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I-270 Over the Mississippi River - Madison County

For Construction Project Updates go to: www.270mrb.com

Welcome to the official website for the I-270 over the Mississippi River project. The Illinois Department of Transportation (IDOT) has created this site to provide information about the progress of the project and to facilitate public input and participation in the project. Please take a few minutes to explore the information available on the site. Project updates, public involvement opportunities, and relevant information will be posted to the site throughout the project. Bookmark this page and check back often for the latest news about the project. If you would like to submit your comments or questions, or sign up for the project mailing list, please visit the Get Involved section of this website. Thank you for your interest in the I-270 over the Mississippi River project. IDOT appreciates your participation and input.


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.


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.


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.


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.

MODOT Riverview Drive Interchange Project


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.


"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 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.  


This Preliminary Engineering and Environmental Study (Phase I) Project Report was prepared following the requirements of the National Environment Policy Act (NEPA) of 1969. NEPA established a national environmental policy intentionally focused on federal activities and the desire for a sustainable environment balanced with other essential needs of present and future generations.

NEPA logo

NEPA requires that any federally funded proposed or future action (such as construction of a roadway) be carefully analyzed for all impacts to natural and cultural resources and to the human environment. This analysis must be documented and made available for public review and comment near the end of the study.

Because transportation projects vary in type, size, complexity, and potential to affect the environment, NEPA encompasses three levels of documentation:

  • Environmental Impact Statement (EIS) – for projects where it is known that the action will have a significant effect on the environment.
  • Environmental Assessment (EA) – for projects in which the significance of the environmental impact is not clearly established.
  • Federally Approved Categorical Exclusions – for actions that do not individually or cumulatively have a significant effect on the environment.

In coordination with the Federal Highway Administration (FHWA) Illinois Division, the I-270 over the Mississippi River study was determined to be a Federal Approved Categorical Exclusion and was approved by the FHWA in July 2018.


The project requires coordination with multiple Federal, State, & Local environmental agencies including:

  • U.S. Fish & Wildlife Service
  • U.S. Army Corp of Engineers
  • U.S. Coast Guard
  • Osage Nation and Miami Tribe of Oklahoma
  • Illinois State Historic Preservation Officer
  • Illinois Department of Natural Resources
  • Missouri Department of Natural Resources
  • Missouri Department of Conservation
  • Chouteau Island Levee & Drainage District


It is anticipated the project will require the following environmental permits:

  • Section 401 Water Quality Certification from the IEPA and MDNR
  • Section 402 NPDES permit from the IEPA and MDNR
  • Section 10 & 404 permits from the USACE
  • Section 9 permit from the USCG
  • Floodplain permit
  • IDNR OWR permit


The following summarize all environmental or engineering commitments required for this project.

Commitment 1:

  1. The use of explosives is prohibited on this construction contract as a method of demolition or construction.
  2. During demolition, the superstructure shall not be dropped into the river.
  3. The use of a cutterhead shall be prohibited as a dredging method.
  4. Mechanical excavation is the preferred method of dredging and shall be utilized where feasible.
  5. If it is discovered during construction that the use of a dust bin will be required for dredging, the area and amount of material to be dredged shall be coordinated with USFWS prior to the contractor starting and dredging activities.

Commitment 2:

All trees shall be removed between the dates of November 1 and March 31 of any given year.

Commitment 3:

To ensure the undertaking will have no adverse effect on the historic bridge, IDOT is to follow the Construction Vibration Monitoring Plan

Commitment 4:

When working in the waterway, the Contractor shall have a drilled shaft installation procedure to minimize disturbing the stream bed outside the permanent casing to comply with the permitting requirements. The Contractor shall use best management practices to minimize excavated
materials from the shaft, from being deposited in the river as means of disposal.

To view the environmental coordination please view the Project Report and the Appendix B by clicking on the following link:





Please go to www.270mrb.com for the most current information

Billie Owen, P.E.
Studies and Plans Project Engineer
Illinois Department of Transportation
Region 5/District 8
1102 Eastport Plaza Drive
Collinsville, IL 62234
Phone: 618-346-3209

Public Involvement

The project is using an intense public involvement program referred to as Context Sensitive Solutions (CSS).  Please read this page as it provides an overview of the public involvement activities to date.  For more detail, please view the Project Report and Technical Report I Public Involvement Record clicking on the following link:


Newsletters & Mailing List Sign Up

During Phase I of the project, IDOT issued three newsletters. Please click on the issues below to learn more about the Phase I portion of the project:Newsletter

Issue 1

Issue 2

Issue 3

During Phase II the following newsletters have been issued:

Issue 4

If you would like to receive the Chain of Rocks Bridge newsletter, please join the mailing list by clicking here.

IDOT held its second Public Meeting for the I-270 bridge replacement project on January 17, 2018, in Granite public meeting photoCity, Illinois.  The meeting was in an open format setting and visitors were welcome to come and go as they please.  Below is a link to the Exhibits that were presented at the meetings.

Public Meeting Announcement

Public Meeting Press Release

Public Meeting Displays including Preferred Alternative

Public Meeting Brochure

IDOT held its first pair of Public Meetings for the I-270 bridge replacement project on June 30, 2016 and July 13, 2016, in Illinois and Missouri, respectively.  The same information was presented at both meetings.    Both meetings were in an open format setting and visitors were welcome to come and go as they please.   Below is a link to the Exhibits that were presented at the meetings.

Public Meeting Displays

Public Meeting Brochure


An important part of the I-270 over the Mississippi River Study is public participation.  IDOT utilizes Context Sensitive Solutions (CSS) as a way to continually engage stakeholdersCSS Logo in the study.  As identified in IDOT’s CSS policies, stakeholder involvement is critical to a study’s success. The CSS process strives to achieve the following:

  • Understand stakeholder’s key issues and concerns
  • Involve stakeholders in the decision-making process early and often
  • Establish an understanding of the stakeholder’s role in the study
  • Consider all modes of transportation
  • Set a project schedule
  • Apply flexibility in design to address stakeholder’s concerns whenever possible

For more information on IDOT’s CSS process, please visit the following website at:



CAG Group

One highlight of our public involvement program is the Community Advisory Group (CAG).

The purpose of the CAG is to provide input on various elements of the study, including developing a problem statement, identifying issues important to the public, and providing feedback on alternatives.

The CAG functions as a liaison between IDOT and the public as a whole, and helps generate interest in and knowledge about the study. This helps ensure opinions, values, and concerns of the public are shared with the project team, and that information developed by the team is distributed to the broader public.

It is important that the CAG be representative of all the varied interests and viewpoints that exist within the study area. The CAG is comprised of volunteers who represent a wide variety of local interests, such as elected leaders, cities/villages, economic development, environment, industry, residents, businesses, tourism, commuters, and others with a stake in the study’s outcome.

The first CAG meeting for the project was held on October 18, 2016. The purpose of the first CAG meeting was to introduce the project, explain the IDOT planning and CSS process, and listen to the CAG members concerns and interests.

A second CAG meeting was held on December 13, 2017. The purpose of the second CAG meeting was to discuss what has happened since the last CAG meeting and to present the potential preferred alternative.  The CAG members viewed the potential preferred alternative and thought the alternative addressed the issues expressed in the project problem statement.    Please click here to read more about the CAG Meetings.


The Stakeholder Involvement Plan (SIP) serves as a guide for implementing stakeholder involvement activities during the I-270 over the Mississippi River Phase I Study.

The goal of the SIP is to outline a program of activities to actively engage stakeholders throughout the planning process. The objectives of the SIP are to:

  • Identify stakeholders
  • Identify the roles and responsibilities of the lead agency
  • Establish the timing and type of outreach activities with all stakeholders
  • Establish stakeholder requirements for providing timely input to the study development process
  • Provide an approach for evaluating the effectiveness of the public-participation program and refine, as appropriate, to respond to public needs and concerns
Please click here to view the Stakeholder Involvement Plan.


What are the project limits?

The portion of I-270 that this project includes is from just west of the Chain of Rocks Canal Bridge in Madison, Illinois to just west of Riverview Drive in St. Louis, Missouri.

 Why is IDOT replacing the bridge?

The bridge is nearing the end of its design life and is in need of extensive repair.  The existing bridge was constructed in 1966.  Over the life of the bridge, numerous repairs have been made. In addition to repairs, this bridge 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.

What did the Phase I Study accomplish?

In Phase I, the proposed geometry, environmental impacts, and right-of-way requirements were identified. The Study concluded with a preferable replacement option of the bridge which was approved by the Federal Highway Administration’s (FHWA). This allowed for the project to move forward to the design phase, or Phase II.

Will the new bridge be six lanes?

The new bridge is proposed to accommodate six 12-foot lanes and include larger shoulders but will be striped for four lanes initially to match the existing I-270 to the east and west of the bridge. Currently, I-270 is four lanes in Illinois and Missouri adjacent to the bridge. 

Is this part of MoDOT’s I-270 Project?

The MoDOT project to widen I-270 from the I-70 interchange to the Mississippi River is currently being constructed.  Please visit the MoDOT project website for information on this project: http://www.i270north.org/

This IDOT bridge replacement project is not part of the MoDOT study.  However, the proposed bridge will be designed to be compatible with the MoDOT project.

How long the Phase II Design take?

The Phase II Design started in 2019 and it is anticipated to take approximately two years to complete.

When will construction begin?

Construction could begin in 2022.

Will the bridge be closed during construction?

The Department strives to manage traffic during construction to minimize inconvenience to the motoring public. Extensive public outreach via the media and social media platforms during construction will be utilized to keep motorists up to date on changes to traffic patterns. 


Volume I of the Project Report is include here.  To view Volumes II-VII, please contact Cindy Stafford at cindy.stafford@illinois.gov.

To view the Project Report Addendum, please click below:

NEWSLETTER - The June 2021 I-270 over the Mississippi River Newsletter is now available. Please click on the Link to read the newsletter for project updates.

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