I-376 Commercial Street Bridge Replacement

Pittsburgh’s Next Infrastructure Marvel: A Sliding Bridge

Project Highlights

• The Parkway East (I-376) is one of the most heavily traveled highways in western Pennsylvania, supporting over 100,000 vehicles per day
• The new bridge will be constructed south of the existing structure on temporary foundations while maintaining traffic on the original bridge
• The completed bridge will weigh just over 19 million pounds (9,000 tons)
• The project will use 7.4 million lbs of structural steel, including an 825-lf steel delta frame girder with seven girder lines, 11,800 cy of concrete, and 275 lf of retaining wall
• The median shoulders will be increased to a standard 4 ft and the right shoulder to 12 ft to allow space for emergency vehicle passage and future maintenance
• During a maximum closure of 25 days in summer 2026, the original structure will be removed using conventional and explosive demolition, and the new structure will be slid into place and tied into the I-376 roadway
• Fay temporarily moved Commercial Street and the Nine Mile Run Trail of Frick Park below the current and future bridges, and erected protective cover
• At completion in 2027, Fay will fully restore the surrounding green space—planting grass and over 5,000 trees and shrubs, returning the Nine Mile Run hiking trail to its original location, and restoring the stream’s natural bed by removing a previously existing concrete structure.

Though the Commercial Street Bridge has had three major rehabilitations since opening in 1951, cracks and its overall condition led PennDOT officials to determine that replacing the bridge is the best option.
 

Challenges

Maintaining traffic on the existing Commercial Street Bridge is critical because I-376 and the bridge connect Pittsburgh’s eastern suburbs to the central business district. PennDOT wanted to lessen the impact of lane closures and detours throughout the project to replace the bridge. Environmental protection is also key, as the existing and proposed bridges are located above Pittsburgh’s Frick Park, including a stream and hiking trail.
 

Solution

In this Design-Bid-Build project, Fay was engaged to bring its decades of heavy-civil construction and bridge-building expertise to help PennDOT use ABC techniques to construct a sliding bridge. The sliding ABC method was chosen over staged construction because this sliding technique will minimize the impact to traffic on I-376 and was determined to be a better solution for this project. The new bridge will be built adjacent to its permanent location on temporary foundations, then slid into place. Fay also brings extensive demolition experience, which will be used to dismantle and remove the existing bridge in 2026 in preparation to slide the new structure into place.

To address the project’s environmental impact, Fay worked with PennDOT, Pittsburgh Parks Conservancy and community stakeholders to develop solutions that will protect this section of park, trail and stream throughout construction, as well as to restore the site at the end of construction.
 

Construction

Once completed, the new bridge will weigh just over 19 million pounds (9,000 tons) and will be slid into place using ABC techniques. The new arched delta frame structure is being built directly beside the existing structure on temporary foundations while the original bridge remains open to traffic.

Fay will build temporary foundations anchored by H-piles to support the new bridge, and will construct the permanent foundations under the existing bridge using micropiles due to the low clearance. The temporary foundations will be removed at the end of the project after the new bridge has been moved onto the permanent foundations.

Once the new bridge has been completed, the original bridge will be closed to traffic for a maximum of 25 days for demolition and removal of the original bridge through a combination of conventional and explosive demolition, then the new bridge will be slid into place. To perform this move, the new bridge will be lifted using hydraulic jacks and moved approximately three feet at a time until it reaches its final position over the newly constructed abutments and piers. Then, the structure will be lowered onto its permanent substructure and secured.
 

Animation of the Construction, Demolition and Sliding Phases

This PennDOT video shows how the new bridge will be constructed beside the current bridge, the demolition and removal of the current bridge, and how the new bridge will be slid into place. 

The slide operation for the new Commercial Street Bridge will span a distance of 100 feet, moving from its temporary position on the south side of the existing bridge once the existing structure has been demolished. To prepare for this operation, the new bridge is being built on four temporary sliding support towers located at the temporary abutments and piers. These support towers create the sliding rail surface of the heavy lifting and moving skid system, which will be used to lift and maneuver the entire bridge in a controlled environment. Prior to the explosive demolition of the current bridge, the slide operation will undergo testing, and protective measures will be implemented at the new permanent abutment and piers to minimize damage during demolition. Throughout the operation, the structure will be monitored for any displacements beyond acceptable limits until it reaches its final position, where it will then be lowered onto its permanent bearings. Once the permanent bearings are secured, the bridge will be disconnected from the skid system, allowing crews to complete the remaining bridge approaches and open the new bridge to traffic.

Site preparation work included the relocation of two sewer lines and the lowering of the Forest Hills exit ramp. Additionally, Commercial Street and Nine Mile Run Trail in the valley below were temporarily relocated and a cover was placed below the existing bridge to protect the site and the public from overhead debris. Additionally, Fay constructed a temporary causeway over Nine Mile Run stream to provide access to both sides of the park area while protecting the stream’s aquatic habitat from debris and pollutants during construction and demolition activities.

After completing the project, removing the temporary foundations, and clearing debris, landscaping will include planting approximately 5,000 new trees and vegetation in this part of Frick Park to restore the site and mitigate the project’s environmental impact.
 

Our Team is Ready to Help You

To learn how our team of heavy construction and demolition experts can help solve your infrastructure challenge with safe and innovative solutions, contact us.