Roundabout interchange
From Wikipedia, the free encyclopedia
A roundabout interchange is an interchange between a freeway and a minor road. It can be formed either by adding an overpass to a roundabout to provide grade separation (with ramps connecting the freeway to the roundabout), or by building the roundabout above the freeway, straddling it on a pair of bridges.
Roundabout interchanges are extremely common in the United Kingdom, with hundreds on the motorway network alone. However, recent cost-cutting has meant that Raindrop interchanges are increasingly used instead. These are essentially diamond 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 in North America, but have been built more frequently since 1995, to improve safety, and to reduce traffic delays and bridge widening costs.
- Roundabout (Rotary) interchanges in Braintree, MA, USA and Gardner, MA, USA
[edit] 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.
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