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.