• Major Project

SR 520 Bridge Replacement and HOV Program

Panorama view of SR 520 across Union Bay. In the foreground is a work zone where crews are construction a new, parallel bridge. The highway is surrounded by a residential neighborhood.

Major Project overview

The SR 520 Bridge Replacement and HOV Program enhances travel safety and mobility with modern, structurally stronger bridges, as well as substantial transit and roadway improvements along this urban corridor. Built in stages, the improvements extend from I-405 in Bellevue to I-5 in Seattle.

Timeline overview

2011 - 2031

Major project status



$5.69 billion

Major project alerts

SR 520 Program
David Goldberg
Community Liaison & Ombudsman

SR 520 advisories

For the most up-to-date information about SR 520 construction activities and planned road closures, visit and bookmark our SR 520 Construction Corner and its interactive construction map. Read the latest SR 520 news in our weekly email update. You can also view Montlake Project construction photos taken 'round the clock by our four mounted construction cameras.

Plans and process

The SR 520 Bridge Replacement and HOV Program is rebuilding one of the Puget Sound region's busiest highway corridors. We’re replacing vulnerable bridges, improving traffic safety, enhancing regional mobility and providing new and better options for nonmotorized travel. To keep traffic flowing during reconstruction, we are rebuilding SR 520 in stages – mainly from east to west. You’ll find more information about the phased work on our Related Projects tab.

Public engagement plays an important role in the planning and project designs of SR 520’s reconstruction. You will find key SR 520 design reports on our Community Engagement tab. 

End result

Here’s what the public will see when the SR 520 corridor’s reconstruction is complete:

  • New, structurally resilient bridges over Lake Washington, Union Bay and Portage Bay.
  • A dedicated bus/carpool lane in each direction between Seattle and Bellevue.
  • Three transit stations for local and regional bus routes.
  • Five landscaped freeway lids over SR 520 – three on the Eastside, two in Seattle.
  • A 14-foot-wide walking and cycling trail between Seattle and Bellevue, a bicycle-pedestrian “land bridge” over SR 520 in Seattle’s Montlake neighborhood and a 30-foot-wide bicycle and pedestrian crossing over I-5.
  • A reversible transit/HOV lane along I-5’s express lanes between the SR 520 and Mercer Street interchanges, with reversible ramps at both interchanges.
  • A system to capture and filter out stormwater pollutants from SR 520 highway runoff.

Benefits of this program

Improves safety

  • The new floating bridge, designed to withstand a 100-year storm, is supported and stabilized by more than twice as many pontoons (77 vs. 33), with heavier anchors and stronger anchor cables. The old SR 520 floating bridge outlived its design life and risked failure in a severe windstorm.
  • The new bridges over Union Bay and Portage Bay will be built to current seismic standards, able to withstand a once-in-a-1,000-year earthquake. The old bridges, supported by hollow columns, are vulnerable to collapse in a severe earthquake.
  • The new floating bridge’s roadway deck sits higher above the water than the old bridge’s roadway. This allows WSDOT crews to perform important maintenance and safety work from the pontoon deck beneath the roadway.
  • Direct-access ramps at 108th Avenue Northeast allow safer and easier highway access for buses and carpoolers. The transit hub on a new Montlake freeway lid over SR 520 also will have direct-access ramps to and from the highway.
  • The highway’s transit/HOV lanes are located along the median, eliminating conflicts between buses and vehicles merging onto or off SR 520's general-purpose lanes.
  • The ADA-compliant transit stations are separated from highway traffic, providing safer access for bus riders.
  • The rebuilt highway’s new interchanges have longer on- and off-ramps with improved sight lines for drivers. 

Relieves congestion

  • The old corridor has only two general-purpose lanes in each direction, with no HOV lanes. The rebuilt corridor features two general-purpose lanes and one bus/carpool lane in each direction.
  • The old highway has no shoulders for disabled vehicles. The rebuilt corridor has full shoulders, which eliminate lengthy backups and traffic safety hazards from disabled vehicles stuck in a travel lane. 
  • Travel time from Seattle to Bellevue in the HOV system, when completed, should decrease by up to 25 minutes during peak periods. Drivers in the general-purpose lanes should save about a half hour. Those time savings compare to travel time under a no-build scenario with no improvements to SR 520.
  • A study of the rebuilt Eastside segment of SR 520 found that drivers should save 1.4 million hours of travel time and $467 million in travel-time savings every year.

Provides multimodal options

  • The 14-foot-wide SR 520 bicycle and pedestrian trail provides a new cross-lake connection for both commuting and recreating, with connections to local trail networks. When SR 520 construction is complete, the SR 520 Trail will extend from Seattle to Redmond.
  • The addition of transit/HOV lanes and the cross-lake shared-use trail provide more travel options and greater reliability to accommodate growth in the region.
  • new, reversible transit/HOV lane will connect SR 520 and Seattle’s I-5 / Mercer Street interchange. Bus and carpool riders will have more reliable trips between the Eastside and Seattle’s South Lake Union and downtown neighborhoods
  • The SR 520 Program helped develop the Montlake Multimodal Center, a key regional transit hub next to Husky Stadium. This hub provides connections to local and regional buses, regional bicycle and pedestrian trails and the University Link light rail station.
  • The new floating bridge is designed to accommodate the addition of light rail – with a retrofit – if voters choose to fund that option in the future.

Enhances the environment

  • The rebuilt highway and its fixed-column bridges will capture and carry roadway runoff to on-land stormwater retention and treatment sites. These sites filter out pollutants and improve water quality in the Lake Washington watershed. Also, the new floating bridge captures runoff and screens out polluting sediments before the runoff flows into the lake.
  • The improved highway reduces carbon emissions by enhancing transit use and nonmotorized travel.
  • The SR 520 Program supports several major enhancement projects in the Washington Park Arboretum. One effort is to remove old ramps that ran through the park. These include the old SR 520 on- and off-ramps and never-used R.H. Thomson "Ramps to Nowhere."
  • Additional SR 520 environmental projects are enhancing parks, streams, wetlands and other natural areas across the region to mitigate for the effects of project construction.
  • The SR 520 Program installed eight large, fish-friendly culverts on the Eastside to aid fish migration.

Visit our Environment tab to learn more about the program's environmental initiatives.

Promotes a smarter design

WSDOT employs a planning process called "practical design" that engages the community early on to help us make project decisions that produce cost-effective, sustainable results. On the SR 520 Program, practical design has reduced costs and improved results in the following ways:

  • A modified design for the West Approach Bridge North reduced the number of in-water columns by 40 percent, which saved money and shrank the bridge’s environmental footprint.
  • Smarter highway technology on the new floating bridge – variable speed-limit signs and reader-board displays with real-time traffic information – boosts traffic efficiency and helps drivers make safer, smarter decisions.
  • A smarter design for the Montlake lid retains desirable public space and improves transit, bicycle and pedestrian accessibility while removing costly ventilation and maintenance systems.
  • A reduced, 45 mph speed limit on a new Portage Bay Bridge will lower the noise caused by tires on bridge pavement and lessen noise in surrounding neighborhoods.