View source for Diamond interchange

{{Short description|Common type of road junction}}
{{Use mdy dates|date=December 2013}}
[[File:I-285 Aerial Facing North - Exit 2 - GA6 Camp Creek Parkway (40207555550).jpg|thumb|right|Diamond interchange between [[Interstate 285 (Georgia)|Interstate 285]] and [[Georgia State Route 6]] in Atlanta. This example has since been converted into a [[diverging diamond interchange]].]]
[[Image:Diamond interchange dual.svg|thumb|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.

== Design ==
[[Image:Florida SR 408 at SR 435.jpg|thumb|A typical diamond interchange]]

The freeway itself is [[grade separation|grade-separated]] from the minor road, one crossing the other over a [[bridge]]. Approaching the [[interchange (road)|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 [[Interchange (road)|ramp]]s meet the road are treated as conventional [[intersection (road)|intersection]]s.  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 [[grade separation#Weaving|interweaving]] traffic flows that occur in interchanges such as the [[cloverleaf interchange|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 light]]s and extra [[lane]]s dedicated to turning traffic.

The at-grade variant of the diamond interchange is the [[split intersection]].

==Variations==
<!-- linked from redirect [[dogbone interchange]], [[double roundabout interchange]], [[dumbbell interchange]] -->

=== Dumbbell ===
{{For|the at-grade intersection design analogous to dumbbell and dogbone interchanges|Bowtie (road)}}
[[File:Holt Road Dogbone.png|thumb|right|A dumbbell interchange along [[Ontario Highway 401]] in [[Clarington|Clarington, Ontario]], Canada. This one features a loop ramp.<br />{{coord|43|53|3|N|78|43|20|W}}]]
The ramp intersections may also be configured as a pair of [[roundabout]]s<ref name="FHWA 9"/> to create a type of diamond interchange often called a '''dumbbell interchange'''{{cn|date=September 2024}} (due to its aerial resemblance to a [[dumbbell]]), and sometimes called a '''double roundabout interchange'''.<ref>[[Federal Highway Administration]] (FHWA): [https://mutcd.fhwa.dot.gov/pdfs/2009r1r2/mutcd2009r1r2edition.pdf Manual on Uniform Traffic Control Devices] ([[MUTCD]]), Edition 2009, Revision 2, May 2012], ''Figure 3C-14. Example of Markings for a Diamond Interchange with Two Circular-Shaped, Roundabout Ramp Terminals'', p.412 (PDF p.452)</ref><ref name="FHWA 9"/> 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-turn]]s.<ref name="ATTAP">{{cite web |publisher= [[University of Maryland, College Park]] / [[Maryland State Highway Administration]] |url= http://attap.umd.edu/UAID_gsus.php?UAIDType=16&iFeature=5 |work= An Applied Technology and Traffic Analysis Program: Unconventional Arterial Intersection Design |title= Double Roundabout Interchange: Design and Operations |year= 2011 |access-date= February 25, 2013 |archive-url= https://web.archive.org/web/20131224095709/http://attap.umd.edu/UAID_gsus.php?UAIDType=16&iFeature=5 |archive-date= December 24, 2013 |url-status= dead }}</ref>

This type of interchange is common in the [[United Kingdom]] and [[Republic of Ireland|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|Medford]], Minnesota, on [[Interstate 87 (New York)|Interstate 87]] in [[Malta, New York|Malta]], New York, on [[Interstate 17]] at Happy Valley Road north of [[Phoenix, Arizona|Phoenix]], Arizona, and on [[Interstate 80]] at [[California State Route 89]] (exit 185) in [[Truckee, California|Truckee]], California. An example in Canada is found on the [[British Columbia Highway 17|Pat Bay Highway]] in [[North Saanich, British Columbia|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 [[Roundabout#Turbo roundabouts|"turbo" dumbbell]] interchange, which was formerly a half cloverleaf, can be seen in [[Jülich]], Germany at {{coord|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|La Floresta]], Uruguay ({{coord|34.7495|S|55.6775|W|dim:300}}).

=== Dogbone ===
[[File:N.C. 108 roundabout.JPG|thumb|right|A "raindrop" of a dogbone interchange along [[Interstate 26 in North Carolina|Interstate 26]] in [[Columbus, North Carolina]], United States<br />{{coord|35|14|43.7|N|82|12|20.2|W}}]]

A variation of the dumbbell interchange, often called a '''dogbone interchange''' (due to its aerial resemblance to a real or toy [[dog toy#Bones|dog bone]]), and sometimes also called a ''double roundabout interchange'',<ref name="FHWA 9"/> occurs when the roundabouts do not form a complete circle but instead have a "[[wiktionary:raindrop|raindrop]]" or "[[wiktionary:teardrop|teardrop]]" shape. These two [[roundabout#Raindrop roundabouts|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.<ref name="ATTAP"/> An example of a dogbone interchange in the United States is located on [[Interstate 70]] in [[Avon, Colorado]], United States;<ref>{{google maps|url=https://maps.google.com/maps?f=q&source=s_q&sll=37.0625,-95.677068&sspn=33.901528,79.101563&ll=39.637253,-106.520707&spn=0.001913,0.006866&t=k&z=18 |title=Teardrop roundabout in Avon, CO}}</ref> 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 [[U.S. Route 31 in Indiana|US 31]] freeway under construction in northern Indiana.<ref>{{ cite web | title = The New US 31 Hamilton County: Frequently Asked Questions | url = http://us31hamiltoncounty.in.gov/faqs/ | date = March 2015 | publisher = [[Hamilton County, Indiana|Hamilton County]], Indiana | access-date = December 3, 2015 }}</ref>

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 (Netherlands)|N7 road]] in [[Groningen]], Netherlands (at {{coord|53.21462|N|6.602509|E}}); and [[Ennis Avenue]] ([[Highway 1 (Australia)|National Route 1]]) at [[Safety Bay Road]] ([[list of road routes in Western Australia#18|State Route 18]] / [[Tourist Drive 202 (Western Australia)|Tourist Drive 202]]) on the border of the suburbs of [[Waikiki, Western Australia|Waikiki]] and [[Warnbro, Western Australia|Warnbro]] in the [[City of Rockingham]], [[Western Australia]] (at {{coord|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 [[right- and left-hand 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]] ([[List of road routes in Western Australia#3|State Route 3]]) and Berkshire Road (at {{coord|31.96945|S|116.00107|E}}).<ref>{{cite web|title=Roe Highway / Berkshire Road Interchange|url=http://gatewaywa.com.au/assets/Uploads/Roe-Highway-Berkshire-Road-Factsheet.pdf|date=April 2015|website=Gateway WA|publisher=[[Gateway WA]]|access-date=26 September 2015|archive-url=https://web.archive.org/web/20150926083217/http://gatewaywa.com.au/assets/Uploads/0413-roe-hwy.berkshire-rd-factsheet.web.pdf|archive-date=September 26, 2015 |url-status=live}}</ref>

=== Tight diamond ===
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 (transportation)|right-of-way]] for a standard diamond interchange. The pair of intersections where the ramps meet the minor road are closely spaced.<ref name="FHWA 9">{{cite web |author= Staff |publisher= [[Federal Highway Administration]] |url= https://www.fhwa.dot.gov/publications/research/safety/09060/009.cfm |work= Alternative Intersections/Interchanges: Informational Report (AIIR) |id= FHWA-HRT-09-060 |title= Chapter 9: Other Interchange Configurations |date= April 2010 |access-date= October 8, 2012 }}</ref><ref>{{cite web |author= Staff |publisher= Federal Highway Administration |url= https://www.fhwa.dot.gov/publications/research/safety/04091/10.cfm |work= Signalized Intersections: Informational Guide |id= FHWA-HRT-04-091 |title= Chapter 10: Alternative Intersection Treatments |date= August 2004 |access-date= October 8, 2012 }}</ref> 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.{{Cn|date=October 2022}} [[Caltrans]] classifies this type as Type L-1.<ref name=":0">https://dot.ca.gov/-/media/dot-media/programs/design/documents/chp0500-032020.pdf {{Bare URL PDF|date=March 2022}}</ref>

=== Single-point urban ===
{{main article|Single-point urban interchange}}
[[File:Florida SR 4080 at Valencia College Lane.jpg|thumb|Single-point urban interchange near [[Orlando, Florida]], demolished in the early 2010s<br />{{coord|28|33|13.7|N|81|16|11.6|W}}]]
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 [[interchange (road)|ramp]]s and the [[interchange (road)|cross street]]. Caltrans classifies this type as Type L-13.<ref name=":0" /> One example is on the [[Westlink (road)|A12]] Westlink in Belfast, Northern Ireland.

=== Contraflow left ===
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 with each other and bringing the long left turn phases from the [[single-point urban interchange]] to the tight urban diamond interchange at {{coord|26.301177|N|80.186479|W|}}.<ref>{{cite report |first1= Indrajit |last1= Chatterjee |first2= Siddharth |last2= Sharma |s2cid= 108139034 |name-list-style= amp |title= Comparative Analysis of Conventional Diamond Interchange and Contra Flow Left Turn (CFL) Interchange |publisher= Center for Transportation Research and Education at Iowa State University |year= 2007}}</ref><ref>{{cite web |publisher= University of Maryland |author= ATTAP |title= Unconventional Intersection/Interchange Designs & Strategies |url= http://attap.umd.edu/uids-knowlege-base/Contraflow-Left-Interchange.php |work= Contraflow Left Interchange |date= March 9, 2017 |access-date= July 15, 2017}}</ref>

=== 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 ===
A single-leg [[continuous-flow intersection]] (CFI) was built in 2014 in [[San Marcos, Texas|San Marcos]], Texas, at the intersection of Aquarena Springs Drive ([[Texas State Highway Loop 82|Loop 82]]), [[Interstate 35 in Texas|Interstate 35]]'s southbound [[frontage road]] and I-35's southbound-to-northbound [[Texas U-turn]].<ref>Amada Dugan: [http://kxan.com/2014/04/30/san-marcos-opens-up-regions-first-continuous-flow-intersection/ San Marcos opens up region’s first continuous flow intersection] {{Webarchive|url=https://web.archive.org/web/20151120070817/http://kxan.com/2014/04/30/san-marcos-opens-up-regions-first-continuous-flow-intersection/ |date=November 20, 2015 }} KXAN News, 30 April 2014.</ref><ref>[http://www.txstate.edu/news/news_releases/news_archive/2014/April-2014/TxDOT043014.html ''Intersection Improvements to SH 80 and Loop 82 at I-35 777 E Hopkins St''] {{Webarchive|url=https://web.archive.org/web/20151119235219/http://www.txstate.edu/news/news_releases/news_archive/2014/April-2014/TxDOT043014.html |date=November 19, 2015 }}, Texas State University, retrieved 30 December 2014.</ref> A two-leg CFI, also in San Marcos, was built in 2015 at the intersection of Hopkins Street ([[Texas State Highway 80|State Highway 80]]), I-35's frontage roads and I-35's Texas U-turns.<ref>{{usurped|1=[https://archive.today/20151104205454/http://smmercury.com/2015/05/18/txdot-to-modify-recently-completed-i-35-hopkins-street-interchange/ TxDOT to modify recently completed I-35, Hopkins Street interchange]}}, San Marcos Mercury, 18 May 2015.</ref> In both intersections, the displaced left turn lanes merge with the Texas U-turn lanes.

===Split diamond===
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.<ref>{{cite web | author = Staff | publisher = [[Federal Highway Administration]], Missouri Division | url = https://www.fhwa.dot.gov/modiv/programs/intersta/idp.cfm | title = Interchange Design Promptlist | date = April 24, 2012 | access-date = November 27, 2017 }}</ref><ref>{{cite web | last = Garcia | first = Rene, P.E. | publisher = [[Texas Department of Transportation]] | url = http://onlinemanuals.txdot.gov/txdotmanuals/rdw/freeways.htm | work = Roadway Design Manual | at = Chapter 3: New Location and Reconstruction (4R) Design Criteria, Section 6 | title = Freeways | date = October 1, 2014 | access-date = November 27, 2017 | archive-date = May 14, 2013 | archive-url = https://web.archive.org/web/20130514043935/http://onlinemanuals.txdot.gov/txdotmanuals/rdw/freeways.htm | url-status = dead }}</ref>

===Other===
Where [[HOV lane]]s are present for [[carpool]]ing, the ramps of a diamond interchange may be folded to the inside lanes instead of the outside. In [[urban area|urban]] areas this saves some space as well as requiring only one intersection instead of the two one-way intersections, which in [[rural area|rural]] or [[suburban area]]s can be turned into a [[single-point urban interchange]]. This in turn reduces waiting time for motorists at [[traffic light]]s on the smaller road, which may be a large local [[thoroughfare]] with heavy traffic.

In [[Henrietta, New York]], Jefferson Road ([[New York State Route 252|NY-252]]) crosses West Henrietta Road ([[New York State Route 15|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-turn]]s and [[Right-in/right-out|RIROs]] on the ramps.

====Gallery====
<gallery>
AS Hantel.svg|A dumbbell interchange
AS Knochen.svg|A dogbone interchange
File:AS TUDI.svg|A tight urban diamond interchange (TUDI)
File:AS CFL.svg|A contraflow left turn interchange
File:TUDI TX-CFI.svg|Continuous-flow diamond
Split diamond interchange.svg|Split diamond interchange
</gallery>

==See also==
* {{portal-inline|Roads}}

==References==
[[File:Overview of West Lancaster.jpg|thumb|Diamond interchange on [[U.S. Route 35|US-35]] to [[I-71]] in [[Jeffersonville, Ohio|Jeffersonville]], Ohio, at {{coord|39.61945|n|83.607858|w|}}]]
{{Reflist|30em}}

==External links==
*[http://www.carmel.in.gov/index.aspx?page=123 City of Carmel, Indiana, USA, Roundabouts (or ''dogbone interchanges'') page] {{Webarchive|url=https://web.archive.org/web/20131210044702/http://carmel.in.gov/index.aspx?page=123 |date=December 10, 2013 }}
*[https://purl.fdlp.gov/GPO/gpo54357 Diverging Diamond Interchange Informational Guide] [[Federal Highway Administration]]

{{Road junction types}}

[[Category:Road interchanges]]
[[Category:Road junction types]]

[[de:Anschlussstelle (Autobahn)#Parallelrampen]]