The agency recommends that the span be replaced rather than retrofitted and says the project could cost at least $450 million.

PMG FILE PHOTO - Legislators and Wilsonville officials are hoping to garner funding for the entire project to retrofit the Boone Bridge and add a southbound auxilary lane on I-5 or for an engineering study.

Wilsonville residents tired of I-5 traffic spilling into local streets and workers who face the Boone Bridge bottleneck in their daily commutes may lament a report released to the Oregon Legislature Jan. 22 by the Oregon Department of Transportation.

In assessing a project to both seismically retrofit the Boone Bridge and add an I-5 southbound auxiliary lane from the Wilsonville Road exit ramp to the Canby-Hubbard exit ramp (OR 551), the report shows that replacing the bridge would be more cost-effective than retrofitting it (which was the initial plan) and that construction would cost between $450 million and $550 million, assuming that it would begin in 2027.

By comparison, state Sen. Alan Olsen had forwarded a bill in 2019 that would have doled out $120 million to complete this project. ODOT Public Information Officer Don Hamilton said the dollar figure was a very rough estimate and more work would need to be done before an exact estimate could be provided. The ODOT representative noted that the Legislature passed a $5.3 billion transportation package in 2017.

"There are significant new costs involved in this effort, but significant new advantages to this, and these are issues that legislators will consider," he said.

Rep. Courtney Neron, D-Wilsonville, who pushed to get the study done and hadn't yet reviewed the report, simply said: "That's a really big price tag."

The Legislature financed this study during the 2019 session but has not attributed funding for the project itself. It will be up to that body to determine when or if the project receives funding.

"The bridge assessment work revealed that the benefits associated with a full bridge replacement outweigh the minimal construction cost savings associated with a retrofit of the existing bridge," the report reads. "Critically, the feasibility assessment found that the entire substructure of the Boone Bridge, including pier supports and foundations, must be replaced in the retrofit option to achieve seismic resiliency."

The report adds that the main spans of the bridge are supported by timber pile foundations that would need to be replaced in order for the bridge to weather a major earthquake. Furthermore, the current foundation's soils would liquefy in the event of an earthquake and seep into the river.

It also says retrofitting the bridge would cost over 85% as much as replacing it and that costs to retrofit may exceed replacement considering future maintenance.

"These two significant issues associated with the retrofit option will necessitate the replacement of the bridge's entire substructure," the report reads. "Furthermore, a retrofitted and widened Boone Bridge would have substantial ongoing costs to monitor structural deficiencies and require the future replacement of the original bridge superstructure, representing an additional future major capital expense."

Hamilton stressed the importance of the bridge as a lifeline for the Portland metro area if a major earthquake were to rock the region.

"We're confident that with the latest seismic designs, the Boone Bridge in its new form will be able to still be operational in the event of an earthquake," he said.

In preparing the report, ODOT also determined that average traffic volume would increase 3% after the addition of the southbound auxiliary lane and that I-5 traffic can be maintained during bridge construction. The Wilsonville I-5 Facility Plan conducted in 2018 determined that the southbound lane would significantly reduce traffic at the bottleneck.

"An auxiliary lane is a very effective tool for reducing the threat of conflict on a freeway because when you reduce the amount of merging people have to do from an on-ramp onto a main line of traffic you're reducing the number of potential crashes. That is a significant safety and congestion improvement," Hamilton said.

There already is a northbound auxiliary lane at the bottleneck from Miley Road to Wilsonville Road, but the study recommends extending that to the Canby-Hubbard exit.

"Auxiliary lanes in both the northbound and southbound directions and associated interchange improvements will alleviate traffic bottlenecks, improve travel time reliability and enhance safety on I-5," the study reads.

An ODOT representative had said at a 2018 meeting in Wilsonville that the department combined the auxiliary lane and retrofitting projects as a way to make the project more likely to receive funding from the Legislature. The project couldn't be decoupled under the scenario of rebuilding the bridge because the bridge would be rebuilt to include auxiliary lanes, Hamilton said.

City of Wilsonville representatives, its lobbyst and employees have consistently stressed the importance of this project.

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