A Vital Connection and New Landmark on Seattle’s Downtown Waterfront

• An iconic new design for one of the busiest pedestrian bridges on the West Coast.
• Replaces an old bridge that did not meet accessibility standards and was seismically vulnerable. 
• The 193-foot main-span bridge features a three-span, cast-in-place concrete superstructure.  
• More than 270 lights on the bridge change colours to celebrate special events in the city.

The Marion Street Pedestrian Bridge in Seattle is one of the busiest pedestrian bridges on the West Coast, helping to serve the Colman Dock Ferry Terminal’s 10 million annual passengers. Replacing the bridge was critical to Seattle’s downtown waterfront transformation. The previous bridge — a combination of segments dating back nearly a century — did not meet current accessibility standards, became very congested during peak periods, was seismically vulnerable and lacked aesthetic appeal.

To deliver the iconic new design for the bridge, HDR worked with an internationally renowned bridge architect, the City of Seattle and the Washington State Department of Transportation. We provided conceptual design, preliminary engineering, final design and design support during construction of the structure.

An Instant Landmark

Replacement of the pedestrian bridge included demolition of multiple structures, including a previous bridge span attached to the Commuter Building and, after completion, a temporary bridge that had been installed to route pedestrians around construction. The new bridge replaces half the original bridge between the Colman Dock Ferry Terminal next to Alaskan Way to 1st Avenue. The remaining original bridge will be replaced when additional funding is available.

The new bridge opened in November 2023 and exudes a clean, sleek appearance and became an instant landmark on the Seattle waterfront. It also meets Americans with Disabilities Act requirements and is wider than the previous bridge to more easily accommodate pedestrians. The 193-foot main-span bridge features a three-span, cast-in-place concrete superstructure.  

There are 279 lights — on the handrails, below the bridge deck and on the bridge’s V and Y-shaped columns — that change colors to celebrate special events in the city. The lighting improves safety, the nighttime experience along the waterfront and showcases the structure of the bridge. The aesthetic design also compliments the Ferry Terminal and stadiums to the south.

Seismic Challenges

One of the project’s biggest challenges stemmed from the region’s high seismicity and proximity to the seawall. The geotechnical team found that the highly liquifiable soils would cause significant loads on the foundation during an earthquake. The solution entailed 10-foot diameter shafts founded over 80-feet-deep, in very dense, glacially overconsolidated soils.

The bridge had to accommodate more than six feet of relative longitudinal seismic movement, avoid impacting the new seawall and significant underground utilities and minimize the superstructure depth where the new bridge crossed city streets tying into the existing structure. A unique expansion joint accommodated the movement and a pipe pin connection limited seismic load transfer to the superstructure, allowing for a shallow structure depth. Seismic pipe pins are an emerging technology, with only one other structure in Washington state using it so far. 

Commitment to Sustainability

The Marion Street Bridge’s holistic sustainability approach started with the removal of the temporary bridge. The City of Seattle donated the temporary bridge to Clallam County with Peninsula Trails Coalition providing the logistic coordination. It will be repurposed as part of an ongoing trail improvement project. All concrete and metal debris was recycled when the existing structure was removed. 

During construction of the pedestrian bridge, our team also limited traffic closures to reduce travel delays and fuel consumption. We also used low maintenance materials and products, such as high strength concrete, stainless steel and LED lights, which all offer the lowest life cycle costs and maintain long life expectancies.