Editing Cloverleaf interchange

{{Short description|A type of interchange using loop ramps}}
{{More citations needed|date=October 2022}}
[[File:VA 28 Cloverleaf - VA 606 (33635098084).jpg|thumb|Cloverleaf interchange in Dulles, Virginia facing east on [[Virginia State Route 606|SR 606]] over [[Virginia State Route 28|SR 28]]]]
[[Image:Cloverleaf interchange.svg|thumb|right|A cloverleaf with [[Local&ndash;express lanes|collector/distributor roads]]]]
[[File:US 131, M-6, 68th St interchange.jpg|thumb|A typical cloverleaf interchange with [[Local&ndash;express lanes|collector/distributor roads]] in [[Cutlerville, Michigan]], facing north on [[U.S. Route 131|US 131]] under [[M-6 (Michigan highway)|M-6]] (located at: {{coord|42.848912|n|85.678689|w}})]]
[[Image:Kathipara.jpg|thumb|268x268px|The [[Kathipara Junction|Kathipara]] Cloverleaf interchange in [[Chennai]], [[India]]]]
[[Image:I-10 at Garfield Avenue.jpg|thumb|right|Many old cloverleaf interchanges elongate the ramps in the direction of the surface road. This one in [[Alhambra, California]] has been supplemented with [[Local&ndash;express lanes|collector/distributor roads]], {{coord|34.071659|n|118.122938|w}}.]]
[[File:Slussen 15 10 1935.jpg|thumb|right|Opening Europe's first cloverleaf (October 1935) at [[Slussen]], [[Stockholm]], {{coord|59.32063|n|18.072501|e}}]]
[[Image:I-405 at CA 19.jpg|thumb|In this cloverleaf in [[Long Beach, California]], two bridges are used to eliminate [[Grade separation#Weaving|weaving]] among cars entering and exiting the westbound lane, facing north on [[California State Route 19|SR 19]] under [[Interstate 405 (California)|I-405]] ({{coord|33.80595|n|118.142047|w}}).]]
<!--[[File:Faizabad Interchange.jpg|thumb|right|200px|The [[Faizabad Interchange]] connects [[Islamabad]] with [[Rawalpindi]] in [[Pakistan]].]]-->
A '''cloverleaf interchange''' is a two-level [[interchange (road)|interchange]] in which all turns are handled by [[slip road]]s. To go left (in right-hand traffic; reverse directions in left-driving regions), vehicles first continue as one road passes over or under the other, then exit right onto a one-way three-quarter 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]].

== Overview ==
[[File:Flyover1.jpg|thumb|A cloverleaf interchange near [[Sharjah International Airport]] in the [[United Arab Emirates]], {{coord|25.298611|n|55.593611|e}}]]
Cloverleaf interchanges, viewed from overhead or on maps, resemble the [[leaf|leaves]] of a [[four-leaf clover]] or less often a 3-leaf clover.
In the [[United States]], cloverleaf interchanges existed long before the [[Interstate highway|Interstate system]].  They were originally created for busier interchanges that the original [[diamond interchange]] system could not handle.  Their chief advantage was that they were free-flowing and did not require the use of such devices as [[traffic signals]]. This not only made them a viable option for interchanges between [[freeways]] (where such devices are typically not an option), but they could also be used for very busy [[arterial (road)|arterials]] where signals could present congestion problems.

They are common in the United States and have been used for over 40 years as the [[Interstate Highway System]] expanded rapidly. One problem is that, frequently, large [[truck]]s exceeding the area [[speed limit]] roll over.<ref>{{Cite book|title = Improved Safety Information to Support Highway Design, Issue 430|last = Peter|first = Ronald| publisher = Transportation Research Board|year = 1999|isbn = 0-309-06608-5|location = Barnes&Noble.com|pages = 96}}</ref>  Another problem is the merging of traffic ([[#Problems|see below]]). For these reasons, cloverleaf interchanges have become a common point of traffic congestion at busy junctions.

[[At-grade intersection|At-grade]] cloverleaf configurations with full four leaves and full outside slip ramps are extremely rare, though one exists in [[Toms River, New Jersey]].<ref>[http://maps.google.co.uk/maps?q=1201%20Hooper%20Avenue%2C%20Toms%20River%2C%20New%20Jersey%2C%20United%20States&um=1&hl=en&ie=UTF-8&sa=N&tab=wl Google Maps<!-- Bot generated title -->]</ref> Any other intersection with merely one, two, or three leaf ramps with outer ramps would not be designated a "cloverleaf" and simply be referred to as a [[jughandle]] or parclo intersection.

== History ==
=== Background ===
The first cloverleaf interchange [[patented]] in the US was by [[Arthur Hale]], a [[civil engineer]] in [[Maryland]], on February 29, 1916.<ref>[http://members.a1.net/wabweb/frames/kreuzf.htm  Wie man Autobahnen kreuzungsfrei kreuzt] (German) {{webarchive |url=https://web.archive.org/web/20050305150510/http://members.a1.net/wabweb/frames/kreuzf.htm |date=March 5, 2005 }}</ref><ref>[https://patents.google.com/patent/US1173505 Patent no. 1173505] at Google Patent Search</ref>

A modified cloverleaf, with the adjacent ramps joined into a single two-way road, was planned in 1927 for the interchange between [[Lake Shore Drive]] ([[US 41 (IL)|US 41]]) and Irving Park Road ([[Illinois Route 19|ILL&nbsp;19]]) in [[Chicago, Illinois]], but a [[diamond interchange]] was built instead.

=== Beginning ===
The first cloverleaf interchange built in the United States was the Woodbridge Cloverleaf<ref name = C>{{Citation |title=The Woodbridge Cloverleaf: Onramps to Innovation |url=https://www.youtube.com/watch?v=25ujQBf3ads |language=en |access-date=2022-07-20}}</ref> at intersection of the [[Lincoln Highway]] ([[New Jersey Route 25|Route&nbsp;25]]) and [[Perth Amboy, New Jersey#Amboy Avenue|Amboy]]—now St. Georges—Avenue ([[New Jersey Route 4|Route&nbsp;4]]) (now [[U.S. Route 1/9|U.S.&nbsp;1/9]] and [[New Jersey Route 35|Route&nbsp;35]]) in [[Woodbridge Township, New Jersey]].<ref name=wrm>{{Cite web|title=The Cloverleaf Interchange| publisher=WhereRoadsMeet| access-date=2008-12-21| url=http://whereroadsmeet.8k.com/article/clover.htm|url-status=dead|archive-url=https://web.archive.org/web/20080514013630/http://www.whereroadsmeet.8k.com/article/clover.htm|archive-date=2008-05-14}}</ref><ref name=lat>{{cite news |last=MartÃn|first=Hugo|access-date=2008-12-21| title=A Major Lane Change|newspaper=[[Los Angeles Times]] |date=April 7, 2004 |url=https://www.latimes.com/archives/la-xpm-2004-apr-07-me-cloverleaf7-story.html}}</ref><ref name=big>{{cite book |last=Swift |first=Earl |date=2011 |title=The Big Roads |location=Boston; New York |publisher=Houghton Mifflin Harcourt |isbn= 978-0-618-81241-7|page=101 }}</ref> It opened in 1929,<ref>{{Cite web |title=Woodbridge Cloverleaf Historical Marker |url=https://www.hmdb.org/m.asp?m=126308 |access-date=2022-07-20 |website=www.hmdb.org |language=en}}</ref> although it has since been replaced with a [[partial cloverleaf interchange]].<ref name=njdot>{{Cite web| title=Routes 1&9-35 Interchange Improvements, Project Description, Construction Updates, Commuter Information|publisher=[[New Jersey Department of Transportation]]|access-date=2008-12-21| url=http://www.state.nj.us/transportation/commuter/roads/routes1935/description.shtm }}</ref> Before the cloverleaf was replaced in the late 2000s, it was judged eligible for inclusion in the [[National Register of Historic Places]]. Because of this, a commemorative film <ref name = C/> was made of the cloverleaf.<ref>{{Cite web |title=Woodbridge Cloverleaf |url=http://www.hunterresearch.com/woodbridge-cloverleaf |access-date=2022-07-20 |website=Hunter Research, Inc. |language=en-US}}</ref> The original cloverleaf interchange design was adapted by the Rudolph and Delano building firm from [[Philadelphia]], from a photo Delano saw on a magazine cover about a highway in [[Buenos Aires]], [[Argentina]]. The original inventor is unknown.

The first cloverleaf west of the [[Mississippi River]] opened on August 20, 1931, at [[Watson Road]] and [[Lindbergh Boulevard]] near [[St.&nbsp;Louis, Missouri]], as part of an upgrade of [[U.S. Route 66|U.S.&nbsp;66]].<ref>[http://www.66postcards.com/hist.html A Bit of Missouri 66 History ]</ref>

The first cloverleaf interchange in Canada opened in 1937 at the junction of the Queen Elizabeth Way (QEW) and Provincial Highway 10 in Port Credit, Ontario (now a part of Mississauga, Ontario). As originally built, Highway 10 passed over the QEW. In 1962, the interchange was rebuilt with sub-collector roads along the QEW, and the orientation was also changed so that Highway 10 then passed under the QEW. The interchange was further modified between 2008 and 2010 by removing all but one loop ramp, creating a partial cloverleaf/diamond hybrid.

The cloverleaf was patented in [[Europe]] in [[Switzerland]] on October 15, 1928. The first cloverleaf in [[Europe]] opened in October 1935 at [[Slussen]] in central [[Stockholm]], [[Sweden]], followed in 1936 by [[Schkeuditzer Kreuz]] near [[Leipzig]], [[Germany]]. This is now the interchange between the [[Bundesautobahn 9|A&nbsp;9]] and [[Bundesautobahn 14|A&nbsp;14]], and has a single [[Overpass|flyover]] from the westbound A&nbsp;14 to the southbound A&nbsp;9. [[Kamener Kreuz]] was the first in continental Europe to open fully in 1937, at [[Bundesautobahn 1|A 1]] and [[Bundesautobahn 2|A 2]] near [[Dortmund]], [[Germany]].<!-- not completely sure about the accuracy of this-->

== Problems ==
The primary drawback of the classic design of the cloverleaf is that vehicles merge onto the highway at the end of a loop immediately before other vehicles leave to go around another loop, creating conflict known as [[Grade separation#Weaving|weaving]]. Weaving limits the number of lanes of turning traffic. Most road authorities have since been implementing new interchange designs with less-curved exit ramps that do not result in weaving. These interchanges include the [[diamond interchange|diamond]], [[parclo interchange|parclo]] and [[single-point urban interchange]]s (SPUI) when connecting to an [[arterial road]] in non [[Free-flow interchange|free-flowing traffic]] on the crossroad and the [[stack interchange|stack]] or [[Interchange (road)#Combination interchange|clover and stack hybrids]] when connecting to another freeway or to a busy arterial in free-flowing traffic where signals are still not desired.

Not only are these ideas true for new interchanges, but they also hold when existing cloverleaf interchanges are upgraded. In [[Norfolk, Virginia]], the interchange between [[U.S. Route 13|US&nbsp;13]] and [[U.S. Route 58|US&nbsp;58]] was originally a cloverleaf—it has since been converted to a [[SPUI]]. Also, many cloverleaf interchanges on [[California]] freeways, such as U.S. 101, are being converted to [[parclo interchange|parclos]]. In [[Hampton, Virginia]], a cloverleaf interchange between [[Interstate 64]] and [[U.S. Route 258|Mercury Boulevard]] has been partially unwound into a partial stack interchange. During 2008 and 2009, four cloverleaf interchanges along [[I-64 (MO)|I-64]]/[[U.S. Route 40 in Missouri|US&nbsp;40]] in [[St. Louis]], [[Missouri]], were replaced with [[Single-point urban interchange|SPUIs]] as part of a major highway-renovation project to upgrade the highway to Interstate standards. The original cloverleaf interchange in [[Delmont, Pennsylvania]] between Routes 22 and 66 was also converted to a [[SPUI]].

A compromise is to add a [[Local-express lanes|collector/distributor road]] next to the freeway; this does not eliminate weaving but moves it off the main lanes of the freeway. An example of this is the [[Wisconsin Highway 23|State Highway 23]]/[[Interstate 43]] interchange in [[Sheboygan, Wisconsin]], where the exit/entrance roads on and off Highway 23 are two lanes next to the main I-43 freeway on the north and southbound sides of the road.

A few cloverleaf interchanges in [[California]] have been rebuilt to eliminate weaving on the freeway while keeping all four loop ramps, by adding bridges, similar to braided ramps.

Several cloverleaf interchanges have been eliminated by adding [[traffic light]]s on the non-freeway route. Sometimes, this is even done at the intersection of two freeways, particularly when one freeway terminates at an interchange with another. An example of this is in [[Lakewood, Washington]], at the interchange between [[Interstate 5 (Washington)|Interstate 5]] and [[Washington State Route 512]], where a visible [[ramp stub]] shows that one of the four leaves was removed, thus eliminating weave on I-5.<ref>{{coord|47.1630484|N|122.4804883|W}}</ref> In the future, the traffic signal will be replaced by a two-lane flyover, completing the freeway-to-freeway interchange once again.{{citation needed|date=July 2021}} Cloverleaf interchanges also tend to occupy much more land than any other kind of interchange.

Numerous cloverleaf intersections in the [[Lower Mainland]] of British Columbia, Canada, require the merging of traffic from the clover directly onto the collector/distributor lane. This requires the slowly moving driver coming around the loop ramp to merge with the quickly moving driver exiting on the collector/distributor lane with no opportunity to accelerate to match the flow of the oncoming driver. This speed differential in merging can be as great as 65&nbsp;km/h (approx. 43&nbsp;mph).

The cloverleaf interchange was not implemented in great numbers in the [[United Kingdom]], because of these performance problems. There were originally three, one in [[Redditch]] and two in [[Livingston, Scotland|Livingston]]. One of the Livingston examples was remodeled in the mid-2000s as part of a public transport project. The Girton interchange near Cambridge was a "half"-cloverleaf interchange that regularly experienced peak-time congestion due to [[A14 road (Great Britain)|A14]] westbound traffic weaving with [[M11 motorway|M11]] traffic.<ref>{{Cite web|last=Atkins|author-link=Atkins_(company)|title=The A14 Girton to Felixstowe Congestion Study Report| url=https://www.eastsuffolk.gov.uk/assets/Planning/Suffolk-Coastal-Local-Plan/Document-Library/Infrastructure/A14-congestion-study-2005-Final-Report-2.pdf|url-status=live|access-date=2021-12-16| website=East Suffolk Council|publisher=[[Highways England|Highways Agency]]| at=Section 5-3|archive-url=https://web.archive.org/web/20211216171544/https://www.eastsuffolk.gov.uk/assets/Planning/Suffolk-Coastal-Local-Plan/Document-Library/Infrastructure/A14-congestion-study-2005-Final-Report-2.pdf |archive-date=2021-12-16 }}</ref> This interchange was [[A14 road (England)#A14 Cambridge to Huntingdon Improvement Scheme|redesigned in 2019]] to remove one of the loops. In [[Ireland]], partial cloverleaf set-ups exist at the interchanges of the main roads out of [[Dublin]] and the M50, allowing free-flow movements in all directions. The [[Red Cow interchange|Red Cow Interchange]] is an example.

Most cloverleaf interchanges have been phased out in Ontario, but some close variants do remain with similar traffic flows. The main difference however is that adjacent on and off ramps are shared together by single bidirectional carriageways. Examples include the [[Ontario Highway 62|Highway 62]] and [[Ontario Highway 401|Highway 401]] interchange in [[Belleville, Ontario]], the [[Ontario Highway 4|Highway 4]] and [[Ontario Highway 401|Highway 401]] in [[London, Ontario]], as well as the [[Lawrence Avenue]] and [[Don Valley Parkway]] interchange in Toronto. The [[Don Mills Road]] and [[Don Valley Parkway]] and the [[Ontario Highway 27|Highway 27]] and [[Dixon Road]] are also other examples; however, one quadrant of each has a loop missing.

==See also==
{{comparison_of_four_legged_interchanges.svg}}
* [[Partial cloverleaf interchange]]
* [[Stack interchange]]
* [[Continuous-flow intersection]]
* [[Diverging diamond interchange]]

==References==
{{Reflist|30em}}

== External links ==
{{commons category|Cloverleaf interchanges}}
* {{Coord|40.571694|N|74.292796|W|}} Map of the Woodbridge, NJ Cloverleaf
* {{Coord|39.978943|N|74.182783|W|}} Map of the Toms River, NJ At Grade Cloverleaf
* [https://web.archive.org/web/20211216172100/https://www.roads.org.uk/index.php/interchanges/cloverleaf UK-based discussion on cloverleaf interchanges]

{{Road junction types}}

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

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