Lid I-5

Lid I-5 Structural System Investigation

The I-5 Lid project addressed a long-standing need to reconnect neighborhoods in downtown Seattle that were divided by the interstate. Building on a broader feasibility study conducted with WSDOT and WSP, this work investigated structural systems that could support a lid over I-5 and help evaluate how new public space, housing, and development might be accommodated above the freeway. The project considered girder concepts for different column-line layouts using structural steel and precast concrete, along with related effects on foundation loading, vehicle clearances, and other site constraints. It also examined how differing elevations at the east and west edges of the lid could affect access across the structure, with particular attention to the complexity of I-5 ramps and potential barriers to accessibility that would need further study. In addition, 3D CAD models of existing conditions and possible lid layouts were created to support continued analysis and future phases of the broader Lid I-5 effort.