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Overview and Scope
The Illinois Department of Transportation (IDOT) has completed the Preliminary Engineering and Environmental Study for the replacement of the bridge that carries I-270 over the Mississippi River connecting Madison County, Illinois and St. Louis, Missouri. This structure is known locally as the Chain of Rocks Bridge. This study identified a preferred alternative for the replacement of the existing bridge and also identified a preferred modification of the interchange at I-270 and Riverview Drive in St. Louis, Missouri. Phase II of the project, which consists of preparing contract plans and acquiring right-of-way, is underway. The third and final phase of the project will be construction.
Background
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 over 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. This has led to the determination by IDOT that this structure be replaced.
WHAT WILL THE NEW BRIDGE LOOK LIKE?
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.
WILL THERE BE LANE CLOSURES DURING CONSTRUCTION?
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.