Project Info

I-5 - NB Interstate Bridge - South Tower Trunnion Replacement - Complete October 2020

What is the Interstate Bridge Trunnion Replacement Project?

In fall 2020, crews replaced mechanical parts that help lift and lower the northbound span of the Interstate Bridge. The southbound span remained open to traffic in both directions during the work. At the center of each wheel that lifts and lowers the bridge is a 20-inch diameter trunnion. A crack has developed in the trunnion on the northbound bridge’s south tower and the trunnion needed to be replaced.

The bridge closure was scheduled in the fall due to the low river levels, which allow most vessels to travel under the Interstate Bridge without a bridge lift. This is essential for marine traffic. The Columbia River is an international shipping channel and, before any section of the river under the bridge is closed, we must coordinate with the U.S. Coast Guard, shipping companies and other river users.

Why is WSDOT working with the Oregon State Department of Transportation (ODOT) to replace the trunnion?
ODOT takes the lead on identifying and administering the preservation and maintenance needs on this bridge.

Why does the trunnion need to be replaced?

A crack had developed in the east trunnion growing from four inches to six-and-a-half inches in two years. If the crack were to grow, the lift span will no longer rise. The trunnion crack was found in 1999 and was regularly monitored.

What other parts are being replaced? 

Other parts replaced, include:

  • Sheave, bearing assemblies and cables.

How many vehicles use the Interstate Bridge?

Over 45 million vehicles travel over the bridge annually.

The End Result

  • Safety: Continued safe operation of this vital bridge, linking Oregon and Washington.
  • Maintain infrastructure: Continued use of the bridge by nearly 130,000 daily users.

Project Benefits
Replacing the northbound span's south tower trunnion allows for continued safe operation of this critical interstate drawbridge. The northbound bridge was opened to traffic in 1917 and the southbound bridge was opened in 1958.

What is the project timeline?

  • 2016: Preliminary engineering and design
  • 2017: Design and environmental work continues
  • 2018-2020: Design and public outreach 
  • August–October 2020: Construction 

What is the estimated cost of the project?

The construction is estimated to cost approximately $13,000,000, shared equally between Washington and Oregon.


Source Amount ($ in thousands)

  • Pre-Existing Funds (PEF) - $8,653
  • Total - $8,653

How can I get more information?

Jessica Bull, JLA Public Involvement, 503-235-5881
Tamara Greenwell, WSDOT Communications, 360-905-2056