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 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 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 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 AT or at may refer to: Geography Austria * Austria (ISO 2-letter country code) * .at, Internet country code top-level domain United States * Atchison County, Kansas (county code) * The Appalachian Trail (A.T.), a 2,180+ mile long mountaino ...

. 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 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 or motorway service area. 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 (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 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 : 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 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, 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 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 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 which can be upgraded to full cloverleafs if the road is extended. US 70 and US 17 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/bus lanes or frontage roads running through the interchange. The stack interchange between I-10 and I-405 in Los Angeles 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 ''Mixmasters'' was a late-night music show, and later a DVD series, of audio-visual and DJ: VJ mixes produced by AV artists Addictive TV.http://www.addictive.tv Addictive TV The series ran from 2000 to 2005 and aired in the United Kingdom on ITV. ...

'' (for a Sunbeam Products brand of electric kitchen mixers), or as ''Spaghetti Bowls'' or '' Spaghetti Junctions'' (being compared to boiled spaghetti). 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, 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 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 most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore was d ...

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 in Birmingham, Alabama () * Interstate 196 and U.S. Route 131 in Grand Rapids, Michigan () *

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 in Charlotte, North Carolina () * South of Riyadh ()

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. 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 implemented ...

, 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 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 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, 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. 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 ...

s, traffic signals, 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)

A diverging diamond interchange (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 French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...

communities of Versailles ( A13 at D182), Le Perreux-sur-Marne ( A4 at N486) and Seclin ( 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 Interstate 695 may refer to: *Interstate 695 (District of Columbia), a partially built connector in Washington, D.C. * Interstate 695 (Maryland), a beltway around Baltimore, Maryland *Interstate 695 (New York), a short connector in Bronx County, New ...

north of

. The first DDI in the United States opened on July7, 2009, in Springfield, Missouri, at the junction of Interstate 44 and Missouri Route 13.

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 with M-59 in Michigan, 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 in the Tampa Bay area of Florida, including the SR 694 interchange in St. Petersburg and SR 60 in Clearwater.

References

External links

Glossary
Part of the publicatio

by the Turner-Fairbank Highway Research Center branch of the U.S. Federal Highway Administration
Kurumi.com U.S. interchanges directory

{{Authority control Bridges Road infrastructure Road junction types