By: Roger Eaton, Nicholas Burdette, and Justin Doornink, Contributing Authors
The Hill District is a historically African-American neighborhood in Pittsburgh, and for decades, it was the cultural center of Black life in the city. Through the early 1950s, the neighborhood benefited from easy pedestrian access to the adjacent downtown Area.
Then, in the summer of 1956, some 1,300 structures along the Hill District’s border with downtown were razed to clear space for the Civic Arena (where the Penguins, the city’s NHL team, began calling home in 1967) and other planned developments, displacing about 1,500 families. Shortly after this, the construction of Interstate 579 further disconnected the remaining Hill residents from downtown with tall retaining walls and a depressed interstate.
Pittsburgh is one of many cities that built highways that divided Black communities. In recent years, interest has increased across North America in the idea of using highway caps — also known as lids, decks, or covers — to mend historic wrongs and reconnect neighborhoods split decades earlier. The basic idea is simple, though the technical considerations are not: Cover a highway with a deck or series of decks, creating new uses and connections over the roadway.
To rebuild access and community connectivity, Pittsburgh leaders conceived of the I-579 Urban Open Space Cap project: a green space over the interstate that once divided this section of the city. Completed late last year, this urban cap has bridged the “concrete canyon” and created a tree-lined park over I-579.
Mending Historic Wrongs
According to the U.S. Department of Transportation, 475,000 households were displaced between 1957 and 1977 to make way for federal interstate construction. Today, cities are seeking methods to reconnect those communities that were separated long ago.
In Pittsburgh, the Civic Arena was demolished in 2011, but the Hill remained isolated from downtown by a sea of parking lots and I-579.
The new Frankie Pace Park over I-579, named after a Hill District civic leader, changes that. The cap and adjacent sidewalks cover about 350 feet of interstate with a 3-acre park that features art, story walls, an outdoor classroom, performance and green spaces, permanent music elements, fully accessible pedestrian/bike pathways, and integrated seating. In the next few years, nearby parking lots will be replaced with an urban street grid and new development to complete the connection. The cap also is intended to serve as a catalyst for development in the area.
Complex Agency Coordination
Because of their locations and the infrastructure involved, highway caps require the cooperation of multiple agencies. Federal, state, and local entities are all involved, with private and nonprofit organizations also frequently included.
In Pittsburgh, the Sports & Exhibition Authority of Pittsburgh and Allegheny County acted as the lead design agency with the city of Pittsburgh as the cap owner. The Pennsylvania Department of Transportation provided oversight with additional review from the U.S. Department of Transportation and Federal Highway Administration. HDR served as design lead for the project.
As project planning progressed, the long list of partners and stakeholders faced questions that will apply to any similar project: Who is going to be responsible for maintenance of which parts of the finished structure? Who will own and have jurisdiction over the space on top? What approvals are needed from which agencies?
The answers to these questions are often unique to each project. Other communities considering similar projects should gather buy-in from all participating agencies, and then communicate early and often about project needs and plans.
Close Community Collaboration
Many highway caps are designed to heal the effects of past development. This means that it’s important to listen to residents about that impact and understand how to address it now. It can take time and effort for government entities to rebuild trust that was lost through development that damaged the communities decades ago. Project teams should understand up front that they are working in neighborhoods where their motives might be treated with suspicion.
The Pittsburgh cap team used an extensive community listening and design review process to obtain input from residents and stakeholders. Trust was built through focused community meeting/design sessions at venues in the heart of the neighborhood, held at times convenient to residents. Residents’ ideas were incorporated through the park landscape design, as well as in integrated art commissioned from local artists. Community organizations based in the Hill District were involved, informed, and interested in progress, including offering letters of support for an initial $19 million TIGER grant that helped fund the construction of the cap.
Unique Technical Needs
Cap design and construction requires a wide range of technical expertise beyond what’s needed for most bridges. Design teams often need to address details more often considered in tunnels, such as air ventilation, fire safety, egress, and lighting. In Pittsburgh, $1 million of the $30 million project was spent on lighting, to ensure that the vision of drivers entering and exiting the space underneath the cap is not adversely affected.
Caps are also often placed in dense urban settings, with complex structures and extensive underground utilities already in place. Constrained construction sites are common, and designs need to consider how to build new foundations without damaging existing structures or utilities and with minimal impacts to the interstate. In Pittsburgh, work had to be staggered to meet this constraint, with a very limited space available for construction equipment and labor crews.
Loading needs of the new structure also need to be determined early in planning, with the future use of the space affecting the design. In Pittsburgh, the park includes a notable elevation change from one side to the other, requiring extra fill that could have significantly added to its weight. To avoid this, the team buried geofoam blocks in the deepest portion of the park, then covered these with soil. These blocks weigh less than 3 pounds per cubic foot but provide support for the load above.
Another challenge of placing park soil on top of a bridge structure is ensuring water does not penetrate the structure deck, where it could freeze and cause damage to the structure. Multiple redundant waterproofing layers were used on the I-579 cap to prevent this condition. These included waterstops between structure units, layers of bituminous paper and waterproofing membrane on the deck and backwalls of the superstructure, and a 4-inch fiber-reinforced concrete protection slab to prevent damage to the waterproofing from future excavation.
A Catalyst for Continued Development
For decades, the Hill District was Pittsburgh’s Black cultural center. The new cap creates convenient, accessible pathways that connect to transit and subway systems and restores the access to downtown enjoyed by residents decades ago. Those community connections will be further strengthened as new development revitalizes the area. Since completion of the cap, ground has broken for a new office building, and plans for a new entertainment space are being developed.
This model and the opportunities it represents can be applied in many other communities throughout America. By pairing technical expertise with a deep understanding of affected communities, agencies and cities can use infrastructure to heal wounds caused by poorly planned designs of the past.
