roundabouts

Roundabouts are circular intersections in which traffic travels around a central island. Entry to the roundabout is regulated by yield signs or lines, and vehicles already circulating in the circle have the right of way. Compared with traditional stop-controlled or signalized intersections, roundabouts aim to improve traffic flow and reduce the likelihood of severe crashes.

Key design features include a raised central island, splitter islands at each approach to slow vehicles and direct pedestrians, and a geometry that deflects speeds. Circulating traffic generally follows the local driving side: clockwise with left-hand traffic, and counterclockwise with right-hand traffic. Pedestrians cross at marked crosswalks; cyclists may share the lane or use separate facilities depending on the design.

Modern roundabouts originated in the United Kingdom in the 1960s as safer alternatives to traffic circles and traffic signals. Their use has since spread to many regions, with various configurations to accommodate different volumes and vehicle types.

Roundabouts often reduce injury crashes by decreasing vehicle conflicts and lowering speeds. They can improve travel times and reduce idling, leading to lower fuel use and emissions in suitable corridors. However, they require more space than some intersections, can be challenging for pedestrians and cyclists, and may be less efficient at very high volumes. Multi-lane roundabouts can also be more complex to navigate.

Common variants include mini-roundabouts (small central islands with circular curb), single-lane roundabouts with one circulating lane, multi-lane roundabouts with several lanes, and turbo roundabouts that attempt to balance high capacity with safety. In planning, roundabouts are typically chosen when reducing speeds, improving safety, and handling modest to moderate traffic volumes is a priority.

Roundabouts are now widely used worldwide, with guidelines from traffic authorities governing design and operation to local conditions.