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New Monongahela River Bridge

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The Pennsylvania Turnpike Commission established an ambitious, 13-section design plan as part of the Mon/Fayette PA Route 51 to I-376 network to reduce congestion, improve safety, and stimulate social and economic development in the Monongahela River Valley. A critical part of the plan, Section 53D, called for the design of a long span bridge over the Monongahela River. Modjeski and Masters (M&M) began by performing a rigorous bridge type selection study to identify the most suitable bridge crossing.

Working with the Commission and various stakeholder groups, our technical experts established evaluation criteria for comparing the alternatives, including cost, constructability, life-cycle maintenance and aesthetics. Next, our engineers used this criteria to develop multiple truss, arch and cable-stayed bridge alternatives. In the end, the dual composite cable-stayed bridge alternative proved to be the most cost competitive, durable and aesthetic choice. M&M completed preliminary design of the cable-stayed bridge, including a study to optimize the tower geometry for both performance and appearance. From this study, we identified a hexagonal tower base cross-section – an innovative solution that reduced the crossing’s overall footprint and impact on the waterway. Although no completion date for final plans has been established, M&M helped bring the Commission’s vision one step closer to reality.

Bridge Geometry
Length of Main Span 1,120 Feet
Total Project Length 2,330 Feet
Number of Lanes on Structure Four lanes in each direction

The bridge that has emerged from the design process represents a combination of innovative ideas and efficiencies from around the world, blended into a unique and visually attractive structure. Members of the Turnpike’s engineering staff were very much a part of the project team, and were instrumental in obtaining such a positive outcome.