Access Management Considerations for High Capacity Multi-Lane Roundabout Design and Implementation

• Authored by:  Mark Johnson
• Co-authored by:  Hillary Isebrands

Johnson, M. and H. Isebrands. “Access Management Considerations for High Capacity Multi-Lane Roundabout Design and Implementation,” Proceedings of the 8^th National Access Management Conference, Baltimore, MD (2008)

      This paper addresses the compatibility of roundabouts with access management principles and their operational differences with signalized intersections. The authors note that roundabouts offer greater “flexibility in balancing the competing objectives of roadway safety, capacity, and access needs of existing and or proposed land uses.” This paper examines the different opportunities that roundabouts can provide and the corresponding effects on how transportation infrastructure is planned and designed. Examples include business access into and near roundabouts, roundabouts in series, and other access management issues compatible with roundabouts in redevelopment, new development and urban constrained environments.  Noted benefits of roundabouts include:

• Roundabouts can be expanded to provide multilane entry at the intersection where greater capacity is needed  without the need for further road widening, making a narrower roadway cross section possible.
• Excess roadway width formerly needed for exclusive through and turn lanes can then be used for medians on the approaches, which become a natural extension of roundabout splitter islands and facilitate access control as well as pedestrian crossings along the roadway link and/or near the intersections.
• Roundabouts make U-turns possible and effortless along corridors and include ¾ accesses at certain locations, while minimizing right-of-way impacts.
• Business accesses may be located closer to intersections due to differences in operations over signalized intersections which cause “queuing during the red phase and ‘at-speed’ conditions and delay.” Existing access problems at mid-block will be similar with the roundabout or signalized alternative.
• Access problems associated with private entrances near interchange ramp terminals can sometimes be mitigated with roundabout designs.

      Roundabouts can offer creative solutions for existing roadway networks, as well as redevelopment areas and new developments. For example, roundabouts can allow for more flexible intersection spacing and increased access opportunities at or near intersections and interchanges. The paper includes a handful of case examples with photos to illustrate how various agencies have successfully implemented roundabouts in series and within close proximity to signals and stop controlled intersections in various environments, including commercial corridors, new and redeveloping areas and interchanges.