- Roundabout interchange
A roundabout interchange is an interchange between a
freeway and a minor road. It can be formed either by adding anoverpass to aroundabout to providegrade separation (with ramps connecting the freeway to the roundabout), or by building the roundabout above the freeway, straddling it on a pair ofbridge s.Roundabout interchanges are extremely common in the
United Kingdom , with hundreds on themotorway network alone. However, recent cost-cutting has meant that Raindrop interchanges (UK: "Dumbell junction") are increasingly used instead. These are essentiallydiamond interchange s 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 in North America, but have been built more frequently since 1995, to improve safety, and to reduce traffic delays and bridge widening costs.
* Modern roundabout with flyover in Johnson City, NY. [http://maps.google.com/maps?f=q&hl=en&geocode=&q=johnson+city,+ny&ie=UTF8&ll=42.106254,-75.967262&spn=0.005683,0.009302&t=k&z=17&iwloc=addr]
* Traffic circle with grade separation in Latham, NY: [http://maps.google.com/maps?f=q&hl=en&geocode=&q=latham,+ny&ie=UTF8&ll=42.748084,-73.760705&spn=0.005625,0.009302&t=k&z=17]
* Roundabout (Rotary) interchanges in [http://maps.google.com/maps?q=Braintree,+MA&ie=UTF8&ll=42.210235,-70.996732&spn=0.0036,0.007296&t=h&z=17&om=1 Braintree, MA, USA] , [http://maps.google.com/maps?q=Gardner,+MA&ie=UTF8&ll=42.564156,-71.979353&spn=0.003429,0.003648&t=h&z=18&om=1 Gardner, MA, USA] , and [http://maps.google.com/maps?f=q&hl=en&geocode=&q=42.5853,+-72.6214&ie=UTF8&ll=42.585263,-72.621142&spn=0.005806,0.013947&t=h&z=17 Greenfield, MA, USA.]
*Shirlington Circle , a roundabout interchange on Interstate 395 on the border between Alexandria and Arlington County,Virginia Three-level stacked roundabout
The three-level stacked roundabout is a variation on the roundabout interchange in which both roads are grade-separated. It is similar to the
three-level diamond interchange except that the small square of that latter interchange is enlarged to a true roundabout.External links
* [http://www.cbrd.co.uk/reference/interchanges/roundabout.shtml CBRD: Roundabout Interchange]
* [http://www.cbrd.co.uk/reference/interchanges/3round.shtml CBRD: Three-Level Stacked Roundabout Interchange]
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