Faculty Profiles - NAKAMURA, Hideki

Papers - NAKAMURA, Hideki

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Modelling discharge flows at signalised intersections with adjustment of downstream effects

Zhu H., Nakamura H.

TRANSPORTMETRICA A-TRANSPORT SCIENCE 2021.3

Language：Japanese Publisher：Transportmetrica A: Transport Science

Former studies revealed that before spillbacks happen intersection capacities can still be greatly affected by downstream queues and signals. However, there is no methodology reasonably accounting for this effect. This research aims to propose adjustment factor models (Adj models) for both saturation flow rate (SFR) and start-up lost time (SLT) in through lane groups considering downstream conditions. An improved cell transmission model is created to build a simulation platform that can well reproduce the downstream influence. By the experimental data, Adj models are derived through heuristic optimisation based regression analyses. Proposed adjustment factors are governed by common traffic indicators. Sensitivity analyses proved that approaches with high volumes, short segment lengths, large green ratios, positive offset, or large cycle lengths are more easily affected by downstream conditions. Through the validation, it is proved that the estimation error of SFR and SLT can be significantly reduced by the proposed adjustment factors.

DOI： 10.1080/23249935.2021.1895360

Web of Science

Scopus

Investigating the Efficiency and Safety of Signalized Intersections Under Mixed Flow Conditions of Autonomous and Human-Driven Vehicles

Pan Ang, Zhang Xin, Nakamura Hideki, Alhajyaseen Wael

ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING Vol. 45 ( 10 ) page： 8607 - 8618 2020.10

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Arabian Journal for Science and Engineering

Field experiments of autonomous driving systems have already been started in several countries around the world. However, investigations on the performance of signalized intersections under the mixed flow condition of autonomous vehicle (AV) and human-driven vehicle (HDV) are still very limited, especially in terms of considering the interaction between vehicles. This study aims at developing a methodology to evaluate the efficiency and safety performance of signalized intersections under the conditions of AV mixed flows. If AVs are set aggressively such as small critical gap acceptance thresholds, approach capacity of signalized intersections may increase. However, the aggressive driving maneuver and the misjudgment by human drivers to AV may lead to some potential safety risks. On the other hand, if AVs are set conservatively to ensure large safety margins, for example by setting large critical gap thresholds or a longer following headway, a significant drop in the capacity is expected while the safety improvements may not be insured since extra delays will be imposed on HDVs which may induce risky behavior. This study finds that AVs with either excessively aggressive or conservative settings will lead to waste of capacity or potential safety hazard. AVs with aggressive settings will enable them to accept a short gap or lag, while AVs with conservative settings will increase the waiting time of the following HDVs, which may induce aggressive driving behavior. Both types of AV settings may contribute to safety risks represented by short time-to-collision and short post encroachment time.

DOI： 10.1007/s13369-020-04810-1

Web of Science

Scopus

Initial comparative analysis of international practice in road traffic signal control

Tang K.

Global Practices on Road Traffic Signal Control: Fixed-Time Control at Isolated Intersections page： 285 - 310 2019.1

Japan

Nakamura H.

Global Practices on Road Traffic Signal Control: Fixed-Time Control at Isolated Intersections page： 163 - 184 2019.1

Principles of road traffic signal control

Boltze M.

Global Practices on Road Traffic Signal Control: Fixed-Time Control at Isolated Intersections page： 7 - 17 2019.1

An Analysis of Heavy Vehicle Impact on Roundabout Entry Capacity in Japan

Kang Nan, Nakamura Hideki

INTERNATIONAL SYMPOSIUM ON ENHANCING HIGHWAY PERFORMANCE (ISEHP), (7TH INTERNATIONAL SYMPOSIUM ON HIGHWAY CAPACITY AND QUALITY OF SERVICE, 3RD INTERNATIONAL SYMPOSIUM ON FREEWAY AND TOLLWAY OPERATIONS) Vol. 15 page： 308 - 318 2016

Language：Japanese Publisher：Transportation Research Procedia

Impact of heavy vehicles on roundabout entry capacity is generally considered through a heavy vehicle adjustment factor fHV which is calculated by heavy vehicle percentage and passenger car equivalent (PCE hereafter) value. The PCE value of trucks is generally set as 2.0 and estimated based on several considerations such as entry capacity and move-up time. All of these considerations are influenced by local driver behavior and geometry conditions. Thus, this paper aims to estimate entry capacity considering the characteristics of heavy vehicle behavior in Japan by microscopic simulation. Then based on the simulation results, the PCE value is also examined. Through the simulation study it is found that entry capacity is reduced when heavy vehicle percentage increases. Moreover, estimated PCE results show that the PCE value of entry flow increases when circulating flow increases but decreases when circulating flow is in high level. Also it is found that PCE of entry flow is lower than that of circulating flow which has priority at roundabouts.

DOI： 10.1016/j.trpro.2016.06.026

Web of Science

Scopus

Functionally Hierarchical Road Classification Considering the Area Characteristics for the Performance-oriented Road Planning

Goto Azusa, Nakamura Hideki

Language：Japanese Publisher：Transportation Research Procedia

This study aims to find out the necessary target travel speeds of roads in functionally hierarchical network which can achieve the target travel times for connecting centers with five different functions, considering the distribution of centers in the subjective area. In this paper, hierarchical road classification scenarios which consists of target travel speeds and road spacings are developed for differentiating road functions. Then travel times under the certain scenario are numerically calculated by an approximate method. Here, the calculation is based on a combination of hypothetical grid network and the actual motorway network. Finally, an application study of Tokaido region in Japan and southwest region in Germany demonstrated the impact of hierarchical road classification scenario on the achievement of the target travel time between centers in different categories.

DOI： 10.1016/j.trpro.2016.06.061

Web of Science

Scopus

An Estimation Method of Roundabout Entry Capacity Considering Pedestrian Impact

Kang Nan, Nakamura Hideki

9TH INTERNATIONAL CONFERENCE ON TRAFFIC AND TRANSPORTATION STUDIES (ICTTS 2014) Vol. 138 page： 460 - 469 2014

A Modified Social Force Model for Pedestrian Behavior Simulation at Signalized Crosswalks

Zeng Weiliang, Nakamura Hideki, Chen Peng

9TH INTERNATIONAL CONFERENCE ON TRAFFIC AND TRANSPORTATION STUDIES (ICTTS 2014) Vol. 138 page： 521 - 530 2014

Lane Utilization Analysis of Shared Left-turn Lane Based on Saturation Flow Rate Modeling

Chen Peng, Nakamura Hideki, Asano Miho

8TH INTERNATIONAL CONFERENCE ON TRAFFIC AND TRANSPORTATION STUDIES (ICTTS) Vol. 43 page： 178 - 191 2012

A method for evaluating the functional hierarchy of road networks Open Access

Sekihara T., Kakimoto Y., Nakamura H., Iryo M., Zhang X.

Transport Policy Vol. 155 page： 178 - 188 2024.9

Publisher：Transport Policy

In Japan, the mobility functions of principal arterial roads are hindered by lined-up roadside facilities and densely located signalized intersections. As one of the solutions, it is necessary to consider a functional hierarchy of road networks, based on the structure and traffic operations of each road. The purpose of this study was to propose an index to evaluate the degree to which the road network could be used hierarchically according to their mobility function, based on the location of the bases and the location of roads at each level of the hierarchy, and to propose a method to evaluate the road network using this index. To accomplish this, we proposed a four-level method for the evaluation of the functional hierarchy of road networks based on the derived index values. As a case study, we calculated the degree of hierarchy for the road networks in northern Mie and western Shizuoka. The results showed that the current evaluations of the functional hierarchy in these regions were low, and that introducing mid-level roads was necessary to improve the current situation. The evaluation method proposed in this study will enable us to examine the ideal network configuration for each road in the region to exhibit its mobility function as a preliminary step to studying solutions to various road network issues, such as ensuring the smooth movement between bases and safety. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the World Conference on Transport Research – WCTR 2023.

DOI： 10.1016/j.tranpol.2024.06.012

Open Access

Scopus

Contribution of the IATSS research projects to disseminating modern roundabouts in Japan Open Access

Nakamura H.

IATSS Research Vol. 48 ( 2 ) page： 189 - 199 2024.7

Publisher：IATSS Research

Until early 2000s, modern roundabouts (RABs) were poorly understood in Japan and were not fully recognized as a form of at-grade intersections. The RAB research projects of the International Association of Traffic and Safety Sciences (IATSS), which began in 2009, started with examining the applicability of RABs in Japan and have steadily progressed to various stages of field experiments, social implementation, and dissemination promotion activities. These RAB research projects, which lasted for approximately seven years, are considered to have played a significant role in the practical application of RAB in Japan. This paper provides a chronological overview of the history, content, and development status of these projects and records and discusses the role that IATSS research projects played in the early days of RABs in Japan.

DOI： 10.1016/j.iatssr.2024.02.006

Open Access

Scopus

An international Comparative Analysis of off-peak travel speeds on arterial roads

INAMOTO Yuichi, ZHANG Xin, NAKAMURA Hideki

JSTE Journal of Traffic Engineering Vol. 10 ( 2 ) page： 1 - 9 2024.4

Language：Japanese Publisher：Japan Society of Traffic Engineers

Although the road network in Japan has been almost completed in recent years, travel speeds are said to be on a low level compared to other countries. It is important to compare travel speeds in Japan and abroad when the influence of traffic volume is negligibly small, and to clarify road structures and traffic operations that result in the differences in travel speeds. Recently, it is getting possible to easily grasp travel speeds and road structures around the world through the collection and publication of location information and aerial photographs by Google Maps. The objective of this paper is to compare the off-peak travel speeds in Japan, the U.S., and Germany using Google Maps, and to analyze the factors that contribute to the differences. It was revealed that the travel speeds in Japan are lower than those in the U.S. and Germany, and that the differences in the density of signalized intersections and the speed limit settings are significant factors to them.

DOI： 10.14954/jste.10.2_1

CiNii Research

Left-Turn Lane Capacity Estimation based on the Vehicle Yielding Maneuver Model to Pedestrians at Signalized Intersections Open Access

Wang Y., Zhang X., Nakamura H.

Sustainability (Switzerland) Vol. 16 ( 6 ) 2024.3

Publisher：Sustainability (Switzerland)

Crossing pedestrians may significantly affect the capacity of the left-turn (LT) lane at signalized intersections while sharing the same signal phase in the left-hand traffic system, the quantitative estimation method is still not intensively discussed when considering the vehicle yielding maneuver. Despite the Road Traffic Act in Japan mandating vehicles to yield to pedestrians, instances of vehicles crossing in front of pedestrians are frequent. This study aims to refine the evaluation of LT lane capacity by introducing a novel vehicle yielding maneuver model, considering factors such as pedestrian numbers, crosswalk length, and signal timing. The model, developed using data from various Japanese crosswalks, is subjected to Monte Carlo simulation for validation. Comparative analysis with existing methods in Japanese and U.S. manuals, along with observed data, highlights the effectiveness of our model. This innovative approach has the potential to mitigate vehicle–pedestrian conflicts and reduce air pollution. By incorporating techniques such as signal optimization and two-stage crossing, our model contributes to sustainability while maintaining efficient traffic flow.

DOI： 10.3390/su16062313

Open Access

Scopus

A Method for Evaluating the Functional Hierarchy of Road Networks by using Road Use Characteristic Indices

SEKIHARA Toshihiro, KAKIMOTO Yuji, NAKAMURA Hideki, IRYO Miho, ZHANG Xin

JSTE Journal of Traffic Engineering Vol. 9 ( 2 ) page： A_69 - A_78 2023.2

Language：Japanese Publisher：Japan Society of Traffic Engineers

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.

DOI： 10.14954/jste.9.2_a_69

CiNii Research

Analysis of the Relationship between the Functionally Hierarchical Characteristics of Road Networks and Road Structure Conditions

TOMINAGA Masahiro, KAKIMOTO Yuji, NAKAMURA Hideki, SEKIHARA Toshihiro

JSTE Journal of Traffic Engineering Vol. 9 ( 2 ) page： A_35 - A_43 2023.2

Language：Japanese Publisher：Japan Society of Traffic Engineers

The road network in Japan has been steadily developed until today, however, some issues are remaining such as low travel speeds on main roads and through-passing traffics into minor streets in residential areas. This is considered because of insufficient consideration of the hierarchical function of each road at the planning stage. For this reason, it is necessary to reconsider the road network from the functional hierarchy perspective of whether each road is hierarchically being used according to its target function. Therefore, the objective of this study is to clarify influencing factors of the functional hierarchy based on questionnaire surveys for experts in road design and planning. As a result, it was found that road conditions such as the trip length and the travel speed affect the functional hierarchy, and the combination of them is necessary for proper evaluation of the functional hierarchy.

DOI： 10.14954/jste.9.2_a_35

CiNii Research

Analysis of factors affecting differences in off-peak travel speeds on arterial roads in Japan and abroad

INAMOTO Yuichi, ZHANG Xin, NAKAMURA Hideki

Proceedings of the Conference of Japan Society of Traffic Engineers Vol. 43 ( 0 ) page： 403 - 410 2023

Defensive or competitive Autonomous Vehicles: Which one interacts safely and efficiently with pedestrians?

Zhu H., Alhajyaseen W., Iryo-Asano M., Nakamura H., Dias C.

Physica A: Statistical Mechanics and its Applications Vol. 606 2022.11

Publisher：Physica A: Statistical Mechanics and its Applications

The emergence of Autonomous Vehicles (AVs) could provoke unexpected challenges in urban traffic environments. One such crucial challenge is the conflicts between pedestrians and AVs, particularly on unsignalized mid-block crosswalks (UMC), where pedestrians are exposed to the AV flow. This study investigates the efficiency and safety performance of a UMC in the presence of both AVs and pedestrians considering the diversities in their behaviors. Through empirical analyses, two pedestrians’ crossing decision models are built and four groups of speed profiles are classified. Meanwhile, based on previous literature, defensive and competitive driving strategies are assumed for AVs. The simulation is implemented on an agent-based framework that can dynamically reproduce the kinematic interactions between pedestrians and vehicles. Results indicated that with a reasonable safety margin (2.5 s), percentages of low post encroachment time events for competitive AVs with different pedestrian types are smaller than defensive AVs with differences of 0.2% to 2.9%. The average delays of competitive AVs for all pedestrian types are smaller than defensive AVs with a maximum estimated difference of 39 s. Moreover, the analysis showed that lowering the speed limit may reduce the crash rate of competitive AV up to 0%. It is also found that the pedestrians who make reckless crossing decisions and change their speed drastically during the crossing process are more likely to incur crashes with competitive AVs. Therefore, if pedestrian behaviors can be regulated reasonably, competitive AVs with appropriate parameter settings are most suitable for UMC in the future.

DOI： 10.1016/j.physa.2022.128083

Web of Science

Scopus

Can automated driving prevent crashes with distracted Pedestrians? An exploration of motion planning at unsignalized Mid-block crosswalks

Zhu H., Han T., Alhajyaseen W.K.M., Iryo-Asano M., Nakamura H.

Accident Analysis and Prevention Vol. 173 page： 106711 2022.8

Language：English Publisher：Accident Analysis and Prevention

Pedestrian distraction may provoke severe difficulties in automated vehicle (AV) control, which may significantly affect the safety performance of AVs, especially at unsignalized mid-block crosswalks (UMCs). However, there is no available motion-planning model for AVs that considers the effect of pedestrian distraction on UMCs. This study aims to explore innovative approaches for safe and reasonable automated driving in response to distracted pedestrians with various speed profiles at UMCs. Based on two common model design concepts, two new models are established for AVs: a rule-based model that solves motion plans through a fixed calculation procedure incorporating several optimization models, and a learning-based model that replaces the deterministic optimization process with policy-gradient reinforcement learning. The developed models were assessed through simulation experiments in which pedestrian speed profiles were defined using empirical data from field surveys. The results reveal that the learning-based model has outstanding safety performance, whereas the rule-based model leads to remarkable safety problems. For distracted pedestrians with significant crossing-speed changes, rule-based AVs lead to a 5.1% probability of serious conflict and a 1.4% crash probability. The learning-based model is oversensitive to risk and always induces high braking rates, which results in unnecessary efficiency loss. To overcome this, a hybrid model based on the learning-based model was developed, which introduces a rule-based acceleration value to regularize the action space of the proposed learning-based model. The results indicate that the hybrid approach outperforms the other two models in preventing crash hazards from distracted pedestrians by employing appropriate braking behaviors. The high safety performance of the hybrid models can be attributed to the spontaneous slowing down of the vehicle that initiates before detecting pedestrians on UMCs. Although such a cautious driving pattern leads to extra delay, the time cost of the hybrid model is acceptable considering the significant improvements in ensuring pedestrian safety.

DOI： 10.1016/j.aap.2022.106711

Web of Science

Scopus

PubMed

Investigating driver reactions to movements of autonomous vehicle in permitted right turn through driving simulator experiments

Zhu H., Zhu S., Iryo-Asano M., Nakamura H.

Transportation Research Part F: Traffic Psychology and Behaviour Vol. 89 page： 385 - 398 2022.8

Publisher：Transportation Research Part F: Traffic Psychology and Behaviour

Traffic safety has always been a hot topic for human-driven (HDV) and autonomous vehicles (AV) mixed flow. The conflict between permitted right-turn vehicles (PRT) and opposing through vehicles (TH) at signalized intersections (left-handed traffic) is extraordinarily critical. AVs with aggressive behaviors are able to accept short gap time without losing safety. However, such a turning maneuver may lead to dangerous feelings and cause unexpected reactions of approaching drivers. This study aims to investigate and model drivers’ reactions in TH movements to PRT AVs considering the trust degree of drivers to AVs. Questionnaire surveys and driving simulator experiments were conducted for 41 participants. Results reveal that the right turn timing of PRT AV will significantly influence drivers’ reactions. Basically, TH drivers will brake with a high probability under the situation of small expected post encroachment time (PET). It is also found that female drivers and drivers with low trust in AVs are more vigilant to PRT AVs than other drivers. Based on this finding a two-layer model for reproducing TH drivers’ reactions to PRT AVs is proposed. The first layer is to determine the braking decision and the second layer is to calculate the parameters of braking behaviors (brake lag, braking time, and speed drop). The significance and coefficients variables in these models proved that the trust in AV will influence drivers’ decisions and braking behaviors (brake lag and braking time). The more the drivers trust AVs, the smaller the expected PET to AVs they can accept for passing without braking, and the more gently they will brake (longer brake lag and shorter braking time) due to the cutting in of PRT AVs. This effect will become significant after drivers have experienced several interactions with AVs.

DOI： 10.1016/j.trf.2022.06.018

Web of Science

Scopus

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Papers - NAKAMURA, Hideki