete that last 100 feet of tunnel after Bertha is taken apart and removed.
July 2015 – Bertha’s destination.
Traffic closures are never easy, but it helps to know the reasons behind them. In the case of this weekend's closure, it's another step in an ongoing transformation at the north portal.