In the field of road transport, an interchange is a road junction that uses grade separations 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, where roads cross at grade. Interchanges are almost always used when at least one road is a controlled-access highway (freeway or motorway) or a limited-access divided highway (expressway), though they are sometimes used at junctions between surface streets.
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.
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 was the first road to feature grade-separations. 24, 1915, though the conceptual roadwork was not realised until a cloverleaf opened on December 15, 1929, in Woodbridge, New Jersey, connecting New Jersey Route 25 and Route 4 (now U.S. Route 1/9 and New Jersey Route 35). It was designed by Philadelphia engineering firm Rudolph and Delano, based on a design seen in an Argentinian magazine.Maryland engineer Arthur Hale filed a patent for the design of a cloverleaf interchange on May
A system interchange connects multiple controlled-access highways, involving no at-grade signalised intersections.
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. 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 May 24, 1915. The first one in North America opened on December 15, 1929, in Woodbridge, New Jersey, connecting New Jersey Route 25 and Route 4 (now U.S. Route 1/9 and New Jersey Route 35). 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 on October 15, 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.
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 (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.
Caltrans classifies 4-level stacks in California as Type F-1. Type F-1 Alt B is a normal stack, while F-1 Alt A is one where the two right turn ramps merging onto one of the freeways merge ahead of the left turn ramps.
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.
In California, Caltrans classifies the combination interchange with one flyover ramp as Type F-2, and with two opposite ramps as Type F-3.
The turbine interchange (also known as a whirlpool[ citation needed ]) 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. A full turbine interchange features a minimum of 18 overpasses, and require more land to construct than a four-level stack interchange' however, the bridges are generally short in length. Coupled with reduced maintenance costs, a turbine interchange is a less costly alternative to a stack.
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, or rotary, on a separated level above, below, or in the middle of the two highways.
This section possibly contains original research .(July 2021)
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 interchanges may be used where one highway terminates at another highway, and are named as such due to their resemblance to the musical instrument. They are sometimes referred to as Jug handles.
These interchanges are very common on toll roads, 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 version 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 the same direction. The turn that isn't used as often would get the slower loop ramp.
Caltrans classifies service trumpet interchanges as Type L-11 where the on-ramp is a loop (right-hand trumpet), and Type L-12 where the off-ramp is a loop (left-hand trumpet). System trumpet interchanges are Type F-6.
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. They get their name due to 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.
It features directional ramps (no loops, or weaving right to turn left) and can use multi-lane ramps in comparatively little space. Some designs have two ramps and the "inside" thru 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 of the terminating road enters and leaves on the passing lane, so the semi-directional T interchange (see below) is preferred instead.
The interchange of Highway 416 and Highway 417 is one of the few directional T interchanges (constructed 1990-93) built, after most transportation departments had switched over to the semi-directional T design.
Like 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.
Semi-directional T interchanges are built as two or three-level junctions, with three-level interchanges typically being 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/near a single point, which will require 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.
Caltrans classifies these as Type F-5.
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.
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 signs, 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.
Caltrans classifies diamond interchanges in California into two types, L-1 and L-2. Type L-1 is a Tight Urban Diamond Interchange (TUDI), and Type L-2 is a standard diamond interchange, with a larger distance between the sets of ramps.
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.
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 controlled-access highway, 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.
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 communities of Versailles (A13 at D182), Le Perreux-sur-Marne (A4 at N486) and Seclin (A1 at D549), in the 1970s. 7, 2009, in Springfield, Missouri, at the junction of Interstate 44 and Missouri Route 13.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 Interstate 95 and I-695 north of Baltimore. The first DDI in the United States opened on July
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, the term single-point diamond interchange is considered the correct vernacular. In California, Caltrans classifies these as Type L-13, because of its relation to the Type L-1 tight urban diamond interchange.
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.
Interstate 27 (I-27) is an Interstate Highway, entirely in the U.S. state of Texas, running north from Lubbock to Interstate 40 in Amarillo. These two cities are the only control cities on I-27; other cities and towns served by I-27 include New Deal, Abernathy, Hale Center, Plainview, Kress, Tulia, Happy, and Canyon. In Amarillo, I-27 is commonly known as the Canyon Expressway, although it is also called Canyon Drive on its access roads. I-27 was officially designated the Marshall Formby Memorial Highway after former attorney and Texas State Senator Marshall Formby in 2005. The entire length of I-27 replaced U.S. Route 87 for through traffic.
An overpass is a bridge, road, railway or similar structure that crosses over another road or railway. An overpass and underpass together form a grade separation. Stack interchanges are made up of several overpasses.
A cloverleaf interchange is a two-level interchange in which all turns are handled by slip roads. To go left, vehicles first continue as one road passes over or under the other, then exit right onto a one-way three-fourths loop ramp (270°) and merge onto the intersecting road. The objective of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by traffic lights. The limiting factor in the capacity of a cloverleaf interchange is traffic weaving.
In civil engineering, grade separation is a method of aligning a junction of two or more surface transport axes at different heights (grades) so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a mixture of roads, footpaths, railways, canals, or airport runways. Bridges, tunnels, or a combination of both can be built at a junction to achieve the needed grade separation.
A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road.
Interstate 664 (I-664) is an auxiliary Interstate Highway in the U.S. state of Virginia. The Interstate runs 20.79 miles (33.46 km) from I-64 and I-264 in Chesapeake north to I-64 in Hampton. I-664 forms the west side of the Hampton Roads Beltway, a circumferential highway serving the Hampton Roads metropolitan area. The Interstate crosses Hampton Roads via the Monitor-Merrimac Memorial Bridge-Tunnel between Suffolk and Newport News. I-664 is connected to the other major cities of the metropolitan area—Portsmouth, Norfolk, and Virginia Beach—by I-264. The Interstate also has a connection to Portsmouth through Virginia State Route 164 and to Suffolk via U.S. Route 13, US 58, and US 460.
A single-point urban interchange, also called a single-point interchange (SPI) or single-point diamond interchange (SPDI), is a type of highway interchange. The design was created in order to help move large volumes of traffic through limited amounts of space safely and efficiently.
A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange.
Interstate 695 (I-695) is a 51.46-mile-long (82.82 km) full beltway Interstate Highway extending around Baltimore, Maryland, United States. I-695 is officially designated the McKeldin Beltway, but is colloquially referred to as either the Baltimore Beltway or 695. The route is an auxiliary route of I-95, intersecting that route southwest of Baltimore near Arbutus and northeast of the city near White Marsh. It also intersects other major roads radiating from the Baltimore area, including I-97 near Glen Burnie, the Baltimore–Washington Parkway near Linthicum, I-70 near Woodlawn, I-795 near Pikesville, and I-83 in the Timonium area. The 19.37-mile (31.17 km) portion of the Baltimore Beltway between I-95 northeast of Baltimore and I-97 south of Baltimore is officially Maryland Route 695 (MD 695), and is not part of the Interstate Highway System, but is signed as I-695. This section of the route includes the Francis Scott Key Bridge that crosses over the Patapsco River. The bridge and its approaches are maintained by the Maryland Transportation Authority (MDTA) while the remainder of the Baltimore Beltway is maintained by the Maryland State Highway Administration (MDSHA).
Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials (AASHTO) in the publication A Policy on Design Standards: Interstate System. For a certain highway to be considered an Interstate Highway, it must meet these construction requirements or obtain a waiver from the Federal Highway Administration.
Interstate 675 (I-675) is an auxiliary interstate highway in the suburbs of Dayton in the U.S. state of Ohio. Interstate 675 serves as an eastern bypass of Dayton. I-675 measures 26.53 miles (42.70 km) in length. As originally proposed, the route was to reconnect with I-75 north of Dayton near Northridge rather than going east towards Springfield and I-70. Construction was completed in 1987, though some have lobbied to extend the highway west of Dayton.
A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a type of diamond interchange in which the two directions of traffic on the non-freeway road cross to the opposite side on both sides of the bridge at the freeway. It is unusual in that it requires traffic on the freeway overpass to briefly drive on the opposite side of the road from what is customary for the jurisdiction. The crossover "X" sections can be traffic-light intersections or one-side overpasses to travel above the opposite lanes without stopping, the latter of which allows nonstop traffic flow when traffic is relatively sparse.
A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges eliminate the problems of weaving, have the highest vehicle capacity, and vehicles travel shorter distances when compared different types of interchanges.
State Route 164 is a 7.27-mile-long (11.70 km) primary state highway in the U.S. state of Virginia that connects the northern parts of Suffolk and Portsmouth with Newport News and Hampton via Interstate 664 (I-664) with Downtown Portsmouth and Norfolk through either the Downtown or Midtown Tunnels.
In the U.S. state of Pennsylvania, Interstate 70 (I-70) runs east–west across the southwest part of the state serving the southern fringe of the Pittsburgh metropolitan area. About half of the route is concurrent with I-76 on the Pennsylvania Turnpike. This is the oldest segment of I-70 in Pennsylvania, having been completed in 1940, and is only one of two segments of I-70 that are tolled, with the other being the Kansas Turnpike. I-70 is one of only a few Interstate Highways to have a traffic signal—in this case, with U.S. Route 30 in Breezewood, where it leaves the Pennsylvania Turnpike and heads toward Maryland.
Interstate 85 Business is a business loop of the Interstate Highway System. It is entirely a freeway running along the old route of I-85 in the vicinity of Spartanburg, South Carolina, United States. It is the only freeway to connect with Interstate 585, which is now an isolated piece of the Interstate Highway System.
A free-flow interchange is an interchange in which all roads are grade-separated, and where movement from one road to another does not require the driver to stop for traffic. Free-flow interchanges are less likely to induce traffic congestion than non-free-flow, but are typically more expensive both in money and in land.
Interstate 77 (I-77) is a south–north Interstate highway, extending 91.2 miles (146.8 km) in the state of South Carolina, extending from the national southern terminus at an interchange with I-26 near Columbia, north to the North Carolina state line near Rock Hill and Charlotte, NC.
Business routes of Interstate 80 exist in four states; California, Nevada, Utah, and Wyoming.
Terminology related to road transport—the transport of passengers or goods on paved routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single country, and some terms differ based on the side of the road traffic drives on. This glossary is an alphabetical listing of road transport terms.
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