The “No Build” alternative does nothing to the existing facility. The project area would remain as
it exists today. The "No Build" alternative (often
called "no action") is required by state and federal regulations to be evaluated in the project's environmental impact statement. This project is unique because the existing SR 520 bridges
may not remain intact through 2030, the project’s
design year. Read below for more details. |
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The fixed and floating spans of the Portage Bay and Evergreen Point bridges are aging and are vulnerable to wind storms and earthquakes.
In 1999, WSDOT estimated that the floating bridge will last 20 to 25 years based on the existing structural integrity and the likelihood of severe windstorms.
Storm wind vulnerability – floating portion of the Evergreen Point Bridge
- Originally designed to withstand sustained wind speed of 57.5 miles per hour (mph)
- Rehabilitated in 1999 to withstand sustained winds of up to 77 mph.
- The current WSDOT design standard for bridges is to withstand a sustained wind speed of 92 mph. In order to bring the floating bridge up to current design standards to withstand 92 mph winds, the floating bridge must be completely replaced.
Seismic vulnerability – fixed structures of the Evergreen Point Bridge and Portage Bay Bridge
- Pier columns are hollow and at risk of failure in an earthquake.
- Retrofitting pier columns to current seismic standards is difficult, expensive and cost prohibitive. Pier columns must be completely replaced.
If nothing is done to replace the Portage Bay and Evergreen Floating bridges, there is a high probability both structures could fail and become unusable to the public before 2030. WSDOT cannot predict when or how these structures would fail, so it is difficult to determine the actual consequences of doing nothing.
Scenarios of what could happen
To illustrate what could happen between now and 2030, two scenarios representing the extremes of what is possible will be evaluated as part of the No Build Alternative. These two scenarios are Continued Operation and Catastrophic Failure.
Continued Operation Scenario
- This scenario is the baseline we use to compare the other alternatives.
- SR 520 would continue to operate as it does today as a 4-lane highway with substandard shoulders and without a bicycle lane.
- No new facilities would be added and no existing facilities (including the R.H. Thompson Expressway Ramps near the Arboretum) would be removed.
- WSDOT would continue to maintain SR 520 as it does today.
- This scenario assumes the Portage Bay and Evergreen Point bridges would remain standing and functional through 2030.
- No catastrophic events (such as earthquakes or high winds) would be severe enough to cause major damage to SR 520 bridges.
Catastrophic Failure Scenario
- Both the Portage Bay and Evergreen Point bridges would be lost due to some type of catastrophic event. Although in a catastrophic event, one structure might fail while the other stands, this Draft EIS assumes the worst-case scenario—that both bridges would fail.
- This scenario assumes that both structures would be seriously damaged and would be unavailable for use by the public for an unspecified length of time.
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