Despite claims from Oregon DOT officials, the only published seismic studies suggest the I-5 bridges will survive a Cascadia earthquake.

It’s far from clear that spending billions to replace this bridges is a good investment to protect lives and the economy

By Robert Liberty

City Observatory is pleased to publish this guest commentary from Robert Liberty, a former Councilor of Portland’s Metro regional government and who has had more than 30 years of experience with transportation policy and project development including serving on the Metro Council during the period it approved the Columbia River Crossing project. 

Much of the Pacific Northwest lives in palpable dread of the next Cascadia Subduction Earthquake, a massive seismic event that has occurred repeatedly over thousands of years, according to the best available interpretations of the geologic record.  The Cascadia fault line, which runs along the coasts of Oregon and Washington could produce a 9.0 quake that would devastate unreinforced buildings and other infrastructure.

As any salesperson will tell you, fear of a possible catastrophe is a great selling proposition. So it’s little surprise that the Oregon Department of Transportation (ODOT) has trotted out concerns about the next Cascadia quake as a reason to pony up billions of dollars to replace the I-5 bridges across the Columbia River that connect Portland Oregon to Vancouver Washington.  According to Oregon Public Broadcasting, ODOT’s Assistant Director Travis Brouwer claimed the I-5 bridges:

 “would likely collapse in a major earthquake.”

That is sounds scary, but the trouble is, there is no basis for that statement according to the technical work commissioned by . . . the Oregon Department of Transportation

Brouwer’s claim is contradicted by a 2009 study ODOT commissioned of the seismic risk to bridge structures: Seismic Vulnerability of Oregon State Highway Bridges: Mitigation Strategies to Reduce Major Mobility Risks.

In the study “bridges” include overpasses, viaducts, ramps, – any elevated structure, whether over a water body or not. The study modeled the impact of several earthquakes in Oregon; one near Klamath Falls, another near Salem, a major earthquake under the West Hills of Portland and magnitude 8.3 and 9.0 Cascadia Subduction Zone earthquakes (9.5 is the highest magnitude earthquake ever recorded.)

According to the study, none of those earthquakes cause the I-5 bridges to collapse.

In the Cascadia Subduction Zone quake of 9.0 magnitude, on I-5 in Multnomah and Clackamas County, five bridges would suffer “slight” damage and one would suffer “moderate” damage with the repair or replacement cost coming to $8 million.  (Page 48.  There is also a hard to read map showing damage levels on the bridges.)

In the 8.3 Cascadia Subduction Zone earthquake, on I-5 in Multnomah and Clackamas Counties, one bridge is slightly damaged, with the repair cost estimated at $400,000.  (Report page 49.)

The most damaging quake is a 6.5 West Hills quake. In the Multnomah-Clackamas section of I-5  that would cause 8 bridge structures slight damage, 11 bridge structures moderate damage, 10 bridge structures extensive damage and one bridge structure would suffer “complete” damage, means collapse.  (Page 50.)

There is no map. However, it is very unlikely that one of the two Interstate Bridges is the one that collapses, since the combined cost to replace or repair these 30 damaged I-5 bridges is estimated at $483 million.  That is quite a bit less than $900 million budgeted for the replacement bridge in the Columbia River Crossing.  (The new bridge represented about a quarter of the total CRC project cost.)

The seismic risk study includes a summary table showing that for $446 million, less than Oregon’s proposed contribution to the Columbia River Crossing project ($500 million) Oregon could retrofit 95 bridge structures on I-5 from the Columbia River to Marion County, to the highest level of earthquake resilience (Phase II standard.)  (Report page 56.)

A limitation of the study was that it did not consider liquefaction, the effect caused by shaking of wet soils (like shaking a bowl of oatmeal in which water rises to the surface.) ODOT has not conducted, or at least published a study of the risks to state highways caused by liquefaction. Yet, in the absence of that study senior ODOT staff feel free to state an unsupported opinion that the bridges would likely collapse.

(Indifference to research and data is not limited to ODOT staff. During the CRC controversy I showed the ODOT seismic bridge risk report to a senior Washington state legislator pointing out the relevant tables and paragraphs. He did not look at the report but simply stared at me and said “That’s your opinion.”)

But this focus on the seismic risk to two bridge on I-5 to justify a $3.4 billion freeway widening project typifies one of the major defects of transportation project analyses – focusing on one issue without considering the broader context, trade-offs or less costly alternatives.

For example the West Hills quake was projected to cause $483 million in damage to the bridge structures on, under and over I-5 between the Columbia River and Marion County including one collapse. But it causes only $14 million in damage to I-205. (page 50.) Why wouldn’t it make more sense to invest $294 million to retrofit I-205 to the Phase II standard to maintain a north-south highway connection through the region including a bridge crossing across the Columbia in the event of a major quake instead of $900 million just to replace two existing bridges?

(It is worth noting that the report shows that the cost of retrofitting of 145 bridge structures on I-5 and I-405 to the Phase I seismic safety standard was estimated at $178 million, less than the CRC study.)

If we broaden our geographic perspective a bit but remain focused just on bridges, the report projects catastrophic damage to the bridges along the Oregon Coast from a 9.0 Cascadia subduction quake and all the approach roads from the interior. If our priority if human life and rapid recovery, should we focus our transportation dollars on where they may save many lives or where they will avoid disruption to commuters?

Applying a statewide perspective leads us to a more basic question: Why does ODOT propose a massive investment in one project to benefit one set of Portland-area commuters while simultaneously documenting that the percentage of ODOT bridges in “good” condition declined from 40% in 2008 to 20% in 2018 and that 43 bridges on I-5 are structurally deficient, according to its 2018 Bridge Condition Report.

But even this perspective is too narrow because the ODOT CRC proposal did not address – and cannot address – the bigger question of whether roads and bridges represent the greatest health risk from a big quake.

Thousands of Oregon students attend school in vulnerable unreinforced masonry buildings. Strengthening pipes supply clean water and to carry away sewage treatment and to maintain energy supplies might be a higher priority in preparing for an earthquake, than keeping open a commuter bridge. Rather than serving as an all-purpose excuse of any big construction project, a serious seismic strategy would prioritize projects that had the biggest benefits in reducing likely casualties, and making the region more resilient in recovery from “The Big One.”

Has Oregon learned anything from the Columbia River Crossing debacle? One clue is who the Oregon Transportation Commission hired as its new Director in September of this year; Kris Strickler. OPB noted that Strickler “directed ODOT’s involvement in the Columbia River Crossing bridge project in the first half of this decade, before the $3.4 billion effort to replace the bridge connecting Portland and Vancouver collapsed in 2014.”

And perhaps that is the kind of collapse we should be worrying about most.