I-270 Bridge Over the Mississippi River Phase I

Illinois Department of Transportation

IDOT is performing a Preliminary Engineering Study to analyze the replacement of the bridge that carries I-270 over the Mississippi River, connecting Madison County, Illinois and St. Louis, Missouri, known locally as the Chain of Rocks Bridge.


The existing Chain of Rocks Bridge was constructed in 1966. The structure is composed of 43 spans with a total length of over 5,400 feet. The structure carries four (4) lanes of traffic, two (2) in each direction. Over the life of the structure, numerous repairs have been made, from expansion joint replacements, pin and link replacements, repairs to the structural steel, and repairs to the substructure. In addition to repairs, this structure has seen a significant increase in traffic from a projected average daily traffic (ADT) of 19,800 vehicles per day in 1975, to more than 51,000 vehicles per day today.

Horner & Shifrin completed the preliminary engineering and environmental study to replace the aging bridge. The study included preparation of a project report, coordination of bicycle and pedestrian facilities, subsurface utility engineering, surveying, location drainage studies, a major river hydraulic report, bridge condition report, interchange alternative analysis, maintenance of traffic studies, regional traffic modeling, HSM safety study, and a crash report. In addition, environmental studies were conducted as required by NEPA and multiple Federal and State (IL & MO) environmental regulatory agencies were coordinated with. This coordination included extensive coordination with the U.S Army Corps of Engineers regarding section 404, 10, and 408 permitting. All environmental studies were included and summarized in a federally approved categorical exclusion.



Site Size

3 Miles


Madison County, Illinois

Year Completed


Innovation. Agility.
Reliability. Horner & Shifrin.