Rendering of single-level extradosed bridge (Interstate Bridge Replacement Program)

Extradosed single-level, truss double-level, and girder moveable span are among the bridge types under consideration for the new I-5 bridge across the Columbia River between the states of Washington and Oregon. Renderings released by the Interstate Bridge Replacement Program at the start of March show what the replacement could look like. However, the project planners have said the designs are not final and do not represent the full range of options being considered.

Rendering of single-level finback bridge (Interstate Bridge Replacement Program)

The designs envision the new bridge will be larger and higher than its predecessor to facilitate river traffic and accommodate shared-use paths and light-rail in addition to vehicle traffic. Another change in the proposed plans suggests the new structure might bypass the mid-river Hayden Island in contrast to the existing bridge which touches down on the island’s northern bank.

Rendering of moveable steel girder bridge (Interstate Bridge Replacement Program)

The existing 1,078m-long bridge carries three vehicle lanes of Interstate 5 which is considered a vital trade route for regional, national and international economies. The structure’s two vertical lift steel through-truss spans were built in 1917 and 1958. When opened, the bridge reaches a vertical clearance of 53.6m above the river.

Rendering of double-level truss bridge (Interstate Bridge Replacement Program)

The old bridge was slated for replacement as it was found to be expensive to upkeep and seismically vulnerable due to its timber pile foundations being set in sandy soil and its location being at risk of a severe earthquake.  

Rendering of single-level steel girder bridge (Interstate Bridge Replacement Program)

The replacement project was jointly initiated by the Washington and Oregon Departments of Transportation in 2019. WSP was assigned as main general engineering consultant on the project. 

Rendering of single-level concrete bridge (Interstate Bridge Replacement Program)

The replacement project is expected to cost US$6 billion in total (link opens in new tab). Construction is tentatively expected to start in 2026.