Interchange (road)
In the field of road transport, an interchange is a road junction that typically uses grade separation, and one or more ramps, to permit traffic on at least one highway to pass through the junction without directly crossing any other traffic stream. It differs from a standard intersection, at which roads cross at grade. Interchanges are almost always used when at least one of the roads is a controlled-access highway (freeway or motorway) or a limited-access divided highway (expressway), though they may occasionally be used at junctions between two surface streets.
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 US) 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).
