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                Roundabouts: An Informational Guide: Second Edition
**Description:**
        The guide provides general information, planning techniques, design guidelines, and evaluation procedures for operations and safety of roundabouts. Chapter 5 presents principles of vehicle, pedestrian, and bicycle conflicts at roundabouts, observed safety performance, intersection level crash prediction, and approach level crash prediction. The safety analysis methodologies are similar to the Highway Safety Manual. Safety performance functions (SPFs) are presented for three, four, and five leg roundabouts with one or two circulation lanes. SPFs are provided for four leg roundabouts with three or four circulating lanes. SPFs are provided for total crash frequency, KAB injury crash frequency, entering-circulating, exiting-circulating, and approach crashes. Crash Modification Factors (CMFs) are provided for the approach level crash prediction methodology. CMFs include entry radius, entry width, approach half width, inscribed circle diameter, central island diameter, circulating width, and angle to next leg.
    
          **Tool Type:**
        Application Guide
    
    
    
          **Owner Source:**
        organization
    
          **Sponsor/Owner:**
        National Cooperative Highway Research Program (NCHRP)
    
        **Published:**
      2010
    
        **Availability:**
      The guide is available free of charge at the following link: Roundabouts: An Informational Guide.
    
          **Disclaimer:**
        This information is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained herein. This information does not constitute a standard, specification, or regulation. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturer's names appear in this information only because they are considered essential to the objective of this publication.
          Any opinions, findings, and conclusions or recommendations, and translations thereof, expressed in this publication are those of the author(s) and do not necessarily reflect the views of the Federal Highway Administration. U.S. DEPARTMENT OF TRANSPORTATION

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