Highway Capacity Manual改訂の動向--テイラ-教授の講演より

The guidance supplied in this document 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.

https://rosap.ntl.bts.gov/view/dot/15382/dot_15382_DS1.pdf

Roundabouts : an informational guide

Modern roundabouts are designed to control traffic flow at intersections without the use of stop signs or traffic signals. U.S. experience with modern roundabouts is rather limited to date, but in recent years there has been growing interest in their potential benefits and a relatively large increase in roundabout construction. This interest has created a need for data regarding the safety effect of roundabouts. Changes in motor vehicle crashes following conversion of 23 intersections from stop sign and traffic signal control to modern roundabouts are evaluated. The settings, located in seven states, are a mix of urban, suburban, and rural environments with the urban sample consisting of both single-lane and multilane designs and the rural sample consisting of only single-lane designs. A before-after study was conducted using the empirical Bayes procedure, which accounts for regression to the mean and traffic volume changes that usually accompany conversion of intersections to roundabouts. For the 23 inte...

Safety Effect of Roundabout Conversions in the United States: Empirical Bayes Observational Before-After Study

Safety of traffic facilities is most often measured by counting the number (and severity) of crashes that occur. It is not possible to apply such a measurement technique to traffic facility designs that have not yet been built or deployed in the real world. This project has resulted in the development of a software tool for deriving surrogate safety measures for traffic facilities from data output by traffic simulation models. This software is referred to as SSAM—an acronym for the Surrogate Safety Assessment Model. The surrogate measures developed in this project are based on the identification, classification, and evaluation of traffic conflicts that occur in the simulation model. By comparing one simulated design case with another, this software allows an analyst to make statistical judgments about the relative safety of the two designs. An open-standard vehicle trajectory data format was designed, and support for this format has been added as an output option by four simulation model vendors/developers— PTV (VISSIM), TSS (AIMSUN), Quadstone (Paramics), and Rioux Engineering (TEXAS). Eleven “theoretical” validation tests were performed to compare the surrogate safety assessment results of pairs of simulated design alternatives. In addition, a field validation exercise was completed to compare the output from SSAM with real-world crash records. Eighty-three intersections from British Columbia, Canada were modeled in VISSIM and simulated under AM-peak traffic conditions. The processed conflict results were then compared with the crash records in a number of different statistical validation tests. Last, sensitivity analysis was performed to identify differences between the SSAM-related outputs of each simulation model vendor’s system on the same traffic facility designs. These comparative analyses provide some guidance to the relative use of surrogate measures data from each simulation system. The SSAM software tool and user manual (FHWA-HRT-08-050) are available to the public at no cost from FHWA.

Surrogate Safety Assessment Model and Validation: Final Report

Node models for macroscopic simulation have attracted relatively little attention in the literature. Nevertheless, in dynamic network loading (DNL) models for congested road networks, node models are as important as the extensively studied link models. This paper provides an overview of macroscopic node models found in the literature, explaining both their contributions and shortcomings. A formulation defining a generic class of first order macroscopic node models is presented, satisfying a list of requirements necessary to produce node models with realistic, consistent results. Defining a specific node model instance of this class requires the specification of a supply constraint interaction rule and (optionally) node supply constraints. Following this theoretical discussion, specific macroscopic node model instances for unsignalized and signalized intersections are proposed. These models apply an oriented capacity proportional distribution of the available supply over the incoming links of a node. A computationally efficient algorithm to solve the node models exactly is included.

A generic class of first order node models for dynamic macroscopic simulation of traffic flows

Many different methods for the estimation of crtical gaps at unsignalized intersections have been published in the international literature. This paper gives an overview of some of the more important methods. These methods are described by their characteristic properties. For comparison purposes a set of quality criteria has been formulated by which the usefulness of the different methods can be assessed. Among these one aspect seems to be of primary importance. This is the objective that the results of the estimation process should not depend on the traffic volume on the major street during the time of observation. Only if this condition is fulfilled can the estimation be applied under all undersaturated traffic conditions at unsignalized intersections. To test the qualification of some of the estimation methods under this aspect, a series of comprehensive simulations has been performed. As a result, the maximum likelihood procedure and the method developed by Hewitt can be recommended for practical application.

Useful estimation procedures for critical gaps

Many different methods for the estimation of critical gaps at unsignalized intersections have been published in the international literature. This paper gives an overview of some of the more important methods. These methods are described by their characteristic properties. For comparison purposes a set of quality criteria has been formulated by which the usefulness of the different methods can be assessed. Among these one aspect seems to be of primary importance. This is the objective, that the results of the estimation process should not depend on the traffic volume on the major street during the time of observation. Only if this condition is fulfilled, the estimation can be applied under all undersaturated traffic conditions at unsignalized intersections. To test the qualification of some of the estimation methods under this aspect a series of comprehensive simulations has been performed. As a result the maximum likelihood procedure, as it has been described by Troutbeck, and the method developed by Hewitt can be recommended for practical application.

/pdf/useful-estimation-procedures-for-critical-gaps-3iiac334c8.pdf

Based on a comprehensive evaluation of roundabouts in the United States, this report presents methods of estimating the safety and operational impacts of roundabouts and updates design criteria for them The report will be useful to geometric designers and traffic engineers who are considering improvements to an intersection

Roundabouts in the United States

This paper focuses on the implementation of the maximum likelihood technique to measure critical gap using data collected in the field. A methodology to define gap events is proposed, so that the accepted gaps and the largest rejected gaps could be obtained. The measurement at multi-lane sites and the treatment of major-street right-turn movement are specifically discussed. The paper points out some unusual situations where the proposed method cannot be applied directly. The proposed methodology has been used in NCHRP 3-46 to measure critical gaps under conditions in the U.S.A.

Rod Troutbeck

Papers

Roundabouts : an informational guide

Useful estimation procedures for critical gaps

Useful estimation procedures for critical gaps

Roundabouts in the United States

Implementing the maximum likelihood methodology to measure driver's critical gap