The work is being carried out in order to improve the US 97 highway's ability to withstand a major earthquake.
The seven bridges that will be the focus of the US$32 million retrofitting project are in the Klamath Falls area. The work, which is funded by the federal government, will begin this year and continue for the next four years. A contractor will be selected this summer by competitive bid.
US 97 is a primary north-south highway and regarded as a ‘lifeline route’ in the event of a major earthquake. Its inland location means that US 97 is expected to fare much better than the other primary north-south routes - I-5 and US 101 – which would probably be badly damaged or completely destroyed in the wake of a Cascadia subduction seismic event.
The State of Oregon has identified the seven bridges as the most vulnerable to a magnitude 8.0 or greater earthquake. This is the impact magnitude that scientists expect when a Cascadia subduction event next occurs off the Oregon coast.
Six of the project bridges will be retrofitted and another – US 97 over Lakeport Boulevard and UP Railroad – will be completely replaced.
US 97 over the Link River and Main Street (pictured below) is the most complex retrofit in the bundle. Bridge replacement isn't an option with the current funding so the construction contractor will be essentially strengthening or completely replacing all of the bridges supports. In addition, connections between the bridge deck and supports will be strengthened.
Geologists believe tectonic plates off the Oregon coast shift about every 300 years, causing a massive earthquake and tsunami. It has now been 321 years since Cascadia last struck, meaning it is now overdue, said the state. In addition, Klamath Falls has localised earthquakes, as evidenced by the Scotts Mill and Klamath Falls earthquakes in 1993.
The new package of bridges is at the south of US 97; a similar bundle was completed last year at the north end of the highway. Completion of the second package will make US 97 the first primary route in the state to achieve its resiliency goal.