Innovative Intersections and Interchanges

 

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Double Roundabout icon
Double Roundabout
Route 9 (Charles Town Pike) at Route 7 (Harry Byrd Highway), Loudoun County, Va.

A double roundabout is also known as:

  • Raindrop interchange

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

Benefits

  • 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

Below shows how to navigate a double roundabout interchange.  Click the image to view a larger version or watch the video.

Double Roundabout navigation diagram

Conflict Points

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

Conventional Intersection conflict diagram.

Legend

Diagram Legend. Filled circle is diverging, half-filled is merging, empty is crossing.
Conflict Type Count
Crossing 6
Merging 8
Diverging 8
Total:

22 Conflicts

Double Roundabout: Conflict Points

Double Roundabout conflict diagram.

Legend

Diagram Legend. Filled circle is diverging, half-filled is merging, empty is crossing.
Conflict Type Count
Crossing 0
Merging 8
Diverging 8
Total:

16 Conflicts

Resources

Virginia Department of Transportation

Page last modified: Nov. 7, 2019