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SR 520 Bridge Replacement and HOV Program

The SR 520 Floating Bridge and Landings Project replaced the longest floating bridge in the world and its approaches to Evergreen Point Road in Medina, Washington.


Following over half-century of use, the existing floating bridge had exceeded its design life and was showing its age. The bridge pontoons had become vulnerable to windstorms, and its support columns are vulnerable to earthquakes.

SR 520 floating bridges in Seattle


As part of the General Engineering Consultant team (Prime: HDR, Inc.), WSP | Parsons Brinckerhoff staff was with the owner’s staff and other consultants at the project office. Our firm provided services in program and project management, advisory services, engineering, procurement support, design oversight, and construction management. One of our key roles included providing revenue forecasting and financial planning for the USD 4.6 billion program and managing the preparation of revenue forecasts and toll scenario development and evaluation. We also assisted the owner in obtaining a USD 300 million TIFIA loan. The 520 Program had multiple construction packages, the main one being the Floating Bridge and Landings Project, which had an overall approximate value of USD 1.5 billion. We were integral to the team that prepared preliminary engineering and procurement documents in a very aggressive schedule for this design-build project. Our structure engineers also advised the owner to address constructability issues with the early pontoons and provided successful solutions. Construction is complete, and the contractor opened the new floating bridge in April 2016.

One of the pontoons being towed


  • Safer structure designed to withstand windstorm up to 89 mph
  • Two general-purpose lanes and one transit/high-occupancy vehicle (HOV) lane in each direction
  • Wider, safer shoulders that will allow vehicles to pull over in the case of a breakdown
  • 14-foot-wide bicycle and pedestrian path on the north side of the bridge
  • Ability to accommodate future light rail if the region chooses to fund it in the future

Construction of the east approach


  • Program and project management
  • Tolling and financial analysis
  • Environmental documentation
  • Preliminary engineering
  • Design build procurement
  • Design and construction oversight
  • Quality management