DOTD Roundabouts

What is a roundabout?

  • Roundabouts are one-way, circular intersections designed to improve safety and efficiency for motorists, bicyclists and pedestrians.
  • In a roundabout, traffic flows through a center island counterclockwise.
  • A roundabout redirects some of the conflicting traffic, such as left turns, which cause crashes at traditional intersections. This is because drivers enter and exit the roundabout through a series of right-hand turns.

What are the advantages of roundabouts?  

  • A well-designed roundabout can improve safety, operations and aesthetics of an intersection.
  • Greater safety is achieved primarily by slower speeds and the elimination of more severe crashes and operation is improved by smooth-flowing traffic with less stop-and-go than a signalized intersection. Aesthetics are enhanced by the opportunity for more landscaping and less pavement.

What do statistics from the Federal Highway Administration (FHWA) say about roundabouts?

  • Roundabouts save lives by Reducing fatalities by up to 90%
  • Reducing injury crashes up to 76%
  • Reducing pedestrian crashes up to 30% to 40%
  • Creating up to 75% fewer conflict points than a four-way intersection. Conflict points are any point where the paths of two through or turning vehicles diverge, merge or cross
  • Roundabouts save money by:
  • Reducing road electricity and maintenance costs by an average of $5,000 per year
  • Eliminating the costs to install and repair signal equipment
  • Providing a 25-year service life when compared to the ten-year service life of signal equipment
  • Roundabouts provide environmental benefits by:
  • Reducing vehicle delay and the number and duration of stops compared with signalized intersections thus decreasing fuel consumption and carbon emissions. Fewer stops and hard accelerations mean less time idling.

How are modern roundabouts different than traffic circles and rotaries?

  • Modern roundabouts are significantly different than older style traffic circles and rotaries in how they operate and are designed:
  • Rotaries and traffic circles may have two-directional flow and are typically much larger than the modern roundabout.
  • The compactness of a modern roundabout helps keep speeds low and makes it easier for drivers to stay oriented and judge the speed of the vehicles before entering the roundabout.
  • Modern roundabouts require entering traffic to yield not merge at all entries. Whereas traffic circles and rotaries may require circulating traffic to yield to entering traffic.

What are the general principles of using a roundabout?

  • Think of roundabouts as a series of “T” intersections, where entering vehicles yield to one-way traffic coming from the left. A driver approaching a roundabout must slow down, stop or yield to traffic already in the roundabout, and yield to pedestrians in the crosswalk.
  • Then, it’s a simple matter of making a right-hand turn onto a one-way street.
  • Once in the roundabout, the driver proceeds around the central island, then takes the necessary right-hand turn to exit.

Can roundabouts accommodate larger vehicles?

  • Yes. Roundabouts are designed to accommodate vehicles with a large turning radius such as buses, fire trucks and eighteen wheelers. Roundabouts provide an area between the circulatory roadway and the central island, know as truck apron, over which the rear wheels of these vehicles can safely track.
More Roundabout information