Oregon is vulnerable to being hit by a major Cascadia Subduction Zone earthquake that would cause significant loss of life and damage to buildings and infrastructure throughout Oregon—including its highway system. Such an earthquake, which is considered likely to occur in the next 50 years, would greatly impair mobility in western Oregon and create major economic distress.
In response to this vulnerability, ODOT has joined other state agencies in developing an Oregon Resilience Plan to identify seismic vulnerabilities of critical facilities and resources and to recommend options to improve resiliency.
One part of this effort is to develop a strategy for the state highway system to support emergency response and recovery efforts by providing a backbone system of “lifeline” highway corridors that connect service providers, incident areas and essential supply lines. This system would allow emergency service providers to do their jobs with minimum disruption and support economic recovery after a disaster event. This study looks at bridge vulnerabilities as well as other elements of the system such as slopes and landslides that could fail in a major earthquake.
- Tier 1 would provide access to and through western Oregon from Central Oregon, Washington and California and provide access to each region within the study area. Tier 1 includes I-5 and I-205, US 97, I-84 between I-205 and US 97, and key routes to the coast including US 30, Oregon 18/22, and Oregon 38, as well as portions of US 101. Together, these routes link virtually all of the state’s major population centers and the largest communities on the coast.
- Tier 2 includes additional roadway segments that extend the reach of the Tier 1 system and provide redundancy in the highly populated areas of the Portland metro region and Willamette Valley. This includes US 26 from the coast to Central Oregon, most of the remainder of US 101, Oregon 126 between Eugene and Florence, Oregon 99W, and other routes.
- Tier 3 includes roadway segments that, when added to the other tiers, provide an interconnected network to serve all of the study area, with redundant paths. This includes US 20 between I-5 and Newport, Oregon 42, and US 199, as well as other routes.
Building on the identification of this network, ODOT has also developed a draft Seismic Options Report that provides a plan to strengthen bridges, highway slopes and landslide areas on the lifeline routes. The plan lists options for investment strategies that could be used to select a backbone system that would allow some level of highway mobility after a major seismic event.
Thanks to the Oregon Transportation Investment Act (OTIA) III State Bridge Program and other investments in bridges, numerous vulnerable bridges built before seismic standards were upgraded in recent decades have been replaced with new structures that would withstand a major earthquake. However, in the future replacement of large numbers of bridges is not feasible given limited resources, leaving retrofitting of existing bridges as the most effective solution. The draft Seismic Options Report finds that retrofit is viable if performed incrementally and strategically on the highest priority routes. By improving mobility and allowing faster response and recovery, this work would achieve a significant reduction in secondary loss of life and long term economic losses.
The Seismic Options Report estimates the cost of retrofitting the backbone routes.
• Two phases of retrofits to Tier 1 routes are estimated to cost $715 million.
• Retrofitting Tier 2 routes is estimated to cost $515 million.
• Tier 3 retrofits would cost an estimated $250 million.
“This report demonstrates that achieving seismic resiliency on key lifeline routes is feasible,” said Paul Mather, ODOT’s Highway Division Administrator. “It may not be cheap, but we have to weigh the cost against the loss of life and economic dislocation that would befall us after a major earthquake.”
ODOT's work on seismic resilience was recently featured in The Oregonian after the state hosted a visiting delegation of Japanese officials to learn more about tsunami-proof bridges. To read the story, go to The Oregonian's webpage.