Intersection (road)

Crossroads in Kharkiv, Ukraine
The intersection between Ayala Avenue and Makati Avenue in Makati City, the Philippines

An intersection is the junction at-grade (that is to say, on the same level) of two or more roads either meeting or crossing. An intersection may be three-way (a T junction or Y junction – the latter also known as a fork if approached from the stem of the Y), four-way (often in the form of a crossroads), or have five (a 5-points) or more arms. Busy intersections are often controlled by traffic lights and/or a roundabout.

This article primarily reflects practice in 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

Road segments

One way to classify intersections is by the number of road segments (arms) that are involved.

Seven or more approaches to a single intersection, such as at Seven Dials, London, are rare.
Intersection along the Veterans Memorial Parkway, an at-grade limited-access road in London, Ontario.

Traffic controls

Another way of classifying intersections is by traffic control technology:

Lane design


At intersections, turns are usually allowed, but 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)[2] 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 and/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.[3]

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. 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,[4] 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 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 can manage turning traffic to increase safety and intersection throughput.[5] These include the Michigan left, "superstreet" and continuous flow intersection.


Intersections generally must manage pedestrian as well as vehicle traffic. Pedestrian aids include crosswalks, pedestrian-directed traffic signals ("walk light") and over/underpasses. Walk lights may be accompanied by audio signals to aid the visually impaired. Medians 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.


Intersections can be made more bicycle-friendly with various interventions such as bike boxes, protected intersections or grade separation.

See also


  1. Steyn, Hermanus. (2014). Displaced Left-turn Intersection Informational Guide. Washington, D.C.: U.S. Department of Transportation, Federal Highway Administration.
  2. "Manual on Uniform Traffic Control Devices (MUTCD), Part 1" (PDF). U.S. DOT, Federal Highway Administration. December 11, 2009. Retrieved November 28, 2011.
  3. D.W. Harwood,et al., Safety Effectiveness of Intersection Left- and Right-Turn Lanes, Federal Highway Administration Office of Safety Research and Development, 2002,
  4. New York State Driver's Manual, Chapter 4.
  5. Badger, Emily. "Could These Crazy Intersections Make Us Safer?". The Atlantic Cities. Atlantic Media Company. Retrieved 29 January 2013.
Wikimedia Commons has media related to Road junctions.
This article is issued from Wikipedia - version of the 11/10/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.