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]
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]
Listed in chronological order:
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. [12]
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.
The redesign of the Redwood Road/6200 South intersection in Taylorsville, Utah cut emissions of carbon dioxide by 19 tons (17 tonnes) per year. [36] 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. [37]
A parallel-flow intersection (PFI) is a variant similar to the CFI, patented in 2006. [38] 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. [39] 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″N75°05′45″W / 39.90412°N 75.095812°W ).
An intersection or an at-grade junction is a junction where two or more roads converge, diverge, meet or cross at the same height, as opposed to an interchange, which uses bridges or tunnels to separate different roads. Major intersections are often delineated by gores and may be classified by road segments, traffic controls and lane design.
A Michigan left or P-turn is an at-grade intersection design that replaces each left (farside) turn at an intersection between a (major) divided roadway and a secondary (minor) roadway with the combination of a right (nearside) turn followed by a U-turn, or a U-turn followed by a right (nearside) turn, depending on the situation. It is in use in numerous countries.
A cloverleaf interchange is a two-level interchange in which all turns are handled by slip roads. To go left, vehicles first continue as one road passes over or under the other, then exit right onto a one-way three-fourths loop ramp (270°) and merge onto the intersecting road. The objective of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by traffic lights. The limiting factor in the capacity of a cloverleaf interchange is traffic weaving.
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A single-point urban interchange, also called a single-point interchange (SPI) or single-point diamond interchange (SPDI), is a type of highway interchange. The design was created in order to help move large volumes of traffic through limited amounts of space efficiently.
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Loop 1604 is the outer highway loop encircling San Antonio, Texas, spanning approximately 95.6 miles (153.9 km). Originally constructed as a two-lane highway, the northern segment of the route, from US 90 in western San Antonio to Kitty Hawk Road in northeastern Bexar County, has been upgraded to a four-lane freeway. Loop 1604 is designated the Charles W. Anderson Loop in honor of former Bexar County Judge Charles W. Anderson, who died from cancer in 1964 after serving for 25 years.
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State Route 741 is a north–south state highway in the southwest portion of the U.S. state of Ohio. The southern terminus of the route is at a diamond interchange with I-71 at its Exit 25 near Kings Mills, adjacent to the Kings Island Amusement Park. State Route 741’s northern terminus is at a partial interchange with I-75 at its Exit 50B in Moraine, just south of Dayton.
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