Reaearch On The Cooperative Control Strategy Of Urban Intersection Based On Mixed Platoons Under The Mixed Environment With Connected Automated Vehicles And Connected Human-driven Vehicles

The intersection is a critical component of urban road networks and a frequent area of traffic conflicts,traffic flow weaving,and vehicle interference.Effective intersection control measures can organize multi-directional traffic flows to pass through intersections safely and efficiently,thereby enhancing the operational capacity of at-grade intersections.In traditional traffic flow environments,the control of intersections is primarily achieved through the allocation of right-of-way.The traffic flow states,such as vehicle position,trajectory,and speed,serve merely as environmental variables for control strategies and cannot be directly controlled.With the development of autonomous driving and V2 X communication,the emergence of Connected and Automated Vehicles(CAVs)has altered the composition of traffic flow.The coexistence of CAVs and Connected and Human-driven Vehicles(CHVs)has become a consensus.The existence of CAVs has altered the control entities of intersections.On one hand,due to the communicative and controllable features of CAVS,trajectory optimization for vehicles demonstrates significant potential in enhancing intersection capacity.On the other hand,CHVs can employ V2 V communication to cooperatively drive with other vehicles,reducing interference with surrounding vehicles,avoiding conflicts,and improving the efficiency of interactions such as car-following,lanechanging,and weaving.Therefore,the control strategies for intersections in mixed traffic flow environment can be designed from two perspectives: optimizing the allocation of right-ofway and optimizing vehicle trajectories.However,the random distribution of mixed traffic flows poses challenges for control strategies as they need to adapt to time-varying control entities.The differences between CAVs and CHVs make it difficult to unify the optimization control of individual vehicle movements.The "1+n" mixed plasoon,as a novel form of mixed traffic flow organization,utilizes CAVs as leader vehicles for the platoons.With the controllability of CAVs,indirect motion control for member vehicles is achieved.Through formation control,the traffic flow transitions from a heterogeneous distribution of vehicles to a homogeneous distribution of platoons,providing a new and unified form of control entities for intersection control strategies in the mixed traffic flow environment.Designing intersection control strategies with mixed platoons as the entities entails addressing two key issues.The first key issue is to control vehicle forming "1+n" platoons in the upstream section of the intersection.The second key issue involves coordinating the allocation of right-of-way for mixed platoons at the intersection and optimizing the trajectory of mixed platoons.Due to the evident temporal sequence and spatial separation of these two issues,the intersection and its upstream section are categorized into four functional zones based on control requirements: Free Zone(FZ),Cooperative Zone(CZ),Buffer Zone(BZ),and Conflict Zone(CZ).Moreover,a two-stage control strategy has been proposed,systematically addressing the control of mixed platoon formation and the coordination of conflicts,as well as trajectory optimization.The main research accomplishments are outlined as follows:(1)We proposed a platoon formation control method considering the intersection movements of vehicles.This method is developed to organize the vehicles into “1+n” platoons in the upstream road section of intersections.The proposed method is divided into two steps.In the first step,an optimal polatoon formation scheme is devised based on the vehicles’ motion states and their movements at the intersection.This scheme can ensure the consistency of the intersection movements within each platoon,and maximizes the utilization of CAVS as leader vehicles.We established an 0-1 integer programming modedl to optimize the carfollowing relationships by allocating optimal car-following target.The formation scheme of mixed platoons can be obtained by assigning the following relation,and the longitudinal position relation between the platoons can be defined.The second step is controlling vehicles to complete the platoon formation as the platoon formation scheme.The platoon formation process is spatially divided into two parts: lateral lane-changing and longitudinal carfollowing.For the lane-changing process,a rule-based lane distribution decision method is proposed to determine the platoons’ lane choices.We designed a coordination framework to coordinate the lane-changing decisions based on the incentives.For the car-following process,a method for calculating acceptable headway based on lane-changing incentives is designed.By introducing acceptable headway as an intermediate variable into the CACC and IDM+models,the longitudinal motion parameters of the vehicles are computed,enabling control of the vehicles’ longitudinal movement.The effectiveness of the proposed method is validated through a series of simulation experiments based on SUMO.Moreover,when compared to banchmark without control,the method demonstrated an improvement in the traffic efficiency of vehicles within the upstream road section.(2)We proposed a coordinated control strategy for a four-arm intersections based on mixed platoons.Typically,the path of mixed platoons within a four-arm intersection corresponds to a line connecting the entrance and exit.Therefore,the conflict positions arised from paths are fixed.The coordinated control of mixed platoons at four-arm intersections can be realized by planning the optimal passing order at conflicting positions.Using the delay caused by yielding betweem conflict platoons as the weight of the directed graph,a conflictdirected graph and a coexistence undirected graph are established based on graph theory,representing conflict relationships between platoons in BZ.We designed an improved minimum cover clique(MCC)algorithm,which utilizing breadth-first search to plan the optimal passing order for platoons in all directions.The effectiveness of the proposed method is validated through a series of simulation experiments based on SUMO.Compared to two benchmark strategies,the First-in-First-out(FIFO)method and fixed-phase signal control method,the proposed method effectively enhanced intersection capacity and reduced vehicle delay while avoiding platoon conflicts.(3)We proposed a coordinated control strategy for roundabouts based on mixed platoons.During the merging and exiting processes of mixed platoons at roundabouts,at least two forced lane changes are required.Additionally,the path taken by platoons through the roundabout is uncertain.Therefore,the coordinated control for platoons at the roundabout intersection can be achieved by addressing three sub-problems: optimizing the merging timing for platoons in BZ,coordinating platoon lane changes,and optimizing the longitudinal trajectories of platoons.To address the first sub-problem,we developed a mixed platoon reorganization optimization model,involving splitting the platoons in BZ into individual vehicles,recombining them with the internal platoons of the roundabout,and deciding the optimal merging gap.To address the second sub-problem,we introduced a rule-based method to coordinate the lane distribution of platoons.These rules aim to ensure that all platoons take the optimal path through the roundabout.Vehicles change lanes according to the recombination platoon scheme and lane distribution solution,forming new platoons in the target lanes.To address the third sub-problem,a mixed-integer linear programming model is established based on the geometric layout of the roundabout.This model uses polar coordinates to represent the trajectories of platoons,minimizes the distance between vehicles and the desired exit at each time step.This approach distributed optimizes the longitudinal motion of each leader vehicle,indirectly optimizing the trajectories of platoons through the roundabout.The effectiveness of the proposed method is validated through a series of simulation experiments based on SUMO.Compared to two benchmark strategies,the Firstin-First-out(FIFO)method and fixed-phase signal control method,the proposed method effectively improved the capacity of the roundabout,reduced queuing in BZ caused by a lack of merging gaps,and decreases the delay for vehicles.The two-stage control strategy proposed in this study provides a new approach for organizing mixed traffic flow on urban roads in the environment mixed with CAVs and CHVs.It systematically addresses the optimization control problem of urban intersections based on“1+n” platoons,demonstrating good generality and expandability.