Type of interchange between highways and minor roads
Roundabout interchange inBelgrade,SerbiaAntalyaspor Interchange ofAntalya. The underpass serve the transit traffic of city center toKonyaaltı, while the upper part Dumlupınar Bulvarı and roundabout are maintained byGeneral Directorate of Highways asD-400 Highway.The western entryway intoLinköping,Sweden (a branch off the backboneE4 highway) passes on a bridge above this roundabout, which connects a national road and a local road into a residential area with ramps leading up to the free-flowing road (note the green signage denoting that in these directions you are entering amotorway).
Aroundabout interchange is a type ofinterchange between a controlled access highway, such as amotorway orfreeway, and a minor road. The slip roads to and from the motorway carriageways converge at a singleroundabout, which isgrade-separated from the motorway lanes with bridges.
A roundabout interchange is similar to arotary interchange, which uses a rotary rather than a roundabout. Roundabouts may also be used in conjunction with other interchange types such as a standard or foldeddiamond interchange, but such use should not be confused with a roundabout interchange.
Roundabout interchanges are extremely common in theUnited Kingdom andIreland with hundreds on themotorway network alone. However, recentcost cutting has meant thatdumbbell interchanges are increasingly used instead. These are essentiallydiamond interchanges with roundabouts instead of signals or stop signs where the slip roads meet the minor road. They are cheaper than roundabout interchanges as only one bridge is required instead of two.
Roundabout interchanges are much less common inNorth America but have been built more frequently since 1995, to improve safety, and to reduce traffic delays and bridge widening costs. However, many of the older and more dangerousrotary-style overpass interchanges have been signalized to improve throughput and safety, such as the former Drum Hill Rotary (now Drum Hill Square) inChelmsford, Massachusetts, inNew England, where such interchanges are unusually common.
Asplit diamond, in which the minor road is separated into four intersections, rather than two, also acts like a roundabout interchange, but it is more square in shape and, typically, has traffic light control.
Washington Circle, inFoggy Bottom,Washington, D.C., is another example of a roundabout interchange similar to the one in Dupont Circle. Here, K Street traverses beneath the intersection.
A roundabout is used as an interchange betweenQuebec Autoroute 20 andQuebec Autoroute 520 inMontreal,Quebec. The roundabout is known as the Dorval Circle. Ramps to side streets are added as well. The interchange is currently[when?] being replaced.
TheRottepolderplein in theNetherlands is a three-level roundabout
The three-level stacked roundabout is a variation on the roundabout interchange in which both roads are grade-separated. It is similar to thethree-level diamond interchange except that the small square of that latter interchange is enlarged to a true roundabout. If the roundabout is sufficiently large, the interchange may require only two levels.[1]
