Washington State Highway Seismic Screening Tool (HSST)
The U.S. Department of Homeland Security’s Regional Resiliency Assessment Program (RRAP) undertook the Washington State Transportation Systems RRAP project in 2017 to assess the seismic vulnerabilities of that state’s transportation system to a Cascadia Subduction Zone (CSZ) earthquake. The specific goal of that project was to assess the vulnerability of, and prioritize, transportation infrastructure for moving goods and supplies from Incident Support Bases to Federal Staging Areas within Washington State following a CSZ earthquake. As part of this analysis, Argonne National Laboratory (Argonne), with input and support from the Washington State Department of Transportation (WSDOT) maintenance and pavements offices and state geotechnical engineer, developed the Highway Seismic Screening Tool (HSST) to inform a system-level analysis of highway recovery and reopening times. This report provides a full discussion of the HSST’s development, implementation, and results for the CSZ scenario earthquake. The primary outcome of the HSST is to determine the approximate reopening times of highway segments or bridges damaged by a CSZ magnitude 9.0 seismic event. This is done by calculating the permanent ground deformation (PGD) caused by soil liquefaction along state highways, which can cause significant damage or displacement of highway pavement structures. The term “reopening time” is different from “restoration time” and is intended to represent the approximate amount of time that would be needed to return highways to a minimum state of repair sufficient to support the limited movement of emergency and response vehicles. Additionally, the HSST is referred to as a “screening tool,” as it uses network- or system-level asset management information that WSDOT provided to assess seismic-related hazards and vulnerabilities of highways; it does not conduct an asset-level engineering analysis of seismic-related vulnerabilities. Accordingly, the results of the HSST analysis should only be used for system- or corridor-level planning and investment, and not for engineering or management decisions at the asset level. The HSST is also applied to assess the exposure of statewide rail systems to soil liquefaction and PGD hazards. However, little information is available about the sensitivity or vulnerability of railways and rail yards to such hazards, and therefore researchers were unable to determine approximate reopening times for the state’s rail system following a CSZ earthquake.