PORTLAND, Ore. — The Interstate Bridge Replacement Program is zeroing in on a configuration for the proposed new bridge to replace the aging twin spans that carry Interstate 5 over the Columbia River, but it will be several more months before the program arrives at a final design, known as a Locally Preferred Alternative or LPA.
Some ideas such as a tunnel have already been nixed, but the project website lists several design pieces that still have multiple options under evaluation, including the alignment of the bridge, the type of included mass transit and whether to retrofit or replace the nearby North Portland Harbor Bridge that carries I-5 from the Oregon mainland to Hayden Island.
However, it appears the last of those questions already has an answer, even if it hasn’t been made official yet.
At a Monday meeting of the project’s bi-state legislative oversight committee, deputy program manager John Willis outlined the various alignment and transit options, but at the bottom of one of the presentation slides was a note: “All options assume replacement of the North Portland Harbor Bridge.”
Program administrator Greg Johnson confirmed the choice in an email.
“Given the increased age of the structure since the past effort and the need for a seismically resilient corridor, the Interstate Bridge Replacement (IBR) program is currently assuming replacement of the North Portland Harbor Bridge is needed. This decision will be finalized as one of the elements that will be incorporated as part of the modified LPA,” he said.
Both the slide and Johnson’s statement mentioned that additional work will be done to identify impacts and mitigation measures for a full replacement, but they leave little room for doubt that keeping the existing Harbor Bridge is off the table.
That’s a change of plan from the Columbia River Crossing, the previous I-5 Bridge replacement effort that fell apart in 2013. The CRC plan initially included replacement of the Harbor Bridge, according to the IBR office, but the final LPA switched to a widen-and-retrofit strategy as a cost-saving measure.
It’s also a change for the IBR project office, which until now has listed the Harbor Bridge as one of the to-be-determined components of the new project, even as recently as December in the program's 2021 Progress Report.
Johnson said the replacement decision was primarily about seismic resiliency, but a new bridge will also give the project more flexibility when designing connections at Hayden Island and Marine Drive on the Oregon side of the river.
The Harbor Bridge is newer than either of the main crossing spans, only dating back to 1987, according to the Oregon Department of Transportation’s Bridge Log. However, its substructure and foundations are built on liquefiable soils, Johnson said, giving it the same seismic vulnerabilities as the main crossing.
A foundation upgrade could partially mitigate those risks, but not to the same extent as a new bridge built to modern seismic standards, he said, and the IBR office concluded that the CRC’s retrofit plan would be too expensive when weighed against the bridge’s remaining lifespan and the lingering seismic issues.
The IBR program schedule calls for choosing a single LPA by the middle of the year and then putting it through the environmental review process with the goal of receiving a federal green light for the project by the end of 2023, with construction targeted to begin in 2025.