Project Info

Budget Information

I-5 - NB Interstate Bridge - South Tower Trunnion Replacement

Project news

  • Crews wrapped up the full closure of the northbound span of the I-5 Interstate Bridge early, but that is not the end of the closures. The left lane of southbound I-5 approaching the bridge will remain closed around-the-clock through Oct. 2, while a new median barrier is installed. 
  • Additional information on the project can be found at
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What is the Interstate Bridge Trunnion Replacement Project?

The northbound span of the Interstate Bridge will close from Sept. 19–27, 2020 as crews replace mechanical parts that help lift and lower the bridge. The southbound span will remain open to traffic in both directions. 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 must be replaced.

During the closure, travelers crossing the Interstate Bridge in both directions will share the three existing lanes and sidewalk on the southbound bridge. A movable concrete barrier will shift the lanes to allow for two lanes of traffic to travel in the heaviest direction during commute times. For example, during the morning commute, the bridge will have two southbound lanes and one northbound lane open. During the evening commute, the bridge will have one southbound lane and two northbound lanes open.

Heavy traffic, congestion and long delays are expected in the region on I-5, I-205, I-84, SR 14 and local streets in north Portland and south Vancouver throughout construction. If travelers do not change their driving habits during the bridge closure, and if traffic levels are at normal levels, the length of back-ups on I-5 may double to 4 miles and the region may experience up to 16 hours of congestion per day.

Travelers should continue to avoid the area and use alternative modes of travel following the bridge closure, as travel delays will continue on southbound I-5 near the Interstate Bridge, from Monday, Sept. 28 through Sunday, Oct. 4, while crews close one lane of the Interstate for median barrier work.

The bridge closure is scheduled for September 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 has developed in the east trunnion growing from four inches to six-and-a-half inches in two years. If the crack continues to grow, the lift span will no longer be able to be raised. The trunnion crack was found in 1999 and is regularly monitored.

What other parts are being replaced? 

Other parts being 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.


Financial Data for PIN 400518T
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $8,653
CWA $0
Total $8,653

How can I get more information?

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