Roundabouts Guide

National Cooperative Highway Research Report (NCHRP) 672 Roundabouts: An Informational Guide, Second Edition (2010) is the update to the Federal Highway Administration (FHWA) Roundabouts: An Informational Guide (2000). Although published as an NCHRP report, this document has been accepted by FHWA as the official update to, and supersedes, the 2000 Guide.

The pedestrian and bicycle guidance has been updated and expanded to reflect best practices. Highlights include these guidelines:

• Sidewalks should be set back from the edge of the circulatory roadway (assists with wayfinding)
• Recommended sidewalk width is 6 feet (10 feet if shared with bicyclists)
• A typical and minimum crosswalk setback is 20 feet from the yield line
• Raised crosswalks can encourage slow vehicle speeds where pedestrians cross
• Bicycle lanes and shoulders should be terminated in advance of roundabouts
• Full-width bicycle lanes should normally end at least 100 feet before the edge of the circulatory roadway
• Bicycle ramps should be placed entirely within the planting strip between the sidewalk and the roadway at a 35 to 45 degree angle to the roadway and the sidewalk to enable cyclists to use the ramp even if pulling a trailer, but to discourage them from entering the sidewalk at high speeds.

The safety benefits for pedestrians at roundabouts remain the same and can be ascribed to these favorable attributes:

• Slow speeds (15-25 mph) for all vehicles at the intersection
• Fewer pedestrian-vehicle conflict points
• Shorter crossing distances for pedestrians
• Pedestrians cross only one direction of conflicting traffic at a time, finding refuge in the splitter island.

Multi-lane roundabouts have not achieved the same level of safety as single-lane roundabouts because of the increased number of conflict points including potential multiple-threat conflicts. Despite these challenges, the overall safety performance of multi-lane roundabouts is often better than comparable signalized intersections, particularly in terms of fatal and injury crashes.

Pedestrians with visual impairments face a significantly more complex auditory environment that may reduce the accessibility of the intersection without additional treatments. NCHRP 674 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities (2011) identifies two potential crossing treatment solutions, raised crosswalks and the Pedestrian Hybrid Beacon, that make roundabouts accessible to and usable by people with disabilities. Additional research in this area is being pursued and may include assessing the Rectangular Rapid Flash Beacons (RRFB) as another potential solution.

For more information contact Hillary Isebrands (hillary.isebrands@dot.gov) or Jeff Shaw (jeffrey.shaw@dot.gov).

Other information of interest:

TRB 3^rd International Conference on Roundabouts is in Carmel, Indiana, May 17-20, 2011. See http://www.trb.org/ for more information.

FHWA Roundabout Peer to Peer (P2P) Program information can be found at http://safety.fhwa.dot.gov/intersection/roundabouts/p2p/

by Hillary Isebrands, Highway Safety Specialist, FHWA Resource Center