Innovative Intersections and Interchanges
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What Is A Double Roundabout?
- A design where all freeway ramps begin or end at one of two roundabouts
- The roundabouts are circular, unsignalized interchanges where traffic moves in a counterclockwise direction around a central island
When Should It Be Considered?
- With heavy left-turn volumes onto the freeway ramps
- Where there is limited room between the ramp intersections for vehicles to wait at traffic signals
- At heavily used off-ramp interchanges where vehicles tend to back up on the freeway
- Improved safety: Reduces the number of points where vehicles can cross paths and eliminates the potential for right-angle and head-on crashes
- Increased efficiency: Decreases the delay for ramp traffic and eliminates signal coordination between the two ramp terminals
- Continuous flow: Yield-controlled design minimizes backups on the freeway, reducing the potential for high-speed, rear-end crashes
- Cost effective: Allows for a narrower bridge as it eliminates at least two turning lanes
How to Navigate
The number of conflict points (locations where vehicle travel paths intersect) is one metric that can be used to evaluate the safety of an innovative intersection or interchange.
There are three categories: crossing, merging or diverging.
In general, merging and diverging conflict points — where vehicles are moving in the same direction — are associated with less severe crash types than crossing conflict points where vehicles are moving in opposite directions.
The diagrams below compare possible vehicle travel movements and associated conflict points at a conventional diamond interchange to a double roundabout interchange.
These diagrams represent a general case, with one travel lane in each direction, and do not take into account pedestrian or bicycle movements at an intersection or interchange.
When compared to a conventional diamond interchange, a double roundabout interchange has six fewer crossing conflict points.
Conventional Diamond Interchange: Conflict Points
Double Roundabout: Conflict Points