I-90 Bridge Design & Light Rail Assessment

  • Client:
    Washington State Department of Transportation (WSDOT)
  • Completion Date:
  • Key Collaborators:
    Sound Transit
  • Project Type:
    Marine Infrastructure
  • Service Categories:
    Marine Engineering
    Ocean Engineering
  • Challenge:
    Re-evaluation of the Homer M. Hadley Memorial Bridge for light rail traffic.


The Washington State Department of Transportation (WSDOT) first engaged Glosten’s ocean engineering services for the I-90 bridge four decades ago. The initial approach we used to evaluate the wind and wave forces impacting I-90 and two other Washington bridges is still used by the state today in conjunction with the latest wind data, 3D hydrodynamic analysis codes, and commercially available structural analysis tools. We have continued to support Washington’s floating bridges ever since, and in 2019 we were tapped to assess the Homer M. Hadley Memorial Bridge for light rail traffic.



The East Link extension of the light rail will route east- and west-bound trains across the I-90 bridge. Since this is a floating bridge, large waves can stress the structure causing it to bend and flex, decreasing the bridge’s lifespan. To increase the bridge’s service life, Sound Transit is required to limit train movements during large wave events. As a result, monitoring and predicting wave conditions a day in advance would allow Sound Transit to safely plan for train delays.

Glosten proposed to predict wave heights based on wind speed data with an algorithm that could feed into the operational input for the rail system. Our ocean engineering team was hired to help with the model verification and testing of a third-party-built wind and wave prediction system that would do just that. We are currently testing the physical sensors and systems that will collect wind and wave data in preparation for commissioning to ensure their reliability and accuracy before the opening of the East Link extension.

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