An
intersection is a
road junctionA junction, when discussed in the context of transport, is a location where traffic can change between different routes, directions, or sometimes modes, of travel.-Historical significance:...
where two or more roads either meet or cross
at gradeAn at-grade intersection is a junction at which two or more transport axes cross at the same level .-Traffic management:With areas of high or fast traffic, an at-grade intersection normally requires a traffic control device such as a stop sign, traffic light or railway signal to manage conflicting...
(they are at the same level). An intersection may be 3-way - a
T junction or
fork, 4-way - a
crossroads, or 5-way or more. It may often be controlled by traffic lights, and may be a
roundaboutA roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...
(
traffic circleA traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...
in America).
This article primarily reflects jurisdictions where vehicles are driven on the right. If not otherwise specified, "right" and "left" can be reversed to reflect jurisdictions where vehicles are driven on the left.
Types of intersections
Some may classify intersections as 3-way, 4-way, 5-way, 6-way, etc. depending on the number of road segments (arms) that come together at the intersection.
- 3-way intersection - A junction between three road segments (arms) is a T junction (two arms form one road) or a Y-junction.
- 4-way intersections are the most common, because they usually involve a crossing over of two streets or roads. In areas where there are blocks
A city block, urban block or simply block is a central element of urban planning and urban design. A city block is the smallest area that is surrounded by streets. City blocks are the space for buildings within the street pattern of a city, they form the basic unit of a city's urban fabric...
and in some other cases, the crossing streets or roads are perpendicularIn geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
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.
- 5-way intersections are less common but still exist, especially in urban areas with non-rectangular blocks.
- 6-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.
- Seven or more approaches to a single intersection, such as at Seven Dials
Seven Dials is a small but well-known road junction in the West End of London in Covent Garden where seven streets converge. At the centre of the roughly-circular space is a pillar bearing six sundials, a result of the pillar being commissioned before a late stage alteration of the plans from an...
, London, are rare.
Another way of classifying intersections is by traffic control:
- Uncontrolled intersection
An uncontrolled intersection is a road intersection where no traffic lights or signs are used to indicate the right-of-way. Mostly, uncontrolled intersections are unmarked. However, in some locations, motorists may be warned by road signage or a warning light...
s, without signs or signals (or sometimes with a warning sign). Priority 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
A Stop sign is a traffic sign to notify drivers that they must stop before proceeding.-Specifications:The Vienna Convention on Road Signs and Signals proposed standard stop sign diameters of 0.6, 0.9 or 1.2 metres. UK and New Zealand stop signs are 750, 900 or 1200 mm, according to sign...
. Two-way stops are common, while some countries also employ four-way stops.
- Signal-controlled intersections depend on traffic signals, usually electric, which indicate which traffic is allowed to proceed at any particular time.
- A traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...
is a 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
A box junction is a traffic control measure designed to prevent gridlock at busy road junctions. The surface of the junction is marked with a criss-cross grid of diagonal painted lines , and vehicles may not enter the area so marked unless their exit from the junction is clear A box junction is a...
can be added to an intersection, generally prohibiting entry to the intersection unless the exit is clear.
- Some intersections employ indirect left turns to increase capacity and reduce delays. The Michigan left
A Michigan left is an at-grade intersection design which replaces each left turn with a permutation of a U-turn and a right turn. The design was given the name due to its frequent use along Michigan roads and highways since the late 1960s. In other contexts, the intersection is called a median...
combines a right turn and a U-turn. JughandleA jughandle is a type of ramp or slip road that changes the way traffic turns left at at-grade intersections. Instead of a standard left turn being made from the left lane, left-turning traffic uses a ramp on the right side of the road...
lefts diverge to the right, then curve to the left, converting a left turn to a crossing maneuver. These techniques are generally used in conjunction with signal-controlled intersections, although they may also be used at stop-controlled intersections.
Turns
At same-grade intersections, turns are usually allowed, but often regulated to avoid interference or collision with other traffic. If the crossing street is a one-way street, a turn into the opposing direction is not allowed, as indicated by "ONE WAY" or "NO LEFT TURN" or "NO RIGHT TURN" signs. In a few other cases, certain turns may be not allowed or limited by regulatory signs or signals, such as a sign saying "NO TURN ON RED" (no turn allowed when a red light is on). In the absence of lane markings indicating otherwise, left turns should be made from the leftmost lane and right turns from the rightmost lane to avoid collision or blocking of traffic going straight.
Turn lanes
At intersections with large proportions of turning traffic, turn lanes (also known as turn bays) may be provided on approaches to the intersection where the street/road approaches the intersection. For example in the intersection shown in the following diagram, there are left turn lanes in the east-west street for traffic approaching the intersection in the eastbound and westbound directions.
Turn lanes may be provided to allow vehicles to turn across oncoming traffic (i.e., a left turn in right-side driving countries, or a right turn in left-side driving countries), or to turn off the 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 turns.
Turn lanes may be provided to increase the capacity of an intersection, or to 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 will be 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. The word "ONLY" in those lanes means that vehicle drivers may only use them to make a turn in the direction of the arrow. In other cases, multi-headed arrows indicate that vehicle drivers may travel in any one of directions shown.
Traffic signals facing vehicles in turn lanes often have arrow-shaped indications. 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 redRight turn on red, or simply right on red, is a principle of law permitting vehicles at a traffic light showing a red signal to turn right when the way is clear, in a country with right-hand traffic...
., while in others, it does not.
Disadvantages to turn lanes include increased pavement area, with associated increases in construction and maintenance costs, as well as increased amounts of
stormwaterStormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...
runoff. They also increase the distance that pedestrians crossing the street are exposed to vehicle traffic.
Fork
A fork (literally "fork in the road") is a type of intersection. When a road splits, the main road steers to the left or right, depending of what side you drive on, and the smaller road heads straight. It is common for 2 lane roads. Heading toward the main road, the traveller must turn left or right. An example of this is the Brevard and Florida Avenue's intersection in
Rockledge, FloridaRockledge is the oldest city in Brevard County, Florida, United States. The population was 20,170 at the 2000 census. As of 2008, the estimated population according to the U.S. Census Bureau is 24,747. It is part of the Palm Bay–Melbourne–Titusville Metropolitan Statistical...
, If a road has a
curbA curb, or kerb , is the edge where a raised pavement/sidewalk/footpath, road median, or road shoulder meets an unraised street or other roadway.-Function:...
that sticks out, it is not classified as a fork.
Other markings
In some places, wider white stop lines (see preceding diagram) indicate where vehicles should stop at an intersection when there is a stop sign or a red light in a traffic signal facing them. Some intersections have pedestrian crosswalks designated on the street pavement. Some possible markings for crosswalks are shown as examples. Note that the stop line is positioned to not allow stopped vehicles to block the crosswalk.
Ghost Island priority junctions are sometimes used in the United Kingdom to provide safer turning areas, which separate turning traffic from through traffic in a similar way to turn lanes (see above).
External links