Intersection (road)
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An intersection or an at-grade junction is a
junction Junction may refer to: Arts and entertainment * ''Junction'' (film), a 2012 American film * Jjunction, a 2002 Indian film * Junction (album), a 1976 album by Andrew Cyrille * Junction (EP), by Basement Jaxx, 2002 * Junction (manga), or ''Hot ...
where two or more roads converge, diverge, meet or cross at the same height, as opposed to an interchange, which uses bridges or tunnels to separate different roads. Major intersections are often delineated by gores and may be classified by road segments, traffic controls and lane design.


Types


Road segments

One way to classify intersections is by the number of road segments (arms) that are involved. * A
three-way intersection A three-way junction (or three-way intersection) is a type of road intersection with three arms. A Y junction (or Y intersection) generally has three arms of equal size coming at an acute or obtuse angle to each other; while a T junction (or T ...
is a junction between three road segments (arms): a T junction when two arms form one road, or a Y junction, the latter also known as a fork if approached from the stem of the Y. * A four-way intersection, or crossroads, usually involves a crossing over of two streets or roads. In areas where there are blocks and in some other cases, the crossing streets or roads are
perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...
to each other. However, two roads may cross at a different angle. In a few cases, the junction of two road segments may be offset from each when reaching an intersection, even though both ends may be considered the same street. * Six-way intersections usually involve a crossing of three streets at one junction; for example, a crossing of two perpendicular streets and a diagonal street is a rather common type of 6-way intersection. * Five, seven or more approaches to a single intersection, such as at Seven Dials, London, are not common.


Traffic controls

Another way of classifying intersections is by traffic control technology: *
Uncontrolled intersection An uncontrolled intersection is a road intersection where no traffic lights, road markings or signs are used to indicate the right-of-way. They are found in either residential neighborhoods or in rural areas. While the intersection itself is unmark ...
s, without signs or
signals In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
(or sometimes with a warning sign). Priority (right-of-way) rules may vary by country: on a 4-way intersection traffic from the right often has priority; on a 3-way intersection 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 stops are common, while some countries also employ
four-way stop An all-way stop – also known as a four-way stop (or three-way stop etc. as appropriate) – is a traffic management system which requires vehicles on all the approaches to a Intersection (road), road intersection to stop at the intersection be ...
s. * Signal-controlled intersections depend on
traffic signal 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 light ...
s, usually electric, which indicate which traffic is allowed to proceed at any particular time.


Lane design

* A
traffic circle 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 Eng ...
is a type of intersection at which traffic streams are directed around a circle. Types of traffic circles include
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 ...
s, "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 A box junction is a road traffic control measure designed to prevent congestion and gridlock at junctions. The surface of the junction is typically marked with a yellow criss-cross grid of diagonal painted lines (or only two lines crossing eac ...
can be added to an intersection, generally prohibiting entry to the intersection unless the exit is clear. * Some (unconventional or alternative) intersections employ indirect left turns to increase capacity and reduce delays. The
Michigan left A Michigan left or P-turn is an at-grade intersection design that replaces each left (farside) turn at an intersection between a (major) divided roadway and a secondary (minor) roadway with the combination of a right (nearside) turn followe ...
combines a right turn and a U-turn.
Jughandle A jughandle is a type of ramp or slip road that changes the way traffic turns left at an at-grade intersection (in a country where traffic drives on the right). Instead of a standard left turn being made from the left lane, left-turning traffic ...
lefts diverge to the right, then curve to the left, converting a left turn to a crossing maneuver, similar to throughabouts. These techniques are generally used in conjunction with signal-controlled intersections, although they may also be used at stop-controlled intersections. * Other designs include
advanced stop line An advanced stop line (ASL), also called advanced stop box or bike box, is a type of road marking at signalised road junctions allowing certain types of vehicle a head start when the traffic signal changes from red to green. Advanced stop lines ar ...
s, parallel-flow and
continuous-flow intersection A continuous flow intersection (CFI), also called a crossover displaced left-turn (XDL or DLT), is an alternative design for an at-grade road junction. Vehicles attempting to turn across the opposing direction of traffic (left in right-hand dr ...
s,
hook turn A hook turn ( Australian English) or two-stage turn (British English), also known as a Copenhagen Left (in reference to cyclists specifically), is a road cycling manoeuvre or a motor vehicle traffic-control mechanism in which vehicles that woul ...
s, quadrants,
seagull intersection A seagull intersectionJohn Harper, Wal Smart, Michael de Roos''Seagull Intersection Layout. Island Point Road – A Case Study'' 2000 – 2010 or continuous green T-intersection (also known as a turbo-T (in Florida) or High-T intersection (in Neva ...
s,
slip lane A slip lane, also known as a filter lane in the United Kingdom, is a road at a junction that allows motorists to change roads without actually entering an intersection. Some intersections that are controlled by lights offer a slip lane, which a ...
s, staggered junctions (in American English referred to as
dogleg Dogleg or dog-leg may refer to: * Dogleg (band), an American indie rock band *Dog-leg (stairs), a configuration of stairs which includes a half-landing before turning and continuing upwards *Dog-leg gearbox, an unusual manual transmission layout ...
s),
superstreet A superstreet, also known as a restricted crossing U-turn (RCUT), J-turn, or reduced conflict intersection (RCI), is a type of road intersection that is a variation of the Michigan left. In this configuration, in contrast to the Michigan left, ...
s,
Texas T A Texas T, also called a ''T-ramp,'' is a T-shaped highway ramp that combines entrance and exit ramps into a single structure that allows entrance and exit to the left (inside) lanes of an expressway. It is intended to avoid traffic congestion c ...
s,
Texas U-turn A Texas U-turn, or Texas turnaround, boomerang, or loop around, is a lane allowing cars traveling on one side of a one-way frontage road to U-turn onto the opposite frontage road (typically crossing over or under a freeway or expressway). Typical ...
s and turnarounds. * 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 ...
and its variants like turbo roundabouts,
bowtie The bow tie is a type of necktie. A modern bow tie is tied using a common shoelace knot, which is also called the bow knot for that reason. It consists of a ribbon of fabric tied around the collar of a shirt in a symmetrical manner so that t ...
s and distributing circles like traffic circles and
right-in/right-out Right-in/right-out (RIRO) and left-in/left-out (LILO) refer to a type of three-way road intersection where turning movements of vehicles are restricted. A RIRO permits only right turns and a LILO permits only left turns. "Right-in" and "left-in" r ...
(RIRO) intersections.


Turns

At intersections, turns are usually allowed, but are often regulated to avoid interference with other traffic. Certain turns may be not allowed or may be limited by regulatory signs or signals, particularly those that cross oncoming traffic. Alternative designs often attempt to reduce or eliminate such potential conflicts.


Turn lanes

At intersections with large proportions of turning traffic, turn lanes (also known as turn bays) may be provided. For example, in the intersection shown in the diagram, left turn lanes are present in the right-left street. Turn lanes allow vehicles, to cross oncoming traffic (i.e., a left turn in right-side driving countries, or a right turn in left-side driving countries), or to exit a road without crossing traffic (i.e., a right turn in right-side driving countries, or a left turn in left-side driving countries). Absence of a turn lane does not normally indicate a prohibition of turns in that direction. Instead, traffic control signs are used to prohibit specific turns. Turn lanes can increase the capacity of an intersection or improve safety. Turn lanes can have a dramatic effect on the safety of a junction. In rural areas, crash frequency can be reduced by up to 48% if left turn lanes are provided on both main-road approaches at stop-controlled intersections. At signalized intersections, crashes can be reduced by 33%. Results are slightly lower in urban areas. Turn lanes are marked with an arrow bending into the direction of the turn which is to be made from that lane. Multi-headed arrows indicate that vehicle drivers may travel in any one of the directions pointed to by an arrow.


Turn signals

Traffic signals facing vehicles in turn lanes often have arrow-shaped indications. North America uses various indication patterns. Green arrows indicate protected turn phases, when vehicles may turn unhindered by oncoming traffic. Red arrows may be displayed to prohibit turns in that direction. Red arrows may be displayed along with a circular green indication to show that turns in the direction of the arrow are prohibited, but other movements are allowed. In some jurisdictions, a red arrow prohibits a
turn on red A turn on red is a principle of law permitting vehicles at a traffic light showing a red signal to turn into the direction of traffic nearer to them (almost always after a complete stop, depending on the jurisdiction) when the way is clear, ...
.New York State Driver's Manual
Chapter 4.
In Europe, if different lanes have differing phases, red, yellow and green traffic lights corresponding to each lane have blacked-out areas in the middle in the shape of arrows indicating the direction(s) drivers in that lane may travel in. This makes it easier for drivers to be aware which traffic light they need to pay attention to. A green arrow may also be provided; when it is on, drivers heading in the direction of the arrow may proceed, but must yield to all other vehicles. This is similar to the right turn on red in the US. Disadvantages to turn lanes include increased pavement area, with associated increases in construction and maintenance costs, as well as increased amounts of stormwater runoff. They also increase the distance over which pedestrians crossing the street are exposed to vehicle traffic. If a turn lane has a separate signal phase, it often increases the delay experienced by oncoming through traffic. Without a separate phase, left crossing traffic does not get the full safety benefit of the turn lane.


Lane management

Alternative intersection configurations, formerly called unconventional intersections, can manage turning traffic to increase safety and intersection throughput. These include the
Michigan left A Michigan left or P-turn is an at-grade intersection design that replaces each left (farside) turn at an intersection between a (major) divided roadway and a secondary (minor) roadway with the combination of a right (nearside) turn followe ...
/
Superstreet A superstreet, also known as a restricted crossing U-turn (RCUT), J-turn, or reduced conflict intersection (RCI), is a type of road intersection that is a variation of the Michigan left. In this configuration, in contrast to the Michigan left, ...
(RCUT/MUT) and
continuous flow intersection A continuous flow intersection (CFI), also called a crossover displaced left-turn (XDL or DLT), is an alternative design for an at-grade road junction. Vehicles attempting to turn across the opposing direction of traffic (left in right-hand dr ...
(CFI/DLT), to improve traffic flow, and also interchange types like
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/DCD) design as part of the
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 ...
's Every Day Counts initiative which started in 2012.


Vulnerable road users

Vulnerable road users include pedestrians, cyclists, motorcyclists, and individuals using motorized scooters and similar devices. Compared to people who are in motor vehicles (like cars and trucks), they are much more likely to suffer catastrophic or fatal injuries at an intersection.


Pedestrians

Intersections generally must manage
pedestrian A pedestrian is a person traveling on foot, whether walking or running. In modern times, the term usually refers to someone walking on a road or pavement, but this was not the case historically. The meaning of pedestrian is displayed with ...
as well as vehicle traffic. Pedestrian aids include
crosswalk A pedestrian crossing (or crosswalk in American English) is a place designated for pedestrians to cross a road, street or avenue. The term "pedestrian crossing" is also used in the Vienna and Geneva Conventions, both of which pertain to road ...
s, pedestrian-directed traffic signals ("walk light") and
over Over may refer to: Places *Over, Cambridgeshire, England *Over, Cheshire, England *Over, South Gloucestershire, England * Over, Tewkesbury, near Gloucester, England ** Over Bridge *Over, Seevetal, Germany Music Albums * ''Over'' (album), by Pe ...
/
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 ...
es. Traffic signals can be time consuming to navigate, especially if programmed to prioritise vehicle flow over pedestrians, while over and underpasses which rely on stairs are inaccessible to those who can't climb them. Walk lights may be accompanied by audio signals to aid the visually impaired.
Medians The Medes ( Old Persian: ; Akkadian: , ; Ancient Greek: ; Latin: ) were an ancient Iranian people who spoke the Median language and who inhabited an area known as Media between western and northern Iran. Around the 11th century BC, th ...
can offer pedestrian islands, allowing pedestrians to divide their crossings into a separate segment for each traffic direction, possibly with a separate signal for each. Some intersections display red lights in all directions for a period of time. Known as a
pedestrian scramble A pedestrian scramble, also known as scramble intersection and scramble corner (Canada), 'X' Crossing (UK), diagonal crossing (US), (Japan), exclusive pedestrian interval, or Barnes Dance, is a type of traffic signal movement that temporarily s ...
, this type of vehicle
all-way stop An all-way stop – also known as a four-way stop (or three-way stop etc. as appropriate) – is a traffic management system which requires vehicles on all the approaches to a road intersection to stop at the intersection before proceeding throu ...
allows pedestrians to cross safely in any direction, including diagonally. All green for non motorists is known from the crossing at
Shibuya Station is a railway station in Shibuya, Tokyo, Japan, operated jointly by East Japan Railway Company (JR East), Keio Corporation, Tokyu Corporation, and Tokyo Metro. With 2.4 million passengers on an average weekday in 2004, it is the fourth-busiest ...
, Tokyo. In 2020, NHTSA reported that more than 50% of pedestrian deaths in the United States (3,262 total) were attributed to failure to yield the right of way-- which typically occurs at intersections.


Cyclists and motorcyclists

Poor visibility at junctions can lead to drivers colliding with cyclists and motorcyclists. Some junctions use
advanced stop line An advanced stop line (ASL), also called advanced stop box or bike box, is a type of road marking at signalised road junctions allowing certain types of vehicle a head start when the traffic signal changes from red to green. Advanced stop lines ar ...
s which allow cyclists to filter to the front of a traffic queue which makes them more visible to drivers.


Safety

A European study found that in Germany and Denmark, the most important crash scenario involving vulnerable road users was: * motor vehicle turning right/left while cyclist going straight; * motor vehicle turning right/left while pedestrian crossing the intersection approach. These findings are supported by data elsewhere. According to the U.S.
National Highway Traffic Safety Administration The National Highway Traffic Safety Administration (NHTSA ) is an agency of the U.S. federal government, part of the Department of Transportation. It describes its mission as "Save lives, prevent injuries, reduce vehicle-related crashes" rela ...
, roughly half of all U.S. car crashes occurred at intersections or were intersection related in 2019.


At grade railways

In the case of
railway Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
s or rail tracks the term at grade applies to a
rail line Rail terminology is a form of technical terminology. The difference between the American term ''railroad'' and the international term ''railway'' (used by the International Union of Railways and English-speaking countries outside the United Sta ...
that is not on an
embankment Embankment may refer to: Geology and geography * A levee, an artificial bank raised above the immediately surrounding land to redirect or prevent flooding by a river, lake or sea * Embankment (earthworks), a raised bank to carry a road, railwa ...
nor in an
open cut Open-pit mining, also known as open-cast or open-cut mining and in larger contexts mega-mining, is a surface mining technique of extracting rock or minerals from the earth from an open-air pit, sometimes known as a borrow. This form of mining ...
. As such, it crosses
street A street is a public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, ...
s and
roads A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types of ...
without going
under Under may refer to: * "Under" (Alex Hepburn song), 2013 * "Under" (Pleasure P song), 2009 *Bülent Ünder (born 1949), Turkish footballer *Cengiz Ünder (born 1997), Turkish footballer *Marie Under Marie Under ( – 25 September 1980) was one o ...
or
over Over may refer to: Places *Over, Cambridgeshire, England *Over, Cheshire, England *Over, South Gloucestershire, England * Over, Tewkesbury, near Gloucester, England ** Over Bridge *Over, Seevetal, Germany Music Albums * ''Over'' (album), by Pe ...
them. This requires
level crossing A level crossing is an intersection where a railway line crosses a road, Trail, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line crossing over or under using an Overpass#Railway, overpass ...
s. At-grade railways may run along the
median In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic fe ...
of a
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 ...
. The opposite is
grade-separated 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 ...
. There may be overpasses 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 ...
es.


See also

* * * * * *
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 ...
*
Street A street is a public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, ...
*


References


External links


Traffic flow measured on 30 different 4-way junctions
by euverus, December 4, 2017 in the video game Cities: Skylines {{DEFAULTSORT:Intersection (Road) Road infrastructure Road junction types