Different driving decisions will cause different processes of phase transition in traffic Bow. To reveal the inner mechanism, this paper built a new cellular automaton (CA) model, based on the driving decision (DD). I...Different driving decisions will cause different processes of phase transition in traffic Bow. To reveal the inner mechanism, this paper built a new cellular automaton (CA) model, based on the driving decision (DD). In the DD model, a driver's decision is divided into three stages: decision-making, action, and result. The acceleration is taken as a decision variable and three core factors, i.e. distance between adjacent vehicles, their own velocity, and the preceding vehicle's velocity, are considered. Simulation results show that the DD model can simulate the synchronized Bow effectively and describe the phase transition in traffic Bow well. Further analyses illustrate that various density will cause the phase transition and the random probability will impact the process. Compared with the traditional NaSch model, the DD model considered the preceding vehicle's velocity, the deceleration limitation, and a safe distance, so it can depict closer to the driver preferences on pursuing safety, stability and fuel-saving and has strong theoretical innovation for future studies.展开更多
Geomatics is an interdisciplinary subject.Many disciplines have teaching demands in this field.A new course on“Geomatics Technology”has been suggested by the Weiyang College of Tsinghua University of China for the m...Geomatics is an interdisciplinary subject.Many disciplines have teaching demands in this field.A new course on“Geomatics Technology”has been suggested by the Weiyang College of Tsinghua University of China for the major of“Mathematical and Scientific Basic Science+Civil,Hydraulic and Marine Engineering”.This paper offers a data-led geomatics teaching mode,developing a customized teaching cloud platform,to explore the cross-integrated innovative teaching methods.Teachers and students can assign and submit assignments on this platform.The platform constitutes a data flow with the data download,data processing and result sharing.It encourages communication among students in various majors,grades and units using data as the medium,from data processing to application upstream and downstream.In the“Geomatics Technology”course,geospatial data has emerged as a vital element of the multidisciplinary approach.This kind of teaching mode has been used in the postgraduate remote sensing course offered by Tsinghua University’s Department of Civil Engineering and Construction Management.Furthermore,the mode will be used for the first time in the autumn semester of 2022 in the undergraduate teaching of Weiyang College and civil engineering,to offer a novel idea for the reform of courses linked to geospatial informatics.展开更多
Since ramps are an important composition of traffic systems and there often exist multi ramps in a tragic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In ...Since ramps are an important composition of traffic systems and there often exist multi ramps in a tragic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang et al. [2009 Communications in Theoretical Physics 51(1) 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex tragic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.展开更多
In recent years, China has launched active exploration and practices in the aspects of the construction of ecological civilization and has made remarkable achievements. In this process, enterprises have played an impo...In recent years, China has launched active exploration and practices in the aspects of the construction of ecological civilization and has made remarkable achievements. In this process, enterprises have played an important role in optimizing the economic growth, promoting energy-saving and emissionreduction, and spreading ecological culture. The paper analyzes the present situation and existing problems of current construction of ecological civilization of enterprises in China. On the basis of current situation of the construction of ecological civilization of enterprises in Beijing and in line with the industrial standard of CRISP-DM, the paper utilizes decision tree algorithm and researches the key elements which infl uence the enterprises' willingness of the construction of ecological civilization. The research result shows that there are three key elements which infl uence the enterprises' willingness of the construction of ecological civilization: enterprises' average sales of the past three years, the categories of enterprises and enterprises' principals' cognition on the responsibility of the construction of ecological civilization; other two variables have no infl uence on the willingness: the ration of research and construction staff in enterprises and that whether enterprises are high-tech ones. Therefore, it is necessary that governments should take the lead to establish strong conception of ecological civilization among citizens, carry out vigorously the publicity and education of the construction of ecological civilization, enhance the cognition levels of enterprises' principals and reduce the costs of the construction of ecological civilization.展开更多
We use the model with the consideration of the traffic study the relationship between the traffic risk coefficient interruption probability (Physica A 387(2008)6845) to and the traffic interruption probability. Th...We use the model with the consideration of the traffic study the relationship between the traffic risk coefficient interruption probability (Physica A 387(2008)6845) to and the traffic interruption probability. The analytical and numerical results show that the traffic interruption probability will reduce the traffic risk coefficient and that the reduction is related to the density, which shows that this model can improve traffic security.展开更多
Segmental tunnel lining strengthened with steel plates is widely used worldwide to provide a permanent strengthening method.Most existing studies assume an ideal steel-concrete interface,ignoring discontinuous deforma...Segmental tunnel lining strengthened with steel plates is widely used worldwide to provide a permanent strengthening method.Most existing studies assume an ideal steel-concrete interface,ignoring discontinuous deformation characteristics,making it difficult to accurately analyze the strengthened structure’s failure mechanism.In this study,interfacial fracture mechanics of composite material was applied to the segmental tunnel lining strengthened with steel plates,and a numerical three-dimensional solid nonlinear model of the lining structure was established,combining the extended finite element method with a cohesive-zone model to account for the discontinuous deformation characteristics of the interface.The results accurately describe the crack propagation process,and are verified by full-scale testing.Next,dynamic simulations based on the calibrated model were conducted to analyze the sliding failure and cracking of the steel-concrete interface.Lastly,detailed location of the interface bonding failure are further verified by model test.The results show that,the cracking failure and bond failure of the interface are the decisive factors determining the instability and failure of the strengthened structure.The proposed numerical analysis is a major step forward in revealing the interface failure mechanism of strengthened composite material structures.展开更多
The accessibility of a destination-based transportation system is defined to quantify the performance of transportation systems which access a distinct destination. The access cost is used to reflect the utility of th...The accessibility of a destination-based transportation system is defined to quantify the performance of transportation systems which access a distinct destination. The access cost is used to reflect the utility of the transportation system including the fatigue and inconvenience in the total cost. The cost is quan- tified by two coefficients which represent the different characteristics of various people. The average cost and the income-relative accessibility are used to describe various aspects of the accessibility and to evaluate the accessibility of a destination-based system. A case study uses data from the Kunming transportation system to evaluate the accessibility of the present city airport. The calibrated coefficients are then used to evaluate the transportation system to the new Kunming international airport. The results show that this transportation accessibility evaluation can be combined with transportation planning to study transportation sub-systems.展开更多
This study aims at analyzing various extents of transportation equity change and the accessibility change of cities along High Speed Rail (HSR) line in China. To evaluate the accessibility change and transportation eq...This study aims at analyzing various extents of transportation equity change and the accessibility change of cities along High Speed Rail (HSR) line in China. To evaluate the accessibility change and transportation equity, certain cities along the transportation corridor which the successfully operating WuGuang HSR lies in are selected as samples of influenced ones first. Cities’ connection with HSR and their sizes are considered as choosing criteria. Weighted mean travel time and Generalized weighed travel time, which integrated with generalized cost, are both calculated in the two different scenarios to indicate accessibility changes of each city. The two scenarios are with or without the advent of WuGuang HSR. Accessibilities in different scenarios were carefully contrasted. It was found out that there is no significant change in the mean accessibility aspect of the region between the two scenarios. Then transportation equity issue of the transportation corridor is discussed based on the results of Gini coefficient using the data of Passenger Transportation Balance index. Passenger Transportation Balance index is proposed in this article to indicate the how much is one city’s transportation demand satisfied. The research found that cities had HSR stations built-in all attained a more accessibility improvement comparing with the others. And the gap between the accessibilities of the cities along the HSR line and those which are not is relatively wider. However, the equity evaluation using Transportation Balance Gini Coefficient reveals that massive investment in HSR has no potent evidence for equity improvement.展开更多
In order to balance the temporal-spatial distribution of urban traffic flow, a model is established for combined urban traffic signal control and traffic flow guidance. With consideration of the wide use of fixed sign...In order to balance the temporal-spatial distribution of urban traffic flow, a model is established for combined urban traffic signal control and traffic flow guidance. With consideration of the wide use of fixed signal control at intersections, traffic assignment under traffic flow guidance, and dynamic characteristics of urban traffic management, a tri-level programming model is presented. To reflect the impact of intersection delay on traffic assignment, the lower level model is set as a modified user equilibrium model. The middle level model, which contains several definitional constraints for different phase modes, is built for the traffic signal control optimization. To solve the problem of tide lane management, the upper level model is built up based on nonlinear 0-1 integer programming. A heuristic iterative optimization algorithm(HIOA) is set up to solve the tri-level programming model. The lower level model is solved by method of successive averages(MSA), the middle level model is solved by non-dominated sorting genetic algorithm II(NSGA II), and the upper level model is solved by genetic algorithm(GA). A case study is raised to show the efficiency and applicability of the proposed modelling and computing method.展开更多
In order to describe the characteristics of dynamic traffic flow and improve the robustness of its multiple applications, a dynamic traffic temporal-spatial model(DTTS) is established. With consideration of the tempor...In order to describe the characteristics of dynamic traffic flow and improve the robustness of its multiple applications, a dynamic traffic temporal-spatial model(DTTS) is established. With consideration of the temporal correlation, spatial correlation and historical correlation, a basic DTTS model is built. And a three-stage approach is put forward for the simplification and calibration of the basic DTTS model. Through critical sections pre-selection and critical time pre-selection, the first stage reduces the variable number of the basic DTTS model. In the second stage, variable coefficient calibration is implemented based on basic model simplification and stepwise regression analysis. Aimed at dynamic noise estimation, the characteristics of noise are summarized and an extreme learning machine is presented in the third stage. A case study based on a real-world road network in Beijing, China, is carried out to test the efficiency and applicability of proposed DTTS model and the three-stage approach.展开更多
A novel anchorage for long-span suspension bridges,called pile-caisson composite structures,was recently proposed by the authors in an attempt to reduce the construction period and costs.This study aims to investigate...A novel anchorage for long-span suspension bridges,called pile-caisson composite structures,was recently proposed by the authors in an attempt to reduce the construction period and costs.This study aims to investigate the displacement and force behavior of piles in a pile-caisson composite structure under eccentric inclined loading considering different stratum features.To this end,both 1g model tests and three-dimensional numerical simulations were performed.Two groups of 1g model tests were used to validate the finite-element(FE)method.Parametric studies were then performed to investigate the effects of groundwater level,burial depth of the pile-caisson composite structure,and distribution of soil layers on the performance of the pile-caisson composite structure.The numerical analyses indicated that the influence of the groundwater level on the stability of the caisson was much greater than that of the piles.In addition,increasing the burial depth of the pile-caisson composite structure can assist in reducing the displacements and improving the stability of the pile-caisson composite structure.In addition,the distribution of soil layers can significantly affect the stability of the pile-caisson composite structure,especially the soil layer around the caisson.展开更多
The theory of complex networks was used to classify public transport networks into public transportation route networks, public transportation transfer networks, and bus station networks. The practical significance of...The theory of complex networks was used to classify public transport networks into public transportation route networks, public transportation transfer networks, and bus station networks. The practical significance of the network parameters was then analyzed. The public transport networks in Langfang, Jining, and Dalian were then chosen as specific research cases. The results show that the public transportation networks have the characteristics of complex networks, In addition, the urban transportation network parameters all significantly affect the accessibility, convenience, and terrorist security capability of the urban public transportation network. The results link the findings with the actual situations to explore means to solve transportation system problems.展开更多
The conventional traffic demand forecasting methods based on revealed preference (RP) data are not able to predict the modal split. Passengers' stated intentions are indispensable for modal split forecasting and ev...The conventional traffic demand forecasting methods based on revealed preference (RP) data are not able to predict the modal split. Passengers' stated intentions are indispensable for modal split forecasting and evaluation of new traffic modes. This paper analyzed the biases and errors included in stated preference data, put forward the new stochastic utility functions, and proposed an unbiased disaggregate model and its approximate model based on the combination of RP and stated preference (SP) data, with analysis of the parameter estimation algorithm. The model was also used to forecast rail transit passenger volumes to the Beijing Capital International Airport and the shift ratios from current traffic modes to rail transit. Experimental results show that the model can greatly increase forecasting accuracy of the modal split ratio of current traffic modes and can accurately forecast the shift ratios from current modes to the new mode.展开更多
The uncontrolled growth in urbanization and motorization generally contributes to an urban land use and transportation system that is socially, economically, and environmentally unsustainable. This paper uses Karachi ...The uncontrolled growth in urbanization and motorization generally contributes to an urban land use and transportation system that is socially, economically, and environmentally unsustainable. This paper uses Karachi as a case study, which is the largest urban and economic centre of Pakistan, passing through an uncontrolled phase of rapid urbanization and motorization. The paper first reviews research related to sustainable transportation systems to comprehend the concept of sustainable development and transportation. The paper then evaluates the existing transportation and infrastructure system, national transportation policies, and urban transportation projects to determine if the current paradigm is moving toward or away from sustainable transportation. Furthermore, the principles for sustainable urban transportation are developed to see what significance national transportation policies have given to urban transportation from a sustainable transportation point of view. Finally some strategies are suggested, adoption of which may lead to a sustainable urban development and transportation system in Karachi.展开更多
This paper reports the effects of using an "odd and even" traffic restriction policy in Beijing during the 2008 Olympic Games. Based on data from 529 traffic detectors on the expressway network and some main arteria...This paper reports the effects of using an "odd and even" traffic restriction policy in Beijing during the 2008 Olympic Games. Based on data from 529 traffic detectors on the expressway network and some main arterials in Beijing, China, a comparative analysis has been carried out on the following parameters: the total traffic volume within the expressway network, the total traffic volume on different ring expressways, the traffic volume and speed of a freeway segment, and an arterial street before and after the implementation of the traffic restriction policy. The results show that during the traffic restriction period, although more than 50% of vehicles were forbidden to travel in Beijing, the traffic volume was only reduced by 20%-40% while the travel speed had been increased by 10%-20%. This suggests that such traffic restriction policy may be an effective shortterm management measure in dealing with increased transportation demand and congestion during major events, such as the Olympic Games. Results also indicate that vehicle travel demand does not decrease with the same proportion as the total vehicles forbidden, at least for the expressway and main arterials in a city.展开更多
This study aims at implementing price discrimination to get maximum revenue on a two-path route expressway, focusing on the problems which occur in traffic forecasting when applying a "profit-maximizing" toll design...This study aims at implementing price discrimination to get maximum revenue on a two-path route expressway, focusing on the problems which occur in traffic forecasting when applying a "profit-maximizing" toll designed to maximize revenue for a certain toll road in Japan. A break-even discussion is inevitable in the process of planning a certain toll road. According to the theory of transportation economics, market segmentation price discrimination is supposed to be efficient in the transportation market to increase the revenue of fixed facilities. In the model, a bypass and an adjacent expressway form a two-path route section. Two different toll levels are implemented for the bypass: one is for through traffic, and the other is for insideinside and inside-outside traffics. This two-path route plus two-toll-level system thus causes difficulty in traffic assignment that is based on the minimum route searching method. In the study, a rational approach of adjusting the through traffic is implemented to predict the traffic flow as well as revenue on two parallel routes with different toll levels. The approximate calculation method that fixes the split rate of the passing through traffic flow is applied to solve the two-path route plus two-toll-level problem since passing through traffic is price elastic. Market segmentation pricing, which gives two toll levels in a toll road, is proved to be practical for increasing revenue. The results are also verified to be rational by using the survey data of Meishin Expressway.展开更多
China’s traffic safety attracts increasing research interest.Official data show that crashes in the western region of China are more severe than those in the eastern region.However,research on crash severity in weste...China’s traffic safety attracts increasing research interest.Official data show that crashes in the western region of China are more severe than those in the eastern region.However,research on crash severity in western China is scarce.This study applied a hierarchical Bayesian logistic model to examine the significant factors related to crash and vehicle/driver levels and their heterogeneous impacts on the severity of drivers’ injury.Crash data were collected from Lintao,a rural mountainous county in western China.A variable was proposed to measure the relative difference between the crashworthiness of one vehicle and the aggressivity of the other vehicle in the mixed traffic flow.Results indicated that the majority of the total variance was induced by between-crash variance,showing the suitability of the utilized hierarchical modeling approach.One crash-level variable and six vehicle/driver-level variables,namely,road type,compatibility difference,age,vehicle type,drunk driving,driving unregistered vehicle,and driving years,significantly affected modeling drivers’ injury severities.Among these variables,road type(national and provincial),age(young and senior drivers),driving unregistered vehicle,and drunk driving tended to increase the odds of crash-related mortality.Driving years(new drivers with less than six years of driving experience) and vehicle type(heavy vehicle) were likely to decrease the probability of fatal outcomes.Compatibility difference was relatively significant,and the possibilities of mortality in single vehicle crashes were higher than those inmultivehicle and pedestrian-involved crashes.The developed methodology and estimation results provided insights into the internal mechanism of rural crashes and effective countermeasures to prevent rural crashes.展开更多
The helmet of riders of electric bicycles plays an important role in reducing injuries and deaths in traffic accidents.This paper conducts a questionnaire survey,data analysis and modelling to investigate the influenc...The helmet of riders of electric bicycles plays an important role in reducing injuries and deaths in traffic accidents.This paper conducts a questionnaire survey,data analysis and modelling to investigate the influencing factors of electric bicycle helmet wearing.First,living area,gender,age,marital status and education level are selected as independent variables for data analysis.The factor analysis divides the sentiments of electric bicyclists for wearing helmets into four aspects:safety perception,practical sensation,satisfaction perception and emergency perception,and ordinal multiple logistic models are built to analyse the influencing factors.The result shows that people aged 18−25,26−35,36−45 and 46−55 are 1.3,1.8,2.0 and 2.3 times more likely,respectively,to have at least a grade higher safety perception than those aged 56 and over;men are 0.77 times more likely than women to feel at least one grade higher about the practical perception and 1.48 times more than women about the satisfaction perception;people with primary school,junior high school,senior high school,junior college and bachelor’s degree education are 1.64,2.44,1.50,1.70 and 1.55 times more likely,respectively,than people with a master’s degree to feel at least one grade higher about the satisfaction perception.展开更多
Traffic signal control is essential to the efficiency of the road network’s operation.In recent years,more and more detailed detection data provide potential data support for traffic signal control,such as license pl...Traffic signal control is essential to the efficiency of the road network’s operation.In recent years,more and more detailed detection data provide potential data support for traffic signal control,such as license plate recognition(LPR)data.This study aims to develop a traffic signal control optimization method based on model predictive control(MPC)and LPR data.The proposed framework of a closed-loop control system is described in detail.First,the control objectives and queue prediction model for signalized intersection are determined.Then,online optimization and feedback compensation are discussed and implemented.Calculations of the arrival rate at the downstream are based on the LPR data detected at the upstream intersection,and dynamic optimization method of the offset is proposed for a coordinated control.The model is validated using the LPR data of two consecutive intersections with a traffic simulation platform.Results demonstrate that the model can restrain extreme long queuing,improve intersection capacity,and reduce intersection average delay.The developed model promotes the system operating efficiency and shows the general advantage of real-time optimization,feedback,and control.The proposed framework can be potentially applied by local traffic management centers to improve the quality of traffic signal control.展开更多
The paper analyzes the equity of road resources distribution in urban areas by modeling the competitive relationship among different road users. A logistic model is used to describe the development of different traffi...The paper analyzes the equity of road resources distribution in urban areas by modeling the competitive relationship among different road users. A logistic model is used to describe the development of different traffic modes in the transportation network. The system is similar to the species competition model, so a two-species model is used to analyze the relationship between users based on the stability of the equilibrium points. The Lotka-Volterra model is then used to describe the multi-species cases with numerical examples, showing that this model can describe the effects of the road space distribution on the competitive user relationships. Policy makers must ensure the equity of road resources distribution so that each urban transportation mode is properly developed for sustainable social development.展开更多
基金Supported by the Program for National High-Tech Research and Development Program of China under Grant No 2007AA11Z233National Key Technology R & D Program under Grant No. 2009BAG13A06China Postdoctoral Science Foundation Funded Project under Grant No. 20090450395
文摘Different driving decisions will cause different processes of phase transition in traffic Bow. To reveal the inner mechanism, this paper built a new cellular automaton (CA) model, based on the driving decision (DD). In the DD model, a driver's decision is divided into three stages: decision-making, action, and result. The acceleration is taken as a decision variable and three core factors, i.e. distance between adjacent vehicles, their own velocity, and the preceding vehicle's velocity, are considered. Simulation results show that the DD model can simulate the synchronized Bow effectively and describe the phase transition in traffic Bow well. Further analyses illustrate that various density will cause the phase transition and the random probability will impact the process. Compared with the traditional NaSch model, the DD model considered the preceding vehicle's velocity, the deceleration limitation, and a safe distance, so it can depict closer to the driver preferences on pursuing safety, stability and fuel-saving and has strong theoretical innovation for future studies.
基金Teaching Reform Project of Tsinghua University(No.DX0702)National Natural Science Foundation of China(No.41971379)。
文摘Geomatics is an interdisciplinary subject.Many disciplines have teaching demands in this field.A new course on“Geomatics Technology”has been suggested by the Weiyang College of Tsinghua University of China for the major of“Mathematical and Scientific Basic Science+Civil,Hydraulic and Marine Engineering”.This paper offers a data-led geomatics teaching mode,developing a customized teaching cloud platform,to explore the cross-integrated innovative teaching methods.Teachers and students can assign and submit assignments on this platform.The platform constitutes a data flow with the data download,data processing and result sharing.It encourages communication among students in various majors,grades and units using data as the medium,from data processing to application upstream and downstream.In the“Geomatics Technology”course,geospatial data has emerged as a vital element of the multidisciplinary approach.This kind of teaching mode has been used in the postgraduate remote sensing course offered by Tsinghua University’s Department of Civil Engineering and Construction Management.Furthermore,the mode will be used for the first time in the autumn semester of 2022 in the undergraduate teaching of Weiyang College and civil engineering,to offer a novel idea for the reform of courses linked to geospatial informatics.
基金Project supported by the Program for New Century Excellent Talents in University,China (Grant No. NCET-08-0038)the National Natural Science Foundation of China (Grant Nos. 70701002,70971007 and 70521001)the National Basic Research Program of China (Grant No. 2006CB705503)
文摘Since ramps are an important composition of traffic systems and there often exist multi ramps in a tragic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang et al. [2009 Communications in Theoretical Physics 51(1) 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex tragic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.
基金supported by the Beijing Outstanding Talent Training Project (Grant No. 2014000020124G071)Project of Beijing Union University (Grant No. Sk10201503)Funding Project for Academic Human Resources Development in Beijing Union University (Rk100201504)
文摘In recent years, China has launched active exploration and practices in the aspects of the construction of ecological civilization and has made remarkable achievements. In this process, enterprises have played an important role in optimizing the economic growth, promoting energy-saving and emissionreduction, and spreading ecological culture. The paper analyzes the present situation and existing problems of current construction of ecological civilization of enterprises in China. On the basis of current situation of the construction of ecological civilization of enterprises in Beijing and in line with the industrial standard of CRISP-DM, the paper utilizes decision tree algorithm and researches the key elements which infl uence the enterprises' willingness of the construction of ecological civilization. The research result shows that there are three key elements which infl uence the enterprises' willingness of the construction of ecological civilization: enterprises' average sales of the past three years, the categories of enterprises and enterprises' principals' cognition on the responsibility of the construction of ecological civilization; other two variables have no infl uence on the willingness: the ration of research and construction staff in enterprises and that whether enterprises are high-tech ones. Therefore, it is necessary that governments should take the lead to establish strong conception of ecological civilization among citizens, carry out vigorously the publicity and education of the construction of ecological civilization, enhance the cognition levels of enterprises' principals and reduce the costs of the construction of ecological civilization.
基金Supported by the Program for New Century Excellent Talents in University under Grant No NCET-08-0038, the National Natural Science Foundation of China under Grant Nos 70701002 and 70521001, and the National Basic Research Program of China under Grant No 2006CB705503.
文摘We use the model with the consideration of the traffic study the relationship between the traffic risk coefficient interruption probability (Physica A 387(2008)6845) to and the traffic interruption probability. The analytical and numerical results show that the traffic interruption probability will reduce the traffic risk coefficient and that the reduction is related to the density, which shows that this model can improve traffic security.
基金the financial support provided by the National Key Basic Research Program of China(No.2015CB057801)the Projects of the Construction Department of Zhejiang Province(Nos.2022K073 and 2022K169).
文摘Segmental tunnel lining strengthened with steel plates is widely used worldwide to provide a permanent strengthening method.Most existing studies assume an ideal steel-concrete interface,ignoring discontinuous deformation characteristics,making it difficult to accurately analyze the strengthened structure’s failure mechanism.In this study,interfacial fracture mechanics of composite material was applied to the segmental tunnel lining strengthened with steel plates,and a numerical three-dimensional solid nonlinear model of the lining structure was established,combining the extended finite element method with a cohesive-zone model to account for the discontinuous deformation characteristics of the interface.The results accurately describe the crack propagation process,and are verified by full-scale testing.Next,dynamic simulations based on the calibrated model were conducted to analyze the sliding failure and cracking of the steel-concrete interface.Lastly,detailed location of the interface bonding failure are further verified by model test.The results show that,the cracking failure and bond failure of the interface are the decisive factors determining the instability and failure of the strengthened structure.The proposed numerical analysis is a major step forward in revealing the interface failure mechanism of strengthened composite material structures.
文摘The accessibility of a destination-based transportation system is defined to quantify the performance of transportation systems which access a distinct destination. The access cost is used to reflect the utility of the transportation system including the fatigue and inconvenience in the total cost. The cost is quan- tified by two coefficients which represent the different characteristics of various people. The average cost and the income-relative accessibility are used to describe various aspects of the accessibility and to evaluate the accessibility of a destination-based system. A case study uses data from the Kunming transportation system to evaluate the accessibility of the present city airport. The calibrated coefficients are then used to evaluate the transportation system to the new Kunming international airport. The results show that this transportation accessibility evaluation can be combined with transportation planning to study transportation sub-systems.
文摘This study aims at analyzing various extents of transportation equity change and the accessibility change of cities along High Speed Rail (HSR) line in China. To evaluate the accessibility change and transportation equity, certain cities along the transportation corridor which the successfully operating WuGuang HSR lies in are selected as samples of influenced ones first. Cities’ connection with HSR and their sizes are considered as choosing criteria. Weighted mean travel time and Generalized weighed travel time, which integrated with generalized cost, are both calculated in the two different scenarios to indicate accessibility changes of each city. The two scenarios are with or without the advent of WuGuang HSR. Accessibilities in different scenarios were carefully contrasted. It was found out that there is no significant change in the mean accessibility aspect of the region between the two scenarios. Then transportation equity issue of the transportation corridor is discussed based on the results of Gini coefficient using the data of Passenger Transportation Balance index. Passenger Transportation Balance index is proposed in this article to indicate the how much is one city’s transportation demand satisfied. The research found that cities had HSR stations built-in all attained a more accessibility improvement comparing with the others. And the gap between the accessibilities of the cities along the HSR line and those which are not is relatively wider. However, the equity evaluation using Transportation Balance Gini Coefficient reveals that massive investment in HSR has no potent evidence for equity improvement.
基金Project(2014BAG01B0403)supported by the High-Tech Research and Development Program of China
文摘In order to balance the temporal-spatial distribution of urban traffic flow, a model is established for combined urban traffic signal control and traffic flow guidance. With consideration of the wide use of fixed signal control at intersections, traffic assignment under traffic flow guidance, and dynamic characteristics of urban traffic management, a tri-level programming model is presented. To reflect the impact of intersection delay on traffic assignment, the lower level model is set as a modified user equilibrium model. The middle level model, which contains several definitional constraints for different phase modes, is built for the traffic signal control optimization. To solve the problem of tide lane management, the upper level model is built up based on nonlinear 0-1 integer programming. A heuristic iterative optimization algorithm(HIOA) is set up to solve the tri-level programming model. The lower level model is solved by method of successive averages(MSA), the middle level model is solved by non-dominated sorting genetic algorithm II(NSGA II), and the upper level model is solved by genetic algorithm(GA). A case study is raised to show the efficiency and applicability of the proposed modelling and computing method.
基金Project(2014BAG01B0403)supported by the National High-Tech Research and Development Program of China
文摘In order to describe the characteristics of dynamic traffic flow and improve the robustness of its multiple applications, a dynamic traffic temporal-spatial model(DTTS) is established. With consideration of the temporal correlation, spatial correlation and historical correlation, a basic DTTS model is built. And a three-stage approach is put forward for the simplification and calibration of the basic DTTS model. Through critical sections pre-selection and critical time pre-selection, the first stage reduces the variable number of the basic DTTS model. In the second stage, variable coefficient calibration is implemented based on basic model simplification and stepwise regression analysis. Aimed at dynamic noise estimation, the characteristics of noise are summarized and an extreme learning machine is presented in the third stage. A case study based on a real-world road network in Beijing, China, is carried out to test the efficiency and applicability of proposed DTTS model and the three-stage approach.
基金support from the National Natural Science Foundation of China(Grant Nos.51778575,52078457).
文摘A novel anchorage for long-span suspension bridges,called pile-caisson composite structures,was recently proposed by the authors in an attempt to reduce the construction period and costs.This study aims to investigate the displacement and force behavior of piles in a pile-caisson composite structure under eccentric inclined loading considering different stratum features.To this end,both 1g model tests and three-dimensional numerical simulations were performed.Two groups of 1g model tests were used to validate the finite-element(FE)method.Parametric studies were then performed to investigate the effects of groundwater level,burial depth of the pile-caisson composite structure,and distribution of soil layers on the performance of the pile-caisson composite structure.The numerical analyses indicated that the influence of the groundwater level on the stability of the caisson was much greater than that of the piles.In addition,increasing the burial depth of the pile-caisson composite structure can assist in reducing the displacements and improving the stability of the pile-caisson composite structure.In addition,the distribution of soil layers can significantly affect the stability of the pile-caisson composite structure,especially the soil layer around the caisson.
文摘The theory of complex networks was used to classify public transport networks into public transportation route networks, public transportation transfer networks, and bus station networks. The practical significance of the network parameters was then analyzed. The public transport networks in Langfang, Jining, and Dalian were then chosen as specific research cases. The results show that the public transportation networks have the characteristics of complex networks, In addition, the urban transportation network parameters all significantly affect the accessibility, convenience, and terrorist security capability of the urban public transportation network. The results link the findings with the actual situations to explore means to solve transportation system problems.
文摘The conventional traffic demand forecasting methods based on revealed preference (RP) data are not able to predict the modal split. Passengers' stated intentions are indispensable for modal split forecasting and evaluation of new traffic modes. This paper analyzed the biases and errors included in stated preference data, put forward the new stochastic utility functions, and proposed an unbiased disaggregate model and its approximate model based on the combination of RP and stated preference (SP) data, with analysis of the parameter estimation algorithm. The model was also used to forecast rail transit passenger volumes to the Beijing Capital International Airport and the shift ratios from current traffic modes to rail transit. Experimental results show that the model can greatly increase forecasting accuracy of the modal split ratio of current traffic modes and can accurately forecast the shift ratios from current modes to the new mode.
基金Supported by the International Corporation Project
文摘The uncontrolled growth in urbanization and motorization generally contributes to an urban land use and transportation system that is socially, economically, and environmentally unsustainable. This paper uses Karachi as a case study, which is the largest urban and economic centre of Pakistan, passing through an uncontrolled phase of rapid urbanization and motorization. The paper first reviews research related to sustainable transportation systems to comprehend the concept of sustainable development and transportation. The paper then evaluates the existing transportation and infrastructure system, national transportation policies, and urban transportation projects to determine if the current paradigm is moving toward or away from sustainable transportation. Furthermore, the principles for sustainable urban transportation are developed to see what significance national transportation policies have given to urban transportation from a sustainable transportation point of view. Finally some strategies are suggested, adoption of which may lead to a sustainable urban development and transportation system in Karachi.
基金supported by National Key Technology R&D Program(No.2012 BAJ05B04)Hang Lung Center for Real Estate,Tsinghua UniversityCollaborative Innovation Center for Capital World City's Smooth Traffic Construction
文摘This paper reports the effects of using an "odd and even" traffic restriction policy in Beijing during the 2008 Olympic Games. Based on data from 529 traffic detectors on the expressway network and some main arterials in Beijing, China, a comparative analysis has been carried out on the following parameters: the total traffic volume within the expressway network, the total traffic volume on different ring expressways, the traffic volume and speed of a freeway segment, and an arterial street before and after the implementation of the traffic restriction policy. The results show that during the traffic restriction period, although more than 50% of vehicles were forbidden to travel in Beijing, the traffic volume was only reduced by 20%-40% while the travel speed had been increased by 10%-20%. This suggests that such traffic restriction policy may be an effective shortterm management measure in dealing with increased transportation demand and congestion during major events, such as the Olympic Games. Results also indicate that vehicle travel demand does not decrease with the same proportion as the total vehicles forbidden, at least for the expressway and main arterials in a city.
文摘This study aims at implementing price discrimination to get maximum revenue on a two-path route expressway, focusing on the problems which occur in traffic forecasting when applying a "profit-maximizing" toll designed to maximize revenue for a certain toll road in Japan. A break-even discussion is inevitable in the process of planning a certain toll road. According to the theory of transportation economics, market segmentation price discrimination is supposed to be efficient in the transportation market to increase the revenue of fixed facilities. In the model, a bypass and an adjacent expressway form a two-path route section. Two different toll levels are implemented for the bypass: one is for through traffic, and the other is for insideinside and inside-outside traffics. This two-path route plus two-toll-level system thus causes difficulty in traffic assignment that is based on the minimum route searching method. In the study, a rational approach of adjusting the through traffic is implemented to predict the traffic flow as well as revenue on two parallel routes with different toll levels. The approximate calculation method that fixes the split rate of the passing through traffic flow is applied to solve the two-path route plus two-toll-level problem since passing through traffic is price elastic. Market segmentation pricing, which gives two toll levels in a toll road, is proved to be practical for increasing revenue. The results are also verified to be rational by using the survey data of Meishin Expressway.
基金The research reported in this paper is part of the project supported by the National Natural Science Foundation of China (71871123)。
文摘China’s traffic safety attracts increasing research interest.Official data show that crashes in the western region of China are more severe than those in the eastern region.However,research on crash severity in western China is scarce.This study applied a hierarchical Bayesian logistic model to examine the significant factors related to crash and vehicle/driver levels and their heterogeneous impacts on the severity of drivers’ injury.Crash data were collected from Lintao,a rural mountainous county in western China.A variable was proposed to measure the relative difference between the crashworthiness of one vehicle and the aggressivity of the other vehicle in the mixed traffic flow.Results indicated that the majority of the total variance was induced by between-crash variance,showing the suitability of the utilized hierarchical modeling approach.One crash-level variable and six vehicle/driver-level variables,namely,road type,compatibility difference,age,vehicle type,drunk driving,driving unregistered vehicle,and driving years,significantly affected modeling drivers’ injury severities.Among these variables,road type(national and provincial),age(young and senior drivers),driving unregistered vehicle,and drunk driving tended to increase the odds of crash-related mortality.Driving years(new drivers with less than six years of driving experience) and vehicle type(heavy vehicle) were likely to decrease the probability of fatal outcomes.Compatibility difference was relatively significant,and the possibilities of mortality in single vehicle crashes were higher than those inmultivehicle and pedestrian-involved crashes.The developed methodology and estimation results provided insights into the internal mechanism of rural crashes and effective countermeasures to prevent rural crashes.
基金supported by The National Natural Science Foundation of China (Grant No.52072214 and Grant No.71871123)Global Road Safety Partnership (GRSP) (Grant No.CHNXX-RD16-1188).
文摘The helmet of riders of electric bicycles plays an important role in reducing injuries and deaths in traffic accidents.This paper conducts a questionnaire survey,data analysis and modelling to investigate the influencing factors of electric bicycle helmet wearing.First,living area,gender,age,marital status and education level are selected as independent variables for data analysis.The factor analysis divides the sentiments of electric bicyclists for wearing helmets into four aspects:safety perception,practical sensation,satisfaction perception and emergency perception,and ordinal multiple logistic models are built to analyse the influencing factors.The result shows that people aged 18−25,26−35,36−45 and 46−55 are 1.3,1.8,2.0 and 2.3 times more likely,respectively,to have at least a grade higher safety perception than those aged 56 and over;men are 0.77 times more likely than women to feel at least one grade higher about the practical perception and 1.48 times more than women about the satisfaction perception;people with primary school,junior high school,senior high school,junior college and bachelor’s degree education are 1.64,2.44,1.50,1.70 and 1.55 times more likely,respectively,than people with a master’s degree to feel at least one grade higher about the satisfaction perception.
基金The National Key Research and Development Program of China(No.2018YFB1601000)Key Program of National Natural Science Foundation of China(Grant No.U21B2089).
文摘Traffic signal control is essential to the efficiency of the road network’s operation.In recent years,more and more detailed detection data provide potential data support for traffic signal control,such as license plate recognition(LPR)data.This study aims to develop a traffic signal control optimization method based on model predictive control(MPC)and LPR data.The proposed framework of a closed-loop control system is described in detail.First,the control objectives and queue prediction model for signalized intersection are determined.Then,online optimization and feedback compensation are discussed and implemented.Calculations of the arrival rate at the downstream are based on the LPR data detected at the upstream intersection,and dynamic optimization method of the offset is proposed for a coordinated control.The model is validated using the LPR data of two consecutive intersections with a traffic simulation platform.Results demonstrate that the model can restrain extreme long queuing,improve intersection capacity,and reduce intersection average delay.The developed model promotes the system operating efficiency and shows the general advantage of real-time optimization,feedback,and control.The proposed framework can be potentially applied by local traffic management centers to improve the quality of traffic signal control.
基金the National Natural Science Foundation of China (No. 70571046)
文摘The paper analyzes the equity of road resources distribution in urban areas by modeling the competitive relationship among different road users. A logistic model is used to describe the development of different traffic modes in the transportation network. The system is similar to the species competition model, so a two-species model is used to analyze the relationship between users based on the stability of the equilibrium points. The Lotka-Volterra model is then used to describe the multi-species cases with numerical examples, showing that this model can describe the effects of the road space distribution on the competitive user relationships. Policy makers must ensure the equity of road resources distribution so that each urban transportation mode is properly developed for sustainable social development.