To determine how bus stop design influences mixed traffic operation near Chinese bus stops,a new theoretical method was developed by using additive-conflict-flows procedure.The procedure was extended from homogeneous ...To determine how bus stop design influences mixed traffic operation near Chinese bus stops,a new theoretical method was developed by using additive-conflict-flows procedure.The procedure was extended from homogeneous traffic flow to mixed traffic flow.Based on the procedure and queuing theory,car capacity and speed models were proposed for three types of bus stops including curbside,bus bay and bicycle detour.The effects of various combinations of bus stop type,traffic volume,bus dwell time,and berth number on traffic operations were investigated.The results indicate that traffic volume,bus dwell time and berth number have negative effects on traffic operations for any type of bus stops.For different types of bus stops,at car volumes above approximately 200 vehicles per hour,the bus bay and bicycle detour designs provide more benefits than the curbside design.As traffic volume increases,the benefit firstly increases in uncongested conditions and then decreases in congested conditions.It reaches the maximum at car volumes nearly 1 100 vehicles per hour.The results can be used to aid in the selection of a preferred bus stop design for a given traffic volume in developing countries.展开更多
The macro modeling and the solution of traffic flow with road width were investigated.Firstly,a new macro model with the consideration of road width was proposed.Secondly,the effects of road width on uniform flow and ...The macro modeling and the solution of traffic flow with road width were investigated.Firstly,a new macro model with the consideration of road width was proposed.Secondly,the effects of road width on uniform flow and small perturbation were studied.The analytical and numerical results show that widening (shrinking) road can enhance (reduce) the equilibrium speed and flow,and the increments (decrements) will increase with the absolute value of road width gradient.In addition,the numerical results illustrate that the new model can describe the effects of road width on the evolutions of uniform flow and small perturbation.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
This paper will develop a model simulation mixing traffic flow in the signal controlintersection. Applying the model, the schemes of traffic channeling and controlling in the typical intersection are analyzed and opti...This paper will develop a model simulation mixing traffic flow in the signal controlintersection. Applying the model, the schemes of traffic channeling and controlling in the typical intersection are analyzed and optimized and the optimal scheme make the average stop frequency be reduced by 31.8% and average stop time be reduced by 27.7%.展开更多
In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch mo...In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch model was improved by adding different slow probabilities, turning deceleration rules and modified lane changing rules. The relationship between the saturated flow rate of stretching-segments and adjacent lanes was tested in numerical simulation. The length of stretching-segment, cycle length and green time were selected as impact factors of the cellular automation model. The simulation result indicates that the geometrics design of stretching-segment and the traffic signal timing scenario have major effects on the saturated flow rate of the intersection approach. The saturated flow rate will continually increase with increasing stretching-segment length until it reaches a threshold. After reaching the threshold, the stretching-segment can be treated as a separate lane. The green time is approximately linearly related to the threshold length of the stretching-segment. An optimum cycle length exists when the length of the stretching-segment is not long enough, and it is approximately linearly related to the length of stretching-segment.展开更多
The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the in...The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the interfaces both without slurry and with bentonite slurry were analyzed.The experimental results show that different slurries exert much influence on the strength and deformation of soil/structure interface.Under mixed soil slurry,strain softening and shear dilatation are observed,while shear dilatation appears under the small normal stress of the interface without slurry,and shear contraction is significant under the condition of the bentonite slurry.The thickness of the interface was determined by analyzing the disturbed height of the sample with both simple shear test and particle flow code (PFC).An elasto-plastic constitutive model incorporating strain softening and dilatancy for thin layer element of interface was formulated in the framework of generalized potential theory.The relation curves of shear stress and shear strain,as well as the relation curves of normal strain and shear strain,were fitted by a piecewise function composed by hyperbolic functions and resembling normal functions.The entire model parameters can be identified by tests.The new model is verified by comparing the measured data of indoor cut-off wall model tests with the predictions from finite element method (FEM).The FEM results indicate that the stress of wall calculated by using Goodman element is too large,and the maximum deviation between the test data and prediction is about 45%.While the prediction from the proposed model is close to the measured data,and the error is generally less than 10%.展开更多
In order to investigate enhancements to cell transmission model (CTM) as a tool for traffic signal timing in oversaturated conditions, randomly distributed saturation flow rates and arrival rates were used instead of ...In order to investigate enhancements to cell transmission model (CTM) as a tool for traffic signal timing in oversaturated conditions, randomly distributed saturation flow rates and arrival rates were used instead of constant values to simulate traffic flow movement, estimate the average delay of the network and search for an optimal traffic signal timing plan. A case study was given to demonstrate that the proposed methodology can capture unique phenomena in oversaturated conditions such as forward wave, spillback and lane entrance blockage. The results show that CTM underestimates travel time by 25% when compared to Simtraffic, while the enhanced CTM underestimates by only 3%. A second case study shows that a dynamic signal timing plan is superior to a fixed signal timing plan in the term of average delay.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
文章采用FLOW-3D软件,通过RNGk-ε模型和volume of fluid(VOF)方法相结合,实现了竖井水平旋流泄洪洞水力特性的三维水流流场数值模拟;对开敞式进水口轴线与旋流洞轴线交角不同时起旋室的压强分布、旋流角和紊动能等水力特性进行了对比...文章采用FLOW-3D软件,通过RNGk-ε模型和volume of fluid(VOF)方法相结合,实现了竖井水平旋流泄洪洞水力特性的三维水流流场数值模拟;对开敞式进水口轴线与旋流洞轴线交角不同时起旋室的压强分布、旋流角和紊动能等水力特性进行了对比分析研究,数值模拟能够客观地反映起旋室旋流的流场特性,成果可为旋流溢洪道的研究应用提供参考.展开更多
基金Project(2012CB725400) supported by the National Basic Research Program of ChinaProjects(70901005, 71071016, 71131001) supported by the National Natural Science Foundation of ChinaProject(2011JBM055) supported by the Fundamental Research Funds for the Central Universities of China
文摘To determine how bus stop design influences mixed traffic operation near Chinese bus stops,a new theoretical method was developed by using additive-conflict-flows procedure.The procedure was extended from homogeneous traffic flow to mixed traffic flow.Based on the procedure and queuing theory,car capacity and speed models were proposed for three types of bus stops including curbside,bus bay and bicycle detour.The effects of various combinations of bus stop type,traffic volume,bus dwell time,and berth number on traffic operations were investigated.The results indicate that traffic volume,bus dwell time and berth number have negative effects on traffic operations for any type of bus stops.For different types of bus stops,at car volumes above approximately 200 vehicles per hour,the bus bay and bicycle detour designs provide more benefits than the curbside design.As traffic volume increases,the benefit firstly increases in uncongested conditions and then decreases in congested conditions.It reaches the maximum at car volumes nearly 1 100 vehicles per hour.The results can be used to aid in the selection of a preferred bus stop design for a given traffic volume in developing countries.
基金Project(NCET-08-0038) supported by the Program for New Century Excellent Talents in Chinese UniversityProjects(70701002,70971007 and 70521001) supported by the National Natural Science Foundation of ChinaProject(2006CB705503) supported by the National Basic Research Program of China
文摘The macro modeling and the solution of traffic flow with road width were investigated.Firstly,a new macro model with the consideration of road width was proposed.Secondly,the effects of road width on uniform flow and small perturbation were studied.The analytical and numerical results show that widening (shrinking) road can enhance (reduce) the equilibrium speed and flow,and the increments (decrements) will increase with the absolute value of road width gradient.In addition,the numerical results illustrate that the new model can describe the effects of road width on the evolutions of uniform flow and small perturbation.
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.
文摘This paper will develop a model simulation mixing traffic flow in the signal controlintersection. Applying the model, the schemes of traffic channeling and controlling in the typical intersection are analyzed and optimized and the optimal scheme make the average stop frequency be reduced by 31.8% and average stop time be reduced by 27.7%.
基金Projects(50422283,51208054) supported by the National Natural Science Foundation of China
文摘In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch model was improved by adding different slow probabilities, turning deceleration rules and modified lane changing rules. The relationship between the saturated flow rate of stretching-segments and adjacent lanes was tested in numerical simulation. The length of stretching-segment, cycle length and green time were selected as impact factors of the cellular automation model. The simulation result indicates that the geometrics design of stretching-segment and the traffic signal timing scenario have major effects on the saturated flow rate of the intersection approach. The saturated flow rate will continually increase with increasing stretching-segment length until it reaches a threshold. After reaching the threshold, the stretching-segment can be treated as a separate lane. The green time is approximately linearly related to the threshold length of the stretching-segment. An optimum cycle length exists when the length of the stretching-segment is not long enough, and it is approximately linearly related to the length of stretching-segment.
基金Project(20110094110002) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(200801014) supported by the Ministry of Water Resources of ChinaProject(50825901) supported by the National Natural Science Foundation of China
文摘The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the interfaces both without slurry and with bentonite slurry were analyzed.The experimental results show that different slurries exert much influence on the strength and deformation of soil/structure interface.Under mixed soil slurry,strain softening and shear dilatation are observed,while shear dilatation appears under the small normal stress of the interface without slurry,and shear contraction is significant under the condition of the bentonite slurry.The thickness of the interface was determined by analyzing the disturbed height of the sample with both simple shear test and particle flow code (PFC).An elasto-plastic constitutive model incorporating strain softening and dilatancy for thin layer element of interface was formulated in the framework of generalized potential theory.The relation curves of shear stress and shear strain,as well as the relation curves of normal strain and shear strain,were fitted by a piecewise function composed by hyperbolic functions and resembling normal functions.The entire model parameters can be identified by tests.The new model is verified by comparing the measured data of indoor cut-off wall model tests with the predictions from finite element method (FEM).The FEM results indicate that the stress of wall calculated by using Goodman element is too large,and the maximum deviation between the test data and prediction is about 45%.While the prediction from the proposed model is close to the measured data,and the error is generally less than 10%.
基金Project(51108343) supported by the National Natural Science Foundation of ChinaProject(06121) supported by University of Transportation Center for Alabama, USA
文摘In order to investigate enhancements to cell transmission model (CTM) as a tool for traffic signal timing in oversaturated conditions, randomly distributed saturation flow rates and arrival rates were used instead of constant values to simulate traffic flow movement, estimate the average delay of the network and search for an optimal traffic signal timing plan. A case study was given to demonstrate that the proposed methodology can capture unique phenomena in oversaturated conditions such as forward wave, spillback and lane entrance blockage. The results show that CTM underestimates travel time by 25% when compared to Simtraffic, while the enhanced CTM underestimates by only 3%. A second case study shows that a dynamic signal timing plan is superior to a fixed signal timing plan in the term of average delay.
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.
文摘文章采用FLOW-3D软件,通过RNGk-ε模型和volume of fluid(VOF)方法相结合,实现了竖井水平旋流泄洪洞水力特性的三维水流流场数值模拟;对开敞式进水口轴线与旋流洞轴线交角不同时起旋室的压强分布、旋流角和紊动能等水力特性进行了对比分析研究,数值模拟能够客观地反映起旋室旋流的流场特性,成果可为旋流溢洪道的研究应用提供参考.
