In the field of road transport, a road junction is a place where two or more roads either meet or cross. The main types of road junctions are intersections and interchanges. A road junction may also be called a crossroads. A junction between 3 road segments (arms) is a T junction (two arms form one road) or a Y-junction. Disruptions in organized traffic flow can create delays lasting hours. ... A road is a strip of land, smoothed or otherwise prepared to allow easier travel, connecting two or more destinations. ... A crossroads (the word rarely appears in singular) is another word for road junction, where two or more roads meet (there are three or more arms). ... A typical T junction A T junction is a type of road junction with three arms where one (often minor) road connects to another (often major) road in a T shape. ...

Terminology

Note: The descriptions of road junctions are for countries where vehicles drive on the right side of the road. For countries where driving is on the left the layout of the junctions is the same, only left/right is reversed. Vehicles are non-living means of transport. ... Red = drive on right Blue = drive on left Rules of the road are the general practices and procedures followed by people on roads, especially those driving cars or on bicycles or other vehicles. ... Layout, in publishing, is the process of arranging editorial content, advertising, graphics and other information in a manner that creates an effective presentation. ...

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 typical rural freeway (Interstate 5 in the Central Valley of California). ... A motorway (Ireland, New Zealand, the United Kingdom and some Commonwealth nations) is both a type of road and a classification. ...

• 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 it and rejoins in the opposite direction.

Weaving is an undesirable situation in which traffic veering right and traffic veering left must cross paths within a limited distance, to merge with traffic on the through lane. Weaving creates both safety and capacity problems. Some areas that had such junctions have gone through the expensive process of "unweaving the weave" to improve traffic flow. Overpass in East Potomac Park, Washington, D.C. Flyover in Miami Beach, Florida An overpass (In UK, India, Hong Kong flyover) is a bridge, road or similar structure that crosses over another road. ... a movie set in superior, arizona ...

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. Autobahn (pronounced in IPA, plural Autobahnen) is the German word for a major high-speed road usually linking one or more cities and towns, similar to motorway or freeway in English-speaking countries. ...

Intersections

4th and San Fernando, San Jose, CA. Three views of an intersection, from above, looking west

4th and San Fernando, San Jose, CA, from a car traveling south.

4th and San Fernando, San Jose, CA, from the ground facing northwest.

An intersection is a road junction at which roads meet at grade. Types of intersections include: Download high resolution version (1000x661, 229 KB)San Jose, CA intersection overview from MLK Library in the early afternoon. ... Download high resolution version (1000x661, 229 KB)San Jose, CA intersection overview from MLK Library in the early afternoon. ... Download high resolution version (1000x750, 257 KB)San Jose, CA intersection southbound in car in the early afternoon. ... Download high resolution version (1000x750, 257 KB)San Jose, CA intersection southbound in car in the early afternoon. ... Download high resolution version (1000x618, 249 KB)San Jose, CA intersection seen from a pedestrians perspective in the early afternoon. ... Download high resolution version (1000x618, 249 KB)San Jose, CA intersection seen from a pedestrians perspective in the early afternoon. ...

• Uncontrolled intersections, without signs or signals (or sometimes with a warning sign). On a 4-way intersection traffic from the right has priority; on a 3-way intersection rules may vary by country: either traffic from the right has priority again, or traffic on the continuing road. For traffic coming from the same or opposite direction, that which goes straight has priority over that which turns off.
• Yield-controlled intersections may or may not have specific "YIELD" signs (known as "GIVE WAY" signs in some countries).
• Stop-controlled intersections have one or more "STOP" signs. Two-way and four-way stops are common.
• Signal-controlled intersections depend on traffic signals, usually electric, which indicate which traffic has the right-of-way at any particular time.
• A traffic circle is a special type of intersection at which traffic streams are directed around a circle. Types of traffic circles include roundabouts, 'mini-roundabouts', 'rotaries', "STOP"-controlled circles, and signal-controlled circles. Some people consider roundabouts to be a distinct type of intersection from traffic circles (with the distinction based on certain differences in size and engineering).
• A box junction can be added to an intersection, generally prohibiting entry to the intersection unless the exit is clear.
• While not a specific type of intersection, the US state of Michigan frequently employs a special arrangement for making left turns, known as a Michigan left. These are generally used in conjunction with Signal-controlled intersections, although it can also apply to Stop-controlled intersections.

Stop sign used in English-speaking countries Former European stop sign consisting of red Give Way triangle inside a circle A stop sign is a traffic sign, usually erected at road junctions, that instructs drivers to make a brief and temporary, but complete, stop upon reaching it, and then to... Traffic lights will sometimes differ where there are several lanes of traffic. ... Right-of-way is a legal term which may have any of several meanings: priority at a crossing, or in traffic. ... A traffic circle is an intersection with a circular shape and, usually, a central island. ... A roundabout, rotary, or gyratory circus is a type of road junction (or traffic calming device) at which traffic streams circularly around a central island after first yielding to the circulating traffic. ... A box junction is a traffic control measure which can be added to other road junctions. ... State nickname: Wolverine State or Great Lakes State Other U.S. States Capital Lansing Largest city Detroit Governor Jennifer Granholm Official languages English Area 250,941 km² (11th)  - Land 147,255 km²  - Water 103,687 km² (41. ... A typical Michigan left setup. ...

Interchanges

A highway 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 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

Cloverleaf interchange

• 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 would be a right 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, Germany, and Netherlands, only three such junctions are found in the short-of-land United Kingdom, none on the motorway network. 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.

Stacked interchange near The Hague

Stacked interchange in Los Angeles

• 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. This is not only expensive, but also unsightly leading to considerable NIMBY opposition.

An alternative to the stack which requires fewer levels while retaining semi-directional ramps throughout has the left-turning ramps sweep around the center of the interchange in a spiral pattern. This has slightly less capacity because the ramps turn and change height more quickly. One example of a freeway-to-surface street ramp in this style would be the Interstate 696/Mound Road interchange in Warren, Michigan. A typical rural freeway (Interstate 5 in the Central Valley of California). ... cloverleaf road junction. ... cloverleaf road junction. ... A cloverleaf interchange is a two-level interchange in which left turns are handled by loop ramps. ... A motorway (Ireland, New Zealand, the United Kingdom and some Commonwealth nations) is both a type of road and a classification. ... Stacked highway interchange near The Hague, Netherlands Source and ©: picture archive of the ministry of traffic (V&W), Netherlands, 1983. ... Stacked highway interchange near The Hague, Netherlands Source and ©: picture archive of the ministry of traffic (V&W), Netherlands, 1983. ... Arms of The Hague The Hague (with capital T; Dutch: Den Haag, or officially s-Gravenhage) is the administrative capital of the Netherlands, located in the west of the country, in the province South Holland of which it is also the capital. ... Los Angeles, California. ... Los Angeles, California. ... Griffith Observatory and the Downtown Los Angeles skyline. ... A permanent, separated high-occupancy vehicle lane on I-91 in Connecticut A high occupancy vehicle (or HOV) is any vehicle with a driver and one or more (or sometimes two or more, or three or more) passengers. ... NIMBY (Not In My Back Yard) is an acronym denoting the opposition by local residents to construction of intrusive facilities, which are often intended primarily to serve people living far away: such as new roads or rail lines, power plants, waste storage facilities or the like; or those intended to... In mathematics, a spiral is a curve which turns around some central point or axis, getting progressively closer to or farther from it, depending on which way you follow the curve. ... Interstate 696 often referred to as Michigans Autobahn by locals, is an interstate highway entirely within the US state of Michigan. ... Mound Rd. ... Warren is a city located in Macomb County, Michigan. ...

• A cloverstack (half cloverleaf, half stack) is an interchange in which left turns are handled by two loop ramps and two semi-directional flyover ramps. The cloverleafs will be opposite each other. A cloverstack avoids the weaving problem associated with cloverleafs, without the expense of a full stack. Cloverleafs are sometimes converted to cloverstacks (by eliminating 2 loop ramps and replacing them with two flyover ramps). Such a conversion improves the capacity and safety of the interchange.

A variation appropriate when the freeways meet at an angle is to have 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.

A junction with two adjacent cloverleafs is sub-optimal and will be the result of a previous junction improvement subject to land restriction.

Trumpet interchange near Arnhem

• 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. 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.
• 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 fast lane.
• Hybrids, variations and rare types

Trumpet highway interchange near Arnhem, Netherlands Source and ©: picture archive of the ministry of traffic (V&W), Netherlands, 1984. ... Trumpet highway interchange near Arnhem, Netherlands Source and ©: picture archive of the ministry of traffic (V&W), Netherlands, 1984. ... Arnhem is a municipality and a city in the east of the Netherlands, located on the Lower Rhine and the capital of the Gelderland province. ... A high-speed toll booth on SR 417 near Orlando, Florida A toll road, turnpike or tollpike is a road on which a toll authority collects a fee for use. ...

Types of interchanges 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 (sometimes signal-controlled) 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.

A typical rural freeway (Interstate 5 in the Central Valley of California). ... A typical diamond interchange. ... A cloverleaf interchange is a two-level interchange in which left turns 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, rotary, or gyratory circus is a type of road junction (or traffic calming device) at which traffic streams circularly around a central island after first yielding to the circulating traffic. ... A satellite composite image of Europe Europe is geologically and geographically a peninsula, forming the westernmost part of Eurasia. ...

External links

Wikimedia Commons has more media related to:

Category:Road junctions

• Kurumi.com US interchanges directory
• Chris Marshall's UK interchanges directory
• Detailed history of interchanges with diagrams, in German