Continuous-flow intersection

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

A continuous flow intersection (CFI), also called a crossover displaced left-turn (XDL), is an alternative design for an at-grade road junction. Vehicles attempting to turn across the opposing direction of traffic (left in right-hand drive jurisdictions; right in left-hand drive jurisdictions) cross before they enter the intersection. No left turn signal in the intersection is then necessary. Instead, vehicles traveling in both directions can proceed, including through vehicles and those turning right or left, when a generic traffic signal/stop sign permits.

History[edit]

A fly-over designed CFI interchange (separated grade) was invented by Francisco Mier. An intersection (at-grade) variant followed. Over 40 have been implemented over since 2000. Mier patented his design, requiring a fee to obtain a license to the design.[1] The patent expired in the United States on 15 October 2003.[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 at Plymouth Road in Redford Charter Township, Michigan.[3]

United States[edit]

A continuous flow intersection between Maryland Route 210 and Maryland Route 228 in Accokeek, Maryland.
Sketch and Traffic Light Sequence

Listed in chronological order:

  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). 39°54′15″N 75°05′45″W / 39.90412°N 75.095812°W / 39.90412; -75.095812
  2. Shirley, New York, opened in 1996, at the entrance to Dowling College.[4] 40°49′35″N 72°52′52″W / 40.826443°N 72.881042°W / 40.826443; -72.881042
  3. Accokeek, Maryland, opened in 2000, at the intersection of Routes 210 and 228.[4] This 3-way junction is a hybrid, also having characteristics of a continuous green T (or seagull) intersection. While neither of the routes is grade-separated, southbound through traffic on Route 210 is free-flowing. 38°39′51″N 77°01′01″W / 38.664126°N 77.016928°W / 38.664126; -77.016928
  4. Baton Rouge, Louisiana, opened in March 2006, at the intersection of Airline Hwy and Siegen Lane.[5] 30°23′56″N 91°03′15″W / 30.398914°N 91.054119°W / 30.398914; -91.054119
  5. West Valley City, Utah, opened in September 2007,[6] at the intersections of Bangerter Highway and
    1. 5400 South (SR 173), 40°39′11″N 111°58′53″W / 40.652993°N 111.981339°W / 40.652993; -111.981339
    2. 4700 South, 40°40′03″N 111°58′54″W / 40.667596°N 111.981567°W / 40.667596; -111.981567
    3. 4100 South, 40°40′56″N 111°58′54″W / 40.682132°N 111.981626°W / 40.682132; -111.981626
    4. 3500 South.[7] 40°41′48″N 111°58′51″W / 40.696629°N 111.980869°W / 40.696629; -111.980869
  6. Fenton, Missouri, opened October 2007,[8] at the intersection of Highway 30 and Summit Drive/Gravois Bluffs Blvd.[9] 38°30′15″N 90°27′25″W / 38.504276°N 90.456995°W / 38.504276; -90.456995
  7. Miami Township, Montgomery County, Ohio, construction spring of 2009, at intersection of SR 741 and Miamisburg-Springboro Road/Austin Pike.[10] 39°35′48″N 84°13′45″W / 39.596709°N 84.229029°W / 39.596709; -84.229029
  8. 6200 South (Bennion Blvd) and 40°37′26″N 111°58′35″W / 40.62402°N 111.976379°W / 40.62402; -111.976379 7000 South - 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. As of March 11, 2011, four of them were in use.[11] 40°38′19″N 111°58′36″W / 40.638586°N 111.976626°W / 40.638586; -111.976626
  9. Natchez, Mississippi, opened January 2010 at the intersection of US 61 and Junkin Drive, designed by ABMB Engineers and constructed by MDOT. 31°31′43″N 91°23′21″W / 31.528599°N 91.389213°W / 31.528599; -91.389213
  10. Lafayette, Louisiana, ground broke January 2010 at the intersection of US 167 (Johnston St.) and Camellia Boulevard. Estimated cost of $3.5 million.[12] 30°11′37″N 92°03′31″W / 30.193744°N 92.058622°W / 30.193744; -92.058622
  11. Loveland, Colorado, ground broke June 2010 at the intersection of US 34 (Eisenhower Blvd.) and Madison Ave. Estimated cost of $4 million.[13] 40°24′27″N 105°03′32″W / 40.407365°N 105.058764°W / 40.407365; -105.058764
  12. Orem, Utah, opened May 22, 2012 at the intersection of University Parkway and Sandhill Road, as part of the Interstate 15 CORE project.[14] 40°16′30″N 111°42′48″W / 40.275014°N 111.713445°W / 40.275014; -111.713445

Operational details[edit]

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 typical, high-volume intersections is to accommodate left-turns; through-traffic must wait for the traffic turning left. The continuous flow intersection moves the left-turn conflict out of the intersection and synchronizes it with the signal cycle of the intersecting road.

In the diagram to the right, while the left/right traffic flows through the main intersection, the left-turn traffic crosses to the right of the oncoming traffic a few hundred feet away. 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.

The Louisiana DOTD article on the Baton Rouge CFI includes a particularly informative diagram of that intersection.[5]

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.

See also[edit]

References[edit]

  1. ^ Hummer, Joseph E. and Jonathan D. Reid. "Unconventional Left-Turn Alternatives for Urban and Suburban Arterials" (PDF). Transportation Research Board. Retrieved 13 June 2007. 
  2. ^ United States Patent and Trademark Office, US  5049000
  3. ^ Telegraph Road, Michigan 42°22′17″N 83°16′32″W / 42.371267°N 83.275563°W / 42.371267; -83.275563
  4. ^ a b Bruce, Michael G., P.E., and Paul W. Gruner, P.E., P.S. (2005-12-28). "Continuous flow intersections". CENews.com. Retrieved 13 June 2007. 
  5. ^ a b Ruiz de Chavez, Lindsay (2006-03-21). "First 'continuous-flow' intersection in the state opens on Airline today". Louisiana Department of Transportation & Development. Retrieved 13 June 2007. 
  6. ^ Whit Johnson. "Continuous Flow Intersection Opens to Rush Hour Traffic". KSL Newsradio. Retrieved 17 September 2007. 
  7. ^ Utah Department of Transportation. "3500 South & Bangerter Highway CFI (Continuous Flow Intersection)". Utah Department of Transportation. Retrieved 13 June 2007. 
  8. ^ Elisa Crouch. "How do you get through this?". St. Louis Post-Dispatch. Retrieved 31 October 2007. 
  9. ^ Missouri Department of Transportation - St. Louis Area District. "Continuous Flow Intersections". Missouri Department of Transportation - St. Louis Area District. Retrieved 13 June 2007. 
  10. ^ "Austin Pike Interchange ODOT". Ohio Department of Transportation-District 7. Retrieved 2009-02-26. 
  11. ^ Jed Boal. "UDOT plans Flex Lanes to ease congestion on 5400 South". KSL Newsradio. Retrieved 13 October 2009. 
  12. ^ Unknown. "Officials break ground on Camillia/Johnston project". The Advertiser. Retrieved 27 January 2010. [dead link]
  13. ^ City of Loveland. "Madison Improvements at US Hwy 34". Cit of Loveland. Retrieved 12 October 2010. 
  14. ^ "University Parkway CFI". 

External links[edit]

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.