Traffic light control device

Abstract

To provide a traffic light control device that targets a wide range of a road network and a vehicle in order to optimize a traffic situation in an entire road network.SOLUTION: A traffic light control device for controlling a display of each traffic light arranged at each intersection included in a road network, comprises: a positional information acquisition unit that acquires positional information of a vehicle present around an intersection; a calculation unit that calculates an optimal display of each traffic light by using an Ising model including a binary variable that represents, in binary, which vehicles on a road are allowed to pass through the intersection based on a display of a traffic light as an evaluation function to evaluate a deviation in the number of vehicles located on each of up to four roads connected to the intersection; and a transmission unit that transmits an instruction signal to instruct the display of each traffic light based on a calculation result by the calculation unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a traffic light control device. [Background technology]

[0002] Conventionally, technologies for controlling the display of traffic lights at intersections have been known with the aim of optimizing traffic conditions by alleviating congestion, etc. Patent Document 1 discloses a traffic light control system that controls the display of traffic lights based on a parameter set for controlling the display of signals for vehicles in each lane group included in a road connected to the intersection. Patent Document 2 discloses a traffic light switching control device that controls the display of traffic lights using switching timing optimized in consideration of major roads connected to the intersection and peripheral roads connected to other adjacent intersections. Furthermore, Non-Patent Document 1 discloses a research example that uses an Ising model to optimize the display of traffic lights at each intersection when vehicles that turn right or left at intersections with a certain probability travel within an isotropic grid-like road network. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-16554 [Patent Document 2] Japanese Patent Application Publication No. 2019-79199 [Non-patent literature]

[0004] [Non-Patent Document 1] Inoue, D., Okada, A., Matsuori, T. et al. Traffic signal optimization on a square lattice with quantum annealing. Sci Rep 11, 3303 (2021). https: / / doi.org / 10.1038 / s41598-021-82740-0 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Documents 1 and 2, the traffic conditions of a part of a road network are optimized by controlling the display of some of the traffic lights among a group of traffic lights arranged in the road network, but sufficient consideration is not given to optimizing the traffic conditions of the entire road network. In contrast, Non-Patent Document 1 considers optimizing the traffic conditions of the entire road network, but there are restrictions on the road network and vehicle driving modes that it targets. For this reason, there has been a demand for a traffic light control device that can be applied to a wide range of road networks and vehicles.

[0006] The present invention has been made to solve at least some of the above-mentioned problems, and aims to provide a traffic light control device that can target a wide range of road networks and vehicles when optimizing traffic conditions across the entire road network. [Means for solving the problem]

[0007] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0008] (1) According to one aspect of the present invention, there is provided a traffic light control device that controls the display of each traffic light located at each intersection included in a road network, the traffic light control device including: a position information acquisition unit that acquires position information of vehicles present around the intersection; a calculation unit that calculates an optimal display of each traffic light using an Ising model including a binary variable that represents, as an evaluation function for evaluating the imbalance in the number of vehicles located on each of up to four roads connected to the intersection, which binary variable indicates which of the vehicles on the road is permitted to pass through the intersection based on the display of the traffic light; and a transmission unit that transmits an instruction signal that instructs the display of each traffic light based on the calculation result by the calculation unit, wherein the Ising model is expressed by the following formula (1):

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[0009] According to this configuration, the evaluation function for evaluating the imbalance in the number of vehicles at each intersection in a road network is expressed using an Ising model, as shown in Equation (1). This allows for high-speed calculation of the optimal display of each traffic light to optimize the traffic conditions throughout the road network. This shortens the time from the start of calculation to the transmission of an instruction signal, enabling rapid control of the display of each traffic light, thereby enabling rapid optimization of the traffic conditions throughout the road network. Furthermore, according to this configuration, the connectivity of the roads constituting the road network is incorporated into the evaluation function expressed by Equation (1) as an adjacency matrix, making the traffic light display control based on Equation (1) applicable to any road network. Furthermore, according to this configuration, the inflow and outflow of vehicles into and from road sections between intersections are incorporated as parameters into Equation (1), making the traffic light display control based on Equation (1) applicable to any type of vehicle traveling on the road network. Furthermore, according to this configuration, a term for predicting traffic conditions a certain time ahead to improve the smoothness of future vehicle flow is incorporated into Equation (1), making it possible to more efficiently determine the display of each traffic light. Therefore, with this configuration, it is possible to provide a traffic light control device that can be applied to any road network or any vehicle showing any driving behavior, and that can efficiently control the display of each traffic light.

[0010] (2) In the traffic light control device of the above aspect, the transmitter may transmit the instruction signal sequentially. With this configuration, the instruction signals are transmitted sequentially, which allows for sequential optimization of the traffic conditions across the entire road network. This sequential transmission of instruction signals is made possible by the fact that the evaluation function is expressed as an Ising model, which allows for high-speed calculations.

[0011] The present invention can be realized in various forms, for example, in the form of a system including a traffic light control device, a traffic light control device and a computer program executed in the system including the traffic light control device, a server device for distributing the computer program, a non-transitory storage medium on which the computer program is stored, etc. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an explanatory diagram illustrating the configuration of a traffic light control device according to an embodiment of the present invention; [Figure 2] FIG. 1 is an explanatory diagram showing a road network in which each traffic light is located. [Figure 3] 10 is a flowchart illustrating an example of a procedure for a display control process. [Figure 4] FIG. 2 is an explanatory diagram showing the performance of a traffic light control device. DETAILED DESCRIPTION OF THE INVENTION

[0013] <Embodiment> FIG. 1 is an explanatory diagram illustrating the configuration of a traffic light control device 1 according to an embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating a road network RN in which traffic lights SG, which are the objects of control of the traffic light control device 1, are arranged. First, the road network RN will be described using FIG. 2. The road network RN is a wide-area road network including multiple intersections CR. For convenience of illustration, the road network RN in FIG. 2 is shown as a grid with orthogonal crossings in the vertical and horizontal directions. However, this is not limited to this, and the road network RN may have any shape, such as an actual urban road network. In other words, the object of control by the traffic light control device 1 may be a road network RN of any shape. On the right side of FIG. 2, an enlarged view of an intersection CR is shown. Two roads Ra and Rb intersect at the intersection CR. Furthermore, because the roads Ra and Rb are connected to the intersection CR from all four sides, they can also be considered four roads connected to the intersection CR. The two roads Ra and Rb are each equipped with traffic lights SGa and SGb that indicate whether vehicles Va and Vb on the roads Ra and Rb are permitted or prohibited from passing through the intersection CR. FIG. 2 shows a state in which vehicle Va on road Ra is permitted to pass through intersection CR, while vehicle Vb on road Rb is prohibited from passing through intersection CR. Road network RN includes countless intersections CR with traffic lights SGa and SGb. Hereinafter, traffic lights installed at each intersection CR included in road network RN will be collectively referred to as traffic lights SG. Vehicles present within road network RN will be collectively referred to as vehicles V.

[0014] Next, the traffic light control device 1 shown in Fig. 1 will be described. The traffic light control device 1 controls the display of each traffic light SG located at each intersection CR included in the road network RN. The display of the traffic light SG is a display that notifies a vehicle V oncoming the traffic light SG whether it is permitted or prohibited to pass through the intersection CR; for example, if passage is permitted, the traffic light SG displays green (or green), and if passage is prohibited, the traffic light SG displays red.

[0015] The traffic light control device 1 includes a position information acquisition unit 10, a calculation unit 20, and a transmission unit 30. The traffic light control device 1 includes a storage medium (not shown), which stores map information indicating a road network RN on which a traffic light SG (the object of control by the traffic light control device 1) is located. The map information includes at least information indicating the connection relationship between intersections CR (which intersections CR are connected to which intersections CR via roads). The map information may also include information indicating the distance of the roads connecting the intersections CR.

[0016] The position information acquisition unit 10 sequentially acquires position information LI of vehicles V present in the vicinity of the intersection CR. In this embodiment, the position information LI of vehicles V present in the vicinity of the intersection CR is acquired by an ultrasonic sensor provided in the vicinity of the intersection CR or at a traffic light SG, and the position information acquisition unit 10 acquires the position information LI of vehicles V present in the vicinity of the intersection CR by receiving a signal indicating the position information LI from the ultrasonic sensor.

[0017] The calculation unit 20 calculates the optimal display of each of the traffic lights SGa and SGb using an evaluation function that evaluates the imbalance in the number of vehicles V located on each of the two roads Ra and Rb that intersect at the intersection CR (the four roads Ra and Rb connected to the intersection CR). Here, the imbalance in the number of vehicles V refers to the difference in the number of vehicles traveling on each of the roads Ra and Rb. In an evaluation function that evaluates this difference, the smaller the evaluation function, the less congestion is evaluated to be near the intersection CR. In this embodiment, the calculation unit 20 calculates the optimal display of each of the traffic lights SGa and SGb using, as such an evaluation function, an Ising model that includes a binary variable that binary-value represents which of the roads Ra and Rb the vehicles V on are allowed to pass through the intersection CR based on the display of the traffic lights SGa and SGb. The Ising model (evaluation function) used by the calculation unit 20 is expressed by the following equation (1).

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[0018] The transmitter 30 transmits an instruction signal instructing each traffic light SG to display information based on the calculation result by the calculator 20. Each traffic light SG that receives the instruction signal performs display according to the instruction signal. In this embodiment, the transmitter 30 sequentially transmits the instruction signal to each traffic light SG. Each traffic light SG that sequentially receives the instruction signal sequentially updates its display according to the instruction signal.

[0019] Now, we will explain the process of deriving formula (1). Here, when a road network RN is made up of N intersections CR and roads connecting the intersections CR, the index of the intersections is represented as i=1,...,N, and when there is a road section from intersection i to intersection j, the index of that road section is represented as (i,j). Also, the set of indexes of all roads that exist in the road network RN is represented as E. Assume that there are at most four roads connected to intersection i. Intersection i may include a three-way intersection where three roads are connected to intersection i.

[0020] Also, the display of the traffic light SG at intersection i at time t is σ i This is written as (t). σ i (t) is the two states (σ i ∈{±1}). Specifically, from the viewpoint of road section (i,j), σ i The value of S ij In other words, σ i S ij =+1 means that the traffic light SG is green (passing through intersection i is permitted) as seen from the road from intersection j to intersection i. i (t) is determined at discrete time t=τk (k∈N (natural number)) using a predetermined control period τ∈R (real number)>0, and once determined, the display σ i (t) is the next control period σ i At time t, the number of vehicles on road section (i,j) is fixed at q ij It is written as (t).

[0021] Using the variables mentioned above, the deviation of the number of vehicles V at intersection i is x i is expressed by the following formula (2).

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[0022] Based on the imbalance x(t) in the number of vehicles V at a certain time t, the display σ(t) of the traffic light SG at that time t can be found by minimizing the evaluation function expressed by the following equation (3).

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[0023] The above equation (3) includes a time in the future than the time t that determines the display of the traffic light SG. In order to predict this, the time evolution of the imbalance x(t) in the number of vehicles V is modeled and expressed as the linear difference equation shown in the following equation (6).

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[0024] Next, we will explain the derivation of the above formula (6) and how the above formula (3) can be expressed as the Ising model (the above formula (1)) by the derivation. Let σ be the flow rate that flows into the road section (i, j) through the intersection j per unit time. j When = +1, the amount of inflow is a 0 ij , σ j When =-1, the amount of inflow is a 1 ij In addition, the flow rate that flows out of road section (i,j) through intersection i per unit time when the traffic light SG is green (passing through intersection i is permitted) as seen from the road side from intersection j to intersection i is defined as o g ij In addition, if there is a lane before intersection i that allows a vehicle to always turn left at intersection i, the flow rate that flows out of road section (i,j) via such a lane is defined as o r ij Here, we define a 0 ij , a 1 ij , o g ij , o r ij In this embodiment, is calculated using the position information LI of the vehicle V that the traffic light control device 1 successively acquires during operation.

[0025] The above-mentioned a0 ij , a 1 ij Using this, the flow rate per unit time flowing into road section (i, j) through intersection j is expressed by the following equation (9).

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[0026] Also, the above-mentioned g ij , o r ij Using this, the flow rate flowing out of the road section (i, j) through the intersection i per unit time is expressed by the following equation (11).

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[0027] Also, the number of vehicles on the road section (i, j) is q ij The change over time is expressed by the following equation (13).

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[0028] According to the above formula (13) and formula (2), the deviation of the number of vehicles V at intersection i is x i The change over time is expressed by the following equation (14).

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[0029] Convert the above equation (14) into vector notation: x iThe vector in which these are arranged is defined as shown in the following equation (15).

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[0030] Moreover, the vector b expressed by the following equation (18) is defined by the following equation (19).

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[0031] Using the above equations (17) and (19), the change over time in the above equation (14) is expressed by the following equation (20).

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[0032] Next, the above formula (21) is substituted into the above formula (3) to convert it into the Ising model (the above formula (1)). First, x(t) arranged in time order is defined as expressed by the following formula (24).

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[0033] Moreover, the unit matrix I is defined as expressed by the following equation (26).

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[0034] Moreover, the adjacency matrix A is defined as expressed by the following equation (27).

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[0035] Also, vector b is defined as expressed by the following equation (28).

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[0036] After defining the above formulas (26) to (28), by using the above formula (21), the following formula (29) can be obtained.

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[0037] Using the above formula (29), the above formula (3) can be expanded as shown in the following formula (30).

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[0038] 3 is a flowchart showing an example of the procedure for display control processing by the traffic light control device 1. The display control processing is processing for controlling the display of each traffic light SG located at each intersection CR included in the road network RN. The display control processing is repeatedly executed while the traffic light control device 1 is operating.

[0039] When the traffic light control process starts, first, the position information acquisition unit 10 of the traffic light control device 1 acquires position information LI of each vehicle V present around the intersection CR (step S10). Next, the calculation unit 20 of the traffic light control device 1 uses the position information LI to calculate the amount of vehicles V flowing into and out of each road section (road section between intersections CR) included in the road network RN (step S20) (see the explanation of the above formulas (9) and (11)). Next, the calculation unit 20 of the traffic light control device 1 calculates the optimal display of each traffic light SG located at each intersection CR using the Ising model shown in the above formula (1) (step S30). Next, the transmission unit 30 of the traffic light control device 1 transmits an instruction signal instructing the display of each traffic light SG based on the calculation result by the calculation unit 20 (step S40). Each traffic light SG that has received the instruction signal performs display according to the instruction signal. After transmitting the instruction signal, the traffic light control device 1 ends the traffic light control process.

[0040] 4(A) to 4(C) are explanatory diagrams showing the performance of the traffic light control device 1. Each of FIGS. 4(A) to 4(C) shows test results when the traffic light control device 1 of this embodiment controlled the display of a traffic light SG, and test results when a traffic light control device of a comparative example controlled the display of a traffic light SG. The test was conducted by using SUMO (Simulation of Urban Mobility), a traffic simulation software, to create an environment in which vehicles traveling in a 5x5 grid road network were driven in driving patterns implemented in SUMO, and by having each traffic light control device control the display of the traffic light SG in that environment. The horizontal axis of each of FIGS. 4(A) to 4(C) indicates the elapsed time from the start of the simulation, and the vertical axis of each of FIGS. 4(A) to 4(C) indicates the average traveling speed of vehicles traveling in the road network.

[0041] FIG. 4(A) shows test results using a traffic light control device of Comparative Example 1. The traffic light control device of Comparative Example 1 controls each traffic light SG so that the display changes randomly for each control cycle. FIG. 4(B) shows test results using a traffic light control device of Comparative Example 2. The traffic light control device of Comparative Example 2 controls each traffic light SG so that the display changes at a fixed cycle length. The cycle length refers to the time it takes for the display of a traffic light SG to change from green to yellow to red in that order and then turn green again. FIG. 4(C) shows test results using the traffic light control device 1 of this embodiment. From the test results shown in FIGS. 4(A) to 4(C), it was inferred that the average vehicle traveling speed was kept constant with the traffic light control device 1 of this embodiment compared to the traffic light control devices of Comparative Examples 1 and 2, and therefore the possibility of the number of vehicles being concentrated in certain areas of the road network is low. Therefore, the traffic light control device 1 of this embodiment can optimize the traffic conditions of the entire road network.

[0042] According to the traffic light control device 1 of the present embodiment described above, the evaluation function for evaluating the imbalance in the number of vehicles V at each intersection CR included in the road network RN is expressed by the Ising model as shown in the above formula (1). Therefore, it is possible to quickly calculate the optimal display of each traffic light SG to optimize the traffic situation throughout the road network RN. This also makes it possible to shorten the time from the start of calculation to the transmission of an instruction signal, and since the display of each traffic light SG can be quickly controlled, it is possible to quickly optimize the traffic situation throughout the road network RN.

[0043] Furthermore, according to the traffic light control device 1 of this embodiment, the connection relationships of the roads that make up the road network RN are incorporated into the evaluation function expressed by the above formula (1) as an adjacency matrix (see the above formula (17)), and therefore the display control of the traffic light SG based on the above formula (1) can be applied to any road network. In this regard, the display control disclosed in the above non-patent document 1 was only targeted at lattice-like isotropic road networks, but the traffic light control device 1 of this embodiment has expanded the range of road networks that are the target of display control.

[0044] Furthermore, according to the traffic light control device 1 of this embodiment, the amount of vehicles V flowing into the road section between the intersections CR and the amount of vehicles V flowing out from the road section are incorporated as parameters into the above equation (1) (the above a 0 ij , a 1 ij , o g ij , o r ij Therefore, the display control of the traffic light SG based on the above formula (1) can be applied to any driving mode of the vehicle V traveling on the road network RN. In this regard, the display control disclosed in the above-mentioned Non-Patent Document 1 targets only vehicles that turn right or left at an intersection with a certain probability, so the traffic light control device 1 of this embodiment does not restrict the vehicles that are the targets of the display control.

[0045] Furthermore, according to the traffic light control device 1 of this embodiment, a term (prediction horizon Kh in the above formula (3)) for predicting traffic conditions a certain time ahead and making the future flow of vehicles V smoother is incorporated into the above formula (1). That is, the traffic light control device 1 of this embodiment incorporates the prediction horizon Kh, which was not incorporated in the above Non-Patent Document 1, thereby making it possible to suppress bias in the flow of vehicles over a longer period of time.

[0046] Therefore, according to the traffic light control device 1 of this embodiment, it is possible to provide a traffic light control device 1 that can be applied to any road network or vehicle V showing any driving mode, and that can efficiently control the display of each traffic light SG.

[0047] Furthermore, according to the traffic light control device 1 of this embodiment, the transmission unit 30 transmits instruction signals to each traffic light SG sequentially, thereby sequentially optimizing the traffic situation of the entire road network RN. Such sequential transmission of instruction signals is made possible by the fact that the evaluation function is expressed as an Ising model, which enables high-speed calculation.

[0048] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0049] [Variation 1] In the above embodiment, the position information LI of the vehicle V is acquired by an ultrasonic sensor installed around the intersection CR or at the traffic light SG, but this is not limited to this. For example, the position information LI of the vehicle V may be acquired by a camera installed around the intersection CR or at the traffic light SG. In this case, the position information LI of the vehicle V is acquired from an image captured by the camera.

[0050] [Variation 2] In the above embodiment, the transmitter 30 sequentially transmits the instruction signal to each traffic light SG, but this is not limiting. For example, the transmitter 30 may transmit the instruction signal at regular intervals. In such a case, the instruction signal includes information indicating the cycle length, and each traffic light SG displays information according to the cycle length indicated by the instruction signal.

[0051] [Variation 3] In the above embodiment, a 0 ij , a 1 ij , o g ij , o r ij is calculated using the position information LI of the vehicle V that is sequentially acquired by the traffic light control device 1 during operation, but is not limited to this. For example, 0 ij , a 1 ij , o g ij , o r ij In this case, the traffic light control device 1 uses the past position information LI to calculate a 0 ij , a 1 ij , o g ij , o r ij This means that the following is calculated.

[0052] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0053] 1...Traffic signal control device 10…Location information acquisition unit 20...Arithmetic section 30...Transmitter

Claims

1. A traffic light control device that controls the display of each traffic light located at each intersection included in a road network, a location information acquisition unit that acquires location information of vehicles present around the intersection; a calculation unit that calculates an optimal display of each of the traffic lights using an Ising model that includes a binary variable that represents, as an evaluation function that evaluates the imbalance in the number of vehicles located on each of up to four roads connected to the intersection, which binary variable indicates which of the vehicles on which roads are permitted to pass through the intersection based on the display of the traffic lights; and a transmitter that transmits an instruction signal that instructs the display of each of the traffic lights based on the calculation result by the calculator, The Ising model is a traffic light control device represented by the following equation (1). [Equation 1]

2. The traffic light control device according to claim 1, The transmission unit sequentially transmits the instruction signals.

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