Modern roundabouts are circular intersections that use a rotating flow of traffic to encourage safer and slower movements of traffic through intersections. All vehicles entering a roundabout are supposed to yield to vehicles already in the circulating roadway, resulting in a constant flow of traffic into and out of the circle.  The combination of lower speeds and shallower entry angles have the potential to lower kinetic energy in the event of a crash, reducing the potential for serious injuries.

Driving Roundabouts

Here are a few things to remember when driving through roundabouts:

• Slow down and watch for pedestrians and bicycles
• Yield to vehicles, pedestrians, and bicycles already in the roundabout
• Once in the roundabout, you have the right of way
• Use your turn signal when exiting the roundabout and watch for pedestrians
• Always be cautious and look for unexpected vehicles, pedestrians or bicycles

Roundabouts are often a great strategy for improving intersection safety.  Conversion of conventional intersections to roundabouts has been shown to reduce injury and fatal crashes by about 75 percent both in the United States and Europe.  The Federal Highway Administration highlights that roundabouts can have 50 percent fewer pedestrian-vehicle conflict points and shorter crossing distances than conventional intersections. (Ref. ITE)

The design of a roundabout includes median islands and a center island that are designed to control and reduce speeds so drivers can navigate the roundabout more safely, with enough visual distance to react to vehicles, bicycles, and pedestrians.

Roundabouts use crosswalks that are set back from the circulating roadway by a distance equal to about one car length.  This allows queued vehicles to leave a gap for pedestrians to use the crosswalk, and drivers don’t have to negotiate both pedestrians and circulating traffic at the same time. The median island allows pedestrians to base their crossing on one lane of traffic at a time.

Most roundabouts in Cary are single-lane roundabouts, meaning they have one lane inside the circle.  While not as common, multi-lane roundabouts are also increasingly being installed as there are many safety and operational advantages to both, either when converting an existing intersection or when constructing a new intersection.

Vision Zero Framework
Roundabouts seek to accommodate human injury tolerance by reducing speed and altering the conflict angle, reducing impact forces.

Why Not More Roundabouts?

Roundabouts are limited in their application since they cannot handle traffic at all types of intersections. Intersections that handle very large volumes of traffic often are safer and more efficient with a traffic signal to process the heavy throughput.  Also, intersections that have a large disparity, with high volumes of traffic on the main road and light volumes on the side road do not benefit from the construction of a roundabout.

Other Helpful Links

• NC Department of Transportation - Roundabouts
• Federal Highway Administration - Roundabouts
• Washington State DOT "Driving Roundabouts" website
• NCDOT Research Presentation – Safety Evaluation of Roundabouts in NC
• National Cooperative Highway Research Program Report 572 – Roundabouts in the United States

Still have questions?  

Reach out to Cary’s Traffic Engineering Division through Cary311