Road surface freezing estimation system

Abstract

To provide a technique for estimating road surface freezing based on a distribution state of a snow melting agent.SOLUTION: A road surface freezing estimation system comprises: a snow melting agent information acquisition unit that acquires a snow melting agent distribution point at which a snow melting agent is distributed; a weather information acquisition unit that acquires an outside air temperature at the snow melting agent distribution point in a target period; a freezing estimation unit that regards the snow melting agent distribution point as an estimated freezing point at which a road surface may be frozen in the target period when the outside air temperature in the target period at the snow melting agent distribution point is lower than a determination criterion; and a guide unit that guides the estimated freezing point.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a road surface freezing estimation system.

Background Art

[0002] Patent Document 1 describes a method for predicting the freezing of a road surface based on the outside air temperature and a freezing promotion factor. Examples of the freezing promotion factor include terrain where humidity is likely to increase, terrain where wind is likely to occur, terrain where shaded areas are likely to occur, and the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Even at a location predicted to be frozen based on the outside air temperature and the freezing promotion factor, the road surface may not actually be frozen due to other factors. Conversely, freezing may also occur at a location where there is no freezing promotion factor. The present invention has been made in view of the above problems, and an object thereof is to provide a technique for estimating the freezing of a road surface based on the distribution status of a snow-melting agent.

Means for Solving the Problems

[0005] To achieve the above object, a road surface freezing estimation system includes a snow-melting agent information acquisition unit that acquires a snow-melting agent distribution point where a snow-melting agent has been distributed, a weather information acquisition unit that acquires the outside air temperature at the snow-melting agent distribution point during a target period, and a freezing estimation unit that regards the snow-melting agent distribution point as a presumed freezing point where there is a possibility that the road surface has been frozen during the target period when the outside air temperature at the snow-melting agent distribution point during the target period is lower than a determination criterion, and a guidance unit that guides the presumed freezing point.

[0006] This road surface freezing estimation system considers locations where de-icing agents are distributed as locations where the likelihood of needing de-icing agents is statistically higher than locations where de-icing agents are not distributed, i.e., locations where road surface freezing is likely to occur. This road surface freezing estimation system considers locations where de-icing agents are distributed as locations where road surface freezing is likely to occur if the ambient temperature at the distribution location during the target period is lower than the judgment criteria. Therefore, road surface freezing can be estimated based on the distribution status of de-icing agents. [Brief explanation of the drawing]

[0007] [Figure 1] A block diagram showing the configuration of the road surface freezing estimation system. [Figure 2] Figure 2A is a flowchart for determining the tendency of de-icing agent use, and Figure 2B is a flowchart for determining potential freezing locations. [Figure 3] Flowchart for freeze estimation process. [Figure 4] Flowchart for level adjustment process. [Modes for carrying out the invention]

[0008] Here, embodiments of the present invention will be described in the following order. (1) Configuration of the road surface freezing estimation system: (2) Road surface freezing estimation process: (3) Other embodiments:

[0009] (1) Configuration of the road surface freezing estimation system: Figure 1 is a block diagram showing the configuration of the road surface freezing estimation system 10 according to the present invention. The road surface freezing estimation system 10 includes a control unit 20 equipped with a CPU, RAM, ROM, etc., a recording medium 30, and a communication unit 41, and the control unit 20 can execute programs stored in the recording medium 30 and ROM. In this embodiment, the road surface freezing estimation program 21 can be executed as this program. The communication unit 41 is equipped with a circuit for communicating with other devices, and the control unit 20 can communicate with the road administrator terminal 300, the weather information server 400, the map information server 500, the patrol vehicle 100, and the vehicle 200 by executing the road surface freezing estimation program 21.

[0010] The road administrator terminal 300 is a terminal used by road administrators and consists of PCs, tablets, smartphones, etc. During the winter, administrators distribute de-icing agents to several locations on roads within their managed area. Locations where de-icing agents are distributed are called de-icing agent distribution points. De-icing agents are distributed to several locations that are known to be prone to freezing, such as locations requested by road users, locations that have frequently frozen in the past, and bridge and tunnel entrances and exits. The de-icing agents are placed along the side of the road. When distributing de-icing agents, road administrators input information such as the location of the distribution point, the date of distribution, and the amount distributed (for example, M bags of N kg each (N is a positive number, M is a natural number)) using the road administrator terminal 300. In addition, road administrators visit each de-icing agent distribution point at their discretion to check the remaining amount of de-icing agent and add more if the amount has decreased. The road administrator inputs information such as the total amount of de-icing agent at the distribution point after distribution (for example, the amount of two bags if two bags are distributed when none remain, or the amount of two bags if one bag remains and another bag is distributed) using the road administrator terminal 300. In this embodiment, for example, if two bags have been distributed but inspection reveals that none have been used and no additional bags were added, the amount distributed is entered as 0, the total amount after distribution is entered as the amount of two bags, and the distribution date is updated. In this embodiment, the road administrator also specifies the link (shooting link) on which the patrol vehicle 100 travels when photographing the de-icing agent distribution point, so that the bags of de-icing agent placed at the distribution point are included in the shooting range of the camera 130 of the patrol vehicle 100, which will be described later. If the link is a road that can be traveled in both directions, the direction of travel for shooting may also be specified. The road administrator terminal 300 transmits this input information to the road surface freezing estimation system 10. The road surface freezing estimation system 10 records information regarding the distribution of de-icing agents transmitted from the road administrator terminal 300 as de-icing agent information 30a on the recording medium 30.

[0011] The weather information server 400 is a server that provides weather information. The weather information provided by the weather information server 400 includes predicted and actual values ​​for rainfall, snowfall, outside temperature, humidity, wind direction, and wind speed for each time period and region. The weather information also includes measured values ​​for snow depth for each time period and region. When the weather information server 400 receives a request for weather information for a specific region from the road surface freezing estimation system 10, which acts as a client, it transmits the weather information for the requested region to the road surface freezing estimation system 10.

[0012] The map information server 500 is a server that provides map information. The map information includes node data that shows the location of nodes set on roads on which vehicles travel, shape interpolation point data that shows the location of shape interpolation points for identifying the shape of roads between nodes, link data that shows the connections between nodes, and facility data that shows the location of facilities on and around roads. The link data includes the location and name of bridges, tunnels, etc., that exist within the link. When the road surface freezing estimation system 10, acting as a client, requests map information for a specified area, the map information server 500 transmits the map information to the road surface freezing estimation system 10.

[0013] The patrol vehicle 100 is a vehicle that travels on roads in the area under management, takes images of the roads, and transmits them to the road surface freezing estimation system 10. The patrol vehicle 100 may be a vehicle specifically for such patrols, or it may be a vehicle such as a garbage truck or a route bus that travels regularly on a fixed route and is configured to function as the patrol vehicle 100.

[0014] The patrol vehicle 100 includes a communication unit 110, a positioning unit 120, a camera 130, and a control unit 150. The control unit 150 includes a CPU, ROM, RAM, and a recording medium, and controls the communication unit 110, the positioning unit 120, and the camera 130 by executing programs recorded on the recording medium and ROM. The communication unit 110 includes a wireless communication circuit for wireless communication with other devices. The control unit 150 can communicate with the road surface freezing estimation system 10 via the communication unit 110.

[0015] The positioning unit 120 includes positioning sensors such as a GNSS receiver, a vehicle speed sensor, and a gyro sensor. The GNSS receiver is a device that receives signals from the Global Navigation Satellite System. The GNSS receiver receives radio waves from navigation satellites and outputs a signal to calculate the current position of the patrol vehicle 100 via an interface (not shown). The vehicle speed sensor outputs a signal corresponding to the rotational speed of the wheels of the patrol vehicle 100. The gyro sensor detects the angular acceleration of the patrol vehicle 100 when turning in the horizontal plane and outputs a signal corresponding to the orientation of the vehicle. The control unit 150 acquires the current position of the patrol vehicle 100 based on the autonomous navigation trajectory, which is the trajectory of the position estimated based on the signals output from the vehicle speed sensor and the gyro sensor, and map information recorded on the recording medium while the vehicle is traveling on the road.

[0016] Camera 130 is mounted on patrol vehicle 100 so as to include the area in front of the patrol vehicle 100 in its field of view. The optical axis of camera 130 is fixed relative to patrol vehicle 100. Specifically, for example, camera 130 is mounted on patrol vehicle 100 in such a manner that the optical axis center is perpendicular to the width direction of patrol vehicle 100, and the area in front of the patrol vehicle 100 in its field of view is included.

[0017] The control unit 150 of the patrol vehicle 100 acquires information regarding de-icing agent distribution locations (information registered by the road administrator) from the road surface freezing estimation system 10 and records it on a recording medium. The information regarding de-icing agent distribution locations includes the location of the de-icing agent distribution location and the link (shooting link [Amano 1]) that the patrol vehicle 100 should travel to when photographing the de-icing agent distribution location.

[0018] The control unit 150 calculates the coordinates of the intersection point between the shooting link and the perpendicular line from the snow-melting agent distribution point to the shooting link. When the current location of the patrol vehicle 100 is on the shooting link and the distance between the current location of the patrol vehicle 100 and the intersection point is equal to or less than a predetermined distance, the control unit 150 causes the camera 130 to take an image. The control unit 150 records the image taken by the camera on the recording medium in association with the position of the snow-melting agent distribution point and the shooting date and time. The control unit 150 transmits the image of the snow-melting agent distribution point, the position of the snow-melting agent distribution point, and the shooting date and time to the road surface freezing estimation system 10 via the communication unit 110. The image, the position of the snow-melting agent distribution point, and the shooting date and time transmitted in this way are stored as road image information 30b in the recording medium 30 of the road surface freezing estimation system 10.

[0019] The vehicle 200 is a vehicle that transmits probe information (travel history) as a probe vehicle or a vehicle to which guidance of an estimated freezing point is provided. The vehicle 200 includes a communication unit 210, a positioning unit 220, a UI unit 240, and a control unit 250. The control unit 250 includes a CPU, a ROM, a RAM, and a recording medium, and the CPU executes programs recorded in the recording medium and the ROM to control the communication unit 210, the positioning unit 220, and the UI unit 240. The communication unit 210 and the positioning unit 220 have the same configurations as the communication unit 110 and the positioning unit 120 described above. The UI unit 240 is an interface unit that receives instructions from the user and provides various types of information to the user, and includes a touch panel display, switches, speakers, microphones, etc. The UI unit 240 receives a control signal from the control unit 250 and displays an image for providing various types of guidance, such as a map including the current location of the vehicle 200 and a planned travel route, on the display.

[0020] When the vehicle 200 functions as a probe vehicle, the control unit 250 transmits the driving history of the vehicle 200 to the road surface freezing estimation system 10 as probe information. The driving history includes the time-series position information of the vehicle 200, which is the locus of the vehicle 200 at every certain distance or every certain time. Specifically, the vehicle 200 identifies the current location of the vehicle and the section (road link ID) in which the vehicle is traveling at every certain distance or every certain time based on the output signals of the GNSS receiver, vehicle speed sensor, and gyro sensor and known map matching. Also, the vehicle 200 acquires the passing time of the node at the start point and the passing time of the node at the end point of the section from a timing unit (not shown). Then, the vehicle 200 generates a driving history by associating the identified current position, road link, and current date and time with the vehicle identification information (vehicle ID). The vehicle 200 temporarily stores the driving history thus generated in the vehicle 200 recording medium and transmits the driving history to the road surface freezing estimation system 10 at a predetermined timing. The transmitted driving history is stored as probe information 30d in the recording medium 30 of the road surface freezing estimation system 10.

[0021] When the vehicle 200 functions as a vehicle to which the estimated freezing point is guided, the control unit 250 acquires from the road surface freezing estimation system 10 a value indicating the position of the estimated freezing point and the level of the possibility of freezing. In the present embodiment, the control unit 250 guides the position of the estimated freezing point and the level of the possibility of freezing to the user of the vehicle 200 by showing an icon indicating the level of the possibility of freezing at the position of the estimated freezing point on the map displayed on the UI unit 240.

[0022] Note that the vehicle 200 may be equipped with a camera, and an image of the road surface captured by the camera of the vehicle 200 and the shooting position, etc. may be transmitted to the road surface freezing estimation system 10 and used in the road surface freezing estimation system 10 to judge the trend of the amount of deicing agent used. Also, of course, the patrol vehicle 100 may function as a probe vehicle.

[0023] The recording medium 30 of the road surface freezing estimation system 10 records de-icing agent information 30a, road image information 30b, and probe information 30c. The de-icing agent information 30a includes the location of the de-icing agent distribution point, the date of distribution, the amount distributed, the total amount of de-icing agent on the distribution point after distribution, and information indicating the trend of de-icing agent usage at the distribution point (points with high usage, points with low usage). The distribution date, amount distributed, and total amount after distribution are accumulated as history each time de-icing agent distribution is carried out. The trend of de-icing agent usage is updated by the control unit 20 based on images taken by the patrol vehicle 100. The de-icing agent information 30a also includes a link to the images taken when photographing the de-icing agent distribution point.

[0024] Road image information 30b includes images of de-icing agent distribution points taken by patrol vehicle 100, along with the location of the de-icing agent distribution points and the date and time the images were taken. This information transmitted from patrol vehicle 100 is stored as road image information 30b.

[0025] The probe information 30c is information indicating the driving history transmitted from the vehicle 200. In this embodiment, the probe information 30c is used to calculate the vehicle speed of a vehicle traveling on a road section that includes a de-icing agent distribution point.

[0026] By executing the road surface freezing estimation program 21, the control unit 20 functions as a de-icing agent information acquisition unit 21a, a weather information acquisition unit 21b, a freezing estimation unit 21c, and a guidance unit 21d. Through the function of the de-icing agent information acquisition unit 21a, the control unit 20 acquires the locations where de-icing agents have been distributed. That is, the location of each de-icing agent distribution location is acquired.

[0027] The control unit 20 obtains the outside temperature at the de-icing agent distribution points for the target period through the function of the weather information acquisition unit 21b. That is, the control unit 20 obtains weather information for the target period in the target area managed by the road administrator from the weather information server 400. The de-icing agent distribution points are located within the target area. The target period is the period for which it is determined whether or not the road surface will freeze or whether or not it is frozen. In this embodiment, the target period is the time period from a predetermined time included in the nighttime period of the first day (which is any date) to a predetermined time included in the morning period of the second day (which is the day after the first day). In this embodiment, the weather information that the control unit 20 obtains and uses from the weather information server 400 is the outside temperature, rainfall, snowfall, and snow depth.

[0028] Based on the function of the freezing estimation unit 21c, the control unit 20 considers a de-icing agent distribution point to be a presumed freezing point where the road surface may be frozen during the target period if the ambient temperature at the de-icing agent distribution point during the target period is lower than the judgment criterion. In this embodiment, the control unit 20 picks up points that have predetermined characteristics as road surfaces prone to freezing. Points with characteristics prone to freezing include, for example, intersections, tunnel entrances and exits, bridges, etc. Based on the map information of the target area obtained from the map information server 500, the control unit 20 picks up points that fall under these categories from among the roads within the target area.

[0029] The control unit 20 selects locations with characteristics that make them prone to freezing as potential freezing locations if the outside temperature during the target period is lower than the judgment criterion and there was rainfall or snowfall during the target period. In this embodiment, the judgment criterion is that the outside temperature during a predetermined time period, designated as the night of the first day within the target period, is below a threshold. Furthermore, for rainfall or snowfall, the condition is that there was rainfall or snowfall during any of the predetermined time periods designated as the night of the first day within the target period. In addition, the control unit 20 excludes locations from the list of potential freezing locations if the amount of snow accumulation during a predetermined time period, designated as the morning of the second day within the target period, is above a threshold. This is because if the amount of snow accumulation is above a threshold, it deviates from the road surface freezing state assumed by the road surface freezing estimation system 10 of this embodiment. In other words, the road surface freezing state is assumed to be a state in which moisture on the road surface freezes over a predetermined area wider than the contact surface of the tire, making the tire slippery (for example, mirror ice or black ice). While driving requires caution when snow accumulation exceeds a certain threshold, in this embodiment, such locations are excluded from the list of potential freezing points.

[0030] The control unit 20 considers locations where the amount of snowfall on the morning of the second day is below a threshold as potential freezing locations. Furthermore, the control unit 20 determines the level of possibility of freezing among the estimated freezing locations as follows: The control unit 20 distinguishes between locations where de-icing agents are distributed and locations where de-icing agents are not distributed among the estimated freezing locations (locations that have characteristics that make them prone to freezing and have experienced rainfall or snowfall), and estimates that locations where de-icing agents are distributed are more likely to be frozen than locations where de-icing agents are not distributed. In this embodiment, the level is expressed in three stages, but of course, the level is not limited to three stages. The control unit 20 determines that locations where de-icing agents are not distributed among the estimated freezing locations have a "low" possibility of freezing. In this way, locations that have characteristics that make them prone to freezing but tend not to freeze in reality due to other factors and where de-icing agents are not used can be judged to have a lower possibility of freezing than locations where de-icing agents are distributed.

[0031] Furthermore, the control unit 20 acquires the trend in the amount of de-icing agent used at the de-icing agent distribution points and estimates that among the de-icing agent distribution points, those with a high amount of de-icing agent used are more likely to have frozen road surfaces during the target period than those with a low amount. In other words, in this embodiment, the control unit 20 determines the level of possibility of freezing for estimated frozen locations, which are de-icing agent distribution points, according to the trend in the amount of de-icing agent used. In order to determine the trend in the amount of de-icing agent used at the de-icing agent distribution points, the control unit 20 performs image recognition processing on each image stored as road image information 30b and estimates the amount of de-icing agent remaining on the side of the road from the images of the de-icing agent bags contained in the image. Specifically, for example, the number of object regions representing one bag of de-icing agent in the image is detected by pattern matching based on the characteristics of the de-icing agent bags. If the number of bags detected from the image is less than the number of bags on the de-icing agent distribution site after a new de-icing agent has been distributed, the control unit 20 identifies the difference as the amount of de-icing agent (i.e., the amount used) corresponding to the number of bags used at the de-icing agent distribution site from the most recent distribution work day to the day the image was taken. In addition, if the shape of the bag differs from that of an unused bag (for example, the overall thickness of the de-icing agent bag is thinner compared to an unused bag), the control unit 20 may determine that the bag is not unused (the amount of de-icing agent has decreased) and estimate the amount used from the shape of the bag.

[0032] The control unit 20 considers de-icing agent distribution points where the amount of de-icing agent used since the most recent distribution day is greater than a threshold as points with high de-icing agent usage, and de-icing agent distribution points where the amount is below the threshold as points with low de-icing agent usage. In this way, the control unit 20 pre-analyzes the trend of de-icing agent usage for each de-icing agent distribution point. In this embodiment, the control unit 20 determines that the possibility of freezing is "high" at de-icing agent distribution points where a large amount is used, and "medium" at de-icing agent distribution points where a small amount is used. In this way, it is possible to determine that there is a high possibility of freezing at de-icing agent distribution points where a large amount of de-icing agent is used. Therefore, it is possible to warn drivers of vehicles passing through such points in the early morning when the road surface is frozen, before the de-icing agent is used.

[0033] The control unit 20, as described above, first determines the possibility of freezing at each estimated freezing point based on whether or not it is a de-icing agent distribution point and the trend of de-icing agent use, and then adjusts the level of possibility of freezing according to the vehicle speed of vehicles traveling through the estimated freezing point during the target period. In this embodiment, the control unit 20 estimates that the road surface at the estimated freezing point is more likely to be frozen than when the vehicle speed of a probe vehicle traveling through the estimated freezing point at a predetermined time on the morning of the second day of the target period is below the threshold speed. The vehicle speed used is a statistical value of the vehicle speed of each probe vehicle when multiple probe vehicles travel through the estimated freezing point. In this embodiment, the control unit 20 raises the level of possibility of freezing by one level when the vehicle speed is below the threshold speed, and lowers it by one level when it is above the threshold speed. This is just an example; the level may be raised by one level when the probe vehicle's speed is below the threshold speed, but not changed even if it is above the threshold speed. Alternatively, the level may not be changed when the probe vehicle's speed is below the threshold speed, but raised by one level when it is above the threshold speed. Furthermore, the greater the difference between the probe vehicle's speed and the threshold speed, the more steps the speed may be increased or decreased. The threshold speed is a value set to distinguish, for example, the expected vehicle speed when the road surface is frozen from the average driving speed at that location when the road surface is not frozen.

[0034] After extracting estimated frozen locations as described above and determining the level of possibility of freezing for each estimated frozen location, the control unit 20 guides the user to the estimated frozen locations using the functions of the guidance unit 21d. In this embodiment, when the control unit 200 receives a request from the vehicle 200 for the presence or absence of estimated frozen locations in a specified area (for example, an area corresponding to the display range of a map displayed on the display) or along the planned route, the control unit 20 returns the location of the relevant estimated frozen location and the level of possibility of freezing to the vehicle 200, and the vehicle 200 guides the user to this information via the UI unit 240.

[0035] As described above, according to this embodiment, the possibility of road surface freezing can be estimated by classifying it into levels based on the distribution and usage status of de-icing agents.

[0036] (2) Road surface freezing estimation process: Next, the process for estimating road surface freezing will be described. In this embodiment, the process for estimating road surface freezing consists of a de-icing agent usage tendency determination process (Figure 2A), a freezing candidate location determination process (Figure 2B), a freezing estimation process (Figure 3), and a level adjustment process (Figure 4). First, the de-icing agent usage tendency determination process will be described with reference to Figure 2A. The de-icing agent usage tendency determination process is a process that is executed at any time. The de-icing agent usage tendency determination process is executed once for each image taken at each de-icing agent distribution point. When the de-icing agent usage tendency determination process is started, the control unit 20 acquires an image of the road surface taken by the camera using the function of the freezing estimation unit 21c (step S100). That is, the control unit 20 acquires an image of the de-icing agent distribution point to be processed from the road image information 30b stored in the recording medium 30.

[0037] Next, the control unit 20 performs image recognition processing using the function of the freeze estimation unit 21c (step S110). Specifically, the control unit 20 performs image recognition processing on the image acquired in step S100 and detects bags of de-icing agent. Next, the control unit 20 determines whether the amount of de-icing agent used is greater than a threshold using the function of the freeze estimation unit 21c (step S115). Specifically, the control unit 20 detects the number of detected bags and considers the difference between the number of bags indicated by the total amount of de-icing agent after the most recent distribution operation and the number of bags detected from the image as the number of bags used. The control unit 20 compares the amount of de-icing agent used, indicated by the number of bags used, with the threshold. If no bags are detected in the image, the control unit 20 considers that all of the de-icing agent placed at the de-icing agent distribution point has been used.

[0038] In step S115, if it is determined that the amount of de-icing agent used is greater than the threshold, the control unit 20 determines, using the function of the freezing estimation unit 21c, that it is a location where a large amount of de-icing agent is used (step S120). In step S115, if it is not determined that the amount of de-icing agent used is greater than the threshold, the control unit 20 determines, using the function of the freezing estimation unit 21c, that it is a location where a small amount of de-icing agent is used (step S125). The control unit 20 then records these determination results from steps S120 and S125 in the de-icing agent information 30a, in association with the de-icing agent distribution locations to be processed.

[0039] Figure 2B is a flowchart showing the process for determining potential freezing locations. In this embodiment, the process for determining potential freezing locations is performed by the control unit 20 during a predetermined time period at night on the first day. When the process for determining potential freezing locations is started, the control unit 20 collects weather information using the functions of the weather information acquisition unit 21b (step S200). That is, the control unit 20 acquires weather information for the target area during the nighttime period on the first day from the weather information server 400.

[0040] Next, the control unit 20 determines whether or not there is rainfall or snowfall based on the function of the freezing estimation unit 21c (step S205). That is, based on the weather information acquired in step S200, the control unit 20 determines whether or not there are areas within the target area where there is rainfall or snowfall during the night of the first day.

[0041] In step S205, if it is determined that there is rainfall or snowfall, the control unit 20 determines, using the function of the freezing estimation unit 21c, whether the nighttime temperature is below a threshold (step S210). In other words, in step S205, it is determined whether there is an area where there is rainfall or snowfall on the night of the first day and where the nighttime temperature on the first day is below a threshold.

[0042] If it is not determined in step S205 that there is rainfall or snowfall, or if it is not determined in step S210 that the nighttime temperature is below the threshold, the control unit 20 terminates the freezing candidate location determination process.

[0043] In step S210, if it is determined that the nighttime temperature is below a threshold, the control unit 20 determines, based on the function of the freezing estimation unit 21c, that the area will freeze the following morning (freezing area) (step S215). In other words, an area that experiences rain or snowfall during the night of the first day and where the nighttime temperature of the first day is below a threshold is determined to be a freezing area that will freeze the following morning.

[0044] Next, the control unit 20, using the function of the freezing estimation unit 21c, acquires points within the frozen area that have predetermined characteristics that make them prone to freezing, and designates these points as candidate freezing points (step S220). That is, the control unit 20 acquires map information of the frozen area from the map information server 500, analyzes the map information, and picks out points such as intersections, tunnel entrances and exits, and bridges within the frozen area as candidate freezing points. The control unit 20 extracts nodes within the frozen area as intersections. The control unit 20 also identifies links within the frozen area that contain tunnels and acquires the positions of tunnel entrances and exits within the links based on the link data of those links. Furthermore, the control unit 20 identifies links within the frozen area that contain bridges and acquires any position within the section corresponding to the bridge within the link (for example, the position of the bridge end) based on the link data of those links.

[0045] Figure 3 is a flowchart showing the freeze estimation process. The freeze estimation process is executed at a predetermined time on the morning of the second day if, as a result of the freeze candidate location determination process, there is one or more locations determined to be freeze candidate locations. The freeze estimation process is executed by the control unit 20 for each freeze candidate location. That is, one location to be processed is selected at a time from the locations determined to be freeze candidate locations by the freeze candidate location determination process executed on the night of the first day, and the freeze estimation process is executed sequentially.

[0046] When the freezing estimation process is started, the control unit 20 uses the functions of the weather information acquisition unit 21b to acquire the amount of snow at the candidate freezing locations to be processed (step S300). Specifically, the control unit 20 acquires the amount of snow in the area including the candidate freezing locations to be processed during the morning hours of the second day (for example, the latest amount of snow at the time the freezing estimation process is executed) from the weather information server 400.

[0047] Next, the control unit 20 determines, using the function of the freezing estimation unit 21c, whether the amount of snow at the freezing candidate location is above a threshold (step S305). That is, it determines whether the amount of snow in the area including the freezing candidate location to be processed during the morning of the second day is above a threshold. If it is determined in step S305 that it is above the threshold, the control unit 20 removes the freezing candidate location to be processed from the list of freezing candidate locations using the function of the freezing estimation unit 21c (step S310).

[0048] If the amount of snow is not determined to be above the threshold in step S305, the control unit 20 leaves the candidate freezing location as a candidate freezing location (step S315). In other words, the control unit 20 does not remove the candidate freezing location from the list of candidate freezing locations, but treats it as such and proceeds with the processing from step S320 onward. Note that the processing in step S315 may be skipped.

[0049] Next, the control unit 20 determines, using the function of the freezing estimation unit 21c, whether or not the candidate freezing location to be processed corresponds to a de-icing agent distribution location (step S320). That is, the control unit 20 refers to the location of each de-icing agent distribution location in the de-icing agent information 30a, and if the distance between any of the de-icing agent distribution locations and the location of the candidate freezing location to be processed is less than a threshold distance, the control unit 20 considers the candidate freezing location to be processed to correspond to a de-icing agent distribution location.

[0050] In step S320, if it is determined that the condition is met, the control unit 20 determines whether the candidate freezing site to be processed (snowmelt agent distribution site) is a site where a large amount of snowmelt agent is used (step S325). That is, the control unit 20 determines whether the candidate freezing site to be processed is a site that was determined to be a site where a large amount of snowmelt agent is used in the snowmelt agent usage tendency determination process (Figure 2A).

[0051] If, in step S325, it is determined that a large amount of de-icing agent is used at a particular location, the control unit 20, using the function of the freezing estimation unit 21c, determines that the potential freezing location to be processed has a "high" probability of being frozen (step S330). In other words, the control unit 20 considers the potential freezing location to be processed as a presumed freezing location that has a high probability of being frozen.

[0052] If the location is not determined to be a location where a large amount of de-icing agent is used in step S325, the control unit 20 determines, based on the function of the freezing estimation unit 21c, that the likelihood of freezing at the target freezing location is "medium" (step S335). In other words, the control unit 20 considers the target freezing location to be an estimated freezing location with a moderate likelihood of freezing. If the location is not determined to be a location where de-icing agent is distributed in step S320, the control unit 20 determines, based on the function of the freezing estimation unit 21c, that the likelihood of freezing at the target freezing location is "low". In other words, the control unit 20 considers the target freezing location to be an estimated freezing location with a low likelihood of freezing.

[0053] Figure 4 is a flowchart of the level adjustment process. The level adjustment process adjusts the level value indicating the possibility of freezing for each estimated freezing point after the freezing estimation process, based on probe information, and is executed in the morning hours of the second day of the target period. One of the estimated freezing points is selected as the processing target and the adjustment process is executed sequentially. When the adjustment process starts, the control unit 20 acquires the vehicle speed based on the probe information (step S400). That is, the control unit 20 identifies the driving history of multiple probe vehicles that passed through the estimated freezing point to be processed in the morning hours of the target period from the probe information 30d. Based on the identified driving history, the control unit 20 acquires the vehicle speed (statistical value) when driving on the link including the estimated freezing point.

[0054] Next, the control unit 20 determines whether the vehicle speed is below the threshold speed using the function of the freezing estimation unit 21c (step S405). If it is determined in step S405 that the vehicle speed is below the threshold speed, the control unit 20 raises the possibility of freezing by one level using the function of the freezing estimation unit 21c (step S410). That is, the control unit 20 considers that if the driving speed of a vehicle traveling on a link including the estimated freezing point to be processed is lower than the threshold speed, the reason is due to road surface freezing. Then, for example, if the possibility of freezing at the estimated freezing point to be processed before the update was "medium", the control unit 20 updates the possibility of freezing to "high", and if the possibility of freezing before the update was "low", it updates the possibility of freezing to "medium". In this embodiment, if the possibility of freezing before the update is "high", the possibility of freezing does not change.

[0055] If the vehicle speed is not determined to be below the threshold speed in step S405, the control unit 20 reduces the probability of freezing by one level using the function of the freezing estimation unit 21c (step S415). That is, if the vehicle speed traveling on the link including the estimated freezing point to be processed is above the threshold speed, the control unit 20 considers the reason to be that the road surface is not frozen. Then, for example, if the probability of freezing at the estimated freezing point to be processed before the update was "medium", the control unit 20 updates the probability of freezing to "low", and if the probability of freezing before the update was "high", it updates the probability of freezing to "medium". In this embodiment, if the probability of freezing before the update is "low", the probability of freezing does not change.

[0056] The control unit 20, after going through the freezing estimation process shown in Figure 3, or both the freezing estimation process and the level adjustment process shown in Figure 4, transmits the outputted estimated freezing locations and the level of the possibility of freezing to the vehicle being guided, in response to a request from the vehicle being guided, and allows the user to be guided in the vehicle being guided 200.

[0057] (3) Other embodiments: The above embodiments are merely examples for carrying out the present invention, and various other embodiments can be adopted. For example, the road surface freezing estimation system 10 may be a device mounted on a vehicle, a device implemented by a portable terminal, or a device implemented by multiple devices (e.g., a client and a server). At least some of the components constituting the road surface freezing estimation system, such as the de-icing agent information acquisition unit 21a, weather information acquisition unit 21b, freezing estimation unit 21c, and guidance unit 21d, may be divided among multiple devices. For example, the functions of the freezing estimation unit 21c and the guidance unit 21d may be implemented in an on-board device of the vehicle 200. Of course, some of the configurations of the above embodiments may be omitted, and the order of processing may be changed or omitted.

[0058] In the de-icing agent information acquisition unit, methods other than registration by the road administrator may be used to determine the location of de-icing agent distribution points. For example, if an image of a road taken by a camera on a patrol vehicle or probe vehicle contains an image indicating de-icing agent, the system may be configured to acquire the location of the de-icing agent distribution point based on the image's shooting location (the vehicle's position at the time of shooting), the vehicle's direction of travel at the time of shooting, the camera's shooting range relative to the vehicle, and the coordinates of the object indicating the de-icing agent within the image.

[0059] Furthermore, the freezing estimation unit may be configured to record, for example, the distribution record at each de-icing agent distribution point in the previous fiscal year, and to determine whether each de-icing agent distribution point tends to have a high amount of de-icing agent usage based on the distribution record from the previous fiscal year. Alternatively, the system may acquire the trend in the amount of de-icing agent used at each de-icing agent distribution point based on the frequency of additional de-icing agent additions. In addition, the system may identify the trend in the number of bags of de-icing agent at each de-icing agent distribution point based on images of each de-icing agent distribution point taken during daily patrols, and determine the trend in usage based on that trend.

[0060] The weather information acquisition unit may acquire the humidity of the target area and determine that the road surface is frozen if the humidity is higher than the humidity threshold and the outside temperature is lower than the temperature threshold. For example, even without rain or snowfall, the road surface may freeze if the humidity is high and the outside temperature is low. Also, even without rain or snowfall, in places where the road surface is constantly wet due to small amounts of spring water, such as on mountain roads, the road surface may freeze if the outside temperature falls below the threshold. Furthermore, even if there is no rain or snowfall on the night of the first day, the road surface may freeze on the morning of the second day if some of the snow accumulated from snowfall before the first day melts and then freezes again. Therefore, the presence of rain or snowfall does not necessarily have to be included as a condition for determining freezing, and information on rain or snowfall does not necessarily have to be acquired from the weather information server.

[0061] The target period can be any time period for which road surface freezing is to be estimated. Therefore, the target period is not limited to the period from nighttime to the following morning. For example, the target period could be from evening to midnight, or it could be during the morning, or it could be during the daytime. Also, for example, if the target period is the morning of any fourth day, the freezing candidate location determination process may be executed during the morning of the fourth day (determination is possible based on actual weather data from the third day, which is the day before the fourth day).

[0062] The freezing estimation unit only needs to be able to consider a de-icing agent distribution point as a presumed frozen point where the road surface may be frozen during the target period if the outside temperature at that point during the target period is lower than the judgment criterion, and the trend in the amount of de-icing agent used does not necessarily need to be considered. The freezing estimation unit may also consider a de-icing agent distribution point where the outside temperature during the target period is lower than the judgment criterion to have a higher probability of freezing than a non-de-icing agent distribution point where the outside temperature during the target period is lower than the judgment criterion.

[0063] In the above embodiment, the system was configured to consider potential freezing locations as locations that have predetermined characteristics of a road surface prone to freezing, where the ambient temperature during the target period is lower than the judgment criterion, and where there was rainfall or snowfall during the target period. However, the presence of rainfall or snowfall during the target period does not necessarily have to be included as a condition for determining a location as a potential freezing location. In other words, the system may be configured to consider potential freezing locations as locations that have predetermined characteristics of a road surface prone to freezing, where the ambient temperature during the target period is lower than the judgment criterion.

[0064] Furthermore, the system may be configured to consider de-icing agent distribution points where the outside temperature during the target period is lower than the judgment criteria and where there was rainfall or snowfall during the target period as estimated freezing points. In other words, the condition for determining an estimated freezing point does not necessarily have to be that the road surface has predetermined characteristics that make it prone to freezing.

[0065] The freezing estimation unit may be configured to estimate that the likelihood of the road surface being frozen at a de-icing agent distribution point is lower than if there were no change, based on whether the amount of de-icing agent at the distribution point has decreased during the target period. For example, if the number of de-icing agent bags identified from images taken during the target period is less than the number of de-icing agent bags identified from images taken the day before the target period, the freezing estimation unit will assume that de-icing agent was used to eliminate the freezing of the road surface during the target period, and will estimate that the freezing of the road surface has been mitigated as a result of the use of de-icing agent. For this reason, the unit may be configured to perform a process such as lowering the level of the likelihood of freezing by one level.

[0066] The guidance unit is not limited to a configuration that transmits the estimated location of the freezing point and the level of likelihood of freezing to the in-vehicle device. It may, of course, be configured to transmit the information to a portable terminal such as a smartphone.

[0067] Furthermore, the methods of the present invention can also be applied as programs and methods. Moreover, such systems, programs, and methods may be implemented as standalone devices, or they may be implemented using parts shared with various components of a vehicle, encompassing a variety of embodiments. They can also be modified as appropriate, such as being partly software and partly hardware. Furthermore, the invention also functions as a recording medium for a program that controls the system. Of course, the recording medium for the program may be a magnetic recording medium, a semiconductor memory, or any recording medium developed in the future can be considered in exactly the same way. [Explanation of Symbols]

[0068] 10…Road surface freezing estimation system, 20…Control unit, 21…Road surface freezing estimation program, 21a…De-icing agent information acquisition unit, 21b…Weather information acquisition unit, 21c…Freezing estimation unit, 21d…Guidance unit, 30…Recording medium, 30a…De-icing agent information, 30b…Road image information, 30c…Probe information, 30d…Probe information, 41…Communication unit, 100…Patrol vehicle, 110…Communication unit, 120…Positioning unit, 130…Camera, 150…Control unit, 200…Vehicle, 210…Communication unit, 220…Positioning unit, 240…UI unit, 240…Positioning unit, 250…Control unit, 300…Road administrator terminal, 400…Weather information server, 500…Map information server

Claims

1. A snowmelt agent information acquisition unit acquires snowmelt agent distribution locations where snowmelt agents have been distributed, A weather information acquisition unit that acquires the outside temperature at the snowmelt distribution point during the target period, A freezing estimation unit that, when the ambient temperature at the de-icing agent distribution point during the target period is lower than the judgment criteria, considers the de-icing agent distribution point to be a presumed frozen location where the road surface may be frozen during the target period, A guide unit that provides directions to the estimated freezing point, A road surface freezing estimation system equipped with the following features.

2. The freeze estimation unit, The trend in the amount of de-icing agent used at the aforementioned de-icing agent distribution points is obtained, and it is estimated that when the amount of use is high, there is a higher probability that the road surface at the estimated frozen area, which is the de-icing agent distribution point, is frozen during the aforementioned period than when the amount of use is low. The road surface freezing estimation system according to claim 1.

3. The freezing estimation unit estimates that if the amount of de-icing agent at the de-icing agent distribution point decreases during the target period, the likelihood of the road surface at the estimated freezing point, which is the de-icing agent distribution point, being frozen is lower than if there were no change. The road surface freezing estimation system according to claim 2.

4. The freeze estimation unit, A road surface that has predetermined characteristics that make it prone to freezing, and where the outside temperature during the target period is lower than the judgment criteria, A road surface that has predetermined characteristics that make it prone to freezing, where the outside temperature during the target period is lower than the judgment criteria and where there was rainfall or snowfall during the target period, The de-icing agent distribution site where the outside temperature during the aforementioned period was lower than the judgment criterion and where there was rainfall or snowfall during the aforementioned period, At least one of the locations is considered to be the estimated freezing point. The road surface freezing estimation system according to claim 1.

5. The freezing estimation unit estimates that if the vehicle speed of a probe vehicle that traveled through the estimated freezing point during the target period is below a threshold speed, the likelihood of the road surface being frozen at the estimated freezing point is higher than if the vehicle speed is above the threshold speed. A road surface freezing estimation system according to any one of claims 1 to 4.

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