2-Leg CFI at Airline Highway and Seigen Lane in Baton Rouge, Louisiana
An innovative traffic, transportation and design solution fixing congested intersections that cannot be solved by traditional remedies
Congested intersections simply don’t fix themselves; they become more congested over time, often despite the traditional remedies available to transportation professionals. Additional turn lanes and signalization may provide short-term congestion relief, but sooner or later adding another turn lane or through lane, or perhaps prohibiting some movement, may be needed. In some cases, the transition to a grade-separated interchange may seem like the only solution.
The team at ABMB Engineers is providing another alternative: a Continuous Flow Intersection (CFI). This innovative traffic, transportation and design solution is increasingly attractive, considering the property impacts and financial burdens tied to grade-separated or multi-level interchanges.
CFI’s inception within ABMB Engineers is significant because the firm was one of the first to study and implement the largest CFI intersection in the United States. Two smaller projects had been completed in other areas of the U.S.
The CFI is an at-grade design that provides comparable levels of vehicular flow to grade-separated interchanges at a fraction of the cost and dramatic, long-term improvements over conventional at-grade approaches.
CFI is based on one of those flashes of insight that seem obvious in retrospect. When points of conflict at an intersection are removed, through movements get more green time and intersection capacity rises.
Since one of the biggest conflicts at many intersections occurs when left-turning vehicles cross oncoming traffic, simply eliminating the left-turn conflict can significantly reduce delay to through vehicles. In a typical CFI intersection, this is accomplished with a signalized left-turn bay placed several hundred feet before the intersection.
The left turn leg feeds a special CFI leg, which in turn empties into the cross street near the main signalized intersection. The signals at the left-turn bay, CFI crossover, and main intersection are all operated by a single controller and coordinated to provide smooth continuous traffic flow.
CFI continues to gain momentum as a viable solution to congested intersections. ABMB Engineers pioneered the CFI through construction at the intersection of Airline Highway and Siegen Lane / Sherwood Boulevard. ABMB proposed the concept, completed the study, and designed the roadway plans and construction documents for this intersection. This two-leg implantation was the first of its kind in the United States. Since the opening in 2006, the intersection has received praise from LADOTD, City officials, police, media, and, most importantly, the driving public.
Since then, dozens of states have studied or implemented the CFI concept and the possibility of CFI utilization. Statewide evaluations of numerous congested intersections have been conducted in both Arkansas and Louisiana.
- 1996: Dowling College in Shirley, New York, opens a CFI prototype.
- 2000: The Maryland DOT opened a one-legged CFI at State Highway 228s and 210, 15 miles south of Washington D.C.
- 2006: First two-legged CFI in the U.S. opens in Baton Rouge, designed by ABMB.
- 2007: Two-legged CFIs are opened in West Valley City, Utah, at Bangerter Highway and West 3500 South, on which ABMB provided subject matter advisory, and in Fenton, Missouri, at Hwy 30 and Summit Drive.
- 2009: Salt Lake City announces plans to develop five more CFIs along Bangerter Highway and Redwood Road.
- 2010: The opening of the one-legged CFI in Natchez, Mississippi, at John R. Junkin Drive and U.S. 61. Similar to the Baton Rouge CFI, ABMB brought the Natchez CFI from initial corridor study to design and construction.
- Currently, CFIs in Lafayette, Louisiana, and Loveland, Colorado, are both under construction. ABMB is providing oversight services for both projects. ABMB also completed the design of another CFI project located in Miami, Ohio, at Austin Pike and Miamisburg-Springboro Road. Although this project is waiting for funding for construction, it is the third CFI project for ABMB.
The Advantages of CFI
Simulations using traffic modeling, as well as analysis of CFIs in operation show that the CFI dramatically outperforms conventional alternatives. In case after case, the CFI produced extraordinary improvements in levels of service under existing traffic loads and reductions in average intersection delay of 90 percent or more.
- Achieves significantly more capacity than conventional at-grade intersection designs.
- Offers substantial savings over grade-separated alternatives while providing equal or better performance.
- Can be deployed in one-, two-, three- and four-legged versions.
- Requires little more right-of-way than a conventional at-grade intersection.
- Provides clear lines of sight, avoiding the visual barriers created by overpasses.
- Helps reduce pollution by reducing congestion.
- Requires shorter construction time and less utility relocation.