Construction Overview

Construction overview

Project schedule

Early work activities will occur from June 2019 to September 2019 and will focus on implementing key traffic shifts to gain access to the West Approach Bridge South structure. We expect the Montlake Project to be complete by early 2023. More schedule detail will be provided as project design and construction advances.

2019 2020 2021 2022 2023

Jan. 7, 2019
Notice to Proceed

January 2019–December 2020
Design project

June 2019–Fall 2019
Conduct early work

Fall 2019
Shift traffic to West Approach Bridge North

Remove existing west
approach bridge

Construct new West
Approach Bridge South

Construct pedestrian
land bridge

Construct Montlake lid

Summer 2021
Remove Montlake Boulevard
and 24th Avenue

Fall 2021–
Winter 2022

Landscape project

Open West
Approach Bridge
South to traffic

Complete project

Construction look-ahead

Map shows project area before construction and general locations of upcoming work.

Click image to magnify.

Photo courtesy of Google Maps.

June 2019 to September 2019—Early work activities

Summary: In this phase, Graham will complete early work with key traffic shifts to gain access to the West Approach Bridge South structure. Major elements in this phase include work affecting:


AJune 22, 2019: Close the eastbound and westbound SR 520 transit flyer stops.

BJuly 2019: Close transit-only lane along westbound off-ramp to Montlake Boulevard.

Bikes and pedestrians

CJuly 2019: Close the existing pedestrian/bicyclist access across 24th Avenue East and provide temporary detour on local streets.

DSeptember 2019: Open the temporary shared-use trail that parallels the new temporary on-ramp to eastbound SR 520. It travels under SR 520 east of 24th Avenue East and connects to the existing SR 520 Trail System north of SR 520.


EJuly 2019: Shift SR 520 westbound off‑ramp traffic for Montlake Boulevard/24th Avenue East to newly constructed off-ramp.

FAugust 2019: Shift traffic to new westbound SR 520 alignment between 24th Avenue East and Montlake Boulevard.

GSeptember 2019: Shift Montlake Boulevard on-ramp and eastbound SR 520 mainline traffic to new roadway alignment.

HSeptember 2019: Open new temporary on-ramp to eastbound SR 520.

October 2019 to April 2020—Phase 1:

Summary: In this phase, Graham will begin work on the Montlake lid structure, the Seattle Public Utilities (SPU) 54-inch water line, and the West Approach Bridge South structure. Major elements in this phase include:

IMontlake lid structure: Construct Pier 2 concrete footing and vertical support wall between Montlake Boulevard and 24th Avenue East.

JSPU 54-inch water line: Construct launching and receiving pits for the jack and bored water line installation under SR 520. Install water line and complete connections to existing systems.

KWest Approach Bridge South structure: Construct the West Approach Bridge South work trestle and begin select demolition of existing eastbound approach bridge.

Arboretum on-ramp changes to come

By the completion of the Montlake Project, the Arboretum on-ramp will have been permanently removed. We’ll add a temporary on-ramp for use during construction while eastbound traffic is shifted to the West Approach Bridge North.

Map showing location of temporary on-ramp in relation to the current Arboretum on-ramp.

Click image to magnify.

Why remove the Arboretum ramp?

Why remove the Arboretum ramp?

  • We heard strong support for removing the ramp during the robust planning and public involvement processes, resulting in the decision to permanently remove the Arboretum on-ramp.
  • During removal of the eastbound SR 520 bridge, all traffic will be shifted to the recently completed West Approach Bridge North. There is an elevation difference between these two bridges, which makes use of the current Arboretum ramp impossible.
  • Changes to the Montlake Boulevard East intersection will improve traffic flow and allow more vehicles to pass through.
What are the benefits of the temporary on‑ramp?

What are the benefits of the temporary on‑ramp?

  • The temporary on-ramp will provide direct access to eastbound SR 520 from the Montlake and Madison Park neighborhoods, minimizing impacts to mobility and operations while construction is underway.
Why is the temporary on‑ramp “temporary”?

Why is the temporary on‑ramp “temporary”?

  • The location of the temporary on-ramp would conflict with the location of the bicycle and pedestrian land bridge that will be built over SR 520.
  • The temporary on-ramp will connect to the new West Approach Bridge North while crews remove the existing south bridge.
When will traffic shift to the temporary on‑ramp?

When will traffic shift to the temporary on‑ramp?

  • Traffic will shift to the temporary eastbound on-ramp in fall 2019, before the closure of the Arboretum on-ramp.

Construction on Lake Washington

The Montlake Project will require Graham crews to work both in and over Lake Washington.

Graham will:

  • Build temporary work bridges in the shallower waters of Lake Washington and the Arboretum to:
    • Remove the old eastbound approach bridge.
    • Construct the new West Approach Bridge South.
    • Remove the Arboretum on‑ramp from Lake Washington Boulevard.
  • Work from barges in the deeper waters of Lake Washington and in the Arboretum.
  • Restrict boater access in and around the Arboretum to keep boaters and paddlers at a safe distance from the construction zone.

Illustration showing temporary structure to be used during construction.

Click image to magnify.

Boat, canoe and kayak restrictions on Lake Washington during construction

Cranes and other waterborne construction equipment will limit water access under SR 520 bridges. The exact boundaries of the construction-zone and in-water boater restrictions will be determined closer to the start of over-water construction. We will provide updates once restriction details are confirmed.

During certain periods of construction, one navigation channel may be blocked periodically for critical construction work. During these blockages, marine vessels should plan to navigate through the unaffected channel. At least one navigation channel will always be open and accessible to boaters.

Canoe and kayak landings in the area are open. Paddlers can use the launches in the Arboretum or at the University of Washington’s Waterfront Activities Center.

Photo of person canoeing near the current bridge.

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