A seagull intersection or continuous green T-intersection (also known as a turbo-T (in Florida) or High-T intersection (in Nevada and Utah)) 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 right-turn lanes make when looking down 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). 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 right into the side road at the intersection, bear right 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 right out of the side road, cross the intersecting carriageway, drive up the other "wing" of the seagull, and merge onto the other carriageway.
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. 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.
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.
List of seagull intersections
- Cotter Road at Streeton Drive – Weston Creek (near Canberra)
- Geelong Road (Princes Highway) at Millers Road - Brooklyn, Victoria (Western Melbourne)
- Pacific Highway (Jersey Street North) at Peats Ferry Road and Wattle Street - Asquith, New South Wales (near Sydney)
- Ginninderra Drive at Coulter Drive - Belconnen (near Canberra)
- Ginninderra Drive at William Slim Drive - Belconnen (near Canberra)
- Ginninderra Drive at Tillyard Drive - Belconnen (near Canberra)
- Highway 1 (Princes Highway) at Island Point Road – Tomerong, New South Wales 
- Highway 1 (Princes Highway) at Kells Road – Tomerong, New South Wales
- Dandenong Road (Princes Highway) at Grange Road - Carnegie, Victoria 37°52'52.0"S 145°02'58.6"E
- Dandenong Road (Princes Highway) at Blackburn Road - Clayton, Australia 37°55'18.6"S 145°08'20.7"E
- Lonsdale Street (Princes Highway) at South Gippsland Highway - Dandenong, Victoria 38°00'02.5"S 145°13'32.7"E
- Chancellor Blvd and Wesbrook Mall
In the City of Saskatoon:
- at College Drive to Central Avenue
- at Circle Drive to Airport Drive
- at Circle Drive to Laurier Drive
- at Circle Drive to Clancy Drive
- at 22nd Street to Hart Road
In the Province of British Columbia:
- at Highway 97 to Okanagan Lake Provincial Park South
- at Highway 97 to Bridgeman Road
- at Highway 97 to Walters Road
- at Highway 97 to Lakeshore Drive S
- at Highway 97 to Pyramid Provincial Park
- at Highway 97 to Sage Mesa Drive
- at Highway 97 to W Bench Hill Road
- at Highway 97 to Warren Avenue W
- at Highway 97 to Green Avenue W
- at Highway 97 to Enterprise Way
- at Hauptstraße (L23) / Bundesstraße 51 in Olzheim
- at Hauptstraße (L204) / Bundesstraße 51 in Dahlem (Nordeifel)
- at Greven Interchange of Bundesautobahn 1 to Bundesstraße 481 and
- at Würselen Interchange of Bundesautobahn 544 to Verlautenheidener Straße (L23)
- CGTLs in Germany
- Upper Harbour Highway (State Highway 18) at Paul Matthews Drive – North Shore, Auckland
- Wairau Road at Forrest Hill Road – Takapuna, Auckland
- Waikato Expressway (SH 1) at Island Block Road, Springhill Road, and Dragway Road – Meremere
- State Highway 1 at Whitford Brown Drive – Porirua
- River Road (SH 2) at Gibbons Street – Upper Hutt
- Western Hutt Road (SH 2)/River Road (SH 2) at Fergusson Drive – Silverstream, Upper Hutt
- aleja Młodzieży Polskiej (National Road 31) at Kościuszki (National Road 29) - Słubice
- US 60 at Mountain View Road – Apache Junction, Arizona
- 24th Street at Lincoln Drive – Phoenix, Arizona
- In Tucson, Arizona:
- US 285 at US 24 – Buena Vista, Colorado
- US 160 at US 550 – Durango, Colorado
- US 50 at SH 141 – Grand Junction, Colorado
- NASA Parkway at Space Commerce Way - Brevard County, Florida east of Titusville, and just west of the Kennedy Space Center Visitor Complex
- US 92 split/join with US 17 - Lake Alfred, Florida
- US 92 at Reynolds Road - Lakeland, Florida
- Sand Lake Road at Greenbrier Parkway - Orlando, Florida
- Radio City Drive (IL 29) at Edgewater Drive (IL 98) - Pekin and North Pekin, Illinois 
- N. Sheridan Road at shopping center entrance - Peoria, Illinois
- MD 210 at MD 228 - Accokeek, Maryland, opened in 2000, is a hybrid, also having characteristics of a continuous-flow intersection.
- MN 13 near its interchange with US 169 and County Road 101 – Savage, Minnesota, is a hybrid, with a partial interchange in the opposite direction of travel.
- In Boulder City, Nevada:
- Cheyenne Avenue in Las Vegas, Nevada has four seagull intersections between Clark County Route 215 and Rampart Boulevard.
- US 52 at the Ben Williamson Memorial Bridge and the Simeon Willis Memorial Bridge – Coal Grove, Ohio, is a continuous green T/inverted SPUI hybrid.
- SR 7 at I-470 - Pultney Township, Belmont County, Ohio, is a continuous green T/inverted SPUI hybrid.
- Oregon Route 213 at its north terminus with Airport Way - Portland, Oregon
- PA 28 at the 40th Street Bridge - Millvale, Pennsylvania, is a continuous green T/inverted SPUI hybrid.
- US 129 at SR 168 – Knoxville, Tennessee, is a hybrid, with a partial interchange in the opposite direction of travel.
- US 83/US 84 east/US 277 (Winters Freeway) at Bus. I-20-R/US 84 west (South 1st Street) – Abilene, Texas. Folded diamond ramps from Winters Freeway form continuous green T intersections with South 1st Street.
- East Riverside Drive at South Lakeshore Boulevard - Austin, Texas
- Allen Parkway at Taft Street – Houston, Texas
- Bicentennial Boulevard at Lark Avenue – McAllen, Texas
- SR-201 at SR-111 – Magna, Utah
- Spout Run Parkway at Lorcom Lane - Arlington, Virginia
- US 15 at Fort Evans Road NE - Leesburg, Virginia
- John Harper, Wal Smart, Michael de Roos: Seagull Intersection Layout. Island Point Road – A Case Study Archived 2013-05-07 at the Wayback Machine 2000 – 2010
- Federal Highway Administration: Alternative Intersections/Interchanges: Informational Report (AIIR), Publication Number: FHWA-HRT-09-060, April 2010
- Jonathan Reid, P.E. (July 2004). "Unconventional arterial intersection design, management and operations strategies" (PDF) (PDF). Parsons Brinckerhoff. Retrieved September 9, 2012.
- Utah DOT: "Archived copy". Archived from the original on 2013-12-13. Retrieved 2013-08-30.CS1 maint: Archived copy as title (link)
- Nevada DOT: US93 Lakeshore v4 Handouts
- Intersection Decision Guide, Indiana Department of Transportation, Version 1.1 published 14 January 2014, retrieved 25 August 2015, P. 44
- Edward S. Jarem: Safety and Operational Characteristics of Continuous Green Through Lanes at Signalized Intersections in Florida, Lake Mary, Florida 2004
- Litsas, Stephen (July 31, 2012). "Evaluation of Continuous Green T-Intersections on Isolated Under-Saturated Four-Lane Highways" (PDF). TRB.org. Retrieved September 19, 2013.
- Cycling past red lights in the Netherlands, YouTube, published 24 October 2012
- Bruce, Michael G., P.E.; Gruner, Paul W., P.E., P.S. (December 28, 2005). "Continuous flow intersections". CENews.com. Retrieved September 9, 2013.
- "Bicentennial Boulevard Extension Project Begins". City of McAllen. January 27, 2010. Retrieved September 14, 2013.
- "Bicentennial & Lark: Continuous Green Intersection" (video). City of McAllen. February 17, 2012. Retrieved September 14, 2013.
- Burkhardt, Gail (November 12, 2012). "Extended Bicentennial Boulevard links North, South McAllen". The Monitor. Retrieved September 14, 2013.