Although there are 6 categories of roundabout, the design process for all is essentially the same. All categories of roundabout have the same defining physical characteristics. The six categories of roundabout are:
- Urban compact roundabouts
- Urban single-lane roundabouts
- Urban double-lane roundabouts
- Rural single-lane roundabouts
- Rural double-lane roundabouts
According to the United States’ Federal Highway Administration (FHWA) the process of designing roundabouts requires a significant amount of “iteration among geometric layout, operational analysis, and safety evaluation.” With roundabout design and using traditional methods, minor geometric adjustments can result in considerable safety, operational, and / or performance alterations.
Before components and the geometry are defined, three fundamental elements that must be resolved:
- The optimal roundabout size
- The optimal position for the roundabout
- The optimal alignment and arrangement of the approach legs
Components of the roundabout are interrelated. Compatibility between components of the geometry is crucial in order to adhere to the specifications and more importantly meet the overall performance and safety objects. As roundabout designs are performance based, each iteration requires the entire design to be evaluated as changes are made.