Roundabouts In The United States

"Research sponsored by the American Association of State Highway and Transporation Officials in cooperation with the Federal Highway Administration."

TRB's National Cooperative Highway Research Program (NCHRP) Report 672: Roundabouts: An Informational Guide - Second Edition explores the planning, design, construction, maintenance, and operation of roundabouts. The report also addresses issues that may be useful in helping to explain the trade-offs associated with roundabouts. This report updates the U.S. Federal Highway Administration's Roundabouts: An Informational Guide, based on experience gained in the United States since that guide was published in 2000.

This is the first ever book devoted to the popular hobby of roundabout spotting, featuring over 80 full-colour favourites from humble painted minis to magnificent landscaped beauties, advice on the practical side of the pastime, and an exposition of the traffic-island's colourful history.

The guidance supplied in this document, Roundabouts: an informational guide, is based on established international and U.S. practices and is supplemented by recent research. The guide is comprehensive in recognition of the diverse needs of transportation professionals and the public for introductory material through design detail, as well as the wide range of potential applications of roundabout intersections. The following topics are addressed: definition of a roundabout and what distinguishes roundabouts from traffic circles; public acceptance and legal issues associated with roundabouts; consideration of all user modes, including heavy vehicles, buses, transit, bicycles, and pedestrians; a methodology for identifying appropriate sites for roundabouts and the range of conditions for which roundabouts offer optimal performance: methodologies for estimating roundabout capacity, delays, and queues with reference to the Highway Capacity Manual; design principles and guidance on safety and geometric design, with reference to applicable national standards such as the AASHTO Policy on Geometric Design of Highways and Streets; guidelines for control features such as signing and pavement markings, with reference to the Manual on Uniform Traffic Control Devices; illumination; and landscaping.

This book presents a history of roundabouts, an introduction to their design, calculations of their capacity and traffic-safety features. It describes the key features of standard roundabouts and their limitations. Alternative types of roundabouts are a fairly recent development and have only been implemented in a few countries to date. The book illustrates a broad variety of these recent alternative types of roundabouts, as well as proposed types still in the development phase, explaining for each the specific needs it meets, its advantages and drawbacks. In closing, the book offers an outlook on the role of roundabouts in future street traffic.

In March 1988, an international workshop on intersections without traffic signals was held at the Ruhr-University in Bochum, Germany. The proceedings of this workshop were published by Springer 1). The workshop was performed in a very harmonious atmosphere, which stimulated the experts from different countries to communicate and exchange their ideas and experiences. The presentations and the written contributions documented the present state of technical solutions for design and engineering of unsi gnalized intersections both regarding scientific research and practical applications. Moreover, numerous unsolved problems were identified. Thus, the 1988 workshop stimulated new developments in the field of unsignalized inter sections in several countries. In the meantime, these investigations have lead to a remarkable progress. For example in Germany a new guideline for unsignalized cross intersections and T-junctions has been finished and is going to be introduced in 1991. New results on roundabout capacity have been worked out as well. Many particularly important developments were made in foreign countries. Especially in the United States, an increasing interest in this subject can be observed. In the annual meetings of the TRB, this item received great attention. Many research institutes in North America have concentrated their activities on that point. A new TRB-circular concerning unsignalized intersections is going to be published. It will contain a new procedure for four-way-stop-control intersections, which seems to be a special feature of North American traffic engineering. However, new results from the US for two-way-stop control intersections are available as well.

"The objective of this research was to provide traffic engineers, transportation planners, and other practitioners with performance measurement and evaluation methods to evaluate comprehensively the performance of functionally interdependent roundabouts on arterials, thus enabling a comparison with signalized intersections, in order to arrive at a design solution."--Project information.