Interchange (road) - Terminology

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 freeway junction or highway interchange (in the U.S.) or motorway junction (in the UK) is a type of road junction, linking one motorway to another; to other roads; or sometimes to just a motorway service station. On the UK motorway network, most (but not all) junctions with other roads are numbered sequentially. In the U.S., interchanges are either numbered according to cardinal interchange number, or by mileage (typically the latter in most states).
• A highway ramp (as in exit ramp and entrance 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. This means that a ramp that makes a left turn exits from the left side of the roadway (a left exit). Left directional ramps are relatively uncommon as the left lane is usually reserved for high-speed through traffic. Ramps for a right turn are almost always right directional ramps. Where traffic drives on the left, these cases are reversed.
• 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.
• A U-turn ramp leaves the road in one driving direction, turns over or under it and rejoins in the opposite direction.

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.

The German Autobahn system splits Autobahn-to-Autobahn interchanges into two types: a four-way interchange, the Autobahnkreuz (AK), where 2 motorways cross, and a three-way interchange, the Autobahndreieck (AD) where two motorways merge.