SR-520 Evergreen Point Floating Bridge and Landings Commissioning
Washington State Department of Transportation
Seattle, WA

Complete: Final commissioning complete October 2017

Size: Bridge: 7,710 feet long; Maintenance Facility and Dock: 25,000 SF  (approx.)

Cost: $1.5 billion

The new SR-520 Bridge is the longest floating bridge in the world.


Lake Washington is more than 200 feet deep and covers 34 square miles, necessitating that bridges over it should float. The new 1.46-mile long SR-520 Bridge is the longest floating bridge in the world and an iconic update to the region’s transportation plan. Wood Harbinger provided commissioning services as well as electrical and fire protection design engineering for this important community project. Our commissioning team worked on the fire protection, electrical, and HVAC systems as well as a bridge’s specialty systems, such as the bridge control, cathodic protection, leak detection, emergency boater response, jib cranes, and lighting systems.

Wood Harbinger developed a tailored commissioning plan, witnessed system installation and startup, developed and performed integrated functional testing for the systems, tracked issues, and conducted regular meetings to resolve those issues and maintain project progress. The bridge control system commissioning program was very detailed. We tested each component (e.g. a float switch), then the sub-systems (e.g. the leak detection system), and then system interactions (e.g. the leak detection system triggering an alarm in the Maintenance Facility Building). We tested all 1,600 float switches in the pontoon cells, which are connected in a network of catwalks and accessed via sealable hatches and ladders. Unique endurance tests were implemented to ensure life safety systems were operational before the bridge was opened to the public.