Roundabouts in the United States (2007) / Chapter Skim
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Pages 4-11
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From page 4... ...
4This report summarizes the findings of NCHRP 3-65, "Applying Roundabouts in the United States." The intended audience for this report is researchers, practitioners, and policy makers who establish federal, state, and local guidelines for roundabouts. Although the content of this document is directly relevant to practitioners, the document is not organized as a guide for easy practitioner use.
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delay, and queue estimates for single-lane and multilane roundabouts • New speed prediction tools for use in design development • A comprehensive study of pedestrian and bicyclist behavior at roundabouts • Updated design guidance incorporating the results from the various studies identified above. It became clear during the early stages of this research effort that the proposed scope of work and associated data collection effort would be insufficient to address issues related to the accommodation of visually impaired pedestrians at roundabouts.
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value of approach-level predictive models. This development involved the same sequence of steps used for the intersection-level model development.
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• What are the geometric or operational characteristics that tend to cause problems for pedestrians or that tend to result in safer and more accessible designs? Are there differences in behaviors between the entry side and exit side of a leg?
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in the modeling of different crash types. However, the various crash types needed to be modeled, as others have done, to guard against the opposite effects of a variable being masked.
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includes a gap acceptance model limited to single-lane roundabouts, and it does not provide any guidance on delay, queues, or level of service. The methods in FHWA's Roundabouts: An Informational Guide (1)
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10 Country Author Type Applicability Input Parameters Comments Wu (11) Gap Acceptance One to three lanes • Circulating flow • Number of lanes • Critical headway • Follow-up headway • Minimum gap Recommended model in Germany.
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these models were directly transferable to the United States. Therefore, a considerable amount of model testing and subsequent model development was required for this research.
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