The existing Chain of Rocks Bridge was constructed in 1966. The structure is composed of 43 spans with a total length of more than 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, with approximately 17 percent of these vehicles being trucks. Because the structure is nearing the end of its design life, additional repairs have become necessary and roadway geometrics have become sub-standard. IDOT has determined that this structure requires replacement. MoDOT has designed a new diamond interchange for Riverview Drive at I-270, which will be reconstructed to accommodate the IDOT replacement of the I-270 Chain of Rocks bridge.


The selected alternative consists of constructing new twin bridges, one on the same alignment as the existing Chain of Rocks bridge, and one directly south of the existing Chain of Rocks bridge. The new bridges will provide inside and outside shoulders that will be wide enough to accommodate a stalled vehicle or emergency responders responding to an accident. These will be much wider compared to the 1-foot shoulders that exist today. In addition, the bridges will be wide enough to accommodate a future expansion of I-270. While I-270 is currently four lanes, MoDOT has completed a study for I-270 in Missouri that proposed expanding I-270 to six lanes up to Riverview Drive in Missouri. Similarly, IDOT has recently initiated a study to potentially expand I-270 to six lanes from Missouri to Illinois Route 157. The Chain of Rocks bridge, as currently proposed, will be wide enough to accommodate the future six lanes when they are needed. The Riverview Drive interchange will be reconstructed to six lanes of traffic as same as the lanes of traffic proposed in the Chain of Rocks bridge project. The interchange and the new bridge will initially be striped for four lanes but will eventually be configured for six lanes when I-270, east and west of Riverview Drive, is widened to six traffic lanes.


Construction is scheduled to begin at the end of 2022 and is anticipated to take four years to complete. While there may be occasional short-term off-peak lane closures, IDOT’s goal is to keep four lanes of traffic open to the public during all stages of construction. The southern bridge will be constructed first. Traffic will be shifted to the southern bridge before removing the existing Chain of Rocks bridge. Once the bridge is demolished, the construction of the northern bridge will begin and be constructed in the same location as the current bridge. In addition, IDOT and MoDOT will be working closely together to ensure all stages of construction will be coordinated between the bridge replacement project and the I-270 Riverview Drive interchange replacement, which will be done at the same time.