A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road.
A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road.
The freeway itself is grade-separated from the minor road, one crossing the other over a bridge. Approaching the interchange from either direction, an off-ramp diverges only slightly from the freeway and runs directly across the minor road, becoming an on-ramp that returns to the freeway in similar fashion.
The two places where the ramps meet the road are treated as conventional intersections. In the United States, where this form of interchange is very common, particularly in rural areas, traffic on the off-ramp typically faces a stop sign at the minor road, while traffic turning onto the freeway is unrestricted.
The diamond interchange uses less space than most types of freeway interchange, and avoids the interweaving traffic flows that occur in interchanges such as the cloverleaf. Thus, diamond interchanges are most effective in areas where traffic is light and a more expensive interchange type is not needed. But where traffic volumes are higher, the two intersections within the interchange often feature additional traffic control measures such as traffic lights and extra lanes dedicated to turning traffic.
The at-grade variant of the diamond interchange is the split intersection.
The ramp intersections may also be configured as a pair of roundabouts [1] to create a type of diamond interchange often called a dumbbell interchange[ citation needed ] (due to its aerial resemblance to a dumbbell), and sometimes called a double roundabout interchange. [2] [1] Because roundabouts can generally handle traffic with fewer approach lanes than other intersection types, interchange construction costs can be reduced by eliminating the need for a wider bridge. This configuration allows other roads to form approach legs to the roundabouts and also allows easy U-turns. [3]
This type of interchange is common in the United Kingdom and Ireland, and is becoming increasingly common in the United States. Examples of dumbbell interchanges in the United States are located on Interstate 35 in Medford, Minnesota, on Interstate 87 in Malta, New York, on Interstate 17 at Happy Valley Road north of Phoenix, Arizona, and on Interstate 80 at California State Route 89 (exit 185) in Truckee, California. An example in Canada is found on the Pat Bay Highway in North Saanich, British Columbia, near Victoria International Airport.
One or both roundabouts in the dumbbell interchange may also contain side lanes to increase the capacity. A good example of such a "turbo" dumbbell interchange, which was formerly a half cloverleaf, can be seen in Jülich, Germany at 50°54′51″N6°19′24″E / 50.914055°N 6.323368°E .
There are interchanges similar to dumbbells in which the ramps do not meet the roundabouts at intersections; these more closely resemble bowtie intersections. One such interchange exists at the junction between the Ruta Interbalnearia and Route 35 North near La Floresta, Uruguay ( 34°44′58″S55°40′39″W / 34.7495°S 55.6775°W ).
A variation of the dumbbell interchange, often called a dogbone interchange (due to its aerial resemblance to a real or toy dog bone), and sometimes also called a double roundabout interchange, [1] occurs when the roundabouts do not form a complete circle but instead have a "raindrop" or "teardrop" shape. These two raindrop roundabouts are fused together, forming a single "squashed" roundabout.
This configuration reduces conflicts between vehicles entering the raindrop roundabouts from the ramps, reducing queueing and delays, compared with the dumbbell interchange. Direct U-turns are not possible, although the movement can be made by circulating around both raindrop roundabouts. [3] An example of a dogbone interchange in the United States is located on Interstate 70 in Avon, Colorado, United States; [4] more compact examples, which show less of the characteristic "dog bone" shape, are located along Keystone Parkway in Carmel, Indiana, United States. Several interchanges similar to those along Keystone Parkway are being built along the new US 31 freeway under construction in northern Indiana. [5]
There are some hybrid interchanges of dumbbell and dogbone having one raindrop and one full roundabout. This is made when the roundabout intersects more roads than the cross street and ramps. Some examples are at exit 38 of the N7 road in Groningen, Netherlands (at 53°12′53″N6°36′09″E / 53.21462°N 6.602509°E ); and Ennis Avenue (National Route 1) at Safety Bay Road (State Route 18 / Tourist Drive 202) on the border of the suburbs of Waikiki and Warnbro in the City of Rockingham, Western Australia (at 32°19′29″S115°46′01″E / 32.32486°S 115.76704°E ).
A tennis ball interchange resembles a dogbone interchange, with the difference being that right turning movements (in a country where traffic drives on the left) cut through the roundabouts like a regular diamond interchange instead of going around the roundabout. Such a design is found in Perth, Western Australia, between Roe Highway (State Route 3) and Berkshire Road (at 31°58′10″S116°00′04″E / 31.96945°S 116.00107°E ). [6]
A tight diamond interchange (TDI), also known as a compressed diamond interchange or a tight urban diamond interchange (TUDI), is sometimes used in areas where there is insufficient right-of-way for a standard diamond interchange. The pair of intersections where the ramps meet the minor road are closely spaced. [1] [7] This spacing forces the turn lanes for each direction to run beside each other, causing the minor road to be wider than it would be if it were a standard diamond.[ citation needed ] Caltrans classifies this type as Type L-1. [8]
A single-point urban interchange (SPUI) is built with a large over- or clear underpass providing space for a single traffic signal controlled intersection with the ramps and the cross street. Caltrans classifies this type as Type L-13. [8]
A contraflow left interchange (CFL) is a modified TUDI, once installed at Lyons Road underneath Florida State Road 869, switching the left turn lanes on the cross street each other and bringing the long left turn phases from the single-point urban interchange to the tight urban diamond interchange at 26°18′04″N80°11′11″W / 26.301177°N 80.186479°W . [9] [10]
In a diverging diamond interchange (DDI) or (DCD), the two directions of traffic on the non-freeway road cross to the opposite side on both sides of the bridge at the freeway to save the third traffic signal phase.
In a three-level diamond interchange , the cross street is built in a third level with free flowing traffic as a second arterial road. The intersection is split up into four intersections, handling just two conflicting directions each.
Its two-level variant is the split diamond interchange.
Its at-grade variant is the town center intersection (TCI).
A single-leg continuous-flow intersection (CFI) was built in 2014 in San Marcos, Texas, at the intersection of Aquarena Springs Drive (Loop 82), Interstate 35's southbound frontage road and I-35's southbound-to-northbound Texas U-turn. [11] [12] A two-leg CFI, also in San Marcos, was built in 2015 at the intersection of Hopkins Street (State Highway 80), I-35's frontage roads and I-35's Texas U-turns. [13] In both intersections, the displaced left turn lanes merge with the Texas U-turn lanes.
A split diamond interchange has its ramps "split" between two crossroads, typically with an exit ramp/entrance ramp pair serving each of the crossroads. The crossroads themselves may be one-way or two-way, and are most often connected by frontage roads, usually one-way. [14] [15]
Where HOV lanes are present for carpooling, the ramps of a diamond interchange may be folded to the inside lanes instead of the outside. In urban areas this saves some space as well as requiring only one intersection instead of the two one-way intersections, which in rural or suburban areas can be turned into a single-point urban interchange. This in turn reduces waiting time for motorists at traffic lights on the smaller road, which may be a large local thoroughfare with heavy traffic.
In Henrietta, New York, Jefferson Road (NY-252) crosses West Henrietta Road (NY-15) on a modified diamond interchange, where traffic merges onto NY-252 at signalized intersections without any merge lanes, as well as Texas U-turns and RIROs on the ramps.
A roundabout, a rotary and a traffic circle are types of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.
Interstate 45 (I-45) is a major Interstate Highway located entirely within the U.S. state of Texas. While most primary Interstate routes which have numbers ending in "5" are cross-country north–south routes, I-45 is comparatively short, with the entire route located within Texas. Additionally, it has the shortest length of all the primary Interstates that have numbers ending in a "5". It connects the cities of Dallas and Houston, continuing southeast from Houston to Galveston over the Galveston Causeway to the Gulf of Mexico.
A frontage road is a local road running parallel to a higher-speed, limited-access road. A frontage road is often used to provide access to private driveways, shops, houses, industries or farms. Where parallel high-speed roads are provided as part of a major highway, these are also known as local lanes. Sometimes a similar arrangement is used for city roads; for example, the collector portion of Commonwealth Avenue in Boston, Massachusetts, is known as a carriage road.
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.
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.
A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange.
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A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of diamond interchange in which the opposing directions of travel on the non-freeway road cross each other on either side of the interchange so that traffic crossing the freeway on the overpass or underpass is operating on the opposite driving side from that which is customary for the jurisdiction. The crossovers may employ one-side overpasses or be at-grade and controlled by traffic lights.
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In the field of road transport, an interchange or a grade-separated junction is a road junction that uses grade separations to allow for the movement of traffic between two or more roadways or highways, using a system of interconnecting roadways to permit traffic on at least one of the routes to pass through the junction without interruption from crossing traffic streams. It differs from a standard intersection, where roads cross at grade. Interchanges are almost always used when at least one road is a controlled-access highway or a limited-access divided highway (expressway), though they are sometimes used at junctions between surface streets.
Contraflow lane reversal is the altering of the normal flow of traffic, typically on a controlled-access highway, to either aid in an emergency evacuation or, as part of routine maintenance activities, to facilitate widening or reconstruction of one of the highway's carriageways.
A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges eliminate the problems of weaving, have the highest vehicle capacity, and vehicles travel shorter distances when compared to different types of interchanges.
A junction is where two or more roads meet.
In the field of road transport, a turnaround is a type of junction that allows traffic traveling in one direction on a road to efficiently make a U-turn typically without backing up or making dangerous maneuvers in the middle of the traffic stream. While many junction types permit U-turns, the term turnaround often applies to road junctions built specifically for this purpose.
A three-level diamond interchange is a type of highway interchange where through traffic on both main roads is grade-separated from intersections which handle transferring traffic. It is similar in design to a three-level stacked roundabout except for its use of conventional intersections, and can be thought of as two diamond interchanges fused together.
A roundabout interchange is a type of interchange between a controlled access highway, such as a motorway or freeway, and a minor road. The slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges.
James River Freeway is a 14-mile-long (23 km) freeway located largely on the south side of Springfield, Missouri. Its western terminus is at Interstate 44 (I-44) north of Brookline and its eastern terminus is at U.S. Route 65 (US 65) in southeastern Springfield. It is named for the James River, which passes near the highway at the freeway's eastern terminus. A total of four highways are routed on the highway: Route 360, US 60, US 160, Route 13, and Business US 65.
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Terminology related to road transport—the transport of passengers or goods on paved routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single country, and some terms differ based on the side of the road traffic drives on. This glossary is an alphabetical listing of road transport terms.
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