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.
Map of the property being evaluated at the Port of Grays Harbor. See
larger map.
A tour group looks at the hatches inside a pontoon.
A tugboat tows a completed floating pontoon in 2007.
Overview
WSDOT is advancing pontoon construction to restore the existing SR 520 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.
We are evaluating a property at the Port of Grays Harbor as a potential location for the construction of pontoons. Construction of a pontoon site could begin in 2010, after the environmental process is completed in 2009.
Crews would construct and store pontoons until they were needed for a recovery effort. If the pontoons are not needed for emergency use, they could be used for the planned replacement of the SR 520 bridge or to repair or replace other WSDOT floating bridges.
What are bridge pontoons?
Pontoons are the foundation of a floating bridge and can take several years to construct. They are large hollow concrete structures designed to supported the weight of the road, plus the cars, trucks and buses that use the bridge daily. Depending on the bridge design, pontoons can be as long as a football field and as tall as a two-story building.
How do pontoons float?
Despite being heavy concrete structures, pontoons float because the water they displace weighs the same as the pontoons, roadway and traffic they support.
Why is pontoon construction important?
The SR 520 Pontoon Construction Project is a critical step towards restoring the existing SR 520 bridge as soon as possible in the event of a catastrophic failure.
SR 520 is a critical link in the regional transportation system. A catastrophic failure of SR 520 could have severe effects on the regional transportation system and economy. Constructing and storing pontoons now would allow the region to avoid an additional three years of closure on SR 520 in the event of a catastrophic failure.
What are the next steps?
We are preparing an environmental impact statement (EIS) to evaluate potential effects to the surrounding environment from constructing and storing pontoons. Building pontoons requires a facility that is along a port or waterfront and is large enough to construct several pontoons simultaneously. We are also examining different locations at Grays Harbor to moor pontoons until they are needed. We expect to release the draft EIS in early 2009.
Why is the Port of Grays Harbor a potential location?
We are reviewing the property owned by the Port of Grays Harbor in the project’s environmental impact statement because it has several features needed to construct pontoons for catastrophic failure planning:
- Sufficient capacity to build several pontoons simultaneously.
- Waterfront access.
- Railroad access.
- Access to deep water.
- No known cultural resources.
- No known chemical contamination.
- Immediate availability.
How will the public be involved?
We are gathering comments from the public, Tribal nations, and federal, state, and local agencies on the project's draft purpose and need, range of alternatives, and environmental topics we will analyze in the project's environmental impact statement.
PLEASE NOTE: We have revised the project's purpose and need statement since the Jan. 17 public scoping meeting in Hoquiam.
Please visit the project library for information presented at the Jan. 17, 2008, public scoping meeting in Hoquiam, and a summary of comments (pdf 68 kb) received during the comment period.
How can I get more information?
WSDOT encourages you to learn about the proposed SR 520 Pontoon Construction Project and give us your input.
There are several ways you can become involved in the project:
- Get information online - check back here for the most up-to-date information.
- E-mail us at pontoons@wsdot.wa.gov with your concerns, comments and questions
- Call us at 1-888-520-6397.
- Write us a letter:
Attn: Susan Haupt, environmental impact statement manager
SR 520 Bridge Replacement and HOV Project
600 Stewart Street, Suite 520
Seattle, WA 98101