Traffic organization of roundabout area and optimization method of upstream intersection signal

Abstract

The application relates to the technical field of traffic organization optimization, and discloses a traffic organization of a roundabout intersection area and an optimization method of an upstream intersection signal, which comprises the following specific steps: taking the roundabout intersection and its adjacent upstream and downstream intersections as the roundabout intersection area; maintaining the right-turn traffic flow of the roundabout intersection in the original passing mode; separating the left-turn traffic flow and the straight traffic flow, the straight traffic flow drives in the clockwise direction in the roundabout, and the left-turn traffic flow is separated from the roundabout and directly left turns through the left-turn special road; interchanging the straight and left-turn traffic flow import roads and the opposite export roads of the upstream intersection; moving the left-turn road cut-off line of the upstream intersection backward; and completing the traffic organization optimization of the roundabout intersection area. The application solves the problem that the prior art does not consider the left turn and exhaust emission, and has the characteristics of high efficiency and environmental protection.

Description

Traffic organization in roundabout areas and optimization methods for upstream intersection signals Technical Field

[0001] This invention relates to the field of traffic organization optimization technology, and more specifically, to a method for optimizing traffic organization in a roundabout area and the signaling of an upstream intersection. Background Technology

[0002] With the rapid development of the national economy and the improvement of people's living standards, urban travel demand has surged, leading to a sharp increase in urban road traffic pressure and frequent traffic congestion, especially in some key areas where congestion has become the norm. Traffic congestion not only reduces travel efficiency but also increases vehicle emissions, further exacerbating the negative environmental impact of urban traffic. To alleviate urban traffic congestion and its negative effects, management departments have sought solutions from the perspectives of traffic resource supply and travel demand management, with the construction or reconstruction of road traffic infrastructure being a crucial measure. However, the construction or reconstruction of road traffic infrastructure often requires substantial financial investment and is constrained by urban land resources. Therefore, how to improve the efficiency of existing road traffic facilities while reducing vehicle emissions has become a critical issue in urban traffic management.

[0003] Roundabouts are crucial infrastructure in urban road traffic systems and key nodes affecting road network capacity. Under low to medium traffic loads, roundabouts facilitate continuous and safe traffic flow. However, with increasing traffic loads, the capacity of roundabouts is challenged, leading to reduced efficiency issues such as decreased vehicle speeds within the roundabout and conflicts between roundabout traffic and approach lane traffic causing roundabout "lockdowns." Existing solutions generally fall into two categories: one is to add signal control to the existing roundabout, using traffic lights to reorganize traffic flow and improve efficiency, but this method is not very effective and can increase intersection delays; the other is to convert the roundabout into a conventional signal-controlled intersection, which can effectively improve capacity, but the conversion cost is high and intersection delays are also increased. Among all traffic flows at an intersection, left-turn traffic has a significant impact on capacity. Existing research on left-turn traffic organization includes: 1. Installing pre-signal lights upstream of the main signal at the intersection to allow left-turning vehicles to enter the dedicated left-turn lane via the pre-signal lights; 2. Proposing a method of using borrowed lanes for left turns and combining it with signal control to optimize intersection traffic organization; 3. Optimizing intersection left-turn traffic organization through lane channelization; 4. Proposing a conceptual design for a grade-separated roundabout with left turns based on the optimization of left turns at roundabouts; 5. Setting up waiting areas at roundabouts and combining them with signal control to optimize intersection capacity; 6. Achieving more realistic network efficiency maximization by only changing the left-turn handling method at signalized intersections; 7. Designing signal timing based on the length of the shifted left-turn lane using the concept of a Displaced Left Turn (DLT).

[0004] Besides improving the efficiency of roundabouts, another current research trend is to reduce pollutant emissions at intersections through signal control. Lu Jie proposed a signal timing optimization model based on vehicle emissions, using the minimum vehicle emissions as the optimization objective and constraining efficient green light time, cycle time, and phase difference. Existing technologies consider the difference in total emissions between idling and normally moving vehicles in emission calculations, and compare emissions at saturated and unsaturated intersections using VISSIM simulations. In research on vehicle emission calculations, the CORERT and MOVES models are most commonly used, but these are mostly based on European vehicle emission standards. Existing technologies analyze and calculate urban traffic energy consumption emissions based on the COPERT model.

[0005] Existing research on traffic flow optimization at roundabouts has the following shortcomings: (1) Optimizing left-turn traffic flow by setting up waiting areas and signal control can improve the capacity of the intersection, but it does not change the current situation of mixed left-turn and straight-through traffic, long travel distance of left-turn traffic within the roundabout, and numerous conflict points, merging points, and diverging points within the roundabout; (2) Existing research focuses more on how to improve the capacity of roundabouts, while neglecting vehicle exhaust emissions in this area. Vehicle exhaust emissions through the roundabout area are related to vehicle travel time, waiting time, and vehicle driving status. Among them, vehicle travel time depends on the vehicle's travel distance and speed, while vehicle waiting time depends on the stagnation time caused by road congestion or signal control. Although existing methods to improve the efficiency of roundabouts can reduce vehicle exhaust emissions to some extent, the emission reduction effect mainly comes from increasing vehicle speed and reducing waiting time, and cannot reduce emissions by reducing vehicle travel distance. At roundabouts, vehicles turning left need to merge into the roundabout and travel three-quarters of the way around the roundabout to make the turn. This not only involves a long travel distance but also creates multiple conflict points, which can easily cause vehicles passing through the roundabout to slow down or even stop briefly multiple times. This has an adverse effect on the traffic efficiency and exhaust emissions of the roundabout.

[0006] Therefore, how to invent a new method for organizing traffic flow at roundabouts that takes into account left turns and exhaust emissions is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the issue that existing technologies do not consider left turns and exhaust emissions, this invention provides a method for optimizing traffic organization in roundabout areas and upstream intersection signals, which is highly efficient and environmentally friendly.

[0008] To achieve the above-mentioned objectives of this invention, the technical solution adopted is as follows:

[0009] The optimization method for traffic organization in roundabout areas includes the following specific steps:

[0010] The roundabout area is defined as the roundabout area consisting of the roundabout itself and its adjacent upstream and downstream intersections.

[0011] The right-turning traffic at the roundabout will maintain its original flow pattern; the left-turning traffic and the straight-through traffic will be separated into lanes, with the straight-through traffic traveling clockwise within the roundabout, while the left-turning traffic will be separated from the roundabout and turn left directly through the dedicated left-turn lane.

[0012] The straight-through and left-turn traffic lanes at the upstream intersection were swapped with the opposite exit lanes; the left-turn lane cut-off line at the upstream intersection was moved back; and the traffic organization of the roundabout area was optimized.

[0013] Preferably, the roundabout area is a two-way six-lane, two- or three-lane roundabout; its upstream and downstream intersections are two-way six-lane intersections.

[0014] An optimization method for the signal phase of the upstream intersection in a roundabout area, used to swap the through and left-turn traffic inlet lanes with the opposite exit lanes of the upstream intersection, includes the following specific steps:

[0015] S1: Considering vehicle lane change delay, average vehicle delay, vehicle overflow delay at intersection, phase difference, regional average delay, and total vehicle emissions, construct an upstream intersection signal timing optimization model;

[0016] S2: Perform timing coordination optimization on the upstream intersection signal timing optimization model to obtain the optimal signal timing scheme.

[0017] Preferably, in step S1, considering vehicle lane-changing delay, average vehicle delay, vehicle overflow delay at intersection, phase difference, regional average delay, and total vehicle emissions, an upstream intersection signal timing optimization model is constructed. The specific steps are as follows:

[0018] S101: Calculate lane change delay based on the positional relationship between the lane-changing vehicle and the vehicle in front, the speed, acceleration, and gear shift duration of the vehicles in front and behind.

[0019]

[0020]

[0021] in, It is the longitudinal distance between the front ends of the vehicle being overtaken and the overtaking vehicle that is able to change lanes;

[0022] v0 is the initial longitudinal distance between the front ends of the overtaken vehicle and the vehicle being overtaken; v0 is the initial speed of the vehicles in the lane-changing area; t is the lane-changing time; a d d is the expected deceleration of the following vehicle; d is the lane-changing delay.

[0023] S102: Calculate the average vehicle delay using the excessive delay model:

[0024] d A =d u +d o

[0025]

[0026]

[0027]

[0028]

[0029]

[0030] Where, d A For the delay of each vehicle; d u Average vehicle delay; d o For random arrival delays; N d The average number of vehicles stuck in traffic; T is the signal cycle duration; t g For green light time; t r λ is the red light duration; s0 is the intersection saturation threshold; s is the directional saturation of the approach lane (s=q / Q=q / S×T / t). g =fr / λ); fr is the traffic flow ratio at the entrance (fr = q / S); W is the time period set for the observation and analysis; S is the saturation flow.

[0031] S103: Considering vehicles in the queue that have both complete stops and starts and intermittent stops and starts, calculate the vehicle overflow delay at the intersection:

[0032]

[0033] Where, d a Traffic congestion at intersections causes delays; S a Average vehicle speed at intersection entrance

[0034] S a =0.9(25.6+0.47S) pl );S pl Speed ​​limits at intersection entrances; S s The threshold speed at which the vehicle comes to a complete stop; r a For vehicle acceleration; r d To slow down the vehicle;

[0035] When optimizing a roundabout and its adjacent upstream and downstream intersections as a whole, the signal timing of the upstream intersections in each direction of the roundabout is optimized collaboratively. In the collaborative optimization, by adding a phase difference, vehicles can pass through the second intersection without waiting after passing through the first signal-controlled intersection, thereby reducing waiting time and reducing overall delay.

[0036] S104: Calculate the green light start time for the first phase:

[0037]

[0038] Where x and y represent different upstream intersections, if there are M upstream intersections, then x, y ∈ [1, L, M] and x ≠ y; t y1 It is the start time of the green light in the first phase of intersection y; t x1 It is the start time of the green light in the first phase at intersection x; It is the relative phase difference between intersection y and intersection x;

[0039] in, Specifically:

[0040]

[0041]

[0042]

[0043]

[0044] Where ω is the weighting coefficient; It is the phase difference when turning left on the uphill route; It is the uplink and downlink phase difference; q l This refers to the volume of traffic turning left on the uphill route; q s d is the upbound straight-through traffic volume; d is the delay caused by straight-through lane changes; v1 is the vehicle speed at the roundabout.

[0045] Assume that the vehicle speed follows a normal distribution:

[0046]

[0047]

[0048] Where: v a σ is the mean speed; σ is the standard deviation of vehicle speed; v b n represents the b-th velocity (b = 1, L, m); b Indicates velocity v b The corresponding number of vehicles is n b ;

[0049] Calculate the normal distribution probability of vehicle speed:

[0050]

[0051] Calculate the expected value of vehicle speeds within the area:

[0052]

[0053] Calculate the relative phase difference between intersection y and intersection x.

[0054]

[0055] S105: Determine the optimal phase difference based on the average delay of each approach vehicle at each upstream signal-controlled intersection to obtain the regional average delay:

[0056]

[0057] in:

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065] Where PI is the average delay per vehicle in the region, which is equal to the total delay divided by the total number of vehicles; d x N represents the average delay at the upstream x-intersection; xy d represents the number of vehicles stranded in the direction from intersection x to intersection y; d represents the lane-changing delay. a Indicates vehicle overflow delay; d 0xy This represents the random arrival delay of vehicles traveling from intersection x to intersection y. and These represent the actual traffic volume of vehicles going straight and turning at the upstream x intersection reaching the next intersection, respectively.

[0066] S106: Calculate the idling emissions of a vehicle waiting at a traffic light at an upstream intersection:

[0067]

[0068] Where D represents the vehicle's idling emissions; t rxi The red light time t for phase i at the upstream x intersection. r Unit: min; K is the air-fuel ratio at idle speed; A is the fuel consumption at idle speed, unit: kg / min;

[0069] Calculate the total emissions of the vehicle during operation:

[0070]

[0071] Among them, E C p represents the total gas emissions within time C, in grams; c represents the travel time, in seconds; p c The instantaneous vehicle power specificity (VSP) at second c, in kW / t; f(p c The instantaneous VSP of the vehicle within the calculation time is p. c The number of times; R(p) c The instantaneous VSP value at second c is p. c The average emission rate of D(t), in g / s; rxi () represents emissions while the vehicle is waiting, in grams;

[0072] Calculate the specific power of a motor vehicle:

[0073] VSP=v×[1.1a+9.81×(atan(sinG))+0.132]+0.000302v 3

[0074] Where VSP is the specific power of the vehicle, in kW / t; v is the vehicle speed, in m / s; and a is the vehicle acceleration, in m / s². 2 G represents the road gradient.

[0075] The emission rate R(p) is calculated based on the exhaust gas mass flow. c ):

[0076]

[0077] Where MF is the exhaust gas mass flow rate, in kg / h; EC is the concentration of a certain pollutant, in ppm; the exhaust gas emissions at the roundabout area are obtained as follows:

[0078]

[0079] Among them, ECT Total regional emissions, in grams; β zw Let q represent the emission factor coefficients for different vehicle types, z represent different emission factors z∈[1,4], and w represent different vehicle types w∈[1,5]. x Let x be the traffic volume at intersection x;

[0080] S107: Considering the targets of average vehicle delay and total emissions, construct an upstream intersection signal timing optimization model:

[0081] min[PI,E CT ]

[0082] st

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090] Among them, T x Let λ be the period duration of the upstream intersection x; xi Let x be the green light ratio of the i-th phase at intersection x, in seconds. If there are M upstream intersections and N phases at each intersection, then x and i take the values ​​x∈[1,M], i∈[1,N], and N. * The set of positive integers is required; the cycle of signalized intersections within the area must be consistent to ensure that the phase difference of the signal cycle is the same in each cycle; the green light time of each phase needs to be set with upper and lower limits to coordinate the smooth passage of vehicles through the intersection; the signal difference must be kept consistent in multiple sets of signal cycles, and the signal difference must satisfy that the phase difference between the up and down directions is an integer multiple of the phase cycle; it is stipulated that the phase difference should be less than the signal cycle of the up and down directions of the intersection; the cycle of signalized intersections within the area must be the same.

[0091] Furthermore, the timing coordination optimization model for the upstream intersection signal timing is performed, and the specific steps are as follows:

[0092] S201: Based on the average vehicle delay calculation formula of the upstream intersection signal timing optimization model and the parameter settings of each intersection in the area, a set of signal timing schemes is calculated without limiting the signal cycle length of each intersection.

[0093] S202: Simulate the timing scheme for each intersection to determine whether all vehicles can pass through the area. If yes, it is deemed feasible and proceeds to step S203; otherwise, it is deemed infeasible and returns to step S201.

[0094] S203: Using the intersection timing scheme with the longest period as the standard, the timing schemes of the other intersections are enlarged proportionally according to their respective phase lengths to make the signal periods of each intersection equal in length, thus obtaining the revised feasible signal timing scheme.

[0095] S204: Let the longest period be T. max A multi-objective genetic algorithm is used to solve the signal timing collaborative optimization model, obtain the Pareto solution of the intersection signal timing scheme, and select the satisfactory solution.

[0096] S205: Simulate the satisfactory solution, output the average vehicle delay and total emissions at each intersection, and compare the standard deviation of several simulation results to verify the effectiveness of the intersection signal timing scheme and obtain the verified effective signal timing scheme.

[0097] S206: Output signal timing scheme.

[0098] Furthermore, in step S204, a multi-objective genetic algorithm is used to solve the signal timing cooperative optimization model. The specific steps are as follows:

[0099] S2401: Initialize the population;

[0100] S2402: Use the revised feasible signal timing scheme as individuals in the initial population to generate the first generation population;

[0101] S2403: Perform crossover and mutation operations on the first-generation population to generate the second-generation population.

[0102] S2404: Merge the parent and child generations in the second generation population;

[0103] S2405: Perform fast non-dominated sorting on the merged second-generation population and calculate crowding.

[0104] S2406: Select a new parent generation based on crowding level using an elite strategy;

[0105] S2407: Perform selection, crossover, and mutation operations on the population to generate new offspring;

[0106] S2408: Determine whether the number of iterations has reached the set threshold. If so, output the Pareto solution of the intersection signal timing scheme. Otherwise, increment the number of iterations by 1 and return to step S2404.

[0107] Furthermore, the population is initialized as follows: taking the roundabout as the center, the upstream intersections of the roundabout are arranged in the order of North-East-South-West, generating individuals composed of M sets of numbers. Each set of numbers represents the duration of the green light signal in four phases of an intersection, and the phase order of each set of numbers is the same; where M is the number of upstream intersections of the roundabout.

[0108] Furthermore, if the phase duration of an individual generated in the initial population is 0 or the total signal duration of the individual exceeds the maximum signal period, then the individual is deemed unqualified and a new individual is generated.

[0109] Furthermore, in step S2405, a rapid non-dominated sorting is performed on the merged second-generation population, and the crowding degree is calculated. Specifically, individuals are non-dominated sorted using average delay and total emissions as indicators. The higher the level, the lower the individual's fitness value, and vice versa. At the same time, the crowding degree of individuals within the same level is calculated, and individuals with higher crowding degree are more likely to be retained.

[0110] Furthermore, the operations on population selection, crossover, and mutation are specifically as follows:

[0111] Selection operation: The population is selected using a roulette wheel method and an elite retention strategy is adopted;

[0112] Mutation operation: Randomly select two gene loci on two individuals in the population as mutation sites, and swap the values ​​of the two mutation sites.

[0113] Crossover operation: Randomly determine the crossover point from the first-generation parent and the second-generation parent, and then swap the crossover points.

[0114] The beneficial effects of this invention are as follows:

[0115] This invention proposes an optimized traffic organization method for roundabout areas. Specifically, it treats the roundabout and its adjacent upstream and downstream intersections as a whole. At the upstream intersections, signal control enables the interchange of left-turn and through traffic inlet lanes with opposite exit lanes, separating left-turning and through traffic flows. This significantly reduces the travel distance of left-turning vehicles within the roundabout and minimizes traffic conflicts. Simultaneously, the signal phases at the upstream intersections are redesigned to facilitate lane interchanges, and the signal timings at upstream intersections in each direction are optimized collaboratively. Ultimately, this improves the traffic efficiency of the roundabout area and reduces vehicle emissions. This novel traffic organization method for roundabouts not only improves the traffic efficiency of the roundabout area road network but also reduces emissions within the area, exhibiting high efficiency and environmental friendliness. Attached Figure Description

[0116] Figure 1 is a schematic diagram of the research area of ​​the optimization method for traffic organization in a roundabout area according to the present invention.

[0117] Figure 2 is a schematic diagram of the conventional traffic flow organization scheme for a roundabout.

[0118] Figure 3 shows the conflict points, divergence points, and merging points under the conventional traffic flow organization scheme of a roundabout.

[0119] Figure 4 is a schematic diagram of the traffic flow organization scheme of the optimization method for traffic organization in the roundabout area of ​​the present invention.

[0120] Figure 5 is a schematic diagram of traffic flow organization at the upstream intersection of the roundabout area according to the present invention.

[0121] Figure 6 is a schematic diagram of the diversion and merging points of the novel traffic flow organization scheme for the upstream intersection of the roundabout area of ​​the present invention.

[0122] Figure 7 is a schematic diagram of the timing coordination optimization process of the optimization method for the upstream intersection signal phase in the roundabout area of ​​the present invention.

[0123] Figure 8 is a schematic diagram of the multi-objective genetic algorithm for solving the signal timing collaborative optimization model of the optimization method for the upstream intersection signal phase in the roundabout area of ​​the present invention.

[0124] Figure 9 shows the contribution rate of major pollutant emission factors for vehicles meeting the China V emission standard.

[0125] Figure 10 is a schematic diagram of the Pareto solution set of the optimization method for the upstream intersection signal phase in the roundabout area of ​​the present invention.

[0126] Figure 11 is an example of the initial population for the optimization method of the upstream intersection signal phase in the roundabout area of ​​the present invention.

[0127] Figure 12 is a schematic diagram of the OX cross operation of the optimization method for the upstream crossroad signal phase in the roundabout area of ​​the present invention.

[0128] Figure 13 is a schematic diagram of the mutation operation of the binary mutation method in the optimization method of the upstream intersection signal phase in the roundabout area of ​​the present invention. Detailed Implementation

[0129] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0130] Example 1

[0131] In one specific embodiment, as shown in Figure 1, the roundabout area is a two-way six-lane, two- or three-lane roundabout; its upstream and downstream intersections are two-way six-lane intersections.

[0132] In this embodiment, the weaving section length of the central area of ​​the roundabout is 26.8m, the lane width is 3.5m, the center width is 21m, and the radius of the central area is 20m.

[0133] In this embodiment, in the conventional traffic flow organization of a roundabout, vehicles typically travel counterclockwise, as shown in Figure 2; the figure uses southbound traffic as an example. Vehicles entering the roundabout need to merge and diverge within the roundabout, resulting in longer vehicle dwell times and increased vehicle delays. Left-turning vehicles need to travel counterclockwise around approximately 3 / 4 of the roundabout, leading to longer travel times within the roundabout and generating multiple conflict points, divergence points, and merging points. Existing roundabout traffic flow organization schemes generate 8 conflict points, 8 divergence points, and 8 merging points within the roundabout, as shown in Figure 3, negatively impacting the roundabout's traffic efficiency.

[0134] To address this problem, as shown in Figure 4, this invention proposes an optimization method for traffic organization in roundabout areas, including the following specific steps:

[0135] The roundabout area is defined as the roundabout area consisting of the roundabout itself and its adjacent upstream and downstream intersections.

[0136] The right-turning traffic at the roundabout will maintain its original flow pattern; the left-turning traffic and the straight-through traffic will be separated into lanes, with the straight-through traffic traveling clockwise within the roundabout, while the left-turning traffic will be separated from the roundabout and turn left directly through the dedicated left-turn lane.

[0137] As shown in Figure 5, the straight-through and left-turn traffic inlet lanes and the opposite exit lanes of the upstream intersection are swapped; the cut-off line of the left-turn lane of the upstream intersection is moved back; in order to provide more queuing space for straight-through vehicles at the upstream intersection, thereby effectively avoiding traffic congestion and completing the traffic organization optimization of the roundabout area.

[0138] In this embodiment, after lane swapping, the traffic flow organization of the roundabout is smoother, and the number of conflict points, merging points, and diverging points is further reduced, which is expected to improve the driving safety and traffic efficiency of the roundabout. The advantages of this traffic flow organization scheme are as follows: (1) The traffic flow around the roundabout is reduced to straight-through vehicles, effectively increasing the straight-through capacity; (2) Dedicated lanes are provided for both left and right turns, and under ideal conditions, the capacity of the dedicated lanes can be regarded as free-flow capacity; (3) The travel distance of left-turning vehicles is only 1 / 4 of the roundabout; (4) The entrance lanes of left-turning and straight-through traffic flows are swapped to two lanes on the other side of the road center divider, significantly reducing the number of conflict points, merging points, and diverging points. The traffic flow organization scheme proposed in this invention has only 4 diverging points and 4 merging points, with 0 conflict points, as shown in Figure 6, which is expected to improve the traffic efficiency and driving safety of the intersection.

[0139] Example 2

[0140] An optimization method for the signal phase of the upstream intersection in a roundabout area, used to swap the through and left-turn traffic inlet lanes with the opposite exit lanes of the upstream intersection, includes the following specific steps:

[0141] S1: Considering vehicle lane change delay, average vehicle delay, vehicle overflow delay at intersection, phase difference, regional average delay, and total vehicle emissions, construct an upstream intersection signal timing optimization model;

[0142] S2: Perform timing coordination optimization on the upstream intersection signal timing optimization model to obtain the optimal signal timing scheme.

[0143] In this embodiment, to enable the interchange of left-turn and straight-through traffic inlet lanes with opposite exit lanes, the present invention also resets the phases of the upstream intersection, as shown in Table 1:

[0144] Table 1. Upstream Intersection Phase Design

[0145]

[0146] In one specific embodiment, step S1 considers vehicle lane-changing delay, average vehicle delay, intersection vehicle overflow delay, phase difference, area average delay, and total vehicle emissions to construct an upstream intersection signal timing optimization model. The specific steps are as follows:

[0147] S101: Calculate lane change delay using the time difference between vehicles changing lanes at constant speed. The lane change delay is calculated based on the positional relationship between the changing vehicle and the vehicle in front, the speeds, accelerations, and gear shift durations of both vehicles.

[0148]

[0149]

[0150] in, It is the longitudinal distance between the front ends of the vehicle being overtaken and the overtaking vehicle that is able to change lanes;

[0151] v0 is the initial longitudinal distance between the front ends of the overtaken vehicle and the vehicle being overtaken; v0 is the initial speed of the vehicles in the lane-changing area; t is the lane-changing time; a d d is the expected deceleration of the following vehicle; d is the lane-changing delay.

[0152] S102: Among various methods for calculating delays, the excessive delay model is applicable to both undersaturated and oversaturated intersections. The research area of ​​this invention is a roundabout prone to congestion; therefore, the excessive delay model is used to calculate the average vehicle delay. The average vehicle delay is calculated as follows:

[0153] d A =d u +d o

[0154]

[0155]

[0156]

[0157]

[0158]

[0159] Where, d A For the delay of each vehicle; d u Average vehicle delay; d o For random arrival delays; N d The average number of vehicles stuck in traffic; T is the signal cycle duration; t g For green light time; t r λ is the red light duration; s0 is the intersection saturation threshold; s is the directional saturation of the approach lane (s=q / Q=q / S×T / t). g =fr / λ); fr is the traffic flow ratio at the entrance (fr = q / S); W is the time period set for the observation and analysis; S is the saturation flow.

[0160] S103: When a vehicle arrives at the downstream intersection, if the signalized intersection has not completely cleared the vehicles left over from the previous cycle, an overflow delay will occur. Considering vehicles in the queue that have completely stopped and started, as well as those that have intermittently stopped and started, calculate the intersection vehicle overflow delay:

[0161]

[0162] Where, d a Traffic congestion at intersections causes delays; S a S is the average vehicle speed at the intersection entrance. a =0.9(25.6+0.47S) pl );S pl Speed ​​limits at intersection entrances; S s The threshold speed at which the vehicle comes to a complete stop; r a For vehicle acceleration; r d To slow down the vehicle;

[0163] When optimizing a roundabout and its adjacent upstream and downstream intersections as a whole, the signal timing of the upstream intersections in each direction of the roundabout is optimized collaboratively. In the collaborative optimization, by adding a phase difference, vehicles can pass through the second intersection without waiting after passing through the first signal-controlled intersection, thereby reducing waiting time and reducing overall delay.

[0164] S104: Overall optimization of a roundabout and its adjacent upstream and downstream intersections requires coordinated optimization of the signal timings of the upstream intersections in each direction of the roundabout. In this coordinated optimization, incorporating phase differences allows vehicles to pass through the first signal-controlled intersection without waiting at the second, reducing waiting time and overall delays. First, calculate the green light start time for the first phase:

[0165]

[0166] Where x and y represent different upstream intersections, if there are M upstream intersections, then x, y ∈ [1, L, M] and x ≠ y; t y1 It is the start time of the green light in the first phase of intersection y; t x1 It is the start time of the green light in the first phase at intersection x; It is the relative phase difference between intersection y and intersection x;

[0167] in, Specifically:

[0168]

[0169]

[0170]

[0171]

[0172] Where ω is the weighting coefficient; It is the phase difference when turning left on the uphill route; It is the uplink and downlink phase difference; q l This refers to the volume of traffic turning left on the uphill route; q s d is the upbound straight-through traffic volume; d is the delay caused by straight-through lane changes; v1 is the vehicle speed at the roundabout.

[0173] In roundabout areas, vehicle speeds are random. Ignoring speed variations may render the calculated optimal phase difference meaningless. This invention assumes that vehicle speeds follow a normal distribution, with the mean and standard deviation as follows:

[0174]

[0175]

[0176] Where: v a σ is the mean speed; σ is the standard deviation of vehicle speed; v b n represents the b-th velocity (b = 1, L, m); b Indicates velocity v b The corresponding number of vehicles is n b ;

[0177] Calculate the normal distribution probability of vehicle speed:

[0178]

[0179] Calculate the expected value of vehicle speeds within the area:

[0180]

[0181] Calculate the relative phase difference between intersection y and intersection x.

[0182]

[0183] S105: Determine the optimal phase difference based on the average delay of each approach vehicle at each upstream signal-controlled intersection to obtain the regional average delay:

[0184]

[0185] in:

[0186]

[0187]

[0188]

[0189]

[0190]

[0191]

[0192]

[0193] Where PI is the average delay per vehicle in the region, which is equal to the total delay divided by the total number of vehicles; d x N represents the average delay at the upstream x-intersection; xy d represents the number of vehicles stranded in the direction from intersection x to intersection y; d represents the lane-changing delay. a Indicates vehicle overflow delay; d 0xy This represents the random arrival delay of vehicles traveling from intersection x to intersection y. and These represent the actual traffic volume of vehicles going straight and turning at the upstream x intersection reaching the next intersection, respectively.

[0194] S106: Total Vehicle Emissions Calculation: Total vehicle emissions include idling emissions and emissions during operation. Calculate idling emissions when the vehicle is waiting at a traffic light at the upstream intersection:

[0195]

[0196] Where D represents the vehicle's idling emissions; t rxi The red light time t for phase i at the upstream x intersection. r Unit: min; K is the air-fuel ratio at idle speed; A is the fuel consumption at idle speed, unit: kg / min;

[0197] Calculate the total emissions of the vehicle during operation:

[0198]

[0199] Among them, E C p represents the total gas emissions within time C, in grams; c represents the travel time, in seconds; p c The instantaneous vehicle power specificity (VSP) at second c, in kW / t; f(p c The instantaneous VSP of the vehicle within the calculation time is p. c The number of times; R(p) c The instantaneous VSP value at second c is p. c The average emission rate of D(t), in g / s; rxi () represents emissions while the vehicle is waiting, in grams;

[0200] Calculate the specific power of a motor vehicle:

[0201] VSP=v×[1.1a+9.81×(atan(sinG))+0.132]+0.000302v 3

[0202] Where VSP is the specific power of the vehicle, in kW / t; v is the vehicle speed, in m / s; and a is the vehicle acceleration, in m / s². 2 G represents the road gradient.

[0203] The emission rate R(p) is calculated based on the exhaust gas mass flow. c ):

[0204]

[0205] Where MF is the exhaust gas mass flow rate, in kg / h; EC is the concentration of a certain pollutant, in ppm;

[0206] This invention divides VSP values ​​into intervals according to certain intervals and takes the average emission rate within each interval to improve the accuracy of emission rate calculation. Since the research scope of this invention is the area composed of urban roundabouts and their upstream and downstream intersections, the vehicle speed in this area is generally 30-40 km / h, and the VSP calculation interval is [1,2). The main gas emission rates in this interval are: 0.02319 g / s (CO), 1.181 g / s (CO2), 0.00101 g / s (HC), and 0.00281 g / s (NO). x Therefore, the vehicle emission calculation of the present invention is based on the above data.

[0207] Considering the diverse types of vehicles at urban roundabouts, this invention incorporates correction coefficients for different vehicle types into the calculation of motor vehicle exhaust emissions. This invention categorizes vehicles within the intersection into small passenger cars, medium-sized passenger cars, buses, medium-sized trucks, and heavy-duty trucks, and adopts the China V emission standard. Using weekday peak-hour slow-moving traffic as a background, the invention obtains the contribution rates of different emission factors for different vehicle types, as shown in Figure 9.

[0208] The coefficients between emissions and vehicle type can be obtained based on the proportion of each type of emission factor, as shown in Table 2:

[0209] Table 2. Coefficients β for different emission factors and different vehicle types

[0210]

[0211] This yields the exhaust emissions from the roundabout area:

[0212]

[0213] Among them, E CT Total regional emissions, in grams; β zw Let q represent the emission factor coefficients for different vehicle types, z represent different emission factors z∈[1,4], and w represent different vehicle types w∈[1,5]. x Let x be the traffic volume at intersection x;

[0214] S107: Considering the targets of average vehicle delay and total emissions, construct an upstream intersection signal timing optimization model:

[0215] min[PI,E CT ]

[0216] st

[0217]

[0218]

[0219]

[0220]

[0221]

[0222]

[0223]

[0224] Among them, T x Let λ be the period duration of the upstream intersection x; xi Let x be the green light ratio of the i-th phase at intersection x, in seconds. If there are M upstream intersections and N phases at each intersection, then x and i take the values ​​x∈[1,M], i∈[1,N], and N. * The set of positive integers is required; the cycle of signalized intersections within the area must be consistent to ensure that the phase difference of the signal cycle is the same in each cycle; the green light time of each phase needs to be set with upper and lower limits to coordinate the smooth passage of vehicles through the intersection; the signal difference must be kept consistent in multiple sets of signal cycles, and the signal difference must satisfy that the phase difference between the up and down directions is an integer multiple of the phase cycle; it is stipulated that the phase difference should be less than the signal cycle of the up and down directions of the intersection; the cycle of signalized intersections within the area must be the same.

[0225] As shown in Figure 7, in a specific embodiment, the timing coordination optimization model of the upstream intersection signal timing optimization is performed. The specific steps are as follows:

[0226] S201: Based on the average vehicle delay calculation formula of the upstream intersection signal timing optimization model and the parameter settings of each intersection in the area, a set of signal timing schemes is calculated without limiting the signal cycle length of each intersection.

[0227] S202: Use Vissim software to simulate the timing scheme of each intersection and determine whether all vehicles can pass through the area. If yes, it is deemed feasible and proceeds to step S203; otherwise, it is deemed infeasible and returns to step S201.

[0228] S203: Using the intersection timing scheme with the longest period as the standard, the timing schemes of the other intersections are enlarged proportionally according to their respective phase lengths to make the signal periods of each intersection equal in length, thus obtaining the revised feasible signal timing scheme.

[0229] S204: Let the longest period be T. max A multi-objective genetic algorithm is used to solve the signal timing collaborative optimization model, obtain the Pareto solution of the intersection signal timing scheme, and select the satisfactory solution.

[0230] S205: The Vissim software is used to simulate the satisfactory solution, output the average vehicle delay and total emissions of each intersection, and compare the standard deviation of several simulation results to verify the effectiveness of the intersection signal timing scheme and obtain the verified effective signal timing scheme.

[0231] S206: Output signal timing scheme.

[0232] In a specific embodiment, as shown in Figure 8, in step S204, a multi-objective genetic algorithm is used to solve the signal timing collaborative optimization model. The specific steps are as follows:

[0233] S2401: Initialize the population;

[0234] S2402: Use the revised feasible signal timing scheme as individuals in the initial population to generate the first generation population;

[0235] S2403: Perform crossover and mutation operations on the first-generation population to generate the second-generation population.

[0236] S2404: Merge the parent and child generations in the second generation population;

[0237] S2405: Perform fast non-dominated sorting on the merged second-generation population and calculate crowding.

[0238] S2406: Select a new parent generation based on crowding level using an elite strategy;

[0239] S2407: Perform selection, crossover, and mutation operations on the population;

[0240] S2408: Generate new offspring;

[0241] S2409: Determine whether the number of iterations has reached the set threshold. If so, output the Pareto solution of the intersection signal timing scheme; otherwise, return to step S2404.

[0242] In one specific embodiment, the population is initialized as follows: taking the roundabout as the center, the upstream intersections of the roundabout are arranged in a clockwise direction from north to east to south to west, generating individuals composed of M sets of numbers. Each set of numbers represents the duration of the green light signal in four phases of an intersection, and the phase order of each set of numbers is the same; where M is the number of upstream intersections of the roundabout.

[0243] In this embodiment, the green light duration for each phase is represented by two digits, with a value range of 01-99; the phase order for each set of numbers is from the first phase to the fourth phase.

[0244] In this embodiment, as shown in Figure 11, the roundabout has 4 upstream intersections, M=4; and each intersection has 4 phases, N=4. The length of the code is 2×4×4=32. The total signal duration of each intersection is the sum of the four two-digit numbers in each group of numbers, plus the yellow light time of the four phases set to 3 seconds, which is a total of 12s. The total signal duration of the upstream intersection (north) is 12+34+56+78+12=192s.

[0245] In one specific embodiment, if the phase duration of an individual generated in the initial population is 0 or the total signal duration of the individual exceeds the maximum signal period, the individual is determined to be unqualified and a new individual is generated.

[0246] In one specific embodiment, step S2405 involves performing a rapid non-dominated sorting of the merged second-generation population and calculating crowding. Specifically, individuals are non-dominated sorted using average delay and total emissions as indicators. The higher the level, the lower the individual's fitness value, and vice versa. At the same time, the crowding of individuals within the same level is calculated, and individuals with higher crowding are more likely to be retained.

[0247] In a specific embodiment, the operations of population selection, crossover, and mutation are as follows:

[0248] Selection operation: The population is selected using a roulette wheel method and an elite retention strategy is adopted;

[0249] Mutation operation: As shown in Figure 13, two gene loci on two individuals in the population are randomly selected as mutation sites, and the values ​​of the two mutation sites are swapped.

[0250] Crossover operation: The OX crossover method is used to update the population, as shown in Figure 12. Crossover points are randomly determined in the first and second generation parents, and then the crossover points are swapped. For example, marker points are inserted at positions 14 and 15 of the parent individuals, and then the genes after the marker points are swapped.

[0251] This invention achieves the interchange of left-turn and straight-through traffic inlet lanes with opposite exit lanes through upstream intersection signal control, and achieves the goal of minimizing average vehicle delay and total vehicle emissions in the study area through signal timing coordination optimization. Its advantages are specifically reflected in the following aspects: (1) It can achieve the separation of left-turn, straight-through, and right-turn traffic flows at roundabouts, and vehicles in each direction of travel do not affect each other, reducing the diversion and merging effects caused by left-turn and straight-through vehicles sharing lanes; (2) It greatly shortens the travel distance of left-turning vehicles in roundabouts, reducing the travel time of left-turning traffic and the conflict points caused; (3) By coordinating the signal control of upstream intersections, it not only improves the overall traffic efficiency of the roundabout area, but also reduces the total vehicle emissions in the area.

[0252] Example 3

[0253] This invention selects the Changyao roundabout intersection at the junction of Baiyang West Road and Changqing Road in the central district of Leshan City, along with its upstream and downstream intersections, as the experimental area to verify the effectiveness of the proposed traffic organization method for the roundabout area and the optimization method for the upstream intersection signal.

[0254] The Changyao roundabout is located in the center of Leshan City. It is a six-lane roundabout in both directions. It is surrounded by large commercial centers such as Shihao Plaza and Xicheng International, as well as relatively dense residential buildings, which increases the pressure on road traffic. During peak hours, the roundabout is very congested. There is a conventional signal-controlled intersection in each of its four directions: east, west, south, and north. The original signal control phase and timing scheme are shown in Table 3.

[0255] Table 3 Original signal timing scheme for the upstream intersection (unit: seconds)

[0256]

[0257]

[0258] The traffic flow organization scheme proposed in this invention is used to reorganize the traffic flow in the Changyao roundabout area. A sawtooth-shaped cutoff line is set at the entrance lane of the upstream intersection, and the left-turn stop line is moved back 15 meters to provide more space for vehicles going straight into the roundabout. The phases of the upstream intersection are redesigned, as shown in Table 4. The signal timing of each phase is solved using the optimization model proposed in this invention and the NSGA-II algorithm. The NSGA-II algorithm is written in Python, and the algorithm parameters are as follows: initial population size of 100, number of iterations of 100, mutation probability of 0.7, and crossover probability of 0.5.

[0259] Table 4. Optimized signal timing scheme for the upstream intersection (unit: seconds)

[0260]

[0261] This invention first aims to minimize the average vehicle delay and generates a set of signal timing schemes, as shown in Table 5:

[0262] Table 5. Signal timing at upstream intersections (unit: seconds)

[0263]

[0264] The signal timing schemes in Table 5 were simulated using Vissim software. The results showed that vehicles could pass through the experimental area within the specified time, thus the signal timing schemes were feasible. In Table 5, the total signal period of the upstream intersection to the south was the longest at 188s. Therefore, the total signal periods of the other three intersections were proportionally increased to 188s according to their respective phase signal durations. After unifying the signal periods, the signal timing schemes for each intersection are shown in Table 6. Using the timing schemes in Table 6 as an individual in the initial population, the NSGA-II algorithm was executed, and the Pareto solution set was obtained as shown in Figure 10. A satisfactory solution was selected, and the final signal timing scheme for the upstream intersection was obtained, as shown in Table 7, with the phase differences shown in Table 8.

[0265] Table 6. Signal Timing at Upstream Intersections (Uniform Period) (Unit: Seconds)

[0266]

[0267] Table 7. Upstream Intersection Signal Timing (Optimized) (Unit: Seconds)

[0268]

[0269] Table 8. Phase differences between directions in the final scheme (after optimization) (unit: seconds)

[0270]

[0271] To compare the effects of the traffic flow organization scheme and signal timing scheme proposed in this invention, based on the actual traffic flow data of the Changyao roundabout area from 8:00 to 8:30 on September 20, 2018, the vehicle traffic status before and after traffic reorganization in the roundabout area was simulated in Vissim software. The number of simulations for both scenarios before and after optimization was set to 100, and the average delay and total vehicle emissions data for each lane were obtained, as shown in Tables 9 and 10.

[0272] Table 9 Average vehicle delays for each lane

[0273]

[0274]

[0275] Table 10 Average Total Vehicle Emissions

[0276]

[0277]

[0278] As shown in Tables 9-10, (1) the average delay of vehicles from different directions at the upstream intersections decreased to varying degrees, especially at the east and south directions where the average delay decreased by about 20%; the average delay of vehicles at the roundabouts decreased by 10% to 60%. (2) Before optimization, the standard deviation of the average delay of vehicles in this area was relatively large, while after optimization, the standard deviation of the average delay decreased by 40% to 60%. (3) The total emissions of vehicles at different entrances at the upstream intersections decreased by 5% to 10%, and the total emissions of vehicles at the north entrance of the northbound intersection and the east entrance of the eastbound intersection decreased by more than 12%. (4) Except for the north entrance of the northbound intersection, the standard deviation of total emissions in other directions decreased to varying degrees.

[0279] The experimental data above demonstrates that the traffic organization and upstream intersection signal optimization method proposed in this invention can significantly improve the traffic efficiency of roundabout areas, including upstream intersections, and also make the traffic conditions in these areas more stable. Furthermore, the traffic organization and upstream intersection signal optimization method proposed in this invention can effectively reduce total vehicle emissions in these areas and improve the stability of total vehicle emissions.

[0280] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for optimizing traffic organization in a roundabout area, characterized by: The specific steps include: defining the roundabout area as the area between the roundabout and its adjacent upstream and downstream intersections; maintaining the original traffic flow pattern for right-turning traffic at the roundabout; separating left-turning and straight-through traffic into lanes, with straight-through traffic traveling clockwise within the roundabout, while left-turning traffic is separated from the roundabout and turns directly using a dedicated left-turn lane; swapping the on-ramp and off-ramp lanes of the upstream intersection; shifting the left-turn lane cutoff line of the upstream intersection; optimizing the traffic organization of the roundabout area; and swapping the on-ramp and off-ramp lanes of the upstream intersection. S1: Considering lane-changing delay, average vehicle delay, intersection overflow delay, phase difference, area average delay, and total vehicle emissions, constructing an upstream intersection signal timing optimization model; S2: The signal timing optimization model of the upstream intersection is optimized through timing coordination to obtain the optimal signal timing scheme. In step S1, considering vehicle lane-changing delay, average vehicle delay, vehicle overflow delay at the intersection, phase difference, regional average delay, and total vehicle emissions, the upstream intersection signal timing optimization model is constructed. The specific steps are as follows: S101: Based on the positional relationship between the lane-changing vehicle and the preceding vehicle, the speed, acceleration, and gear change duration of the preceding and following vehicles, the lane-changing delay is calculated. in, It is the longitudinal distance between the front ends of the vehicle being overtaken and the overtaking vehicle that is able to change lanes; It is the initial longitudinal distance between the front ends of the vehicle being overtaken and the overtaking vehicle; This refers to the initial speed of vehicles in the lane-changing area; This refers to the lane-changing time of the vehicles; It is the expected deceleration of the following vehicle; For lane change delays; S102: Using an excessive delay model, calculate the average vehicle delay: in, For the delay of each vehicle; Average vehicle delay; For random arrival delays; This represents the average number of vehicles stranded. The duration of the signal period; Green light time; Red light time; For green credit ratio; This represents the critical value for intersection saturation. Saturation in the direction of the inlet channel ； Traffic flow ratio of the entrance road ； The time period set for observation and analysis; S103: Considering vehicles in the queue that have completely stopped and started, and those that have intermittently stopped and started, calculate the vehicle overflow delay at the intersection: in, Traffic congestion at intersections caused delays. Average vehicle speed at intersection entrance ； Speed ​​limits at intersection entrances; The threshold speed at which the vehicle comes to a complete stop; To accelerate the vehicle; Reduce vehicle speed; when optimizing a roundabout and its adjacent upstream and downstream intersections as a whole, coordinate the signal timing of the upstream intersections in each direction of the roundabout; in the coordinated optimization, by adding a phase difference, vehicles can pass through the second intersection without waiting after passing the first signal-controlled intersection, reducing waiting time and overall delay; S104: Calculate the green light start time of the first phase: in, These represent different upstream intersections. If there are upstream intersections... One, then and ； It is an intersection The start time of the first phase green light; It is an intersection The start time of the first phase green light; It is an intersection relative to the intersection The relative phase difference; where, Specifically: in, These are the weighting coefficients; It is the phase difference when turning left on the uphill route; It is the upward straight-line phase difference; This refers to the volume of traffic turning left on the uphill route; This refers to the upbound straight-through traffic volume; The delay was caused by changing lanes while going straight; It refers to the speed of vehicles traveling at a roundabout; in: The average speed; The standard deviation of vehicle speed; Indicates the first Type of speed ( ）； Indicates speed The corresponding number of vehicles is ; Calculate the normal distribution probability of vehicle speed: Calculate the expected value of vehicle speeds within the area: Calculate intersections relative to the intersection relative phase difference ： S105: Determine the optimal phase difference based on the average delay of each approach vehicle at each upstream signal-controlled intersection to obtain the regional average delay: in: in, The average delay for vehicles in the region is equal to the total delay divided by the total number of vehicles. Indicates upstream Average delay at intersections; express Intersection to The number of vehicles stranded at the intersection in either direction; This indicates a delay in lane changing for the vehicle; This indicates vehicle overflow delays; express Intersection to Random arrival delays of vehicles in different directions at the intersection; and They represent the upstream The actual traffic volume of vehicles going straight and turning at the intersection reaching the next intersection; S106: Calculate the idling emissions of vehicles waiting at the traffic light at the upstream intersection: in, Emissions at vehicle idle speed; upstream intersection red light time of phase ,unit: ； The air-fuel ratio at vehicle idle speed; Fuel consumption at idle, unit: ; Calculate the total emissions of the vehicle during operation: in, For time Total gas emissions within the unit ； For travel time, in units ； For the first Instantaneous vehicle power ratio per second ,unit ； For the vehicle to appear instantaneously within the calculation time for The number of times; For the first Second Average emission rate, in units ； Emissions while vehicles are waiting, per unit ; Calculate the specific power of a motor vehicle: in, Power-to-weight ratio of motor vehicles, in units of ； For motor vehicle speed, unit ； For motor vehicle acceleration, the unit is... ； The road slope is used as the basis for calculating the emission rate based on the exhaust gas mass flow. ： in, For exhaust gas mass flow, unit ； The concentration of a certain pollutant, in units: The exhaust emissions at the roundabout area were obtained. in, The exhaust emissions of the roundabout area, per unit ； These are the emission factor coefficients for different types of vehicles. For different emission factors ， For different vehicle types ； for Traffic volume at the intersection; S107: Considering the targets of average vehicle delay and total emissions, construct an optimization model for signal timing at the upstream intersection: s.t. in, upstream intersection The duration of the cycle; Represented as The first intersection Phase green ratio, unit If there are M upstream intersections and N phases at each intersection, then and The value is ， ， The set of positive integers is required; the cycle of signalized intersections within the area must be consistent to ensure that the phase difference of the signal cycle is the same in each cycle; the green light time of each phase needs to be set with upper and lower limits to coordinate the smooth passage of vehicles through the intersection; the signal difference must be kept consistent in multiple sets of signal cycles, and the signal difference must satisfy that the phase difference between the up and down directions is an integer multiple of the phase cycle; it is stipulated that the phase difference should be less than the signal cycle of the up and down directions of the intersection; the cycle of signalized intersections within the area must be the same.

2. The method for optimizing traffic organization in a roundabout area according to claim 1, characterized in that: The roundabout area is a two-way six-lane, two- or three-ring roundabout; its upstream and downstream intersections are two-way six-lane intersections.

3. The method for optimizing traffic organization in a roundabout area according to claim 1, characterized in that: The signal timing optimization model of the upstream intersection is optimized through timing coordination. The specific steps are as follows: S201: Based on the average vehicle delay calculation formula of the upstream intersection signal timing optimization model and the parameter settings of each intersection in the area, a set of signal timing schemes is calculated without limiting the signal cycle length of each intersection; S202: The timing schemes of each intersection are simulated to determine whether all vehicles can pass through the area. If so, it is deemed feasible, and step S203 is executed; otherwise, it is deemed infeasible, and step S201 is returned; S203: Taking the timing scheme of the intersection with the longest cycle as the standard, the timing schemes of the remaining intersections are scaled up proportionally according to their respective phase lengths to make the signal cycles of each intersection equal in length, resulting in a revised feasible signal timing scheme; S204: Let the longest cycle be... A multi-objective genetic algorithm is used to solve the signal timing collaborative optimization model to obtain the Pareto solution of the intersection signal timing scheme, and the satisfactory solution is selected; S205: The satisfactory solution is simulated, the average vehicle delay and total emissions of each intersection are output, and the standard deviation of several simulation results are compared to verify the effectiveness of the intersection signal timing scheme and obtain the verified effective signal timing scheme; S206: The signal timing scheme is output.

4. The method for optimizing traffic organization in a roundabout area according to claim 3, characterized in that: In step S204, a multi-objective genetic algorithm is used to solve the signal timing collaborative optimization model. The specific steps are as follows: S2401: Initialize the population; S2402: Use the sorted feasible signal timing schemes as individuals in the initial population to generate the first generation population; S2403: Perform crossover and mutation operations on the first generation population to generate the second generation population; S2404: Merge the parent and offspring generations of the second generation population; S2405: Perform fast non-dominated sorting on the merged second generation population and calculate the crowding degree; S2406: Select a new parent generation according to the crowding degree using an elite strategy; S2407: Perform selection, crossover, and mutation operations on the population; S2408: Generate new offspring generation; S2409: Determine whether the number of iterations has reached the set threshold. If so, output the Pareto solution of the intersection signal timing scheme; otherwise, return to step S2404.

5. The method for optimizing traffic organization in a roundabout area according to claim 4, characterized in that: Initialize the population by arranging the upstream intersections of the roundabout in a north-east-south-west order, centered on the roundabout, to generate a population composed of... Each group of numbers represents the duration of the green light signal in four phases at an intersection, and the phase order is the same for each group of numbers; This represents the number of intersections upstream of the roundabout.

6. The method for optimizing traffic organization in a roundabout area according to claim 5, characterized in that: If the phase duration of an individual generated in the initial population is 0 or the total signal duration of the individual exceeds the maximum signal period, the individual is deemed unqualified and a new individual is generated.

7. The method for optimizing traffic organization in a roundabout area according to claim 4, characterized in that: In step S2405, a rapid non-dominated sorting is performed on the merged second-generation population, and the crowding degree is calculated. Specifically, individuals are non-dominated sorted using average delay and total emissions as indicators. The higher the level, the lower the fitness value of the individual, and vice versa. At the same time, the crowding degree of individuals within the same level is calculated. Individuals with higher crowding degree are more likely to be retained.

8. The method for optimizing traffic organization in a roundabout area according to claim 7, characterized in that: The selection, crossover, and mutation operations for the population are as follows: Selection operation: The population is selected using a roulette wheel method and an elite retention strategy is adopted; Mutation operation: Two gene loci on two individuals in the population are randomly selected as mutation loci, and the values ​​of the two mutation loci are swapped; Crossover operation: A crossover point is randomly determined from the first and second generation parents, and then the crossover points are swapped.

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