Due to the fact that there is no protected signal phase for right turns at most signalized intersections, the conflict between pedestrians and right-turning vehicles is one of the most common conflict types for pedest...Due to the fact that there is no protected signal phase for right turns at most signalized intersections, the conflict between pedestrians and right-turning vehicles is one of the most common conflict types for pedestrians. A pedestrian safety analysis of the common right-turn mode at four-phase signalized intersections is presented. Relative risk is used as a measure of the effect of behaviors. The analysis mainly includes five pedestrian factors that affect the conflict process between pedestrians and right-turning vehicles. Pedestrians tend to have a higher risk of being involved in conflicts in the following six situations: crossing with others, running over the crossing, entering the intersection, being near the exit lane, crossing in the middle or at the end of a green light when the right-turn lane is shared, crossing at the beginning of a green light or red period when the right-turn lane is exclusive. It is easier for pedestrians to get priority when crossing the street in the following situations: running over a crossing, entering the intersection, being near the entrance lane, and not using the crosswalk. However, pedestrians are more inclined to yield to right-turning vehicles when pedestrians are crossing in the middle of the green light time. Some measures to alleviate the conflict are put forward according to the conclusion. Video observations also indicate that a clear pedestrian waiting area must be marked for both pedestrian safety and right-turning vehicle efficiency at major flat intersections, particularly when the arms cover the lateral dividing strips.展开更多
Field observations illustrated that, right-turn vehicles stopped at various positions when proceeding within the right-turn lanes, while some of them trespassed on the crosswalks with multiple stops. In this case, ped...Field observations illustrated that, right-turn vehicles stopped at various positions when proceeding within the right-turn lanes, while some of them trespassed on the crosswalks with multiple stops. In this case, pedestrians and bikes (ped/bike) are encountered unsmooth and hazardous crossings when right-turn vehicles encroaching their lanes. Meanwhile, this also causes conflicts between right-turn and through vehicles at the crossing street. To better protect ped/bike at crossings with right-turn vehicles, this paper proposes a concept of “right-turn vehicle box” (RTVB) as a supplemental treatment within right-turn lanes. Sight distance, geometric conditions, and behaviors of vehicles and ped/bike are key factors to consider so as to set up the criteria and to design the suitable treatment. A case study was conducted at an intersection pair in Houston, USA to shape the idea of RTVB, together with driving simulator tests under relevant scenarios. The preliminary crosscheck examination shows that the right-turn vehicle box could possibly provide ped/ bike with smoother and safer crossings. In the interim, the safety and efficiency of right-turn operations were also improved. To further validate the effects, implementation studies should be conducted before the RTVB can make its debut in practice. Future works will focus on the complete warrants and design details of this treatment. Moreover, the concept of “vehicle box” could also be transplanted to other places where turning movement(s) needs assistance or improvements.展开更多
With the development of connected and automated vehicles(CAVs),forming strategies could extend from the typically used first-come-first-served rules.It is necessary to consider passing priorities when crossing interse...With the development of connected and automated vehicles(CAVs),forming strategies could extend from the typically used first-come-first-served rules.It is necessary to consider passing priorities when crossing intersections to prevent conflicts.In this study,a hierarchical strategy based on a cooperative game was developed to improve safety and efficiency during right-turning merging.A right-turn merging conflict model was established to analyze the right-turning vehicle characteristics of the traffic flow.The proposed three-layered hierarchical strategy includes a decision-making layer,a task layer,and an operation layer.A decision-making-layer cooperative game strategy was used to determine the merging priority of straight-going traffic and right-turning flows.In addition,a task-layer cooperative game strategy was designed for the merging sequence.A modified consensus algorithm was utilized to optimize the speed of vehicles in the virtual platoon of the operation layer.Traffic simulations were performed on the PYTHON-SUMO integrated platform to verify the proposed strategy.The simulation results show that,compared with other methods,the proposed hierarchical strategy has the shortest travel time and loss time and performs better than other methods when the straight-going traffic flow increases during right-turning merging at the intersection.The proposed method shows superiority under a significant traffic flow with a threshold of 900 vehicle/(h·lane).This satisfactory application of right-turning merging might be extended to ramps,lane-changing,and other scenarios in the future.展开更多
The location of U-turn bays is an important consideration in indirect driveway left-turn treatments.In order to improve the performance of right-turns followed by U-turns（RTUTs）,this study evaluates the impacts of t...The location of U-turn bays is an important consideration in indirect driveway left-turn treatments.In order to improve the performance of right-turns followed by U-turns（RTUTs）,this study evaluates the impacts of the separation distances between driveway exits and downstream U-turn locations on the safety and operational performance of vehicles making RTUTs.Crash data are investigated at 179 selected roadway segments,and travel time data are measured using video cameras at 29 locations in the state of Florida,USA.Crash rate models and travel time models are developed based on data collected in the field.It is found that the separation distance between driveway exits and downstream U-turn locations significantly impacts the safety and operational performance of vehicles making right turns followed by U-turns.Based on the research results,the minimum and optimal separation distances between driveways and U-turn locations under different roadway conditions are determined to facilitate driver use of RTUTs.The results of this study can be used for future intersection improvement projects in China.展开更多
Through and right-turn shared lanes are widely designed to increase the capacity of through traffic,but they can also cause delays for right-turn vehicles.This study presents a dynamic control method for a shared lane...Through and right-turn shared lanes are widely designed to increase the capacity of through traffic,but they can also cause delays for right-turn vehicles.This study presents a dynamic control method for a shared lane that prioritizes right-turn vehicles at the beginning of the cycle and subsequently allows through traffic to queue in the shared lane for saturated discharge.The traffic wave model is employed to reveal the dynamics of the traffic flow under this control and to derive the relationships among major traffic parameters.Constrained by the major relationship,a linear programming approach to minimize the total queue length is developed to determine the proper values of control parameters,including the shared area length,subordinate signal time lag,and shared or exclusive duration.A sensitivity analysis of the control parameters for different arrival rates and flow ratios is performed.Comparisons are conducted among the dynamic shared lane,the fixed exclusive lane,and the fixed shared lane.The results show that the dynamic control method results in a lower delay for both through and total traffic.展开更多
基金The National Natural Science Foundation of China(No.51278220)
文摘Due to the fact that there is no protected signal phase for right turns at most signalized intersections, the conflict between pedestrians and right-turning vehicles is one of the most common conflict types for pedestrians. A pedestrian safety analysis of the common right-turn mode at four-phase signalized intersections is presented. Relative risk is used as a measure of the effect of behaviors. The analysis mainly includes five pedestrian factors that affect the conflict process between pedestrians and right-turning vehicles. Pedestrians tend to have a higher risk of being involved in conflicts in the following six situations: crossing with others, running over the crossing, entering the intersection, being near the exit lane, crossing in the middle or at the end of a green light when the right-turn lane is shared, crossing at the beginning of a green light or red period when the right-turn lane is exclusive. It is easier for pedestrians to get priority when crossing the street in the following situations: running over a crossing, entering the intersection, being near the entrance lane, and not using the crosswalk. However, pedestrians are more inclined to yield to right-turning vehicles when pedestrians are crossing in the middle of the green light time. Some measures to alleviate the conflict are put forward according to the conclusion. Video observations also indicate that a clear pedestrian waiting area must be marked for both pedestrian safety and right-turning vehicle efficiency at major flat intersections, particularly when the arms cover the lateral dividing strips.
文摘Field observations illustrated that, right-turn vehicles stopped at various positions when proceeding within the right-turn lanes, while some of them trespassed on the crosswalks with multiple stops. In this case, pedestrians and bikes (ped/bike) are encountered unsmooth and hazardous crossings when right-turn vehicles encroaching their lanes. Meanwhile, this also causes conflicts between right-turn and through vehicles at the crossing street. To better protect ped/bike at crossings with right-turn vehicles, this paper proposes a concept of “right-turn vehicle box” (RTVB) as a supplemental treatment within right-turn lanes. Sight distance, geometric conditions, and behaviors of vehicles and ped/bike are key factors to consider so as to set up the criteria and to design the suitable treatment. A case study was conducted at an intersection pair in Houston, USA to shape the idea of RTVB, together with driving simulator tests under relevant scenarios. The preliminary crosscheck examination shows that the right-turn vehicle box could possibly provide ped/ bike with smoother and safer crossings. In the interim, the safety and efficiency of right-turn operations were also improved. To further validate the effects, implementation studies should be conducted before the RTVB can make its debut in practice. Future works will focus on the complete warrants and design details of this treatment. Moreover, the concept of “vehicle box” could also be transplanted to other places where turning movement(s) needs assistance or improvements.
基金the National Key Research and Development Program of China(No.2020YFB1600400)。
文摘With the development of connected and automated vehicles(CAVs),forming strategies could extend from the typically used first-come-first-served rules.It is necessary to consider passing priorities when crossing intersections to prevent conflicts.In this study,a hierarchical strategy based on a cooperative game was developed to improve safety and efficiency during right-turning merging.A right-turn merging conflict model was established to analyze the right-turning vehicle characteristics of the traffic flow.The proposed three-layered hierarchical strategy includes a decision-making layer,a task layer,and an operation layer.A decision-making-layer cooperative game strategy was used to determine the merging priority of straight-going traffic and right-turning flows.In addition,a task-layer cooperative game strategy was designed for the merging sequence.A modified consensus algorithm was utilized to optimize the speed of vehicles in the virtual platoon of the operation layer.Traffic simulations were performed on the PYTHON-SUMO integrated platform to verify the proposed strategy.The simulation results show that,compared with other methods,the proposed hierarchical strategy has the shortest travel time and loss time and performs better than other methods when the straight-going traffic flow increases during right-turning merging at the intersection.The proposed method shows superiority under a significant traffic flow with a threshold of 900 vehicle/(h·lane).This satisfactory application of right-turning merging might be extended to ramps,lane-changing,and other scenarios in the future.
文摘The location of U-turn bays is an important consideration in indirect driveway left-turn treatments.In order to improve the performance of right-turns followed by U-turns（RTUTs）,this study evaluates the impacts of the separation distances between driveway exits and downstream U-turn locations on the safety and operational performance of vehicles making RTUTs.Crash data are investigated at 179 selected roadway segments,and travel time data are measured using video cameras at 29 locations in the state of Florida,USA.Crash rate models and travel time models are developed based on data collected in the field.It is found that the separation distance between driveway exits and downstream U-turn locations significantly impacts the safety and operational performance of vehicles making right turns followed by U-turns.Based on the research results,the minimum and optimal separation distances between driveways and U-turn locations under different roadway conditions are determined to facilitate driver use of RTUTs.The results of this study can be used for future intersection improvement projects in China.
基金supported by the National Natural Science Foundation of China(Nos.52325210,52131204,and 52302411)the Shanghai Science and Technology Innovation Action Plan Project(No.19DZ1209004)the Fundamental Research Funds for the Central Universities(No.22120220137).
文摘Through and right-turn shared lanes are widely designed to increase the capacity of through traffic,but they can also cause delays for right-turn vehicles.This study presents a dynamic control method for a shared lane that prioritizes right-turn vehicles at the beginning of the cycle and subsequently allows through traffic to queue in the shared lane for saturated discharge.The traffic wave model is employed to reveal the dynamics of the traffic flow under this control and to derive the relationships among major traffic parameters.Constrained by the major relationship,a linear programming approach to minimize the total queue length is developed to determine the proper values of control parameters,including the shared area length,subordinate signal time lag,and shared or exclusive duration.A sensitivity analysis of the control parameters for different arrival rates and flow ratios is performed.Comparisons are conducted among the dynamic shared lane,the fixed exclusive lane,and the fixed shared lane.The results show that the dynamic control method results in a lower delay for both through and total traffic.
