Toshio Yoshii

Special Section on Dynamic Traffic Assignment: A Tool for Evaluating and Assessing Dynamic Traffic Management Schemes

Intelligent transportation system (ITS) technologies have enabled efficient traffic control. One important issue pertains to extensions of traffic management and data collection schemes over the temporal dimension. For instance, dynamic traffic information extracted from electronic data can improve the spatial concentration of traffic flow, and provide more detailed and accurate origin–destination (OD) information. To discuss the effect of such traffic management measures, we need a model to forecast the time-varying traffic conditions as accurately as possible. Dynamic traffic assignment (DTA) is indispensable for evaluating traffic operations and for planning. In this special issue, we have four articles discussing the use of DTA for implementing and evaluating traffic management schemes, based on ITS technologies. The first article, by Chen et al. (2014), reports on an investigation of the time-dependent reliable shortest path problem, to help travelers choose their optimal route under travel time uncertainty. They considered two aspects of the shortest path problem: first, the determination of the earliest arrival time and associated reliable shortest path for a given departure time, and second, the determination of the latest departure time and associated reliable shortest path for a given preferred arrival time. They approached the optimal traffic route determination as a mathematical problem, providing key insights into proper characterization of this problem, as well as efficient algorithms for

The Suitable Index of Flow and Density in the Mixed Traffic

Some traffic indices were developed to consider the existence of vehicle variance either in the homogeneous or mixed traffic. This study investigates the proper index of flow and density in the mixed traffic. There are eight pairs of indices of traffic flow and density that will be compared, in which it was varied by the concept and the measurement interval. The concept was distinguished according to the respond to the variance of vehicles in the traffic analysis, and the measurement interval was differentiated over time and time-space. The traffic was observed over a short section of a road which set as the detection zone. All pairs of indices will be applied and evaluated on the Fundamental Diagram to describe the actual traffic state in the density-flow plane. Then, the R-square of each density-flow curve will be compared. The result shows that the existence of vehicle variance in the share of traffic can be described more properly by considering the projected area of vehicles. The index of flow and density which considers the projected area of vehicles can explain the actual traffic state more appropriately by increasing the R-square of the model. In addition, the result does not provide a significant difference between the measurement over time and time-space in a short section of the road.

Development of discrete choice model considering internal reference points and their effects in travel mode choice context

In the conventional travel behavior models such as logit and probit, decision makers are assumed to conduct the absolute evaluations on the attributes of the choice alternatives. On the other hand, many researchers in cognitive psychology and marketing science have been suggesting that the perceptions of attributes are characterized by the benchmark called reference points and the relative evaluations based on them are often employed in various choice situations. Therefore, this study developed a travel behavior model based on the mental accounting theory in which the internal reference points are explicitly considered. A questionnaire survey about the shopping trip to the CBD in Matsuyama city was conducted, and then the roles of reference points in travel mode choice contexts were investigated. The result showed that the goodness-of-fit of the developed model was higher than that of the conventional model, indicating that the internal reference points might play the major roles in the choice of travel mode. Also shown was that the respondents seem to utilize various reference points: some tend to adopt the lowest fuel price they have experienced, others employ fare price they feel in perceptions of the travel cost.

DEVELOPMENT OF A SIGNAL CONTROL SYSTEM USING MOVABLE MONITORING TOOLS

This study develops the framework of a temporary signal control system using the traffic counts from movable vehicle detectors and the vehicle trajectory data from probe vehicles equipped with Global Positioning Systems (GPS). Also it includes not only the concept of minimizing the volume of total travel time but also CO(2) emission. In order to achieve effective signal control, signal parameters should be determined in accordance with traffic flows. However, monitoring systems, which are installed on roads as a fixed infrastructure, is usually not installed for temporary use. Therefore, after a method of estimating the volume of CO(2) emission is proposed, this study develops a framework of signal control system with movable monitoring tools and validates the movable detectors by checking the accuracy of their counts. Through the validation, the paper confirms that the accuracy of the observed traffic volume is fairly good but the estimated saturation flow rate has the tendency of over-estimation.