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Location where two or more roads meet

A junction is where two or more roads meet.

Roads began as a means of linking locations of interest: towns, forts and geographic features such as river fords. Where roads met outside of an existing settlement, these junctions often led to a new settlement. Scotch Corner is an example of such a location. In the United Kingdom and other countries, the practice of giving names to junctions emerged, to help travellers find their way. Junctions took the name of a prominent nearby business or a point of interest. As of the road networks increased in density and traffic flows followed suit, managing the flow of traffic across the junction became of increasing importance, to minimize delays and improve safety. The first innovation was to add traffic control devices, such as stop signs and traffic lights that regulated traffic flow. Next came lane controls that limited what each lane of traffic was allowed to do while crossing. Turns across oncoming traffic might be prohibited, or allowed only when oncoming and crossing traffic was stopped. This was followed by specialized junction designs that incorporated information about traffic volumes, speeds, driver intent and many other factors.

The most basic distinction among junction types is whether or not the roads cross at the same or different elevations. More expensive, grade separated interchanges generally offer higher throughput at higher cost. Single grade intersections are lower cost and lower throughput. Each main type comes in many variants.

At interchanges, roads pass above or below each other, using grade separation and slip roads. The terms motorway junction and highway interchange typically refer to this layout. They can be further subdivided into those with and without signal controls. Signalized (traffic light controlled) interchanges include such "diamond" designs as the diverging diamond, Michigan urban diamond, three level diamond, and tight diamond. Others include center turn overpass, contraflow left, single loop, and single point urban overpass. dumbbell (grade separated bowtie), echelon, free flow interchange, partial cloverleaf, raindrop, single and double roundabouts (grade separated roundabout), single point urban, stack, and windmill. continuous Green T, double wide, hook turn, jughandle, median u turn, Michigan left, paired, quadrant, seagulls, slip lane, split, staggered, superstreet, Texas T, Texas U turn and turnarounds. Non signalized designs include unsignalized variations on continuous flow 3 and 4 leg, median u turn and superstreet, along with Maryland T/J, roundabout and traffic circle. During the 2006–2015 decade, this means around 20% of road fatalities occur at junctions. Cyclists ideally have a protected bike lane on the approach to the intersection, separated by a concrete median with splay kerbs if possible, and have a protected bike lane width of at least 2 metres if possible (one way). In the Netherlands, most one way cycle paths are at least 2.5 metres wide. Bicycle traffic can be accommodated with the low grade bike lanes in the roadway or higher grade and much safer protected bicycle paths that are physically separated from the roadway. In Manchester, UK, traffic engineers have designed a protected junction known as the Cycle Optimised Signal (CYCLOPS) Junction. This design places a circulatory cycle track around the edge of the junction, with pedestrian crossing on the inside. This design allows for an all red pedestrian / cyclist phase with reduced conflicts. Traffic signals are timed to allow cyclists to make a right turn (across oncoming traffic) in one turn). It also allows for diagonal crossings (pedestrian scramble) and reduces crossing distances for pedestrians.

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.