Roundabouts

Usage: Limited

An intersection with circular, one-way (counter-clockwise) traffic around a central circle in which entering traffic yields to traffic already in the roundabout. Roundabouts can vary in size (diameter) and number of lanes and can be modified with signalized crosswalks. Roundabouts are distinguished from “old-style” traffic circles/rotaries by their rules for yielding on entry and key design features targeting low design speeds.

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Intervale Avenue and Dawson Street, Bronx
153rd Avenue and 88th Street, Queens

Benefits

  • Slows all traffic in all directions at all times, thereby decreasing the number and severity of crashes
  • Allows simultaneous movement of crossing vehicular streams, often processing vehicular traffic more efficiently than signalization
  • Eliminates possibility of vehicle head-on collisions
  • Reduces the number of potential vehicular conflict points as compared to a standard signalized intersection
  • Eliminates left turns, a primary cause of crashes
  • Enhances pedestrian safety when used at appropriate intersections
  • When used in place of a stop- or signal-controlled intersection, may reduce vehicle emissions and travel times by reducing start-and-stop driving
  • Reduces need to widen streets approaching intersection to store vehicles under signalized operation
  • Can green and beautify the streetscape with trees and/or plantings, improving environmental quality and potentially incorporating stormwater source controls
  • Inclusion of features not directly accessed by the public within the roundabout island, such as Roadway Plantings or Public Art, creates an attractive focal point for the neighborhood

Considerations

  • May require increased spatial footprint for intersection, but not approaches
  • May impact street drainage or require catch basin relocation
  • May impact underground utilities
  • May require loss of curbside parking
  • May impact circulation at existing driveways adjacent to intersection
  • May impact direct pedestrian access and circulation
  • Landscaping or stormwater source controls require a partner for ongoing maintenance, including executing a maintenance agreement
  • If outfitted to capture stormwater, careful consideration must be given to design, overflow control, and plant species
  • Attention should be given to accommodation of and navigation by people with ambulatory and vision disabilities

Application

  • Intersections with:
    • 1) no more than 90% of volume on the main facility and
    • 2) having at least three approaches, high vehicle-turning volumes or percentages, or speeding issues
  • Consider at locations with poor safety records, or where signalization has led or may lead to operational issues for pedestrians and/or cyclists

Design

  • Deflection should be created for entering vehicles to reinforce yielding behavior; at two-way legs of the intersection, use splitter islands to provide deflection as well as to allow pedestrians to cross in two segments
  • Detectable Warning Surface should be provided at all crosswalk locations, and should be red when adjoining light-colored sidewalks, such as Unpigmented Concrete, or bright white when adjoining dark-colored surfaces, such as Pigmented Concrete, Asphalt Pavers, or Bluestone
  • Limit entry and exit speeds through deflection and/or raised crosswalks
  • Roundabout geometry should accommodate the design vehicle; use an apron of visually-contrasting paving around the central island and/or adjacent to intersection corners to slow motor vehicle movements while accommodating larger vehicles such as trucks
  • To improve center island visibility, use reflective signs within the center island and reflective materials along the curb
  • Locate trees and/or plantings within roundabout center islands; include planted areas and stormwater source controls when a maintenance partner is identified where compatible with required sight distance. Review Tree Beds and Roadway Plantings in the Landscape chapter
  • Where feasible and if there is a maintenance partner, design planted areas within roundabout islands so as to capture stormwater according to current standards. Review Stormwater Management Practices in the Landscape chapter
  • If work includes tree planting, consider the location of utility infrastructure, including DEP sewers and water mains
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