Organization of the Guide

This guide has been structured to address the needs of a variety of readers including the general public, policy-makers, transportation planners, operations and safety analysts, conceptual and detailed designers. This chapter distinguishes roundabouts from other traffic circles and defines the types of roundabouts addressed in the remainder of the guide. The remaining chapters in this guide generally increase in the level of detail provided.

Chapter 2—Policy Considerations: This chapter provides a broad overview of the performance characteristics of roundabouts. The costs associated with roundabouts versus other forms of intersections, legal issues, and public involvement techniques are discussed.

Chapter 3—Planning: This chapter discusses general guidelines for identifying appropriate intersection control options, given daily traffic volumes, and procedures for evaluating the feasibility of a roundabout at a given location. Chapters 2 and 3 provide sufficient detail to enable a transportation planner to decide under which circumstances roundabouts are likely to be appropriate, and how they compare to alternatives at a specific location.

Chapter 4—Operational Analysis: Methods are presented for analyzing the operational performance of each category of roundabout in terms of capacity, delay, and queuing.

Chapter 5—Safety: This chapter discusses the expected safety performance of roundabouts.

Chapter 6—Geometric Design: Specific geometric design principles for roundabouts are presented. The chapter then discusses each design element in detail, along with appropriate parameters to use for each type of roundabout.

Chapter 7—Traffic Design and Landscaping: This chapter discusses a number of traffic design aspects once the basic geometric design has been established. These include signs, pavement markings, and illumination. In addition, the chapter provides discussion on traffic maintenance during construction and landscaping.

Chapter 8—System Considerations: This chapter discusses specific issues and treatments that may arise from the systems context of a roundabout. The material may be of interest to transportation planners as well as operations and design engineers. Signal control at roundabouts is discussed. The chapter then considers the issue of rail crossings through the roundabout or in close proximity. Roundabouts in series with other roundabouts are discussed, including those at freeway interchanges and those in signalized arterial networks. Finally, the chapter presents simulation models as supplementary operational tools capable of evaluating roundabout performance within an overall roadway system