Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisor: Ardeshir Faghri, Dept. of Civil & Environmental Engineering Includes bibliographical references.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on May 12, 2009) Includes bibliographical references.

Thesis (M. Arch.)--University of Hong Kong, 2004. / Includes special report study entitled: Lost space: prodigy of Hong Kong. Also available in print.

Roundabouts have become an alternative for traditional intersections due to the safer operational performance. Previous research has provided crash modification factors (CMFs) as a criterion based on before-after studies as to evaluate the safety performance of roundabouts. One drawback of assessment based on crash modification factors, however, is that a before-after study includes too many variations at a time that it only provides a general idea of the safety performance for roundabouts. Since the industrial world is interested in the safety outcome of converting traditional intersections to roundabouts, safety performance functions (SPFs) will provide more specific details on estimating crashes than that of crash modification factors. This thesis will adopt a similar methodology that has been used in the current Highway Safety Manual (HSM) to develop safety performance functions for roundabouts based on Oregon data. The outcome of this thesis will help the Oregon Department of Transportation (ODOT) to evaluate existing roundabouts in the State of Oregon. Furthermore, this thesis will function as an additional case study from Oregon to contribute to the national effort of evaluating the safety performance of roundabouts. / Graduation date: 2013

There is increased interest in building modern roundabouts in Georgia and in the United States because of the safety and operational benefits that can be realized from this type of intersection. With this interest comes the increasing need to be able to estimate the capacity that a roundabout can provide after it is built. In the early 2000s, a National Cooperative Highway Research Program (NCHRP) study was conducted that, among other tasks, developed single-lane and multi-lane roundabout capacity estimation equations. These equations, presented in the Highway Capacity Manual 2010 (HCM 2010), can be calibrated using locally determined values of follow-up headway and critical headway. This study was designed to calibrate the HCM 2010 roundabout capacity equation for single-lane roundabouts to driving conditions in Georgia. In order to develop estimates of the calibration parameters, video imagery was recorded for 13 approaches at six roundabouts in Georgia for approximately two hours during the peak period. A total of 29.5 hours of video was recorded. Data from three of these roundabouts forms the basis of this thesis. The videos were processed by a Java program to collect time stamps that were subsequently used in Microsoft Excel to calculate the follow-up and critical headway values required for calibration. The values of critical headway and follow-up headway that were found from the video data are presented in the results as well as the single-lane capacity equations calibrated from the data. Two types of analysis were done, one that includes exiting vehicles and one that does not include exiting vehicles. When exiting vehicles were excluded, the weighted average of follow-up and critical headway were found to be 3.46 and 4.17 seconds respectively and when exiting vehicles were included in the analysis the weighted averages of the follow-up and critical headway were found to be 2.80 seconds and 3.34 seconds respectively. It was found that exiting vehicles do have an impact on the operations at the roundabout in most cases, and including exiting vehicles in the analysis tends to increase the capacity predicted by the calibrated equations.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "May 2007." Includes bibliographical references (leaves 84-85). Online version available on the World Wide Web.

Traditional intersections have always caused congestion, delay, and accidents. There are numerous geometric intersection designs that best fit each situation. This study performed an operational and safety comparison with unsignalized/signalized offset, Tintersections, a two-lane roundabout, and a modified roundabout to decrease the overall travel delay and increase the safety using a case study. Using data from a government source, all designs were tested in a calibrated micro simulation model and traffic signals were optimized using a signal optimization platform. Each design was tested with various balancing schemes, left turn percentages, and hourly volumes to determine the failure point. The unsignalized/signalized offset T-intersections, two-lane roundabout, and modified roundabout were compared by throughputs, travel delay, and travel time. After analysis, it was determined that the modified roundabout performed the best out of any design. All approaches had minimum travel delay while reducing the number of conflict points considerably with the modified roundabout. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

The operational performance of an existing or proposed roundabout can be assessed through capacity models. In order to provide improved capacity predictions for existing and proposed Georgia roundabouts, the 2010 HCM roundabout capacity equations need to be locally calibrated based on Georgia drivers. The purpose of this study is to collect field data necessary to calculate follow-up and critical headways at Georgia roundabouts in order to calibrate the 2010 HCM capacity equations to yield improved capacity predictions. The research team filmed 28 approaches at thirteen Georgia roundabouts for a total of 56.5 hours. The video was processed manually using an in-house computer program. Based on analyst keystrokes during the video review the program would extract timestamps of events that are necessary for calculating follow-up and critical headway. The follow-up and critical headway values were calculated for two different data sets: 1) including exiting vehicles and 2) excluding exiting vehicles. The critical and follow-up headway for an analysis including exiting vehicles is 4.192 seconds and 2.788 seconds respectively. The critical and follow-up headway for an analysis excluding exiting vehicles is 4.747 seconds and 3.265 seconds respectively. This study found that including the exiting vehicles impacts the capacity. The capacity increases or decreases based on the percentage of conflicting vehicles that are exiting vehicles. In addition, this study’s calibrated model excluding exiting vehicles predicts higher capacity than the 2010 HCM model that GDOT recommends which also excludes exiting vehicles.

published_or_final_version / Architecture / Master / Master of Architecture

As the modern roundabout continues to grow in popularity within the United States, more states are considering or implementing statewide roundabout programs and policies. To assist states with the implementation of statewide roundabout programs and policies, an analytical review of statewide roundabout programs and policies was conducted through an examination of literature, interviews, and data pertaining to the construction of roundabouts. The roundabout policy type for each state and the District of Columbia was located, and assigned to a roundabout policy type based on the strength of the identified policy type. In addition, a series of per capita analyses of the statewide roundabout policies was performed, as was a qualitative SWOT (Strengths, Weaknesses, Opportunities and Threats) analysis. The results of the analysis show that the strength of a statewide roundabout policy is correlated to the number of roundabouts in a state, and states should consider implementing or strengthening their policies if they seek to expand the use of roundabouts in their jurisdiction. In addition, the perception of roundabouts, both by the general public and internal to the state DOTs, also continues to hinder the further implementation of roundabouts, and education should be utilized to minimize these obstacles. Furthermore, states should utilize identified successful implementation procedures, and should be cognizant of reasons for implementation failure, as they pursue the further use of roundabouts by their agency.