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Multnomah County has narrowed its list of ideas for replacing or retrofitting the Burnside Bridge, a project it says is necessary to make sure at least one downtown Willamette River bridge could survive an earthquake, to four options.

According to a draft document published Aug. 31, the county wants to further study the following: Seismically retrofitting the 1926-era structure; building a new bridge without a lift span; replicating the drawbridge in the same height and location; or building a new drawbridge while splitting westbound traffic into a separate approach to address a growing bottleneck at Northeast Couch Street.

All of the options would cost more than $500 million to build. The Burnside Bridge was chosen as the best option to invest in because the street runs 17 miles in between Gresham and Washington County and could provide a significant life-line for the region if a Cascadia Subduction Zone rupture ravages the city.

According to the county, the current bridge is not expected to survive following a magnitude 8 or greater Cascadia Subduction Zone earthquake. A simulation of the expected earthquake destroying the bridge has been viewed in 96 countries and watched more than 74,000 times.

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The county says the price tag will be worth it.

“The post-earthquake community costs when infrastructure fails are substantially more expensive compared to proactively investing in seismically-resilient infrastructure,” the county report said.

Mike Pullen, Multnomah County’s bridge spokesman, said officials want to hear what Portlanders have to say about the various options. On Nov. 1, the Board of County Commissioners is expected to approve the report and chart a course for further studying each of the remaining option.

“We want to have a range that shows all the reasonable options that should move forward,” Pullen said.

The county is early in the replacement discussion and likely a year-and-a-half away from settling on a preferred option to replace the bridge. Construction wouldn’t begin until 2024 at the earliest and may last until 2028.

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Samantha Swindler/Staff

A committee of transportation representatives, local businesses and nonprofits and Portland, Beaverton and Gresham civic officials narrowed the list of options from 123 to four after two years of study.

The county won’t consider tunneling under the river, replacing or upgrading the Morrison Bridge, building a stacked bridge with pedestrians and bikes beneath vehicle travel lanes or splitting traffic into two separate bridges. Planners also ditched a 120-foot-tall bridge, comparable to the Ross Island bridge.

One looming decision that isn’t broached in the feasibility study is what to do while the county starts construction on the project. Pullen said one option would be to build a temporary two-lane detour bridge.

Keeping a detour in place would push project costs upwards of $800 million for all options except for the seismic retrofitting proposal.

The county is collecting public comments online through September 30 at its website.

In-person open houses are scheduled for the following:

Sept. 13, 5 to 7 p.m., Mercy Corps, 43 SW Naito Parkway

Sept. 25, 5 to 7 p.m., Fair-Haired Dumbbell, 11 NE Martin Luther King Jr. Blvd.

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Beth Nakamura/Staff

Here’s a breakdown of what we know about the four options now. Cost estimates are in 2027 dollars:

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Seismic retrofit

What: This proposal would upgrade the current bridge, but not the spans over Interstate 5 and the railroad tracks. Those approaches would need to be replaced altogether.

Project estimate: More than $500 million

Estimate with detour bridge: Less than $750 million

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New bridge with no lift span

What: This proposal would create a bridge with up to a maximum of 97-foot clearance for river traffic, at basically the same spot. Because of the additional height, the west bound landing would have to be extended about three blocks further west, or roughly to Northwest Fifth Avenue.

Project estimate: $695 million

Estimate with detour bridge: $882 million

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New like the old

What: Love your Burnside Bridge? You can keep it. This option would create a new lift span at the same height and location.

Project estimate: $655 million

Estimate with detour bridge: $837 million

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New bridge with new approach

What: The Burnside Bridge’s eastside is humming with new buildings and businesses. This proposal would split the traffic on the eastside to make it easier for freight and vehicle traffic headed west. The new approach would be from Northeast Couch Street.

Project estimate: $681 million.

Estimate with detour bridge: $863 million