Route 109 and Route CC Intersection Improvement

What is the current situation?

The intersection of Route CC and Route 109 in St. Louis County is getting congested.  With 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 set aside for projects that address congestion mitigation and air quality (CMAQ).

Information shared during the virtual public hearing held on December 3, 2020, is available on this page.

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.

Can Route 109 be taken over Route CC (or vice versa)?

Traffic levels on both Route 109 and Route CC are not high enough to make separating the two roadways an effective use of available money. Our goal here is to improve the flow of traffic now and into the future, while minimizing the impacts to local property owners. All planned road projects need to be able to keep up with anticipated traffic growth – putting one road under the other is typically used with roadways with much higher (and more consistent) levels of traffic, which we don’t anticipate to be the case here, even with the expected growth 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.

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 partial 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. 

What is currently underway?

Right now, MoDOT has completed some surveying and identified the soil types in the area and used this information to develop a preliminary plan showing the layout and potential impacts to surrounding properties

Because of the amount of property owners impacted, MoDOT will hold a virtual public hearing on December 3, 2020. Information on accessing that meeting will be available on this web page.

What is the current timeline?