Continuous-flow intersection

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 or DLT), 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

A fly-over designed CFI interchange (separated grade) was invented by Francisco Mier. An intersection (at-grade) variant followed. Over 40 have been implemented 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]

Usage

Australia
Germany
Mexico
United Kingdom
United States
A continuous flow intersection between Maryland Route 210 and Maryland Route 228 in Accokeek, Maryland.
Sketch and traffic light sequence of a four-way intersection with displaced left turns on two of the legs.

Listed in chronological order:

  1. Haddon Township, Audubon and Audubon Park, New Jersey, New Jersey Route 168 at Nicholson Road, is a hybrid one-leg continuous flow intersection that also employs a jughandle. 39°53′39″N 75°05′29″W / 39.894161°N 75.091435°W / 39.894161; -75.091435
  2. Shirley, New York, opened in 1996, at the entrance to Dowling College.[6] 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.[6] This is an example of a CFI-T, which is a T intersection containing one CFI leg. This junction also has characteristics of a continuous green T (or seagull) intersection.[7] 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 Highway and Siegen Lane.[8] 30°23′56″N 91°03′15″W / 30.398914°N 91.054119°W / 30.398914; -91.054119
  5. Along Utah State Route 154 (Bangerter Highway) at
    1. 5400 South (SR-173) in Taylorsville, 40°39′11″N 111°58′53″W / 40.652993°N 111.981339°W / 40.652993; -111.981339
    2. 4700 South in Taylorsville and West Valley City, 40°40′03″N 111°58′54″W / 40.667596°N 111.981567°W / 40.667596; -111.981567
    3. 4100 South in West Valley City, 40°40′56″N 111°58′54″W / 40.682132°N 111.981626°W / 40.682132; -111.981626
    4. 3500 South (SR-171) in West Valley City,[9] opened in September 2007,[10] 40°41′48″N 111°58′51″W / 40.696629°N 111.980869°W / 40.696629; -111.980869
    5. 3100 South in West Valley City, 40°42′14″N 111°58′48″W / 40.703918°N 111.980076°W / 40.703918; -111.980076
  6. Fenton, Missouri, opened October 2007,[11] at the intersection of Highway 30 and Summit Drive/Gravois Bluffs Boulevard.[12] 38°30′15″N 90°27′25″W / 38.504276°N 90.456995°W / 38.504276; -90.456995
  7. Miami Township, Montgomery County, Ohio, a two-leg CFI constructed in the spring of 2009, at the intersection of SR 741 and Miamisburg-Springboro Road/Austin Boulevard.[13] 39°35′48″N 84°13′45″W / 39.596709°N 84.229029°W / 39.596709; -84.229029
  8. Salt Lake County, Utah, in October 2009, the Utah Department of Transportation announced plans for five more continuous flow intersections along Bangerter Highway and Redwood Road (SR-68). As of March 11, 2011, four of them were in use.[14]
    1. 13400 South and Bangerter Highway in Riverton, 40°30′28″N 111°58′58″W / 40.507803°N 111.982747°W / 40.507803; -111.982747
    2. 7000 South and Bangerter Highway in West Jordan, 40°37′26″N 111°58′35″W / 40.623983°N 111.976422°W / 40.623983; -111.976422
    3. 6200 South (Bennion Boulevard) and Bangerter Highway in Taylorsville, 40°38′19″N 111°58′36″W / 40.638581°N 111.976637°W / 40.638581; -111.976637
    4. W 5400 S (SR-173) and Redwood Road in Taylorsville, 40°39′11″N 111°56′20″W / 40.653176°N 111.938802°W / 40.653176; -111.938802
    5. 6200 South (Bennion Boulevard) and Redwood Road in Taylorsville, 40°38′19″N 111°56′20″W / 40.638574°N 111.938824°W / 40.638574; -111.938824
  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.[15] 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 Boulevard) and Madison Avenue. Estimated cost of $4 million.[16] 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.[17] 40°16′30″N 111°42′48″W / 40.275014°N 111.713445°W / 40.275014; -111.713445
  13. Durango, Colorado, at the intersection of US 160 and US 550. Estimated cost of $6.1 million.[18] 37°16′07″N 107°53′06″W / 37.268540°N 107.884992°W / 37.268540; -107.884992
  14. San Marcos, Texas, two CFIs were constructed. One is a single-leg CFI at the intersection of Loop 82 (Aquarena Springs Drive), Interstate 35's southbound frontage road and I-35's southbound-to-northbound Texas U-turn (29°53′35″N 97°54′48″W / 29.893048°N 97.913367°W / 29.893048; -97.913367). The other, a two-leg CFI, is at the intersection of State Highway 80 (Hopkins Street), I-35's frontage roads and I-35's Texas U-turns (29°52′58″N 97°55′19″W / 29.882639°N 97.921915°W / 29.882639; -97.921915). In both intersections, the displaced left turn lanes merge with the Texas U-turn lanes. The estimated cost for both CFIs is $4.7 million.[19]

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 typical, high-volume intersections is to accommodate left-turns; through-traffic must wait for the traffic turning left because it crosses the path of the through traffic. 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 adjacent diagram, while the left/right traffic flows through the main intersection, the left-turn traffic crosses to the opposite side of the oncoming traffic a few hundred feet away. Doing this removes the crossing conflict. When the north/south through traffic is allowed through the main intersection, the north/south left-turn lanes are also allowed through the intersections as their paths are no longer crossing. 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.[8]

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.

Case studies

The redesign of the Redwood Road/6200 South intersection in Taylorsville, Utah cut emissions of carbon dioxide by 19 tons (17 tonnes) per year.[20] Compared to the previous design, the redesign of the Bangerter Highway/3500 South intersection saves  3 1⁄2 minutes of travel time per vehicle and 800,000 U.S. gallons (3,000,000 liters) of fuel per year, and has 60% fewer accidents nearby; it also cost $20 million to $40 million less in construction costs than a grade-separated alternative.[21]

Parallel-flow intersection

A parallel-flow intersection (PFI) is a variant similar to the CFI, patented in 2006.[22] It arranges the left-turning traffic in a different manner; it is not displaced, instead turning left closer to the intersection onto a parallel roadway, to the left of oncoming traffic.[23] This was first used in Haddon Township and Camden, New Jersey between New Jersey Route 168 and US Highway 130 at 39°54′15″N 75°05′45″W / 39.90412°N 75.095812°W / 39.90412; -75.095812.

See also

References

  1. ↑ Hummer, Joseph E.; 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
  4. ↑ http://www.theage.com.au/victoria/radical-plan-to-ease-hoddle-street-gridlock-20150321-1m4iyz.html
  5. ↑ Areal photos in Google Earth of 31 December 2002, retrieved 22. July 2015
  6. 1 2 Bruce, Michael G. & Paul W. Gruner (2005-12-28). "Continuous flow intersections". CENews.com. Retrieved 13 June 2007.
  7. ↑ Xianfeng Yang and Yang Lu Gang-Len Chang: An Integrated Computer System for Analysis Selection and Evaluation of Unconventional Intersections Report, University Of Maryland and Maryland State Highway Administration, Publication No. MD-11-SP909B4H, March 2011, retrieved 25 march 2015
  8. 1 2 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.
  9. ↑ Utah Department of Transportation. "3500 South & Bangerter Highway CFI (Continuous Flow Intersection)". Utah Department of Transportation. Retrieved 13 June 2007.
  10. ↑ Whit Johnson. "Continuous Flow Intersection Opens to Rush Hour Traffic". KSL Newsradio. Retrieved 17 September 2007.
  11. ↑ Elisa Crouch. "How do you get through this?". St. Louis Post-Dispatch. Retrieved 31 October 2007.
  12. ↑ Missouri Department of Transportation - St. Louis Area District. "Continuous Flow Intersections". Missouri Department of Transportation - St. Louis Area District. Retrieved 13 June 2007.
  13. ↑ "Austin Pike Interchange ODOT". Ohio Department of Transportation-District 7. Retrieved 2009-02-26.
  14. ↑ Jed Boal. "UDOT plans Flex Lanes to ease congestion on 5400 South". KSL Newsradio. Retrieved 13 October 2009.
  15. ↑ Unknown. "Officials break ground on Camillia/Johnston project". The Advertiser. Retrieved 27 January 2010.
  16. ↑ City of Loveland. "Madison Improvements at US Hwy 34". Cit of Loveland. Retrieved 12 October 2010.
  17. ↑ "University Parkway CFI".
  18. ↑ US 160/US 550 Durango Continuous Flow Intersection
  19. ↑ Intersection Improvements to SH 80 and Loop 82 at I-35, Texas State University, retrieved December 30, 2014
  20. ↑ FHWA: DLT Case Study – Redwood Road at 6200 South in Taylorsville (Utah), published July 31, 2014
  21. ↑ FHWA: DLT Case Study – Bangerter Highway in Salt Lake County (Utah), published July 31, 2014
  22. ↑ B2 US patent 7135989 B2, Gregory Fife Parsons, "Parallel flow vehicle turn system for traffic intersections", issued 2006-11-14, assigned to Gregory Fife Parsons
  23. ↑ Federal Highway Administration: Alternative Intersections/Interchanges: Informational Report (AIIR), Publication Number: FHWA-HRT-09-060, April 2010
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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