A seagull intersection [1] or continuous green T-intersection [2] (also known as a turbo-T [3] (in Florida) or High-T intersection (in Nevada and Utah) [4] [5] ) is a type of three-way road intersection, usually used on high traffic volume roads and dual carriageways. This form of intersection is popular in Australia and New Zealand, and sometimes used in the United States and other countries.
Seagull intersections get their name from the pattern that the two cross-traffic turn lanes make when looking down at them from the air.
In a seagull intersection, one or more lanes of traffic on the arterial road, on the carriageway opposite the intersecting side road, are free flowing, that is, one direction of traffic on the arterial is allowed to travel straight through without stopping. The free-flowing lane(s) are called "continuous green through lane(s)" (CGTL). [6] For the free-flowing through lanes, access into and out of the side road is provided via turn lanes separated from the through lanes in a configuration similar to exit and entrance ramps at an interchange; however, the turn lanes are at the same grade as both carriageways of the arterial and are located on the same side as the oncoming traffic.
Those wishing to turn across traffic into the side road at the intersection drive into the turn lane, which forms one "wing" of the seagull. Here, they meet the opposite carriageway and the side road. Traffic wishing to turn across traffic out of the side road, cross the intersecting carriageway, drive up the other "wing" of the seagull, and merge onto the other carriageway. [7]
For the arterial carriageway adjacent to the side road, access into and out of the side road is ordinarily handled like a conventional T intersection. However, some seagull intersections may have a second, smaller "seagull" formed by two left turning lanes into and out of the side road.
Different methods are used to control traffic where two right-turning movements and the through movement meet. Most intersections use traffic lights, while others use give way (yield) and stop signs, and sometimes roundabouts.
This design type has been proven to provide sustainable benefits when compared the traditional T-intersection design. By reducing delay through the intersection, automobiles use less fuel on average passing through the intersection, and thus emissions are reduced across the intersection. The savings per vehicle may not seem very significant, but when scaled to account for all automobiles passing through the intersection, the total emission savings are significant. Additionally, there are economic and social benefits to reducing delay time and allowing drivers to pass through the intersection quicker. [9] In the Netherlands, this type of intersection occurs by default when a T-junction has a bicycle path on the continuing road, and is not intersected by a roadway for motorized vehicles. The bicycle path may ignore red lights; it is only turning cyclists that must wait for the red light. [10]
An experiment was done[ by whom? ][ when? ] in Illinois, United States to allow going straight on red (following rules analogous to those used for turns on red) when approaching a T junction on the main road, with the intersecting road on the left. It was a failure. However, at some T junctions where the main road includes at least two lanes on the side away from the intersecting road, the farthest (rightmost, in areas where traffic drives to the right) lane is given the right of way to proceed straight through the intersection at all times, denoted by a "green arrow" signal if a traffic light is installed at the intersection. In such cases, often that lane is also specially delimited with pavement markings or other lane separation devices, to keep left-turning traffic on the intersecting road from colliding with traffic proceeding through the intersection on the main road. The seagull intersection was developed as a safer variation of this. [3]
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.
An intersection is an at-grade junction where two or more roads converge, diverge, meet or cross. Major intersections are often delineated by gores and may be classified by road segments, traffic controls and lane design.
A three-way junction is a type of road intersection with three arms. A Y junction generally has three arms of equal size. A T junction also has three arms, but one of the arms is generally a minor road connecting to a larger road.
A pedestrian crossing or crosswalk is a place designated for pedestrians to cross a road, street or avenue. The term "pedestrian crossing" is also used in some international treaties that pertain to road traffic and road signs, such as the Vienna Convention on Road Traffic and the Vienna Convention on Road Signs and Signals.
Traffic lights, traffic signals, stoplights or robots are signalling devices positioned at road intersections, pedestrian crossings, and other locations to control flows of traffic.
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.
A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road.
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.
An arterial road or arterial thoroughfare is a high-capacity urban road that sits below freeways/motorways on the road hierarchy in terms of traffic flow and speed. The primary function of an arterial road is to deliver traffic from collector roads to freeways or expressways, and between urban centres at the highest level of service possible. As such, many arteries are limited-access roads, or feature restrictions on private access. Because of their relatively high accessibility, many major roads face large amounts of land use and urban development, making them significant urban places.
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, traffic on the minor road is not permitted to proceed straight across the major road or highway. Drivers on the minor road wishing to turn left or go straight must turn right onto the major road, then, a short distance away, queue (wait) into a designated U-turn lane in the median. When traffic clears, they complete the U-turn and then either go straight or make a right turn when they intersect the other half of the minor road.
A continuous flow intersection (CFI), also called a crossover displaced left-turn, is an alternative design for an at-grade road junction. Vehicles attempting to turn across the opposing direction of traffic cross before they enter the intersection. No left turn signal in the intersection is then necessary. Instead, vehicles traveling in both directions can proceed, including through vehicles and those turning right or left, when a generic traffic signal/stop sign permits.
Wanneroo Road is a 44-kilometre (27 mi) arterial highway in the northern suburbs of Perth, Western Australia linking Joondanna and Yokine in the south with Wanneroo and Yanchep in the north. As part of State Route 60, it begins from Charles Street in the inner city and becomes Indian Ocean Drive up to Dongara.
A junction is where two or more roads meet.
In traffic engineering, there are regional and national variations in traffic light operation. This may be in the standard traffic light sequence or by the use of special signals.
Access management, also known as access control, when used in the context of traffic and traffic engineering, generally refers to the regulation of interchanges, intersections, driveways and median openings to a roadway. Its objectives are to enable access to land uses while maintaining roadway safety and mobility through controlling access location, design, spacing and operation. This is particularly important for major roadways intended to provide efficient service to through-traffic movements.
Springvale Junction is a particularly notorious road intersection in Melbourne. It is situated on the boundary of the suburbs of Mulgrave and Springvale.
A slip lane or slip road is a road at a junction that allows people to change roads without actually entering an intersection. They are primary seen at the junction of two busy roads, as an entrance to a busy highway such as a dual carriageway and are the only means to join a motorway.
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.
An offset T-intersection is an at-grade road intersection where a conventional four leg intersection is split into two three-leg T-intersections to reduce the number of conflicts and improve traffic flow. Building the offset T-intersections as continuous green T-intersections, there is a single stop on the arterial road, only. A higher volume of through traffic on the cross road, or on unsignalized intersections, a rebuild to a conventional four-leg intersection may be adequate, also when the offset is a few feet only like staggered junctions causing slower traffic for a longer time on the arterial road.