Roundabout Resources - Roundabout vs. Traffic Circle

Roundabout vs. Traffic Circle

What is the Difference?

Roundabouts are not the same as traffic circles or rotaries. Traffic circles or rotaries have high-speed entries, allow lane changes within the circle, are low capacity, and have many high-speed crashes. Sometimes motorists in the circle must yield to those entering. They are large and scary to drive – a “free for all.”

Roundabouts are the opposite. They require motorists to yield on entry, don't allow lane changes, speeds are low, capacity is high, and crashes are few and minor.

The photo below shows a roundabout being constructed within the central island of a large rotary in New York State. The roundabout is much smaller, and will be safer and have higher-capacity.

The specific design features that distinguish roundabouts from traffic circles and rotaries are yield at entry, deflection, and (often) flare.

	Modern Roundabout	Nonconforming Traffic Circle
Yield at Entry	Entering traffic yields to circulating traffic. Circulating traffic doesn't stop Works well with heavy traffic. No weaving distance necessary. Roundabouts are compact.	Entering traffic merges or weaves into circulating traffic. Circulating traffic comes to a dead stop when the circle fills with entering traffic. Breaks down with heavy traffic. Long weaving distances for merging entries cause circles to be large.
Deflection	Entering traffic aims at the center of the central island and is deflected slowly around it. Slows traffic on fast roads, reducing accidents. Deflection promotes the yielding process.	Entering traffic aims to the right of the central island and proceeds straight ahead at speed. Causes serious accidents if used on fast roads. Fast entries defeat the yielding process
Flare	Upstream roadway often flares at entry, adding lanes. Provides high capacity in a compact space. Permits two-lane roads between roundabouts, saving pavement, land, and bridge area.	Lanes are not added at entry. Provides low capacity even if circle is large. For high capacity, often requires multilane roads between circles, wasting pavement, land, and bridge area.

Traffic calming circles constructed for traffic calming purposes, tend to be small and of low capacity. Large vehicles are often not accommodated, or must turn left in advance of the circle in opposition to other traffic. Many do not have splitter islands, which direct motorists and provide refuge areas for pedestrians.

For more information, the Insurance Institute for Highway Safety has a good Q&A on Roundabouts.