State Route (SR) 520 is one of two major east-west roadways crossing Lake Washington, located within King County and the Seattle metropolitan area in the State of Washington. The roadway extends from its western terminus at Interstate 5 eastward across Lake Washington, intersecting with Interstate 405, and continuing east to Redmond where it terminates at SR 202. Construction stretches from Seattle's University District to 108th Avenue NE in Bellevue, with restriping continuing out to Redmond.

The SR 520 Floating Bridge and Eastside plus West Approach Bridge Projects include:

• Pontoon Construction Project - Construction of 33 bridge pontoons and a 55-acre site on Grays Harbor in Aberdeen. Pontoon construction includes 21 longitudinal pontoons 360 feet in length, weighing approximately 11,000 tons, as well as 10 supplementary stability pontoons, and two cross pontoons;
• Floating Bridge and Landings Project - Construction of a new six-lane floating bridge across Lake Washington to replace the aging four- lane bridge, including removal of the existing floating bridge;
• Eastside Project - Widening of SR 520 between the eastern shore of the lake and I-405 to six lanes, constructing three community-connecting lids and other corridor-wide improvements to add a HOV lane in each direction; and
• West Approach Bridge Project - Construction of a permanent west approach bridge structure to connect westbound traffic from the floating bridge to the Montlake Boulevard Interchange near the University of Washington in Seattle, as well as to complete the bicycle/pedestrian path from the eastside to Seattle.

The project will provide an efficient connection between the major population areas and employment centers between Seattle and the region's eastern suburbs, including Bellevue and Redmond. The project includes the addition of new HOV lanes and the utilization of an all-electronic toll collection system to improve travel time reliability. Wider lanes and shoulders also prevent congestion, further improving travel times and roadway safety. The project also focuses on multi-modal accessibility by creating new links to the area’s transit, bicycle, and pedestrian paths. According to WSDOT, construction of the project is estimated to generate approximately 1,400 jobs. TIFIA financing allowed WSDOT to raise an additional $200 million in construction funding compared to conventional financing means, accelerating the project’s timeline, while providing flexibility to increase scope.