I-376 Commercial Street Bridge Replacement
| Location: | Pittsburgh, PA |
| Owner: | PennDOT |
| Construction Company: | Fay, S&B USA Construction |
| Project Status: | Under construction since May 2024, expected completion in summer 2027 |
Fay, S&B USA Construction (Fay) replaced the Commercial Street Bridge on I-376. Although the structure had undergone three major rehabilitations since opening in 1951, cracking and its overall deteriorated condition led PennDOT officials to determine that a full replacement was the most effective long-term solution.
The original bridge, a dual open-spandrel concrete arch structure located between the Squirrel Hill Tunnel and the Braddock Avenue Interchange, played a vital role in connecting Pittsburgh’s eastern suburbs to the central business district. To avoid major disruptions to traffic on this critical roadway, Fay constructed an arched delta frame bridge alongside the original structure and had a maximum 25-day closure of the I-376 Parkway to demolish the original bridge and slide the new structure into place using accelerated bridge construction (ABC) techniques—the team reopened the bridge in just 17 days, 8 days early, earning the following praise from PennDOT Secretary Mike Carrol:
“This is the most impressive bridge project I’ve ever seen,” said Carroll on visiting the bridge site after the slide operation was complete. “I am not a civil engineer, but you do not have to be one to appreciate what has already been accomplished here… an engineering feat.”
Additional work included relocating two sewer lines and lowering the Forest Hills exit ramp. The project will continue into summer 2027 as Fay returns Commercial Street below the bridge to its original alignment, removes the temporary bridge foundations, and clears all remaining debris. Fay will also restore Frick Park’s Nine Mile Run stream and hiking trail, and plant approximately 5,000 new trees and shrubs to restore the project site.
Pittsburgh’s Latest Engineering 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 was constructed south of the existing structure on temporary foundations to maintain traffic on the original bridge.
- The completed bridge weighs just over 22 million lbs, including 7.4 million lbs of structural steel for the 825-lf steel delta frame girder with seven girder lines and 11,800 cy of concrete. The longest girders are 126 lf.
- Fay constructed 275 lf of new retaining wall to support the new structure’s approaches. To build the wall within in the constraints of a small footprint, Fay constructed a temporary trestle adjacent to the parkway for crane and drill rig access.
- The median shoulders were increased to a standard 4 ft and the right shoulder to 12 ft to allow space for emergency vehicle passage and future maintenance.
- Fay temporarily moved Commercial Street and the Nine Mile Run Trail of Frick Park below the current and future bridges, and erected protective cover.
- Due to clearance limits under the original bridge, micropile ranging from approximately 30 ft to 100 ft long were used to anchor the new structure’s permanent piers and abutments.
- To complete the slide, PennDOT had originally planned to shut down the I-376 Parkway for a maximum of 25 days starting in July 2026 for demolishing the current bridge and sliding the new structure into position. Fay’s team reopened the bridge after only 17 days—nearly a week early.
- A specialized system of 42 hydraulic jacks and skid shoes slid the new bridge into position at a pace of about 14 ft per hour, moving the bridge 96 ft on the first day and the remaining 6 ft the next morning — a total of 102 ft.
- Demolition crews dismantled the original structure using a combination of conventional demolition and a controlled implosion in less than a week.
- Upon completion in 2027, Fay will fully restore the surrounding green space by 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.
Challenges
Limiting the impact of lane closures and detours was of the utmost importance to PennDOT because I-376 and the bridge provide a vital connection between Pittsburgh’s eastern suburbs and the central business district for an average of 100,000 vehicles per day.
Additionally, the project posed several environmental challenges, as the bridge is located above Pittsburgh’s Frick Park, including a stream and hiking trail.
Solutions
The lateral sliding ABC method was chosen over staged construction because it minimized the impact to traffic on I-376 and helped avoid more than four-plus years of long-term lane closures and traffic restrictions. Fay built the new bridge adjacent to its permanent location on temporary foundations, then slid it into place. Fay also brought its extensive demolition experience to expedite dismantling the existing bridge in preparation for the slide.
This project contained key design-build elements; in a close collaboration between PennDOT (owner), HDR (engineer of record), COWI (Fay’s construction engineer), and Fay (general contractor), the design-build team engineered and constructed the temporary piers (2) and temporary abutments (2) supporting the new bridge to work with the specialized skidding system specified for the lateral slide.
To address the project’s environmental impact and protect both the park and trail, Fay took several precautionary measures to limit the impact on the project site and restore its original state once the project is complete. The bridge design was created in collaboration with the Department of Environmental Protection, and the construction plan ensured that proper mitigation measures were maintained. Additionally, UpstreamPgh, the Pittsburgh Parks Conservancy, and other stakeholders participated in the plan review process and provided feedback on the site restoration, erosion and sediment control, and post-construction stormwater management plans. This feedback was incorporated into the final plans.
Construction
The new bridge weighs just over 22 million pounds (11,000 tons) and was slid into place using ABC techniques. The new arched delta frame was built directly beside the existing structure on temporary foundations, allowing the original bridge to remain open to traffic.
Fay designed and constructed temporary foundations anchored by H-piles to support the new bridge and anchored the new permanent foundations under the existing bridge using micropiles due to the low clearance. The temporary foundations will be removed toward the end of the project. Fay also constructed new abutments anchored by micropiles below each end of the existing bridge.
To limit disruptions to I-376 traffic during approximately 140 deliveries of steel two times per week over five months for the new structure’s delta frames, the project developed a process for trucks to cross the highway at the Squirrel Hill Tunnels plaza and drive down the construction access road to the laydown yard. Compared to a lengthy closure of one bridge lane for a crane to lift and lower the steel to the yard below, this alternative only required the roadway to close for approximately five minutes per delivery.
Prior to and during the closure, Fay’s construction and demolition teams worked 24/7 to advance the project. Fay’s Demolition Group conventionally removed the bridge deck, barriers, and overhangs in approximately four days, followed by a controlled implosion using 2,500 charges that dropped the columns and arches. Demolition crews then processed and cleared enough debris for the next phase.
The slide operation utilized Mammoet’s specialized skidding system to precisely jack and move the new bridge from the temporary to permanent foundations on continuous rails. A total of 42 skid shoes were spread over four primary support runs: two at the bridge piers and one at each of the abutments. During the slide, the skidding system moved the bridge approximately ten feet at a time until it reached its final position over the newly constructed abutments and piers. Then the structure was lowered onto its permanent substructure and secured.
Throughout and after the slide, Fay construction crews continued the finishing work to prepare the abutments, approaches, and other preparations.