County Highway 21 Bridges over Lake Fork Creek and Tributaries

CLIENT: Macon County, Illinois

Three bridges along County Highway 21 needed replacement. Some were posted for less than legal loads, limiting the road’s use for transporting grain and other freight between neighboring towns. Changes in stream conditions also brought high water close to the undersides of the existing bridges.

Clark Dietz provided Phase I planning and Phase II design services for all three replacements. The team completed surveys, hydraulic analysis, environmental studies, and roadway and bridge design, along with the reports and plans required for state and federal review. Macon County used federal funds to construct the bridges.

Each bridge was designed to suit its stream crossing while using a similar three-span concrete design. The shallow bridge decks provided clearance for high water without requiring major changes to the road’s flat profile. Integral abutments reduced the need for joints that require maintenance, while the pier design allowed debris to pass through the streams.

Clark Dietz also coordinated with IDOT on the use of metal railings, which allowed water to drain from the bridges and helped reduce construction costs. Designed and replaced over several years, the final bridge was completed in 2018, restoring crossings suited to the road’s freight and local traffic needs.