Editing Intersection (road) (section)

== 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''')<ref>{{cite web | url = https://mutcd.fhwa.dot.gov/pdfs/2009/part1.pdf | title = Manual on Uniform Traffic Control Devices (MUTCD), Part 1 | publisher = [[United States Department of Transportation|U.S. DOT]], [[Federal Highway Administration]] | date = December 11, 2009 | access-date = November 28, 2011}}</ref> may be provided. For example, in the intersection shown in the diagram,{{clarify|reason=Not obvious which diagram this refers to - there isn't one nearby|date=August 2020}} 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.<ref>{{Cite web |title=Traffic Signals Brochure - How is it Determined if a Traffic Signal is Needed? |url=https://www.roads.maryland.gov/Index.aspx?PageId=277 |publisher=Maryland State Highway Administration}}</ref>

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.<ref>D.W. Harwood, et al., ''Safety Effectiveness of Intersection Left- and Right-Turn Lanes'', Federal Highway Administration Office of Safety Research and Development, 2002, [http://www.tfhrc.gov/safety/pubs/02089/02089techbrief.htm] {{Webarchive|url=https://web.archive.org/web/20100326161435/http://www.tfhrc.gov/safety/pubs/02089/02089techbrief.htm|date=2010-03-26}}</ref>

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 ===
[[File:Right turn on red Belgrade, Serbia.JPG|thumb|"Right turn on red" traffic light in [[Belgrade]], [[Serbia]]. Right turn only after pedestrians and traffic pass from left.]]
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 [[right turn on red|turn on red]].<ref name="NYS DMV Driver's Manual&nbsp;— Chapter 4">[http://dmv.ny.gov/dmanual/chapter04-manual.htm#tra-sig New York State Driver's Manual] {{Webarchive|url=https://web.archive.org/web/20131030085729/http://dmv.ny.gov/dmanual/chapter04-manual.htm#tra-sig |date=2013-10-30 }}, Chapter 4.</ref> 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.<ref>[[Vienna Convention on Road Signs and Signals]]</ref>

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.<ref>{{cite web|last=Badger|first=Emily|title=Could These Crazy Intersections Make Us Safer?|url=http://www.theatlanticcities.com/commute/2013/01/could-these-crazy-intersections-make-us-safer/4467/|work=The Atlantic Cities|publisher=[[Atlantic Media Company]]|access-date=29 January 2013|archive-date=26 January 2013|archive-url=https://web.archive.org/web/20130126093734/http://www.theatlanticcities.com/commute/2013/01/could-these-crazy-intersections-make-us-safer/4467/|url-status=dead}}</ref> These include the [[Michigan left]]/[[Superstreet]] (RCUT/MUT) and [[continuous flow intersection]] (CFI/DLT), to improve traffic flow, and also [[interchange (road)|interchange types]] like [[Diverging diamond interchange]] (DDI/DCD) design as part of the [[Federal Highway Administration]]'s Every Day Counts initiative which started in 2012.<ref>https://rosap.ntl.bts.gov/view/dot/29474/dot_29474_DS1.pdf?download-document-submit=Download {{Bare URL PDF|date=March 2022}}</ref>

[[Image:Street intersection diagram.svg|frame|center|Diagram of an example intersection of two-way streets as seen from above (traffic flows on the right side of the road). The east-west street has left turn lanes from both directions, but the north-south street does not have left turn lanes at this intersection. The east-west street [[traffic light]]s also have green left turn arrows to show when unhindered left turns can be made. Some possible markings for crosswalks are shown as examples.]]