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High-capacity freeway interchange in Los Angeles, California.

Approaching a freeway exit.

• A freeway junction or highway interchange (in the US) or motorway junction (in the UK) is a type of road junction, linking one motorway to another; to other roads; or sometimes to just a motorway service station. In the UK, all junctions on a motorway with other roads are numbered - the first being called "Junction 1", etc. In the US, interchanges are either numbered according to cardinal interchange number, or by mileage.
• A highway ramp (as in exit ramp and entrance ramp) or slip road is a short section of road which allows vehicles to enter or exit a freeway (motorway).
• A directional ramp always tends toward the desired direction of travel. This means that a ramp that makes a left turn exits from the left side of the roadway (a left exit). Left directional ramps are relatively uncommon as the left lane is usually reserved for high-speed through traffic. Right ramps are almost always directional.
• A non-directional ramp goes in a direction opposite to the desired direction of travel. Many loop ramps (as in a cloverleaf) are non-directional.
• A semi-directional ramp exits a road in a direction opposite from the desired direction of travel, but then turns toward the desired direction of travel. Many 'flyover ramps' (as in a stack) are semi-directional.
• A U-Turn ramp leaves the road in one driving direction, turns over or under it and rejoins in the opposite direction.

The German Autobahn system splits Autobahn-to-Autobahn interchanges into two types - Autobahnkreuz (AK, translates as motorway cross), a crossing of two Autobahns (or something more complicated), and Autobahndreieck (AD, translates as motorway triangle), an interchange where one of the Autobahns ends. It has been suggested that German Autobahns be merged into this article or section. ...

Complete interchanges

A complete interchange has enough ramps to provide access from any direction of any road in the junction to any direction of any other road in the junction.

Barring u-turns, a complete interchange between two freeways requires eight ramps, while a complete interchange between a freeway and another road (not a freeway) requires at least four ramps. Using u-turns these numbers can be halved to four and two respectively, by making cars that want to turn left pass by the other road first, then make a u-turn and turn right. The use of u-turn ramps is common in less wealthy countries.

The general rule today is that freeways should have at least one mile between interchanges to prevent excessive weaving between entering and leaving traffic. Unfortunately, most older freeway interchanges do not follow this rule (and are congested as a result).

Types of interchanges

Between two freeways

A compact highway interchange (Circle Interchange) in Chicago, Illinois,USA.
A typical cloverleaf interchange with collector/distributor roads
Stacked interchange near Den Haag (The Hague), Netherlands.
Stack Interchange in Farmington, Connecticut, USA.
Stacked interchange in Los Angeles, California, USA.
Trumpet interchange near Arnhem, Netherlands
• A cloverleaf is a two-level interchange in which left turns are handled by loop ramps. To go left, vehicles first pass either over or under the other road, then bear right onto a one-way ramp that loops 270 degrees to the right and then merges onto the intersecting road. (In countries where cars drive on the left, this is a left turn.) The major advantage of cloverleafs is that they require only one bridge, which makes such junctions cheap if land is plentiful. A major problem with cloverleafs is weaving (see definition of weaving, above). Cloverleafs also have a considerable land consumption which means that while they are common in the United States, Canada (mainly parclos), Germany, and Netherlands, only four such junctions are found in the land-scarce United Kingdom, with just one on the motorway network (partial cloverleaf exists where the M25 meets the M40 west of London). In Germany the standard design is to separate all turning traffic into a parallel lane so that the extra road space minimizes the problem of weaving. Collector-distributor roads are similar, but are separated from the main freeway lanes by a divider. Collector-distributor roads can be seen at the junction of Interstate 64 and Interstate 295 east of Richmond, Virginia, USA. Cloverleafs are often seen in urban highways within cities that grow out instead of up.
• A stack is an interchange in which left turns are handled by semi-directional flyover ramps. In order to go left, vehicles first turn slightly right (on a 'right-turn' ramp), then go left on a ramp which goes over (or under) both freeways and connects to the 'right-turn' ramp in the opposite quadrant of the interchange. A stack interchange, then, has two pairs of left-turning ramps, which can be "stacked" in various configurations above or below the two through routes. Stacks do not suffer from the problem of weaving associated with cloverleafs, but require massive construction works. A basic stack involves roads on four levels, but in stacks including ramps for direct movement between high occupancy vehicle lanes, even more levels of stack can be needed; the interchange between Interstate 105 and Interstate 110 in Los Angeles County, California, is a five-level stack. This is not only expensive, but also unsightly, leading to considerable NIMBY opposition. Large stacks with multiple levels are sometimes referred to as Mixmasters in the United States.

• A variation appropriate when the freeways meet at an angle is the cloverdirectional interchange, which has cloverleafs for the sharp left turns (less than 270° turning) and adjacent semi-directional ramps for the gentle left turns, one inside and one outside the junction. This design is compact and has no serious drawbacks. Other variations of half-cloverleaf-half-directional interchanges include the cloverstack (in which the stack ramps pass over the cloverleaf loop ramps) and the cloverturbine (where two turbine ramps surround the cloverleaf ramps. Other variations have three directional ramps and one cloverleaf loop.

A junction with two adjacent cloverleafs is sub-optimal and will be the result of a previous junction improvement subject to land restriction. There are also variations with three cloverleaf loops and one directional ramp (usually a turbine ramp).

• A trumpet is an interchange traditionally used where one freeway terminates at another freeway; it involves at least one loop ramp connecting traffic either entering or leaving the terminating freeway with the far lanes of the continuous freeway. These junctions are also useful for toll roads as they concentrate all entering and leaving traffic in a single stretch of road, where toll booths can be installed. Double Trumpet interchanges can usually be found when a toll road meets another toll road or a freeway.
• A Directional T provides for high-speed ramps in all directions at a three-way interchange. A semi-directional T does the same, but some of the splits and merges are switched to avoid ramps to and from the passing lane.
• Hybrids, variations and rare types

This article or section does not cite any references or sources. ... This article or section does not cite any references or sources. ... Interstate 80 (Eastshore Freeway) in Berkeley, California: a typical American freeway (MUTCD definition) A freeway, also known as a highway, superhighway, autoroute, autobahn, autostrada, dual carriageway, expressway, Autosnelweg or motorway, depending on the country of discussion, is a type of road designed for safer high-speed operation of motor vehicles... Diagram showing lanes and road layout, with Irish road markings. ...

Between a freeway and a non-freeway road

• Diamond interchange
• Cloverleaf interchange
• Parclo interchange (partial cloverleaf - sometimes called a folded diamond when only four ramps, in two quadrants, are used)
• Single Point Urban Interchange
• Roundabout interchange--this uses a single roundabout or traffic circle which spans the freeway with two over/underpasses (either above or below the freeway). These are very common in the UK, Ireland and France, but almost unknown in the rest of Europe and the United States. Such junctions can be improved by adding a flyover for straight-through traffic on the non-freeway, creating a stacked roundabout.
• Dumbbell interchange - this is similar to a diamond except that it uses roundabouts rather than signals or stop signs where the ramps meet the non-freeway road.
• Inner diamond interchange -- this type of interchange allows opposing left turns to proceed concurrently where the ramps meet the surface street due to all four ramps meeting at a single intersection either above or below the freeway median, just as if it were an intersection of two surface streets. However, all of the ramps enter and exit the freeway from the innermost passing lanes, creating the potential for confusion to people not familiar with the area. The only known freeways in the U.S. to have such an interchange are Interstate 290 in Chicago, Illinois at the Austin Avenue and Harlem Avenue interchanges, Interstate 244 in Tulsa, Oklahoma at the Sheridan Avenue and Memorial Drive interchanges, and New York State Routes 9A, 100 at 117, and U.S. Route 422 (Benjamin Franklin Highway) at Bingaman St/E. Lancaster Ave in Reading, Pennsylvania.

A typical diamond interchange A diamond interchange is a common type of road junction. ... A cloverleaf interchange is a two-level interchange in which right turns (in countries that drive on the left) are handled by loop ramps. ... The parclo interchange (short for partial cloverleaf interchange) is a successor to the cloverleaf interchange. ... A typical Single Point Urban Interchange. ... A roundabout interchange is an interchange between a freeway and a minor road. ... A roundabout or rotary is a type of road junction (or traffic calming device) at which traffic enters a stream around a central island after first yielding (giving way) to the circulating traffic. ... Columbus Circle, New York City, NY; site of the first traffic circle in the United States completed in 1905 DeSoto Fountain sits in the center of a traffic circle in the city of Coral Gables, Florida. ... For other uses, see Europe (disambiguation). ... Route 9A is a 47. ... Junction Location I-87 0. ... Junction Location US-9 0. ... This U.S. Highway article needs to be cleaned up to conform to both a higher standard of article quality and accepted design standards outlined in the WikiProject U.S. Highways. ... , Reading (IPA:) is the county seat of Berks County, Pennsylvania and the center of the Greater Reading Area. ...

Wikimedia Commons has media related to:

Image File history File links Commons-logo. ... A free-flow interchange is an interchange in which all roads are grade-separated, and where no movement from one road to another requires the driver to stop for traffic (for example, the interchange may not include traffic lights or roundabouts). ... An example of a four-level stack interchange in the Netherlands. ... A junction, when used in the context of traffic is a place where several traffic routes cross, eg. ... In the field of road transport, an intersection is a road junction where two or more roads either meet or cross at grade (they are at the same level). ... An unused highway may reference a highway that was partially or fully constructed but was unused. ...

Results from FactBites:

 Interchange (road) - Wikipedia, the free encyclopedia (1382 words) In the field of road transport, an interchange is a road junction that utilizes grade separation, and one or more ramps, to permit traffic on at least one road to pass through the junction without crossing any other traffic stream. A highway ramp (as in exit ramp and entrance ramp) or slip road is a short section of road which allows vehicles to enter or exit a freeway (motorway). A trumpet is an interchange traditionally used where one freeway terminates at another freeway; it involves at least one loop ramp (for traffic leaving the terminating freeway) whose overpass is shared by traffic connecting to the terminating freeway.
 Interchange - Wikipedia, the free encyclopedia (303 words) In the UK an interchange is a transport node for more than one form of transport; see also intermodal passenger transport. In Australian rules football, interchange refers to a group of players in a sporting team that can be subsituted into a match, replacing players coming off the ground. The level of interchange is determined by many different factors according to the way the transaction occurred and the type of card used.
More results at FactBites »

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