Decades of Program Management Leadership Across a 7-Mile Highway Corridor

• World's longest floating bridge
• Safety, sustainability and multimodal upgrades across 7-mile corridor
• Seven major projects delivered under one megaprogram umbrella

The SR 520 Bridge Replacement and High Occupancy Vehicle (HOV) Program is a $5.7 billion effort to modernize a critical 7-mile corridor of Washington’s State Route 520, from I-405 in Bellevue to I-5 in Seattle. It addresses seismic vulnerability concerns while improving safety, transit options, and biking/pedestrian access. This phased, community-oriented program reflects strong local demand for resilient infrastructure, efficient travel and vibrant neighbourhood livability.

As the program’s general engineering consultant, HDR has provided comprehensive leadership and technical expertise for nearly two decades. Our team provides key program management and risk management, cost and schedule controls, and financial forecasting while guiding design development, including the oversight of three design-build contracts. We have also led environmental planning and permitting, urban design, real estate services, and robust community engagement to maintain transparency and trust. These efforts have been complemented by constructability reviews, document management and claims analysis, helping the program align with Washington State Department of Transportation's (WSDOT) goals for safety, sustainability and multimodal connectivity.

A Program of Projects

Developing a strategic delivery plan was an early task for our team, part of determining the sequence of projects to address key goals and maintain long-term progress. The entire corridor was developed under one environmental impact statement with additional environmental assessments prepared to advance the Eastside Transit and HOV project and pontoon construction in Grays Harbor. Altogether, the SR 520 program consists of seven major projects:

1. The Pontoon Construction Project: Our team led preliminary design and documentation for this project, which began construction in 2011. It built a casting basin facility at the 55-acre Pontoon Construction Project site in Aberdeen, Washington. The largest concrete pontoons needed for the subsequent floating bridge project were cast at this site. These pontoons — some of which were 360 feet long, 75 feet wide and nearly 30 feet tall — were the largest ever built in Washington. Transporting the pontoons required an open ocean tow through the Strait of Juan de Fuca to Puget Sound before  transiting the Ballard Locks to reach Lake Washington.  The project was completed in 2015.
2. Eastside Transit & HOV – This project, which was constructed from 2011-2015, improved 2.3 miles of the HOV system on the east side of the corridor. It included two general-purpose lanes and one transit/HOV lane in each direction, the first leg of a 14-foot-wide regional, cross-lake bicycle and pedestrian path, and wider shoulders. It also provided environmental and community enhancements such as stream improvements, fish-friendly culverts and wetlands restoration, noise-reduction systems, stormwater detention and treatment facilities, and three new highway lids.
3. Floating Bridge & Landings – Construction began in 2012 on the 1.5-mile floating bridge and associated new interchanges. The award-winning bridge was designed to withstand stronger windstorms while expanding capacity from four lanes to six. It also added shoulders and a bike/pedestrian path. When completed in 2016, the 7,700-foot bridge was the longest of its kind in the world. 
4. West Approach Bridge North – Built from 2014 to 2017, the West Approach Bridge North extended SR 520’s westbound lanes from the new floating bridge to Seattle’s Montlake neighbourhood. Designed to be seismically resilient, it provides a safer, more reliable connection and a dedicated transit/HOV lane. 

5. I-5 Express Lanes Connection – This project, constructed 2021-2025, created a dedicated transit/HOV reversible ramp connecting the SR 520 HOV lanes with the I-5 Express Lanes. The ramp will be available for service once the Portage Bay Phase is completed and HOV lanes are extended from Montlake to I-5.
6. Montlake Project – The Montlake project, completed in 2025 after six years of construction, replaced a vulnerable eastbound bridge and added an HOV/transit lane, lid, and land bridge east of Montlake.
7. Portage Bay Bridge / Roanoke Lid – The last of the major projects in the corridor, construction began in 2024 on a new Portage Bay Bridge and a landscaped lid in Seattle’s Roanoke neighbourhood. The project will replace the current aging structure with a seismically resilient bridge and add a highway lid, open space and bike/pedestrian trail connectivity. It is scheduled to be completed in 2031. 

Design Expertise

Our team’s design leadership has shaped every element of the SR 520 corridor. We developed conceptual and preliminary designs for interchanges, bridges and urban features, including a six-lane corridor with reversible transit/HOV operations. Our team refined floating bridge designs to accommodate future light rail and integrated a 14-foot-wide bicycle and pedestrian path that links regional trails to downtown Seattle and the University of Washington. 

Environmental stewardship guided our work, from stormwater systems embedded within pontoons to wetlands restoration and fish-passage improvements. We also designed noise walls and retaining structures with context-sensitive finishes to blend with the natural and urban landscape. Each design decision reflects our commitment to multimodal connectivity, environmental responsibility and community character.

Project Controls and Oversight

Managing a program of this scale requires disciplined oversight, and our project controls team has delivered just that. Working alongside WSDOT, we implemented a suite of tools to track cost, schedule and risk across all projects. Our team developed and maintained an interface schedule to synchronize timelines and identify potential conflicts, while producing detailed progress reports for stakeholders and federal agencies. 

Cost management efforts included early-phase budgeting, earned value analysis and market-based estimating. Risk management was integrated into every phase, combining quantitative assessments with value engineering strategies to reduce exposure and improve delivery certainty. Through transparent reporting, claims analysis and proactive schedule monitoring, the team provided WSDOT with actionable insights and confidence in program performance.

Community Transformation

As a long-term partner and program leader, our team of local professionals has collaborated with WSDOT as well as Seattle agencies and communities to transform an aging corridor into a resilient, multimodal spine for the Puget Sound region. As the SR 520 program nears completion in the coming years, HDR remains a trusted partner delivering complex infrastructure at scale, advancing healthier and more connected communities.