ODOT is initiating a seismic retrofit project for bridges along the Interstate 5 corridor in the Portland metropolitan area. Five bridges between Portland’s South Waterfront district and the Tualatin River comprise the initial package of work. ODOT and consultant staff are currently in the preliminary design phase of the project. Construction will begin in early 2014 and end late 2015.
Why a Seismic Retrofit Program?
Most bridges in Oregon built prior to 1990, the year modern seismic design specifications for bridges were developed, are vulnerable to a major earthquake. The March 11, 2011 earthquake in Japan provided a stark reminder of the importance of building structures so they can survive a major seismic event. Many scientists believe the Pacific Northwest is overdue for the same type of seismic event that struck the Japanese coast (a subduction zone or "megathrust" earthquake) where sustained shaking of the ground can cause extensive damage to buildings and infrastructure. The 2011 Japanese earthquake was a magnitude 9.0. The last megathrust earthquake in this region was the Cascadia earthquake in 1700, which had a magnitude 8.7 to 9.2. According to research conducted by the Oregon Department of Geology and Mineral Industries, there is a 40 percent chance a similar powerful earthquake will occur along the Oregon coast sometime in the next 50 years.
In response to these findings, ODOT conducted a seismic vulnerability study of the state highway bridges to assess the risks to Oregon’s only north-south interstate highway. The result? Only a small portion of I-5 would remain passable if the state suffered a substantial seismic event; most of the older bridges would either collapse or experience severe damage and become impassable without major and very costly repair work.
ODOT’s initiative to retrofit the state’s older bridges to meet modern seismic specifications will ensure I-5 would remain open in the event Oregon experiences a powerful earthquake. The sites selected to begin receiving improvements represent just the first phase of an expected multi-phase program to improve the seismic rating on bridges throughout the region.
Project Locations (click on each project location below for more information)
Anticipated Traffic Impacts
SW Hood Avenue, SW Barbur Boulevard and SW Lower Boones Ferry Road bridge construction sites will experience temporary traffic impacts from occasional lane closures or restrictions. The bike lane and sidewalk on SW Lower Boones Ferry Road at the I-5 interchange will be re-routed during construction, but will connect to existing facilities at either end of the interchange. There is also the likelihood there will be channel narrowing and a riverbank path closure at the Tualatin River Bridge location during construction. This may impact river recreational users. Detailed information of traffic impacts at each project location will be available in the fall of 2013.
Under current conditions, older bridges on the I-5 corridor would not be able to withstand a major seismic event. The seismic retrofit work – strengthening the piers, pilings and bridge abutments – brings those structures up to modern seismic design specifications, which will make them better able to withstand a powerful earthquake.
The project increases the safety of Oregon drivers using the state-maintained transportation system. It also helps ensure that a major transportation and freight route remains accessible to speed vital supplies and services to areas needing assistance.
The seismic retrofit work maximizes taxpayers’ dollars by increasing the lifecycle of the existing network of bridges, thereby lowering the costs required to replace an entire freeway system following a major earthquake.
To receive project updates electronically or for more information, contact:
Lili Boicourt, Community Affairs Coordinator