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In the field of road transport, a road junction is a place where two or more roads either meet or cross. The main types of road junctions are intersections and interchanges. A road junction may also be called a crossroads. A junction between 3 road segments (arms) is a T junction (two arms form one road) or a Y-junction.1 Terminology
Note: The descriptions of road junctions are for countries where vehicles drive on the right side of the road. For countries where driving is on the left the layout of the junctions is the same, only left/right is reversed.
A ramp (as in off-ramp and on-ramp) or slip road is a short section of road which allows vehicles to enter or exit a freeway ( motorway).
- A directional ramp always tends toward the desired direction of travel.
- A non-directional ramp goes in a direction opposite to the desired direction of travel. Many loop ramps (as in a cloverleaf) are non-directional.
- A semi-directional ramp exits a road in a direction opposite from the desired direction of travel, but then turns toward the desired direction of travel. Many 'flyover ramps' (as in a stack) are semi-directional.
Weaving is an undesirable situation in which traffic veering right and traffic veering left must cross paths within a limited distance, to merge with traffic on the through lane. Weaving creates both safety and capacity problems. Some areas that had such junctions have gone through the expensive process of "unweaving the weave" to improve traffic flow.
2 Intersections
An intersection is a road junction at which roads meet at grade. Types of intersections include:
- Uncontrolled intersections, without signs or signals (or sometimes with a warning sign). On a 4-way intersection traffic from the right has priority; on a 3-way intersection rules may vary by country: either traffic from the right has priority again, or traffic on the continuing road. For traffic coming from the same or opposite direction, that which goes straight has priority over that which turns off.
- Yield-controlled intersections may or may not have specific "YIELD" signs (known as "GIVE WAY" signs in some countries).
- Stop-controlled intersections have one or more "STOP" signs. Two-way and four-way stops are common.
- Signal-controlled intersections depend on traffic signals, usually electric, which indicate which traffic has the right-of-way at any particular time.
- A traffic circle is a special type of intersection at which traffic streams are directed around a circle. Types of traffic circles include roundabouts, 'mini-roundabouts', 'rotaries', "STOP"-controlled circles, and signal-controlled circles. Some people consider roundabouts to be a distinct type of intersection from traffic circles (with the distinction based on certain differences in size and engineering).
- A box junction can be added to an intersection, generally prohibiting entry to the intersection unless the exit is clear.
- While not a specific type of intersection, the US state of Michigan frequently employs a special arrangement for making left turns, known as a Michigan leftA Michigan left is an automobile traffic maneuver in which a U-turn and a right turn replace a prohibited left turn. The term comes from the fact that the arrangement is quite common along Michigan roads and highways, and extremely rare anywhere else.. These are generally used in conjunction with Signal-controlled intersections, although it can also apply to Stop-controlled intersections.
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