• Project

SR 520 Floating Bridge and Landings Project

Project overview

We replaced the world's longest floating bridge – a four-lane, 1960s-era structure – with a safer, six-lane bridge designed to withstand stronger windstorms and waves. Opened in April 2016, the new bridge also added shoulders for disabled vehicles and a separated, 14-foot-wide path for cyclists and pedestrians.

Bridge construction began in spring 2012 and was completed in summer 2017.
Project status
$849 million

What to expect

We opened the West Approach Bridge North in 2017 to carry three lanes of westbound-only traffic across Union Bay from the new floating bridge to Seattle. However, to enable the removal and replacement of the old, structurally vulnerable eastbound bridge over Union Bay, we temporarily shifted all traffic onto the West Approach Bridge North in 2019, with two lanes in both directions and no shoulders. To promote traffic safety on this structure, we temporarily lowered the speed to 40 mph.

When a new, three-lane eastbound bridge is completed in 2023, the north bridge will revert to a westbound-only span and the speed limit across Union Bay will increase.

Area map of the completed SR 520 Floating Bridge and Landings Project. The new floating bridge extends from the east shore of Lake Washington, in Medina, to Union Bay, about a mile from the lake's western shore in Seattle.