Patent Publication Number: US-2023150507-A1

Title: Travel Assistance Method and Travel Assistance Device

Description:
TECHNICAL FIELD 
     The present invention relates to a travel assistance method and a travel assistance device. 
     BACKGROUND ART 
     In recent years, a system that detects a state of an obstacle that may be present on a travel route of a host vehicle and assists traveling of the host vehicle according to the state of the obstacle has been studied. JP 2017-140993 A discloses a method for controlling a host vehicle when a crosswalk crossing a travel route is present at a turning destination in a case where the host vehicle turns across an opposite lane at an intersection. 
     According to a technique disclosed in JP 2017-140993 A, when a pedestrian walking on the crosswalk is detected, a stop position of the host vehicle is controlled according to a distance from the intersection to the crosswalk. Specifically, when the distance from the intersection to the crosswalk is shorter than an entire length of the host vehicle, the host vehicle is stopped without turning. On the other hand, when the distance from the intersection to the crosswalk is longer than the entire length of the host vehicle, the host vehicle is stopped before the crosswalk after turning. By such control, it is possible to avoid approaching a pedestrian or an oncoming vehicle that may be present on the travel route of the host vehicle. 
     SUMMARY OF INVENTION 
     According to the technique disclosed in JP 2017-140993 A, it is possible to prevent the host vehicle from approaching an obstacle such as a pedestrian or an oncoming vehicle that may exist on the travel route of the host vehicle. However, in a case where the host vehicle performs a lane change or the like, even another vehicle (for example, an oncoming vehicle) traveling outside the travel route of the host vehicle may face and approach the host vehicle in front of the host vehicle. 
     An object of the present invention is to provide a lane change assistance method and a lane change assistance device capable of suppressing another vehicle traveling outside a travel route of a host vehicle from approaching the host vehicle in a state of facing the host vehicle in front of the host vehicle. 
     According to an aspect of the invention, a travel assistance method for performing a lane change of a host vehicle using a determined route and vehicle speed is provided. The travel assistance method includes: detecting an oncoming vehicle traveling in an opposite lane opposite to a lane in which the host vehicle travels when the host vehicle starts the lane change; determining a crossing point between a virtual advancing route and a linear advancing route in which the oncoming vehicle advances linearly, the virtual advancing route differing from the route and being a virtual extension of an advancing route of the host vehicle in an advancing direction during a period from start to end of the lane change; executing a lane change using the route and the vehicle speed in a case where a time difference between a first predicted time when it is assumed that the host vehicle reaches the crossing point and a second predicted time until the oncoming vehicle reaches the crossing point is outside a predetermined range; and when the time difference is within the predetermined range, executing a lane change by changing at least one of the route and the vehicle speed such that the time difference is outside the predetermined range. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic configuration diagram of a travel assistance device common to embodiments. 
         FIG.  2    is a diagram showing a situation around a host vehicle in a case where a determined route and vehicle speed (driving control information) is changed in travel assistance control according to a first embodiment. 
         FIG.  3    is a flowchart showing the travel assistance control. 
         FIG.  4 A  is an explanatory diagram of an example of changing a vehicle speed. 
         FIG.  4 B  is an explanatory diagram of an example of changing a route. 
         FIG.  4 C  is an explanatory diagram of an example of changing a route. 
         FIG.  5 A  is an explanatory diagram of an example of changing a vehicle speed. 
         FIG.  5 B  is an explanatory diagram of an example of changing a route. 
         FIG.  6    is a flowchart showing travel assistance control according to a modification. 
         FIG.  7    is a diagram showing a situation around a host vehicle in a case where a route and/or a vehicle speed is changed in travel assistance control according to a second embodiment. 
         FIG.  8    is a flowchart showing the travel assistance control. 
         FIG.  9    is an explanatory diagram of an oncoming vehicle used for determining whether it is necessary to change a route and/or a vehicle speed in a third embodiment. 
         FIG.  10    is an explanatory diagram of an oncoming vehicle used for determining whether it is necessary to change a route and/or a vehicle speed. 
         FIG.  11    is an explanatory diagram of an example in which a median strip is present. 
         FIG.  12    is a diagram showing a situation around a host vehicle in a case where a route and/or a vehicle speed is changed in travel assistance control according to a fourth embodiment. 
         FIG.  13    is a diagram showing a situation around a host vehicle in a case where a route and/or a vehicle speed is changed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. 
     First Embodiment 
       FIG.  1    is a schematic configuration diagram of a driving assistance device  100  common to the embodiments of the present invention. 
     As shown in  FIG.  1   , the driving assistance device  100  includes a camera  110 , a GPS receiver  120 , a sensor  130 , a communication interface  140 , a map database  150 , a direction indicator  160 , an actuator  170 , and a controller  180 . The driving assistance device  100  is mounted on, for example, a vehicle (a host vehicle A) having an autonomous driving function or a driving assistance function. 
     The camera  110  is an imaging device that images an external situation of the host vehicle A, and acquires imaging information on the external situation of the host vehicle A. The camera  110  is, for example, around view monitor cameras provided on vehicle exterior sides of front, rear, and left and right doors of the host vehicle A, a front camera provided on a vehicle exterior or interior side of a windshield, and a rear camera provided on a rear of the host vehicle A. The camera  110  outputs the imaging information on the external situation to a controller  180 . 
     The GPS receiver  120  periodically receives a signal (GPS data) transmitted from a GPS satellite. The GPS receiver  120  outputs the received GPS data to the controller  180 . 
     The sensor  130  includes a radar  131 , a gyro sensor  132 , a vehicle speed sensor  133 , and the like, and detects a traveling state of the host vehicle A. The radar  131  detects an object outside the host vehicle A using radio waves. The radio waves are, for example, millimeter waves, and the radar  131  transmits the radio waves to surroundings of the host vehicle A and receives radio waves reflected by an object to detect the object. The radar  131  can acquire, for example, a distance or a direction to a surrounding object as object information. The gyro sensor  132  detects a direction of the host vehicle A. The vehicle speed sensor  133  detects a vehicle speed of the host vehicle A. The sensor  130  outputs the acquired object information and the detected direction and vehicle speed of the host vehicle A to the controller  180 . 
     The communication interface  140  acquires a surrounding situation of the host vehicle A from an outside by wireless communication. The communication interface  140  receives various types of information from an intelligent transportation system (ITS) that transmits, for example, traffic information such as traffic jam information and traffic regulation information, wear information, and the like in real time. The ITS includes vehicle-to-vehicle communication with another vehicle, road-to-vehicle communication with a roadside device, and the like. The communication interface  140  acquires acceleration and deceleration of another vehicle around the host vehicle A, a relative position with respect to the host vehicle A, and the like, for example, by the vehicle-to-vehicle communication. 
     The map database  150  stores map information. The map information includes information on a shape, a gradient, a width, a speed limit, an intersection, a traffic light, the number of lanes, and the like of a road including a curvature of a curve and the like. The map information stored in the map database  150  can be referred to at any time by the controller  180  to be described later. 
     The direction indicator  160  is operated and stopped by an operation of a driver or a command from the controller  180 . Operation and stop information of the direction indicator  160  is output to the controller  180 . 
     The actuator  170  is a device that executes traveling control of the host vehicle A based on a command from the controller  180 . The actuator  170  includes a drive actuator  171 , a brake actuator  172 , a steering actuator  173 , and the like. 
     The drive actuator  171  is a device for adjusting a drive force of the host vehicle A. 
     When the host vehicle A is an internal combustion engine vehicle equipped with an engine as a traveling drive source, the drive actuator  171  includes a throttle actuator that adjusts an amount of air supplied to the engine (a throttle opening) and a fuel injection valve that adjusts an amount of fuel supplied to the engine (a fuel injection amount). 
     When the host vehicle A is a hybrid vehicle or an electric vehicle equipped with a motor as a traveling drive source, the drive actuator  171  includes a circuit (an inverter, a converter, and the like) capable of adjusting electric power supplied to the motor. 
     The brake actuator  172  is a device that operates a brake system in response to a command from the controller  180  and adjusts a braking force applied to wheels of the host vehicle A. The brake actuator  172  includes a hydraulic brake or a regenerative brake. 
     The steering actuator  173  includes an assistance motor that controls a steering torque in an electric power steering system, or the like. The controller  180  controls an operation of the steering actuator  173  to control an operation of the wheels, thereby assisting a lane change of the host vehicle A. 
     The controller  180  is constituted with a computer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input/output interface (an I/O interface). The controller  180  executes processing for implementing specific control by executing a specific program. The controller  180  may include one computer or a plurality of computers. 
     The controller  180  generates driving control information indicating a travel route (including a steering timing), a traveling vehicle speed (including acceleration and deceleration), and the like, and assists traveling of the host vehicle A according to the route and the vehicle speed indicated by the generated driving control information. When a lane change is included in the travel route, the controller  180  changes the route and the vehicle speed in the driving control information according to a situation around the host vehicle A, and assists the traveling of the host vehicle A according to the changed driving control information. 
       FIG.  2    is a diagram showing an example in which the route and the vehicle speed indicated by the driving control information are changed when the lane change is performed in a state where the travel assistance control is performed. In the figure, a four-lane road with two lanes on each side is shown, and it is assumed that traveling on a left side is prescribed by law. 
     In two lanes on a lower side of the figure, the host vehicle A travels from a right side to a left side of the figure. Two lanes on an upper side of the figure are opposite lanes opposite to a travel lane of the host vehicle A, and an oncoming vehicle B travels from the left side to the right side of the figure in the opposite lanes. In the figure, a position of the host vehicle A at each of three times t1 to t3 is indicated by A 1  to A 3 , and a position of the oncoming vehicle B at each of the three times t1 to t3 is indicated by B 1  to B 3 . 
     Before the time t1, the host vehicle A is traveling in an outer lane that is not in contact with the opposite lane among the travel lanes of two lanes. It is assumed that an obstacle C is present in an inner lane in contact with the opposite lane. The obstacle C is, for example, a construction site or a stopping vehicle due to a breakdown. 
     At the time t1, the host vehicle A reaches the side of the obstacle C, and at the time t2, the host vehicle A passes the side of the obstacle C and starts a lane change to the inner lane. Then, at the time t3, the host vehicle A starts traveling in the inner lane and completes the lane change, and after the time t3, the host vehicle A travels in the inner lane. 
     It is assumed that the oncoming vehicle B is traveling in an opposite inner lane that is in contact with the travel lane of the host vehicle A, and the oncoming vehicle B does not perform a lane change. In the figure, oncoming vehicles B 1  to B 3  at the times t1 to t3 are shown. 
     In the figure, the travel route of the host vehicle A is indicated by a thick solid line, and the travel route includes a traveling track during the lane change (time t2 to time t3). The travel route predicted for the oncoming vehicle B is indicated by a thin solid line. 
     A virtual advancing route intersects with the predicted travel route of the oncoming vehicle B at a crossing point X, the virtual advancing route differing from the route and being a virtual extension of the advancing route of the host vehicle in an advancing direction during the lane change (any time from the time t2 when the lane change starts to the time t3 when the lane change ends) of the host vehicle A indicated by a broken line. This means that the host vehicle A and the oncoming vehicle B advance toward the crossing point X while facing each other, and approach each other. That is, since the host vehicle A and the oncoming vehicle B travel toward the crossing point X although the travel routes do not cross each other, both vehicles approach each other from the front. In such a situation, the driver of the host vehicle A performs a steering wheel operation in order to avoid the approach of the oncoming vehicle B from the front, and as a result, the driving assistance control may be interrupted. 
     Therefore, when both the host vehicle A and the oncoming vehicle B travel toward the crossing point X, the controller  180  changes the driving control information of the host vehicle A, and performs the travel assistance of the host vehicle A according to the changed driving control information. Accordingly, the host vehicle A and the oncoming vehicle B do not travel toward the crossing point X while facing each other during the lane change, and it is possible to suppress both vehicles from approaching from the front. 
     Referring again to  FIG.  1   , the controller  180  that performs such control includes a host vehicle position detection unit  181 , a travel route generation unit  182 , a surrounding vehicle information acquisition unit  183 , a change necessity determination unit  184 , and a lane change assistance unit  185 . Hereinafter, these configurations will be described in detail. 
     The host vehicle position detection unit  181  constantly detects a current position, vehicle speed, and traveling direction of the host vehicle A based on the GPS data from the GPS receiver  120  and the direction and vehicle speed of the host vehicle A detected by the sensor  130 . The host vehicle position detection unit  181  detects a position of the host vehicle A on a map with reference to the map database  150 . 
     The host vehicle position detection unit  181  acquires road information on a road around the host vehicle A based on the detected current position, vehicle speed, traveling direction, and position on the map of the host vehicle A, the imaging information on the external situation acquired by the camera  110 , and the object information acquired by the sensor  130 . The road information includes information on a shape, a gradient, a width, a speed limit, an intersection, a traffic light, a type of lane, the number of lanes, and the like of the road around the host vehicle A. 
     The travel route generation unit  182  generates a travel route of the host vehicle A based on information such as the position or surrounding road condition of the host vehicle A detected by the host vehicle position detection unit  181  and a set destination. In the travel route, a travel position in a vehicle width direction on the road is shown. Further, the travel route generation unit  182  generates speed information (including acceleration and deceleration, the steering timing, and the like) in a case where the host vehicle A travels along the travel route. 
     In this way, the travel route generation unit  182  generates driving control information including the travel route and the speed information. In the example shown in  FIG.  2   , the driving control information indicating the travel route (including the steering timing) and the travel speed (including acceleration and deceleration) is generated so as to avoid the obstacle C on the side of the road and change the lane to the inner lane after passing the side of the obstacle C. 
     The surrounding vehicle information acquisition unit  183  acquires surrounding vehicle information based on the imaging information on the external situation acquired by the camera  110 , the object information acquired by the sensor  130 , and the surrounding situation of the host vehicle A acquired by the communication interface  140 . The surrounding vehicle information includes a travel situation of another vehicle including the oncoming vehicle traveling in the opposite lane of the host vehicle A. 
     The change necessity determination unit  184  determines whether it is necessary to change the driving control information according to the situation around the host vehicle A. Specifically, as shown in  FIG.  2   , the change necessity determination unit  184  obtains the crossing point X between the virtual advancing route of the host vehicle A and a predicted linear advancing route of the oncoming vehicle B at the time t2 when the host vehicle A starts the lane change. Further, a virtual arrival time to predicted to be required for the host vehicle A to virtually reach the crossing point X and a predicted arrival time tb until the oncoming vehicle B reaches the crossing point X are obtained, and it is determined whether it is necessary to change the driving control information according to whether a time difference td between the two vehicles is within a predetermined range. Details of determination processing performed by the change necessity determination unit  184  will be described later with reference to  FIG.  4   . 
     The lane change assistance unit  185  performs the travel assistance involving the lane change of the host vehicle A. When the change necessity determination unit  184  determines that a change of the driving control information is necessary, the lane change assistance unit  185  changes the driving control information and performs the travel assistance of the host vehicle A based on a route and a vehicle speed indicated by the changed driving control information. 
       FIG.  3    is a flowchart of the travel assistance control executed by the controller  180 . The travel assistance control is repeatedly executed at a predetermined cycle. The travel assistance control may be performed by executing a program stored in the controller  180 . 
     In step S1, the controller  180  (the travel route generation unit  182 ) generates an approximate travel route and speed information of the host vehicle A based on the information such as the position of the host vehicle A detected by the host vehicle position detection unit  181 , the set destination, and the like. 
     In step S2, the controller  180  (the travel route generation unit  182 ) determines whether to start a lane change after a predetermined time (for example, after 3 seconds) using the travel route calculated in step S1. In the example of  FIG.  2   , it is determined at the time t1 that the lane change is performed after the predetermined time, and the lane change is started at the time t2. 
     When it is determined that the lane change is started after the predetermined time (S2: Yes), processing of step S3 is performed next. When it is not determined that the lane change is performed after the predetermined time (S2: No), next, in processing of step S9, the travel assistance control is performed such that the vehicle travels on a determined travel route at a determined speed or acceleration. 
     In step S3, the controller  180  (the travel route generation unit  182 ) operates the direction indicator  160  to notify surrounding vehicles that the lane change is to be performed. 
     In step S4, the controller  180  (the travel route generation unit  182 ) creates driving control information indicating a traveling track, speed information, and the like when the lane change is performed. In the example of  FIG.  2   , a travel route along which the vehicle travels in the outer lane in front of the obstacle C and changes lanes to the inner lane after passing the side of the obstacle C, and speed information that the vehicle accelerates and decelerates without largely shaking in the travel route are generated. 
     In step S5, the controller  180  (the surrounding vehicle information acquisition unit  183 ) acquires a state of the surroundings of the host vehicle A, and detects presence or absence of the oncoming vehicle B facing the travel route of the host vehicle A after the lane change. When the oncoming vehicle B is present, the controller  180  further predicts a travel route of the oncoming vehicle B. 
     When the oncoming vehicle B is present (S5: Yes), processing of step S6 is performed next, and the crossing point X used for determining whether it is necessary to change the driving control information is calculated. When the oncoming vehicle B is not present (S5: No), the processing of step S9 is performed next, and the travel assistance is performed such that the lane change is performed according to the route and the speed indicated by the driving control information generated in step S4. 
     In step S6, the controller  180  (the change necessity determination unit  184 ) obtains the crossing point X used for determining whether it is necessary to change the driving control information in a subsequent step S7. Specifically, the controller  180  obtains the virtual advancing route, which is the virtual extension of the advancing route of the host vehicle forward in the advancing direction during the lane change, and obtains the crossing point X between the virtual advancing route and the predicted travel route of the oncoming vehicle B obtained in step S5. 
     In step S7, the controller  180  (the change necessity determination unit  184 ) obtains the virtual arrival time ta (a first predicted time) until the host vehicle A virtually reaches the crossing point X and the predicted arrival time tb (a second predicted time) until the oncoming vehicle B reaches the crossing point X, and determines whether it is necessary to change driving assistance information according to whether the time difference td between the virtual arrival time ta and the predicted arrival time tb is within the predetermined range. 
     Specifically, as shown in  FIG.  2   , the controller  180  obtains the virtual arrival time ta until the host vehicle A reaches the crossing point X in a case where it is assumed that the host vehicle A advances linearly on the virtual advancing route without completing the lane change. At the same time, the controller  180  predicts the predicted arrival time tb until the oncoming vehicle B reaches the crossing point X. 
     Further, the controller  180  obtains the time difference td between the virtual arrival time ta and the predicted arrival time tb, and determines whether correction is necessary according to whether the time difference td is within the predetermined range (for example, 1 second). When the time difference td is within the predetermined range, the controller  180  determines that the host vehicle A and the oncoming vehicle B may advance toward the crossing point X while facing each other at the same timing. In such a case, since the driver of the host vehicle A manually controls the vehicle in order to avoid traveling from the front of the oncoming vehicle B and driving control processing is likely to be interrupted, it is determined that correction of the driving control information is necessary. 
     In this way, when the time difference td is within the predetermined range, it is determined that the correction of the driving control information is necessary (S7: Yes), and then processing of step S8 is performed. When the time difference td is outside the predetermined range, it is determined that the correction of the driving control information is unnecessary (S7: No), and then the processing of step S9 is performed. 
     In step S8, the controller  180  (the lane change assistance unit  185 ) changes the route and the speed indicated by the driving control information of the host vehicle A. Due to the change of the driving control information, at least one of the crossing point X, the virtual arrival time ta, and the predicted arrival time tb is changed, and the time difference td is outside the predetermined range. As a result, since the host vehicle A and the oncoming vehicle B are suppressed from advancing to the crossing point X while facing each other at the same timing, it is possible to reduce a possibility that the driver of the host vehicle A manually performs control and the driving control processing is interrupted. A specific modification example of the driving control information will be described later with reference to  FIGS.  4 A to  4 C,  5 A, and  5 B . 
     In step S9, the controller  180  (the lane change assistance unit  185 ) assists the lane change of the host vehicle A according to the driving control information. When the driving control information is changed in step S8, the travel assistance is performed based on the changed driving control information. Accordingly, the time difference td is outside the predetermined range, and it is possible to suppress that the driving control processing is interrupted due to the operation of the driver of the host vehicle A and a behavior of the host vehicle A is unstable. 
     Examples of a case where the driving control information is changed in step S8 are shown in  FIGS.  4 A to  4 C  and  FIGS.  5 A and  5 B .  FIGS.  4 A to  4 C  show examples in which the driving control information is changed when the time difference td is within the predetermined range and the change is determined to be necessary (S7: Yes) and when the virtual arrival time ta of the host vehicle A is longer (later) than the predicted arrival time tb of the oncoming vehicle B.  FIGS.  5 A and  5 B  show examples in which the driving control information is changed when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes) and when the virtual arrival time ta is shorter (earlier) than the predicted arrival time tb. 
     In an example of  FIG.  4 A , the controller  180  (the lane change assistance unit  185 ) changes the speed information (the driving control information) such that a speed of the host vehicle A is slower than a speed that has already been set before the start of the lane change without changing the travel route. Due to the change, a time t2′ when the lane change is started according to the driving control information after the change is later than the time t2 when the lane change is started according to the driving control information before the correction. In the figure, positions of the host vehicle A and the oncoming vehicle B corresponding to times t1, t2, and t2′ are shown. A position A 2  of the host vehicle A at the time t2 before the correction is omitted for readability. 
     Since the start time t2′ of the lane change is delayed by decelerating the host vehicle A before the start of the lane change, the virtual arrival time ta until the host vehicle A virtually reaches the crossing point X becomes longer. The virtual arrival time ta longer than the predicted arrival time tb becomes even longer, and thus the time difference td is outside the predetermined range. As shown in the figure, a position B 2 ′ of the oncoming vehicle B is located in front of the crossing point X at the time t2′ when the host vehicle A starts the lane change, and the host vehicle A advances toward the rear of the oncoming vehicle B, and thus it is suppressed that the host vehicle A and the oncoming vehicle B travel so as to approach each other while facing each other. 
     In an example of  FIG.  4 B , the controller  180  (the lane change assistance unit  185 ) changes the travel route (the driving control information) during the lane change such that a steering angle of the host vehicle A during the lane change is smaller than an angle that has already been set. Due to the change, the start time t2 of the lane change of the host vehicle A is not changed, and thus it is unnecessary to consider the start time t2′ of the lane change after the change as in the example shown in  FIG.  4 A . In the figure, positions A 1  and A 2  of the host vehicle A and positions B 1  and B 2  of the oncoming vehicle B are shown corresponding to times t1 and t2, respectively. Regarding the virtual advancing route of the host vehicle A, the virtual advancing route before the correction is indicated by a dotted line, and the virtual advancing route after the correction is indicated by a broken line. 
     As shown in the figure, by making the steering angle smaller than that before the change, the crossing point X is changed to the front side in the advancing direction of the host vehicle A, and thus the virtual arrival time ta until the host vehicle A virtually reaches the crossing point X becomes shorter. Further, since a distance between the oncoming vehicle B and the crossing point X increases, the predicted arrival time tb to the crossing point X of the oncoming vehicle B becomes longer. As a result, the virtual arrival time ta longer than the predicted arrival time tb becomes even longer, the predicted arrival time tb shorter than the virtual arrival time ta becomes even shorter, and at the same time, the predicted arrival time tb longer than the virtual arrival time ta becomes even longer, and thus the time difference td is outside the predetermined range. As shown in the figure, a position B 2 ′ of the oncoming vehicle B is located in front of the crossing point X at the time t2′ when the host vehicle A starts the lane change, and the host vehicle A advances toward the rear of the oncoming vehicle B, and thus it is suppressed that the host vehicle A and the oncoming vehicle B travel so as to approach each other while facing each other. 
     In an example of  FIG.  4 C , the controller  180  (the lane change assistance unit  185 ) changes the travel route (the driving control information) during the lane change such that a start position of the lane change is located on the front side in the advancing direction of the host vehicle A with respect to the position that has already been set. Due to the change, a time t2′ when the lane change is started according to the driving control information after the change is later than the time t2 when the lane change is started according to the driving control information before the correction. In the figure, positions of the host vehicle A and the oncoming vehicle B corresponding to times t1, t2, and t2′ are shown. A position A 2  of the host vehicle A at the time t2 before the correction is omitted for readability. 
     Since the crossing point X is changed to the front side in the advancing direction by changing the start position of the lane change to the front side in the advancing direction of the host vehicle A, the virtual arrival time ta until the host vehicle A virtually reaches the crossing point X becomes longer. Further, since a distance between the oncoming vehicle B and the crossing point X decreases, the predicted arrival time tb to the crossing point X of the oncoming vehicle B becomes shorter. As a result, the virtual arrival time ta longer than the predicted arrival time tb becomes even longer, and at the same time, the predicted arrival time tb shorter than the virtual arrival time ta becomes even shorter, and thus the time difference td is outside the predetermined range. As shown in the figure, the position B 2 ′ of the oncoming vehicle B is located on the front side of the crossing point X at the time t2′ when the host vehicle A starts the lane change, and the host vehicle A advances toward the rear of the oncoming vehicle B, and thus it is suppressed that the host vehicle A and the oncoming vehicle B travel so as to approach each other while facing each other. 
     In an example of  FIG.  5 A , the controller  180  (the lane change assistance unit  185 ) changes the speed information (the driving control information) such that the speed of the host vehicle A is faster than a speed that has already been set before the start of the lane change without changing the travel route. Due to the change, the time t2′ when the lane change is started according to the driving control information after the change is earlier than the time t2 when the lane change is started according to the driving control information before the correction. In the figure, positions of the host vehicle A and the oncoming vehicle B are shown corresponding to the times t1, t2′, and t2, respectively. A position A 2  of the host vehicle A at the time t2 before the correction is omitted for readability. 
     Since the start time t2′ of the lane change becomes earlier by accelerating the host vehicle A before the start of the lane change, the virtual arrival time ta to the crossing point X of the host vehicle A becomes shorter. In this way, the virtual arrival time ta shorter than the predicted arrival time tb becomes even longer, and thus the time difference td is outside the predetermined range. As shown in the figure, the position B 2 ′ of the oncoming vehicle B is located in the rear of the crossing point X at the time t2′ when the host vehicle A starts the lane change, and the host vehicle A advances toward the front of the oncoming vehicle B, and thus it is suppressed that the host vehicle A and the oncoming vehicle B travel so as to approach each other while facing each other. 
     In an example of  FIG.  5 B , the controller  180  (the lane change assistance unit  185 ) changes the travel route (the driving control information) during the lane change such that the steering angle of the host vehicle A during the lane change is larger than the angle that has already been set. Due to the change, the start time t2 of the lane change of the host vehicle A is not changed, and thus it is unnecessary to consider the start time t2′ of the lane change after the change as in the example shown in  FIG.  5 A . Similarly to  FIG.  4 B , in the figure, positions A 1  and A 2  of the host vehicle A and positions B 1  and B 2  of the oncoming vehicle B are shown corresponding to times t1 and t2, respectively. Regarding the virtual advancing route, which is the virtual extension of the advancing route of the host vehicle in the advancing direction during the lane change of the host vehicle A, the virtual advancing route before the correction is indicated by a dotted line, and the virtual advancing route after the correction is indicated by a broken line. 
     As shown in the figure, by making the steering angle larger than that before the change, the crossing point X is changed to a near side in the advancing direction of the host vehicle A, and thus the virtual arrival time ta until the host vehicle A virtually reaches the crossing point X becomes shorter. Further, since a distance between the oncoming vehicle B and the crossing point X increases, the predicted arrival time tb to the crossing point X of the oncoming vehicle B becomes longer. As a result, the virtual arrival time ta shorter than the predicted arrival time tb becomes even shorter, and at the same time, the predicted arrival time tb longer than the virtual arrival time ta becomes even longer, and thus the time difference td is outside the predetermined range. As shown in the figure, the position B 2 ′ of the oncoming vehicle B is located in the rear of the crossing point X at the time t2′ when the host vehicle A starts the lane change, and the host vehicle A advances toward the rear of the oncoming vehicle B, and thus it is suppressed that the host vehicle A and the oncoming vehicle B travel so as to approach each other while facing each other. 
     The determination of the crossing point X (S6) and the calculation of a time difference between the virtual arrival time ta and the predicted arrival time tb (S7) may be performed at a plurality of timings from the time t2 when the lane change is started to the time t3 when the lane change is ended. Accordingly, during the lane change from the start to the end of the lane change, it is possible to suppress the host vehicle A and the oncoming vehicle B from traveling so as to approach each other while facing each other. 
     In the present embodiment, as shown in  FIGS.  4 A to  5 B , an example in which the set route and speed of the host vehicle A is changed is used, but the present invention is not limited thereto. The time difference may be outside the predetermined range by changing both of the path and the speed instead of changing either of the path and the speed. 
     According to the first embodiment, the following effects can be obtained. 
     According to the travel assistance method of the first embodiment, the controller  180  determines the crossing point X between the predicted travel route of the oncoming vehicle B and the virtual advancing route of the host vehicle A during the lane change (S6). Further, the virtual arrival time ta until the host vehicle A virtually reaches the crossing point X and the predicted arrival time tb until the oncoming vehicle B reaches the crossing point X are obtained, and it is determined whether it is necessary to change the driving control information according to whether the time difference td between the virtual arrival time ta and the predicted arrival time tb is within the predetermined range (S7). 
     When the time difference td is within the predetermined range, there is a possibility that the host vehicle A and the oncoming vehicle B advance toward the crossing point X while facing each other at the same timing. Therefore, the controller  180  changes the driving control information such that the time difference td is outside the predetermined range (S8), and performs the driving assistance of the host vehicle A based on the changed driving control information (S9). 
     Here, when the oncoming vehicle B approaches the host vehicle A while facing each other, the driver of the host vehicle A does not prefer such a situation, and there is a possibility that the driver of the host vehicle A performs a driving operation to prevent both vehicles from traveling while facing each other. However, since the time difference td is outside the predetermined range by correcting the driving control information described above, the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. As a result, the behavior of the host vehicle A is suppressed from becoming an unstable point caused by the driver performing an operation during the driving assistance, and thus it is possible to improve stability of the driving assistance control. 
     According to the travel assistance method of the first embodiment, as shown in  FIG.  4 A , when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), the controller  180  (the lane change assistance unit  185 ) changes the speed information (the driving control information) so as to decelerate the host vehicle A before the start of the lane change. 
     Since the start time t2′ of the lane change is delayed by decelerating the host vehicle A before the start of the lane change, the virtual arrival time ta becomes longer. The virtual arrival time ta becomes longer in this way, and thus the time difference td is outside the predetermined range. Due to the change, at the time t2′ when the host vehicle A starts the lane change, the oncoming vehicle B is located further forward, and thus the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     Due to the change, the virtual arrival time ta longer than the predicted arrival time tb becomes even longer when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes) and when the virtual arrival time ta of the host vehicle A is longer (later) than the predicted arrival time tb of the oncoming vehicle B. As a result, at the time t2′ when the host vehicle A starts the lane change, the oncoming vehicle B is located further forward, and thus, the travel route of the host vehicle A becomes a travel route toward the rear of the oncoming vehicle B, and the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     As shown in  FIG.  4 B , when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), the controller  180  (the lane change assistance unit  185 ) changes the travel route (the driving control information) during the lane change such that the steering angle of the host vehicle A during the lane change becomes smaller. 
     By reducing the steering angle, the crossing point X is changed to the front side in the advancing direction of the host vehicle A, and thus the virtual arrival time ta becomes longer. Further, since the distance between the oncoming vehicle B and the crossing point X decreases, the predicted arrival time tb becomes shorter. Due to the change, the virtual arrival time ta becomes longer, and at the same time, the predicted arrival time tb becomes shorter, and thus the time difference td is outside the predetermined range. Due to the change, at the time t2 when the host vehicle A starts the lane change, the crossing point X is located further rearward, and the oncoming vehicle B is located further forward, and thus the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     When the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), and when the virtual arrival time ta of the host vehicle A is longer (later) than the predicted arrival time tb of the oncoming vehicle B, due to the change, the virtual arrival time ta longer than the predicted arrival time tb becomes even longer, and at the same time, the predicted arrival time tb shorter than the virtual arrival time ta becomes even shorter, and thus the virtual arrival time ta longer than the predicted arrival time tb becomes even longer. As a result, at the time t2′ when the host vehicle A starts the lane change, the crossing point X is located further rearward, and the oncoming vehicle B is located further forward, and thus, the travel route of the host vehicle A becomes a travel route toward the rear of the oncoming vehicle B and the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     As shown in  FIG.  4 C , when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), the controller  180  (the lane change assistance unit  185 ) changes the travel route (the driving control information) during the lane change such that the start position of the lane change is on the front side in the advancing direction of the host vehicle A. 
     By changing the start position of the lane change to the front side, the crossing point X is changed to the front side, and thus the virtual arrival time ta becomes longer. Further, since the distance between the oncoming vehicle B and the crossing point X decreases, the predicted arrival time tb becomes shorter. In this way, the virtual arrival time ta becomes longer, and at the same time, the predicted arrival time tb becomes shorter, and thus the time difference td is outside the predetermined range. Due to the change, at the time t2′ when the host vehicle A starts the lane change, the crossing point X is located further rearward, and the oncoming vehicle B is located further forward, and thus the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     When the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), and when the virtual arrival time ta of the host vehicle A is longer (later) than the predicted arrival time tb of the oncoming vehicle B, due to such a change, the virtual arrival time ta longer than the predicted arrival time tb becomes even longer, and at the same time, the predicted arrival time tb shorter than the virtual arrival time ta becomes even shorter, and thus the time difference td is outside the predetermined range. As a result, the crossing point X is located further rearward, and the oncoming vehicle B is located further forward, and thus, the travel route of the host vehicle A becomes a travel route toward the rear of the oncoming vehicle B and the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     As shown in  FIG.  5 A , when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), the controller  180  (the lane change assistance unit  185 ) changes the speed information (the driving control information) so as to accelerate the host vehicle A before the start of the lane change. 
     Since the start time t2′ of the lane change becomes earlier by accelerating the host vehicle A before the start of the lane change, the virtual arrival time ta becomes shorter. The virtual arrival time ta becomes shorter in this way, and thus the time difference td is outside the predetermined range. Due to the change, at the time t2′ when the host vehicle A starts the lane change, the oncoming vehicle B is located further rearward, and thus the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     When the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), and when the virtual arrival time ta of the host vehicle A is shorter (earlier) than the predicted arrival time tb of the oncoming vehicle B, the virtual arrival time ta shorter than the predicted arrival time tb becomes even shorter due to such a change, and thus the time difference td is outside the predetermined range. As a result, at the time t2′ when the host vehicle A starts the lane change, the oncoming vehicle B is located further rearward, and thus, the travel route of the host vehicle A becomes a travel route toward the front of the oncoming vehicle B and the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     As shown in  FIG.  5 B , when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), the controller  180  (the lane change assistance unit  185 ) changes the travel route (the driving control information) during the lane change such that the steering angle of the host vehicle A during the lane change becomes larger. 
     By increasing the steering angle, the crossing point X is changed to the near side in the advancing direction of the host vehicle A, and thus the virtual arrival time ta to the crossing point X of the host vehicle A becomes shorter. Further, since the distance between the oncoming vehicle B and the crossing point X increases, the predicted arrival time tb to the crossing point X of the oncoming vehicle B becomes longer. Therefore, the virtual arrival time ta becomes shorter, and at the same time, the predicted arrival time tb becomes longer, and thus the time difference td is outside the predetermined range. Due to the change, at the time t2′ when the host vehicle A starts the lane change, the crossing point X is located further forward, and the oncoming vehicle B is located further rearward, and thus the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     When the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), and when the virtual arrival time ta of the host vehicle A is shorter (earlier) than the predicted arrival time tb of the oncoming vehicle B, due to such a change, the virtual arrival time ta shorter than the predicted arrival time tb becomes even shorter, and at the same time, the predicted arrival time tb longer than the virtual arrival time ta becomes even longer, and thus the time difference td is outside the predetermined range. As a result, at the time t2′ when the host vehicle A starts the lane change, the crossing point X is located further forward, and the oncoming vehicle B is located further rearward, and thus, the travel route of the host vehicle A becomes a travel route toward the front of the oncoming vehicle B and the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     Although not illustrated, when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), the controller  180  (the lane change assistance unit  185 ) may change the driving control information such that the start position of the lane change is in the rear of the host vehicle A. 
     Since the crossing point X is changed to the rear side by changing the start position of the lane change to the rear side of the host vehicle A, the virtual arrival time ta to the crossing point X of the host vehicle A becomes shorter. Further, since the distance between the oncoming vehicle B and the crossing point X increases, the predicted arrival time tb to the crossing point X of the oncoming vehicle B becomes longer. Therefore, the virtual arrival time ta becomes shorter, and at the same time, the long predicted arrival time tb becomes even longer, and thus the time difference td is outside the predetermined range. As a result, at the time t2′ when the host vehicle A starts the lane change, the crossing point X is located further forward, and the oncoming vehicle B is located further rearward, and thus the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     When the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes), and when the virtual arrival time ta of the host vehicle A is shorter (earlier) than the predicted arrival time tb of the oncoming vehicle B, due to such a change, the virtual arrival time ta shorter than the predicted arrival time tb becomes even shorter, and at the same time, the predicted arrival time tb longer than the virtual arrival time ta becomes even longer, and thus the time difference td is outside the predetermined range. As a result, at the time t2′ when the host vehicle A starts the lane change, the crossing point X is located further forward, and the oncoming vehicle B is located further rearward, and thus, the travel route of the host vehicle A becomes a travel route toward the front of the oncoming vehicle B and the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     (Modification) 
     In the first embodiment, the controller  180  changes the route and the speed indicated by the driving control information as shown in  FIGS.  4 A to  4 C,  5 A, and  5 B  according to whether the time difference td between the virtual arrival time ta and the predicted arrival time tb is within the predetermined range. 
     Here, as described above,  FIGS.  4 A to  4 C  show the examples in which the driving control information is changed when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes) and when the virtual arrival time ta of the host vehicle A is longer (later) than the predicted arrival time tb of the oncoming vehicle B.  FIGS.  5 A and  5 B  show the examples in which the driving control information is changed when the time difference td is within the predetermined range and the correction is determined to be necessary (S7: Yes) and when the virtual arrival time ta is shorter (earlier) than the predicted arrival time tb. 
     Therefore, a change (a first change) shown in  FIGS.  4 A to  4 C  and a change (a second change) shown in  FIGS.  5 A and  5 B  may be switched according to a magnitude relation between the virtual arrival time ta and the predicted arrival time tb. 
       FIG.  6    is a flowchart of travel assistance control according to the present modification. According to the flowchart, as compared with the travel assistance control of the first embodiment shown in  FIG.  2   , determination processing of step S 71  is provided after step S7, and a change of step S 81  or step S 82  is selectively performed according to the determination processing of step S 71 . 
     In step S 71 , the controller  180  (the change necessity determination unit  184 ) determines whether the virtual arrival time ta is longer than the predicted arrival time tb. 
     When the virtual arrival time ta is longer than the predicted arrival time tb (S 71 : Yes), as shown in  FIGS.  4 A to  4 C , change processing of step S 81  is performed next such that the host vehicle A travels toward the rear of the oncoming vehicle B. In step S 81 , the driving control information is changed such that the travel route of the host vehicle A becomes a travel route toward the rear of the oncoming vehicle B. 
     On the other hand, when the virtual arrival time ta is shorter than the predicted arrival time tb (S 71 : No), as shown in  FIGS.  5 A and  5 B , change processing of step S 82  is performed next such that the host vehicle A travels toward the front of the oncoming vehicle B. In step S 82 , the driving control information is changed such that the travel route of the host vehicle A becomes a travel route toward the front of the oncoming vehicle B. 
     According to the travel assistance method in such a modification, when a time difference td between a virtual arrival time tx and a predicted arrival time tb is within a predetermined range (S7: Yes) and the virtual arrival time ta is longer than the predicted arrival time tb (S 71 : Yes), the driving control information shown in  FIGS.  4 A to  4 C  is changed such that the host vehicle A travels toward the rear of the oncoming vehicle B (S 81 ). In this way, the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other, and a behavior of the host vehicle A is suppressed from becoming an unstable point caused by the driver performing an operation during the driving assistance, and thus it is possible to improve stability of the driving assistance control. 
     When the time difference td between the virtual arrival time tx and the predicted arrival time tb is within the predetermined range (S7: Yes) and the virtual arrival time ta is shorter than the predicted arrival time tb (S 71 : No), the driving control information shown in  FIGS.  5 A and  5 B  is changed such that the host vehicle A travels toward the front of the oncoming vehicle B (S 82 ). In this way, the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other, and the behavior of the host vehicle A is suppressed from becoming the unstable point caused by the driver performing an operation during the driving assistance, and thus it is possible to improve stability of the driving assistance control. 
     Second Embodiment 
     In the first embodiment, the controller  180  predicts the virtual arrival time ta (a first time) to the crossing point X and the predicted arrival time tb (a second time) until the oncoming vehicle B reaches the crossing point X, and determines whether it is necessary to change the driving control information according to whether the time difference td between the virtual arrival time ta (the first time) and the predicted arrival time tb (the second time) is within the predetermined range, but the present invention is not limited thereto. In the second embodiment, an example will be described in which the controller  180  sets a crossing region Y in a vicinity of the crossing point X, and determines whether a change is necessary according to whether the time difference td is within a predetermined range or the oncoming vehicle B is present in the crossing region Y at the virtual arrival time ta. 
     Specifically, as shown in  FIG.  7   , the controller  180  sets an crossing region Y having a predetermined region length in a front-rear direction along an advancing route direction of the oncoming vehicle B with the crossing point X as a center. The controller  180  obtains a virtual arrival time tx in a case where it is assumed that the host vehicle A advances linearly on a virtual advancing route and reaches the crossing point X without completing a lane change. 
     The controller  180  estimates a position Bx of the oncoming vehicle B at the virtual arrival time tx, and determines whether correction is necessary according to whether the estimated position Bx of the oncoming vehicle B is present in the crossing region Y. When the position Bx is within the crossing region Y, the host vehicle A and the oncoming vehicle B travel toward the crossing point X while facing each other at the same timing, and there is a high possibility that both vehicles approach each other, and thus it is determined that the correction of the driving control information is necessary. 
       FIG.  8    is a flowchart of travel assistance control according to the second embodiment. According to the flowchart, as compared with the travel assistance control of the first embodiment shown in  FIG.  2   , processing of step S 61  is provided after step S6. 
     In step S 61 , the controller  180  sets an crossing region Y having a predetermined region length in a front-rear direction along an advancing route direction of the oncoming vehicle B with the crossing point X as a center. Here, the region length may be a fixed value obtained by multiplying a speed of the oncoming vehicle B by the time difference td, or may be a variable value as shown in a modification to be described later. 
     In step S7, the controller  180  estimates a position Bx of the oncoming vehicle B at the virtual arrival time tx, and determines whether correction is necessary according to whether the estimated position Bx of the oncoming vehicle B is present in the crossing region Y. When the position Bx of the oncoming vehicle B at the virtual arrival time tx is within the crossing region Y, it is determined that the correction of the driving control information is necessary. 
     In this way, when the position Bx of the oncoming vehicle B at the virtual arrival time tx is within the crossing region Y, it is determined that the correction of the driving control information is necessary (S7: Yes), and then correction processing of step S8 is performed. When the position Bx of the oncoming vehicle B is outside the crossing region Y, it is determined that the correction of the driving control information is unnecessary (S7: No), and then assistance processing of step S9 is performed. 
     According to the travel assistance method of the second embodiment, as shown in  FIG.  7   , the controller  180  determines the crossing point X between the predicted travel route of the oncoming vehicle B and the virtual advancing route of the host vehicle A during the lane change (S6), and further determines the crossing region Y having the region length in the front-rear direction of the oncoming vehicle B with respect to the crossing point X (S 61 ). Then, the controller  180  determines whether the oncoming vehicle B is present in the crossing region Y at the virtual arrival time tx predicted on an assumption that the host vehicle A reaches the crossing point X (S7). 
     When the oncoming vehicle B is present in the crossing region Y, the host vehicle A and the oncoming vehicle B advance toward the crossing point X while facing each other. Therefore, the controller  180  changes the driving control information (S8), and performs the driving assistance of the host vehicle A based on the changed driving control information (S9), thereby performing control such that the oncoming vehicle B is not present in the crossing region Y at the virtual arrival time tx. Specifically, when the correction as shown in  FIGS.  4 A to  4 C  is performed, the oncoming vehicle B is located in front of the crossing region Y at the virtual arrival time tx, and when the correction as shown in  FIGS.  5 A and  5 B  is performed, the oncoming vehicle B is located in the rear of the crossing region Y at the virtual arrival time tx. 
     Here, in a case where the oncoming vehicle B is present in the crossing region Y at the virtual arrival time tx, before the virtual arrival time tx, the host vehicle A and the oncoming vehicle B advance toward the crossing point X while facing each other at the same timing, and thus both vehicles approach each other. Due to such approach, the driver of the host vehicle A may perform a driving operation to prevent both vehicles from traveling while facing each other. However, since the oncoming vehicle B is outside the crossing region Y at the virtual arrival time tx by correcting the driving control information described above, the host vehicle A and the oncoming vehicle B are suppressed from approaching each other while facing each other. 
     As described above, according to the travel assistance method of the second embodiment, it is possible to determine whether it is necessary to correct the driving control information by obtaining the crossing region Y and the position Bx of the oncoming vehicle B at the virtual arrival time tx instead of calculating the predicted arrival time tb as in the first embodiment. As a result, flexibility of a design method is improved, and the behavior of the host vehicle A is suppressed from becoming an unstable point caused by the driver performing an operation during the driving assistance, and thus it is possible to improve stability of the driving assistance control. 
     (Modification) 
     In the first and second embodiments, the crossing region Y is set so as to have the predetermined region length in the front-rear direction of the oncoming vehicle B with respect to the crossing point X. In the present modification, an example in which the region length of the crossing region Y in the front-rear direction is changed by an external factor will be described. 
     As a first example, the faster a relative speed between the host vehicle A and the oncoming vehicle B, the longer a region length of a crossing range in the front-rear direction. As the relative speed increases, the driver of the host vehicle A tends not to prefer that the oncoming vehicle B approaches the host vehicle A while facing each other. Therefore, by increasing the region length of the crossing region Y as the relative speed between the host vehicle A and the oncoming vehicle B increases, the oncoming vehicle B is more likely to be included in the crossing region Y, and thus the driving control information is more likely to be changed. As a result, it is possible to suppress the host vehicle A and the oncoming vehicle B approaching each other. 
     As a second example, the narrower a road width of the host vehicle A or the oncoming vehicle B, the longer the region length of the crossing region Y. As the road width is narrower, the driver of the host vehicle A tends not to prefer that the oncoming vehicle B approaches the host vehicle A while facing each other. Therefore, by further increasing the region length of the crossing region Y as road widths of the host vehicle A and the oncoming vehicle B are narrower, the oncoming vehicle B is more likely to be included in the crossing region Y, and thus the driving control information is more likely to be changed. As a result, it is possible to suppress the host vehicle A and the oncoming vehicle B approaching each other. 
     Similarly, as the host vehicle A or the oncoming vehicle B is smaller, the driver of the host vehicle A tends not to prefer that the oncoming vehicle B approaches the host vehicle A while facing each other. For example, the controller  180  may determine a size of the host vehicle A or the oncoming vehicle B based on a vehicle type of the host vehicle A stored in advance or an outer shape of the oncoming vehicle B imaged by the camera  110 . In another example, the controller  180  may set the region length in accordance with a vehicle width of the host vehicle A or the oncoming vehicle B. 
     In this way, by the controller  180  further increasing the region length of the crossing region Y as the host vehicle A and the oncoming vehicle B are smaller, the oncoming vehicle B is more likely to be included in the crossing region Y, and thus the driving control information is more likely to be changed. As a result, it is possible to suppress the host vehicle A and the oncoming vehicle B approaching each other. 
     Third Embodiment 
     In the first or second embodiment, a case where one oncoming vehicle B is traveling in the opposite lane has been described, but the present invention is not limited thereto. In the third embodiment, it may be determined whether the correction of the driving control information is necessary in a case where a plurality of oncoming vehicles B are present. 
     When detecting a plurality of oncoming vehicles B traveling in an opposite lane of an advancing route after a lane change, the controller  180  determines whether it is necessary to change the driving control information for the plurality of oncoming vehicles B. When it is determined that it is necessary to change the driving control information for at least one oncoming vehicle B, the driving control information is changed. However, for a purpose of reducing a processing load, the necessity of the change may not be determined for some oncoming vehicles B. Such a situation will be described with reference to  FIGS.  9  to  11   . 
       FIGS.  9  and  10    are diagrams showing a situation in which travel assistance control according to the third embodiment is performed. According to the figures, the host vehicle A and a plurality of oncoming vehicles D 1  to D 3  are shown. 
     In an example of  FIG.  9   , oncoming vehicles D 1 , D 2 , and D 3  travel in the opposite lane in an order of an advancing direction. The oncoming vehicles D 1  and D 3  are traveling in an inner travel lane, and the oncoming vehicle D 2  is traveling in an outer opposite lane. It is assumed that the oncoming vehicle D 1  intends to change a lane to an outer lane. It is assumed that the controller  180  can predict an advancing route of each of the oncoming vehicles D 1  to D 3  using imaging information of the camera  110 . 
     In such a case, the controller  180  omits the determination of whether it is necessary to change the driving control information for the oncoming vehicle D 2  advancing linearly in the outer lane and the oncoming vehicle D 1  attempting to change the lane to the outer lane, and determines whether it is necessary to change the driving control information for the oncoming vehicle D 3  traveling in the inner lane. In this way, it is possible to reduce the number of target oncoming vehicles D, and thus it is possible to reduce the processing load of the travel assistance control. 
     In an example of  FIG.  10   , oncoming vehicles D 1 , D 2 , and D 3  travel in the opposite lane in an order of an advancing direction. The oncoming vehicles D 1  and D 2  are traveling in an outer travel lane, and the oncoming vehicle D 3  is traveling in an inner opposite lane. It is assumed that the oncoming vehicle D 1  intends to change a lane to an inner lane, and the oncoming vehicle D 3  intends to change a lane to an outer lane. 
     In such a case, the controller  180  omits the determination of whether it is necessary to change the driving control information for the oncoming vehicle D 2  advancing linearly in the outer lane and the oncoming vehicle D 3  changing the lane to the outer lane, and determines whether it is necessary to change the driving control information for the oncoming vehicle D 1  changing the lane to the inner lane. In this case, a crossing point X between a virtual advancing route of the host vehicle A during the lane change and a predicted travel route of the oncoming vehicle D 1  that performs the lane change is determined. In this way, it is possible to reduce the number of the target oncoming vehicles D, and thus it is possible to reduce the processing load of the travel assistance control. 
     As shown in  FIG.  11   , in a case where a median strip E is present between the travel lane of the host vehicle A and the opposite lane in which the oncoming vehicle B travels, even if the host vehicle A and the oncoming vehicle B advance toward the crossing point X, the driver of the host vehicle A is less likely to feel anxiety. Therefore, it is possible to reduce the processing load of the travel assistance control by omitting the change control of the driving control information. 
     Fourth Embodiment 
     In the first to third embodiments, the lane change performed by the host vehicle has been described, but the present invention is not limited thereto. In the fourth embodiment, an example of a lane change will be described in which a host vehicle turns and enters the linear advancing lane from a side road at a T junction where the linear advancing lane and the side road intersect with each other. 
       FIGS.  12  and  13    are diagrams showing a situation in which travel assistance control according to the fourth embodiment is performed. 
     In an example of  FIG.  12   , it is assumed that at a T intersection where a travel lane of one lane on each side intersects with a side road, a lane change is performed such that a host vehicle A turns and enters the travel lane from the side road. In the lane change, a left turn is made at the T intersection to enter a travel lane on a side adjacent to the side road, instead of making a right turn at the T intersection crossing an opposite lane. 
     Regarding the host vehicle A, a host vehicle A 1  at a time t1 when the lane change (turning) is started, a host vehicle A 2  at a time t2 when the host vehicle A is turning, and a host vehicle A 3  at a time t3 when the lane change (turning) is ended are shown. Similarly, regarding the oncoming vehicle B, oncoming vehicles B 1  to B 3  corresponding to times t1 to t3 are shown. 
     Also in such a case, the controller  180  obtains a crossing point X between a predicted travel lane of the oncoming vehicle B and a virtual advancing route being a virtual extension of an advancing route of the host vehicle A in an advancing direction during the lane change. A virtual arrival time ta until the host vehicle A reaches the crossing point X and a predicted arrival time tb until the oncoming vehicle B reaches the crossing point X may be obtained, and it may be determined whether it is necessary to change driving control information according to whether a time difference td between the virtual arrival time ta and the predicted arrival time tb is within a predetermined range. 
     In the figure, a following vehicle F is shown on a right side of the host vehicle A during the lane change, that is, behind the host vehicle A after the lane change. The controller  180  may determine a crossing point according to a crossing point between a virtual advancing route during turning of the host vehicle A and a predicted advancing route of the following vehicle F, and may determine whether it is necessary to change the driving control information according to a time difference between a time until the host vehicle A reaches the crossing point and a predicted time until the following vehicle F reaches the crossing point. In this way, it is possible to suppress the host vehicle A and the following vehicle F from approaching each other. 
       FIG.  13    shows an example in which the host vehicle A turns toward a main lane when the oncoming vehicle B is a two-wheeled vehicle on a T junction without a lane. Even in this case, by performing the travel assistance control, the controller  180  may determine whether the driving control information is changed by determining a crossing region Y from a crossing point X between a virtual advancing route during turning of the host vehicle A and a predicted travel lane of the oncoming vehicle B and determining whether the oncoming vehicle B is within the crossing region Y at a virtual arrival time tx. 
     The travel assistance control described above is not limited to a case where the host vehicle performs a lane change such as changing a lane or a travel route as described above, and includes a case where the host vehicle starts from a road shoulder. 
     Although the embodiments of the present invention have been described above, the embodiments merely exemplify some of application examples of the present invention and do not intend to limit the technical scope of the present invention to the specific configurations of the embodiments. 
     Each of the embodiments described above has been described as a single embodiment, but may be appropriately combined.