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.
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.