Counties Impacted
St. Louis
Project Status
Planning Phase

Project milestones

Complete
Conceptual plans

An evaluation of the area and a determination of potential solutions.

In Progress
Evaluation and preliminary design

Evaluating the area for the potential improvement. May include investigations of the roadway bed, soil and rock around the roadway, surveying property lines (with owner approval).

Not Started
Public Hearing

Once preliminary plans for the project have been completed, the department will hold a public hearing to share information with the public and answer questions. At this point, this is anticipated for late summer/early fall 2020.

Not Started
Right of Way negotiations

MoDOT starts negotiations for needed right of way and easements to construct the project. Typically starts about 12-18 months before construction begins

Not Started
Construction begins

Construction begins on the project. Currently scheduled to begin in fall 2022.

What is the current situation?

The intersection of Route CC and Route 109 in St. Louis County is getting congested.  With several ongoing and anticipated developments in Wildwood, Franklin County and the Chesterfield Valley, that congestion will continue to get worse as times goes by.

MoDOT engineers studied the area to see what possible improvements could be made to the intersection to improve the flow of traffic and help reduce congestion. The department also applied for, and received, Federal funds for this intersection that are specifically for projects that address congestion mitigation and air quality (CMAQ).

What is the current plan?

Based on that study, MoDOT determined that the best solution to keep traffic flowing in the area would be a two-lane roundabout, similar to those constructed further south on Route 109 between Clayton Road and Manchester. This would reduce backups and improve the movement of traffic in the area.

Why a roundabout? Why not a signal?

When traffic levels range widely over the course of a day, roundabouts can help move traffic more effectively than a traffic signal. Traffic ebbs and flows at the intersection of Route CC and Route 109.  There are some peak traffic times during the morning and evening rush, but most of the remainder of the time, traffic is generally light, but steady in all directions.  A signal, even one with detection, cannot adjust quickly to varying levels of traffic.

A roundabout also takes up less space, which minimizes impact to nearby property. You need more lanes for a signalized intersection than you do for a roundabout.

As a whole, roundabouts are also safer.  Since traffic heads in the same direction around the roundabout, there are fewer opportunities for crashes, and those that do occur are potentially much less serious than the crashes at a four-way stop (as it is currently) or a signalized intersection.

How do you use the roundabout?

The current plan calls for a two lane roundabout.  Just like any other roundabout, traffic entering the roundabout would yield to any traffic already in the roundabout. Traffic on the outside lane would generally be turning right, while traffic on the inside lane would be heading though the roundabout or heading around the roundabout to turn left. 

Roundabouts

Embed
Title
General roundabout information
Summary

General information about roundabouts.

Is Responsive
Embed Code
Embed
Title
Traveling on a two lane roundabout
Summary

General information on traveling through a two lane roundabout.

Is Responsive
Embed Code
Embed
Title
Making a left turn through a two lane roundabout
Summary

How to make a left turn through a two lane roundabout.

Is Responsive
Embed Code

What is currently underway?

Right now, MoDOT has determined a conceptual plan – based on their study of the flow of traffic and evaluation of the area.  The next steps will be to do surveying around the intersection and checks of the soil in the location to get the exact conditions so that designers know exactly what any project might encounter during construction. As a part of this, we have reached out to property owners who may be in the footprint of the roundabout to get their permission to access portions of their property.  When that work is completed, designers will complete the preliminary plans.

Because of the amount of property owners impacted, MoDOT will hold a public hearing late this summer or in early fall to get the public’s thoughts about the project. Details on that meeting will be available later.

What is the current timeline?

Task

Completion

Conceptual plan

Completed

Evaluation and preliminary design

Summer 2020

Public hearing

Late summer/early fall 2020

Right of way negotiations

Summer 2021

Construction begins

Fall 2022