Continuous flow intersection

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Continuous flow intersection between Maryland Route 210 and Maryland Route 228 in Accokeek, Maryland.
Continuous flow intersection between Maryland Route 210 and Maryland Route 228 in Accokeek, Maryland.

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 signal phase. The CFI is a patented design invented by Francisco Mier, of Mexico, where over 40 have been implemented over the past decade. As the design is patented, agencies must pay to obtain the rights for use of the design[1]; however, the patent has expired in the United States.[2] This general configuration is not new, as it appeared in various versions in various places with the implementation of channelization in the United States the 1950s, such as the Telegraph Road section of U.S. Route 24 in Michigan.

Contents

[edit] Locations outside of Mexico

Listed in order of implementation:

  1. Oaklyn, New Jersey, New Jersey Route 168 at U.S. Route 130.
  2. Shirley, New York, opened in 1996, at the entrance to Dowling College.[3]
  3. Accokeek, Maryland, opened in 2000, at the intersection of Routes 210 and 228.[3].
  4. Baton Rouge, Louisiana, opened in March 2006, at the intersection of Airline Hwy and Siegen Lane.[4]
  5. West Valley City, Utah, opened in September 2007,[5] at the intersection of Bangerter Highway and 3500 South[6]
  6. Fenton, Missouri, opened October 2007,[7] at the intersection of Highway 30 and Summit Drive/Gravois Bluffs Blvd.[8].

[edit] Operational details

Sample continuous flow intersection implemented for north/south traffic while east/west traffic has a regular left-turn lane
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 signals; through-traffic must wait for the traffic turning left. The continuous flow intersection moves the left-turn conflict to the signal 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 signals 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.

This type of intersection can require a significant amount of right-of-way to implement, which is why such configurations are not frequently used in urban areas[1]. 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] References

  1. ^ a b Hummer, Joseph E. and Jonathan D. Reid. Unconventional Left-Turn Alternatives for Urban and Suburban Arterials. Transportation Research Board. Retrieved on 13 June 2007.
  2. ^ United States Patent and Trademark Office, patent #5049000
  3. ^ a b Bruce, Michael G., P.E., and Paul W. Gruner, P.E., P.S. (28 December 2005). Continuous flow intersections. CENews.com. Retrieved on 13 June 2007.
  4. ^ Ruiz de Chavez, Lindsay (21 March 2006). First 'continuous-flow' intersection in the state opens on Airline today. Louisiana Department of Transportation & Development. Retrieved on 13 June 2007.
  5. ^ Whit Johnson. Continuous Flow Intersection Opens to Rush Hour Traffic. KSL Newsradio. Retrieved on 17 September 2007.
  6. ^ Utah Department of Transportation. 3500 South & Bangerter Highway CFI (Continuous Flow Intersection). Utah Department of Transportation. Retrieved on 13 June 2007.
  7. ^ Elisa Crouch. How do you get through this?. St. Louis Post-Dispatch. Retrieved on 31 October 2007.
  8. ^ Missouri Department of Transportation - St. Louis Area District. Continuous Flow Intersections. Missouri Department of Transportation - St. Louis Area District. Retrieved on 13 June 2007.

[edit] External links


Note that due to the relatively recent installation of the CFI in Baton Rouge, West Valley, UT, and Fenton, MO, some images may not show the existing conditions.
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Types of road junction
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