Innovative Intersections and Interchanges

 

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Innovative Intersection: Mini Roundabout
Park and Locust Streets in Vienna, Va.

Mini roundabouts are not the same as larger roundabouts. They are smaller with a paved central island that larger vehicles like trucks and buses can drive over.

What Is A Mini Roundabout?

  • A circular, unsignalized intersection where all traffic moves in a counter clockwise direction around a central island
  • Traffic entering the mini roundabout slows down and yields to traffic already inside
  • The defining feature is a fully traversable central island and splitter islands that larger vehicles can drive over
  • Flush central islands may be appropriate for those frequently used by buses
  • Uses the same operating principles of modern roundabouts

When Should It Be Considered?

  • With heavy left-turn traffic or with similar traffic volumes on each leg
  • With low truck and bus volumes
  • With crashes involving through and left-turn vehicles
  • With a posted speed of 35 miles per hour or less
  • Where vehicles from adjacent intersections will not queue into the roundabout

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: Yield-controlled design means fewer stops, less delay and shorter queues for overall improved efficiency
  • Safer speeds: Promotes lower vehicle speeds, giving drivers more time to react
  • Long-term, cost-effective savings: No traffic signal equipment means lower long-term costs for operations and maintenance

How to Navigate

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

Mini 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 four-leg intersection to a mini roundabout.

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 four-leg intersection, a mini roundabout has no crossing conflict points, 4 fewer merging conflict points, and 4 fewer diverging conflict points.

Conventional Intersection: Conflict Points

Conventional Intersection conflict diagram.

Legend

Diagram Legend. Filled circle is diverging, half-filled is merging, empty is crossing.
Conflict Type Count
Crossing 16
Merging 8
Diverging 8
Total:

32 Conflicts

Mini Roundabout: Conflict Points

Mini Roundabout conflict diagram.

Legend

Diagram Legend. Filled circle is diverging, half-filled is merging, empty is crossing.
Conflict Type Count
Crossing 0
Merging 4
Diverging 4
Total:

8 Conflicts

Resources

Virginia Department of Transportation

Federal Highway Administration

Page last modified: Nov. 7, 2019