Adaptive Reuse of Mount Carbon Historic Bowstring Truss

In 2021, the Pennsylvania Department of Transportation (PennDOT) District 5-0 and PennDOT’s Office of Multimodal Transportation discovered an abandoned 100-foot truss spanning the Schuylkill River in Mount Carbon, Pennsylvania. The ownership of the bridge was a mystery, yielding a thorough collaboration among the Schuylkill County Municipal Authority (SCMA), the Schuylkill River Greenway Association (SRGA), Federal Highway Administration (FHWA), PennDOT, and community advocates to determine the bridge owner, which was revealed to be the SCMA.

Initially erected in Palo Alto, the Mount Carbon bridge is one of only three remaining bowstring trusses in Pennsylvania. The truss, which dates back to 1878 and is eligible for the National Register of Historic Places, was previously moved from Palo Alto to Mt. Carbon in the late 1800s.

PennDOT identified this project as a pilot to promote the adaptive reuse of historic bridges that cannot be used on today’s highway network but are worthy of preserving for other purposes. PennDOT assumed ownership of the bridge restoration and asked GFT to complete the truss design for the new owners, SRGA.

The intensive bowstring truss preservation involved carefully removing, rehabilitating, and relocating the truss five miles north of the Mount Carbon site. Construction warranted lifting the bridge from its abutments and moving it to a staging area for disassembly. The construction team made significant documentation and markings during disassembly before shipping the parts to an Ohio blacksmith.

Without formal drawings from the original historic structure, our team inspected the bridge, taking detailed measurements and assessing conditions to preserve as many structural members as possible. A combination of original materials, technology, and new details were used to replace members in a way that maintained the structure’s original character. Because the existing bridge didn’t have a deck, railing, or stringer elements, the team used a postcard from the early 20th century to develop a modern pedestrian railing suitable for its trail use. With this postcard as the only known record of its original character, we designed a railing that retained its historic bridge preservation qualities while modernizing it to meet current standards — ensuring the bridge’s historic nature was carefully preserved.

To respect the truss’ unique features, the project used hot-driven rivets, where possible, in lieu of modern high-strength bolts. When the cast connections needed to be replaced during truss construction, PennDOT and the contractor, Fabcor, fabricated new cast elements instead of designed weldments. This decision further respected the original character by using similar 19th-century technology and reinforced the benefit of stakeholder collaboration.

The bridge reinstallation occurred in an active business zone, requiring careful coordination to ensure uninterrupted business operations. New abutments were constructed at Coal Creek Commons, and the staging area was prepared for reassembly. The rehabilitated truss now serves as a multi-use recreational crossing, a vital link in a planned extension of the 120-mile SRGA Trail. It accommodates pedestrians and bicyclists crossing Mill Creek at Coal Creek Commons in St. Clair. Upon completion, ownership was transferred from PennDOT to the SRGA, securing its place in the community’s future.