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I-270 Preliminary Engineering Study 

The Illinois Department of Transportation (IDOT) is conducting a Phase I Engineering study of I-270 from Riverview Drive in St. Louis, Missouri to Illinois Route 157 in Madison County, Illinois.

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.


Overview and Scope

The Illinois Department of Transportation (IDOT) is conducting a Phase I Engineering study of I-270 from Riverview Drive in St. Louis, Missouri to Illinois Route 157 in Madison County, Illinois. This study, referred to as the Illinois I-270 Preliminary Engineering Study, will investigate how to:

  • address traffic growth,
  • decrease congestion, and
  • improve safety along the route.

The study will develop the engineering and environmental analysis required by Federal Law, the National Environmental Protection Act (NEPA).  It is anticipated, that this project will be processed as a Federally Approved Categorical Exclusion.

This study will also closely examine the reconstruction of the I-270 and IL Route 111 interchange, which will be funded and constructed as a separate project.

An inclusive, responsive public involvement program is an essential part of this project. The public involvement program is being implemented using the Context Sensitive Solutions (CSS) process as developed by IDOT. This process helps ensure that any recommended transportation improvements will enhance the quality of life for those who have a stake in the system. This collaborative approach also preserves scenic, aesthetic, historic, and environmental resources while maintaining safety and mobility. For more information on CSS please visit the Get Involved page of this website.


The most northern connection between St. Louis, Missouri and Madison County, Illinois is I-270. This portion of the interstate, from IL 157 to the Missouri state line, is largely a four-lane highway which travels over several railroads, has interchanges with several state routes and is adjacent to urban development, distribution and logistics parks, residential subdivisions, and farm land.  This portion of I-270 carries traffic through or near St. Louis, Missouri; and Granite City, Mitchell, Pontoon Beach, and Glen Carbon, IL.

As a direct route to and from St. Louis County into Illinois, I-270 is a common corridor for many motorists who work, live, and/or go to school on opposite sides of the Mississippi River. With population density increasing in St. Louis County and nationwide freight movement expanding through the area, the four-lane highway has seen significant increases in traffic volume and the number of crashes. Current Average Annual Daily Traffic on I-270 is nearly 57,000 vehicles.  IDOT will evaluate these issues and other concerns identified during the Illinois I-270 Preliminary Engineering Study.


IDOT has a three-phase project development process, as shown on the timeline graphic below. Projects in Phase I, like the Illinois I-270 Preliminary Engineering Study, include funds to conduct a Preliminary Engineering and Environmental Study which provides 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 will result in developing contract plans and acquiring land. The third and final phase will focus on construction. Phase I is currently the only phase funded in IDOT’s Multi-Year Program, while Phase II and III are not funded.



The Illinois I-270 Preliminary Engineering Study (Phase I) Project Report will be 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 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 effects to 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 Illinois I-270 Preliminary Engineering study will be processed as a Federally Approved Categorical Exclusion.

Get Involved

IDOT held its first Public Meeting for the Illinois I-270 Preliminary Engineering Study on Tuesday, September 18, 2018, at Southwestern Illinois College’s (SWIC) Sam Wolfe – Granite City campus in Granite City, Illinois. The meeting was an open format where attendees were welcome to come and go as they please. Informational display boards and aerial maps were available for review and the public was invited to discuss the study with IDOT staff and the study team. Below is a link to the Exhibits and handouts that were presented at the meeting.

Public Meeting Flyer

Public Meeting Handout

Public Meeting Displays

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 Illinois I-270 Preliminary Engineering Study and will not be distributed to any entity outside of IDOT.


An important part of the Illinois I-270 Preliminary Engineering Study is public participation.  IDOT will utilize Context Sensitive Solutions (CSS) as a means to engage continually stakeholders throughout the study process.  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 stakeholders’ 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;
  • Address all modes of transportation;
  • Set a project schedule; and
  • 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:



The Stakeholder Involvement Plan (SIP) provides guidelines for implementing stakeholder involvement activities during the Illinois I-270 Preliminary Engineering Study.

The SIP calls for early and continuous involvement by key stakeholders and the public so that the study team can meet the following objectives:

  • Understand key issues, concerns, opportunities, and challenges of the study area;
  • Establish a process that allows all stakeholder types to obtain information and provide input;
  • Build trust with key stakeholders; and
  • Use stakeholder input to inform the decision-making process and final recommendation.

Please click here to view the Stakeholder Involvement Plan.


What is this study?

This is the Illinois I-270 Preliminary Engineering Study; a Preliminary Engineering and Environmental Study to determine the preferred option for addressing traffic growth, decreasing congestion and improving safety along I-270 from the Riverview Drive interchange in St. Louis, Missouri to Illinois Route 157 in Madison County, Illinois.

Why is IDOT conducting this study?
There are significant traffic issues concerning congestion and safety along the study corridor. The purpose of this study is to investigate the best method for addressing these issues while also addressing traffic growth.

How long will this study last?
The first phase of the Illinois I-270 Preliminary Engineering Study will last approximately 30 months and is anticipated to be completed in mid-2020.

When does construction begin?
A timeframe for construction has not yet been established.

Does the public get a chance to comment on alternatives being developed or which alternatives are selected for moving forward? If so, how?
The public will have several opportunities to comment on alternatives developed by the study team and to provide their input on what alternative(s) should be considered for further study. Providing your input can be done through various means such as completing comment forms at public meetings, visiting the study website and leaving a comment and/or writing letters or emails to the IDOT point of contact for this study. Each comment will be logged, reviewed and addressed accordingly.

Who can I contact to provide my comments?

Tiffany Brase
Studies & Plans Engineer
Illinois Department of Transportation
District 8
1102 Eastport Plaza Drive
Collinsville, IL 62234
Phone: 618-346-3175
Email: Tiffany.Brase@Illinois.gov

Future public informational meeting will provide additional opportunities to receive study information and provide comment.


Documents and Exhibits

During the Illinois I-270 Preliminary Engineering Study, several documents and exhibits will be produced. Please visit this page often to view these documents.

I-270 / IL 111 Diverging Diamond Interchange Simulation


Press Releases:

September 10, 2018 - Public Meeting for I-270 Preliminary Engineering Study from Riverview Drive Interchange in Missouri to IL Route 157 in Madison County, Illinois

Belleville News-Democrat: IDOT wants to know what you think of this stretch of Interstate 270
Illinois Business Journal: Public meeting set for plans along I-270 corridor
AdVantage News: IDOT to gather input about I-270 project

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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