Creating a Stormwater Park over an Interstate: Restoring Community Connections with a Highway Cap and Green Infrastructure

The Interstate 579 'Cap' Urban Connector Project and creation of the new three-acre Frankie Pace Park provides a vital urban green space link and repairs broken community connections between Pittsburgh's historic Lower Hill District and the city's downtown business and cultural centers. Over 60 years ago, as part of 1950s and 60s national urban renewal initiatives and interstate highway expansion, over eight thousand Hill District residents were forcibly displaced by the construction of the new Crosstown Boulevard through Pittsburgh's Lower Hill District. The Lower Hill District was a vibrant and primarily Black neighborhood with a rich history of Pittsburgh born Jazz greats and the famous Pittsburgh Crawfords of the professional Negro League baseball. Access to the downtown area was significantly impacted for residents that remained adjacent to the eight-lane highway and its 40-ft deep concrete canyon. The construction of Frankie Pace park is a literal and metaphorical bridge, helping repair broken connections for the Hill District neighborhood residents and spur economic development. The $32 million park was opened to the public on November 22, 2021. The park is named in honor of longtime Hill District resident and community activist, Frankie Mae Pace. The park consists of over 250 newly planted trees, 4000 perennials and shrubs, 0.7 acres of pervious lawn, six (6) terraced rain gardens, 300 linear feet of artistic surface trench drains, and over 500 CY of topsoil placed on top of the cap structure. The 52,000 SF cap over the interstate serves as one of the largest public green roof projects in the region, if not the nation. The design of the cap structure was iterative process considering key design feature such as the weight of the engineered soil, landscaping plans, and potential event spaces on the structure. All these elements work together to capture, detain, and filter stormwater prior to entering the Pittsburgh Water and Sewer Authority's combined sewer system at the bottom of the site. Overall, an estimated 1.5 to 2.0 million gallons of stormwater is managed annually in the park and the lawns can store up to 6 inches of rain during a single rainfall event capturing a total of 2.1 acres of impervious area. In addition to the enhanced stormwater features, the park intertwines artistic and interpretive artwork from local artists allowing park users to learn the history of the Hill District and the importance of stormwater management. The presentation, if selected, will provide a brief history of the historical importance of Pittsburgh's Lower Hill District, an overview of how the project came to be, explain the design and construction of the cap and associated stormwater management features, and quantify the hydrologic and water quality performance of the site through design hydrologic and hydraulic modeling. The presentation will also highlight federal funding opportunities related to highway cap projects including USDOT's Reconnecting Communities Pilot Program. Attached are images of the before and after photos of the site and photos of the trench drain system and tiered rain gardens at the bottom entrance to the park..