Roundabouts: An Informational Guide – Second Edition (2010) / Chapter Skim
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Pages 20-42
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Chapter 2/Roundabout Considerations Page 2-1 Roundabouts: An Informational Guide CHAPTER 2 ROUNDABOUT CONSIDERATIONS CONTENTS 2.1 INTRODUCTION .
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Roundabouts: An Informational Guide Page 2-2 Chapter 2/Roundabout Considerations LIST OF EXHIBITS Exhibit 2-1 Wide Nodes, Narrow Roads Concept .
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Chapter 2/Roundabout Considerations Page 2-3 Roundabouts: An Informational Guide 2.1 INTRODUCTION This chapter provides a general overview of the characteristics of roundabouts and considerations for all users. A discussion of legal considerations and user education provides policy makers with the information they need to make appropriate decisions and convey direction to the public.
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Roundabouts: An Informational Guide Page 2-4 Chapter 2/Roundabout Considerations Single-lane roundabouts designed for low-speed operation are one of the safest treatments available for at-grade intersections. Drivers have no lane use decisions to make.
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Chapter 2/Roundabout Considerations Page 2-5 Roundabouts: An Informational Guide major street through movements from both directions, as well as the major street left and right turns and opposing minor through and right turns. Signalized intersections attempt to simplify the decision-making process for drivers, especially at locations where protected left-turn phasing is provided, by separating conflicts in time and space.
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Roundabouts: An Informational Guide Page 2-6 Chapter 2/Roundabout Considerations the circulating traffic. The faster the circulating traffic, the larger this gap must be.
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Chapter 2/Roundabout Considerations Page 2-7 Roundabouts: An Informational Guide may be lower than before. In these cases the overall total delay, stops, and queues may be reduced.
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Roundabouts: An Informational Guide Page 2-8 Chapter 2/Roundabout Considerations Exhibit 2-1 Wide Nodes, Narrow Roads Concept Exhibit 2-2 Example of Wide Nodes, Narrow Roads Concept Vail, Colorado Most roundabouts on arterial streets are designed to accommodate traffic volume estimated for a future horizon year, which can extend 20 years or more from the construction date. Collector and local-street roundabouts are typically designed for full build-out conditions.
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Chapter 2/Roundabout Considerations Page 2-9 Roundabouts: An Informational Guide cross section can negatively impact bicycle and pedestrian movements. Therefore, a phased implementation may be an appropriate way to accommodate current users' needs while still providing an opportunity for the roundabout to be expanded for future traffic volume growth.
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Roundabouts: An Informational Guide Page 2-10 Chapter 2/Roundabout Considerations Landscaping issues are discussed in detail in Chapter 9. the ongoing operations and maintenance cost of a roundabout can be less than that for a signal, with the possible exception of increased illumination needs for a roundabout.
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Chapter 2/Roundabout Considerations Page 2-11 Roundabouts: An Informational Guide hard objects directly facing the entries do not create a safety hazard. Additional guidance for landscaping and art at roundabouts is presented in Chapter 9.
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Roundabouts: An Informational Guide Page 2-12 Chapter 2/Roundabout Considerations access management. The trade-offs involved when implementing a roundabout should be considered at a policy level when introducing roundabouts into a region or on a project-by-project basis at specific locations where a roundabout is one of the alternatives being considered.
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Chapter 2/Roundabout Considerations Page 2-13 Roundabouts: An Informational Guide Exhibit 2-5 (cont.) Summary of Roundabout Advantages and Disadvantages Space • Often require less queue storage space on intersection approaches -- can allow for closer intersection and access spacing.
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Roundabouts: An Informational Guide Page 2-14 Chapter 2/Roundabout Considerations • Separate vehicle–vehicle and vehicle–pedestrian conflict points, and • Allow the second entering driver to devote attention to crossing pedestrians while waiting for the driver ahead to enter the circulatory roadway. As discussed in Chapter 5, relatively slow vehicle speeds and a reduced number of conflicts are two primary reasons that roundabouts are safer than most other intersection types.
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Chapter 2/Roundabout Considerations Page 2-15 Roundabouts: An Informational Guide impaired and elderly pedestrians. However, pedestrians at signalized intersections are vulnerable to unprotected right-turn and left-turn movements.
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Roundabouts: An Informational Guide Page 2-16 Chapter 2/Roundabout Considerations • Alignment. Likewise, roundabouts do not typically include the normal audible and tactile cues used by pedestrians with vision impairments to align themselves with the crosswalk.
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Chapter 2/Roundabout Considerations Page 2-17 Roundabouts: An Informational Guide Bicycle lanes are not recommended on the circulatory roadway. The Federal Highway Administration has issued a memo stating that "the Draft Guidelines are the currently recommended best practices, and can be considered the state of the practice that could be followed for areas not fully addressed by the present ADAAG standards" (6)
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Roundabouts: An Informational Guide Page 2-18 Chapter 2/Roundabout Considerations may not feel comfortable traversing some roundabouts in the same manner as other vehicles, bicycle ramps can be provided to allow access to the sidewalk or a shared use path at the roundabout. Bicycle ramps at roundabouts have the potential to be confused as pedestrian ramps, particularly for pedestrians who are blind or who have low vision.
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Chapter 2/Roundabout Considerations Page 2-19 Roundabouts: An Informational Guide These findings apply to older drivers and pedestrians encountering all types of intersections, including roundabouts. The excerpts above all imply that lower, more conservative design speeds are appropriate.
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Roundabouts: An Informational Guide Page 2-20 Chapter 2/Roundabout Considerations 2.3.6 TRANSIT Transit vehicles are a special type of large vehicle and have unique requirements, many of which are similar to those at other types of intersection treatments. If the roundabout has been designed using the appropriate design vehicle, a bus should have no physical difficulty negotiating the intersection.
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Chapter 2/Roundabout Considerations Page 2-21 Roundabouts: An Informational Guide 2.4 POLICY AND LEGAL ISSUES Policy plays an important role in the implementation of roundabouts, particularly at the state level. There are two key aspects to policy implementations: • Decision-making process and • Legal issues, including rules of the road.
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Roundabouts: An Informational Guide Page 2-22 Chapter 2/Roundabout Considerations The Road of the Oregon Revised Statutes (ORS 811.400)
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Chapter 2/Roundabout Considerations Page 2-23 Roundabouts: An Informational Guide Environments for Older Drivers." Proc., Traffic Safety on Three Continents Conference, Moscow, Russia, 2001.
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