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What is the Interstate Bridge Trunnion Replacement Project?

In September 2020, the northbound bridge of the Interstate Bridge between Vancouver and Portland will close for up to two weeks as crews replace a cracked trunnion and other parts that help lift and lower the bridge. 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.

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 long will the northbound bridge be closed?

The northbound bridge will close for two weeks in fall 2020. During the closure period, travelers crossing the Interstate Bridge in both directions will share the three lanes and sidewalk on the southbound bridge. Movable concrete barrier will allow two lanes of traffic to travel in the heaviest direction. For example, during the morning commute, two southbound lanes (and one northbound lane) will open for traffic. Crews will move the concrete barrier mid-day to provide two northbound lanes (and one southbound lane) for the evening commute.

During this time the bridge will not raise. To pass under the bridge, marine traffic will use the high span of the bridge to pass through. The closure will allow crews to safely bring in heavy equipment to remove and replace the trunnion, which is 20 inches in diameter and 4 feet long.

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
• Summer/Fall 2020: Construction scheduled to begin

What is the estimated cost of the project?

The project is estimated to cost between $5,000,000-$10,000,000.