Language：Japanese   Publisher：Japan Society of Traffic Engineers  

<p>The concept of a functional hierarchical road network is important as one of the solutions to the road traffic problems that still occur in Japan, where the road network has been steadily developed. This study aims to propose a method to evaluate in which degree of functional hierarchy the road network is being used. In a virtual road network with three levels of hierarchy, the shortest routes are searched under the free flow conditions, and the road use characteristic indices are calculated such as trip lengths and use rates of each hierarchical level. Based on the conditions of the road network represented by these index values, a method to evaluate its functional hierarchy in four degrees is proposed. As a case study, the degree of hierarchy was calculated for the road networks in southern Gifu and western Shizuoka. The results revealed that the current evaluations of the functional hierarchy in these areas were low, and that the mid-level roads are required for improving the current situation.</p>

DOI： 10.14954/jste.9.2_a_69

CiNii Research

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (conference, symposium, etc.)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

Publisher：Transportation Research Part C: Emerging Technologies  

Merging sections on freeways are typical bottlenecks for traffic efficiency and safety. The connected and automated vehicles (CAV) technology has great capability in improving traffic performance of merging bottlenecks. Current approaches of system optimal cooperative merging control assume single fixed merging point (CMC-SMP) for on-ramp vehicles to reduce the complexity of their models. Non-fixed merging positions have the potential to further improve merging operations but may lead to the computational explosion. To solve this core contradiction, this study proposes a novel hierarchical system optimal cooperative merging control model considering flexible merging positions (CMC-FMP) to realize safe and efficient merging processes. The upper-level – the tactical planning model is formulated as a non-convex mixed integer quadratically constrained programming, aiming at minimal total travel time in the control zone. It optimizes not only the merging sequence but also vehicles’ critical states in merging processes, such as the state of on-ramp vehicles when they merge. The lower-level - the motion planning model generates feasible trajectories and the next step actions for every vehicle. A Monte Carlo Tree Search-based decomposition algorithm (MCTS-DA) is further designed to improve the computational efficiency of the tactical planning model. Meanwhile, solutions of MCTS-DA are proved to have good optimality compared to the direct solving method. A batch-based scheme is developed to realize real-time control. The results reveal that the average delays of CMC-FMP are remarkably lower than those of CMC-SMP. Especially in low on-ramp ratio scenarios, the difference in improvement can reach 64%. Furthermore, the sensitivity analysis indicates that large safe merging margins and short merging sections are disadvantageous for traffic efficiency for the merging flow controlled by CMC-FMP.

DOI： 10.1016/j.trc.2022.103650

Web of Science

Scopus

Language：Japanese   Publisher：Japan Society of Traffic Engineers  

DOI： 10.14954/jste.8.4_b_18

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

Publisher：International Journal of Intelligent Transportation Systems Research  

Field experiments of autonomous vehicles (AVs) have been conducted in many countries. However, efficiency evaluation of AV mixed flow and safety evaluation of conflicts between AVs and pedestrians in the real-world case are still limited. This study aims at evaluating the efficiency and safety of left-turn (LT) vehicles and pedestrians in signalized intersections, under the condition of AV mixed flow, by developing a simulation model. Post Encroachment Time (PET) and LT capacity were obtained. Further, gap/lag acceptance behavior and reaction time of LT vehicles were found to be critical parameters that affect efficiency and safety evaluations.

DOI： 10.1007/s13177-021-00276-z

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.trc.2022.103650

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.eastsj.2022.100070

Language：English   Publisher：Eastern Asia Society for Transportation Studies  

<p>Full signalized traffic circles are operating in some countries to serve the heavy turning traffic flows at large-sized road junctions. Their capacities are influenced by many factors, such as the traffic conditions, signal control types and geometric layouts. The objective of this study is to find out the specified traffic demand conditions that signalized traffic circles are preferred in different cases of the number of lanes and lane configurations. A signal optimization model for the traffic circles is proposed for investigating five cases of signalized traffic circles under various traffic demand conditions. The results showed that signalized traffic circles have higher capacity than signalized intersections in some specific cases, e.g. when the total number of approach lanes reaches five or when more than one right-turn lanes are required. Besides, an analysis on the relationship between the capacity and the occupied area is conducted to further consider the geometric influence.</p>

DOI： 10.11175/easts.14.1958

CiNii Research

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.14954/jste.8.2_A_15

Language：Japanese   Publisher：Japan Society of Traffic Engineers  

DOI： 10.14954/jste.8.2_a_15

CiNii Research

Publisher：Asian Transport Studies  

Conflicts between pedestrians and left-turning vehicles cause pedestrian safety hazards and decrease vehicle turning capacity at signalized intersections. This commonly occurs in Japan where they share the same traffic light phase. Road capacity is influenced by the interaction between them. Autonomous vehicles (AVs) promise to improve the safety and efficiency of road networks. However, they will face the same problems as human-driven vehicles with pedestrian avoidance. Thus, this study estimated the capacity of the left-turn lane, in Japan, under AV mixed flows taking into account AV penetration rates, pedestrian flow rates, and crosswalk length. The impact of AVs on capacity was analyzed with different settings for the critical gap between vehicles and pedestrians. It was found that if AVs comply perfectly with traffic law, the capacity of the left-turn lane sharply decreases, especially in the case of long crosswalks.

DOI： 10.1016/j.eastsj.2022.100070

Scopus

Language：Japanese   Publisher：Japan Society of Traffic Engineers  

DOI： 10.14954/jsteproceeding.42.0_455

CiNii Research

Publisher：Accident Analysis and Prevention  

A critical safety problem in road networks is the conflicts on unsignalized crosswalks. Thus, a proactive approach to assess pedestrian safety performance is required. Simulating the microscopic road user behavior in a virtual platform is one of the typical approaches. However, current simulation tools are not flexible enough to properly reproduce various behaviors of pedestrians and drivers considering their interactions with the road environment and other road users. Therefore, the objective of this paper is to propose a novel agent-based framework for evaluating pedestrian safety at unsignalized crosswalks. Unsignalized mid-block crosswalks with refuge islands (UMCR) are considered as an example facility to implement the proposed framework, where relevant behavioral elements such as the reaction time, visual field with obstacles, and minimum safety margin time are addressed. Not only the pedestrian-vehicle interaction is modeled but also the vehicle-vehicle interaction is considered. Empirical validation on a UMCR shows that the proposed framework can reproduce reliable distributions of the post encroachment time compared to the observed distributions within an acceptable error range. The sensitivity analysis reveals that the high reaction time of drivers, small safety margin time, and visual obstacles near crosswalks increase the probability of serious conflicts. The results also show that the framework can reproduce traffic crashes under assumed extreme road conditions.

DOI： 10.1016/j.aap.2021.106288

Web of Science

Scopus

Publisher：Asian Transport Studies  

Turbo roundabouts have been a popular choice of road intersections in the European countries in recent years, since they have better operational and safety performance than conventional roundabouts. To serve the heavy traffic demands, signal controls can be implemented on turbo roundabouts. The objective of this study is to clarify the specific traffic conditions, under which signalized turbo roundabouts are selected to install compared with signalized intersections. The twice-stop-right-turn control method is used for turbo roundabouts under the left-hand driving system. A signal control optimization model for turbo roundabouts is developed. Sensitivity analysis is made to capture the influence of entry volume and the right-turn movement ratio on capacity and average delay. Furthermore, the trend of the capacity of roundabouts with the radius of the central island is studied. It is found that under heavy balanced entry volumes, signalized turbo roundabouts have better operational performance than signalized intersections.

DOI： 10.1016/j.eastsj.2021.100033

Scopus

Language：English   Publisher：Japan Society of Civil Engineers  

<p>Crossing pedestrians is one of the critical factors in proper estimation of turning vehicle capacities at signalized intersections. Although individual pedestrian walking speeds and consequent pedestrian platoon maneuver are influenced by traffic signal settings, crosswalk length and bidirectional interactions of pedestrian flows, the existing capacity estimation methods of left-turning vehicles did not consider these impacts. This study aims to propose a method to estimate the expected pedestrian presence-time that pedestrian platoon occupies the conflict-area, considering the characteristics of pedestrian platoon maneuvers. Referring to the existing method to estimate time-dependent pedestrian presence probability distributions, this study re-estimated the parameters of the model using the additional database with higher pedestrian demand conditions. The model revealed that the increase of opposing pedestrian flow significantly reduces spatial variation. This model was applied to calculate expected pedestri</p>

DOI： 10.2208/jscejipm.76.5_i_1485

CiNii Research

Publisher：Arabian Journal for Science and Engineering  

DOI： 10.1007/s13369-020-04810-1

Web of Science

Scopus

Language：English   Publisher：Japan Society of Civil Engineers  

<p>Entry capacity is one of the most important indexes to evaluate the roundabout operational performance. Both the geometric elements and vehicle types have an impact on the entry capacity. Passenger Car Equivalent (PCE) for heavy vehicles is utilized for roundabout entry capacity estimation. In the Japanese Roundabout Manual (JRM), PCE is proposed as a constant value. However, it cannot reflect that the capacity of roundabouts varies with different geometric elements and heavy vehicle percentages. Therefore, the objective of this study is to estimate the PCE for heavy vehicles depending on various geometric elements. Entry capacity and PCE were estimated by the entry capacity equation in JRM and traffic simulator VISSIM, respectively. The results revealed that the entry capacity changes with different geometric elements and is significantly related to inscribed circle diameter. It was also concluded that PCE changes with increasing heavy vehicle percentages in the entering and circulating flows.</p>

DOI： 10.2208/jscejipm.75.i_1167

CiNii Research

Publishing type：Research paper (international conference proceedings)   Publisher：Transportation Research Part A: Policy and Practice  

The selection of proper control types at intersections at the planning stage is an important concern considering the difficulty in comparing the performance of different control types. Therefore, several manuals proposed selection charts to guide traffic engineers in identifying the control strategy that yields to the lowest delay and the highest level of service. However, most of these methodologies consider only total major and minor street traffic flows. They do not necessarily suggest to investigate the impact of turning traffic and pedestrian flows, which limits the applicability of their recommendations. Thus, this study aims to propose a procedure to assess the selection of the optimum control strategies among two-way stop, roundabout and signalization using average intersection vehicle delay as the evaluation criterion. The impact of turning traffic on the major and minor streets as well as the impact of pedestrians are integrated into the developed analytical methodology for the estimation of average intersection vehicle delay. A typical layout of isolated four-leg two-way intersection is assumed for the model development. It is concluded that turning traffic and pedestrians play essential roles in the performance of intersections. As pedestrian flow increases, signal control becomes prevailing over the other control types.

DOI： 10.1016/j.tra.2018.08.039

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publisher：Japan Society of Civil Engineers  

Entry capacity of roundabouts should be confirmed when considering their introduction. However, since there are still few roundabouts in Japan, the impact of roundabout geometry on entry capacity is still unclear. In addition, although the roundabout entry capacity in Japan is calculated based on the gap acceptance theory, the impact of roundabout geometry on the necessary gap parameters has not been clarified. Therefore, in this study the impact of roundabout geometry on entry capacity of roundabouts was analyzed using empirical data from Japan, and an estimation model of the gap parameters using geometry and traffic conditions as explanatory variables was proposed. Based on this, the influence of roundabout geometry on entry capacity was quantitatively clarified.

DOI： 10.2208/jscejipm.74.i_1399

CiNii Research

Language：English   Publishing type：Research paper (other academic)  

CiNii Books

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Traffic Engineers  

One of the measures to inhibit conflicts between pedestrian and left-turning vehicle at crosswalk of signalized intersections is, to provide separate phases for pedestrian and turning vehicle, such as exclusive pedestrian phase or Leading Pedestrian Interval (LPI). LPI is the phase which pedestrian green is displayed a few seconds ahead of vehicle green phase, and in this preceding time interval, a part of pedestrians can be protected from the conflicting left-turning vehicles. From the viewpoint of safety and mobility performance, LPI can be positioned between the conventional four-phase type in which the concurrent pedestrians and vehicles share the same signal phase and the exclusive pedestrian phase type. However, the safety and mobility performance of these three types of signal phasing is unclear. Thus, this study investigates and compares delays of pedestrian and vehicle, degree of saturation, capacity and pedestrian exposure time under those three types of signal phase types. Then an application range of LPI and the boundary condition of exclusive pedestrian phase are discussed.

DOI： 10.14954/jste.3.5_11

CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)  

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.8

Language：Japanese   Presentation type：Oral presentation (general)