Innovative Intersections and Interchanges

 

← Innovative intersections main page

Roundabout icon
Innovative Intersection: Roundabout
Givens Lane at Progress Street, Blacksburg, Va.

Roundabouts are not the same as neighborhood traffic circles. Roundabouts are larger and designed for faster speeds.

What Is Roundabout?

  • A circular, unsignalized intersection where all traffic moves counterclockwise around a central island
  • Traffic entering the roundabout slows down and yields to traffic already inside the roundabout
  • Roundabouts can be designed with one or more circulating lanes
  • Design options allow for right turns to be channelized to bypass the circulating lanes

When Should It Be Considered?

  • At intersections:
    • With heavy left-turn traffic or with similar traffic volumes on each leg
    • With crashes involving conflicting through and left-turn vehicles
    • With limited room for storing vehicles
    • Where there are limited nearby driveways

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, fewer delays and shorter queues
  • Safer speeds: Promotes lower vehicle speeds, giving drivers more time to react
  • Long-term cost effectiveness: No traffic signals means lower long-term costs for operations and maintenance
  • Aesthetics: Allows for landscaping and beautification

How to Navigate

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

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 conventional four-leg intersections to a 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 roundabout has 16 fewer crossing, 4 fewer merging, and 4 fewer diverging conflict points.

Conventional Intersection: Conflict Points

Conflict Point Diagram

Roundabout: Conflict Points

Conflict Point Diagram

Design Considerations and Screening

For detailed roundabout design criteria, see the Virginia Department of Transportation (VDOT) Road Design Manual, Appendix F, Section 2 (Intersection design, spacing standards)

Resources

Federal Highway Administration

Page last modified: Sept. 13, 2018