Diamond interchange

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Visual showing how diamond interchanges are used, with an expressway running across and a local road running in the center. Left image is for left-side traffic (UK), right image is for right-side traffic (US). Large arrows show where turns are made; smaller arrows show traffic flow. Diamond interchange dual.svg
Visual showing how diamond interchanges are used, with an expressway running across and a local road running in the center. Left image is for left-side traffic (UK), right image is for right-side traffic (US). Large arrows show where turns are made; smaller arrows show traffic flow.

A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road.



A typical diamond interchange Florida SR 408 at SR 435.jpg
A typical diamond interchange

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.



A dumbbell interchange. AS Hantel.svg
A dumbbell interchange.

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 [2] (due to its aerial resemblance to a dumbbell), and sometimes called a double roundabout interchange. [3] [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. [4]

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 / 50.914055; 6.323368 .

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 / -34.7495; -55.6775 ).


A dogbone interchange. AS Knochen.svg
A dogbone interchange.

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. [4] An example of a dogbone interchange in the United States is located on Interstate 70 in Avon, Colorado; more compact examples, which show less of the characteristic "dog bone" shape, are located along Keystone Parkway in Carmel, Indiana. 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 / 53.21462; 6.602509 ); 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 / -32.32486; 115.76704 ).

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 / -31.96945; 116.00107 ). [6]

Tight diamond

A tight urban diamond interchange (TUDI) AS TUDI.svg
A tight urban diamond interchange (TUDI)

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. [8] Caltrans classifies this type as Type L-1. [9]

Single-point urban

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. [9]

Contraflow left

A contraflow left turn interchange AS CFL.svg
A contraflow left turn interchange

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 / 26.301177; -80.186479 . [10] [11]

Diverging diamond

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.

Three-level diamond

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).

Continuous-flow diamond

Continuous-flow diamond TUDI TX-CFI.svg
Continuous-flow diamond

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. [12] [13] 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. [14] In both intersections, the displaced left turn lanes merge with the Texas U-turn lanes.

Split diamond

Split diamond interchange Split diamond interchange.svg
Split diamond interchange

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. [15] [16]


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.

See also

Related Research Articles

Roundabout Traffic intersection

A roundabout is a type 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.

Frontage road Type of road

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-express lanes.

Cloverleaf interchange

A cloverleaf interchange is a two-level interchange in which left turns are handled by ramp 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 red lights, even for left and right turns. The limiting factor in the capacity of a cloverleaf interchange is traffic weaving.

Grade separation Type of road junction

In civil engineering, grade separation is a method of aligning a junction of two or more surface transport axes at different heights (grades) so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a mixture of roads, footpaths, railways, canals, or airport runways. Bridges, tunnels, or a combination of both can be built at a junction to achieve the needed grade separation.

Single-point urban interchange Highway interchange design

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 safely and efficiently.

Partial cloverleaf interchange

A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange.

Superstreet Type of high capacity intersection

A superstreet, also known as a restricted crossing U-turn (RCUT), J-turn, or reduced conflict intersection (RCI), is a type of road intersection that is a variation of the Michigan left. In this configuration, in contrast to the Michigan left, traffic on the minor road is not permitted to proceed straight across the major road or highway. Drivers on the minor road wishing to turn left or go straight must turn right onto the major road, then, a short distance away, queue (wait) into a designated U-turn lane in the median. When traffic clears, they complete the U-turn and then either go straight or make a right turn when they intersect the other half of the minor road.

Diverging diamond interchange Freeway interchange design

A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a type of diamond interchange in which the two directions of traffic on the non-freeway road cross to the opposite side on both sides of the bridge at the freeway. It is unusual in that it requires traffic on the freeway overpass to briefly drive on the opposite side of the road from what is customary for the jurisdiction. The crossover "X" sections can either be traffic-light intersections or one-side overpasses to travel above the opposite lanes without stopping, to allow nonstop traffic flow when relatively sparse traffic.

Interchange (road) Road junction, typically using grade separation

In the field of road transport, an interchange is a road junction that uses grade separation, and typically one or more ramps, to permit traffic on at least one highway to pass through the junction without interruption from other 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.

Stack interchange

A stack interchange is a particular, free-flowing type of design for interchanges, meaning grade-separated road junctions. It is referred to as a directional interchange in the American Association of State Highway and Transportation Officials Policy on Geometric Design of Highways and Streets.

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.

Interstate 85 Business is a business loop of the Interstate Highway System. It is entirely a freeway running along the old route of I-85 in the vicinity of Spartanburg, South Carolina, United States. It is the only freeway to connect with Interstate 585, which is now an isolated piece of the Interstate Highway System.

Three-level diamond interchange Type of highway interchange

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.

State Route 500 (SR 500) is a state highway in Clark County, Washington, United States. The east–west highway runs through Vancouver as an expressway and its eastern suburbs as a country road, connecting Interstate 5 (I-5) to I-205 in eastern Vancouver and SR 14 in Camas. SR 500 runs concurrent to SR 503 within Orchards and also uses a section of the county-built Padden Parkway.

Roundabout interchange

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.

There are 13 active business routes of Interstate 70 in Colorado. I-70 spans Colorado in an east-west fashion, holding many business loops and spurs along the way varying from lengths of 0.22 mi (0.35 km) to 27.47 mi (44.21 km), with a total of 55.51 miles. Four other business routes also used to exist within the state.

Glossary of road transport terms Wikipedia glossary

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.


Diamond interchange on US-35 to I-71 in Jeffersonville, Ohio, at
39deg37'10''N 83deg36'28''W / 39.61945degN 83.607858degW / 39.61945; -83.607858 Overview of West Lancaster.jpg
Diamond interchange on US-35 to I-71 in Jeffersonville, Ohio, at 39°37′10″N83°36′28″W / 39.61945°N 83.607858°W / 39.61945; -83.607858
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  9. 1 2 https://dot.ca.gov/-/media/dot-media/programs/design/documents/chp0500-032020.pdf
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  13. Intersection Improvements to SH 80 and Loop 82 at I-35 777 E Hopkins St, Texas State University, retrieved 30 December 2014.
  14. TxDOT to modify recently completed I-35, Hopkins Street interchange, San Marcos Mercury, 18 May 2015.
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