When John Hock, transportation manager at EDSI introduced the concept of a Continuous Flow Intersection (CFI) to the Missouri Department of Transportation (MoDOT) in 2004, he never dreamed he would be the lead engineer designing the first CFI in the Midwest. However, this idea became a reality when he was tasked with designing the intersection at Route 30 and Summit Drive in Fenton, Missouri.
In early 2006, St. Louis local developer G.J. Grewe was expanding a large retail development in South St. Louis County at Gravois Bluffs. The traffic in the area was already very high volume, and with the addition of the new shopping center, the congestion would be even worse. In order to accommodate the additional traffic, a new intersection was needed on Route 30 at the intersection of Summit Drive. This intersection was important to prevent further congestion at the busy neighboring intersections at Route 30 and Route 141.
EDSI was selected as part of Pickett, Ray and Silver’s team (PRS) to design a conventional intersection layout that had been detailed in a traffic study completed by Crawford, Bunte and Brammeir (CBB) for MoDOT.
After being selected for the job, MoDOT requested additional analysis of the traffic study. They were considering a very innovative concept called a Continuous Flow Intersection or CFI to mitigate some of the congestion in this high traffic corridor. EDSI’s Transportation Group Leader John Hock had presented the idea of a CFI to MoDOT several years before, and they had been looking for an opportunity to apply it. Mr. Hock and the project team were extremely pleased when MoDOT announced they had decided that the project on Route 30 was the perfect opportunity to try this revolutionary CFI concept.
This project is the first application of a “continuous-flow intersection” (CFI) in the state of Missouri, which removes the conflict between left-turning vehicles and oncoming traffic by introducing a left-turn bay placed to the left of oncoming traffic. Traffic is permitted to load the left-turn bay, crossing the oncoming traffic lanes, during the signal phase servicing cross-street traffic. CFI’s are a great way to mitigate traffic congestion, since they increase the amount of “green” time at the light, thus increasing traffic capacity and reducing traffic delay by simply moving the left turn lanes.
Research has shown that this innovative design should reduce delays at the intersection from an average of 25 seconds per vehicle to just more than 17 seconds per vehicle. In 20 years, assuming a 25 percent increase in the number of vehicles, this type of intersection is projected to reduce delays from almost two minutes to just about 30 seconds.
This project provides relief not only to the intersection at Route 30 and Summit Road, but also to the surrounding intersections including Route 141 at Gravois (Route 30) as well as Route 141 at Gravois Bluffs. According to MoDOT, the intersection will provide more movement along Route 30, since the main route will have green lights nearly 64 percent of the time. This improvement project is also an economical choice. The intersection costs less than building a bridge to separate traffic from Route 30. The intersection design is innovative, unique and provides benefits to the community. The Route 30 CFI has improved safety for pedestrians and drivers throughout the corridor, enhanced access to commerce, reduced traffic congestion and in turn decreased vehicle emissions in the area.
As the first CFI in the Midwest and only the 5th in the United States, the Route 30 CFI has served as a case study for other communities to consider the benefits of alternative intersections. The design itself reduces traffic delays, provides more “green” time at lights by eliminating the left turn phase, improves safety and reduces the pollution caused by idle vehicles.
Return Home