Faculty Profiles - NAKAMURA, Hideki

Passenger Car Equivalent of Heavy Vehicles for Roundabout Entry Capacity Estimation Reviewed

GOTO Azusa, KANG Nan, NAKAMURA Hideki, MASHIMA Kiminori

JSTE Journal of Traffic Engineering Vol. 2 ( 6 ) page： 11 - 19 2016

Language：Japanese Publisher：Japan Society of Traffic Engineers

As implementation of roundabouts is being discussed at more numbers of places after the partial revision of Road Traffic Law in 2014, quantifying the impact of heavy vehicles on entry capacity is an important and urgent task in Japan. The objective of this study is to estimate passenger car equivalent (PCE) of heavy vehicles at roundabouts in Japan. Since the number of actual roundabouts is still limited, this study adopts a microscopic traffic simulator for obtaining entry capacity under various heavy vehicle percentages in either entry or circulating flow. Then, passenger car equivalents at entry and circulatory roadway are derived based on the simulated capacities. As a result, it is found that the estimated passenger car equivalent is higher at entry than at circulatory roadway. At the end, entry capacity with heavy vehicles in both entry and circulating flows simultaneously is reasonably calculated by using the estimated passenger car equivalents.

DOI： 10.14954/jste.2.6_11

A STUDY ON COMPOSITION OF FUNCTIONALLY HIERARCHICAL ROAD NETWORK WHICH CONSIDERS TRAVEL PERFORMANCE BETWEEN CENTERS

GOTO Azusa, NAKAMURA Hideki

Journal of Japan Society of Civil Engineers, Ser. D3 (Infrastructure Planning and Management) Vol. 72 ( 5 ) page： I_939 - I_954 2016

Language：Japanese Publisher：Japan Society of Civil Engineers

In Japan, reorganization of road network into functionally hierarchical form becomes more important so as to efficiently improve travel performance between centers where daily-life and/or urban services are provided. This study aims at investigating the appropriate composition of a functionally hierarchical road network which can achieve the target travel times set for various connections of centers in the subjective region. Here, composition is defined as a combination of the number of hierarchical road levels, target travel speed, road spacing and access spacing of each road level. In this paper, alternatives of such a composition are derived by considering the impact of road crossings as well as roadside access. At the end, a case study is conducted in Tokaido region, Japan, and travel performance indices, namely travel time and average travel speed, between various types of centers are estimated under each alternative composition of a functionally hierarchical road network. The result shows that road level with higher travel speed (i.e., 50~60km/h) can significantly work especially for the communities in peninsula and mountainous rural area by enhancing the accessibility to urban centers.

DOI： 10.2208/jscejipm.72.i_939

Gap acceptance analysis of right-turn vehicles considering positions of opposing through vehicles

WATANABE Kazuki, Nakamura Hideki

JSTE Journal of Traffic Engineering Vol. 2 ( 2 ) page： A_85 - A_91 2016

Language：Japanese Publisher：Japan Society of Traffic Engineers

The gap acceptance behavior to the opposing through traffic of “permitted” right-turn vehicles is one of the important events for evaluating the safety of signalized intersections. In this study, a decision-making process of gap acceptance was carefully investigated through paying attention to a difference by the number of opposing approach lanes. Moreover, a gap acceptance model of permitted right-turn vehicles at the multilane signalized intersection was developed considering arriving vehicles’ positions in the multiple opposing approach lanes by using binomial logit model. The model estimation result quantitatively showed that the gap acceptance decision is being influenced not only by gap times and arrival through vehicle speeds but also by their driving positions at the intersection approach lane. Furthermore, the calculation result of the critical gap time suggested that it varies depending on the positions of opposing through vehicles in the multilane intersection comparing to the case of single opposing lane intersection.

DOI： 10.14954/jste.2.2_a_85

Modeling pedestrian density distribution on crosswalk of signalized intersections and its application for setting Leading Pedestrian Interval (LPI)

ZHANG Xin, NAKAMURA Hideki

JSTE Journal of Traffic Engineering Vol. 2 ( 2 ) page： A_183 - A_192 2016

Language：Japanese Publisher：Japan Society of Traffic Engineers

Timing of pedestrian phase plays an important role in the safety and mobility performance at signalized intersections. In order to evaluate the performance, it is useful to understand effects of crosswalk length and signal timing on pedestrian presence position and timing. This study investigates the effects of elapsed pedestrian green time, waiting time, crosswalk length and pedestrian volume on the spatiotemporal probability of pedestrian presence and models its distributions considering these influencing factors. It was found that pedestrian presence probability distributions shift to the moving direction as pedestrians proceed. The shorter pedestrian waiting time and longer crosswalk length lead to the wider distribution of pedestrian presence probability. In addition, application of the pedestrian presence probability model for setting Leading Pedestrian Interval (LPI) is discussed. Possible ranges of LPI are investigated dependent on crosswalk length, vehicle flow rate and ratio of pedestrian having passed the conflict area according to pedestrian directional rate.

DOI： 10.14954/jste.2.2_a_183

QUANTITATIVE ANALYSIS ON RISK FACTORS FOR ROAD TRAFFIC ACCIDENTS CONSIDERING GEOMETRIC FEATURES OF INTERSECTIONS

SHIOMI Yasuhiro, WATANABE Kazuki, NAKAMURA Hideki, AKAHANE Hirokazu

Journal of Japan Society of Civil Engineers, Ser. D3 (Infrastructure Planning and Management) Vol. 72 ( 4 ) page： 368 - 379 2016

Language：Japanese Publisher：Japan Society of Civil Engineers

More than half of traffic accidents on arterial road networks occur at intersections. To enhance traffic safety, it is essential to identify the risk factors with qualitative manner, and to reform the configuration of intersections and improve the traffic management for removing the risk factors. In this study, first we collected the data of intersection geometric attributes and lane configurations by using virtual database (cf. Google Earth and Google Street View), which was integrated with the data of traffic accidents, road networks, and traffic volume. Then, Poisson regression models were applied to statistically identify the risk factors on categorized traffic accidents. Finally, the expected number of reduction of traffic accidents are estimated based on the regression models when the reformations are applied to the intersections in Kagawa. As a result, those findings are obtained; (i) the geometric attributes of intersections are significantly varied among prefectures (Kagawa, Shiga, and Aichi), which can be considered as regional characteristics; (ii) as the size of intersections becomes large, the risk of traffic accidents becomes worse, which implies that downsizing of intersection may contribute to improve the traffic safety; (iii) according to the proposed reforming scenario for intersections in Kagawa, there is a potential that the total number of traffic accidents could be reduced by more than 35%.

DOI： 10.2208/jscejipm.72.368

Analysis and Modeling of Pedestrian Crossing Behavior During the Pedestrian Flashing Green Interval

交差点の安全対策としてのラウンドアバウト

中村英樹

自動車技術 Vol. 70-3 page： 74 - 78 2016

Iryo-Asano, M; Alhajyaseen, WKM; Nakamura, H

IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS Vol. 16 ( 2 ) page： 958 - 969 2015.4

Language：Japanese Publisher：IEEE Transactions on Intelligent Transportation Systems

Pedestrian-vehicle conflicts are considered one of the most common safety problems at signalized intersections. In Japan, the pedestrian flashing green (PFG) is considered a safe time interval for pedestrians at crosswalks to finish crossing before conflicting vehicle streams are released. In most common phasing schemes, pedestrians have the right-of-way along with left-turning vehicles (in left-hand traffic). By law, pedestrians should not enter a crosswalk during the PFG. However, many of them rush into crosswalks without necessarily heeding approaching turning vehicles, which could increase the probability of severe conflicts. The objective of this paper is to analyze and model the probabilistic behavior of pedestrians after the onset of the PFG, which contains the pedestrians' decision of whether to give up crossing, as well as the pedestrian speed distribution. Empirical data analysis showed that longer crosswalks lead to significantly higher pedestrian stop probabilities. Furthermore, there is a significant difference between the pedestrians' speeds in the first and second halves of crosswalks. The results of a Monte Carlo simulation showed that the estimated models closely represent the overall stochastic behavior of the pedestrians from the onset of the PFG until the completion of crossing.

DOI： 10.1109/TITS.2014.2346154

Esimation of Roundabout Entry Capacity That Considers Conflict with Pedestrians

Kang, N; Nakamura, H

TRANSPORTATION RESEARCH RECORD Vol. 2517 ( 2517 ) page： 61 - 70 2015

Language：Japanese Publisher：Transportation Research Record

At roundabouts, the main streams that conflict with entry flow and have a significant effect on entry capacity are circulating flow and pedestrian flow. Pedestrian impact is estimated with an adjustment factor ( fped) in existing methods that were developed under standard roundabout designs, such as a physical splitter island at entry and exit. However, available space may limit these geometric designs in some locations (e.g., in Japan), and, as a result, the impact of driver and pedestrian behaviors on entry capacity probably changes. In a microscopic approach, entry vehicles cross pedestrian flow through available pedestrian gaps. Therefore, gap acceptance behavior is used to reproduce conflict with pedestrians. This analysis aimed to estimate roundabout entry capacity that considers conflict with pedestrians by gap acceptance behavior as well as several influencing factors, including presence or absence of a physical splitter island and the farside pedestrian yield rate (i.e., number of drivers yielding to the total farside pedestrian demand). Entry capacity was estimated two ways, with simulation analysis and a theoretical model. The estimated entry capacity results from the two approaches were compared, and the limitations of each approach were interpreted. Results from the two proposed approaches also were compared with those from the existing fped model that was applied in Highway Capacity Manual 2010 (referred to as HCM fped). Findings imply that HCM fped is not appropriate for Japanese situations. Both proposed approaches are expected to be used in the planning and design stages for roundabout implementation not only in Japan but also in other countries that must consider space limitations and pedestrians.

DOI： 10.3141/2517-07

Modeling Pedestrian Presence Probability on Signalized Crosswalks for the Safety Assessment Considering Crosswalk Length and Signal Timing

ZHANG Xin, NAKAMURA Hideki

Journal of the Eastern Asia Society for Transportation Studies Vol. 11 ( 0 ) page： 1403 - 1415 2015

Language：English Publisher：Eastern Asia Society for Transportation Studies

Quantifying effects of crosswalk length and signal timing on pedestrians' presence position and timing is an important requirement for evaluating the probability of conflict. It can be utilized to provide a rational safety assessment and improve existing operational policies at signalized intersections. This study investigates the effects of crosswalk length and pedestrian green time on the spatiotemporal probability of pedestrian presence. It was found that the longer pedestrian green time and crosswalk length leads to the wider distribution of pedestrian presence probability. In addition, a surrogate safety measure for assessing pedestrian safety is proposed by utilizing the pedestrian presence probability model.

DOI： 10.11175/easts.11.1403

AN ANALYSIS ON ENTRY CAPACITY AND OBSERVED MAXIMUM TRAFFIC FLOWS AT ROUNDABOUTS IN JAPAN

KANBE Nobuto, ODAKA Shinji, KANG Nan, NAKAMURA Hideki, MORITA Hirohisa

Journal of Japan Society of Civil Engineers, Ser. D3 (Infrastructure Planning and Management) Vol. 71 ( 5 ) page： I_1017 - I_1025 2015

Language：Japanese Publisher：Japan Society of Civil Engineers

In recent years, field operational tests and implementation of roundabout are actively promoted at several places in Japan, and roundabout has been legally positioned through the amendment of the Road Traffic Act in June 2013. Entry capacity is one of the most important indices for performance evaluation related to the application of roundabouts. However, a criterion of entry capacity including impacts of pedestrians and cyclists based on the observation has not been available in Japan due to the limited observation examples. This paper aims to analyze characteristics of roundabout entry traffic flows based on the field data observed at several existing and/or experimental roundabouts. Entry capacity observed at Roppontsuji roundabout in Karuizawa Town is also examined and compared with the estimated values by a proposed entry capacity estimation model.

DOI： 10.2208/jscejipm.71.i_1017

A STATISTICAL MODEL ANALYSIS ON TRAFFIC ACCIDENT FACTORS BASED ON ROAD TRAFFIC AND SOCIAL ENVIRONMENTAL CONDITIONS

WATANABE Kazuki, NAKAMURA Hideki

Journal of Japan Society of Civil Engineers, Ser. D3 (Infrastructure Planning and Management) Vol. 71 ( 5 ) page： I_889 - I_901 2015

Language：Japanese Publisher：Japan Society of Civil Engineers

The objective of this study is to clarify a relationship between the road traffic conditions and accident frequency through statistical model analysis towards implementing effective safety measures. A rich accident database was combined with relevant road traffic information by using GIS software, and two different models, i.e. negative binomial regression and multiple regression models were independently applied for estimating accident frequency. As a result, it was found that accident frequency is closely related to average travel speeds and distance between intersections in arterial roads. Regarding non-arterial roads, the result specified different influencing factors by accident type. Furthermore, it suggested a high potential of frequent accident occurrence in non-arterial roads particularly at positions close to the arterial roads with low average travel speed. Finally, the necessity of improving quality of traffic flow and hierarchical road network for road safety was discussed.

DOI： 10.2208/jscejipm.71.i_889

Setting the Target Performance for Functionally Hierarchical Road Network Planning

GOTO Azusa, NAKAMURA Hideki

JSTE Journal of Traffic Engineering Vol. 1 ( 2 ) page： A_107 - A_115 2015

Language：Japanese Publisher：Japan Society of Traffic Engineers

For functionally hierarchical road planning, it is important to set the appropriate target network defined by the number of road levels, road spacing and target travel speed of each road level, considering distribution of urban city centers, target travel time among them and demand characteristics. This study proposes a methodology to determine the variables that define target network based on the percentage of urban centers between which their target travel time is achieved as well as construction cost. In this methodology, target travel speed ratio is assumed to be proportional to road spacing ratio between two connected road levels, and the road levels with the highest or lowest target travel speed needs to be given in advance. These assumptions enable to limit the number of scenarios with realistic combinations of road spacing and target travel speed under the trade-off between mobility and access functions. Finally, a simple case study is conducted with a hypothetical grid network assuming some typical urban center distribution. As a result, the effects of number of road levels and target travel speeds on travel time by trip length and construction cost are demonstrated.

DOI： 10.14954/jste.1.2_a_107

A Study on Roundabout Entry Capacity Model Considering Pedestrians under Japanese Conditions Reviewed

KANG Nan, NAKAMURA Hideki, KANBE Nobuto

JSTE Journal of Traffic Engineering Vol. 1 ( 5 ) page： 19 - 28 2015

Language：Japanese Publisher：Japan Society of Traffic Engineers

The existing methodology for roundabout entry capacity estimation is assuming the standard geometric layout and user behavior in other countries. However in Japan, it is often likely that the physical splitter islands are not implemented mainly due to space limitations, and thus pedestrian behavior and its impacts on entry capacity are different from those in the other countries. In this paper, simulation analyses were carried out with respect to impacts of geometry and user behavior conditions that are typical in Japan on entry capacity, and by using their results a multiple regression model for entry capacity estimation was developed. The model was validated with data observed at Roppontsuji roundabout in Karuizawa, Nagano. It was found that the estimation performance of the proposed model was very satisfactory while the existing methodology overestimates the capacity.

DOI： 10.14954/jste.1.5_19

Application of social force model to pedestrian behavior analysis at signalized crosswalk

Zeng, WL; Chen, P; Nakamura, H; Iryo-Asano, M

TRANSPORTATION RESEARCH PART C-EMERGING TECHNOLOGIES Vol. 40 page： 143 - 159 2014.3

Language：Japanese Publisher：Transportation Research Part C: Emerging Technologies

Limited pedestrian behavior models shed light on the case at signalized crosswalk, where pedestrian behavior is characterized by group or individual evasion with surrounding pedestrians, collision avoidance with conflicting vehicles, and response to signal control and crosswalk boundary. This study fills this gap by developing a microscopic simulation model for pedestrian behavior analysis at signalized intersection. The social force theory has been employed and adjusted for this purpose. The parameters, including measurable and non-measurable ones, are either directly estimated based on observed dataset or indirectly derived by maximum likelihood estimation. Last, the model performance was confirmed in light of individual trajectory comparison between estimation and observation, passing position distribution at several cross-sections, collision avoidance behavior with conflicting vehicles, and lane-formation phenomenon. The simulation results also concluded that the model enables to visually represent pedestrian crossing behavior as in the real world. © 2014 Elsevier Ltd.

DOI： 10.1016/j.trc.2014.01.007

Estimation of Roundabout Entry Capacity Under the Impact of Pedestrians by Applying Microscopic Simulation

Kang, N; Nakamura, H; Asano, M

TRANSPORTATION RESEARCH RECORD Vol. 2461 ( 2461 ) page： 113 - 120 2014

Language：Japanese Publisher：Transportation Research Record

Entry capacity is one of the most important indexes for performance evaluation of roundabouts. In addition to circulating vehicles, pedestrian flow is another key conflicting stream that has a significant impact on entry capacity. Pedestrian impact is considered by an adjustment factor in the Highway Capacity Manual 2010. However, this method is limited in estimating pedestrian impact by several influencing factors [e.g., pedestrian approaching side, farside pedestrian recognition rate (FPRR) of drivers, and physical splitter island] that are considered to be significant for representing the characteristics of the Japanese situation. The impacts of these influencing factors are examined by microscopic simulation in this study. Results from the simulation study showed that under the condition without a physical splitter island, entry capacity was reduced more significantly when more pedestrians were from the farside of the crosswalk, whereas capacity relatively increased with decreasing FPRR. Moreover, entry capacity was also increased after the installation of a physical splitter Island. The significance and the necessity of a physical splitter island were demonstrated in this analysis for roundabout design and operation in Japan. This research also showed that those influencing factors (i.e., pedestrian approaching side, FPRR, and physical splitter island) should be coasidered in entry capacity estimation.

DOI： 10.3141/2461-14

ANALYSIS OF RIGHT-TURN VEHICLE BEHAVIOR IN PROTECTED RIGHTTURN PHASE FOR PLANNING SIGNALIZED INTERSECTION IMPROVEMENT

WATANABE Kazuki, NAKAMURA Hideki, IRYO-ASANO Miho

Journal of Japan Society of Civil Engineers, Ser. D3 (Infrastructure Planning and Management) Vol. 70 ( 5 ) page： I_1013 - I_1022 2014

Language：Japanese Publisher：Japan Society of Civil Engineers

It is of great importance to analyze right-turning behavior at signalized intersection given high accident records related to right-turn vehicles, which also helps provide valuable insights into safety assessment of signalized intersection. This study aims to analyze the right-turn vehicle behavior in protected right-turn phase by considering the influencing factors of geometric characteristics and signal operation. It was found based on empirical modeling results that the right-turn vehicle behavior is closely related to geometric characteristics such as intersection angle and setback distance of stop bar. Furthermore, in order to make a balance of both positive and negative impact, the potential strategies may bring upon safety performance of signalized intersection, all the influencing factors related to right-turn behavior were summarized and evaluated. Finally, the necessity of employing microscopic simulation to enable a comprehensive evaluation of surrogate safety meausure (SSM) at signalized intersection was examined.

DOI： 10.2208/jscejipm.70.i_1013

MODELING PEDESTRIAN SPEED AT SIGNALIZED CROSSWALKS CONSIDERING CROSSWALK LENGTH AND PEDESTRIAN SIGNAL TIMING

ZHANG Xin, NAKAMURA Hideki, IRYO-ASANO Miho, CHEN Peng

Journal of Japan Society of Civil Engineers, Ser. D3 (Infrastructure Planning and Management) Vol. 70 ( 5 ) page： I_1031 - I_1040 2014

Language：Japanese Publisher：Japan Society of Civil Engineers

Quantifying the effects of crosswalk length and signal timing on pedestrian walking speed is an important requirement for providing a rational safety assessment at signalized intersections. This study investigates the effects of pedestrian green time (PG), crosswalk length and pedestrian crossing direction on pedestrian walking speed at signalized crosswalk. It is assumed that the pedestrian walking speeds consist of two components v1 and v2 at two consecutive halves of crosswalk. Empirical analysis shows that the longer crosswalk tends to induce the higher walking speed. Pedestrian walking speed increases as PG proceeds. Furthermore, a comparison of pedestrian speed models for PG and PF (pedestrian flashing green time) demonstrates that pedestrian walking speeds at PF are higher and more variable than at PG. The sensitivity analysis helps understand how these models behave depending on change of each variable.

DOI： 10.2208/jscejipm.70.i_1031

Application of surrogate safety measures for assessment of pedestrian versus left-turning vehicle conflict at signalized crosswalks

横断歩行者を考慮したラウンドアバウト流入交通容量のシミュレーション分析 Reviewed

中村英樹

国際交通安全学会誌IATSS Review Vol. 39-1 page： 56 - 64 2014

Chen P., Nakamura H., Asano M.

Advances in Transportation Studies Vol. 1 ( SPECIAL ISSUE ) page： 37 - 50 2014

Publisher：Advances in Transportation Studies

Pedestrian safety improvement at signalized intersections remains a critical issue. The major threat comes from frequent interaction with turning vehicles, especially left-turners (left-hand traffic system). This study gains insights into how surrogate safety measure (SSM) can be utilized for pedestrian versus left-turning vehicle conflict assessment, and although a small step, how to relate SSM to limited crash records for crash risk estimation. Based on the video data collected at several crosswalks in Nagoya City, Japan, SSMs, i.e., Post Encroachment Time (PET) and vehicle passing speed at conflict point were extracted for analysis. PETs were estimated for both near-side and far-side approaching pedestrians by identifying the potential conflict points and considering the physical size of left-turning vehicles. The effectiveness of SSMs to reflect the impact of site-specific geometric characteristics and operational conditions upon conflict risk has been demonstrated. Furthermore, crash risk estimation models were developed by using Poisson regression methods based on mean PET, the number of short PETs per hour and average vehicle passing speed at conflict point at each crosswalk. It demonstrates that high turning speed, in conjunction with higher frequency of short PETs result in higher crash rates.

DOI： 10.4399/97888548735445