• Overview
• Greater mobility for SR 520 users
• Regional congestion relief
• New SR 520/I-5 transit/HOV connection
• Transit improvements complete on Eastside, floating bridge
• A light rail-ready SR 520 floating bridge

When the original, four-lane SR 520  floating bridge across Lake Washington opened in 1963, fewer than 1 million people lived in King County, and Bellevue, the Eastside’s largest community, had only about 13,000 residents. Since then, the county’s population has more than doubled, while Bellevue’s has swelled tenfold. And the area’s robust growth continues: The Puget Sound Regional Council predicts the Central Puget Sound region will add 1.2 million more workers and another 1.8 million residents by 2050.

Traffic congestion on an old, unimproved stretch of SR 520.

The region’s growth has long overtaxed SR 520’s six-decade-old design. Prior to the start of the highway’s reconstruction, vehicle speeds during peak commute times routinely averaged below 20 mph.

In addition to replacing aging bridges at risk of failure in a severe earthquake or windstorm, the SR 520 Bridge Replacement and HOV Program is making significant improvements to the SR 520 corridor that will enhance the public’s transportation options and mobility for generations to come. Many of these enhancements are now complete, while others are fully funded for construction in the coming years.

Greater mobility for SR 520 users

We are constructing new, multimodal highway features that provide greater mobility options for all users, including drivers, transit riders, bicyclists, and pedestrians.

Riders board a Seattle-bound bus from SR 520's new Evergreen Point transit station in Medina.

When SR 520 is fully built out, the highway’s corridor improvements will give the public:

• A dedicated transit/HOV lane in both directions between Seattle and the Eastside, providing bus riders and carpoolers safer, quicker and more reliable travel while freeing up space in the general-purpose lanes.
• Safer transit connections, with median transit stations at Evergreen Point Road and 92nd Avenue Northeast, and a regional transit hub atop a new freeway lid in Montlake.
• Direct-access ramps at Mercer Street, Montlake Boulevard, and 108th Avenue Northeast that make entering and exiting the highway safer and more reliable for buses and carpools.
• A regional, cross-lake bicycle and pedestrian path alongside SR 520, between I-5 and Redmond, with connections to other local and regional trails, bus stops, and light rail.
• Five community-connecting highway lids that provide better connections to transit stops, shared-use paths, local streets, and SR 520 itself.
• A floating bridge design that accommodates light rail on SR 520 if the region chooses that retrofit option in the future.

Regional congestion relief

The improved SR 520 corridor will enhance highway safety, reduce congestion and lower travel times for bus riders, carpoolers and drivers. According to traffic studies (pdf 13.9 mb), the regional benefits of SR 520 reconstruction will include: 

• More reliable and quicker trips between Seattle and the Eastside. When compared to a no-build scenario with no improvements to SR 520, peak-period travel time from Seattle to Bellevue in the HOV lane should decrease by up to 25 minutes. Drivers in the general-purpose lanes should save about a half hour.
• Improved on-ramp merge conditions, and reduced traffic queues onto local arterials.
• Wide shoulders for disabled vehicles to pull off and not block traffic, eliminating a frustrating feature of the old, shoulderless four-lane roadway.
• Significant economic savings thanks to less time spent in traffic slowdowns and backups. A study of the rebuilt Eastside segment (pdf 182 kb) found that drivers there are expected to save 1.4 million hours of travel time every year – and $467 million in travel-time savings.

When fully built out, SR 520 will have transit/HOV lanes along its entire length, from Redmond to I-5. Shown here is a stretch of the Eastside’s reconstructed corridor.

• A 39% increase in the number of people using SR 520's HOV lanes daily, by 2030.
• A 15% to 17% increase in the number of people SR 520 carries during the morning and evening commutes as more people use buses and carpools. This increase in person trips occurs with only a 5% to 10% increase in vehicles on the highway.
• A 5% to 10% reduction in vehicle miles traveled on SR 520 and a nearly 10% reduction in vehicles’ greenhouse gas emissions when compared to a no-build option with no highway improvements.

New SR 520/I-5 transit and HOV connection

To help meet rising travel demand between the Eastside’s growing cities and Seattle’s booming South Lake Union area, we plan to construct a reversible transit/HOV connection between SR 520 and the I-5 express lanes, with direct access to Mercer Street. We expect this new connection to open as early as 2023 for transit. The connection will open to carpools after a new Portage Bay Bridge and Roanoke lid are completed, in approximately 2029.

Learn more on our SR 520/I-5 Express Lanes Connection Project webpage.

Transit improvements complete on Eastside, floating bridge

A bus stops at the Evergreen Point median transit station in Medina before crossing the new SR 520 floating bridge.

We opened major transit improvements on SR 520’s Eastside segment in 2014. Two years later, we further enhanced the corridor’s transit operations when we opened the new, six-lane floating bridge on Lake Washington. These improvements are prioritizing bus trips, reducing unsafe merges, and providing a more reliable trip for transit riders between the Eastside and Seattle.

The Eastside’s new transit infrastructure includes:

• One continuous transit/HOV lane on SR 520 in each direction from Medina to I-405, with transit/HOV lanes moved to the inside.
• Landscaped lids with ADA-compliant, median transit stations below the lids at Evergreen Point Road and 92nd Avenue Northeast, providing a safer, more pleasant rider experience than the previous roadside stops.
• Direct-access ramps at 108th Avenue Northeast that make it safer and quicker for buses and carpools to enter and exit the highway's HOV lanes.

The new six-lane floating bridge, unlike its four-lane predecessor, also has transit/HOV lanes operating in both directions.

(Note: During Montlake Project construction, we are removing the old, 1960s-era west approach bridge over Union Bay and building a new bridge for eastbound traffic, parallel to the westbound bridge that opened in 2017. During this time, all traffic between Montlake and the floating bridge travels on the new westbound bridge, with two general-purpose lanes in each direction, and no transit/HOV lanes.)

A light rail-ready SR 520 floating bridge

Although there currently are no proposals or funding to build light rail across SR 520, WSDOT engineers designed the new SR 520 floating bridge so that additional supplemental pontoons could be added in the future to support the weight of light rail. As shown in the graphics below, the bridge could accommodate light rail either by converting the bridge's transit/HOV lanes to light rail, or by adding more width.

Adding light rail to the SR 520 floating bridge would require analysis of transit connections and routes, additional funding, regional decision-making, and a separate environmental review process. WSDOT estimates a cost of $150 million to $200 million to construct and install the 30 additional pontoons needed to support light rail. There would be additional costs associated with the bridge-deck expansion and other infrastructure, including rail lines.

Floating bridge layouts for light rail

 The current SR 520 floating bridge

With two general-purpose lanes and one transit/HOV lane in each direction.

Scenario 1: With light rail displacing the transit/HOV lanes

Scenario 2: With light rail in addition to the transit/HOV lanes