Cox Bridge over Kaskaskia River

Nestled over the Kaskaskia River, the historic Cox Bridge has long been a link to the Carlyle Lake State Fish and Wildlife Area.  Safety concerns of the aging structure caused its closure, but an operational need necessitated its replacement.

The original pin-connected, 7-panel Pratt through truss bridge was constructed in 1911 and in the 1960s, the structure was closed to vehicle traffic because of damage to the substructure by debris and deterioration found in the truss superstructure.  From that point on, the structure was limited to lawnmowers and pedestrian traffic only.  In 1978, the structure was removed from the state inventory list and abandoned.  In 2001, the structure was barricaded and closed to all forms of traffic based on several inspections and recommendations from the Illinois Department of Natural Resources (IDNR).  Without the use of Cox Bridge, the travel time for site personnel was over 30 minutes between the site office and the wildlife habitat area when required to use a detour.

Oates Associates worked with the Illinois Capital Development Board (CDB) and IDNR to replace the structure.  The new structure is a 200’ span pre-engineered steel truss bridge with a concrete deck on pile supported abutments.  An 800’ long, 12’ wide aggregate path was constructed on the west side of the bridge, and an embankment fill height of 11’ was placed at the west abutment, transitioning down to meet the existing grade.  ADA compliant concrete sidewalks were constructed on the east side from the bridge to the existing parking lot and restroom facility.  Additional features are a solar powered dusk to dawn light at the entrance of the structure, Corten guardrail on the east side of the structure, and pipe bollards to limit vehicular access.

Preliminary engineering included a full hydraulic analysis of the crossing, structure borings, geotechnical analysis of settlement of the embankments, and structural design of the foundation.  There was extensive coordination with the U.S. Army Corps of Engineers, IDNR and IDNR Office of Water Resources (OWR), requiring permits including a Joint Application Form, 404 permit, wildlife habitat, tree clearing, and tree mitigation.

The new Cox Bridge restores operational efficiency, accessibility, and safety for IDNR personnel and visitors alike – preserving the legacy of the site while meeting modern infrastructure needs.