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SR 520 - West Approach Bridge North Project: What's Happening Now?

Updated: August 23, 2016

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Project photos

See more photos of SR 520 construction
on our Flickr site .

Project overview

The West Approach Bridge North (WABN) project is underway in the Montlake area and on Lake Washington. Work hours may vary depending on the construction activity. Construction crews will continue to employ best management practices throughout construction to minimize impacts on the community and environment. Due to the dynamic nature of construction activities, construction plans are subject to change. WSDOT will provide the public with ample notice before construction activities or closures occur.

In the next few weeks, crews will begin the following activities within project boundaries:


Construction activities under a city of Seattle temporary noise variance

Construction activities

SR 520 full weekend closure: Cancelled

The full closure of SR 520, scheduled from Aug. 26 to Aug. 29, has been postponed to a later date to allow additional time for the West Approach Bridge North (WABN) contractor to make refinements to the westbound SR 520 off-ramp from Lake Washington Boulevard removal plan. SR 520 will remain open this weekend, as usual, as will the bicycle-pedestrian path on the floating bridge. As soon as a future closure date is confirmed, we will let you know through these email updates, through our SR 520 Twitter feed (@wsdot_520) and through our SR 520 Orange Page

Arboretum Waterfront Trail Closure

The Arboretum Waterfront Trail is scheduled to close Monday, Aug. 22, to Wednesday evening, Aug. 24 just north and south of SR 520, shown in the map below.

During the closure, crews plan to deliver a large vibratory hammer to install piles for temporary falsework that will support the permanent West Approach Bridge North (WABN) structure during construction. The trail is scheduled to re-open the evening of Wednesday, Aug. 24, in plenty of time for the weekend.

Click image for larger, printable version. (pdf 5 mb)

Early morning concrete pours

On Tuesday, Aug. 23, and Thursday, Aug. 24, crews plan to pour two sections of deck for the new WABN structure. These pours must start early in the morning, around 3 a.m.

A number of factors contribute to why the contractor needs to start pouring deck early in the morning. Concrete placement needs to be relatively consistent to ensure joints do not occur at unintended locations. Concrete must be placed no later than 90 minutes after mixing at the concrete batch plant so crews schedule deck pours early in the morning to avoid traffic delays to concrete trucks traveling from the concrete plant to the construction site. There are also strict temperature requirements for bridge deck concrete. Components of the concrete (primarily rock and cement) increase in temperature throughout the day. We batch concrete in the early morning so it is less likely to be heated by the sun and assist us in keeping the concrete mix within the temperature requirements. Pouring deck sections in the early morning, along with many other steps, ensures a long lasting, quality bridge.

Expect an increase in construction activities from 5 a.m. to 11 p.m. throughout the summer

In addition to regular round-the-clock construction operations, crews plan to begin an additional summer shift next week. The work that has typically been taking place during the day, between 7 a.m. and 3:30 p.m., will now take place between 5 a.m. and 11 p.m. This extra shift will enable crews to continue to make progress on the West Approach Bridge North (WABN). As crews continue to make progress on the new WABN structure and move further west, you can expect that construction of the permanent structure will move closer to the MOHAI staging area.

During this new shift, neighbors can expect to see and/or hear:

  • An increase in truck traffic in the MOHAI staging area in the early morning and late evening hours.
  • Mobilization of equipment and preparation for construction activities.
  • Crews pouring concrete shafts, columns and deck for the permanent WABN structure.
  • Crews constructing falsework to support future girders for the new WABN structure.

This work will be in accordance with the temporary noise variance (TNV) granted to Flatiron by the city of Seattle. Use of noisy impact equipment, such as jackhammers, will occur before 5 p.m. as required by the current TNV.

Continued bicycle/pedestrian detour on Montlake Boulevard

Since the 24th Avenue overpass closed last fall, bicyclists and pedestrians have been detoured from 24th Avenue to the Montlake Boulevard sidewalk, via East North Street. For your safety, please continue to use the signed detour route along Montlake Boulevard, as shown in the map below. To avoid potential conflicts between bicyclists and pedestrians with construction vehicles and off-ramp drivers, the bicycle-pedestrian path across 24th Avenue East bridge will remain closed during this temporary configuration. For more information on this topic, check out our "Frequently Asked Questions" document.

Stay tuned for updates on bicycle-pedestrian access through this area as the WABN project is completed in 2017. WSDOT secured full funding in 2015 to build the remaining west side portions of SR 520 and is currently evaluating how to phase the remaining portions of the SR 520 Bridge Replacement and HOV Program. There may be additional changes as we identify how the next phase of construction interfaces with the WABN project.

Detour route

Click image for larger, printable version. (pdf 5 mb)

City of Seattle temporary noise variances

When needed, a temporary noise variance can be granted to WSDOT by the city of Seattle to allow the contractor to conduct noisier work outside the typical hours of construction.

  • The city's noise ordinance allows for variances for nighttime work between 10 p.m. and 7 a.m. on weekdays and 10 p.m. to 9 a.m. on weekends.
  • Use of noisy impact equipment, like jackhammers, will occur before 10 p.m. as required by the temporary noise variance.
  • WSDOT inspectors will monitor nighttime activities to be sure work complies with city of Seattle requirements.

Watercraft restrictions

Crews will continue on-lake construction activities near the Montlake shoreline and the Arboretum. Cranes and other waterborne construction equipment limit water access under SR 520 near the Arboretum. Canoers and kayakers should use caution when navigating near the construction zone and stay at least 150 feet away from all construction equipment.

During construction, many of the canoe/kayak landings in the area will remain open but we recommend using the launches in the Arboretum or the University of Washington's Waterfront Activities Center. If you are unsure which boat launch to use, take a look at the map below and/or contact our construction hotline at 206-708-4657.

Click image for larger, printable version.
(pdf 262 kb)

Tree protection and removal

To make way for the temporary bridge and staging areas, crews removed trees as necessary on Foster Island and in the Montlake area. WSDOT worked with the city of Seattle to remove as few trees as possible, and will continue to mark trees for protection with orange fencing and will coordinate on replacement plantings.