A ramp merging area vehicle merging track planning method considering multi-objective optimization in a pure network environment

Abstract

The application discloses a ramp merging area vehicle merging track planning method considering multi-objective optimization in a pure network environment, and steps include: if a main line has a safety gap and ramp vehicles can safely merge into the safety gap, the position of the ramp vehicle when entering an acceleration lane is determined according to the positions and speeds of vehicles before and after the safety gap and the position of the acceleration lane starting point, and a merging starting point and a merging ending point are sampled, and a merging track set is calculated according to the merging starting point and the merging ending point; a safe track set is obtained by selecting a merging track matching collision relationship formulas of the ramp vehicle and front and rear vehicles and the end of the acceleration lane; a multi-objective optimization model of the merging track is established to calculate all tracks of the safe track set, and the ramp vehicle is controlled to drive into the main line along a merging track with the minimum function value. The application can effectively plan a safe ramp merging area vehicle merging track, greatly improves traffic safety and passing efficiency, and has corresponding practical value.

Description

Technical Field

[0001] This invention relates to the field of traffic control, and specifically to a method for planning vehicle merging trajectories in ramp merging areas under a pure connected environment, considering multi-objective optimization. Background Technology

[0002] Merging zones on highway ramps are bottlenecks that limit highway capacity and are prone to traffic congestion and accidents. There are two main reasons why merging zones become bottlenecks: First, road conditions limit visibility, creating blind spots and making it difficult to accurately judge distances. Furthermore, due to varying speed limits, ramp vehicles often travel slower than mainline vehicles, increasing the risk of collisions during lane changes. Second, driver behavior plays a crucial role. Successful merging depends heavily on driver skill. Ramp drivers must consider the surrounding environment, assess the speed and distance of mainline vehicles, and accelerate or decelerate accordingly. Mainline vehicles, in turn, need to adjust their speed or change lanes to accommodate ramp vehicles. Improper driver operation greatly increases the risk of accidents. Additionally, different drivers have varying abilities and styles. Some drivers are overly aggressive, merging at the slightest opportunity without considering safe distances, forcing mainline vehicles to slow down and compromising safety. Others are overly conservative, delaying merging and causing congestion on the ramps. The uncertainty and information asynchrony of human drivers make it difficult to properly solve the problem of ramp merging zones.

[0003] The application of intelligent connected vehicles is expected to improve traffic conditions in merging ramp areas. Vehicles can communicate with each other, eliminating blind spots and the influence of human drivers. Furthermore, during merging, vehicles cooperate to make optimal decisions and controls, thus planning collision-free trajectories. This can, to some extent, prevent accidents and improve traffic efficiency in merging ramp areas. Therefore, planning the merging trajectories of intelligent connected vehicles in highway merging ramp areas is significant for improving safety and efficiency.

[0004] Currently, there are two main methods for planning vehicle merging trajectories in ramp merging areas:

[0005] 1. A vehicle trajectory optimization method based on conflict elimination. For example, the invention patent application with publication number CN114863681A proposes a vehicle trajectory optimization method for conflict elimination in the merging area of ​​the mainline entrance ramp. The optimization objective is to maximize the overall average speed of vehicles. Considering vehicle constraints, safety constraints, and merging constraints, the model is expressed using a linear programming algorithm, and the solution is used to control the speed of each vehicle at each moment to obtain the trajectory of the controlled vehicle.

[0006] 2. A multi-objective control method for ramp merging based on artificial intelligence. For example, patent application CN114241778A proposes a multi-objective optimization control method and system for highway connected vehicle cooperative ramp merging. Based on the acceleration control adjustment of merging vehicles and auxiliary vehicles by the selected guiding vehicle, the optimal control under multiple objectives is solved. This ensures that merging vehicles can successfully merge into the main line while optimizing the energy consumption of merging vehicles and ensuring efficient and safe passage of the road.

[0007] However, existing research focuses on the merging process of vehicles on ramps, with little mention of vehicle status adjustments before merging. Regarding the determination of merging gaps, it is usually assumed that ramp vehicles can safely merge into that gap, which does not reflect reality. Furthermore, when planning trajectories, the optimal selection of the merging start and end points is rarely considered; usually, only the start and end points of the given trajectory are taken into account, and the limitations on acceleration lane length are also given little consideration. Summary of the Invention

[0008] The technical problem this invention aims to solve is the inadequacy of existing vehicle merging trajectory planning methods in ramp merging areas. To address these issues, this invention proposes a multi-objective optimization method for vehicle merging trajectory planning in ramp merging areas under a purely connected environment. This method comprehensively considers the actual clearance on the mainline, the vehicle's motion state, and the road structure of the merging area, conducting a more in-depth study of ramp vehicle merging trajectory planning.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a purely connected environment includes the following steps:

[0011] If a safe gap exists on the main line and vehicles on the ramp can safely merge into the safe gap, then the safe gap is determined as the target merging gap.

[0012] Based on the vehicle positions and speeds of the vehicles before and after the target merging gap, as well as the starting position of the acceleration lane, the positions of each vehicle when entering the acceleration lane are determined. Then, the merging start and merging end points are sampled based on the positions of the vehicles when entering the acceleration lane. Finally, trajectory planning is performed based on the sampled merging start and merging end points to obtain a preliminary merging trajectory set.

[0013] The collision relationships between the vehicle ahead of the target merging gap, the vehicle behind the target merging gap, and the end of the acceleration lane are calculated separately during the merging process of the vehicle on the ramp. The merging trajectory that satisfies each collision relationship is selected from the merging trajectory set. The starting point and ending point of the selected merging trajectory are then used for trajectory planning to obtain the safe trajectory set.

[0014] Set constraints and a multi-objective optimization function. Based on the constraints and the multi-objective optimization function, establish a multi-objective optimization model for the merging trajectory. Use the multi-objective optimization model for the merging trajectory to calculate the corresponding function values ​​of all merging trajectories in the safe trajectory set. Select the merging trajectory with the smallest function value as the optimal merging trajectory and control the ramp vehicles to drive into the target merging gap along the optimal merging trajectory.

[0015] Furthermore, the safety clearance specifically refers to the clearance where the front-end distance is greater than or equal to the minimum safe front-end distance, expressed as follows:

[0016]

[0017] V V1 (t0)≥V V3 (t0)

[0018] Where T is the headway; t0 is the moment the gap is selected; X V1 (t0) represents the position of the preceding vehicle V1 at time t0; X V3 (t0) represents the position of vehicle V3 behind the gap at time t0; L is the vehicle length; V V3 (t0) represents the velocity of the rear vehicle V3 at time t0; T safe Minimum safe headway; V V1 (t0) represents the speed of the vehicle V1 ahead of the gap at time t0.

[0019] Furthermore, determining whether a safe gap exists on the main line and whether ramp vehicles can safely merge into the safe gap includes the step of determining whether ramp vehicles can safely merge into the safe gap, specifically including:

[0020] The speed of the vehicles on the ramp is adjusted to be close to that of the vehicles on the designated mainline. The positions of each vehicle at the moment the speed adjustment of the ramp vehicles ends are calculated. If the positions of the ramp vehicles and the vehicles ahead in the gap both meet the safe merging condition, then the ramp vehicles can safely merge into the safe gap. The expression for the safe merging condition is as follows:

[0021] X V2 (t1)≤X end

[0022] X V2 (t1)>X V3 (t1)+L

[0023]

[0024] Where t1 is the moment when the speed adjustment of vehicles on the ramp ends; X V1 (t1) represents the position of the preceding vehicle V1 at time t1; X V2(t1) represents the position of vehicle V2 on the ramp at time t1; X V3 (t1) represents the position of vehicle V3 after the gap at time t1; X end This is the location of the end of the acceleration lane.

[0025] Furthermore, it also includes the step of adjusting the clearance when there is no safe clearance on the main line, or when vehicles on the ramp cannot safely merge into the safe clearance, specifically including:

[0026] If there is no safe gap on the main line, or if the vehicles on the ramp cannot safely merge into the safe gap, the speed of the vehicles on the main line corresponding to the vehicles on the ramp will be adjusted, including: the vehicle in front of the gap maintains a constant speed and the vehicle behind the gap decelerates, or the vehicle in front of the gap accelerates and the vehicle behind the gap maintains a constant speed, or the vehicle in front of the gap accelerates and the vehicle behind the gap decelerates.

[0027] If the mainline vehicles meet the specified conditions after speed adjustment, the system continues to determine whether a safe gap exists on the mainline and whether ramp vehicles can safely merge into the safe gap. The specified condition expression is as follows: 0 <t ad <t c1

[0028]

[0029] V V1 (t ad )≥V V3 (t ad )

[0030] Among them, t ad Adjust the interval time; t c1 X is the maximum time for a vehicle to accelerate on the ramp. V1 (t ad ) is the gap between the preceding vehicle V1 and t ad Position after seconds; X V3 (t ad () is the gap after vehicle V3 at t ad Position after seconds; V V1 (t ad ) is the gap between the preceding vehicle V1 and t ad Speed ​​after seconds; V V3 (t ad () is the gap after vehicle V3 at t ad The car's speed seconds later.

[0031] Furthermore, the formula for calculating the position of each vehicle when entering the acceleration lane from the ramp is as follows:

[0032]

[0033] X V2 (t2)=X start

[0034] X V1 (t2)=X V1 (t1)+V V1 (t1)×t2

[0035] X V3 (t2)=X V3 (t1)+V V3 (t1)×t2

[0036] Where t2 is the time taken for vehicle V2 on the ramp to move to the starting point of the acceleration lane after the speed adjustment is completed; X V1 (t2), X V3 (t2) represents the positions of the vehicle in front of V1 and the vehicle behind V3 when vehicle V2 on the ramp enters the acceleration lane; X V2 (t2) represents the position of vehicle V2 when it enters the acceleration lane; t1 represents the moment when the vehicle's state adjustment ends; X V1 (t1) represents the position of the preceding vehicle V1 at time t1; X V2 (t1) represents the position of vehicle V2 on the ramp at time t1; X V3 (t1) represents the position of vehicle V3 after the gap at time t1; V V1 (t1) represents the speed of vehicle V1 before the gap at time t1; V V2 (t1) represents the speed of vehicle V2 on the ramp after time t1; V V3 (t1) represents the speed of vehicle V3 after the gap at time t1; X start This indicates the location of the starting point of the acceleration lane.

[0037] Furthermore, based on the position of the vehicle entering the acceleration lane from the ramp, sampling is performed at equal intervals between the position of the vehicle entering the acceleration lane and the end point of the acceleration lane to obtain the sampling point of the merging starting point. Then, sampling of the merging ending point is performed for each merging starting point. The calculation formula is as follows:

[0038]

[0039] in, S1 represents the location of each merging starting point; S2 represents the sampling interval of the merging starting points; t2 represents the time taken for vehicle V2 on the ramp to move to the starting point of the acceleration lane after the speed adjustment is completed; X V2 (t2) represents the position of vehicle V2 when it enters the acceleration lane, X end The end of the acceleration lane; S1 represents the location of each merging endpoint; S2 represents the sampling interval of the merging endpoint; S ′To ensure the distance the vehicle moves forward during lane changing; S is the maximum longitudinal movement distance calculated based on the vehicle speed V2 on the ramp and the maximum permissible acceleration.

[0040] Furthermore, when calculating the collision relationships between a vehicle merging onto the target lane and the vehicle ahead of the gap, the vehicle behind the gap, and the end of the acceleration lane during the merging process of a vehicle on the ramp, the specific calculations are based on a rectangular model and the col function. These calculations cover the collision relationships between the ramp vehicle and the vehicle behind the gap, the ramp vehicle and the vehicle ahead of the gap, and the ramp vehicle and the end of the acceleration lane.

[0041] The collision relationship between vehicles on the ramp and vehicles following behind in the gap is as follows:

[0042]

[0043] Where τ is the inflow duration; X V2 (t), Y V2 (t) represents the set of x and y coordinates of the vertices of vehicle V2 on the ramp, respectively. V2a (t), X V2b (t), X V2c (t), X V2d (t) represents the x-coordinates of the four vertices of vehicle V2 on the ramp, Y and Y respectively. V2a (t), Y V2b (t), Y V2c (t), Y V2d (t) represents the ordinates of the four vertices of vehicle V2 on the ramp; X V3 (t), Y V3 (t) represents the set of x and y coordinates of the vertices of the rear vehicle V3 after the gap, X V3a (t), X V3b (t), X V3c (t), X V3d (t) represents the x-coordinates of the four vertices of the vehicle V3 after the gap, Y and Y respectively. V3a (t), Y V3b (t), Y V3c (t), Y V3d (t) represents the ordinates of the four vertices of the vehicle V3 after the gap;

[0044] The collision relationship between a vehicle on a ramp and the vehicle ahead in the gap is as follows:

[0045]

[0046] Among them, X V1 (t), Y V1 (t) Let X be the x and y coordinates of the vertices of the vehicle V1 before the gap. V1a (t), X V1b (t), XV1c (t), X V1d (t) represents the x-coordinates of the four vertices of the vehicle V1 before the gap, Y and Y respectively. V1a (t), Y V1b (t), Y V1c (t), Y V1d (t) represents the ordinates of the four vertices of the vehicle V1 in front of the gap;

[0047] The collision relationship between vehicles on the ramp and the end of the acceleration lane is as follows:

[0048]

[0049] Among them, X p Y p Let X be the set of x and y coordinates of the two endpoints of the end segment of the acceleration lane. p1 X p2 Y represents the x-coordinate of each of the two endpoints of the end segment of the acceleration lane. p1 Y p2 These are the ordinates of the two endpoints of the end segment of the acceleration lane.

[0050] Furthermore, the formula for calculating the constraint conditions is as follows:

[0051] v min ≤v9(t)≤v max

[0052] |a x (t)| <min{a xmax ,μg}

[0053]

[0054] k p (t)≤k max

[0055]

[0056] TTC i (t)≥TTC Safe orTTC i (t)≤0

[0057]

[0058] Among them, v p (t) represents the velocity at each discrete point on the trajectory; v max For maximum vehicle speed limit; v min Minimum speed limit; a x (t) represents the longitudinal acceleration at each discrete point on the trajectory; a y(t) represents the lateral acceleration at each discrete point on the trajectory; a xmax Maximum longitudinal acceleration limit; a ymax Maximum lateral acceleration limit; μ is the road adhesion coefficient; g is the acceleration due to gravity; k p (t) represents the curvature at each discrete point; k max Maximum curvature constraint; x(t) e y(t) represents the target longitudinal position of the vehicle; e ) represents the target lateral position of the vehicle; The initial longitudinal velocity of the vehicle; TTC safe The minimum safe TTC value; TTC1(t) is the collision time between ramp vehicle V2 and the following vehicle V3 in the gap; TTC2(t) is the collision time between ramp vehicle V2 and the preceding vehicle V1 in the gap; TTC3(t) is the collision time between ramp vehicle V2 and the end of the acceleration lane; X V1 (t), X V3 (t) represents the positions of the front car V1 and the rear car V3 at time t along the main line; X V2 (t) represents the position of vehicle V2 on the ramp at time t; V V1 (t), V V2 (t), V V3 (t) represents the speeds of vehicle V1 ahead of the gap, vehicle V2 on the ramp, and vehicle V3 behind the gap at time t, respectively; X end To the end of the acceleration lane.

[0059] Furthermore, the specific formula for the multi-objective optimization function is as follows:

[0060]

[0061] J c =k d J d +k s J s

[0062]

[0063] In the formula, J u Let L be the objective function for the merging urgency of the trajectory starting from merging point i; L0 is the length of the acceleration lane; L si J is the distance from the starting point i to the end of the acceleration lane; safe Let TTC1(t) be the collision time between vehicle V2 on the ramp and vehicle V3 behind in the gap; TTC2(t) be the collision time between vehicle V2 on the ramp and vehicle V1 in front in the gap; TTC3(t) be the collision time between vehicle V2 on the ramp and the end of the acceleration lane; J c Let J be the comfort objective function; τ be the merging duration; J be the merging objective function.d J s These are the longitudinal and lateral comfort weighting terms, respectively; k d k s These are the weighting coefficients; The impact intensity of longitudinal and lateral vehicles, respectively; J k The objective function is smoothness; k p (t) represents the curvature of each discrete point on the trajectory; k pmax It represents the maximum curvature among all trajectory curves.

[0064] Furthermore, when establishing a multi-objective optimization model for the merging trajectory based on the aforementioned constraints and multi-objective optimization function, the following steps are included:

[0065] Using the aforementioned constraints as constraints in the multi-objective optimization model of the merging trajectory, and normalizing each objective function of the multi-objective optimization model, the objective function of the multi-objective optimization model of the merging trajectory is obtained. The expression of the multi-objective optimization model of the merging trajectory is as follows:

[0066]

[0067] Among them, J u J is the objective function for the urgency of merging a trajectory with merging starting point i as the merging starting point; u,min and J u,max These represent the maximum and minimum values ​​of the objective function for urgency, respectively; J safe The objective function is a safe equilibrium function; J safe,min and J safe,max These represent the maximum and minimum values ​​of the objective function for safe equilibrium, respectively; J c J is the comfort objective function; c,min and J c,max These represent the maximum and minimum values ​​of the comfort objective function, respectively; J k J is the smoothness objective function; k,min and J k,max Let ω1, ω2, ω3, and ω4 be the maximum and minimum values ​​of the smoothness objective function, respectively; ω1, ω2, ω3, and ω4 are the weights of each objective function, and ω1 + ω2 + ω3 + ω4 = 1; v p (t) represents the velocity at each discrete point on the trajectory; v max For maximum vehicle speed limit; v min Minimum speed limit; a x (t) represents the longitudinal acceleration at each discrete point on the trajectory; a y (t) represents the lateral acceleration at each discrete point on the trajectory; a xmax Maximum longitudinal acceleration limit; a ymax Maximum lateral acceleration limit; μ is the road adhesion coefficient; g is the acceleration due to gravity; k p(t) represents the curvature at each discrete point; k max Maximum curvature constraint; x(t) e y(t) represents the target longitudinal position of the vehicle; e ) represents the target lateral position of the vehicle; This represents the initial longitudinal velocity of the vehicle.

[0068] Compared with the prior art, the advantages of the present invention are as follows:

[0069] This invention proposes a safe gap search method and sets a safe gap evaluation standard. Based on the existence of a safe gap, and according to the actual movement of vehicles, a target speed for ramp vehicles is set, and the speed of ramp vehicles is adjusted to determine whether vehicles can merge into the safe gap. This lays the foundation for subsequent trajectory planning and makes up for the deficiencies in existing research on merging gap search in ramp merging areas.

[0070] In the merging trajectory planning stage, this invention proposes a process of "initial trajectory planning" and "re-planning trajectory planning" considering the selection of the merging start and end points. On the one hand, it can achieve the goal of obtaining the optimal merging start point, and on the other hand, it can determine the safe end point area, ensuring the vehicle safety of the entire merging process. Moreover, the entire process is simple and easy to implement. At the same time, the limitation of the acceleration lane length is considered in the entire planning process, and finally a trajectory with optimal comprehensive performance is obtained, which has the optimal merging start and end points, making up for the deficiencies in existing research on merging trajectory planning in merging areas. Attached Figure Description

[0071] Figure 1 This is a flowchart of an embodiment of the present invention;

[0072] Figure 2 This is the import trajectory planning strategy diagram in this embodiment of the invention;

[0073] Figure 3 This is a diagram illustrating the process of determining the inflow gap in an embodiment of the present invention;

[0074] Figure 4 This is a diagram showing the initial planning result of the imported trajectory in an embodiment of the present invention;

[0075] Figure 5 This is a diagram showing the safety detection results in an embodiment of the present invention;

[0076] Figure 6 This is an example diagram of the optimal trajectory in an embodiment of the present invention;

[0077] Figure 7 This is a diagram showing the changes in vehicle state on the optimal trajectory in this embodiment of the invention. Detailed Implementation

[0078] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0079] This embodiment provides a vehicle merging trajectory planning method for ramp merging areas that considers multi-objective optimization in a pure connected environment. Based on existing merging trajectory planning strategies, it considers the motion of mainline vehicles and combines multi-objective optimization theory to consider the urgency, safety balance, driver comfort, and trajectory smoothness of vehicle merging in a pure connected environment. It plans a safe, smooth, collision-free, and optimal merging trajectory for ramp vehicles and provides theoretical support for trajectory planning methods for CAVs in highway merging areas.

[0080] like Figure 1 As shown, the method in this embodiment includes the following steps:

[0081] Step S1: Based on the headway and vehicle status, determine the target merging gap;

[0082] Specifically, based on the headway of the mainline vehicles, it is determined whether there is a safe gap on the mainline and whether the ramp vehicles can safely merge into the safe gap. If so, the safe gap is determined as the target merging gap. Otherwise, the speed of the mainline vehicles is adjusted, and then the headway of the mainline vehicles is used to determine whether there is a safe gap on the mainline and whether the ramp vehicles can safely merge into the safe gap.

[0083] Step S2: Based on the fifth-order polynomial planning algorithm, obtain the preliminary vehicle merging trajectory;

[0084] Specifically, based on the vehicle positions and speeds of the vehicles before and after the target merging gap, as well as the starting position of the acceleration lane, the positions of each vehicle when entering the acceleration lane are determined. Then, the merging start and merging end points are sampled based on the positions of the vehicles when entering the acceleration lane. Finally, a fifth-order polynomial planning algorithm is used to perform trajectory planning based on the sampled merging start and merging end points to obtain a preliminary merging trajectory set.

[0085] Step S3: Based on the rectangular model and the col function, perform safety detection on the vehicle merging trajectory to obtain the collision-free endpoint area.

[0086] Specifically, based on the rectangular model and the col function, the collision relationships between the vehicle ahead of the target merging gap, the vehicle behind the target merging gap, and the end of the acceleration lane during the merging process of the ramp vehicle are calculated respectively. The merging trajectory set that matches each collision relationship is selected. The fifth-order polynomial planning algorithm is used again to plan the trajectory again according to the merging start point and merging end point of the matched merging trajectory to obtain the safe trajectory set.

[0087] Step S4: Based on the multi-objective merging vehicle trajectory optimization method, obtain the optimal trajectory for vehicles merging into the ramp;

[0088] Specifically, constraints and multi-objective optimization functions are set, and a multi-objective optimization model for the merging trajectory is established based on the constraints and multi-objective optimization functions. The corresponding function values ​​of all merging trajectories in the safe trajectory set are calculated using the multi-objective optimization model for the merging trajectory. The merging trajectory with the smallest function value is selected as the optimal merging trajectory, and the ramp vehicles are controlled to enter the target merging gap along the optimal merging trajectory.

[0089] By following the steps above, the merging trajectory planning of vehicles in the ramp merging area under a pure connected environment can be completed.

[0090] Step S5: Use MATLAB software to simulate and analyze the merging process to verify the effectiveness of the trajectory planning method.

[0091] The following reference Figure 2 The above steps will be explained in detail.

[0092] Step S1 in this embodiment specifically includes the following steps:

[0093] Step S1.1: Determine the safety clearance.

[0094] This embodiment uses the headway between mainline vehicles to determine whether the clearance between mainline vehicles is safe. The clearance that meets the conditions is called the safe clearance. Specifically, the safe clearance is the clearance where the headway is greater than or equal to the minimum safe headway, and the expression is as follows:

[0095]

[0096] V V1 (t0)≥V V3 (t0)

[0097] Where T is the headway; t0 is the moment the gap is selected; X V1 (t0) represents the position of the preceding vehicle V1 at time t0; X V3 (t0) represents the position of vehicle V3 behind the gap at time t0; L is the vehicle length; V V3 (t0) represents the velocity of the rear vehicle V3 at time t0; T safe Minimum safe headway; V V1 (t0) represents the speed of the vehicle V1 ahead of the gap at time t0.

[0098] Before determining whether a safe gap exists on the main line and whether vehicles on the ramp can safely merge into the safe gap, if a gap selection is required, the gap with the maximum headway between vehicles on the main line should be selected first for safe gap determination. If it is a safe gap, then the subsequent vehicle merging determination will be carried out.

[0099] Step S1.2: Vehicle entry judgment.

[0100] Before merging into the gap between mainline vehicles, ramp vehicles need to adjust their speed to be close to that of mainline vehicles. Then, the positions of the ramp vehicles and the corresponding mainline vehicles at the end of the speed adjustment are calculated. Based on the conditions that must be met for the ramp vehicles to safely merge into the safety gap, it is determined whether the gap created by the mainline vehicle's current position allows for safe merging. Specifically, the following steps are included:

[0101] Calculate the positions of each vehicle at the moment the ramp speed adjustment ends. When vehicles accelerate on the ramp, the length of the acceleration lane must be considered; therefore, it is necessary to compare the critical speed V at which vehicles reach the end of the acceleration lane with constant acceleration. c and the target speed set by ramp vehicle V2 The expression is as follows:

[0102]

[0103] Among them, X end t represents the position of the end of the acceleration lane. acc The time it takes for the vehicle on the ramp to accelerate from time t0;

[0104] right and These two cases will be discussed separately:

[0105] when At that time, calculate the position of each vehicle at the moment when the speed adjustment of the ramp ends, that is:

[0106]

[0107] t1 = t0 + t c1

[0108] X V1 (t1)=V V1 (t0)×t1+X V1 (t0)

[0109] X V3 (t1)=V V3 (t0)×t1+X V3 (t0)

[0110]

[0111] Among them, t c1 X represents the maximum acceleration time of the vehicle on the ramp, t1 represents the time when the vehicle state adjustment ends, i.e., the time when the vehicle speed adjustment on the ramp ends. V1 (t1) represents the position of the preceding vehicle V1 at time t1; X V2 (t1) represents the position of vehicle V2 on the ramp at time t1; X V3 (t1) represents the position of vehicle V3 after the gap at time t1; a acc For maximum comfort acceleration.

[0112] when At that time, calculate the position of each vehicle at the moment when the speed adjustment of the ramp ends, that is:

[0113]

[0114] t0+t acc ≤t1≤t0+t c2

[0115] X V1 (t1)=V V1 (t0)×t1+X V1 (t0)

[0116] X V3 (t1)=V V3 (t0)×t1+X V3 (t0)

[0117]

[0118] Among them, t c2 This represents the time it takes for a vehicle on the ramp to travel from time t0 to the end of the acceleration lane.

[0119] After calculating the positions of the vehicles on the ramp and the corresponding vehicles on the mainline, the target merging gap is determined based on the conditions that the vehicles on the ramp must meet to safely merge into the safety gap. Specifically, if the positions of both the vehicles on the ramp and the vehicles ahead of the gap meet the safe merging conditions, then the vehicles on the ramp can safely merge into the safety gap. The expression for the safe merging conditions is as follows:

[0120] X V2 (t1)≤X end

[0121] X V2 (t1)>X V3 (t1)+L

[0122]

[0123] Where t1 is the moment when the speed adjustment of vehicles on the ramp ends; X V1(t1) represents the position of the preceding vehicle V1 at time t1; X V2 (t1) represents the position of vehicle V2 on the ramp at time t1; X V3 (t1) represents the position of vehicle V3 after the gap at time t1; X end This is the location of the end of the acceleration lane. If the speed adjustment of vehicles on the ramp meets the above safe merging conditions, the selected gap is the target merging gap.

[0124] Step S1.3: Gap adjustment.

[0125] If the gaps between vehicles on the main line are not safe gaps, or if the selected safe gaps do not meet the requirements for vehicles on the ramps to safely merge, then gap adjustments are required, specifically including:

[0126] The speed of the mainline vehicles corresponding to the ramp vehicles (i.e., the vehicles in front of the selected gap and the vehicles behind the selected gap) is adjusted. In this embodiment, there are three options for adjusting the speed of the mainline vehicles. In order to reduce the interference to the mainline traffic flow, option one is given priority, followed by option two, and finally option three.

[0127] Option 1: During the gap, the vehicle in front maintains a constant speed (V1), while the vehicle behind decelerates (V3). The expression is as follows:

[0128] V V1 (t ad ) = V V1 (t0)

[0129] V V3 (t ad ) = max(V min V V3 (t0)+a dec ×t ad )

[0130] X V1 (t ad ) = V V1 (t ad )×t ad +X V1 (t0)

[0131] Option 2: During the gap, the vehicle in front accelerates (V1), while the vehicle behind maintains a constant speed (V3). The expression is as follows:

[0132] V V1 (t ad )=min(V max V V1 (t0)+a acc ×t ad )

[0133] V V3 (tad ) = V V3 (t0)

[0134]

[0135] Option 3: During the gap, the vehicle in front accelerates with V1, and the vehicle behind decelerates with V3. The expression is as follows:

[0136] The calculation of the speed and position of the vehicle V1 in front of the gap is consistent with that of Scheme 2, that is...

[0137] V V1 (t ad )=min(V max V V1 (t0)+a acc ×t ad )

[0138]

[0139] The speed and position calculations for vehicle V3 after the gap are consistent with Scheme 1, that is...

[0140] V V3 (t ad ) = max(V min V V3 (t0)+a dec ×t ad )

[0141]

[0142] In the above formulas, V min The minimum speed limit for the main line; a dec To decelerate the vehicle; V max The maximum speed limit for the main line; t ad Adjust the interval time; X V1 (t ad ) is the gap between the preceding vehicle V1 and t ad Position after seconds; X V3 (t ad () is the gap after vehicle V3 at t ad Position after seconds; V V1 (t ad ) is the gap between the preceding vehicle V1 and t ad Speed ​​after seconds; V V3 (t ad () is the gap after vehicle V3 at t ad The car's speed seconds later.

[0143] If the mainline vehicles meet the specified conditions after speed adjustment, the system continues to determine whether a safe gap exists on the mainline and whether ramp vehicles can safely merge into the safe gap. The specified conditions, i.e., the conditional expression for gap adjustment, are as follows: 0 <t ad <t c1

[0144]

[0145] V V1 (t ad )≥V V3 (t ad )

[0146] Among them, t ad Adjust the interval time; t c1 X is the maximum time for a vehicle to accelerate on the ramp. V1 (t ad ) is the gap between the preceding vehicle V1 and t ad Position after seconds; X V3 (t ad () is the gap after vehicle V3 at t ad Position after seconds; V V1 (t ad ) is the gap between the preceding vehicle V1 and t ad Speed ​​after seconds; V V3 (t ad () is the gap after vehicle V3 at t ad The car's speed seconds later.

[0147] It should be noted that when further determining whether a safe gap exists on the main line and whether vehicles on the ramp can safely merge into the safe gap, the following conditions must be met for vehicles on the ramp to safely merge into the safe gap:

[0148] X V2 (t ad )≤X end

[0149] X V2 (t ad )>X V3 (t ad )+L

[0150]

[0151] Ramp vehicle V2 by V V2 (t0) accelerates to Requires t c3 Seconds, need to be based on t c3 With t ad Calculating small relationships X V2 (t ad The size of ).

[0152] When t c3 ≤t ad hour,

[0153]

[0154] When t c3 >t ad hour,

[0155]

[0156] In the formula, The target speed for V2; X V2 (t ad ) is V2 at t ad Position after seconds; t c3 It is V V2 (t0) accelerates to Time required; V V2 (t0) represents the velocity of vehicle V2 on the ramp at time t0; X V2 (t0) The position of vehicle V2 on the ramp at time t0.

[0157] If the selected gap corresponds to a safe gap formed by the mainline vehicles after speed adjustment, and the ramp vehicles can merge into the safe gap after speed adjustment, then the selected gap is the target gap.

[0158] like Figure 3 As shown, after the state adjustment in step S1, the mainline vehicles V1 and V3 before and after the selected gap can form a safe gap, and the ramp vehicle V2 can merge into the gap after speed adjustment.

[0159] The specific steps of step S2 in this embodiment are as follows:

[0160] Step S2.1: Determine the vehicle location.

[0161] To ensure that vehicles on the ramp have entered the acceleration lane, it is necessary to determine the position of merging vehicles when they enter the acceleration lane. Based on the position and speed of each vehicle at the end of the speed adjustment phase, obtained during the target merging gap determination stage, and the starting position of the acceleration lane, the position and speed information of the ramp vehicles and mainline vehicles when they enter the acceleration lane can be determined. The calculation formula is as follows:

[0162] When X V2 (t1) <X start At that time, the vehicles on the ramp moved at a constant speed.

[0163]

[0164] X V2 (t2)=X start

[0165] X V1 (t2)=X V1 (t1)+V V1 (t1)×t2

[0166] X 53 (t2)=X 53 (t1)+V V3 (t1)×t2

[0167] Where t2 is the time taken for vehicle V2 on the ramp to move to the starting point of the acceleration lane after the speed adjustment is completed; X V1 (t2), X V3 (t2) represents the positions of the vehicle in front of V1 and the vehicle behind V3 when vehicle V2 on the ramp enters the acceleration lane; X V2 (t2) represents the position of vehicle V2 when it enters the acceleration lane; t1 represents the moment when the vehicle's state adjustment ends; X V1 (t1) represents the position of the preceding vehicle V1 at time t1; X V2 (t1) represents the position of vehicle V2 on the ramp at time t1; X V3 (t1) represents the position of vehicle V3 after the gap at time t1; V V1 (t1) represents the speed of vehicle V1 before the gap at time t1; V V2 (t1) represents the speed of vehicle V2 on the ramp after time t1; V V3 (t1) represents the speed of vehicle V3 after the gap at time t1; X start This indicates the location of the starting point of the acceleration lane.

[0168] Step S2.2: Sample the starting point and ending point of the import.

[0169] When a vehicle on the ramp reaches the target speed and enters the acceleration lane, it can begin merging from any position within the acceleration lane. Before planning the merging trajectory, the starting and ending points of the merging process need to be determined. Therefore, sampling the starting and ending points based on the position of the vehicle entering the acceleration lane includes: performing equally spaced sampling between the vehicle's initial position and the acceleration lane's endpoint, such as... Figure 2 The diagram illustrates the sampling of the inflow starting point. The sampling points constitute the inflow starting point sampling. Then, for each inflow starting point i, the inflow ending point is sampled, and the sampling ending point j... i Construct the inflow and outflow sampling set J corresponding to the sampling start point i. i The calculation formula is as follows:

[0170]

[0171] in, S1 represents the location of each merging starting point; S2 represents the sampling interval of the merging starting points; t2 represents the time taken for vehicle V2 on the ramp to move to the starting point of the acceleration lane after the speed adjustment is completed; X V2 (t2) represents the position of vehicle V2 when it enters the acceleration lane, X end The end of the acceleration lane; S1 represents the location of each merging endpoint; S2 represents the sampling interval of the merging endpoint; S ′ To ensure the distance the vehicle moves forward during lane changing; S is the maximum longitudinal movement distance calculated based on the vehicle speed V2 on the ramp and the maximum permissible acceleration.

[0172] Step S2.3: Import trajectory planning.

[0173] For each starting sampling point i, there is a corresponding set of ending sampling points J. i Match the starting point i and each ending point j i Using a fifth-order polynomial programming algorithm in the Frenet coordinate system, the merging trajectory is generated, such as... Figure 2 The initial trajectory planning diagram is shown in the figure. For each pair of starting point i and sampling ending point j, i Both can generate corresponding alternative trajectories. The calculation formula is:

[0174]

[0175] In the formula, a i b i , i = 0, 1, ..., 5 are the coefficients of the polynomial; x(t), y(t), These represent displacement, velocity, and acceleration in the longitudinal and lateral directions, respectively; t is the lane-changing time.

[0176] Steps S2.1 and S2.2 yield the vehicle's starting and ending points. Combining this with the formula in step S2.3, we can then calculate a. i and b i Solving for the merging trajectory yields the merging trajectory and adds it to the merging trajectory set. The planning results of the merging trajectory in the merging trajectory set are as follows: Figure 4 As shown.

[0177] The specific steps of step S3 in this embodiment are as follows:

[0178] Step S3.1: Calculate the collision risk of the vehicle behind with respect to the gap.

[0179] First, consider the collision relationship between vehicles on the ramp and vehicles following in the gap. The collision relationship between vehicles on the ramp and vehicles following in the gap is as follows:

[0180]

[0181]

[0182] Where τ is the inflow duration; X V2 (t), Y V2 (t) represents the set of x and y coordinates of the vertices of vehicle V2 on the ramp, respectively. V2a (t), C V2p (t), x V2c (t), X V2d (t) represents the x-coordinates of the four vertices of vehicle V2 on the ramp, Y and Y respectively. V2a (t), Y V2b (t), Y V2c (t), Y V2d (t) represents the ordinates of the four vertices of vehicle V2 on the ramp; X V3 (t), Y V3 (t) represents the set of x and y coordinates of the vertices of the rear vehicle V3 after the gap, X V3a (t), X V3b (t), X V3c (t), X V3d (t) represents the x-coordinates of the four vertices of the vehicle V3 after the gap, Y and Y respectively. V3a (t), Y V3b (t), Y V3c (t), Y V3d (t) represents the ordinates of the four vertices of the vehicle V3 after the gap.

[0183] By constructing rectangular models of the vehicles on the ramp and the corresponding vehicles behind them on the main line using the above formula, a collision occurs if the two rectangles overlap during the merging process. Figure 2 As shown in the schematic diagram of trajectory safety detection, the candidate trajectories generated for each sampling starting point are traversed according to the collision relationship formula. When a trajectory satisfies the above formula, then the trajectory is a safe trajectory. Based on the positional distribution of the sampling endpoints of the safe trajectories, the collision-free endpoint candidate region Θ of the current sampling starting point i can be obtained. i1 .

[0184] Step S3.2: Calculate the collision risk with the vehicle ahead of you in the gap.

[0185] During the merging process on a ramp, vehicles may collide not only with vehicles following behind in the gap, but also with vehicles preceding in the gap. The collision relationship between ramp vehicles and vehicles preceding in the gap is as follows:

[0186]

[0187] Among them, X V1 (t), Y V1 (t) Let X be the x and y coordinates of the vertices of the vehicle V1 before the gap. V1a (t), XV1b (t), X V1c (t), X V1d (t) represents the x-coordinates of the four vertices of the vehicle V1 before the gap, Y and Y respectively. V1a (t), Y V1b (t), Y V1c (t), Y V1d (t) represents the ordinates of the four vertices of the vehicle V1 before the gap.

[0188] By constructing a rectangular model of the vehicles on the ramp and the vehicle ahead on the main line using the above formula, a collision occurs if the two rectangles overlap during the merging process. Figure 2 As shown in the schematic diagram of the mid-trajectory safety detection, in the collision-free endpoint candidate area Θ i1 Based on this, collision detection of the preceding vehicle is performed on the trajectory generated at each sampling starting point i. When the above formula is satisfied, it is considered a collision-free trajectory. According to the position distribution of the sampling endpoints of the collision-free trajectories, the candidate region Θ for the collision-free endpoints of the current sampling starting point i can be obtained. i2 .

[0189] Step S3.3: Calculate the collision risk at the end of the acceleration lane.

[0190] If the distance between the merging point and the end of the acceleration lane is too close, a collision may occur during the merging process. The collision relationship between ramp vehicles and the end of the acceleration lane is as follows:

[0191]

[0192] Among them, X p Y p Let X be the set of x and y coordinates of the two endpoints of the end segment of the acceleration lane. p1 X p2 Y represents the x-coordinate of each of the two endpoints of the end segment of the acceleration lane. p1 Y p2 These are the ordinates of the two endpoints of the end segment of the acceleration lane.

[0193] The end of the acceleration lane is simplified into a line segment. Collision detection is then performed on the ramp vehicles and the end of the acceleration lane based on the collision detection function principles for rectangles and line segments. Figure 2 As shown in the schematic diagram of the mid-trajectory safety detection, in the collision-free endpoint candidate area Θ i2 Based on this, a safety detection of the acceleration lane end is performed on the trajectory generated for each sampling starting point i. When the above formula is satisfied, it is considered a collision-free situation, and the collision-free endpoint candidate area Θ of the current sampling starting point i is obtained. i3 .

[0194] Combining the collision detection methods described above, the final collision-free endpoint region can be obtained, which is Θ. i1 Θ i2 Θ i3 The intersection region. For example... Figure 2 As shown in the schematic diagram of trajectory replanning, for Θ i1 Θ i2 Θ i3 The sampling endpoints and corresponding sampling start points of the intersection region are used to generate the merging trajectory again using a fifth-order polynomial programming algorithm in the Frenet coordinate system, such as... Figure 5 As shown.

[0195] The specific steps of step S4 in this embodiment are as follows:

[0196] Step S4.1: Design constraints.

[0197] In this embodiment, constraints are imposed on five indicators: speed, acceleration, curvature, vehicle rollover prevention, and safety. These constraints are set for the speed, acceleration, curvature, vehicle rollover prevention, and safety of vehicles merging onto the ramp to ensure smooth vehicle merging. The calculation formulas are as follows:

[0198] v min ≤v p (t)≤v max

[0199] |a x (t)| <min{a xmax ,μg}

[0200]

[0201] k p (t)≤k max

[0202]

[0203] TTC i (t)≥TTC safe orTTC i (t)≤0

[0204]

[0205] Among them, v p (t) represents the velocity at each discrete point on the trajectory; v max For maximum vehicle speed limit; v min Minimum speed limit; a x (t) represents the longitudinal acceleration at each discrete point on the trajectory; a y (t) represents the lateral acceleration at each discrete point on the trajectory; a xmaxMaximum longitudinal acceleration limit; a ymax Maximum lateral acceleration limit; μ is the road adhesion coefficient; g is the acceleration due to gravity; k p (t) represents the curvature at each discrete point; k max Maximum curvature constraint; x(t) e y(t) represents the target longitudinal position of the vehicle; e ) represents the target lateral position of the vehicle; The initial longitudinal velocity of the vehicle; TTC safe The minimum safe TTC value; TTC1(t) is the collision time between ramp vehicle V2 and the following vehicle V3 in the gap; TTC2(t) is the collision time between ramp vehicle V2 and the preceding vehicle V1 in the gap; TTC3(t) is the collision time between ramp vehicle V2 and the end of the acceleration lane; X V1 (t), X V3 (t) represents the positions of the front car V1 and the rear car V3 at time t along the main line; X V2 (t) represents the position of vehicle V2 on the ramp at time t; V V1 (t), V V2 (t), V V3 (t) represents the speeds of vehicle V1 ahead of the gap, vehicle V2 on the ramp, and vehicle V3 behind the gap at time t, respectively; X end To the end of the acceleration lane.

[0206] Step S4.2: Design the objective function:

[0207] In this embodiment, a multi-objective optimization function is designed based on four indicators: urgency of merging vehicles on the ramp, safety balance, comfort, and trajectory smoothness, in order to obtain the optimal merging trajectory under the current environment. The specific formula is as follows:

[0208]

[0209] J c =k d J d +k s K s

[0210]

[0211] In the formula, J u Let L be the objective function for the merging urgency of the trajectory starting from merging point i; L0 is the length of the acceleration lane; L si J is the distance from the starting point i to the end of the acceleration lane; safeLet TTC1(t) be the collision time between vehicle V2 on the ramp and vehicle V3 behind in the gap; TTC2(t) be the collision time between vehicle V2 on the ramp and vehicle V1 in front in the gap; TTC3(t) be the collision time between vehicle V2 on the ramp and the end of the acceleration lane; J d J s These are the longitudinal and lateral comfort weighting terms, respectively; k d k s J is the weighting coefficient; c Let τ be the comfort objective function; τ be the merging duration. The impact intensity of longitudinal and lateral vehicles, respectively; J k The objective function is smoothness; k p (t) represents the curvature of each discrete point on the trajectory; k pmax It represents the maximum curvature among all trajectory curves.

[0212] Step S4.3: Establish a multi-objective optimization model for the merging trajectory.

[0213] By integrating the above constraints and multiple optimization objectives, a multi-objective optimization model for the merging trajectory is established. Specifically, the constraints are used as the constraints of the multi-objective optimization model for the merging trajectory. After normalizing each objective function of the multi-objective optimization model, the objective function of the multi-objective optimization model for the merging trajectory is obtained. The expression of the multi-objective optimization model for the merging trajectory is as follows:

[0214]

[0215] Among them, J u J is the objective function for the urgency of merging a trajectory with merging starting point i as the merging starting point; u,min and J u,max These represent the maximum and minimum values ​​of the objective function for urgency, respectively; J safe The objective function is a safe equilibrium function; J safe,min and J safe,max These represent the maximum and minimum values ​​of the objective function for safe equilibrium, respectively; J c J is the comfort objective function; c,min and J c,max These represent the maximum and minimum values ​​of the comfort objective function, respectively; J k J is the smoothness objective function; k,min and J k,max Let ω1, ω2, ω3, and ω4 be the maximum and minimum values ​​of the smoothness objective function, respectively; ω1, ω2, ω3, and ω4 are the weights of each objective function, and ω1 + ω2 + ω3 + ω4 = 1; v p (t) represents the velocity at each discrete point on the trajectory; v max For maximum vehicle speed limit; v min Minimum speed limit; ax (t) represents the longitudinal acceleration at each discrete point on the trajectory; a y (t) represents the lateral acceleration at each discrete point on the trajectory; a xmax Maximum longitudinal acceleration limit; a ymax Maximum lateral acceleration limit; μ is the road adhesion coefficient; g is the acceleration due to gravity; k p (t) represents the curvature at each discrete point; k max Maximum curvature constraint; x(t) e y(t) represents the target longitudinal position of the vehicle; e ) represents the target lateral position of the vehicle; This represents the initial longitudinal velocity of the vehicle.

[0216] like Figure 2 As shown in the diagram, the optimal trajectory is obtained by using the multi-objective function of the multi-objective optimization model of the merging trajectory to calculate the function values ​​of all merging trajectories in the safe trajectory set. When the function value is minimized, the merging trajectory is optimal, thus obtaining the merging trajectory with the best overall performance. Figure 6 As shown.

[0217] The specific steps of step S5 in this embodiment are as follows:

[0218] Using MATLAB software, a merging scenario was set up: the minimum speed limit on the main line was 60 km / h, and the maximum speed limit was 120 km / h; the minimum speed limit on the ramp was 40 km / h; the control area started 300m upstream of the acceleration lane starting point; and the acceleration lane length was 200m. Using the control area starting point as the origin of the coordinate axis, the x-coordinate of the acceleration lane starting point was 300, and the x-coordinate of the acceleration lane ending point was 500. Initial position, initial speed, and initial acceleration parameters were designed for both mainline and ramp vehicles. Based on the speed and position relationship between mainline and ramp vehicles, vehicle states were adjusted and merging judgments were made to obtain the final target merging gap. The merging trajectory of ramp vehicles was planned and simulated; the vehicle state changes on the optimal trajectory are shown below. Figure 7 As shown, the simulation results show that at the initial and final moments of merging, the simulation results of the vehicle state values ​​on the ramp are consistent with the actual lane-changing scenario, and each state value is within the limit range. The method of this embodiment can obtain the optimal merging trajectory and simultaneously meet the requirements of driver and passenger comfort and vehicle smoothness.

[0219] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment, characterized in that, Includes the following steps: If a safe gap exists on the main line and vehicles on the ramp can safely merge into the safe gap, then the safe gap is determined as the target merging gap. Based on the vehicle positions and speeds of the vehicles preceding and following the target merging gap, and the starting position of the acceleration lane, the positions of each vehicle when entering the acceleration lane are determined. Then, the merging start and end points are sampled based on the positions of the vehicles entering the acceleration lane. Finally, trajectory planning is performed based on the sampled merging start and end points to obtain a preliminary merging trajectory set. Sampling the merging start and end points based on the positions of the vehicles entering the acceleration lane includes: sampling at equal intervals between the positions of the vehicles entering the acceleration lane and the end point of the acceleration lane to obtain sampling points for the merging start points; then, sampling the merging end points for each merging start point. The calculation formula is as follows: in, The location of each merging point; The sampling interval at the starting point of the merge; The time taken for ramp vehicle V2 to move to the start of the acceleration lane after the speed adjustment is completed; This represents the position of vehicle V2 when it enters the acceleration lane. The end of the acceleration lane; The location of each confluence point; The sampling interval at the endpoint of the merge; To ensure the distance a vehicle travels forward during a lane change; The maximum longitudinal distance of motion is calculated based on the vehicle speed V2 of the ramp vehicle and the maximum permissible acceleration; The collision relationships between the vehicle merging onto the target merging gap and the vehicle ahead of the gap, the vehicle behind the gap, and the end of the acceleration lane are calculated separately. Specifically, based on the rectangular model and the col function, the collision relationships between the vehicle on the ramp and the vehicle behind the gap, the vehicle on the ramp and the vehicle ahead of the gap, and the vehicle on the ramp and the end of the acceleration lane are calculated separately. The merging trajectory in the merging trajectory set where the calculation result of each collision relationship is 0 is selected. The starting point and ending point of the selected merging trajectory are re-planned to obtain the safe trajectory set. Constraints and a multi-objective optimization function including merging urgency, safety balance, comfort, and smoothness are set. The safety balance objective function in the multi-objective optimization function is to minimize the variance of the collision time between the ramp vehicle and the vehicle in front of the gap, the vehicle behind the gap, and the end of the acceleration lane during the merging process. A multi-objective optimization model of the merging trajectory is established based on the constraints and the multi-objective optimization function. The corresponding function values ​​of all merging trajectories in the safe trajectory set are calculated using the multi-objective optimization model of the merging trajectory. The merging trajectory with the smallest function value is selected as the optimal merging trajectory, and the ramp vehicle is controlled to enter the target merging gap along the optimal merging trajectory.

2. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that, The safety clearance specifically refers to the clearance where the front-end distance is greater than or equal to the minimum safe front-end distance, expressed as follows: in, This refers to the headway of the train. The moment when the gap is selected; For the gap, the front vehicle V1 is in The position at that moment; For the gap, the V3 car is in The position at that moment; The length of the vehicle; For the rear vehicle V3 in The speed of time; Minimum safe headway; For the gap, the front vehicle V1 is in The speed of time.

3. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that, When determining whether a safe gap exists on the main line and whether vehicles on the ramp can safely merge into the safe gap, the process includes the step of determining whether vehicles on the ramp can safely merge into the safe gap, specifically including: The speed of the vehicles on the ramp is adjusted to be close to that of the vehicles on the designated mainline. The positions of each vehicle at the moment the speed adjustment of the ramp vehicles ends are calculated. If the positions of the ramp vehicles and the vehicles ahead in the gap both meet the safe merging condition, then the ramp vehicles can safely merge into the safe gap. The expression for the safe merging condition is as follows: in, The moment when the speed adjustment of vehicles on the ramp ends; For the gap, the front vehicle V1 is in The position at that moment; For ramp vehicle V2 in The position at that moment; For the gap, the V3 car is in The position at that moment; This is the location of the end of the acceleration lane; This refers to the length of the vehicle.

4. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that, It also includes steps for adjusting the clearance when there is no safe clearance on the main line, or when vehicles on the ramp cannot safely merge into the safe clearance, specifically including: If there is no safe gap on the main line, or if the vehicles on the ramp cannot safely merge into the safe gap, the speed of the vehicles on the main line corresponding to the vehicles on the ramp will be adjusted, including: the vehicle in front of the gap maintains a constant speed and the vehicle behind the gap decelerates, or the vehicle in front of the gap accelerates and the vehicle behind the gap maintains a constant speed, or the vehicle in front of the gap accelerates and the vehicle behind the gap decelerates. If the mainline vehicles meet the specified conditions after speed adjustment, the system continues to determine whether a safe gap exists on the mainline and whether ramp vehicles can safely merge into the safe gap. The specified conditions are expressed as follows: in, Adjust the time for the interval; The maximum time for vehicles to accelerate on the ramp; For the gap, the front vehicle V1 is in Position after seconds; For the gap, the V3 car is in Position in seconds; For the gap, the front vehicle V1 is in The car's speed seconds later; For the gap, the V3 car is in The car's speed seconds later; Minimum safe headway; This refers to the length of the vehicle.

5. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that, The formula for calculating the position of each vehicle when entering the acceleration lane from the ramp is as follows: in, The time taken for ramp vehicle V2 to move to the start of the acceleration lane after the speed adjustment is completed; , These represent the positions of the vehicle in front of vehicle V1 and the vehicle behind vehicle V3 when vehicle V2 on the ramp enters the acceleration lane. This refers to the position of vehicle V2 when it enters the acceleration lane. The moment when vehicle status adjustment ends; For the gap, the front vehicle V1 is in The position at that moment; For ramp vehicle V2 in The position at that moment; For the gap, the V3 car is in The position at that moment; For the gap, the front vehicle V1 is in The vehicle speed after the specified time; For ramp vehicle V2 in The vehicle speed after the specified time; For the gap, the V3 car is in The vehicle speed after the specified time; This indicates the location of the starting point of the acceleration lane.

6. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that: The collision relationship between vehicles on the ramp and vehicles following behind in the gap is as follows: in, For the duration of the inflow; , Let x and y be the sets of vertex coordinates of vehicle V2 on the ramp. These are the x-coordinates of the four vertices of vehicle V2 on the ramp. These are the ordinates of the four vertices of vehicle V2 on the ramp; , These are the sets of x and y coordinates of the vertices of vehicle V3 after the gap. These are the x-coordinates of the four vertices of vehicle V3 after the gap. These are the ordinates of the four vertices of the vehicle V3 after the gap; The collision relationship between a vehicle on a ramp and the vehicle ahead in the gap is as follows: in, , Let the x and y coordinates of the vertices of the vehicle V1 before the gap be separated. These are the x-coordinates of the four vertices of the vehicle V1 before the gap. These are the ordinates of the four vertices of the vehicle V1 before the gap; The collision relationship between vehicles on the ramp and the end of the acceleration lane is as follows: in, , These are the sets of horizontal and vertical coordinates of the two endpoints of the end segment of the acceleration lane. These are the x-coordinates of the two endpoints of the end segment of the acceleration lane. These are the ordinates of the two endpoints of the end segment of the acceleration lane.

7. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that, The formula for calculating the constraint conditions is as follows: or in, The velocity corresponding to each discrete point on the trajectory; Maximum speed limit; Minimum speed limit; This represents the longitudinal acceleration at each discrete point on the trajectory; This represents the lateral acceleration at each discrete point on the trajectory; Maximum longitudinal acceleration limit; Maximum lateral acceleration limit; The road surface adhesion coefficient; It is the acceleration due to gravity; Let be the curvature at each discrete point; Maximum curvature limit; The target longitudinal position of the vehicle; The target lateral position of the vehicle; This represents the initial longitudinal velocity of the vehicle. Minimum safe TTC value; The collision time between vehicle V2 on the ramp and vehicle V3 following behind in the gap; The collision time between vehicle V2 on the ramp and vehicle V1 in front of it in the gap; The collision time between ramp vehicle V2 and the end of the acceleration lane; , The positions of the front vehicle V1 and the rear vehicle V3 at time t in the main line segment; Let V2 be the position of vehicle V2 on the ramp at time t; , , Let V1 be the speed of the vehicle in front of the gap, V2 be the vehicle on the ramp, and V3 be the speed of the vehicle behind the gap at time t. To the end of the acceleration lane.

8. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment according to claim 1, characterized in that, The specific formula for the multi-objective optimization function is as follows: In the formula, To merge into the starting point The objective function for determining the urgency of merging the trajectory at the merging starting point; To increase the length of the acceleration lane; For the starting point of the merge The distance from the end of the acceleration lane; The collision time between vehicle V2 on the ramp and vehicle V3 following behind in the gap; The collision time between vehicle V2 on the ramp and vehicle V1 in front of it in the gap; The collision time between ramp vehicle V2 and the end of the acceleration lane; The objective function is comfort. For the duration of the inflow; , These are weighted terms for longitudinal and lateral comfort, respectively. , These are the weighting coefficients; , The impact intensity is measured by the longitudinal and lateral forces of the vehicle, respectively. The objective function is smoothness. Let be the curvature of each discrete point on the trajectory; It represents the maximum curvature among all trajectory curves.

9. The method for planning vehicle merging trajectory in a ramp merging area considering multi-objective optimization in a pure connected environment as described in claim 1, characterized in that, When establishing a multi-objective optimization model for the merging trajectory based on the aforementioned constraints and multi-objective optimization function, the following are included: Using the aforementioned constraints as constraints in the multi-objective optimization model of the merging trajectory, and normalizing each objective function of the multi-objective optimization model, the objective function of the multi-objective optimization model of the merging trajectory is obtained. The expression of the multi-objective optimization model of the merging trajectory is as follows: in, To merge into the starting point The objective function for determining the urgency of merging the trajectory at the merging starting point; and These represent the maximum and minimum values ​​of the objective function to be imported. The objective function is a safe equilibrium function; and These represent the maximum and minimum values ​​of the objective function for safe equilibrium, respectively. The objective function is comfort. and These represent the maximum and minimum values ​​of the comfort objective function, respectively. The objective function is smoothness. and These represent the maximum and minimum values ​​of the smoothness objective function, respectively. , , , The weights assigned to each objective function, and ; The velocity corresponding to each discrete point on the trajectory; Maximum speed limit; Minimum speed limit; This represents the longitudinal acceleration at each discrete point on the trajectory; This represents the lateral acceleration at each discrete point on the trajectory; Maximum longitudinal acceleration limit; Maximum lateral acceleration limit; The road surface adhesion coefficient; It is the acceleration due to gravity; Let be the curvature at each discrete point; Maximum curvature limit; The target longitudinal position of the vehicle; The target lateral position of the vehicle; This represents the initial longitudinal velocity of the vehicle.

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