In the mid 1960's Interstate 5 was built through Seattle in a location adjacent and immediately to the east of downtown, essentially cutting the central business district in two and separating it from the neighboring center city neighborhoods of First Hill and Capitol Hill. Though there was a citizen effort at that time to have that section of the freeway buried or at least lidded, the proponents of this effort were not successful and the freeway was completed as it exists today, which is essentially an open trench that generates air and noise pollution and cuts center city in half.
In the years since the freeway's construction, Seattle has made several efforts to stitch back together pedestrian routes disrupted by the freeway, achieving part of Paul Thiry's proposed " lid." The most visible of these efforts are Freeway Park (opened 1976), built as a lid over the freeway and connecting Downtown to First Hill, and the Washington State Convention and Trade Center (built 1982-1988) adjacent to Freeway Park, also bridging the freeway. The 7.5-acre I-5 Colonnade mountain bike park (opened 2007) uses the freeway as a roof and reconnects Eastlake to Capitol Hill.
Our hope is to continue to build on these efforts, mitigating the damage done and re-stitching center city back together. To find good examples of what can be done one need look no further than Mercer Island's Park on the Lid and it's heavily landscaped overpasses, the Median SR 520 lid currently under construction,or the planned Montlake 520 lid. Other cities around the country including Dallas, Duluth, St Louis, and Trenton have either lidded or have plans to lid their center city freeways. Hopefully these and others will inspire us to consider the same.