Continuous flow intersection

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A continuous flow intersection (CFI), also called a crossover displaced left-turn (XDL), is an at-grade intersection that moves the turn conflict (to the left where traffic drives on the right and vice versa) out of the main intersection. A CFI moves the left-turn down the road several hundred feet eliminating the left-turn traffic light phase. The CFI is a patented design invented by Francisco Mier, of Mexico, where over 40 have been implemented over the past decade. As of March 2006, there are only three CFIs in the United States -- one in Shirley, New York (at the entrance to Dowling College) [1][2], one in Baton Rouge, Louisiana (at the intersection of Airline Hwy and Siegen Lane)[3], and one in Accokeek, Prince George's County, Maryland (at the intersection of Routes 210 and 228).

This type of intersection can require a notable amount of right-of-way to implement, which is why such configurations are not frequently used in urban areas. However, the amount of land necessary for construction and final operation is still typically less than that of an interchange. Additionally, as there is no grade separation involved, costs are considerably less than that of an interchange alternative.

[edit] Operation details

Sample continuous flow intersection implemented for north/south traffic while east/west traffic has a regular left-turn lane

Part of the delay at a regular, high-volume intersection is because of the left-turn cycle of the traffic semaphores; through-traffic must wait for the traffic turning left. The continuous flow intersection moves the left-turn conflict to the light cycle of the cross-traffic.

In the diagram to the right, while the east/west traffic is flowing through the intersection, the north/south left-turn traffic is allowed through each of the smaller intersections that are a few hundred feet from the main intersection. When the north/south through traffic is allowed through the main intersection, the north/south left-turn lanes are also allowed through the intersections. All traffic flow is controlled by traffic semaphores as at a regular intersection.

To reduce confusion regarding the left-turn lane, the left-turn lane and the straight-through lanes are usually separated by a concrete barrier or traffic island. This diagram shows the straight-through lanes offset by one lane through the intersection and are guided by lines painted through the intersection. But this is just a sample configuration; the lanes may be offset by more lanes or none at all.

Nonetheless, due to the provision of traffic between two directions of opposing traffic, some motorists tend to maintain an ongoing criticism of the intersection. Additionally, as in the case of the half-CFI in Accokeek, the offset left-turn traffic reenters the main traffic stream via a half-signal, requiring motorists to merge from a stop condition onto the higher-speed mainline. Motorists sometimes cite discomfort due to this, though conflicts can be reduced through the provision of an adequate acceleration lane and merge area.

[edit] External links

• Federal Highway Administration, Alternative Intersection Treatments - CFI
• 40.826443° N 72.881042° W Map of a CFI in Shirley, New York, USA
• 38.664126° N 77.016928° W Map of a CFI in Accokeek, Maryland, USA
• 30.398914° N 91.054119° W Map of a CFI in Baton Rouge, Louisiana, USA

Note that due to the relatively recent installation of the CFI in Baton Rouge, some images may not show the existing conditions.

• Deseret News story about CFI
• KSL News story about CFI
• U.S. Department of Transportation
• PB CFI Engineering Website

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