A major scope of work on the project is construction of a braided ramp system that separates traffic from vehicles merging onto State Route 522 and vehicles entering I-405 from a local street. Flatiron reengineered the ramp and roadway geometry to avoid construction of a 70-foot-high retaining wall in the middle of a historic landslide area, reducing retaining wall quantities on the project by 167,000 square feet, cutting the earthwork in half.

Other value engineering and design changes included using precast concrete barriers instead of cast-in-place, and a precast bridge instead of a cast-in-place bridge, eliminating paving by reusing existing asphalt or doing an overlay instead of a full replacement.

The corridor includes new advanced storm water treatment systems, including 15,000 linear feet of new media filter drains, and, for the first time on a WSDOT project, 10,000 linear feet of compost-amended biofiltration swale. Work includes extensive wetland and stream mitigation work to restore salmon habitat in Yarrow Creek, adjacent to the project.

Flatiron closely coordinated with multiple stakeholders on the project, which included the owner, a separate tolling vendor, the cities of Bellevue, Kirkland, Bothell and Woodinville, the utility owners in each city, the metro and the tolling authority.

In addition to congestion relief, the new roadway will increase safety by reducing sideswipe and other heavy traffic-related accidents.