世界経済・社会統計 = World development indicators

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

Generalized Linear Models (2nd ed.)

Gaining a better understanding of the factors that affect the likelihood of a vehicle crash has been an area of research focus for many decades. However, in the absence of detailed driving data that would help improve the identification of cause and effect relationships with individual vehicle crashes, most researchers have addressed this problem by framing it in terms of understanding the factors that affect the frequency of crashes - the number of crashes occurring in some geographical space (usually a roadway segment or intersection) over some specified time period. This paper provides a detailed review of the key issues associated with crash-frequency data as well as the strengths and weaknesses of the various methodological approaches that researchers have used to address these problems. While the steady march of methodological innovation (including recent applications of random parameter and finite mixture models) has substantially improved our understanding of the factors that affect crash-frequencies, it is the prospect of combining evolving methodologies with far more detailed vehicle crash data that holds the greatest promise for the future.

http://ceprofs.tamu.edu/dlord/Papers/Lord-Mannering_Review.pdf

The statistical analysis of crash-frequency data: A review and assessment of methodological alternatives

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 Current methods of vehicle coordination, which are all designed to work with human drivers, will be outdated.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

Bayesian methodology to estimate and update safety performance functions under limited data conditions: A sensitivity analysis

Guidelines for the installation of median barriers presented in the AASHTO Roadside Design Guide have remained essentially unchanged for more than 30 years. In recent years, the need for improved guidance has prompted several states to reevaluate their guidelines and has also precipitated a nationwide research project administered by the Transportation Research Board. The objective of the study, on which this paper is based, was to develop improved guidelines for the use of median barriers on new and existing high-speed, multilane, divided highways in Texas. The purpose here is to present some modeling and benefit-cost analysis results from that study, with a focus on the results from a particular data set developed under a cross-sectional with-without study design. The highways of interest are those classified as Interstates, freeways, and expressways with four or more lanes and posted speed limits of 55 mph (88 km/h) or higher. The models employed to estimate median-related crash frequencies and severit...

Part 1: Roadside Safety Design: Developing Guidelines for Median Barrier Installation: Benefit-Cost Analysis with Texas Data

In recent years the development and use of crash prediction models for roadway safety analyses have received substantial attention. These models, also known as safety performance functions (SPFs), relate the expected crash frequency of roadway elements (intersections, road segments, on-ramps) to traffic volumes and other geometric and operational characteristics. A commonly practiced approach for applying intersection SPFs is to assume that crash types occur in fixed proportions (e.g., rear-end crashes make up 20% of crashes, angle crashes 35%, and so forth) and then apply these fixed proportions to crash totals to estimate crash frequencies by type. As demonstrated in this paper, such a practice makes questionable assumptions and results in considerable error in estimating crash proportions. Through the use of rudimentary SPFs based solely on the annual average daily traffic (AADT) of major and minor roads, the homogeneity-in-proportions assumption is shown not to hold across AADT, because crash proportions vary as a function of both major and minor road AADT. For example, with minor road AADT of 400 vehicles per day, the proportion of intersecting-direction crashes decreases from about 50% with 2,000 major road AADT to about 15% with 82,000 AADT. Same-direction crashes increase from about 15% to 55% for the same comparison. The homogeneity-in-proportions assumption should be abandoned, and crash type models should be used to predict crash frequency by crash type. SPFs that use additional geometric variables would only exacerbate the problem quantified here. Comparison of models for different crash types using additional geometric variables remains the subject of future research.

Differences in the Performance of Safety Performance Functions Estimated for Total Crash Count and for Crash Count by Crash Type

http://ceprofs.tamu.edu/dlord/Papers/Vieira_Gomes_et_al_Predictive_Models.pdf

Estimating the safety performance of urban intersections in Lisbon, Portugal

For Texas, the average number of pedestrian fatalities for 2007 to 2011 is about 400 per year. Due to the high number of pedestrian crashes, Texas is considered by the Federal Highway Administration (FHWA) to be a “focus” state. Researchers found that 2 percent of all Texas Department of Transportation (TxDOT)-reportable traffic crashes and 15 percent of all TxDOT-reportable fatal crashes were pedestrian related. Most non-fatal crashes are associated with daylight, at intersections, and on city streets, whereas most fatal crashes are associated with dark conditions, midblock locations, and high-speed roadways. Twenty-one percent of all fatal TxDOT-reportable pedestrian crashes occurred on freeways—a location where pedestrians are least expected. Additional research into how to address pedestrian crashes, especially freeway crashes, is needed, perhaps using FHWA’s new systematic safety project selection tool. In the past decade, the pedestrian hybrid beacon (PHB) and rectangular rapid-flashing beacon (RRFB) have shown great potential in improving driver yielding rates and conditions for crossing pedestrians. Researchers conducted a field study at 7 traffic control signal (TCS) sites, 22 RRFB sites, and 32 PHB sites in Texas with the effectiveness measure being the percent of drivers yielding to a staged pedestrian. Results showed that driver yielding rates varied by type of treatment. Overall, TCSs in Texas have the highest driver yielding rates (98 percent), followed by PHBs (89 percent) and RRFBs (86 percent). Those cities with a greater number of a particular device (i.e., Austin for the PHB and Garland for the RRFB) had higher driver yielding rates as compared to cities where the device was only used at a few crossings. Also, as drivers became more familiar with the PHB, a greater proportion yielded, perhaps because they gained a better understanding of expectations or requirements over time. As part of this study, researchers conducted a before-and-after field study at four RRFB sites and one PHB site to identify the changes in driver yielding and selected pedestrian behaviors resulting from installing these treatments at previously untreated crosswalks. The installations resulted in noticeable improvement in the number of yielding vehicles.

Dominique Lord

Papers

Bayesian methodology to estimate and update safety performance functions under limited data conditions: A sensitivity analysis

Part 1: Roadside Safety Design: Developing Guidelines for Median Barrier Installation: Benefit-Cost Analysis with Texas Data

Differences in the Performance of Safety Performance Functions Estimated for Total Crash Count and for Crash Count by Crash Type

Estimating the safety performance of urban intersections in Lisbon, Portugal

Characteristics of Texas Pedestrian Crashes and Evaluation of Driver Yielding at Pedestrian Treatments