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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). * A ''highway ramp'' (as in ''exit ramp / off-ramp'' and ''entrance ramp / on-ramp'') (North American usage) or ''slip road'' is a short section of road which allows vehicles to enter or exit a controlled-access highway (freeway or 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 two motorways cross, and a three-way interchange, the ''Autobahndreieck'' (AD) where two motorways merge. Some on-ramps have a ramp meter, which is a dedicated ramp-only traffic light that throttles the flow of entering vehicles. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Interchange (road)」の詳細全文を読む スポンサード リンク
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