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SR 520 - West Approach Bridge North Project Construction Progress Tracker

Updated: April 20, 2017

Construction of the West Approach Bridge North (WABN) project began in fall 2014. Prior to starting construction of the permanent WABN structure, the contractor built a temporary work bridge. This structure, nearly a mile long, serves a platform for crews to store materials and deploy equipment for constructing the permanent bridge over shallow water. 

West Approach Bridge North Assembly 

Click image above for West Approach Bridge North progress tracker. (pdf 231 kb)

The bridge-building process

In February 2015, crews began installing the first casings for the permanent WABN structure. After the casings were fixed into the lakebed, crews drilled out soils, placed metal rebar inside for added strength, and filled the casings with concrete. Once the concrete cures, crews removed the top portion of the casing to create the shafts. These shafts support new, solid bridge columns. (The existing west approach, in contrast, is supported by hollow columns.)

After solid columns were in place, crews installed all 108 bearings and 353 girders and finally all 41 sections of the bridge deck - finishing the placement of the last section of deck on April 17, 2017. The last work will be paving and striping the bridge for traffic. When open to traffic in late summer 2017, the new WABN structure will connect westbound traffic and a new cross-lake bicycle and pedestrian path from the new floating bridge into the Montlake area of Seattle.

The pieces that make up the West Approach Bridge North (WABN)

 Casing Shaft Installation 

Casings - 100% installed
A bridge casing is a large steel pile that provides the permanent mold for the bridge's concrete foundation. After the casing was fixed into the lakebed, crews drilled out soils, placed metal rebar inside for strength and then filled the casing with concrete to create the shaft. 

Shaft installation - 100% installed
This large machine drilled soils out of the casing before crews placed metal rebar inside for added strength. Once the rebar was placed inside, crews filled the casing with concrete to create the shaft.

 Rebar Cage  

Rebar cages - 100% installed
Rebar cages are used to strengthen the foundation and columns of the West Approach Bridge North. All 194 rebar cages for shafts and columns were tied by hand.

Columns - 100% installed
The current west approach bridge has hollow columns that are vulnerable to earthquake. All new WABN columns are solid concrete that is strengthened with rebar. WSDOT also worked with the Seattle Design Commission to incorporate fluted columns into the WABN design for aesthetic appeal.

 Bearings  Girder

Bearings - 100% installed
The current west approach bridge structure does not use bearings, which makes it vulnerable to earthquakes. The new WABN structure uses isolation bearings to allow each section of the bridge to move independently as needed during an earthquake.

Girders - 100% installed
More than 350 girders were set in place before the bridge deck was poured to create a new roadway for drivers.


Roadway deck - 100% installed
Crews poured 41 sections of roadway deck to complete the 1.2-mile-long WABN structure. Now that the deck has been poured, crews will grind, pave and stripe the deck before opening the bridge to traffic.

Construction at a glance