Spokane St Swing Bridge Projects

Spokane St Swing Bridge Projects

Updated October 20, 2022

What's Happening Now?

The West Seattle Bridge is open

The West Seattle Bridge reopened in the late evening on September 17 after 2 ½ years of closure and repair work. All people driving and taking the bus are welcome on the bridge.

Additionally, all restrictions on the Spokane Street Swing Bridge (low bridge) have ended. The low bridge is now open for all to use at any time.

Proactive strengthening work is underway on the low bridge as crews are filling cracks with an epoxy compound and applying sheets of carbon-fiber wrapping on exterior and interior concrete. This work will help keep the low bridge in service for decades to come.

Project Overview

The Spokane St Swing Bridge (low bridge) is an essential route for emergency vehicles, transit, heavy freight, and people biking and walking. It provides an important connection between the maritime and industrial businesses on the west side of the Duwamish Waterway to those on the east side, especially with respect to the marine cargo terminals.

Due to recent bridge inspections and elevated traffic demand during the closure of the high bridge, we are proactively taking measures to preserve the low bridge through a series of projects outlined on this page. 

We have no reason to think that the low bridge is in any imminent risk of being taken out of service, but because the bridge played such an out-sized role as the link between West Seattle and the rest of the city, we have developed a forward-thinking plan to strengthen it further and have been taking numerous precautionary steps to monitor and care for this bridge since 2020.

The structure and system that opens the low bridge includes:       

  • Two concrete spans that swing back and forth    
  • Two pivot points where the spans rest on the bridge piers 
  • An electric control system that lets operators open and close the bridge and stop traffic

Each of these three parts will be rehabilitated to extend the life of the low bridge and improve the resiliency of our system. Thank you for your understanding and patience as we continue this important work.

Structural rehabilitation graphic

Project Background

The low bridge is a critical crossing of the Duwamish Waterway, connecting West Seattle and Harbor Island with streets to SODO and Duwamish Valley neighborhoods, business districts, and Port of Seattle facilities. It was built in 1991 and opens for vessels about 1,500 times per year.

The bridge is made of concrete with two main sides (spans). The center span is 480 feet long, and when we need to open it for vessels on the Duwamish Waterway, the spans rotate 45 degrees to open instead of raising into the air like a drawbridge. To open the bridge, each bridge side "floats" on a steel barrel (called a cylinder) in hydraulic oil located on the center bridge piers. This allows for a smooth opening and closing each time. It is said to be the only bridge of its type in the world.

Low bridge swings open for maritime traffic

The Spokane St Swing Bridge (low bridge) swings open for maritime traffic to pass. 

For people traveling on the bridge, the roadway carries 2 lanes of traffic (one in each direction) and a 12-foot pedestrian and bicycle path. This is a popular route for many people biking to and from West Seattle.

Following the recent 2 ½- year closure of the high bridge, we are focused on how the low bridge is operating and carrying traffic, as well as how the structure itself is functioning. In the next year, we will make multiple upgrades to the bridge to ensure it continues to serve the West Seattle peninsula and surrounding communities for years to come. Through the construction of these upgrades, we will also do everything we can to minimize impacts to those businesses and maritime operations in the vicinity that continue to rely on accessing the low bridge.

SPOKANE ST SWING BRIDGE PROJECT DESCRIPTIONS

Structural Rehabilitation Project

The Spokane St Swing Bridge (low bridge) does not pose any imminent risk of closure or failure. The bridge is routine inspected per Federal requirements. Due to the high demand on the low bridge during the West Seattle Bridge closure, we have increased the frequency of in-person inspections at least once a month and installed a structural health instrumentation monitoring system that provides real‑time data of the bridge. We are currently making rehabilitation improvements as a preventive measure to ensure the bridge will continue to support vehicles and heavy freight in the years ahead. 

low bridge rehab graphic

On the low bridge, we are injecting epoxy resin into any existing cracks and adding carbon-fiber wrapping in several locations, on both interior and exterior surfaces. We wrap sections of the bridge with carbon-fiber wrapping to strengthen the bridge, much like putting a cast on an injured arm or leg. When we add carbon-fiber wrapping to surfaces of the bridge, it's working in tandem with the steel already inside the bridge to increase bridge strength.  

carbon fiber wrap and bridge girders

Carbon-fiber wrapping can be applied inside and outside the girders to further strengthen the bridge, as shown here during phase 1 stabilization efforts on the high bridge.

Control Project

We awarded a contract to improve the control system that opens and closes the low bridge. Taurus Power & Controls, Inc. was the winning bidder, and has prior experience with movable bridges in Seattle. We are currently working to procure components and develop the system off-site. During this off-site development stage, we will test the system to ensure that it is ready for installation in the low bridge in 2023.

The low bridge swings open and closed using the original electronic system of buttons, switches, and wires that are now about 30 years old. We already had a plan in place to replace this system in 2020, but then the high bridge was closed, and the project was reassessed until we had a better understanding of the high bridge's condition. Ultimately, the project also included rerouting the wires connecting the control tower with the motors that open and close the bridge off the high bridge - where they are today - to a new conduit under the East Duwamish Waterway. We will complete this work as part of the West Seattle Bridge Program to increase resiliency to the overall West Seattle bridge system and decouple the low bridge from the high bridge.

low bridge control tower

The low bridge control tower, part of the low bridge's controls system.

The system includes computers that control the machinery that lifts and swings the spans and activates the gates that prevent traffic and people from crossing when it's open. It also includes the communication lines that connect the computers, control tower, and the moving parts to one another. Without making these updates now, we run the risk of component failures associated with operating the bridge in the future.

To complete the upgrades, we'll drill new conduit (like a small pipe) for the communications line beneath the East Duwamish Waterway. The new conduit will be roughly 4-inches in diameter and about 20 feet below the bottom (the riverbed) of the Duwamish Waterway.

We'll then route the new communication cables into the new conduit, test them, and connect them to the newly installed control system. The final step involves removing existing equipment and reinstalling new equipment for the control system.

Existing

Controls project existing graphic

New Communications Lines

Controls project after graphic

Lift Cylinder Project

Two large hydraulic cylinders, located on the east and west side of the low bridge, do the heavy lifting that allows the bridge to swing open for ships and boats in the Duwamish Waterway. Think of the cylinder as a pivot point where each span rotates out of the way of waterway traffic. Without the lift from the cylinders, we would not have a functioning swing bridge. 

In addition to the two active cylinders, the bridge has a third, spare cylinder in case one of the active cylinders needs to be repaired. In 2018, we removed the west cylinder and replaced it with the spare. In 2023, we'll install the rehabilitated cylinder on the east side of the waterway. After the swap, we'll inspect and refurbish the removed cylinder, replacing seals and determine if any other repairs are needed. 

To help make future maintenance more efficient and less impactful to those traveling on the bridge, we have redesigned and fabricated a new lifting frame that is used to remove the cylinders from the bridge; the new lifting frame will shorten any future closures for this type of work.

A photo of cylinder on the west side of Duwamish Waterway during removal in 2018.

Low bridge projects schedule

  • 2020-2022: Community engagement
  • 2020-2022: Planning and design
  • 2023: Construction begins

Community engagement

We are committed to working with the community to keep you informed of progress and milestones as we rehabilitate the bridge. We will seek your continued feedback on how to improve mobility and safety for West Seattle, as well as the South Park and Georgetown neighborhoods. Thank you to everyone who has helped us make this project better with your ongoing engagement.

  • Learn more, get involved, and tell us what you think: Invite us to meet virtually with your neighborhood group, local business, or place of worship.
  • Email or call us at WestSeattleBridge@seattle.gov or (206) 400-7511 to let us know how to improve safety and mobility in your neighborhood.
  • Sign up to receive program update emails.