When the Washington State Dept. of Transportation opened the world’s longest floating bridge to fanfare in 2016, it marked the most impressive portion of the $4.5-billion reconstruction of State Route 520. 

But by no means did it signify the completion of the project.

The first of the four final projects to complete the SR 520 reconstruction in Seattle has started now that crews have begun construction on the Montlake Project, a new SR 520-Montlake Boulevard interchange near the University of Washington. 

In August, WSDOT’s selected contractor, Graham, started preparing a work zone directly north of the existing highway and east of Montlake Boulevard. The initial work will allow for constructing a landscaped lid over the highway and an improved Montlake Boulevard interchange. 

Early work involves installation of fencing, erosion control and a water-treatment facility ahead of the removal of trees and vegetation, closure of a temporary transit-only lane along the shoulder of the westbound SR 520 off-ramp and closure of the SR 520 Trail across the 24^thAvenue East overpass. 

This fall, crews will construct a temporary on-ramp from East Lake Washington Boulevard to eastbound SR 520, followed by permanent closure and removal of the existing eastbound on-ramp that passes through the Washington Park Arboretum. In addition, crews will shift eastbound traffic onto the West Approach Bridge North, which currently carries only westbound traffic. This temporary shift allows the replacement of the 1960s-era west approach bridge with a seismically stronger, three-lane bridge for eastbound-only SR 520 traffic. 

In the future, after the Montlake Boulevard interchange improvements, crews will remove the temporary on-ramp and construct a bicycle and pedestrian bridge over the highway, east of the new Montlake lid. 

WSDOT expects the Montlake Project to run about four years. 

“We refined our delivery plan for upcoming construction to assure we keep traffic flowing while building multiple SR 520 corridor improvements,” says Denise Cieri, SR 520 Program administrator, in a statement. “These improvements are needed to replace the aging and seismically vulnerable corridor structures west of the new floating bridge.”

In 2020, crews will begin building the remaining projects — all four have been dubbed the “Rest of the West” — that includes new bus and carpool connection between SR 520 and South Lake Union via the Interstate 5 express lanes and two bridges, completing reconstruction of a highway that connects Seattle to points east such as Bellevue.

Overall, all four projects will take about 10 years to complete.

The I-5 Express Lanes Connection Project adds a new reversible transit/HOV ramp between SR 520 and the I-5 express lanes, providing enhanced service between areas east of Seattle and South Lake Union. WSDOT expects the project to begin construction in 2020 and complete no earlier than 2023.

For the Montlake Cut Bascule Bridge Project, WSDOT plans to build a second, parallel drawbridge across the Montlake Cut near the University of Washington. The project is currently in the planning phase.

A new Portage Bay Bridge and Roanoke Lid Project, expected to start in 2023 and wrap up no earlier than 2029, will replace the 1960s-era Portage Bay Bridge, currently supported by hollow concrete columns. The new bridge will replace the old structure with more security while extending SR 520’s transit/HOV system and cross-lake bicycle and pedestrian trail.

To replace the current four-lane bridge, WSDOT plans two parallel three-lane bridges, one for eastbound traffic and one for westbound traffic.

A landscaped Roanoke lid over SR 520 is included in the project, along with a 30-ft-wide bicycle and pedestrian crossing over I-5.