Continuous Flow Intersections (CFI) are a new style of intersection, developed in Mexico. In the U.S., CFIs have been implemented in Louisiana, Maryland, New York, and Utah. The first CFI in Missouri was constructed in South St. Louis County, at the intersection of Route 30 and Summit Drive.
What is a CFI?
A continuous flow intersection has traffic turning left placed to the left of oncoming traffic, opposite where it is normally. This removes the conflict between on-coming traffic and traffic turning left. Vehicles turning left access the lane a few hundred feet in front of the intersection.
How is this better than a traditional intersection?
Since left-turning traffic doesn't have to cross on-coming traffic, using this type of intersection will increase the amount of "green" time on the main-line route. At the intersection in Baton Rouge, Louisiana, wait time was reduced from four minutes to less than a minute. This type of intersection provides a comparable level of vehicle flow as that on an interstate at a fraction of the cost, and is a dramatic improvement over conventional intersections.
How does this look and work?
The attached animations should give a general idea of the difference between a traditional and continuous flow intersection, as well as how vehicles making left turns would travel:
Traditional intersection (24.5 Mb)
Continuous flow intersection (21.2 Mb)
Making a left at a CFI (14.1 Mb)
Why does a CFI work better at Gravois Bluffs?
Because the intersection of Route 30 and Summit Drive is very near the intersection of Route 30 and Route 141, MoDOT needed to make sure it reduced how much time vehicles were stopped at this intersection. Currently, projections show that this should reduce delays at this intersection from an average of 25 seconds per vehicle to a little more than 17 seconds per vehicle. In 20 years, assuming a 25 percent increase in the number of vehicles, this type of intersection should reduce delays from almost two minutes to just about 30 seconds.
A vehicle makes a left turn at Summit Drive using the Continuous Flow Intersection. This view is looking east on Route 30.
This project will provide relief to Route 141 at Gravois (Route 30) as well as Route 141 at Gravois Bluffs. It will cost less to make this improvement than building a bridge and separating the two Routes. Finally, it will provide more movement along Route 30, since the main route will have green lights nearly 64 percent of the time.
Who is constructing the project at Route 30 and Summit Drive?
This project was built and paid for by G.J. Grewe, a St. Louis development firm that is expanding Gravois Bluffs.
Do you have additional information?
Here are two Power Point shows -- one has animation included and the other has the animation removed.
Continuous Flow Intersection Presentation with No Animation
Continuous Flow Intersection Presentation with Animation (2.11 mb)
Who do I contact for more information?
For general traffic questions, contact 1-888-ASK MODOT (275-6636).
For questions about construction or traffic in the south St. Louis County area, contact Kristy Yates at 1-888-ASK MODOT (275-6636).
For other questions, or for media interviews, contact Jack Wang at 1-888-ASK MODOT.