Drivers exiting the Pennsylvania Turnpike and heading into Pittsburgh most likely will be using I-376 to get there. The highway travels through a wooded area and then enters the Squirrel Hill Tunnel, a twin-bore opening stretching nearly a mile long. The interstate passes through the Swissvale area, east of the city within sight of the Monongahela River.
The Commercial Street Bridge serves as an important conduit to this major artery, carrying approximately 100,000 vehicles into and out of the city daily. Built in the 1950s, the bridge has been targeted for replacement by the Pennsylvania Department of Transportation (PennDOT). The project is expected to cost $95 million.
The undertaking began in the summer of 2024, and the construction team expects to finish by 2027.
PennDOT photo
The highlight of the project is the use of Accelerated Bridge Construction techniques to laterally slide the new bridge onto the existing alignment of I-376 (Parkway East). This effort would be one of the largest slide projects done in the state.
The prime contractor for the job is Joseph B. Fay with the bridge slide performed by Mammoet, a company that specializes in heavy lifts and moves. This gigantic undertaking will allow the new bridge to be constructed without interrupting traffic on the Commercial Street Bridge. The new bridge will be a steel delta frame structure and assembled on top of the temporary foundations and slider plates which will allow for the bridge to slide into place once it is completed.
The construction team has scheduled the slide to be ready in 2026. Once the new bridge is slid into place the old bridge will be crushed and reused for aggregate.
Road Relocation
Last year, contractors accomplished numerous steps that will make the bridge slide possible, including reconstructing and lowering the westbound I-376 off-ramp to exit 78B. This will help to accommodate over-height trucks when this ramp is used for the I-376 detour.
This work will enable traffic to seamlessly connect when the new bridge is moved into place. The team also relocated sewer lines and portions of phased Intelligent Transportation Systems (ITS). The ITS is an electronic communication that helps traffic coordinators keep traffic flowing smoothly.
Workers have begun a busy schedule for 2025, which will include installing new signs, temporary and permanent piers, abutments and piles for temporary and permanent foundations and steel assembly. The construction team plans nine overnight full closures and detours of eastbound I-376, a full weekend closure and detour of I-376 in each direction. The team also plans 35 extended weeknight single-lane restrictions on eastbound I-376.
Work this year also will prepare for next year's most innovative piece of the project: the bridge slide. Contractors will be constructing the new steel bridge on temporary foundations. When the new bridge is completed, the old Commercial Street Bridge will be removed, and the new bridge will slide into place. Before traffic can resume, safety features will be installed such as guard rails and medians. As those tasks are being completed, workers will connect auxiliary roads and new paving will connect the bridge so traffic can resume.
PennDOT photo
PennDOT performed a yearlong traffic study and found the month of July to be the lowest traffic volume with vacations and schools/colleges off for the summer.
The work team will prepare for the big slide by building foundations for the bridge. Much of the work will be done this year said John Myler, who is directing the overall project for PennDOT.
"Our team needs to install over 15,000 linear feet of micropiles for the new bridge," said Myler. "We will be drilling and installing steel casing down to the rock. Then, we will install 1-inch steel bars in the rock socket, followed by filling up the casing with grout all the way up to the foundation footing."
Although this process is often used for retaining walls, the team decided to use the procedure in this case because of the minimal foundation for the old bridge and because of the minimal clearance under the old bridge to install the new foundations.
The new deck will be 10 in. thick and will be placed prior to the move. Once the bridge has been moved into place, workers will overlay the deck with a 1-in.-thick layer of polyester polymer concrete. Myler said this material will protect the bridge deck from the chloride traditionally used to keep the bridge free from road salt used in the winter.
"The epoxy is messy to mix and finish," said Myler. "But in the end, it bonds to itself and leaves no joints for water to get into. The overlay should seal the deck and keep the chloride from getting through to the deck. We are hoping that when the epoxy wears out in 20 years, we will still have a like-new bridge deck." CEG
(All photos courtesy of PennDOT.)
