Case Study: I-579 Urban Open Space Cap

October 24, 2023

Case Study: Building a Park Over an Interstate Highway

The construction of Interstate 579 (I-579) through Pittsburgh, PA, more than 60 years ago separated the Hill District from the downtown. With the help of federal grant money from the Transportation Investment Generating Economic Recovery program, the Urban Open Space Cap project creates a new modern park with room for outdoor events and reconnects the disenfranchised district to the city’s economic core.

The I-579 project functions as a “cap” over the interstate that provides a walkable link from the Hill District to the downtown. The new park includes art installations, story walls, outdoor classroom space, and an amphitheater, as well as bike and pedestrian pathways.


I-579 Urban Open Space Cap Team:



There are no standard design codes for bridges carrying a park, so the expert project team developed specific criteria to meet the complex demands associated with the intended use of the park area. They evaluated both the final in-service condition of the bridge and the construction loadings associated with placing the fill and amenities on the bridge.


Key project attributes:

  • As Pennsylvania’s first park over an interstate, this urban, 3-acre green space reconnects Pittsburgh’s historic Hill District with the city’s downtown.
  • The precast concrete adjacent box-beam superstructure is both economical and strong enough to support the unique park loading, including up to 5 ft of soil.
  • The precast concrete beams also support the hanging lighting for the vehicular tunnel below.

Project scope:

  • The project used 12,190 linear ft of 48” × 66” precast, prestressed concrete box beams.
  • The maximum span length is 121 ft.
  • Erection of the 126 precast concrete adjacent box beams took 38 days, and the entire project was completed in November 2021.

Check out the complete case study to get all the details:


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