Burnside Bridge will close for 5 years for seismic upgrade
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The Burnside Bridge facing downtown. Photo: Moriah Ratner/Bloomberg via Getty Images
Portland's Burnside Bridge — one of the busiest transportation arteries connecting the east and west sides of the city over the Willamette River — will close for five years starting in 2027 as it's retrofitted to withstand an earthquake.
Why it matters: If an earthquake were to occur along the Cascadia Subduction Zone, the majority of bridges in Portland, which are not built to withstand prolonged shaking, almost certainly would collapse.
- In addition to potentially billions of dollars in damage to surrounding infrastructure, portions of the city would be completely cut off from each other.
- Burnside Bridge was chosen as the first bridge to get a seismic rebuild because it is part of the corridor dedicated as an emergency route between Washington County, Gresham and Portland.
Threat level: Right now, the Burnside Bridge (built in 1926) is hoisted up by nearly 400 tree trunks driven into the mud in the riverbed and reinforced with steel and concrete.
- If a major magnitude earthquake were to hit, the soil would liquify and violent shaking would cause the concrete columns to crumble and the piers on both sides to sink into water.
- Other transportation pathways, bike lanes and popular walkways that are also located under the bridge — including TriMet's blue and red MAX lines, I-84, I-5, Naito Parkway and Tom McCall Waterfront Park — would be demolished and littered with debris in its collapse, one simulation suggests.
- Experts predict there is a greater than a 1 in 3 chance of an 8-plus magnitude earthquake hitting the Pacific Northwest in the next 50 years.
State of play: After the project was pushed back a year, Multnomah County officials tapped Burnside Bridge Partners (a joint venture with local firm Stacy Witbeck, which built the city's streetcar system) as the contractors to demolish, design and construct the new bridge.
- The project is now in the design phase. Construction could begin as early as 2026 and be completed by 2031 if full funding is granted.
- The county's Board of Commissioners plans to submit a grant proposal for $447 million from the federal government's bridge investment program. The state already OK'd $20 million for the project from lottery revenue bonds.
However, the project's target budget is closer to $895 million.
What's happening: Developers won't just be building one bridge, but three because of the soil's instability along both sides of the Willamette River.
- A decision has yet to be made on whether — to ensure the bridge stays intact after an earthquake — it should be a cable stay bridge or a tied arch bridge, Emily Miletich, the county's construction manager. told OPB.
Aside from that, other design decisions have already been nailed down.
- Steel-reinforced concrete columns measuring 10 feet in diameter will be driven into bedrock, a moveable deck will still allow for the passage of large ships, and a girder bridge (similar to what is there now) will be utilized for the longer stretches.
The bottom line: While the Burnside Bridge is closed, all traffic will be detoured to other bridges.