Traffic signal control system, traffic signal control device, control method, and computer program

Abstract

This traffic signal control system comprises: a first acquisition unit that acquires specific vehicle information indicating the traffic state of a specific vehicle traveling on a major road toward an intersection where the major road and a minor road intersect; and a control device. The control device comprises a processing unit that executes a selection process for selecting, on the basis of the specific vehicle information, a control process to be executed by the control device from among a first control process for controlling a signal light installed at the intersection and a second control process for controlling the signal light such that the priority degree for prioritizing passage of vehicles on the major road over passage of vehicles on the minor road is higher than that in the first control process.

Description

Traffic signal control system, traffic signal control device, control method, and computer program

[0001] This disclosure relates to a traffic signal control system, a traffic signal control device, a control method, and a computer program. This application claims priority to Japanese Application No. 2024-144455, filed on August 26, 2024, and incorporates by reference all of the contents of said Japanese application.

[0002] Conventionally, methods such as MODERATO (Management by Origin-Destination Related Adaptation for Traffic Optimization) have been adopted as methods for controlling traffic signals (for example, see Patent Document 1).

[0003] International Publication No. 2016 / 147350

[0004] A traffic signal control system according to an embodiment includes a first acquisition unit that acquires specific vehicle information indicating a traffic state of a specific vehicle traveling on a main road toward an intersection where a main road and a minor road intersect, and a control device. The control device includes a processing unit that executes a selection process that selects, based on the specific vehicle information, a control process to be executed by the control device from among a first control process that controls a traffic light installed at the intersection and a second control process that controls the traffic light so that a priority ranking for vehicles on the main road is higher than that for vehicles on the minor road.

[0005] FIG. 1 is a perspective view showing an example of the overall configuration of a traffic signal control system according to this embodiment. FIG. 2 is a block diagram showing an example of a central device and a traffic signal controller included in the traffic signal control system. FIG. 3 is a diagram showing an example of an intersection where a main road and a minor road intersect. FIG. 4 is a flowchart showing an example of a selection process performed in signal control at an intersection. FIG. 5 is a flowchart showing an example of a first control process. FIG. 6 is a flowchart showing an example of a second control process. FIG. 7 is a diagram showing a part of a flowchart of the second control process according to a modified example. FIG. 8 is a diagram showing a main road on which a traffic signal control system according to another embodiment is installed.

[0006] [Problem to be Solved by the Present Disclosure] In recent years, the logistics industry has been actively working to shorten the travel time of transport vehicles transporting cargo. Main roads, which are frequently used by transport vehicles, often have intersections where minor roads with less traffic volume than the main road intersect. If traffic signal control such as that in the conventional example is performed at such intersections, a certain amount of green light time is also given to the minor roads, which may disrupt traffic flow on the main road. Disruption of traffic flow on the main road results in longer travel times for transport vehicles.

[0007] Therefore, an object of the present disclosure is to disclose a technology that can smooth traffic flow on trunk roads when specific vehicles such as transport vehicles are traveling.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to smooth the traffic flow on the main road when a specific vehicle is traveling.

[0009] [Description of the embodiment of the present disclosure] First, the contents of the embodiment will be listed and described. [Outline of the embodiment]

[0010] (1) An embodiment of a traffic signal control system includes a first acquisition unit that acquires specific vehicle information indicating the traffic status of specific vehicles traveling on a main road toward an intersection where the main road and a minor road intersect, and a control device. The control device includes a processing unit that executes a selection process that selects, based on the specific vehicle information, one of a first control process that controls signal lights installed at the intersection and a second control process that controls the signal lights so that a priority ranking for vehicles on the main road over vehicles on the minor road is higher than that of the first control process. According to the above configuration, by calculating the traffic volume of specific vehicles from the specific vehicle information and executing the second control process when the traffic volume increases, it is possible to give higher priority to the passage of specific vehicles traveling on the main road and to smooth traffic flow on the main road when the specific vehicles are traveling.

[0011] (2) In the traffic signal control system described in (1) above, if the system further includes a second acquisition unit that acquires mobile object information indicating the traffic conditions of mobile objects attempting to enter the intersection from the secondary road, the second control process may include switching the display of a traffic light installed at the intersection from a display prohibiting entry into the intersection from the secondary road to a display permitting entry into the intersection from the secondary road when the mobile object information satisfies a predetermined condition. In this case, increasing the difficulty of satisfying the predetermined condition significantly restricts the passage of mobile objects on the secondary road, but allows vehicles on the main road to be given higher priority. As a result, traffic flow on the main road when a specific vehicle is traveling can be made smoother.

[0012] (3) In the traffic signal control system of (2), the predetermined condition may include that at least one of the queue length of the secondary road, the number of queuing vehicles on the secondary road, and the waiting time at a traffic light on the secondary road, which are obtained based on the mobile object information, is equal to or greater than a threshold value set corresponding to the queue length, the number of queuing vehicles, and the waiting time at a traffic light, respectively. In this case, the difficulty of satisfying the predetermined condition can be easily adjusted by adjusting the threshold value.

[0013] (4) In the traffic signal control system of (3), the second control process may further include a process of setting the threshold value based on the specific vehicle information. In this case, the difficulty of satisfying the predetermined condition can be adjusted according to the traffic state of the specific vehicle.

[0014] (5) In the traffic signal control system according to any one of (2) to (4), the second control process may further include a process of determining, based on the mobile object information, a duration for which the display is continued after switching to a display permitting entry into the intersection from the minor road. In this case, the stopping time of a vehicle traveling on a main road when stopped at an intersection can be minimized.

[0015] (6) In the traffic signal control system according to any one of (1) to (5) above, if the processing unit further executes a control process for controlling a nearby signal lamp installed at a nearby intersection located near the intersection on the main road, the control process may synchronize the display of the nearby signal lamp with the display of the signal lamp, thereby more effectively facilitating smooth traffic flow on the main road.

[0016] (7) In the traffic signal control system according to any one of (1) to (6), the specific vehicle may be a transport vehicle for transporting cargo. In this case, traffic flow on the main road can be made smooth when the transport vehicle is traveling.

[0017] (8) In the traffic signal control system according to any one of (1) to (7), the first acquisition unit may include at least one of a traffic volume observation device that observes an approach road of the intersection and an on-board device that is mounted on the specific vehicle and capable of collecting probe information and transmitting the probe information. In this case, the specific vehicle information can be appropriately acquired.

[0018] (9) In the traffic signal control system according to any one of (2) to (5), the second acquisition unit may include at least one of a vehicle detector provided on the secondary road and an on-board device mounted on a vehicle capable of collecting probe information and capable of transmitting the probe information. In this case, mobile object information can be appropriately acquired.

[0019] (10) A traffic signal control device, which is an embodiment from another perspective, is a traffic signal control device that controls signal lights installed at an intersection where a main road and a minor road intersect, and is equipped with a processing unit that executes a selection process that selects the control process to be executed from among a first control process that controls the signal lights and a second control process that controls the signal lights so that the priority level of vehicles on the main road is higher than that of vehicles on the minor road, based on specific vehicle information that indicates the traffic status of specific vehicles traveling on the main road toward the intersection.

[0020] (11) Another embodiment is a control method for controlling a traffic light installed at an intersection where a main road and a minor road intersect, the control method including a step of selecting a control process to be executed from among a first control process for controlling the traffic light and a second control process for controlling the traffic light so that a priority level for giving priority to vehicles on the main road over vehicles on the minor road is higher than that of the first control process, based on specific vehicle information indicating a traffic state of a specific vehicle traveling on the main road toward the intersection.

[0021] (12) Another embodiment is a computer program for causing a computer to control a traffic light installed at an intersection where a main road and a minor road intersect, the computer program causing the computer to execute a step of selecting, based on specific vehicle information indicating a traffic state of a specific vehicle traveling on the main road toward the intersection, one of a first control process for controlling the traffic light and a second control process for controlling the traffic light so that a priority level for vehicles on the main road is higher than that of the first control process.

[0022] [Details of the embodiment] Preferred embodiments will now be described with reference to the drawings. Note that at least some of the embodiments described below may be combined in any desired manner.

[0023] [Overall System Configuration] Fig. 1 is a perspective view showing an example of the overall configuration of a traffic signal control system according to this embodiment. Fig. 2 is a block diagram showing an example of a central unit and traffic signal controllers included in the traffic signal control system 1. As shown in Figs. 1 and 2, the traffic signal control system 1 includes a central unit 2, on-board devices 4 of multiple probe vehicles 3, multiple vehicle detectors 5, multiple traffic flow observation devices 12, and multiple traffic signal controllers 6.

[0024] A plurality of traffic signal controllers 6 are installed at a plurality of intersections Ji (i = 1 to 12 in the illustrated example) included in the traffic control area of ​​the central unit 2. Each of the plurality of traffic signal controllers 6 has the function of controlling the signal lights 14 installed at the intersection Ji. The plurality of traffic signal controllers 6 are remotely controlled by the central unit 2. However, the traffic control area may also include a stand-alone traffic signal controller that is not subject to remote control by the central unit 2 and performs point control (such as fixed-cycle control) that independently determines the signal light color.

[0025] The traffic signal controller 6 is connected to a router 15 via a communication line 9. The router 15 is connected to the central device 2 via the communication line 9. The central device 2 and the traffic signal controllers 6 at each intersection Ji form a LAN (Local Area Network). Therefore, the central device 2 and the multiple traffic signal controllers 6 can communicate with each other.

[0026] A plurality of vehicle detectors 5 are installed on the approach roads of a plurality of intersections Ji. Each of the vehicle detectors 5 is connected to a traffic signal controller 6 located downstream of the vehicle detector 5 via a dedicated communication line. The vehicle detector 5 has the function of detecting whether or not a moving object such as a vehicle is present in its detection area using ultrasound, radio waves, light, etc. The detection area is located in the center of the lane width. The vehicle detector 5 outputs a detection result indicating the result of detecting the moving object. The detection result is provided from the vehicle detector 5 to the traffic signal controller 6 connected to the vehicle detector 5. The traffic signal controller 6 provides the provided detection result to the central device 2. The detection result indicates the traffic status of moving objects on the approach roads of the intersections Ji. The detection result is used to calculate traffic indicators necessary for controlling the traffic signal controller 6.

[0027] A plurality of traffic flow observation devices 12 are installed at a plurality of intersections Ji. Each of the plurality of traffic flow observation devices 12 includes an imaging device and a millimeter-wave sensor. The traffic flow observation devices 12 have the function of observing the entrance roads of the intersections Ji. The traffic flow observation devices 12 are connected to a router 15 via a communication line 9. Therefore, the traffic flow observation devices 12 and the central unit 2 can communicate with each other. The traffic flow observation devices 12 provide the central unit 2 with observation results of vehicles traveling on the entrance roads. The observation results include imaging data on the entrance roads and point cloud data detected on the entrance roads. The observation results indicate the traffic conditions of moving objects on the entrance roads of the intersections Ji. The observation results are used to calculate traffic indicators necessary for controlling the traffic signal controller 6.

[0028] The multiple on-board devices 4 are mounted on multiple probe vehicles 3. Each of the multiple on-board devices 4 is capable of wireless communication with a wireless base station 7 (e.g., a base station of a mobile communication system) located in various locations. The wireless base station 7 is capable of communication with the central device 2 via a public communication network 8 such as the Internet. Therefore, the on-board devices 4 and the central device 2 can communicate with each other. The on-board devices 4 provide probe information to the central device 2. Note that a probe vehicle is a vehicle that senses probe information and transmits the sensed probe information to an external device. Furthermore, probe information refers to various information about a vehicle sensed by a probe vehicle traveling on a road. The probe information is also referred to as probe data or floating car data. The probe information includes various vehicle data such as the identification information of the probe vehicle, vehicle position, vehicle speed, vehicle direction, and the time of measurement of these.

[0029] The central device 2 has the function of a control device that determines traffic indicators based on the detection results from the traffic signal controllers 6 at the intersections, the observation results from the traffic volume observation devices 12, and probe information, and controls each traffic signal controller 6 based on the traffic indicators.

[0030] [Configuration of Central Device] As shown in Fig. 2, the central device 2 includes a server 10. The server 10 has a function of comprehensively controlling the traffic signal controllers 6 at intersections Ji included in the traffic control area of ​​the central device. The server 10 is configured by a computer or the like including a processing unit 10a, a storage unit 10b, and a communication unit 10c. The processing unit 10a is, for example, a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a quantum processor, or any of various other processors suitable for computer control.

[0031] The storage unit 10b includes, for example, a flash memory, a hard disk, an SSD (Solid State Drive), a ROM (Read Only Memory), etc. The storage unit 10b stores a computer program 11 to be executed by the processing unit 10a and other necessary information. The processing unit 10a executes a computer program stored in a computer-readable, non-transitory recording medium such as the storage unit 10b, thereby realizing various processing functions of the server 10.

[0032] The communication unit 10c includes a communication interface for communicating with the traffic signal controller 6 and the traffic volume observation device 12 via the communication line 9. The communication unit 10c also includes a communication interface for communicating with the wireless base station 7 via the public communication network 8. Note that the communication between the probe vehicle 3 and the wireless base station 7 may be communication via optical communication between the on-board device 4 and an optical beacon, or communication via ITS (Intelligent Transport Systems) wireless communication in the 700 MHz band.

[0033] The processing unit 10a has a function of calculating traffic indices for each intersection Ji based on the sensing results, observation results, and probe information. The calculated traffic indices include the traffic volume of vehicles traveling on the incoming roads toward the intersection, the queue length on the incoming road, the number of vehicles in the queue, the waiting time at traffic lights, and the load factor for each incoming road at each intersection Ji.

[0034] Note that traffic volume refers to the number of vehicles passing through within a unit time. A queue refers to a line of vehicles stopped in front of an intersection waiting for a red light. The queue length refers to the length of the queue, and the number of vehicles in the queue refers to the number of vehicles in the queue. The waiting time for a red light refers to the time elapsed since the first vehicle in the queue stopped. Furthermore, a red light refers to a state in which the light color of the signal lamp 14 is red. A green light refers to a state in which the light color of the signal lamp 14 is green. According to Japanese laws and regulations, a red light indicates that vehicles on the approaching road of an intersection do not have the right of way at the intersection. A green light indicates that vehicles on the approaching road of an intersection have the right of way at the intersection. This embodiment has a configuration that complies with Japanese laws and regulations, but embodiments in other countries may be configured to comply with laws and regulations of other countries.

[0035] The processing unit 10a also has a function of remotely controlling the signal lights 14 based on the traffic indicators of each intersection Ji. The processing unit 10a issues a signal control command to the traffic signal controller 6 corresponding to the target intersection to be remotely controlled. The processing unit 10a controls the traffic signal controller 6 by issuing the signal control command to the traffic signal controller 6, thereby performing signal control of each intersection Ji.

[0036] The processing unit 10a also has a function of calculating signal control parameters for the signal lamps 14 at each intersection Ji using MODERATO or the like. MODERATO is the name of a system that automatically generates signal control parameters from the load factor of each incoming road at an intersection.

[0037] The processing unit 10a provides the calculated signal control parameters as signal control commands to the traffic signal controller 6 at the intersection Ji. The traffic signal controller 6 determines the timing for switching the light color of the signal lamp 14 in accordance with the provided signal control parameters.

[0038] Furthermore, the processing unit 10a also has a function of generating a display command for causing the signal lamps at the target intersection to display a specific signal light color. The processing unit 10a provides the display command as a signal control command to the traffic signal controller 6 at the intersection Ji. The traffic signal controller 6 controls the signal light color of the signal lamp 14 in accordance with the provided display command.

[0039] The processing unit 10a also has a function of executing a selection process. The selection process is a process related to the selection of signal control for the signal lamps 14 installed at intersections where main roads and minor roads intersect. The selection process will be described in detail later.

[0040] The central device 2 further includes a map database 21 and a probe database 22. Both databases 21 and 22 may be stored in the storage unit 10b of the server 10 or may be stored in an external server. When the databases 21 and 22 are stored in the external server, the server 10 accesses the databases 21 and 22 via the communication unit 10c.

[0041] The map database 21 stores road map data 25 covering the entire country. The road map data 25 includes "node data" and "link data." A node is an intersection or other nodal point on the road network. A link is a section connecting a pair of adjacent nodes. "Node data" is data that associates IDs assigned to domestic nodes with location information of the nodes. "Link data" is data that associates link IDs of specific links assigned to domestic roads with information about the specific links. Information about the specific links includes location information of the start and end points of the specific links, IDs of links connecting to the start and end points of the specific links, etc.

[0042] The road map data 25 forms a network corresponding to the actual road alignment and driving direction of the road. For this reason, the road map data 25 is a network in which road sections between nodes representing intersections are connected by directed links l (lowercase L). Specifically, the road map data 25 is configured as a directed graph in which a node n is set for each intersection and each node n is connected by a pair of directed links l in opposite directions. Therefore, in the case of a one-way road, only one-way directed links l connect the node n.

[0043] The road map data 25 also includes road attribute information of the road corresponding to the directed link 1. The road attribute information includes, for example, road type information indicating whether the road is a main road or a secondary road, and facility information indicating the type of facility, such as a toll gate or a parking area, included in the directed link 1.

[0044] The probe database 22 stores probe information received from pre-registered probe vehicles 3 for each piece of identification information of the probe vehicles 3. The stored probe information includes at least the vehicle position and the time of passing. The probe information may also include vehicle data such as vehicle speed, vehicle direction, and vehicle status information (stop / running events). The sensing cycle of the probe information is at a granularity that allows the travel history of the probe vehicle 3 to be accurately identified, and is, for example, 0.1 to 1.0 seconds. Therefore, the travel trajectory of the probe vehicle 3 is stored in the probe database 22 as a plurality of discrete trajectory points. Each of the plurality of trajectory points is associated with at least the vehicle position and the time of passing.

[0045] The probe information stored in the probe database 22 includes information indicating the traffic conditions of vehicles on the approach road to the intersection Ji. Therefore, the processing unit 10a can use the probe information stored in the probe database 22 to calculate traffic indicators necessary for controlling the traffic signal controller 6.

[0046] [Configuration of Traffic Signal Controller] As shown in FIG. 2, the traffic signal controller 6 is configured by a computer or the like that includes a processing unit 6a, a storage unit 6b, and a communication unit 6c.

[0047] The processing unit 6 a can be implemented by a circuit including a processor, and the processor may be any of various processors suitable for computer control, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a quantum processor.

[0048] The storage unit 6b includes, for example, a flash memory, a hard disk, an SSD (Solid State Drive), a ROM (Read Only Memory), etc. The storage unit 6b stores a computer program 30 to be executed by the processing unit 6a and necessary information. The processing unit 6a executes the computer program stored in a computer-readable non-transitory recording medium such as the storage unit 6b, thereby realizing various processing functions of the traffic signal controller 6. The communication unit 6c includes a communication interface for communicating with the central device 2 via the communication line 9. The communication unit 6c also includes a communication interface for communicating with the detector 5.

[0049] The processing unit 6a has a function of controlling the signal lights 14 installed at the intersection Ji based on a signal control command given from the central unit 2. The processing unit 6a also has a function of giving the central unit 2 the detection results given from the detectors 5. The processing unit 6a also has a function of giving the central unit 2 the indication of the signal lights 14 that it controls.

[0050] [Regarding the Selection Process] FIG. 3 is a diagram showing an example of an intersection where a main road and a minor road intersect. The intersection Jk shown in FIG. 3 is one of multiple intersections Ji included in the traffic control area of ​​the central device 2. The intersection Jk is an intersection where a main road M and a minor road B intersect. In this embodiment, the main road refers to the road with the heavier traffic volume at the intersection, and the minor road refers to the road with the lighter traffic volume than the main road. The probe vehicles 3 present on the main road M and the minor road B include general vehicles 3a and specific vehicles 3b. In this embodiment, the specific vehicles 3b include transport vehicles such as trucks that transport luggage. The general vehicles 3a are probe vehicles 3 other than the specific vehicles 3b among the probe vehicles 3. Therefore, the general vehicles 3a include passenger cars and the like.

[0051] In addition, there are also non-probe vehicles 13 on the main roads M and the secondary roads B that are not equipped with an on-board device 4. The non-probe vehicles also include general vehicles 13a and specific vehicles 13b. The specific vehicles 13b are transport vehicles such as trucks that transport cargo. The general vehicles 13a are non-probe vehicles 13 other than the specific vehicles 13b among the non-probe vehicles 13. Therefore, the general vehicles 13a include not only passenger cars but also bicycles and the like.

[0052] A traffic flow observation device 12 is provided on the approach road to the intersection Jk on the trunk road M. The traffic flow observation device 12 shown in FIG. 3 is, for example, an imaging device. The traffic flow observation device 12 captures images of the approach road of the trunk road M at any time and provides the captured image data as observation results to the central unit 2. The central unit 2 stores the observation results provided at any time in the memory unit 10b. Here, the vehicles captured in the observation results may include the specific vehicle 3b and the specific vehicle 13b. As described above, the observation results are information indicating the traffic conditions on the approach road, but they also constitute specific vehicle information indicating the traffic conditions of the specific vehicles 3b and 13b traveling on the trunk road M toward the intersection Jk. Thus, the traffic flow observation device 12 constitutes a first acquisition unit that acquires specific vehicle information.

[0053] Furthermore, the probe information of the specific vehicle 3b can also be used as specific vehicle information indicating the traffic conditions of the specific vehicles 3b, 13b traveling on the main road M toward the intersection Jk. In this case, the on-board device 4 of the specific vehicle 3b constitutes a first acquisition unit that acquires the specific vehicle information.

[0054] A vehicle detector 5 is provided on the entrance road to intersection Jk on minor road B. The vehicle detector 5 is provided at a distance L upstream from stop line s1. Stop line s1 is the stop line on minor road B just before intersection Jk. Distance L is a value that, for example, results in a queue of approximately five vehicles when a queue occurs due to waiting at a traffic light on minor road B. The vehicle detector 5 provides the detection results to the central unit 2 via the traffic signal controller 6. The central unit 2 stores the detection results provided as needed in memory unit 10b.

[0055] As described above, the detection result of the vehicle detector 5 on the secondary road B is mobile object information indicating the traffic conditions of vehicles (mobile objects) attempting to enter the intersection Jk from the secondary road B side. Therefore, the vehicle detector 5 constitutes a second acquisition unit that acquires mobile object information. Furthermore, the probe information can also be used as mobile object information indicating the traffic conditions of vehicles attempting to enter the intersection Jk from the secondary road B side. In this case, the on-board device 4 of the probe vehicle 3 constitutes a second acquisition unit that acquires mobile object information.

[0056] Signal control at the intersection Jk shown in Figure 3 will now be described. Figure 4 is a flowchart showing an example of a selection process performed in signal control at the intersection Jk. The processing unit 10a of the central device 2 first references specific vehicle information (step S1). In this embodiment, the processing unit 10a references the observation results of the trunk road M acquired by the traffic volume observation device 12 as specific vehicle information. Based on the observation results of the trunk road M, the processing unit 10a calculates the traffic volume of specific vehicles 3b, 13b traveling on the trunk road M toward the intersection Jk. The processing unit 10a performs image processing on the imaging data included in the observation results and identifies the specific vehicles 3b, 13b included in the imaging data. Based on the specific vehicles 3b, 13b identified from the imaging data, the processing unit 10a calculates the traffic volume of the specific vehicles 3b, 13b traveling on the trunk road M.

[0057] Next, the processing unit 10a determines whether the traffic volume of the specific vehicles 3b, 13b traveling on the trunk road M is greater than the threshold value Th1 (step S2). If it is determined that the traffic volume of the specific vehicles 3b, 13b traveling on the trunk road M is not greater than the threshold value Th1, the processing unit 10a proceeds to step S3, executes the first control process (step S3), and returns to step S1.

[0058] FIG. 5 is a flowchart showing an example of the first control process. The first control process is a process for controlling the light color of the signal lamp 14 using the signal control parameters calculated by the processing unit 10a. In the first control process, the processing unit 10a first calculates traffic indices based on the sensing results, observation results, and probe information (step S6). The calculated traffic indices include the load factor for each approach road at the intersection, which is used in MODERATO. Next, the processing unit 10a uses the calculated traffic indices to calculate signal control parameters based on MODERATO (step S7). The processing unit 10a then transmits the calculated signal control parameters as a signal control command to the traffic signal controller 6 at the intersection Jk (step S8).

[0059] The traffic signal controller 6 determines the timing for changing the light color of the signal light 14 according to the given signal control parameters. The traffic signal controller 6 controls the signal light 14 at the intersection Jk according to the determined light color change timing. In the first control process, the signal light 14 is controlled based on the signal control parameters regardless of the traffic volume of the specific vehicles 3b, 13b traveling on the main road M.

[0060] On the other hand, if the processing unit 10a determines that the traffic volume of specific vehicles 3b, 13b traveling on the main road M is greater than the threshold value Th1, the processing unit 10a proceeds to step S4, executes the second control process (step S4), and returns to step S1.

[0061] The second control process is a process for controlling the signal lamp 14 so that the priority level for giving priority to vehicles on the main road M over vehicles on the minor road B is higher than that of the first control process. In the second control process, the processing unit 10a controls the signal lamp 14 by issuing a display command to the traffic signal controller 6. In this way, in the selection process, the process to be executed by the processing unit 10a is selected based on the traffic volume of the specific vehicles 3b, 13b.

[0062] 6 is a flowchart showing an example of the second control process. In the second control process, the processing unit 10a first determines whether the light color of the signal lamp 14 on the minor road B is red (step S11). The processing unit 10a repeats step S11 until it determines that the light color of the signal lamp 14 on the minor road B is red. If it determines that the light color of the signal lamp 14 on the minor road B is red, the processing unit 10a refers to the moving object information on the minor road B (step S12). Here, the processing unit 10a refers to the detection result acquired by the vehicle detector 5 as the moving object information.

[0063] Next, the processing unit 10a determines whether the mobile object information for secondary road B satisfies predetermined conditions (step S13). The predetermined conditions include that at least one of the queue length, the number of vehicles in the queue, and the waiting time at a traffic light is equal to or greater than a predetermined threshold. A threshold value Th2 is set for the queue length. A threshold value Th3 is set for the number of vehicles in the queue. A threshold value Th4 is set for the waiting time at a traffic light. In step S13, it is determined whether at least one of these three conditions is satisfied.

[0064] The detection result of the vehicle detector 5 on the secondary road B indicates the traffic volume on the secondary road B and whether the queue length on the secondary road B is equal to or greater than distance L (FIG. 3). The detection result output by the vehicle detector 5 on the secondary road B also indicates the number of vehicles waiting in the queue until the queue length on the secondary road B reaches distance L (FIG. 3). Furthermore, the processing unit 10a can use the detection result to calculate the waiting time for a vehicle waiting at a traffic light on the secondary road B. For example, the processing unit 10a calculates the waiting time by measuring the time from when the light on the secondary road B changes to red to when the vehicle detector 5 detects the passage of a vehicle.

[0065] For example, in FIG. 3 , assume that the processing unit 10a is executing the second control process, the signal light 14 on the minor road B is red, and a vehicle is waiting at a traffic light at the stop line s1 on the minor road B. Also assume that the threshold value Th2 is "L" and the threshold value Th3 is "5." Furthermore, assume that the waiting time for the traffic light is less than the threshold value Th4. At this time, when a new vehicle 13a1 stops at the end of the queue, the processing unit 10a can determine, based on the detection result of the vehicle detector 5, that the queue length has reached or exceeded the threshold value Th2 and that the number of vehicles in the queue has reached or exceeded the threshold value Th3. In this way, the processing unit 10a determines whether the mobile object information on the minor road B satisfies the predetermined condition.

[0066] If it is determined in step S13 that the predetermined conditions are not satisfied (none of the three conditions are satisfied), the processing unit 10a returns to step S12 and repeats the same process. If it is determined in step S13 that the predetermined conditions are satisfied (at least one of the three conditions is satisfied), the processing unit 10a calculates the green time for the minor road B (step S14). The green time refers to the time during which the signal for the minor road B remains green after it changes from red to green.

[0067] The processing unit 10a calculates the green time according to the current number of vehicles in the queue or the queue length. The green time is calculated so that it is sufficient time for all vehicles currently in the queue on the secondary road B to pass through the intersection Jk.

[0068] Next, the processing unit 10a proceeds to step S15 and issues a display command to the traffic signal controller 6 at the intersection Jk to change the light color of the signal lamp 14 on the secondary road B to green and change the light color of the signal lamp 14 on the main road M to red. That is, the processing unit 10a performs processing to change the display of the signal lamp 14 installed at the intersection Jk from a display prohibiting entry into the intersection Jk from the secondary road B side to a display permitting entry into the intersection Jk from the secondary road B side. As a result, the light color of the signal lamp 14 on the secondary road B becomes green and the light color of the signal lamp 14 on the main road M becomes red (step S15).

[0069] In this way, the processing unit 10a controls the light color of the traffic light unit 14 on the minor road B to be red until it determines that the mobile object information on the minor road B satisfies the predetermined condition. The thresholds Th2, Th3, and Th4 included in the predetermined condition are parameters that determine the priority level of vehicle passage on the main road M at the intersection Jk. The priority level of vehicle passage on the main road M at the intersection Jk refers to the priority level when giving priority to vehicle passage on the main road M over vehicle passage on the minor road B at the intersection Jk. Giving priority to vehicle passage on the main road M over vehicle passage on the minor road B at the intersection Jk means, for example, setting the time during which entry into the intersection Jk from the main road M side is permitted to be longer than the time during which entry into the intersection Jk from the minor road B side is permitted.

[0070] The thresholds Th2, Th3, and Th4 are set so that the priority of vehicle traffic on the main road M at the intersection Jk in the second control process is higher than the priority of vehicle traffic on the main road M at the intersection Jk in the first control process.

[0071] Next, the processing unit 10a determines whether the green time calculated in step S14 has elapsed since the signal light 14 of the minor road B was switched to green (step S16). The processing unit 10a repeats step S16 until the green time has elapsed. If it determines that the green time has elapsed, the processing unit 10a proceeds to step S17 and issues a display command to the traffic signal controller 6 at the intersection Jk to switch the signal light 14 of the minor road B to red and the signal light 14 of the main road M to green. As a result, the signal light 14 of the minor road B becomes red and the signal light 14 of the main road M becomes green (step S17).

[0072] After step S17, the processing unit 10a determines whether a predetermined time has elapsed since the start of the second control process (step S18). If it determines that the predetermined time has not elapsed, the processing unit 10a returns to step S12 and performs the same process again. That is, if the processing unit 10a determines that the predetermined time has not elapsed since the start of the second control process, it continues the second control process. On the other hand, if it determines that the predetermined time has elapsed, the processing unit 10a ends the second control process. In other words, the predetermined time is a value that determines the time for which the second control process will continue. After ending the second control process, the processing unit 10a proceeds again to step S1 (FIG. 4) and repeats the above-described process.

[0073] According to the above configuration, the processing unit 10a executes a selection process to select, from the first control process and the second control process for controlling the signal lamps 14 so that the priority level for giving priority to the passage of vehicles on the main road M over the passage of vehicles on the minor road B is higher than that of the first control process, the control process to be executed by the processing unit 10a (central device 2) based on the traffic state of the specific vehicle on the main road M. In other words, the processing unit 10a calculates the traffic volume of the specific vehicles 3b, 13b from the traffic state of the specific vehicles on the main road M, and when this traffic volume increases and exceeds the threshold value Th1 (step S2), executes the second control process (step S4) for giving priority to the passage of vehicles on the main road M. Therefore, the passage of the specific vehicles 3b, 13b traveling on the main road M can be given higher priority, and traffic flow on the main road M when the specific vehicles 3b, 13b are traveling can be smoothed.

[0074] Furthermore, the second control process includes a process of switching the display of the signal lamp 14 installed at the intersection Jk from a display prohibiting entry into the intersection Jk from the secondary road B to a display permitting entry into the intersection Jk from the secondary road B (step S15) when the information about the moving object on the secondary road B satisfies a predetermined condition (step S13). Therefore, if the difficulty of satisfying the predetermined condition is increased, the passage of moving objects on the secondary road B is significantly restricted, but priority can be given to the passage of vehicles on the main road M. As a result, traffic flow on the main road M when the specific vehicles 3b and 13b are traveling can be made smoother.

[0075] As described above, the predetermined conditions include that at least one of the queue length of the secondary road B, the number of vehicles queuing on the secondary road B, and the waiting time at a traffic light on the secondary road B is equal to or greater than the predetermined thresholds Th2, Th3, and Th4. Therefore, by adjusting these thresholds Th2, Th3, and Th4, the difficulty of satisfying the predetermined conditions can be easily adjusted.

[0076] The second control process also includes a process (step S14) for calculating the green time based on the mobile object information (current number of vehicles in queue or queue length) on the secondary road B. This allows the green time to be calculated to be a necessary and sufficient time. As a result, the stopping time of vehicles traveling on the main road M when stopped at an intersection can be minimized.

[0077] In the present embodiment, the thresholds Th2, Th3, and Th4 in step S13 are set in advance. However, the thresholds Th2, Th3, and Th4 may be set based on the specific vehicle information of the trunk road M. For example, the processing unit 10a may be configured to set the thresholds Th2, Th3, and Th4 according to the traffic volume of the specific vehicles 3b and 13b obtained from the specific vehicle information of the trunk road M. In this case, appropriate thresholds Th2, Th3, and Th4 are set according to the traffic volume of the specific vehicles 3b and 13b.

[0078] Furthermore, in the second control process, the specific vehicle information on the trunk road M may be referenced to determine the traffic volume of the specific vehicles 3b and 13b, and the thresholds Th2, Th3, and Th4 may be set according to this traffic volume. FIG. 7 is a diagram showing a part of a flowchart of the second control process according to a modified example. Steps S14 to S17 in FIG. 6 are omitted in FIG. 7. This modified example differs from the above embodiment in that a process (step S20) for setting the thresholds Th2, Th3, and Th4 based on the traffic volume of the specific vehicles 3b and 13b is provided between steps S11 and S12, and a process (step S21) for referencing the specific vehicle information on the trunk road M is provided when returning from steps S13 and S18 to step S12.

[0079] In this modification, while the second control process is repeated because the predetermined condition is not satisfied or the predetermined time has not elapsed, the processing unit 10a references the specific vehicle information (observation results) on the trunk road M and sets the thresholds Th2, Th3, and Th4 based on the traffic volume of the specific vehicles 3b and 13b. The processing unit 10a determines whether the predetermined condition is satisfied using the successively set thresholds Th2, Th3, and Th4.

[0080] In this case, if the traffic volume of the specific vehicles 3b, 13b increases during execution of the second control process, the processing unit 10a can increase the thresholds Th2, Th3, and Th4 to make it more difficult to satisfy the predetermined conditions, thereby increasing the priority of the main road M. This allows more specific vehicles 3b, 13b to pass preferentially. Conversely, if the traffic volume of the specific vehicles 3b, 13b decreases, the processing unit 10a can maintain the thresholds Th2, Th3, and Th4 at their current levels or decrease them, thereby maintaining the conditions for allowing mobile bodies on the secondary road B to enter the intersection Jk at a certain level.

[0081] In this way, according to this modification, even if the traffic volume of the specific vehicles 3b, 13b changes while the second control process is being executed, the thresholds Th2, Th3, and Th4 can be set to appropriate values.

[0082] [Regarding Other Embodiments] Figure 8 is a diagram showing a main road on which a traffic signal control system according to another embodiment is installed. In Figure 8, main road M intersects with minor roads B1 and B2. A traffic signal controller 6A is installed at intersection Jk1 where main road M intersects with minor road B1. The traffic signal controller 6A controls the signal lamps 14 installed at intersection Jk1.

[0083] Intersection Jk2, where main road M intersects with minor road B2, is a nearby intersection of intersection Jk1. Intersection Jk1 and intersection Jk2 are adjacent to each other. A traffic signal controller 6B is installed at intersection Jk2. The traffic signal controller 6B controls the signal lights 14 (neighboring signal lights) installed at intersection Jk2.

[0084] The processing unit 10a of the central device 2 can control the traffic signal controllers 6A and 6B in the same manner as in the above embodiment. When the mobile object information for either the minor road B1 or the minor road B2 satisfies a predetermined condition, the processing unit 10a of this embodiment switches both the signal lamps 14 for the minor road B1 and the signal lamps 14 for the minor road B2 to green and switches the signal lamps 14 for the main road M to red. In this case, the display of the signal lamps 14 for the intersection Jk2 can be synchronized with the display of the signal lamps 14 for the intersection Jk1. As a result, traffic flow on the main road M can be more effectively smoothed.

[0085] In the above embodiment, an example is given of controlling the signal lights 14 at intersection Jk1 and the signal lights 14 at intersection Jk2, which is a nearby intersection, but the processing unit 10a may also be configured to control nearby signal lights installed in a location near intersection Jk1 but not at the intersection, in the above manner, in addition to the signal lights 14 at intersection Jk1.

[0086] [Others] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. In the present embodiment, the specific vehicles 3b, 13b include transport vehicles for transporting luggage. However, the present invention is not limited to this, and the specific vehicles 3b, 13b may include public vehicles such as fire engines and ambulances. Furthermore, the specific vehicles 3b, 13b may include buses for transporting a large number of people.

[0087] In the above embodiment, the predetermined condition in the second control process includes at least one of the queue length of the secondary road B, the number of queuing vehicles on the secondary road B, and the waiting time at a traffic light on the secondary road B being equal to or greater than the threshold values ​​Th2, Th3, and Th4. However, the predetermined condition may include at least one of the three conditions relating to the number of queuing vehicles on the secondary road B and the waiting time at a traffic light on the secondary road B. For example, the predetermined condition may include only that the number of queuing vehicles on the secondary road B is equal to or greater than the threshold value Th2.

[0088] In the above embodiment, the case where the observation results of the trunk road M are used as the specific vehicle information in step S1 in FIG. 4 has been exemplified. However, the processing unit 10a may also use probe data as the specific vehicle information. In this case, the processing unit 10a refers to the probe database 22 and obtains an estimate of the traffic volume of the specific vehicles 3b, 13b traveling on the trunk road M based on the probe data of the specific vehicle 3b. The processing unit 10a uses the estimate as the traffic volume of the specific vehicles 3b, 13b traveling on the trunk road M. Furthermore, the processing unit 10a may use both the observation results of the trunk road M and the probe data. In other words, the first acquisition unit that acquires the specific vehicle information includes at least one of the traffic volume observation device 12 and the on-board device 4 that is mounted on the specific vehicle 3b and is capable of transmitting probe information.

[0089] In the above embodiment, the detection results of the vehicle detector 5 are used as the moving object information for the secondary road B in step S12 in FIG. 6 . However, if a traffic volume observation device for observing moving objects on the secondary road B is installed at the intersection Jk or the secondary road B, the observation results of the traffic volume observation device for the secondary road B may be used as the moving object information for the secondary road B. In this case, the processing unit 10a can perform image processing on the image data included in the observation results for the secondary road B to identify the moving objects included in the image data. Therefore, the processing unit 10a can calculate the queue length, number of queueing vehicles, and waiting time at a traffic light for the secondary road B based on the moving objects identified from the image data. The processing unit 10a can use the calculated queue length, number of queueing vehicles, and waiting time at a traffic light to determine whether the predetermined conditions are met. In this case, moving objects other than vehicles, such as pedestrians P ( FIG. 3 ) waiting for a traffic light on the secondary road B or on a sidewalk beside the secondary road B, can also be identified.

[0090] Furthermore, probe data may be used as mobile object information for secondary road B. In this case, the processing unit 10a can refer to the probe database 22 and obtain estimated values ​​for the queue length, number of queueing vehicles, and waiting time at traffic lights for secondary road B based on the probe data. In this case, the processing unit 10a uses these estimated values ​​as the queue length, number of queueing vehicles, and waiting time at traffic lights to determine whether or not the predetermined conditions are met. The processing unit 10a may also use the detection results of the vehicle detector 5 in combination with the probe data. In other words, the second acquisition unit that acquires mobile object information includes at least one of the vehicle detector 5 and the on-board device 4 that is mounted on the probe vehicle 3 and is capable of transmitting probe information.

[0091] In the above embodiment, the central device 2 functions as a processing device that executes the selection process, but the traffic signal controller 6 may function as a processing device instead of the central device 2. In this case, the traffic signal controller 6 is provided with necessary information such as probe information from the central device 2.

[0092] The scope of the present invention is defined by the claims, not by the meaning described above, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0093] REFERENCE SIGNS LIST 1 Traffic signal control system 2 Central device 3 Probe vehicle 3a General vehicle 3b Specific vehicle 4 On-board device 5 Vehicle detector 6 Traffic signal controller 6A Traffic signal controller 6B Traffic signal controller 6a Processing unit 6b Memory unit 6c Communication unit 7 Wireless base station 8 Public communication network 9 Communication line 10 Server 10a Processing unit 10b Memory unit 10c Communication unit 11 Computer program 12 Traffic volume observation device 13 Non-probe vehicle 13a General vehicle 13a1 Vehicle 13b Specific vehicle 14 Signal lamp 15 Router 21 Map database 22 Probe database 25 Road map data 30 Computer program Ji, Jk, Jk1, Jk2 Intersection L Distance M Main road B, B1 Minor road l Directed link n Node s1 stop line

Claims

1. A traffic signal control system comprising: a first acquisition unit that acquires specific vehicle information indicating the traffic status of specific vehicles traveling on a main road toward an intersection where the main road intersects with a minor road; and a control unit, wherein the control unit comprises a processing unit that executes a selection process that selects, based on the specific vehicle information, the control process to be executed by the control unit from among a first control process that controls signal lights installed at the intersection and a second control process that controls the signal lights so that the priority ranking of vehicles on the main road over vehicles on the minor road is higher than that of the first control process.

2. A traffic signal control system as described in claim 1, further comprising a second acquisition unit that acquires mobile object information indicating the traffic conditions of mobile objects attempting to enter the intersection from the secondary road, wherein the second control process includes a process of switching the display of a traffic light installed at the intersection from a display prohibiting entry into the intersection from the secondary road to a display permitting entry into the intersection from the secondary road when the mobile object information satisfies a predetermined condition.

3. A traffic signal control system as described in claim 2, wherein the predetermined conditions include that at least one of the queue length of the secondary road, the number of vehicles queuing on the secondary road, and the waiting time at a traffic light on the secondary road, which are obtained based on the mobile object information, is equal to or greater than a threshold value set corresponding to the queue length, the number of vehicles queuing, and the waiting time at a traffic light, respectively.

4. A traffic signal control system according to claim 3, wherein the second control process further includes a process of setting the threshold value based on the specific vehicle information.

5. A traffic signal control system as described in any one of claims 2 to 4, wherein the second control process further includes a process for determining, based on the mobile object information, the time for which the switched display is to continue after switching to a display that allows entry into the intersection from the secondary road side.

6. A traffic signal control system as described in any one of claims 1 to 5, wherein the processing unit further executes a control process for controlling a nearby traffic light installed at a nearby intersection located near the intersection on the main road, and in the control process, the display of the nearby traffic light is synchronized with the display of the traffic light.

7. A traffic signal control system according to any one of claims 1 to 6, wherein the specific vehicle is a transport vehicle for transporting cargo.

8. A traffic signal control system as described in any one of claims 1 to 7, wherein the first acquisition unit includes at least one of a traffic volume observation device that observes the entrance road of the intersection, and an on-board device that is mounted on the specific vehicle capable of collecting probe information and is capable of transmitting the probe information.

9. A traffic signal control system as described in any one of claims 2 to 5, wherein the second acquisition unit includes at least one of a vehicle detector installed on the secondary road side and an on-board device mounted on a vehicle capable of collecting probe information and capable of transmitting the probe information.

10. A traffic signal control device that controls signal lights installed at an intersection where a main road and a minor road intersect, comprising a processing unit that executes a selection process that selects, from among a first control process that controls the signal lights and a second control process that controls the signal lights so that the priority level of vehicles on the main road is higher than that of vehicles on the minor road, which control process to be executed based on specific vehicle information that indicates the traffic status of specific vehicles traveling on the main road toward the intersection.

11. A control method for controlling traffic lights installed at an intersection where a main road and a minor road intersect, comprising a step of selecting a control process to be executed from among a first control process for controlling the traffic lights and a second control process for controlling the traffic lights so that a priority ranking for giving priority to vehicles on the main road over vehicles on the minor road is higher than that of the first control process, based on specific vehicle information indicating the traffic status of specific vehicles traveling on the main road toward the intersection.

12. A computer program for causing a computer to execute control of traffic lights installed at an intersection where a main road and a minor road intersect, the computer program executing a step of selecting, based on specific vehicle information indicating the traffic status of specific vehicles traveling on the main road toward the intersection, a control process to be executed from among a first control process for controlling the traffic lights and a second control process for controlling the traffic lights so that the priority level for vehicles on the main road is higher than that of the first control process.

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