Non-circular Roundabouts Have Their Place

Most drivers think about roundabouts as perfect circles: You pull up to the roundabout, yield to the cars coming from your left, enter the roundabout, and drive counter-clockwise until exiting onto your desired road.

At some intersections, however, a roundabout needs to be designed as more of an oval. The design of these non-circular – or elliptical – roundabouts can be dictated by numerous factors, the most important being the location of the intersecting legs of the roundabout.

Working the Angles

Typically circular roundabouts work well when two roads intersect at right angles. You may not notice when you are driving in a non-circular roundabout, but that slightly oval shape is a critical component of the design when roads intersect at odd, or skewed, angles.

Each roundabout requires distinctive design choices, depending on the unique design constraints, traffic volumes, roadway speeds, existing topography, roadway alignments, and other elements. For a comprehensive look at roundabout design, see our blog titled, “Good Roundabout Design Balances Safety and Performance.”

Digging into the Designer’s Toolbox

Roundabouts come in all shapes and sizes: single-lane, multi-lane, circular, oval, and even mini roundabouts. Designers evaluate and investigate different sizes, shapes, locations, and approach alignments, validating each option using design checks.

Minor adjustments in geometry can result in significant changes in safety and/or operational performance. Using a non-circular design is just one tool available to roundabout designers.