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

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

https://www.ce.utexas.edu/prof/bhat/ABSTRACTS/AMAR_review_article.pdf

Analytic methods in accident research: Methodological frontier and future directions

How to estimate queue length in real-time at signalized intersection is a long-standing problem. The problem gets even more difficult when signal links are congested. The traditional input-output approach for queue length estimation can only handle queues that are shorter than the distance between vehicle detector and intersection stop line, because cumulative vehicle count for arrival traffic is not available once the detector is occupied by the queue. In this paper, instead of counting arrival traffic flow in the current signal cycle, we solve the problem of measuring intersection queue length by exploiting the queue discharge process in the immediate past cycle. Using high-resolution "event-based" traffic signal data, and applying Lighthill-Whitham-Richards (LWR) shockwave theory, we are able to identify traffic state changes that distinguish queue discharge flow from upstream arrival traffic. Therefore, our approach can estimate time-dependent queue length even when the signal links are congested with long queues. Variations of the queue length estimation model are also presented when "event-based" data is not available. Our models are evaluated by comparing the estimated maximum queue length with the ground truth data observed from the field. Evaluation results demonstrate that the proposed models can estimate long queues with satisfactory accuracy. Limitations of the proposed model are also discussed in the paper.

Real-time queue length estimation for congested signalized intersections

http://www.stat.columbia.edu/~gelman/stuff_for_blog/Lord%20AA&P%202006.pdf

Modeling motor vehicle crashes using Poisson-gamma models: examining the effects of low sample mean values and small sample size on the estimation of the fixed dispersion parameter.

Vehicle delay and queue length are quantitative measures of intersection performance. The technological advancement in the field of vehicle sensors and traffic controllers has reached a point where it has enabled efficient measurement of these performance measures. Two techniques are presented for real-time measurement of vehicle delay and queue length at a signalized intersection, and these automated delay and queue estimates are compared with manually ground-truthed measurement. These techniques were evaluated at an instrumented intersection in Noblesville, Indiana. The root-mean-square error by both techniques was below 0.7 veh-s for estimation of average delay and less than 0.15 vehicle for estimation of average maximum queue length, both on a cycle-by-cycle basis.

/pdf/input-output-and-hybrid-techniques-for-real-time-prediction-15wt0mcl48.pdf

Input–Output and Hybrid Techniques for Real-Time Prediction of Delay and Maximum Queue Length at Signalized Intersections

The goal for the calibration process is to use predictive models developed with data collected from other jurisdictions and apply them to the jurisdiction of interest by adapting the models for local conditions and characteristics. Given the large costs associated with data collection, this process is often the only method available to transportation agencies for estimating the safety of different transportation facilities. Thus, recalibrating models produced from other jurisdictions allows agencies to produce their own models at relatively low costs. The objective for the research was to recalibrate a set of crash prediction models for different ramp design configurations. The ramp design configurations addressed included diagonal ramps, non-free-flow loop ramps, free-flow loop ramps, and outer connection ramps. A total of 44 ramps located in and around Austin, Texas, were used in the calibration process. The results of the study showed that more crashes occur on exit ramps than entrance ramps by a ratio of about 6 to 4. The results also showed that the non-free-flow ramp experiences twice as many crashes as other types of ramp. Similarly, more crashes occur on rural than urban ramps.

https://ceprofs.civil.tamu.edu/dlord/Papers/Lord_&_Bonneson_Ramp_Safety_TRB2005_March_2005.pdf

Calibration of Predictive Models for Estimating Safety of Ramp Design Configurations

Over the past few years, transportation agencies have placed greater emphasis on incorporating safety into the highway design process. The main assumption is that a highway designed with an explicit attention to safety could significantly reduce the frequency and the severity of crashes. One tool that is rapidly gaining popularity is the use of accident modification factors (AMFs) to estimate the change in safety following implementation of a countermeasure, a significant change in a geometric design element, or a planned construction upgrade of a highway facility. Although AMFs will play an extremely important role in coming years, especially with the forthcoming publication of the "Highway Safety Manual" (HSM), no document currently exists that addresses how they potentially could be used with the process to design highways. This paper describes the role and application of AMFs in the highway geometric design process. More specifically, it provides guidelines for applying these factors within the preliminary design stage, for assessing design consistency, and for evaluating design exceptions. For each design application, a proposed procedure is described in detail. Finally, an example is provided to illustrate more clearly the descriptions of two of the procedures.

/pdf/role-and-application-of-accident-modification-factors-within-4m74wv8k1m.pdf

Role and application of accident modification factors within highway design process

Highway safety is an ongoing concern to the Texas Department of Transportation (TxDOT). As part of its proactive commitment to improving highway safety, TxDOT is moving toward including quantitative safety analyses earlier in the project development process. The objectives of this research project are: (1) the development of safety design guidelines and evaluation tools to be used by TxDOT designers, and (2) the production of a plan for the incorporation of these guidelines and tools in the planning and design stages of the project development process. This document describes a procedure for using accident modification factors in the highway design process. Application of the procedure entails the use of several factors, where each factor addresses one specific design element (such as lane width, shoulder width, curve radius, etc.). Collectively, the factors can be used to estimate the effect of a change in one or more design elements. The procedure can be used to evaluate the safety benefits associated with alternative geometric designs.

Procedure for Using Accident Modification Factors in the Highway Design Process

This paper describes a procedure for developing accident modification factors (AMFs) by using a cross-sectional study. It is recognized that AMFs are most accurately derived from controlled experiments and observational before-after studies. However, the execution of experiments and before-after studies is not always practical or feasible. The procedure described in this paper is intended to be used in this situation. The procedure is demonstrated through the development of a curve radius AMF for rural two-lane highways.

Procedure for Developing Accident Modification Factors from Cross-Sectional Data

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