Multnomah County wants to spend about a half-billion dollars to prepare the Burnside Bridge for emergency crews to safely cross the Willamette River after a major earthquake.

An estimated $496 million project to either replace or significantly upgrade the 89-year-old span can be found in a 20-year improvement plan for the county's six bridges.

Chairwoman Deborah Kafoury offered the proposal Thursday. The plan calls for 52 other projects with an estimated $1.3 billion total price tag. Approximately 200,000 people use the county's six bridges on a daily basis, according to the plan.

Burnside Street runs from Gresham to Washington County. It has been designated by the Oregon Department of Transportation and Metro as a crucial roadway for response after a catastrophe, said Mike Pullen, county spokesman.

The county wants the bridge to structurally withstand a magnitude-9.0 earthquake from the Cascadia subduction zone, he said. The zone sits 40 to 80 miles off Oregon's coast.

The new Sellwood Bridge, once it's complete, is seismically designed to open for emergency responders and the public within 72 hours of a similar earthquake, Pullen said. The bridge replacement is expected to cost more than $307.5 million, making it the most expensive project in county history.

The county built the Burnside, Broadway, Morrison and Hawthorne bridges before the seismic risk was known, Pullen said. The Sauvie Island Bridge, which opened in 2008, is built to "survive the big 9.0 earthquake geologists tell us is coming," he added.

The county's 20-year plan also includes $189.4 million for seismic upgrades to the Broadway, Morrison and Hawthorne bridges, but those upgrades don't offer the same guarantee of immediate use after an earthquake, Pullen said.

Those three projects could begin by the end of the 2020s, according to the plan. All cost estimates are adjusted for potential inflation, Kafoury said.

She's considering a proposal to set aside $3 million in next year's budget to study the feasibility of either major renovations or replacement of the Burnside Bridge. The new Sellwood Bridge, for example, took more than a decade to develop, Kafoury said.

The plan also includes $17 million to be spent on an environmental study for Burnside over the next five years.

Kafoury expects it would take at least a decade before any crews would begin work on the Burnside Bridge if approved, she said.

Over the past few years, big-ticket bridge projects have come with a few black eyes for county leaders.

Most recently, the general contractor of the $307.5 million Sellwood Bridge filed a lawsuit against the county over who should pay for $1.6 million in costs related to unexpected ground conditions.

The county is also embroiled in a separate lawsuit over the decking problems on the Morrison Bridge. It seeks millions from the bridge contractor to replace failed decking.

Pullen said the proposed county plan also includes projects that were requested by the public while the document was being crafted.

He said the county plans to "change drainage grates on Burnside Bridge so they don't go parallel to bike tires" and to add pedestrian lighting on the north side of the Morrison Bridge under the east approach's freeway ramps.

The county approved its last capital improvement plan for bridges in March 1993. It included a $115 million estimate for all projects, records show. Some projects never came to fruition, and the county has since spent more than $400 million for bridge work, Pullen said.

The Board of Commissioners will vote on the new plan in May, but county leaders want the public's input on the 132-page document before commissioners vote on next year's budget. Comments can be sent to bridgeplan@multco.us.

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-- Tony Hernandez

thernandez@oregonian.com

503-294-5928

@tonyhreports