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I-57 / IL-16 Interchange Reconstruction at Mattoon

To view and comment on the project information, please visit the Public Meeting tab below

IDOT is proposing to reconstruct the I-57/IL 16 interchange located east of Mattoon.  At this location, I-57 is a rural four-lane divided interstate and IL 16 is a rural four-lane divided highway.  This section of IL 16 provides access between the cities of Mattoon and Charleston.  The interchange is currently a cloverleaf configuration that has four inner loop ramps and four outer ramps to provide access between I-57 and IL 16.

The I-57/IL 16 interchange is being reconstructed to eliminate over-height vehicle impacts to the I-57 bridges over IL 16, to address the structural deficiencies of these bridges and to address the geometric deficiencies of the cloverleaf interchange while minimizing the effects on capacity. 

As part of the reconstruction, the I-57 bridges over IL 16 will be replaced and raised to provide a minimum vertical clearance of 16’-6” from the IL 16 pavement to the bottom of the bridge beams.  Also, the cloverleaf interchange configuration will be removed and replaced with a new raindrop diamond interchange.  The ramps of the new interchange will extend through the I-57 bridges over the Lincoln Prairie Grass Trail.  To accommodate the new ramps, the existing bridges over the trail will be removed and replaced with a 16’ wide by 14’ tall box culvert.  This project will address the stated issues for the interchange while maintaining a smooth, continuous, safe, and efficient flow for large volumes of traffic.

Update 2/1/2023:  IDOT continues to coordinate with the City of Mattoon.  Design plans are continuing to be developed and the land acquisition process has started.  Construction of this project is tentatively scheduled to begin in late 2023 or early 2024.  Construction should last approximately 3 years.

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.

FAQs - Mattoon Interchange

What is wrong with the existing cloverleaf interchange?  Why is it being removed?

Due to the necessary reconstruction and grade raise of the structures carrying I-57 over IL 16, the location and configuration of the entrance and exit ramps will be impacted making it impossible to keep the existing ramps as they are.  The existing cloverleaf interchange has substandard ramp curves as well as substandard acceleration lanes and multiple weaving/merging traffic conflict points, all contributing to unsafe conditions.  In order to keep a cloverleaf interchange configuration and adhere to required geometric standards, excessive land acquisition and costs would be needed making the project prohibitive.  The raindrop diamond interchange configuration meets both geometric and traffic capacity standards at a lower cost with minimal land acquisition.

Why not use traffic signals rather than the raindrop interchange?

Traffic signals at the intersections of IL 16 with the I-57 entrance and exit ramps would require a larger interchange resulting in a significant amount of additional right-of-way.  Traffic signals introduce stop conditions at these intersections making the traffic capacity, operations, and safety worse.  Also, due to the larger interchange, the entrance and exit ramps would need to be longer and would require reconstruction of the I-57 structures over IL 316 resulting in increased costs. 

Why do the bridges have to be raised?

The existing structures are scheduled for full replacement due to their age and condition.  The vertical clearance above IL 16 is substandard and the beams have been impacted frequently in the past by over-height vehicles, including one accident causing fatalities.  These impacts have resulted in costly repairs to the structures.  The new structures will provide a minimum vertical clearance of 16’-6” meeting current policy.

How long will the project take to construct?

The construction duration for the entire project is expected to be 3-4 years.

Will there be road closures and detours?

It is anticipated that the project will be constructed utilizing lane closures, keeping at least one lane open to traffic in each direction for the majority of the work on I-57 and IL 16.  IL 16 may be closed for short durations as needed.  I-57 entrance and exit ramps will remain open for most of project but intermittent ramp closures are expected.  It is expected that some local traffic will use alternate routes.

Why build a tunnel for the bike path instead of bridges?

The existing structures over the Lincoln Prairie Grass Trail are not wide enough to accommodate the proposed ramp configuration.  Because of this and in addition to the age and deteriorated condition of the structures, the existing structures will need to be removed.  A 16’ wide by 14’ high box culvert with lighting is proposed to be constructed instead of two new structures.  The box culvert will provide significant initial and future maintenance cost savings over new structures and the box culvert will provide a longer service life.

What are the “rules of the road” for driving through roundabouts?

Traffic entering the raindrop portion of the interchange will be required to yield to traffic already in the raindrop.  Proper signage and pavement markings will be a critical part of this project.

Do any other raindrop diamond interchanges exist?

Although only a couple of similar type interchanges have been constructed in Illinois, many have been constructed throughout the US.  Several raindrop type interchanges have been constructed in neighboring states including Indiana and Wisconsin. 



Public Review and Comment - Lincoln Prairie Grass Trail 4(f)

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

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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