Project overview
The purpose of this project is to preserve the existing structural integrity of Bridge 99/530E over the Duwamish River, extend the service life of the structure, keep the old control tower and the lower levels of the bridge dry, and allow for the operation and inspection of the lower levels of the Bridge. It is also intended to preserve the structural integrity of the Bridge 99/530W control tower and extend its service life.
What to expect
Travelers can expect several north and southbound nighttime single and triple-lane closures at the 1st Avenue South Bridge on SR 99 between Spring and Fall 2026.
This project will replace watertight doors, install waterproof membranes on the towers and demolish the East Control Tower’s top two floors on the northbound SR 99 1st Avenue South Bridge, in addition to replacing the waterproof membrane of the West Control Tower on the southbound side.
The 1st Avenue South Bridge on SR 99 was built in 1956 and rebuilt in 1998. Today, over 54,000 vehicles use this bridge daily. The East Control Tower of the 1st Avenue Bridge is no longer in service with the West Control Tower now managing both bridges. The East Control Tower has deteriorated over time, is leaking and is a visual barrier. The roof on the West Control Tower needs repairs, as well.
We will remove the top two floors of the East Control Tower of the bridge as this tower. The stairwell opening will be closed with reinforced concrete and turned into the new roof with a skim coating and waterproof membrane. The roofs of the other 3 corners of the east bridge will also be replaced with waterproof membranes. Finally, the watertight doors are badly corroded and will be replaced. The new watertight doors will seal the water out and allow the bridge inspectors to access all watertight compartments of the bridge.
On the West Control Tower, we will perform roof work to keep the tower in a state of good repair.