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Preferred Alternative
During the alternative development process, IDOT studied a range of replacement options for the bridge and the potential effect of those alternatives. Many factors were considered during this process and ultimately the preferred alternative selection. Factors considered included but were not limited to: potential impacts to environmental resources, public comments, surrounding land use, river elevation, traffic statistics, crash history, engineering feasibility, long term maintenance, handling of traffic during construction and how the alternative fits in with the overall roadway infrastructure. An additional factor that played a key role in the selection of the preferred alternative was the Project Problem Statement. The Project Problem Statement was developed by the project’s Community Advisory Group (CAG) and identified the problems within the Chain of Rocks study area that need to be addressed. IDOT continually referred back to this statement to ensure the preferred alternative that was selected addressed these issues. IDOT has achieved this with the preferred alternative.
PROJECT PROBLEM STATEMENT
"The existing bridge carrying I-270 over the Mississippi River connecting Illinois and Missouri is aging and in need of continual repairs. There is a need to provide a sustainable, long-term solution that increases safety, accommodates future traffic growth, and provides for continued movement of regional and national goods and services while preserving the environmental, recreational and economic viability within the project area.”
IDOT’S Three-Phase Project Development Process
IDOT has a three-phase project development process, as shown on the timeline graphic below. A Phase I Study consists of a Preliminary Engineering and Environmental Study which provides the support for the determination of a preferred option. During this phase, proposed geometry, environmental concerns, and proposed right-of-way are identified. Subsequently, a Phase II design of the preferred option that results in contract plans and the acquisition of land is completed followed by Phase III, construction. Phase I and Phase II for the I-270 over the Mississippi River has been completed and Phase III is currently underway.
