Map of properties being evaluated for pontoon construction. See
larger map.
WSDOT employees and a tour group walking on the pontoons supporting the columns and roadway of the SR 520 Evergreen Floating Bridge across Lake Washington.
Waves batter the pontoons of the SR 520 bridge over Lake Washington during a winter storm.
A tour group looks at the hatches inside a pontoon.
Overview
WSDOT is advancing pontoon construction to restore the SR 520 floating bridge in the event of a catastrophic failure. If the SR 520 bridge failed, it could take several years to construct pontoons and restore the bridge for drivers.
Crews would construct and store pontoons until they were needed for a recovery effort. If the pontoons are not needed for emergency use, they would be used for the planned replacement of the SR 520 bridge.
We are currently evaluating two sites to build a pontoon construction site. These sites are:
1. Aberdeen Log Yard (pdf 874 kb)
Ownership: Weyerhaeuser Company
Size: 55 acres
2. Anderson & Middleton Hoquiam (pdf 554 kb)
Ownership: Anderson & Middleton Company
Size: 90 acres
We have identified the Aberdeen Log Yard as the preferred alternative for building a new pontoon construction facility because the site development is less costly, and the conditions below ground pose fewer construction and schedule challenges. We considered several factors, including environmental effects, engineering constraints, construction and schedule risks, and coordination with regulatory agencies and tribal nations.
We will continue to evaluate both sites in the draft environmental impact statement, planned for public release later this year.
We will also build pontoons at an additional existing facility in Tacoma. Using this existing facility and the new pontoon construction facility together will help us expedite pontoon construction.
Why is WSDOT
building pontoons?
Pontoons are the foundation of a floating bridge and can take several years to construct. They are large, hollow concrete structures designed to support the weight of the road, plus the cars, trucks and buses that use the bridge daily. The Pontoon Construction Project is a critical step toward restoring the existing SR 520 bridge as soon as possible in the event of a catastrophic failure.
The timely availability of new pontoons is a critical element of restoring the bridge for drivers and maintaining a critical link - the SR 520 corridor - to the region's transportation system and economy.
The End Result
If the SR 520 bridge were to fail, we would be prepared with pontoons to replace the floating section of the SR 520 bridge in a timely manner. If the SR 520 bridge does not fail, we would store the pontoons until they are needed for the planned replacement of the SR 520 bridge.
Project Benefits
Safety
The pontoons for the SR 520 bridge will be designed and built to:
- Withstand a 1,000-year earthquake event.
- Withstand windstorms up to 92 mph.
Reliability
Currently, 115,000 vehicles cross the SR 520 bridge each day. There is not an available detour designed for or capable of accommodating additional traffic at equivalent speeds or travel times.
Economic and social impacts on the region are likely to be substantial if the SR 520 bridge were to fail. Advancing pontoon construction would allow the region to avoid an additional three years of SR 520 bridge closure and the resulting adverse effects on the transportation system and economy.
What is the project timeline?
2009
- Identify preferred pontoon construction site alternative.
- Begin advanced construction methods and engineering effort.
- Advertise and select contractor for design/build of new pontoon construction site.
2010
- Issue draft environmental impact statement (EIS).
- Issue final EIS.
- Begin pontoon construction at existing facility in Tacoma.
- Build new casting basin in Grays Harbor.
2012
- Begin construction of pontoons at new facility.
Financial Information
The project is funded through the following sources:
With the passage of ESHB 2211 in the 2009 legislative session, WSDOT is authorized to collect tolls on the SR 520 floating bridge beginning in 2010. This will expedite the replacement of the SR 520 floating bridge and allow us to move forward with pontoon construction.
How can I get more information?
Contact:
For comments and questions about the project, or to be added to the mailing list or e-mail list, please e-mail pontoons@wsdot.wa.gov.
To listen to a recording of the latest project information and leave a verbal comment or question, please call the project hot line at 1-888-520-6397.
To contact the project office by mail:
Pontoon Construction Project
600 Stewart Street, Suite 520
Seattle, WA 98101
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