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Continuous flow intersection in West Valley City, Utah showing the layout and normal traffic flow in the southwest portion of the intersection.

Continuous flow intersection (CFI), also called a crossover displaced left-turn (XDL), is an at-grade intersection that moves the turning vehicles, conflicting with the through movements, (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. A fly-over designed CFI (non at-grade) was a previously patented design invented by Francisco Mier, of Mexico. Over 40 have been implemented over the past decade. As the design was patented, agencies previously had to pay to obtain the rights for use of the design[1]; however, the patent has expired in the United States.[2] This general configuration has appeared in different versions in various places, with the implementation of channelization in the United States since the 1950s, such as the Telegraph Road section of U.S. Route 24 in Michigan.

Contents

Locations outside of Mexico

Listed in order of implementation:

  1. Haddon Township, New Jersey and Audubon Park, New Jersey, New Jersey Route 168 at Nicholson Road, is a hybrid continuous flow intersection that also employs a jughandle. (A nearby intersection on New Jersey Route 168 at US Highway 130 in Haddon Township, New Jersey and Camden, New Jersey resembles a Parallel Flow Intersection, or PFI).
  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].
  7. Miami Township, Ohio, construction spring of 2009, at intersection of SR 741 and Miamisburg-Springboro Road/ Austin Pike.[9]
  8. Salt Lake County, Utah, announced October 2009, the Utah Department of Transportation revealed plans for five more continuous flow intersections along Bangerter Highway and Redwood Road. [10]
  9. Natchez, MS, opened January 2010 at the intersection of US 61 and Junkin Drive, designed by ABMB Engineers and constructed by MDOT
  10. Lafayette, Louisiana, ground broke January 2010 at the intersection of US 165 (Johnston St.) and Camellia Boulevard. Estimated cost of $3.5 Million.[11]

Operational 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 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 the speed differential, a known cause of accidents, though conflicts could be reduced through the provision of an adequate acceleration lane and merge area. The Accokeek, MD CFI also has notable inequalities in traffic flow depending upon the direction of travel.

This type of intersection can require a significant amount of right-of-way to implement (dependent upon the configuration), which is why the technique is not frequently used in urban areas. However, the amount of right-of-way 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.

References

  1. ^ Hummer, Joseph E. and Jonathan D. Reid. "Unconventional Left-Turn Alternatives for Urban and Suburban Arterials" (PDF). Transportation Research Board. http://www.urbanstreet.info/1st_symp_proceedings/Ec019_e3.pdf. Retrieved 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. (2005-12-28). "Continuous flow intersections". CENews.com. http://www.cenews.com/article.asp?id=312. Retrieved 13 June 2007. 
  4. ^ Ruiz de Chavez, Lindsay (2006-03-21). "First 'continuous-flow' intersection in the state opens on Airline today". Louisiana Department of Transportation & Development. http://www.dotd.louisiana.gov/press/pressrelease.asp?nRelease=627. Retrieved 13 June 2007. 
  5. ^ Whit Johnson. "Continuous Flow Intersection Opens to Rush Hour Traffic". KSL Newsradio. http://www.ksl.com/?nid=148&sid=1818294. Retrieved 17 September 2007. 
  6. ^ Utah Department of Transportation. "3500 South & Bangerter Highway CFI (Continuous Flow Intersection)". Utah Department of Transportation. http://www.udot.utah.gov/cfi/. Retrieved 13 June 2007. 
  7. ^ Elisa Crouch. "How do you get through this?". St. Louis Post-Dispatch. http://www.stltoday.com/stltoday/news/stories.nsf/stlouiscitycounty/story/98FA052BF09ED6468625738500198B0C?OpenDocument. Retrieved 31 October 2007. 
  8. ^ Missouri Department of Transportation - St. Louis Area District. "Continuous Flow Intersections". Missouri Department of Transportation - St. Louis Area District. http://www.modot.org/stlouis/links/ContinuousFlowIntersections2.htm. Retrieved 13 June 2007. 
  9. ^ "Austin Pike Interchange ODOT". http://www.dot.state.oh.us/districts/D07/Projects/Pages/AustinPike.aspx. Retrieved 2009-02-26. 
  10. ^ Jed Boal. "UDOT plans Flex Lanes to ease congestion on 5400 South". KSL Newsradio. http://www.ksl.com/?nid=148&sid=8295471. Retrieved 13 October 2009. 
  11. ^ Unknown. "Officials break ground on Camillia/Johnston project". The Advertiser. http://www.theadvertiser.com/article/20100127/NEWS01/100127019/Officials+break+ground+on+Camellia/Johnston+project. Retrieved 27 January 2010. 

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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