In the field of

road transport Road transport or road transportation is a type of transport using roads. Transport on roads can be roughly grouped into the transportation of goods and transportation of people. In many countries licensing requirements and safety regulations e ...

, an interchange (American English) or a grade-separated junction (British English) is a

road junction A junction is where two or more roads meet. History Roads began as a means of linking locations of interest: towns, forts and geographic features such as river fords. Where roads met outside of an existing settlement, these junctions often led ...

that uses

grade separation In civil engineering (more specifically highway 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 tran ...

s to allow for the movement of traffic between two or more roadways or

highway A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In some areas of the United States, it is used as an equivalent term to controlled-access ...

s, 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 In mathematics, the intersection of two or more objects is another object consisting of everything that is contained in all of the objects simultaneously. For example, in Euclidean geometry, when two lines in a plane are not parallel, their i ...

, where roads cross at grade. Interchanges are almost always used when at least one road is a

controlled-access highway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms i ...

(freeway or motorway) or a limited-access divided highway (expressway), though they are sometimes used at junctions between surface streets. Lakalaivan eritasoliittymä 1

Terminology

''Note:'' The descriptions of interchanges apply to countries where vehicles

drive on the right Left-hand traffic (LHT) and right-hand traffic (RHT) are the practices, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes referred to ...

side of the road. For left-side driving, the layout of junctions is mirrored. Both North American (NA) and British (UK) terminology is included. ; Freeway junction, highway interchange (NA), or motorway junction (UK) : A type of road junction linking one controlled-access highway (freeway or motorway) facility to another, to other roads, or to a

rest area A rest area is a public facility located next to a large thoroughfare such as a motorway, expressway, or highway, at which drivers and passengers can rest, eat, or refuel without exiting onto secondary roads. Other names include motorway servi ...

motorway service area Motorway service areas in the United Kingdom and Ireland, also known as services or service stations, are rest areas where drivers can leave a motorway to refuel/recharge, rest, eat and drink, shop or stay in an on-site overnight hotel. The vas ...

. Junctions and interchanges are often (but not always) numbered either sequentially, or by distance from one terminus of the route (the "beginning" of the route). :The

American Association of State Highway and Transportation Officials The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test quality control, protocols, and guidelines that are used in highway design and construction through ...

(AASHTO) defines an interchange as "a system of interconnecting roadways in conjunction with one or more grade separations that provides for the movement of traffic between two or more roadways or highways on different levels." ; System interchange : A junction that connects multiple controlled-access highways. ; Service interchange : A junction that connects a controlled-access facility to a lower-order facility, such as an

arterial An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...

or collector road. : The mainline is the controlled-access highway in a service interchange, while the crossroad is the lower-order facility that often includes at-grade intersections or roundabouts, which may pass over or under the mainline. ; Complete interchange : A junction where all possible movements between highways can be made from any direction. ; Incomplete interchange : A junction that is missing at least one movement between highways. ; Ramp (NA), slip road (UK), or link (Ireland) : A short section of road that allows vehicles to enter or exit a controlled-access highway. :''Ingressing'' traffic is entering the highway via an on-ramp or entrance ramp, while ''egressing'' traffic is exiting the highway via an off-ramp or exit ramp. ; Directional ramp : A ramp that curves toward the desired direction of travel; i.e., a ramp that makes a left turn exits from the left side of the roadway (a left exit). ; Semi-directional ramp : A ramp that exits in a direction opposite from the desired direction of travel, then turns toward the desired direction. Most left turn movements are provided by a semi-directional ramp that exits to the right, rather than exiting from the left. ;

Weaving Weaving is a method of textile production in which two distinct sets of yarns or threads are interlaced at right angles to form a fabric or cloth. Other methods are knitting, crocheting, felting, and braiding or plaiting. The longitudinal th ...

: An undesirable situation where traffic entering and exiting a highway must cross paths within a limited distance.

History

The concept of the controlled-access highway developed in the 1920s and 1930s in Italy, Germany, the United States and Canada. Initially, these roads featured at-grade intersections along their length. Interchanges were developed to provide access between these new highways and heavily-travelled surface streets. The

Bronx River Parkway The Bronx River Parkway (sometimes abbreviated as the Bronx Parkway) is a long parkway in downstate New York in the United States. It is named for the nearby Bronx River, which it parallels. The southern terminus of the parkway is at Story Avenue ...

was the first road to feature grade-separations.

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

engineer Arthur Hale filed a patent for the design of a cloverleaf interchange on May24, 1915, though the conceptual roadwork was not realised until a cloverleaf opened on December15, 1929, in

Woodbridge, New Jersey Woodbridge Township is a township in Middlesex County, in the U.S. state of New Jersey. The township is both a regional hub for Central New Jersey and a major bedroom suburb of New York City in the New York metropolitan area located within the ...

, connecting

New Jersey Route 25 Route 25 was a major state highway in New Jersey, United States prior to the 1953 renumbering, running from the Benjamin Franklin Bridge in Camden to the Holland Tunnel in Jersey City. The number was retired in the renumbering, as the whole road ...

and Route 4 (now U.S. Route 1/9 and

New Jersey Route 35 Route 35 is a state highway in the U.S. state of New Jersey, primarily traveling through the easternmost parts of Middlesex, Monmouth, and Ocean counties. It runs from the entrance to Island Beach State Park in Berkeley Township, Ocean County ...

). It was designed by

Philadelphia Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Sinc ...

engineering firm Rudolph and Delano, based on a design seen in an Argentinian magazine.

System interchange

A system interchange connects multiple controlled-access highways, involving no at-grade signalised intersections.

Four-legged interchanges

Cloverleaf interchange

A cloverleaf interchange is a four-legged junction where left turns across opposing traffic are handled by non-directional loop ramps. It is named for its appearance from above, which resembles a

four-leaf clover The four-leaf clover is a rare variation of the common three-leaf clover. According to traditional sayings, such clovers bring good luck, though it is not clear when or how this idea began. One early mention of "Fower-leafed or purple grasse" is ...

. A cloverleaf is the absolute minimum interchange required for a four-legged system interchange. Although they were commonplace until the 1970s, most highway departments and ministries have sought to rebuild them into more efficient and safer designs. The cloverleaf interchange was invented by Maryland engineer Arthur Hale, who filed a patent for its design on May24, 1915. The first one in North America opened on December15, 1929, in Woodbridge, New Jersey, connecting New Jersey Route25 and Route4 (now U.S. Route1/9 and New Jersey Route35). It was designed by Philadelphia engineering firm Rudolph and Delano, based on a design seen in an Argentinian magazine. The first cloverleaf in Canada opened in 1937 at the junction of Highway 10 and what would become the

Queen Elizabeth Way The Queen Elizabeth Way (QEW) is a 400-series highway in the Canadian province of Ontario linking Toronto with the Niagara Peninsula and Buffalo, New York. The freeway begins at the Peace Bridge in Fort Erie and travels around the western ...

. The first cloverleaf outside of North America opened in

Stockholm Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...

on October15, 1935. Nicknamed Slussen, it was referred to as a "traffic carousel" and was considered a revolutionary design at the time of its construction. A cloverleaf offers uninterrupted connections between two roads, but suffers from weaving issues. Along the mainline, a loop ramp introduces traffic prior to a second loop ramp providing access to the crossroad, between which ingress and egress traffic mixes. For this reason, the cloverleaf interchange has fallen out of favour in place of combination interchanges. Some may be half cloverleaf containing

ghost ramps An unused highway is a highway or highway ramp that was partially or fully constructed, but went unused or was later closed. An unused roadway or ramp may often be referred to as an abandoned road, ghost road, highway to nowhere, stub ramp, g ...

which can be upgraded to full cloverleafs if the road is extended.

US 70 U.S. Route 70 or U.S. Highway 70 (US 70) is an east–west United States highway that runs for from eastern North Carolina to east-central Arizona. It is a major east–west highway of the Southeastern, Southern and Southwestern United States. ...

and

US 17 U.S. Route 17 or U.S. Highway 17 (US 17), also known as the Coastal Highway, is a north–south United States Highway that spans in the southeastern United States. It runs close to the Atlantic Coast for much of its length, with ...

west of

New Bern, North Carolina New Bern, formerly called Newbern, is a city in Craven County, North Carolina, United States. As of the 2010 census it had a population of 29,524, which had risen to an estimated 29,994 as of 2019. It is the county seat of Craven County and t ...

is an example.

Stack interchange

A stack interchange is a four-way interchange whereby a semi-directional left turn and a directional right turn are both available. Usually access to both turns is provided simultaneously by a single offramp. Assuming right-handed driving, in order to cross over incoming traffic and go left, vehicles first exit onto an off-ramp from the rightmost lane. After demerging from right-turning traffic, they complete their left turn by crossing both highways on a flyover ramp or underpass. The penultimate step is a merge with the right-turn on-ramp traffic from the opposite quadrant of the interchange. Finally an onramp merges both streams of incoming traffic into the left-bound highway. As there is only one offramp and one onramp (in that respective order), stacks do not suffer from the problem of weaving, and due to the semi-directional flyover ramps and directional ramps, they are generally safe and efficient at handling high traffic volumes in all directions. A standard stack interchange includes roads on four levels, also known as a four-level stack: including the two perpendicular highways, and one more additional level for each pair of left-turn ramps. These ramps can be stacked (cross) in various configurations above, below, or between the two interchanging highways. This makes them distinct from Turbine interchanges, where pairs of left-turn ramps are separated but at the same level. There are some stacks that could be considered five-level; however, these remain four-way interchanges, since the fifth level actually consists of dedicated ramps for

HOV A high-occupancy vehicle lane (also known as an HOV lane, carpool lane, diamond lane, 2+ lane, and transit lane or T2 or T3 lanes) is a restricted traffic lane reserved for the exclusive use of vehicles with a driver and one or more passengers, i ...

/bus lanes or frontage roads running through the interchange. The stack interchange between I-10 and I-405 in

Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...

is a three-level stack, since the semi-directional ramps are spaced out far enough so they do not need to cross each other at a single point as in a conventional four-level stack. Stacks are significantly more expensive than other four-way interchanges, due to the design of the four levels. Additionally they may suffer from objections of local residents, because of their height and high visual impact. Large stacks with multiple levels may have a complex appearance and are often colloquially described as ''Mixing Bowls'', '' Mixmasters'' (for a

Sunbeam Products Sunbeam Products is an American brand that has produced electric home appliances since 1910. Its products have included the Mixmaster mixer, the Sunbeam CG waffle iron, Coffeemaster (1938–1964) and the fully automatic T20 toaster. The comp ...

brand of electric kitchen mixers), or as ''Spaghetti Bowls'' or ''

Spaghetti Junction Spaghetti junction is a nickname sometimes given to a complex or massively intertwined road traffic interchange that is said to resemble a plate of spaghetti. Such interchanges may incorporate a variety of interchange design elements in orde ...

s'' (being compared to boiled

spaghetti Spaghetti () is a long, thin, solid, cylindrical pasta.spaghetti
Dictionary.com. Dictionary.com Unabridg ...

). However, they consume a significantly smaller area of land compared to a cloverleaf interchange.

Combination interchange

A combination interchange (sometimes referred to by the portmanteau, ''cloverstack'') is a hybrid of other interchange designs. It uses loop ramps to serve slower or less-occupied

traffic flow In mathematics and transportation engineering, traffic flow is the study of interactions between travellers (including pedestrians, cyclists, drivers, and their vehicles) and infrastructure (including highways, signage, and traffic control devi ...

, and flyover ramps to serve faster and heavier traffic flows. If local and express ways serving the same directions and each roadway is connected righthand to the interchange, extra ramps are installed. The combination interchange design is commonly used to upgrade cloverleaf interchanges to increase their capacity and eliminate weaving.

Turbine interchange

The turbine interchange is an alternative four-way directional interchange. The turbine interchange requires fewer levels (usually two or three) while retaining directional ramps throughout. It features right-exit, left-turning ramps that sweep around the center of the interchange in a clockwise

spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are: A windmill interchange is similar to a turbine interchange, but it has much sharper turns, reducing its size and capacity. The interchange is named for its similar overhead appearance to the blades of a

windmill A windmill is a structure that converts wind power into rotational energy using vanes called windmill sail, sails or blades, specifically to mill (grinding), mill grain (gristmills), but the term is also extended to windpumps, wind turbines, and ...

. A variation of the windmill, called the diverging windmill, increases capacity by altering the direction of traffic flow of the interchanging highways, making the connecting ramps much more direct. There also is a hybrid interchange somewhat like the diverging windmill in which left turn exits merge on the left, but it differs in that the left turn exits use left directional ramps.

Braided interchange

A braided or diverging interchange is a two-level, four-way interchange. An interchange is braided when at least one of the roadways reverses sides. It seeks to make left and right turns equally easy. In a pure braided interchange, each roadway has one right exit, one left exit, one right on-ramp, and one left on-ramp, and both roadways are flipped. The first pure braided interchange was built in

Baltimore Baltimore ( , locally: or ) is the List of municipalities in Maryland, most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic (United States), Mid-Atlantic, and List of United States cities by popula ...

Interstate 95 Interstate 95 (I-95) is the main north–south Interstate Highway on the East Coast of the United States, running from U.S. Route 1, US Route 1 (US 1) in Miami, Miami, Florida, to the Houlton–Woodstock Border Crossing between M ...

at Interstate 695; however, the interchange was reconfigured in 2008 to a traditional stack interchange. ;Examples *

Interstate 65 Interstate 65 (I-65) is a major north–south Interstate Highway in the central United States. As with most primary Interstates ending in 5, it is a major crosscountry, north–south route, connecting between the Great Lakes and the Gulf ...

and

Interstate 20 Interstate 20 (I‑20) is a major east–west Interstate Highway in the Southern United States. I-20 runs beginning at an interchange with Interstate 10, I-10 in Scroggins Draw, Texas, and ending at an interchange with Interstate 95, I-95 in Flo ...

Interstate 59 Interstate 59 (I-59) is an Interstate Highway located in the southeastern United States. It is a north–south route that spans from a junction with I-10 and I-12 at Slidell, Louisiana, to a junction with I-24 near Wildwood, Georgia. The ...

Birmingham, Alabama Birmingham ( ) is a city in the north central region of the U.S. state of Alabama. Birmingham is the seat of Jefferson County, Alabama's most populous county. As of the 2021 census estimates, Birmingham had a population of 197,575, down 1% fr ...

() *

Interstate 196 Interstate 196 (I-196) is an auxiliary Interstate Highway that runs for in the US state of Michigan. It is a state trunkline highway that links Benton Harbor, South Haven, Holland, and Grand Rapids. In Kent, Ottawa, and Allegan counties, I-1 ...

and

U.S. Route 131 US Highway 131 (US 131) is a north–south United States Highway, of which all but 0.64 of its 269.96 miles (1.03 of 434.46 km) are within the state of Michigan. The highway starts in rural Indiana south of the state line as a sta ...

Grand Rapids, Michigan Grand Rapids is a city and county seat of Kent County, Michigan, Kent County in the U.S. state of Michigan. At the 2020 United States census, 2020 census, the city had a population of 198,917 which ranks it as the List of municipalities in Mi ...

() *

Interstate 77 Interstate 77 (I-77) is a north–south Interstate Highway in the eastern United States. It traverses diverse terrain, from the mountainous state of West Virginia to the rolling farmlands of North Carolina and Ohio. It largely supplants the ...

and

Interstate 85 Interstate 85 (I-85) is a major Interstate Highway in the Southeastern United States. Its southern terminus is at an interchange with I-65 in Montgomery, Alabama; its northern terminus is an interchange with I-95 in Petersburg, Virginia, n ...

Charlotte, North Carolina Charlotte ( ) is the most populous city in the U.S. state of North Carolina. Located in the Piedmont region, it is the county seat of Mecklenburg County. The population was 874,579 at the 2020 census, making Charlotte the 16th-most populo ...

() * South of

Riyadh Riyadh (, ar, الرياض, 'ar-Riyāḍ, lit.: 'The Gardens' Najdi pronunciation: ), formerly known as Hajr al-Yamamah, is the capital and largest city of Saudi Arabia. It is also the capital of the Riyadh Province and the centre of the R ...

()

Three-level roundabout

A three-level roundabout interchange features a grade-separated roundabout which handles traffic exchanging between highways. The ramps of the interchanging highways meet at a

roundabout 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.''The New Shorter Oxford En ...

, or rotary, on a separated level above, below, or in the middle of the two highways.

Three-legged interchanges

These interchanges can also be used to make a "linking road" to the destination for a service interchange, or the creation of a new basic road as a service interchange.

Trumpet interchange

Trumpet interchanges may be used where one highway terminates at another highway, and are named as such for to their resemblance to

trumpets The trumpet is a brass instrument commonly used in classical and jazz ensembles. The trumpet group ranges from the piccolo trumpet—with the highest register in the brass family—to the bass trumpet, pitched one octave below the standard B ...

. They are sometimes called ''jug handles''. These interchanges are very common on

toll roads A toll road, also known as a turnpike or tollway, is a public or private road (almost always a controlled-access highway in the present day) for which a fee (or '' toll'') is assessed for passage. It is a form of road pricing typically implemente ...

, as they concentrate all entering and exiting traffic into a single stretch of roadway, where toll plazas can be installed once to handle all traffic, especially on ticket-based tollways. A double-trumpet interchange can be found where a toll road meets another toll road or a free highway. They are also useful when most traffic on the terminating highway is going in the same direction. The turn that is used less often would contain the slower loop ramp. Trumpet interchanges are often used instead of directional or semi-directional T or Y interchanges because they require less bridge construction but still eliminate weaving.

T and Y interchanges

A full Y-interchange (also known as a directional T interchange) is typically used when a three-way interchange is required for two or three highways interchanging in semi-parallel/perpendicular directions, but it can also be used in right-angle case as well. Their connecting ramps can spur from either the right or left side of the highway, depending on the direction of travel and the angle. Directional T interchanges use flyover/underpass ramps for both connecting and mainline segments, and they require a moderate amount of land and moderate costs since only two levels of roadway are typically used. Their name derives from their resemblance to the capital letter T, depending upon the angle from which the interchange is seen and the alignment of the roads that are interchanging. It is sometimes known as the "New England Y", as this design is often seen in the northeastern United States, as with the

Braintree Split The Braintree Split is the major interchange of Interstate 93 (I-93), U.S. Route 1 (US 1), and Route 3 in the South Shore of Massachusetts, on the city line between Braintree and Quincy. Traveling northbound, the routes merge into a three-way ...

and the northern terminus of MA Route 24, both south of Boston. This type of interchange features directional ramps (no loops, or weaving right to turn left) and can use multilane ramps in comparatively little space. Some designs have two ramps and the "inside" through road (on the same side as the freeway that ends) crossing each other at a three-level bridge. The directional T interchange is preferred to a trumpet interchange because a trumpet requires a loop ramp by which speeds can be reduced, but flyover ramps can handle much faster speeds. The disadvantage of the directional T is that traffic from the terminating road enters and leaves on the passing lane, so the semi-directional T interchange (see below) is preferred. The interchange of Highway 416 and Highway 417 in Ontario, constructed in the early 1990s, is one of the few directional T interchanges, as most transportation departments had switched to the semi-directional T design. As with a directional T interchange, a semi-directional T interchange uses flyover (overpass) or

underpass A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube constr ...

ramps in all directions at a three-way interchange. However, in a semi-directional T, some of the splits and merges are switched to avoid ramps to and from the

passing lane A passing lane (North American English) or overtaking lane (English outside of North America) is a lane on a multi-lane highway or motorway closest to the median of the road (the central reservation). In some countries, lanes are described as bein ...

, eliminating the major disadvantage of the directional T. Semi-directional T interchanges are generally safe and efficient, though they do require more land and are costlier than trumpet interchanges. Knooppunt halve ster

Semi-directional T interchanges are built as two- or three-level junctions, with three-level interchanges typically used in urban or suburban areas where land is more expensive. In a three-level semi-directional T, the two semi-directional ramps from the terminating highway cross the surviving highway at or near a single point, which requires both an overpass and underpass. In a two-level semi-directional T, the two semi-directional ramps from the terminating highway cross each other at a different point than the surviving highway, necessitating longer ramps and often one ramp having two overpasses. Highway 412 has a three-level semi-directional T at Highway 407 and a two-level semi-directional T at

Highway 401 King's Highway 401, commonly referred to as Highway 401 and also known by its official name as the Macdonald–Cartier Freeway or colloquially referred to as the four-oh-one, is a controlled-access 400-series highway in the Canadian provin ...

. File:Knooppunt half klaverblad.png, Half-clover
Samples:

51.314277°N 7.266172°E
File:Knooppunt half barok.png, 3/4-volley File:As-gruszka.svg, T-bone
Samples:

File:Echangeur 3 routes rond point.svg, Three-way roundabout
Samples:

File:TrumpetRoundabout.png, Roundabout T
Samples:

File:Semi-directional T.svg

Service interchange

Service interchanges are used between a controlled-access route and a crossroad that is not controlled-access. A full cloverleaf may be used as a system or a service interchange.

Diamond interchange

A diamond interchange is an interchange involving four ramps where they enter and leave the freeway at a small angle and meet the non-freeway at almost right angles. These ramps at the non-freeway can be controlled through

stop sign A stop sign is a traffic sign designed to notify drivers that they must come to a complete stop and make sure the intersection is safely clear of vehicles and pedestrians before continuing past the sign. In many countries, the sign is a red oc ...

traffic signals Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic lights ...

, or turn ramps. Diamond interchanges are much more economical in use of materials and land than other interchange designs, as the junction does not normally require more than one bridge to be constructed. However, their capacity is lower than other interchanges and when traffic volumes are high they can easily become congested. ;Double roundabout diamond Holt Road Dogbone

A double roundabout diamond interchange, also known as a dumbbell interchange or a dogbone interchange, is similar to the diamond interchange, but uses a pair of roundabouts in place of intersections to join the highway ramps with the crossroad. This typically increases the efficiency of the interchange when compared to a diamond, but is only ideal in light traffic conditions. In the dogbone variation, the roundabouts do not form a complete circle, instead having a teardrop shape, with the points facing towards the center of the interchange. Longer ramps are often required due to line-of-sight requirements at roundabouts.

Partial cloverleaf interchange

A partial cloverleaf interchange (often shortened to the portmanteau, ''parclo'') is an interchange with loops ramps in one to three quadrants, and diamond interchange ramps in any number of quadrants. The various configurations are generally a safer modification of the cloverleaf design, due to a partial or complete reduction in weaving, but may require traffic lights on the lesser-travelled crossroad. Depending on the number of ramps used, they take up a moderate to large amount of land, and have varying capacity and efficiency. Parclo configurations are given names based on the location of and number of quadrants with ramps. The letter ''A'' denotes that, for traffic on the

, the loop ramps are located in ''advance'' of (or ''approaching'') the crossroad, and thus provide an onramp to the highway. The letter ''B'' indicated that the loop ramps are ''beyond'' the crossroad, and thus provide an offramp from the highway. These letters can be used together when opposite directions of travel on the controlled-access highway are not symmetrical, thus a parclo AB features a loop ramp approaching the crossroad in one direction, and beyond the crossroad in the opposing direction, as in the example image.

Diverging diamond interchange

Camp Creek at I-285 Aerial (50924270112)

diverging diamond interchange 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 inte ...

(DDI) or double crossover diamond interchange (DCD) is similar to a traditional diamond interchange, except the opposing lanes on the crossroad cross each other twice, once on each side of the highway. This allows all highway entrances and exits to avoid crossing the opposite direction of travel and saves one signal phase of traffic lights each. The first DDIs were constructed in the French communities of

Versailles The Palace of Versailles ( ; french: Château de Versailles ) is a former royal residence built by King Louis XIV located in Versailles, about west of Paris, France. The palace is owned by the French Republic and since 1995 has been managed, u ...

( A13 at D182),

Le Perreux-sur-Marne Le Perreux-sur-Marne (, literally ''Le Perreux on Marne'') is a commune in the Val-de-Marne department in the eastern suburbs of Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 re ...

( A4 at N486) and

Seclin Seclin () is a commune in the Nord department in northern France. It is part of the Métropole Européenne de Lille. Population Notable residents * Andre Ayew, Ghana national football team footballer *Victor Mollet, architect *Jonathan Rouss ...

( A1 at D549), in the 1970s. Despite the fact that such interchanges already existed, the idea for the DDI was "reinvented" around 2000, inspired by the freeway-to-freeway interchange between

and I-695 north of

. The first DDI in the United States opened on July7, 2009, in

Springfield, Missouri Springfield is the third largest city in the U.S. state of Missouri and the county seat of Greene County. The city's population was 169,176 at the 2020 census. It is the principal city of the Springfield metropolitan area, which had an estimat ...

, at the junction of

Interstate 44 Interstate 44 (I-44) is a major Interstate Highway in the central United States. Although it is nominally an east–west road as it is even-numbered, it follows a more southwest–northeast alignment. Its western terminus is in Wichita Fal ...

and

Missouri Route 13 Route 13 is a highway in Missouri which runs almost the entire north–south length of the state. Its northern terminus is at U.S. Route 69/ 136 in Bethany. Its southern terminus is at the Arkansas state line in downtown Blue Eye, Misso ...

Single-point urban interchange

A single-point urban interchange (SPUI) or single-point diamond interchange (SPDI) is a modification of a diamond interchange in which all four ramps to and from a controlled-access highway converge at a single, three-phase traffic light in the middle of an overpass or underpass. While the compact design is safer, more efficient, and offers increased capacity—with three light phases as opposed to four in a traditional diamond, and two left turn queues on the arterial road instead of four—the significantly wider overpass or underpass structure makes them more costly than most service interchanges. Since single-point ''urban'' interchanges can exist in ''rural'' areas, such as the interchange of

U.S. Route 23 } U.S. Route 23 or U.S. Highway 23 (US 23) is a major north–south U.S. Highway between Jacksonville, Florida, and Mackinaw City, Michigan. It is an original 1926 route which originally reached only as far south as Portsmouth, Ohio, and has sinc ...

with M-59 in

Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...

, and US-131 and M-179, the term single-point diamond interchange is considered the correct vernacular. Single-point interchanges were first built in the early 1970s along

U.S. Route 19 U.S. Route 19 (US 19) is a north–south U.S. Highway in the Eastern United States. Despite encroaching Interstate Highways, the route has remained a long-haul road, connecting the Gulf of Mexico with Lake Erie. The highway's southern ...

in the

Tampa Bay area The Tampa Bay area is a major populated area surrounding Tampa Bay on the west coast of Florida in the United States. It includes the main cities of Tampa, St. Petersburg, and Clearwater. It is the 18th largest metropolitan area in the United St ...

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, including the SR 694 interchange in

St. Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...

and SR 60 in

Clearwater Clearwater or Clear Water may refer to: Places Canada * Clear Water Academy, a private Catholic school located in Calgary, Alberta * Clearwater (provincial electoral district), a former provincial electoral district in Alberta * Clearwater, Briti ...

References

External links

Glossary
Part of the publicatio

by the Turner-Fairbank Highway Research Center branch of the U.S.

Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program a ...

Kurumi.com U.S. interchanges directory

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