Patent Publication Number: US-2022214684-A1

Title: Monitoring center, monitoring system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2019-177194 filed Sep. 27, 2019, the description of which is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a monitoring center for an autonomous vehicle and a monitoring system including the same. 
     Related Art 
     There have been known remote monitoring techniques for ensuring safety of autonomous vehicles during autonomous traveling. 
     SUMMARY 
     As an aspect of the present disclosure, a monitoring center is provided which is configured to communicate with an autonomous vehicle via a network and monitor the autonomous vehicle. The monitoring center includes: a threshold storage unit that stores a threshold of a vehicle stop duration for determining whether it is necessary to provide operator&#39;s assistance; a communication unit that receives vehicle state data from the autonomous vehicle; an analysis unit that obtains a vehicle stop duration from the vehicle state data, the vehicle stop duration being a period of time for which the autonomous vehicle has been stopped up to a current time; a determination unit that determines whether the vehicle stop duration of the autonomous vehicle is greater than or equal to the threshold stored in the threshold storage unit; an operator cooperation unit that notifies an operator of data concerning the autonomous vehicle when the vehicle stop duration of the autonomous vehicle is greater than or equal to the threshold; a vehicle stop period storage unit that obtains a vehicle stop period from the vehicle state data and stores the vehicle stop period, the vehicle stop period being a period of time from when the autonomous vehicle makes a stop to when the autonomous vehicle resumes traveling without operator&#39;s assistance; and a threshold determining unit that determines the threshold based on a distribution of the vehicle stop period. The threshold determining unit stores the determined threshold in the threshold storage unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a diagram showing a configuration of a monitoring system of a first embodiment; 
         FIG. 2  is a diagram showing a probability distribution of vehicle stop periods; 
         FIG. 3  is a diagram showing operation of a monitoring center of the first embodiment; 
         FIG. 4  is a diagram showing an example of data stored in a threshold storage unit of a second embodiment; 
         FIG. 5  is a diagram showing operation of a monitoring center of the second embodiment;  FIG. 6  is a diagram showing an example of data stored in a threshold storage unit of a third embodiment; 
         FIG. 7  is a diagram showing operation of a monitoring center of the third embodiment; 
         FIG. 8  is a diagram showing an example of data stored in a threshold storage unit of a fourth embodiment; 
         FIG. 9  is a diagram showing operation of a monitoring center of the fourth embodiment; 
         FIG. 10  is a diagram showing an example of data stored in a threshold storage unit of a fifth embodiment; 
         FIG. 11  is a diagram showing operation of a monitoring center of the fifth embodiment; 
         FIG. 12  is a diagram showing an example of data stored in a threshold storage unit of a sixth embodiment; 
         FIG. 13  is a diagram showing operation of a monitoring center of the sixth embodiment; 
         FIG. 14  is a diagram showing a configuration of a monitoring system of a seventh embodiment; 
         FIG. 15  is a diagram showing a configuration of a monitoring system of an eighth embodiment; and 
         FIG. 16  is a diagram showing a configuration of a monitoring system of a ninth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     There have been known remote monitoring techniques for ensuring safety of autonomous vehicles during autonomous traveling. In JP 2019-87015 A, an autonomous vehicle automatically stops upon detection of an obstacle based on information acquired from an autonomous sensor including a camera, and transmits an image of the surroundings of the vehicle captured by the camera to a remote monitoring center. When the autonomous vehicle automatically stops, the remote monitoring center determines, based on the received image captured by the camera, whether it should resume traveling of the autonomous vehicle. In this configuration, an observer (operator) in the remote monitoring center supplements the detection performance of the sensor of the autonomous vehicle to ensure safety in autonomous traveling of the vehicle. 
     According to the invention disclosed in JP 2019-87015 A, the operator is called every time the vehicle makes a stop even in a situation where the vehicle can resume traveling after waiting for a while. As a consequence, a monitoring task is given to the operator regardless of whether remote operation is actually necessary. This causes a problem that a load is applied on the operator and a labor cost (cost) for the operator increases. 
     In view of the above circumstances, the present disclosure aims to provide a monitoring system capable of reducing a load on an operator. 
     With reference to the drawings, a monitoring system of an embodiment of the present disclosure will be described. 
     First Embodiment 
       FIG. 1  is a diagram showing a configuration of a monitoring system  1  of a first embodiment. The monitoring system  1  includes a monitoring center  10  and a plurality of autonomous vehicles  30 . The monitoring center  10  monitors the autonomous vehicles  30 . The autonomous vehicles  30  are configured to communicate with the monitoring center  10  via a network. The autonomous vehicles  30  are monitored by the monitoring center  10 . 
     [Monitoring Center] 
     The monitoring center  10  is connected to operator terminals  40  that are operated by operators. When an autonomous vehicle  30  requires assistance, the monitoring center  10  transmits data concerning the autonomous vehicle  30  to the operator terminal  40  to cooperate with the operator. When a period of time for which the autonomous vehicle  30  has been stopped (hereinafter, referred to as a “vehicle stop duration”) becomes greater than or equal to a predetermined threshold, the monitoring center  10  sends a notification to the operator to cooperate with the operator. 
     The monitoring center  10  includes a communication unit  11 , an analysis unit  12 , a determination unit  13 , an operator cooperation unit  14 , a threshold determining unit  15  and a database  20 . The database  20  includes a vehicle stop period storage unit  21  and a threshold storage unit  22 . The threshold storage unit  22  stores a threshold of the vehicle stop duration for determining whether it is necessary to provide operator&#39;s assistance. The threshold is determined based on statistical data of vehicle stop periods acquired from a large number of autonomous vehicles  30 . 
     The communication unit  10  has a function of communicating with the autonomous vehicles  30 . The communication unit  10  receives data (vehicle state data) from the autonomous vehicle  30  regarding vehicle states of the autonomous vehicle  30 . The vehicle state data includes data regarding traveling states of the vehicle (e.g., acceleration, speed and traveling direction), a current position, operation states of on-vehicle devices (e.g., blinkers, wipers, light, brake and accelerator) and the like. The analysis unit  12  has a function of calculating a period of time for which the vehicle has been continuously stopped based on the speed data included in the vehicle state data. 
     Here, it is preferred that the analysis unit  12  also uses data regarding the surrounding environment of the autonomous vehicle  30  to calculate the vehicle stop duration. In this case, the monitoring center  10  receives data regarding the surrounding environment in addition to the vehicle state data from the autonomous vehicle  30 . The data concerning the surrounding environment is the sensor data acquired by a surroundings monitoring unit  33  of the autonomous vehicle  30 , and may include, for example, detection data of an object detected by a LIDAR and an image captured by a camera. Further, when the autonomous vehicle  30  has acquired data concerning the surroundings from infrastructure, other vehicles, networks, or the like via a V2X communication, such data may also be used. 
     The analysis unit  12  determines, from the vehicle state data and the surrounding environment data, whether the vehicle is in a specific situation where it needs to be stopped such as waiting for a traffic light, having arrived at a destination or waiting for getting on and off of passengers, and calculates a vehicle stop duration by adding a period of time during which the vehicle is not in such a situation. Whether the vehicle is waiting for a traffic light can be determined from the color of the traffic light by extracting the traffic light from an image of the surroundings of the vehicle captured by a camera. Whether the vehicle has arrived at a destination can be determined from the destination position and the current position in the travel route information. Whether the vehicle is waiting for getting on and off of passengers can be determined from an image captured by an in-vehicle camera. 
     The determination unit  13  has a function of determining whether the vehicle stop duration of the autonomous vehicle  30  is greater than or equal to the threshold stored in the threshold storage unit  22 . When the vehicle stop duration is greater than or equal to the predetermined threshold, the determination unit  13  notifies the operator cooperation unit  14  that the vehicle stop duration is greater than or equal to the threshold. Upon receiving the notification, the operator cooperation unit  14  transmits a notification requesting the operator terminal  40  to provide assistance to the autonomous vehicle  30 . Here, the operator cooperation unit  14  transmits the data concerning the autonomous vehicle  30  to the operator terminal  40 . 
     Next, a method of determining a threshold stored in the threshold storage unit  22  will be described below. The threshold determining unit  15  determines a threshold based on the data of the vehicle stop period acquired from the autonomous vehicles  30 . The vehicle stop period is obtained by measuring a period of time from when the autonomous vehicle  30  makes a stop to when the autonomous vehicle  30  starts moving. When the autonomous vehicle  30  starts moving with operator&#39;s assistance, it is triggered by the operator&#39;s assistance, and the autonomous vehicle does not autonomously start moving. In this case, the period of time is excluded from the data of the vehicle stop period. On the other hand, when the operator decides that it is not necessary to provide assistance in spite of the assistance request being sent to the operator (for example, when the autonomous vehicle is at the tail of a traffic jam and just has to wait), the autonomous vehicle autonomously resumes traveling afterwards. In this case, the period of time until the autonomous vehicle resumes traveling can be included in the data of the vehicle stop period. The data of the vehicle stop period thus measured are stored in the vehicle stop period storage unit  21 . 
     The threshold determining unit  15  determines a threshold based on the data of the vehicle stop period stored in the vehicle stop period storage unit  21 . In the present embodiment, the threshold is determined based on a distribution of the data of the vehicle stop period. 
       FIG. 2  is a diagram showing a probability distribution of vehicle stop periods. The horizontal axis represents the vehicle stop period, and the vertical axis represents a probability density of an event corresponding to the vehicle stop period. In the present embodiment, the period of time longer than the mean value of the vehicle stop period by 2.5 σ is set to the threshold. The threshold for determining whether to request the operator to provide assistance is a situation where the autonomous vehicle  30  has been stopped for a period of time longer than the vehicle stop period normally expected, which indicates that an abnormality may have occurred in the autonomous vehicle  30 . 
     Therefore, the threshold is set to a period of time longer than the mean value of the vehicle stop period. Although the threshold in this embodiment is set to +2.5 σ from the mean value, the value added to the mean value may not necessarily be 2.5 σ. The threshold determining unit  15  stores the determined threshold in the threshold storage unit  22 . 
     [Autonomous Vehicle] 
     The autonomous vehicle  30  includes a traveling control unit  31 , a passenger compartment monitoring unit  32 , the surroundings monitoring unit  33  and a communication unit  34 . The traveling control unit  31  has a function of controlling traveling of the autonomous vehicle  30 . The traveling control unit  31  controls throttle, braking, steering, and the like. The passenger compartment monitoring unit  32  has a function of monitoring the state of a driver and occupants. The passenger compartment monitoring unit  32  may be, for example, a camera capturing images inside a passenger compartment, or a seating sensor. The surroundings monitoring unit  33  has a function of monitoring the surroundings of the vehicle. The surroundings monitoring unit  33  may include, for example, a camera, a LIDAR device, a millimeter-wave radar device, an ultrasonic sensor, and the like. The communication unit  34  has a function of communicating with the monitoring center  10 . The communication unit  34  includes a communication device, an antenna, and the like. In addition, the communication unit  34  may further have a function of communicating with infrastructure or other vehicles. 
     The autonomous vehicle  30  transmits control data from the traveling control unit  31  and sensing data acquired by the passenger compartment monitoring unit  32  and the surroundings monitoring unit  33  to the monitoring center  10  via the communication unit  34 . The vehicle state data may be transmitted to the monitoring center  10  on a periodic basis, or when the autonomous vehicle  30  stops upon detection of a danger. 
     [Operation of Monitoring Center] 
       FIG. 3  is a flowchart showing operation of the monitoring center  10 . The monitoring center  10  receives vehicle state data from the autonomous vehicle  30  (S 10 ). The analysis unit  12  of the monitoring center  10  determines whether the autonomous vehicle  30  is stopped based on the vehicle state data (S 11 ). If it is determined that the autonomous vehicle  30  is stopped (YES in S 11 ), the analysis unit  12  calculates a vehicle stop duration of the autonomous vehicle  30  (S 12 ). Specifically, the analysis unit  12  stores the time when the state of the autonomous vehicle  30  has changed from “traveling” to “stopped” as a vehicle stop time, and calculates a difference between the current time and the vehicle stop time. 
     Then, the determination unit  13  of the monitoring center  10  determines whether the vehicle stop duration is greater than or equal to the threshold (S 13 ). If it is determined that the vehicle stop duration is greater than or equal to the threshold (YES in S 13 ), the operator cooperation unit  14  transmits a notification requesting the operator terminal  40  to provide assistance to the autonomous vehicle  30 , and calls an operator (S 14 ). The operator checks images or the like transmitted from the autonomous vehicle  30 , and provides instructions to the autonomous vehicle. If it is determined that the vehicle stop duration is not greater than or equal to the threshold (NO in S 13 ), the process returns to the step (S 10 ) in which the monitoring center  10  receives the vehicle state data. 
     If the analysis unit  12  determines that the autonomous vehicle  30  is not stopped as a result of the determination of whether the vehicle is stopped based on the vehicle state data (NO in S 11 ), the analysis unit  12  determines whether the vehicle has resumed traveling (S 15 ). Specifically, when the previous state of the autonomous vehicle  30  was “stopped”, which in turn changed to “traveling”, it is determined that the vehicle has resumed traveling. When the previous state was “traveling,” it is determined that the vehicle has continued traveling (that is, the vehicle is traveling) (NO in S 15 ). 
     If it is determined that the vehicle has resumed traveling (YES in S 15 ), it is then determined whether the autonomous vehicle  30  has resumed traveling with operator&#39;s assistance (S 16 ). If it is determined that the vehicle has resumed traveling without operator&#39;s assistance (NO in S 16 ), a period of time from when the vehicle made a stop to when the vehicle resumed traveling, that is, a vehicle stop period, is stored in the vehicle stop period storage unit  21  (S 17 ). The threshold determining unit  15  determines a threshold in a timely manner based on the data of the vehicle stop period stored in the vehicle stop period storage unit  21  (S 18 ). For example, the threshold determining unit  15  may determine a threshold by using a predetermined number of recent samples (e.g., 1,000 samples). Thus, an appropriate threshold can be determined based on the recent situations. In the flowchart of  FIG. 3 , determination of the threshold by the threshold determining unit  15  is indicated by a dotted line because it is not performed every time the vehicle stop period is stored. 
     Although  FIG. 3  illustrates the operation as being triggered by communication with one autonomous vehicle  30 , the monitoring center  10  monitors a plurality of autonomous vehicles  30  and performs the procedure shown in  FIG. 3  simultaneously for each of the plurality of autonomous vehicles  30 . 
     The configuration of the monitoring center  10  according to the present embodiment has been described. An example of hardware of the monitoring center  10  is a computer including a CPU, a RAM, a ROM, a hard disk, a communication interface, and the like. The RAM or ROM stores programs having modules implementing the functions described above so that the monitoring center  10  is implemented by the CPU executing the programs. Such programs are also included in the scope of the present disclosure. 
     The monitoring system  1  of the first embodiment performs operator cooperation when the vehicle stop duration has become greater than or equal to the threshold, and does not send a notification to the operator unless the vehicle stop duration becomes greater than or equal to the threshold. Accordingly, the operator is called only in a situation where the autonomous vehicle is highly likely to require remote assistance from the operator, which reduces the number of notifications to the operator. For example, according to the invention disclosed in JP 2019-87015 A, when an autonomous vehicle makes a stop upon detection of an obstacle, it transmits a vehicle stop signal to a remote monitoring center even in a situation where the vehicle can resume traveling after waiting for a while, and requests an observer (operator) in the remote monitoring center to check the surrounding situation of the vehicle. Thus, a monitoring task is given to the operator every time the vehicle makes a stop. On the other hand, according to the monitoring system  1 , a notification is not sent to the operator every time the autonomous vehicle makes an automatic stop. The notification is sent only when the vehicle stop duration becomes greater than or equal to the threshold. Accordingly, the operator is called only in a situation where the autonomous vehicle is highly likely to require remote assistance from the operator. Therefore, the load on the operator can be reduced. Further, since the threshold is determined based on past vehicle stop periods, the operator is notified about the autonomous vehicle  30  that requires assistance at an appropriate timing while the number of notifications to the operator is reduced. 
     Although it has been described in the present embodiment that the operator is not notified immediately when the autonomous vehicle makes a stop, and is notified when the vehicle stop duration has become greater than or equal to the threshold, an exception in this procedure can be set. The threshold is determined based on the past vehicle stop information. Therefore, when the vehicle makes a stop at a place that is not usually expected (for example, in the middle of a railroad crossing), a notification to the operator can be immediately sent without waiting until the vehicle stop duration becomes greater than or equal to the threshold. 
     Second Embodiment 
     Next, a monitoring system according to a second embodiment will be described. The basic configuration of the monitoring system according to the second embodiment is the same as the monitoring system  1  of the first embodiment (see  FIG. 1 ). The second embodiment is different from the first embodiment in that a threshold for determining the vehicle stop duration corresponds to a driving scene. 
     The monitoring center  10  includes a threshold storage unit  23  ( FIG. 4 ) that stores thresholds corresponding to driving scenes, instead of the threshold storage unit  22 . 
       FIG. 4  is a diagram showing the data stored in the threshold storage unit  23 . The threshold storage unit  23  stores thresholds associated with driving scenes. As shown in  FIG. 4 , the driving scene may include, for example, “going straight,” “waiting for a left turn,” “waiting for a right turn,” and the like. The threshold is determined from a distribution of the data of the vehicle stop period acquired for each driving scene. 
       FIG. 5  is a flowchart showing operation of the monitoring center  10  according to the second embodiment. The basic operation of the monitoring center  10  according to the second embodiment is the same as that of the monitoring center  10  of the first embodiment. The monitoring center  10  of the second embodiment is different from that of the first embodiment in that it performs processing according to a driving scene. Accordingly, the following description focuses on the differences from the first embodiment. 
     The monitoring center determines whether the autonomous vehicle  30  is stopped based on the vehicle state data transmitted from the vehicle (S 11 ). If it is determined that the vehicle is stopped (YES in S 11 ), the monitoring center  10  calculates a vehicle stop duration of the autonomous vehicle  30  (S 12 ). Then, the monitoring center  10  specifies the driving scene in which the autonomous vehicle  30  is located, based on the vehicle state data (S 12 - 2 ). For example, the analysis unit  12  can specify the scene in which the vehicle is located from among the “going straight,” “waiting for a left turn,” and “waiting for a right turn,” based on the data of a lighting state of the blinker. The monitoring center  10  reads the threshold corresponding to the driving scene from the threshold storage unit  23 , and compares the threshold with the vehicle stop duration (S 13 ). If the vehicle stop duration is greater than or equal to the threshold, the monitoring center  10  transmits the data concerning the autonomous vehicle  30  to the operator terminal  40 , and calls an operator (S 14 ). 
     If it is determined that the autonomous vehicle  30  has resumed traveling (YES in S 15 ) and that the vehicle has resumed traveling without operator&#39;s assistance (NO in S 16 ), the monitoring center  10  specifies the driving scene in which the autonomous vehicle  30  was stopped (S 16 - 2 ). Then, the monitoring center  10  stores the vehicle stop period associated with the specified driving scene in the vehicle stop period storage unit  21  (S 17 ). Thus, the threshold determining unit  15  can determine the threshold for each driving scene. 
     The monitoring system of the second embodiment performs operator cooperation when the vehicle stop duration has become greater than or equal to the threshold, and does not send a notification to the operator unless the vehicle stop duration becomes greater than or equal to the threshold. Therefore, the number of notifications to the operator can be reduced. Further, since the threshold corresponds to the driving scene, a notification can be performed at a timing appropriate for the characteristics of each driving scene. For example, in the scene waiting for a right turn, the vehicle stop duration tends to be long due to the time required to wait for a timing when the vehicle can make a right turn. 
     Third Embodiment 
     Next, a monitoring system according to a third embodiment will be described. The basic configuration of the monitoring system according to the third embodiment is the same as the monitoring system  1  of the first embodiment (see  FIG. 1 ). The third embodiment is different from the first embodiment in that a threshold for determining the vehicle stop duration corresponds to an area in which the autonomous vehicle  30  is present. The monitoring center  10  includes a threshold storage unit  24  ( FIG. 6 ) that stores thresholds corresponding to areas, instead of the threshold storage unit  22 . 
       FIG. 6  is a diagram showing data stored in the threshold storage unit  24 . The threshold storage unit  24  stores thresholds associated with areas. As shown in  FIG. 6 , the area may include, for example, “area A,” “area B,” “area C,” and the like. The threshold is determined from the distribution of the data of the vehicle stop period acquired for each area. 
     For example, the areas can be defined by dividing a lane or a road having a set of lanes at specific distances, or dividing a map into a mesh at specific intervals. 
       FIG. 7  is a flowchart showing operation of the monitoring center  10  according to the third embodiment. The basic operation of the monitoring center  10  according to the third embodiment is the same as that of the monitoring center  10  of the first embodiment. The monitoring center  10  of the third embodiment is different from that of the first embodiment in that it performs processing according to the driving scene. Accordingly, the following description focuses on the differences from the first embodiment. 
     The monitoring center  10  determines whether the autonomous vehicle  30  is stopped, based on the vehicle state data transmitted from the vehicle (S 11 ). If it is determined that the vehicle is stopped (YES in S 11 ), the monitoring center  10  calculates a vehicle stop duration of the autonomous vehicle (S 12 ). Then, the monitoring center  10  specifies an area in which the autonomous vehicle  30  is present based on the vehicle state data (S 12 - 3 ). For example, the analysis unit  12  can specify the area by collating the data of the current position of the vehicle with the map data. The monitoring center  10  reads the threshold corresponding to the area from the threshold storage unit  24 , and compares the threshold with the vehicle stop duration (S 13 ). If the vehicle stop duration is greater than or equal to the threshold (YES in S 13 ), the monitoring center  10  transmits the data concerning the autonomous vehicle  30  to the operator terminal  40 , and calls an operator (S 14 ). 
     If it is determined that the autonomous vehicle  30  has resumed traveling and that the vehicle has resumed traveling without operator&#39;s assistance, the monitoring center  10  specifies an area in which the autonomous vehicle  30  was stopped. Then, the monitoring center  10  stores the vehicle stop period associated with the specified area. Thus, the threshold determining unit  15  can determine the threshold for each area. 
     The monitoring system of the third embodiment performs operator cooperation when the vehicle stop duration has become greater than or equal to the threshold, and does not send a notification to the operator unless the vehicle stop duration becomes greater than or equal to the threshold. Therefore, the number of notifications to the operator can be reduced. Further, since the threshold is determined based on the past vehicle stop periods for each area, the operator is notified at a timing appropriate for the characteristics of each area, such as an area that is likely to be congested or not likely to be congested. The vehicle stop period cannot be observed in the area in which the vehicle is not normally expected to be continuously stopped. 
     Accordingly, the threshold corresponding to such an area can be initialized to a small value (e.g., zero) so that the operator is immediately notified when the vehicle is found to be continuously stopped in such an area, which indicates that an abnormality has occurred. 
     Fourth Embodiment 
     Next, a monitoring system according to a fourth embodiment will be described. The basic configuration of the monitoring system according to the fourth embodiment is the same as the monitoring system  1  of the first embodiment (see  FIG. 1 ). The fourth embodiment is different from the first embodiment in that a threshold for determining the vehicle stop duration corresponds to a road structure. The monitoring center  10  includes a threshold storage unit  25  ( FIG. 8 ) that stores thresholds corresponding to road structures, instead of the threshold storage unit  22 . 
       FIG. 8  is a diagram showing the data stored in the threshold storage unit  25 . The threshold storage unit  25  stores thresholds associated with road structures. As shown in  FIG. 8 , the road structure may include, for example, “vicinity of a crosswalk,” “vicinity of an intersection,” “vicinity of a T-junction,” and the like. The threshold is determined from the distribution of the data of the vehicle stop period acquired for each road structure. The vicinity of the road structure can be defined by a predetermined threshold. For example, a position within  50  m from a predetermined road structure can be defined as the vicinity of the road structure. 
       FIG. 9  is a flowchart showing operation of the monitoring center  10  according to the fourth embodiment. The basic operation of the monitoring center  10  according to the fourth embodiment is the same as that of the monitoring center  10  of the first embodiment. The monitoring center  10  of the fourth embodiment is different from that of the first embodiment in that it performs processing according to the road structure of the road on which the autonomous vehicle  30  is present. Accordingly, the following description focuses on the differences from the first embodiment. 
     The monitoring center  10  determines whether the autonomous vehicle  30  is stopped based on the vehicle state data transmitted from the vehicle (S 11 ). If it is determined that the vehicle is stopped (YES in S 11 ), the monitoring center  10  calculates a vehicle stop duration of the autonomous vehicle  30  (S 12 ). Then, the monitoring center  10  specifies the road structure of the road on which the autonomous vehicle  30  is present, based on the surrounding environment data transmitted from the vehicle (S 12 - 4 ). For example, the analysis unit  12  can analyze images of the outside of the vehicle to specify the location at which the autonomous vehicle  30  is located from among the “vicinity of a crosswalk,” “vicinity of an intersection,” and “vicinity of a T-junction.” Further, the analysis unit  12  may use the road structure data included in the map data to specify the road structure based on the current position of the vehicle and the map data. 
     The monitoring center  10  reads the threshold corresponding to the road structure from the threshold storage unit  25 , and compares the threshold with the vehicle stop duration (S 13 ). If the vehicle stop duration is greater than or equal to the threshold (YES in S 13 ), the monitoring center  10  transmits the data concerning the autonomous vehicle  30  to the operator terminal  40 , and calls an operator (S 14 ). 
     If it is determined that the autonomous vehicle  30  has resumed traveling (YES in S 15 ) and that the vehicle has resumed traveling without operator&#39;s assistance (NO in S 16 ), the monitoring center  10  specifies the road structure of the road on which the autonomous vehicle  30  was stopped (S 16 - 4 ). Then, the monitoring center  10  stores the vehicle stop period associated with the specified road structure in the vehicle stop period storage unit  21  (S 17 ). Thus, the threshold determining unit  15  can determine the threshold for each road structure. 
     The monitoring system of the fourth embodiment performs operator cooperation when the vehicle stop duration has become greater than or equal to the threshold, and does not send a notification to the operator unless the vehicle stop duration becomes greater than or equal to the threshold. Therefore, the number of notifications to the operator can be reduced. Further, since the threshold corresponds to the road structure, a notification can be performed at a timing appropriate for the characteristics of each road structure. For example, in the vicinity of a crosswalk, the vehicle stop duration tends to be long due to waiting for pedestrians to cross a road. 
     Fifth Embodiment 
     Next, a monitoring system according to a fifth embodiment will be described. The basic configuration of the monitoring system according to the fifth embodiment is the same as the monitoring system  1  of the first embodiment (see  FIG. 1 ). The fifth embodiment is different from the first embodiment in that a threshold for determining the vehicle stop duration corresponds to a time period. The monitoring center  10  includes a threshold storage unit  26  ( FIG. 10 ) that stores thresholds corresponding to time periods, instead of the threshold storage unit  22 . 
       FIG. 10  is a diagram showing the data stored in the threshold storage unit  26 . The threshold storage unit  26  stores thresholds associated with time periods. As shown in  FIG. 10 , the time period may include, for example, “0:00-6:00,” “6:00-12:00,” “12:00-18:00” and “18:00-0:006.” The threshold is determined from the distribution of the data of the vehicle stop period acquired for each time period. The time periods shown in  FIG. 10  are merely examples, and may also be every three hours, or may include a night time, morning and evening rush hours, and the like. 
       FIG. 11  is a flowchart showing operation of the monitoring center  10  according to the fifth embodiment. The basic operation of the monitoring center  10  according to the fifth embodiment is the same as that of the monitoring center  10  of the first embodiment. The monitoring center  10  of the fifth embodiment is different from that of the first embodiment in that it performs processing according to the time period. Accordingly, the following description focuses on the differences from the first embodiment. 
     The monitoring center  10  determines whether the autonomous vehicle  30  is stopped, based on the vehicle state data transmitted from the vehicle (S 11 ). If it is determined that the vehicle is stopped (YES in S 11 ), the monitoring center  10  calculates a vehicle stop duration of the autonomous vehicle  30  (S 12 ). Then, the monitoring center  10  specifies the time period including the current time (S 12 - 5 ). The monitoring center  10  reads the threshold corresponding to the time period from the threshold storage unit  26 , and compares the threshold with the vehicle stop duration (S 13 ). If the vehicle stop duration is greater than or equal to the threshold (YES in S 13 ), the monitoring center  10  transmits the data concerning the autonomous vehicle  30  to the operator terminal  40 , and calls an operator (S 14 ). 
     If it is determined that the autonomous vehicle  30  has resumed traveling (YES in S 15 ) and that the vehicle has resumed traveling without operator&#39;s assistance (NO in S 16 ), the monitoring center  10  specifies a time period in which the autonomous vehicle  30  was stopped (S 16 - 5 ). Then, the monitoring center  10  stores the vehicle stop period associated with the specified time period in the vehicle stop period storage unit  21  (S 17 ). Thus, the threshold determining unit  15  can determine the threshold for each time period. 
     The monitoring system of the fifth embodiment performs operator cooperation when the vehicle stop duration has become greater than or equal to the threshold, and does not send a notification to the operator unless the vehicle stop duration becomes greater than or equal to the threshold. Therefore, the number of notifications to the operator can be reduced. Further, since the threshold corresponds to the time period, a notification can be performed at a timing appropriate for each of the crowded time period and the non-crowded time period. 
     Sixth Embodiment 
     In the examples described in the above second to fifth embodiments, the threshold associated with the driving scene, area, road structure or time period is used to perform the operator cooperation when the vehicle stop duration becomes appropriate for the driving scene, area, road structure or time period. 
     It is also possible to use a combination of two, three or all of the driving scene, area, road structure and time period. In a sixth embodiment, an example will be described in which a combination of an area and a road structure is used. 
     The basic configuration of the monitoring system according to the sixth embodiment is the same as the monitoring system  1  of the first embodiment (see  FIG. 1 ). The sixth embodiment is different from the first embodiment in that a threshold for determining the vehicle stop duration corresponds to an area and a road structure. The monitoring center  10  includes a threshold storage unit  27  ( FIG. 12 ) that stores thresholds corresponding to areas and road structures, instead of the threshold storage unit  22 . 
       FIG. 12  is a diagram showing the data stored in the threshold storage unit  27 . The threshold storage unit  27  stores thresholds associated with areas and road structures. As shown in  FIG. 12 , the areas may include “area A,” “area B,” “area C,” and the like, and the road structures may include “vicinity of a crosswalk,” “vicinity of an intersection,” “vicinity of a T-junction,” and the like. The threshold corresponding to both the “area A” and “vicinity of a crosswalk,” the threshold corresponding to both the “area A” and “vicinity of an intersection,” . . . are stored. The threshold is determined from the distribution of the data of the vehicle stop period acquired for each situation 
       FIG. 13  is a flowchart showing operation of the monitoring center  10  according to the sixth embodiment. The basic operation of the monitoring center  10  according to the sixth embodiment is the same as that of the monitoring center  10  of the first embodiment. The monitoring center  10  of the sixth embodiment is different from that of the first embodiment in that it performs the processing according to a plurality of situations. Accordingly, the following description focuses on the differences from the first embodiment. 
     The monitoring center  10  determines whether the autonomous vehicle  30  is stopped, based on the vehicle state data transmitted from the vehicle (S 11 ). If it is determined that the vehicle is stopped (YES in S 11 ), the monitoring center  10  calculates a vehicle stop duration of the autonomous vehicle  30  (S 12 ). Then, the monitoring center  10  specifies the situation in which the autonomous vehicle  30  is located, based on the vehicle state data (S 12 - 6 ). In this case, the area and the road structure in which the autonomous vehicle  30  is located is specified. The method of specifying the area and the road structure has been described in the third and fourth embodiments. 
     The monitoring center  10  reads the threshold corresponding to the situation from the threshold storage unit  27 , and compares the threshold with the vehicle stop duration (S 13 ). If the vehicle stop duration is greater than or equal to the threshold (YES in S 13 ), the monitoring center  10  transmits the data regarding the autonomous vehicle  30  to the operator terminal  40 , and calls an operator (S 14 ). 
     If it is determined that the autonomous vehicle  30  has resumed traveling (YES in S 15 ) and that the vehicle has resumed traveling without operator&#39;s assistance (NO in S 16 ), the monitoring center  10  specifies the situation in which the autonomous vehicle  30  was stopped 
     (S 16 - 6 ). Then, the monitoring center  10  stores the vehicle stop period associating with the specified situation in the vehicle stop period storage unit  21  (S 17 ). Thus, the threshold determining unit  15  can determine the threshold for each situation. 
     The monitoring system of the sixth embodiment performs operator cooperation when the vehicle stop duration has become greater than or equal to the threshold, and does not send a notification to the operator unless the vehicle stop duration becomes greater than or equal to the threshold. Therefore, the number of notifications to the operator can be reduced. Further, since the threshold corresponds to the specific situation in which the autonomous vehicle  30  is present, a notification can be performed at a timing appropriate for each of the specific situations. 
     Seventh Embodiment 
       FIG. 14  is a diagram showing a configuration of a monitoring system  7  of a seventh embodiment. In the monitoring system according to the first to sixth embodiments, the monitoring center  10  calculates a vehicle stop duration of the autonomous vehicle  30  based on the vehicle state data transmitted from the autonomous vehicle  30 . 
     However, in the seventh embodiment, the autonomous vehicle  30  calculates a vehicle stop duration and transmits the data of the calculated vehicle stop duration to the monitoring center  10 . 
     The autonomous vehicle  30  includes an analysis unit  35  in addition to the configuration of the autonomous vehicle  30  described in the first embodiment. The analysis unit  35  obtains a vehicle stop duration, which is a period of time for which the autonomous vehicle  30  has been stopped up to the current time, based on the vehicle speed data. Further, the analysis unit  35  obtains a vehicle stop period, which is a period of time from when the autonomous vehicle  30  makes a stop to when the autonomous vehicle  30  resumes traveling. Then, the autonomous vehicle  30  transmits the data of the obtained vehicle stop duration or the data of the obtained vehicle stop period to the monitoring center  10 . 
     The above analysis unit  35  may also be implemented by a program. Such a program causes a computer to execute functions of measuring a period of time for which the vehicle has been stopped upon reception of the detection data indicating that the vehicle has made a stop, and transmitting the result of measurement to the monitoring center  10  as a vehicle stop duration. 
     As described above, since the autonomous vehicle  30  obtains the vehicle stop duration or the vehicle stop period, it is not necessary for the monitoring center  10  to calculate a vehicle stop duration or a vehicle stop period of a large number of autonomous vehicles  30 . 
     Accordingly, the calculation load can be reduced. 
     Eighth Embodiment 
       FIG. 15  is a diagram showing a configuration of a monitoring system  8  of an eighth embodiment. In the monitoring system according to the first to sixth embodiments, the monitoring center  10  determines whether the vehicle stop duration becomes greater than or equal to the threshold. However, in the monitoring system  8  according to the eighth embodiment, the autonomous vehicle  30  performs this determination. 
     After the threshold determining unit  15  determines the threshold, the monitoring center  10  distributes the data of the threshold to each autonomous vehicle  30 . The autonomous vehicle  30  stores the data of the threshold distributed from the monitoring center  10  in the threshold storage unit  37 . The autonomous vehicle  30  includes the analysis unit  35  that obtains a vehicle stop duration based on the vehicle speed data, and a determination unit  36  that determines whether the vehicle stop duration is greater than or equal to the threshold. When the determination unit  36  determines that the vehicle stop duration is greater than or equal to the threshold, it transmits a signal to the monitoring center  10  to request assistance from the operator. 
     The above analysis unit  35  and determination unit  36  may also be implemented by a program. Such a program causes a computer to execute functions of measuring a vehicle stop duration for which the vehicle has been stopped upon reception of the detection data indicating that the vehicle has made a stop, determining whether the vehicle stop duration is greater than or equal to the threshold read from the threshold storage unit  22 , and transmitting a request for assistance to the monitoring center  10  when the vehicle stop duration is determined to be greater than or equal to the threshold. 
     As described above, the autonomous vehicle  30  determines whether the vehicle stop duration has become greater than or equal to the threshold, and transmits a request for assistance to the monitoring center  10  when the vehicle stop duration has become greater than or equal to the threshold. Accordingly, the number of communications from the autonomous vehicle  30  to the monitoring center  10  can be reduced, and the calculation load on the monitoring center  10  can be reduced 
     Ninth Embodiment 
       FIG. 16  is a diagram showing a configuration of a monitoring system  9  of a ninth embodiment. The monitoring center  10  of the ninth embodiment includes the threshold storage units  23  to  26  described in the second to fifth embodiments. The analysis unit  12  of the monitoring center  10  obtains the driving scene, area, road structure and time period in which the autonomous vehicle  30  is present, based on the vehicle state data and the surrounding environment data transmitted from the autonomous vehicle  30 , and reads the threshold corresponding to each item from the threshold storage units  23  to  26 . Then, the determination unit  13  compares the vehicle stop duration of the autonomous vehicle  30  with each threshold corresponding to each item. The determination unit  13  counts the number of items for which the vehicle stop duration has become greater than or equal to the threshold. The determination unit  13  determines to perform operator cooperation when the vehicle stop duration has become greater than or equal to the threshold for two or more items (for example, the threshold corresponding to the driving scene, the threshold corresponding to the area, or the like). Although two or more items are used as examples in the above description, operator cooperation may also be performed when the vehicle stop duration becomes greater than or equal to the threshold for three or more items, or all the items. 
     Alternatively, the priority of notifications to the operator may be determined depending on the number of items for which the vehicle stop duration becomes greater than or equal to the threshold. That is, the priority may be set to “high” when the vehicle stop duration has become greater than or equal to the threshold for all the four items, “medium” when the vehicle stop duration has become greater than or equal to the threshold for three items, and “low” when the vehicle stop duration has become greater than or equal to the threshold for two items. Accordingly, assignment to the operator is made from the higher priority, and a notification is sent to the operator terminal of the assigned operator. 
     The monitoring system according to the present disclosure is useful as a system for monitoring autonomous vehicles. A monitoring center according to the present disclosure is a monitoring center configured to communicate with an autonomous vehicle ( 30 ) via a network and monitor the autonomous vehicle. The monitoring center includes: a threshold storage unit ( 22 ) that stores a threshold of a vehicle stop duration for determining whether it is necessary to provide operator&#39;s assistance; a communication unit ( 11 ) that receives vehicle state data from the autonomous vehicle; an analysis unit ( 12 ) that obtains a vehicle stop duration from the vehicle state data, the vehicle stop duration being a period of time for which the autonomous vehicle has been stopped up to a current time; a determination unit ( 13 ) that determines whether the vehicle stop duration of the autonomous vehicle is greater than or equal to the threshold stored in the threshold storage unit; an operator cooperation unit ( 14 ) that notifies an operator of data concerning the autonomous vehicle when the vehicle stop duration of the autonomous vehicle is greater than or equal to the threshold; a vehicle stop period storage unit ( 21 ) that obtains a vehicle stop period from the vehicle state data and stores the vehicle stop period, the vehicle stop period being a period of time from when the autonomous vehicle makes a stop to when the autonomous vehicle resumes traveling without operator&#39;s assistance; and a threshold determining unit that determines the threshold based on a distribution of the vehicle stop period. The threshold determining unit stores the determined threshold in the threshold storage unit. 
     According to the present disclosure, a notification to an operator is sent when a predetermined vehicle stop duration has elapsed. Accordingly, the frequency of calling an operator decreases, thereby reducing a load on the operator.