This paper provides an overview of the unique approach taken by a multi-discipline team consisting of Washington State Ferries (WSF) personnel, structural and geotechnical engineers, and economists to perform a risk assessment of a portion of WSF's aging timber trestle inventory. The intent of the assessment was to establish the cost-effectiveness of trestle replacement compared to refurbishment by quantifying risk for a range of seismic events and incorporating that risk into WSF's Asset Management Model. Failure scenarios developed using site-specific characteristics such as trestle condition and site seismicity were coupled with life cycle cost modeling techniques to assess the risks associated with doing nothing, refurbishing the existing trestles, or completely replacing the trestles at seven ferry terminals. This paper describes the approach developed to create an economic model and evaluate the efficacy of trestle upgrade and replacement options. A case study of the trestle at the Vashon Island terminal is included to demonstrate direct implementation of the approach and the results obtained.
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