[4] The freeway gains a set of HOV lanes and continues east on a pair of causeways through the marshlands of Union Bay and Foster Island, at the north end of the Washington Park Arboretum.

[7] Tolls are collected electronically using the state's Good to Go pass or by mail, and vary based on time of day and the vehicle's number of axles.

[8] The freeway reaches the eastern end of Lake Washington at Evergreen Point in northern Medina, where it travels under a landscaped park lid and next to a median-side bus station.

[12] The freeway crosses the Sammamish River and turns east, passing to the south of the Redmond Town Center mall and Bear Creek and to the north of Marymoor Park.

[22][23] New towns along the eastern shore of Lake Washington were established in the late 19th century and initially served by steamship ferries, bringing passengers and goods to and from Seattle.

[40][41] Construction of the western approach, an expressway between the Roanoke Interchange, Portage Bay, Montlake, and the Washington Park Arboretum, began in early 1962.

[42] The eastern approach was constructed between 1962 and 1963, connecting the bridge to Medina, Secondary State Highway 2A in southern Houghton, and Northup Way—a local road that continued east towards Redmond.

[43][44] The Evergreen Point Floating Bridge opened on August 28, 1963, along with the Roanoke Expressway, part of the Seattle Freeway,[45] and the eastern approach to Houghton and Bellevue up to a temporary interchange with 104th Avenue Northeast.

The state government announced plans in 1968 to begin construction on the remaining freeway to Redmond, via a northeastward course through the Overlake area and across Marymoor Park.

[64] Contract bidding for the last segment was halted in 1978 by a lawsuit filed by a group of Eastside residents in opposition to the freeway, claiming that its environmental impact had been improperly assessed.

[65] U.S. District Judge Morell Edward Sharp ruled in favor of the state government in March 1979, allowing for the bid to be awarded to a contractor.

[69][70] The completion of SR 520 spurred new development in Downtown Redmond and the Overlake area, contributing to major traffic congestion on the freeway.

[73] In late 1996, the highway's terminus at SR 202 was converted from a signalized intersection to an interchange, including an overpass connecting to Avondale Road.

[76] A new interchange was built at Northeast 40th Street in 2000 to serve the Microsoft Redmond Campus and other nearby employers, along with a set of collector–distributor lanes through the area, and ramp meters to manage traffic flow.

[77][78] Between 1994 and 2002, portions of a multi-use pedestrian and bicycle path on the north side of the freeway were completed and opened, forming a 4.5-mile-long (7.2 km) trail from northern Bellevue to Marymoor Park in Redmond.

[88][89] The package also funded $40.9 million to engineer and acquire land for an expanded interchange at 124th Avenue Northeast in Bellevue to serve the Spring District.

[90] Since the opening of the Evergreen Point Floating Bridge in 1963, several proposals from local governments have requested the construction of a parallel span or additional pontoons to increase capacity and add infrastructure for rapid transit and bicyclists.

[94][95] The bridge underwent a major rehabilitation in 1999, including a seismic retrofit, and increased resistance to stronger sustained winds, to extend its life expectancy to 20 to 25 years.

[98][99] The $5.69 billion megaproject,[100] which encompasses the SR 520 corridor between I-5 and I-405, was funded using a state gas tax and electronic tolls on the floating bridge introduced on December 29, 2011, to repay construction bonds over a 40-year period.

[98] The project, completed in 2014, also included the construction of new bus stations and direct access ramps, new interchanges, park lids covering SR 520, and a multi-use trail.

[111] Improvements to the remaining segment of the SR 520 corridor, between I-5 and the floating bridge, were initially left unfunded, but underwent design and environmental review.

[114][115] The eastbound approach to the floating bridge was opened to limited traffic in July 2023 and expanded to carry three lanes in its permanent configuration the following month.

[112][118][119] The express lane ramp, planned to cost $68 million, was expected open in early 2024, but it was later delayed to 2030 due to the inability to increase transit service on the corridor.

[120][121] The Portage Bay bridge and Roanoke lid are expected to begin construction in late 2024 and be finished in 2031, in tandem with the express lane ramp, at a cost of up to $1.4 billion.