Issaquah Highlands is a large mixed-use development designed to promote community-centered design principles and walkability. By necessity, an arterial roadway bisected the most important part of the commercial and retail area. Free pedestrian access across the arterial was necessary to implement the design goals for the community, but the estimated $1.2 million cost of an elevated and dedicated pedestrian bridge was not feasible. RH2 proposed a lightweight prefabricated aluminum bridge that could be installed between two existing retaining walls due to its light weight and subsequent low structural loads. This configuration minimized footing and abutment design and construction costs.
To use an existing MESA-type retaining wall as a foundation, the bridge loads needed to be less than the weight of a standard commercial truck since an H20 load rating was designed into the wall backfill system. Through location selection, careful design detailing, and clever structural design, the finished bridge was installed at a cost of $340,000, less than a third of the original cost of the proposed bridge.
The bridge, which was built off-site in a computer-controlled manufacturing facility, was shipped intact and lifted into place during a 2-hour road closure. The structure is the definition of efficient infrastructure in that O&M costs are virtually eliminated (no painting, no corrosion) and pedestrians are free to move about the retail/commercial core without impacting capacity on the arterial roadway.