I-5 Study Shows Benefits of Capping Urban Freeways

Putting a lid on the interstate through downtown Seattle could create new space for parks and housing, reduce pollution, and reconnect the disrupted street grid.

February 8, 2021, 8:00 AM PST

By Diana Ionescu @aworkoffiction


Freeway park over I-5

Freeway Park has spanned the I-5 in another part of downtown Seattle since 1976. | Scott Bonjukian / Freeway park over I-5

Doug Trumm reports on Seattle's "quiet" release of the Lid I-5 Feasibility Study, which highlights the benefits of capping freeways in cities. The report, funded through a community benefits package from the Washington State Convention Center expansion project, was "designed to understand the technical and financial feasibility of lidding the freeway and to look at opportunities for maximizing public benefits."

Trumm assesses the top takeaways from the study, which analyzed the potential impacts and effects of putting a "lid" on a 17-acre area of Interstate 5. According to the study, the lid could accommodate a 2.5-9.8 acre park, reconnect the street grid, reduce noise pollution, and improve stormwater drainage. The project would also create more space for housing construction in Seattle's dense downtown. "WSP did some structural engineering analysis to determine how much development could go atop the lid, and, while each section is different, the short answer is a lot. Bicknell’s 2019 article on earlier lid feasibility research had hinted midrise and some highrise development was possible. The final report estimated up to 4.7 million square feet of new housing is feasible–enough space for 4,500 homes–and between two and five million square feet of commercial/office space."

Lid I-5 Seattle's Scott Bonjukian told The Urbanist that "getting some more money for studies and planning in the next state transportation package is the next major goal."

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