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Seismic Bridge Safety

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EUGENE, Ore. — Officials in Oregon say an earthquake of the magnitude like the one in Northern California could cause catastrophic damage.

The Oregon Department of Transportation says bridges built nowadays have seismic standards they must adhere to; but some of the state’s oldest bridges, could cause the transportation system to shut down if a major earthquake shook the Willamette Valley.

The I-5 bridge over the Willamette River is one of the newest bridges in the state.

“The analysis and design for the Willamette River bridge in Eugene was only done in 2010, it is one of the more safer bridges in town for earthquake resistance,” said Bruce Johnson, ODOT Bridge Engineer.

But, 80 percent of the bridges in Oregon were built before guidelines for seismic safety were put in place. This means of the 6,000 bridges in Oregon, only 1,200 are built to withstand a major earthquake.

“It’s fine for the people across the Willamette River in Eugene, they can cross the river, but they’re not gonna travel very far on other roads until they run into a bridge that probably will be damaged,” Johnson said.

This could become a major problem if earthquake predictions about “the big one” are accurate.

“We’re very vulnerable to a subduction zone earthquake that we call the Cascadia subduction zone and if we have a Cascadia subduction zone earthquake it would affect all of western Oregon,” Johnson said.

ODOT says the transportation corridor throughout all of western Oregon could be impossible to travel, impacting safety and the economy.

“The gross domestic product of Oregon would go down significantly after an event because we wouldn’t be able to travel anywhere,” Johnson said.

ODOT is proposing a phased program to improve the bridges and increase resilience of both bridges and landslides over the next 50 years. To make roads easier to travel if an earthquake shakes the valley.

ODOT says it can’t identify which bridges built before 1990 would be most likely to collapse because studying the bridges costs money that the state doesn’t have.

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  1. Mike Speiser says:

    Didn’t we just spend billions to upgrade a ton of the bridges throughout the state? Why isn’t this addressed in the article?

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