I-270 Over the Mississippi River - Madison County

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

Note: IDOT projects typically have three distinct phases. Phase I (or the project Study) consists of developing the project scope, environmental studies and preliminary design of a project. Phase II (Design) consists of refining the design to develop contract plans and land acquisition. Phase III (Construction) consists of the actual construction of the project.



The 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. This structure is known locally as the Chain of Rocks Bridge.

This study, referred to as the I-270 over the Mississippi River study, will take a detailed look at the replacement of the existing structure carrying I-270 over the Mississippi River and constructing a new structure or structures.  The study may also include a modification of the interchange at I-270 and Riverview Drive in St. Louis, Missouri.  The Missouri Department of Transportation (MoDOT) currently has an on-going Environmental Assessment (EA) of the I-270 widening in Missouri that includes the Riverview Drive Interchange.  Coordination between IDOT and the FHWA-Illinois Division with MoDOT and the FHWA-Missouri Division will take place continually throughout this study.

IDOT and its engineering consultant team, aided by input from the public, will inventory existing conditions (such as traffic data and crash history), identify and document environmental constraints, and develop and refine improvement options (alternatives). The result of the study will be a preferred alternative that addresses identified transportation issues and serves the area’s future needs.

About 51,000 vehicle trips are made each day across the bridge, with approximately 17 percent of these trips being truck traffic. 

An inclusive, responsive public involvement program is an essential part of the study. The public involvement program is being implemented using the principles of Context Sensitive Solutions (CSS), and follows the policies and procedures for CSS as developed by IDOT. CSS is a collaborative approach that involves all stakeholders to develop a transportation facility that fits into its surroundings and preserves scenic, aesthetic, historic, and environmental resources while maintaining safety and mobility. More information on CSS and how to provide your input to the study can be found in the Get Involved section of this website.


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.  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.


IDOT has a three-phase project development process, as shown on the timeline graphic below. The I-270 over the Mississippi River Study includes funds to conduct a Phase I Study.  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 are currently funded in IDOT’s Multi-Year Program, while Phase III is not funded.

Project Timeline


This study will be prepared following the requirements of the National Environment Policy Act (NEPA) of 1969. NEPA 

NEPA logo

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 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, it is anticipated that the I-270 over the Mississippi River study will be processed as a Federally Approved Categorical Exclusion.



To read the first issue of the Chain of Rocks Bridge newsletter, please click here.

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

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

CAG Interest form

IDOT values your comments and questions. We provide responses to all questions and strive to do so in a timely manner.

All contact information is kept private and is for the sole use of the I-270 over the Mississippi River Study and will not be distributed to any entity outside of IDOT.

Please click here to fill out our online comment form, or if you prefer, you may contact us by U.S. mail, phone, or e-mail:

IDOT logo

Karen Geldert, P.E.
Senior Project Studies Engineer
Illinois Department of Transportation
Region 5/District 8
1102 Eastport Plaza Drive
Collinsville, IL 62234
Phone: 618-346-3157


An important part of the I-270 over the Mississippi River Study is public participation.  IDOT utilizes Context Sensitive CSS LogoSolutions (CSS) as a way to continually engage stakeholders 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 GroupOne highlight of our public involvement program is the formation of a 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 will function as a liaison between IDOT and the public as a whole, and will help generate interest in and knowledge about the study. This will help 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 expected to be 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 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 the continued movement of regional and national goods and services while preserving the environmental, recreational and economic viability within the project area.

The first CAG meeting for the project was held on October 18, 2016.  Please click here to read more about the first CAG Meeting.


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 is this study?

The study is a Preliminary Engineering and Environmental Study to determine the preferable replacement option of the bridge that carries I-270 over the Mississippi River connecting Madison County, Illinois and St. Louis, Missouri.

Why is IDOT conducting this study?

The purpose of the study is to replace the existing bridge that carries I-270 over the Mississippi River.  Because the structure is nearing the end of its design life, it is in need of extensive repair.  The existing bridge was constructed in 1966.  Over the life of the structure, numerous repairs have been made. 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. The study will identify options to replace the existing bridge.

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

The Missouri Department of Transportation (MoDOT) currently is preparing an Environmental Assessment (EA) for the widening of I-270 from the I-70 interchange to the western limits of the bridge over the Mississippi River. Information on that project can be found at http://modot.mo.gov/stlouis/I-270NorthEnvironmentalAssessment.htm.

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

Will the new bridge be six lanes?

A bridge size has not yet been determined.

Will the new bridge accommodate bicycles and pedestrians?

Bicycle and pedestrian accommodations will be considered as the project moves forward.  If you would like to learn more about IDOT’s policy and procedures regarding bicycle and pedestrian accommodations, please view Chapter 17 of the IDOT Bureau of Design and Environment Manual by clicking here.

Will the new bridge be one structure or two structures?

One of the purposes of this study is to determine if one or two structures is needed.  A bridge type and size has not yet been determined.

How long will this study last?

This study, known as Phase I, includes a preliminary engineering and an environmental study and would last approximately 36 months.  It is anticipated that the study would be completed in early 2019.

What happens at the end of the study (Phase I)?

In Phase I, proposed geometry, environmental concerns, and right-of-way requirements are identified.  These will be documented in a Project Report. The Study will conclude with design approval and the Federal Highway Administration’s (FHWA) granting of the Federally Approved Categorical Exclusion. Then the project can move forward to the design phase, or Phase II.

When will construction begin?

There is no timeframe established for construction at this point.

Will the bridge be closed during construction?

It is too early in the study to know how traffic will be managed during construction.  The Department strives to manage traffic during construction to minimize inconvenience to the motoring public. 

Does the public get a chance to comment on the bridge alternatives being developed or which alternatives are selected for moving forward? If so, how?

The public will be given several opportunities to comment on the bridge alternatives developed by the study team and to provide their opinion on what bridge alternative(s) should be considered for further study. Providing your comments and opinions could be done through various means such as open house public meetings, the study website, and written letters or emails to the IDOT study team. Each comment will be included in a database of public comments and will be reviewed and addressed accordingly.

Who can I contact to provide my comments?

There are numerous ways to provide comments on the study:

Phone: 618-346-3157 (Karen Geldert, IDOT)


Additional opportunities to receive study information and provide comments will include newsletters, small group meetings, and future public informational meetings.


This site will be updated periodically as the project progresses. The Illinois Department of Transportation (IDOT) wishes to thank you for your support and patience.

IDOT is currently at the early stages of Phase I for this project. As we make changes, this website will be updated accordingly.

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