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

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A User’s Guide

Artificial intelligence research is ushering in a new era of sophisticated, mass-market transportation technology. While computers can already fly a passenger jet better than a trained human pilot, people are still faced with the dangerous yet tedious task of driving automobiles. Intelligent Transportation Systems (ITS) is the field that focuses on integrating information technology with vehicles and transportation infrastructure to make transportation safer, cheaper, and more efficient. Recent advances in ITS point to a future in which vehicles themselves handle the vast majority of the driving task. Once autonomous vehicles become popular, autonomous interactions amongst multiple vehicles will be possible. Current methods of vehicle coordination, which are all designed to work with human drivers, will be outdated. The bottleneck for roadway efficiency will no longer be the drivers, but rather the mechanism by which those drivers' actions are coordinated. While open-road driving is a well-studied and more-or-less-solved problem, urban traffic scenarios, especially intersections, are much more challenging.

We believe current methods for controlling traffic, specifically at intersections, will not be able to take advantage of the increased sensitivity and precision of autonomous vehicles as compared to human drivers. In this article, we suggest an alternative mechanism for coordinating the movement of autonomous vehicles through intersections. Drivers and intersections in this mechanism are treated as autonomous agents in a multiagent system. In this multiagent system, intersections use a new reservation-based approach built around a detailed communication protocol, which we also present. We demonstrate in simulation that our new mechanism has the potential to significantly outperform current intersection control technology--traffic lights and stop signs. Because our mechanism can emulate a traffic light or stop sign, it subsumes the most popular current methods of intersection control. This article also presents two extensions to the mechanism. The first extension allows the system to control human-driven vehicles in addition to autonomous vehicles. The second gives priority to emergency vehicles without significant cost to civilian vehicles. The mechanism, including both extensions, is implemented and tested in simulation, and we present experimental results that strongly attest to the efficacy of this approach.

/pdf/a-multiagent-approach-to-autonomous-intersection-management-ndv1gqtnse.pdf

A multiagent approach to autonomous intersection management

Safety is emerging as an area of increased attention and awareness within transportation engineering. Historically, the safety of new and innovative traffic treatments has been difficult to assess, primarily because of a lack of good predictive models of crash potential and a lack of consensus on what constitutes a safe or unsafe facility. An FHWA-sponsored research project investigated the potential to derive surrogate measures of safety from existing traffic simulation models. These surrogate measures could then be used to support evaluations of various traffic engineering alternatives, including facilities that have not yet been built and strategies that have not yet been used. Each surrogate measure is collected on the basis of the occurrence of a conflict event, which is an interaction between two vehicles in which one vehicle must take evasive action to avoid a collision. The surrogate measures that are proposed as the best are time to collision, postencroachment time, deceleration rate, maximum spe...

/pdf/surrogate-safety-measures-from-traffic-simulation-models-3eff0up90z.pdf

Surrogate safety measures from traffic simulation models

§ 149. Congestion mitigation and air quality improvement program (a) Establishment.— The Secretary shall establish and implement a congestion mitigation and air quality improvement program in accordance with this section. (b) Eligible Projects.— Except as provided in subsection (c), a State may obligate funds apportioned to it under section 104 (b)(2) for the congestion mitigation and air quality improvement program only for a transportation project or program if the project or program is for an area in the State that is or was designated as a nonattainment area for ozone, carbon monoxide, or particulate matter under section 107(d) of the Clean Air Act (42 U.S.C. 7407 (d)) and classified pursuant to section 181(a), 186(a), 188(a), or 188(b) of the Clean Air Act (42 U.S.C. 7511 (a), 7512 (a), 7513 (a), or 7513 (b)) or is or was designated as a nonattainment area under such section 107 (d) after December 31, 1997, or is required to prepare, and file with the Administrator of the Environmental Protection Agency, maintenance plans under the Clean Air Act (42 U.S.C. 7401 et seq.) and— (1)(A)(i) if the Secretary, after consultation with the Administrator determines, on the basis of information published by the Environmental Protection Agency pursuant to section 108(f)(1)(A) of the Clean Air Act (other than clause (xvi)) that the project or program is likely to contribute to— (I) the attainment of a national ambient air quality standard; or (II) the maintenance of a national ambient air quality standard in a maintenance area; and (ii) a high level of effectiveness in reducing air pollution, in cases of projects or programs where sufficient information is available in the database established pursuant to subsection (h) to determine the relative effectiveness of such projects or programs; or, (B) in any case in which such information is not available, if the Secretary, after such consultation, determines that the project or program is part of a program, method, or strategy described in such section 108(f)(1)(A); (2) if the project or program is included in a State implementation plan that has been approved pursuant to the Clean Air Act and the project will have air quality benefits; (3) the Secretary, after consultation with the Administrator of the Environmental Protection Agency, determines that the project or program is likely to contribute to the attainment of a national ambient air quality standard, whether through reductions in vehicle miles traveled, fuel consumption, or through …

A. Federal Highway Administration

Current design and marking standards for passing and no- passing zones are based on the results of field studies conducted more than 35 years ago. Many of the assumptions used to derive these standards are not valid for current highway operations. In addition, design and marking standards are almost exclusively concerned with passing sight distance. Design standards contain no provision to establish the minimum length over which the design passing sight distance must be made available to the passing driver to constitute a safe passing zone. Marking standards indirectly set the minimum length of passing zones at 122 m (400 ft). This zone length is inadequate for the majority of higher speed passes. A review of recent research, especially studies dealing directly and design or marking practice, indicates that sufficient data are available to develop design and marking standards based on the contemparary field measurements. The results of a study on short passing zones demonstrate the safety and operational deficiences of passing zones less than 268 m (880 ft) long. Therefore, it is recommended that design and marking standards consider both passing sight distance and passing zone length. Because the design of highway geometrics should be based on analysis of subsequent highway operations, the authors recommend that design and marking standards be identical. Specific criteria for the design and marking of passing and no-passing zones are suggested. /Author/

Framework for design and operation of passing zones on two- lane highways

This research report presents the findings on the identification and evaluation of the use of highway geometric design features on freeways to reduce nonrecurrent congestion and improve travel time reliability. General guidance is provided on the range of design elements that could be used by transportation agencies to improve travel time reliability and reduce nonrecurrent congestion, analysis procedures and models to measure their operational and safety effectiveness, as well as a life-cycle benefit–cost method to support decision making on the possible use of individual treatments to address actual nonrecurring traffic conditions. For the safety effectiveness analysis, a new relationship between safety and congestion was explored and a mathematical model developed to quantify crash frequency at various levels of service.

Identification and Evaluation of the Cost-Effectiveness of Highway Design Features to Reduce Nonrecurrent Congestion

This report describes the impact of the controlling roadway design criteria on safety and operations for urban and rural roads. In 1985, the FHWA designated 13 specific design elements as controlling criteria for roadway design. The 13 controlling criteria are (1) design speed, (2) lane width, (3) shoulder width, (4) bridge width, (5) structural capacity, (6) horizontal alignment, (7) vertical alignment, (8) grade, (9) stopping sight distance, (10) cross slope, (11) superelevation, (12) vertical clearance, and (13) horizontal clearance. Federally assisted highway construction and reconstruction projects must meet the established design criteria for these elements, or a formal design exception must be prepared and approved. Different procedures apply to rehabilitation projects, but these design elements are still key considerations in design. Since their designation, the 13 controlling criteria and their application have not been reconsidered as new knowledge has been gained about the relationships between geometric design elements and safety and operations. In this research project, the research team investigated what is known about the safety and operational effects of the 13 controlling and other important geometric design criteria. Several small studies were done to augment the information found in the literature. This information was used to assess the sensitivity of safety and operations to design decisions for these criteria for different types of roads. The research also addressed how to reduce confusion related to the definitions of the controlling criteria. The use of the controlling criteria in design exception processes was also explored, including through interviews with state department of transportation (DOT) personnel. This report will be useful to geometric designers and those responsible for reviewing designs, particularly in agencies that are transitioning away from “standards-based design.”

Evaluation of the 13 Controlling Criteria for Geometric Design

The U.S. Road Assessment Program, in cooperation with road assessment programs in other countries, has developed a protocol to assign ratings to roads on the basis of the presence or absence of key design features related to safety. This protocol rates roads by assigning them one to five stars according to approximately 20 key roadway safety features. A recently developed web-based software tool uses the roadway inventory data on which the star ratings are based to identify cost-effective safety improvement programs for the road networks covered by the ratings. The research results are presented to validate the relationship between the star ratings and crash rates for selected roadways. The research developed star ratings for approximately 3,000 mi of rural and urban roadways of various types in Iowa and Washington State and compared the star ratings with crash rates for the same roads. Relationships between star ratings and crash rates were found for two-lane undivided highways, four-lane undivided highways, and four-lane divided nonfreeways. No clear relationships could be demonstrated for freeways because the design characteristics of freeways are very uniform.

Validation of U.S. Road Assessment Program Star Rating Protocol: Application to Safety Management of U.S. Roads

Passing lanes and short four-lane sections are installed to provide increased opportunities for passing slow-moving vehicles on two-lane highways. An operational and safety evaluation of these treatments was performed by using traffic operational field data collected at 15 sites and traffic accident data for 76 sites. It was found that passing lanes decrease the percentage of vehicles platooned on two-lane highways and that the magnitude of this benefit varies with passing lane length, traffic volume, and the level of platooning upstream of the passing lanes. Passing lanes increase the rate of passing maneuvers on two-lane highways but have only a small effect on mean travel speeds. Passing lanes and short four-lane sections do not increase accident rates above the levels found on comparable untreated two-lane highways; in fact, they probably improve safety.

Operational and safety effectiveness of passing lanes on two-lane highways

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