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Continuous-flow intersection

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Sample continuous-flow intersection with typical lane variation, turn restrictions, and traffic light position
A continuous flow intersection in West Valley City, Utah showing the layout and normal traffic flow in the southwest portion of the intersection.
Driving through a continuous flow intersection on Utah State Route 154 (Bangerter Highway) at 4100 South in summer 2013.

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.

Its design also is promoted as part of the Federal Highway Administration's Every Day Counts initiative which started in 2011.[1]

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 and required a fee to obtain a license to the design.[2] The patent expired in the United States on 15 October 2003.[3]

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.[4]

Usage

List of places where a CFI is used
Country State/Province City Roads Opening date Coordinates Notes
Australia Queensland Gold Coast Salerno Street, Bundall Road and Ashmore Road December 2017
Victoria Melbourne Hoddle Street 2017
New South Wales Moore Park Intersection of Anzac Parade, Alison Road and Dacey Avenue 2017
Canada Prince Edward Island Charlottetown Charlottetown Perimeter Highway and St. Peters Road November 29, 2020 46.268692°N 63.114001°W
China Guangdong Shenzhen Caitian Road and Fuhua October 7, 2017
Germany Hamburg Breitenfelder Straße (Bundesstraße 5) and Tarpenbekstraße (Bundesstraße 433) 53.590267°N 9.982989°E
Mexico Coahuila Saltillo Paseo de la Reforma and Periférico und Luis Echeverría 25.42739°N 100.969859°W
Chihuahua Juárez Municipality Manuel Gómez Morin Bermúdez aund De La Industria 31.70368°N 106.401998°W
Nuevo León Guadalupe Island Between Chapultepec, Puesta del Sol and Av Eloy Cavazos 25.661967°N 100.258747°W
United Kingdom Swindon A4311 road, Cricklade Road and Thamesdown Drive 2003 51.601158562°N 1.7812545°W
New Jersey Camden New Jersey Route 168 at US Route 130
Audubon, New Jersey New Jersey Route 168 at Nicholson Road 39.894161°N 75.091435°W
New York Shirley 1996 40.826443°N 72.881042°W
Maryland Accokeek Routes 210 and 228 2000 38.664126°N 77.016928°W
Louisiana Baton Rouge Airline Highway and Siegen Lane March 2006 30.398914°N 91.054119°W
Utah Taylorsville Bangerter Highway and 5400 South (SR-173) 40.652993°N 111.981339°W No longer exists
West Valley City Bangerter Highway and 4700 South 40.667596°N 111.981567°W No longer exists
Bangerter Highway and 4100 South 40.682132°N 111.981626°W
Bangerter Highway and 3500 South (SR-171) September 2007 40.696629°N 111.980869°W
Bangerter Highway and 3100 South 40.703918°N 111.980076°W
Bangerter Highway and 6200 South (Bennion Boulevard) 40.638581°N 111.976637°W No longer exists
5400 S (SR-173) and Redwood Road 40.653176°N 111.938802°W
6200 South (Bennion Boulevard) and Redwood Road 40.638574°N 111.938824°W
Riverton Bangerter Highway and 13400 South 40.507803°N 111.982747°W
West Jordan Bangerter Highway and 7000 South 40.623983°N 111.976422°W No longer exists
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.
Map all coordinates using OpenStreetMap

Download coordinates as:

Operational details

Part of the delay at a typical high-volume right-hand traffic intersection 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.[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.

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.[6] 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.[7]

Parallel-flow intersection

A parallel-flow intersection (PFI) is a variant similar to the CFI, patented in 2006.[8] 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.[9] This was first used in New Jersey at the junction of New Jersey Route 168 and US Highway 130, between Haddon Township and Camden (39°54′15″N 75°05′45″W / 39.90412°N 75.095812°W / 39.90412; -75.095812).

See also

References

  1. ^ Schroeder, Bastian; Cunningham, Chris; Ray, Brian; Daleiden, Andy; Jenior, Pete; Knudsen, Julia (August 2014). Diverging Diamond Interchange Informational Guide (PDF). Washington, DC: Federal Highway Administration Office of Safety.
  2. ^ Hummer, Joseph E.; Reid, Jonathan D. "Unconventional Left-Turn Alternatives for Urban and Suburban Arterials" (PDF). Transportation Research Board. Archived from the original (PDF) on 30 September 2007. Retrieved 13 June 2007.
  3. ^ United States Patent and Trademark Office, US  5049000
  4. ^ Telegraph Road, Michigan 42°22′17″N 83°16′32″W / 42.371267°N 83.275563°W / 42.371267; -83.275563
  5. ^ Ruiz de Chavez, Lindsay (2006-03-21). "First 'continuous-flow' intersection in the state opens on Airline today". Louisiana Department of Transportation & Development. Archived from the original on 2010-05-27. Retrieved 4 August 2018.
  6. ^ FHWA: DLT Case Study – Redwood Road at 6200 South in Taylorsville (Utah), published July 31, 2014
  7. ^ FHWA: DLT Case Study – Bangerter Highway in Salt Lake County (Utah), published July 31, 2014
  8. ^ 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 
  9. ^ Federal Highway Administration: Alternative Intersections/Interchanges: Informational Report (AIIR), Publication Number: FHWA-HRT-09-060, April 2010
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