Patent Publication Number: US-2023154334-A1

Title: Driving assistance apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-185413 filed on Nov. 15, 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a driving assistance apparatus that assists a driving operation of a driver. 
     Description of the Related Art 
     Conventionally, as an apparatus of this type, there is a known apparatus that that notifies a driver of a vehicle of an approach of a railway vehicle is known. Such a device is described, for example, in in Japanese Unexamined Patent Publication No. 2008-293269 (JP2008-293269A). In the apparatus described in JP2008-293269A, when a vehicle turns right across a track of a railway vehicle, the approach of the railway vehicle is detected by the road-to-vehicle communication, and the approach of the railway vehicle is notified to the driver. 
     However, the apparatus described in JP2008-293269A require a communication beacon to be installed on a road or on a track of a railway vehicle, resulting in an increase in cost. Therefore, it is desired to provide an apparatus that suppresses a decrease in the smoothness of traffic while suppressing an increase in cost and improving the safety of the traffic without hindering the traffic flow in the vicinity. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is a driving assistance apparatus, configured to assist a driving by a driver of a subject vehicle, the subject vehicle locating on a side of a travel path on which a railway vehicle travels. The driving assistance apparatus includes an approach detection part detecting an approach of the railway vehicle along the travel path from a diagonally backward of the subject vehicle to the subject vehicle without using a road-to-vehicle communication, a notification part notifying the driver of information, and an electronic control unit including a microprocessor and a memory connected to the microprocessor. The microprocessor is configured to perform estimating a traveling direction of the subject vehicle at an intersection, and controlling the notification part so as to notify the driver of the approach of the railway vehicle when the traveling direction crossing the travel path is estimated and the approach of the railway vehicle to the subject vehicle is detected by the approach detection part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, and advantages of the present invention will become clearer from the following description of embodiments in relation to the attached drawings, in which: 
         FIG.  1    is a diagram showing an example of a travel scene to which a driving assistance apparatus according to an embodiment of the present invention is applied; 
         FIG.  2    is a block-diagram illustrating a configuration of a main part of the driving assistance apparatus according to the embodiment of the present invention; 
         FIG.  3    is a diagram showing an example of the travel scene different from those in  FIG.  1   ; 
         FIG.  4    is a flowchart illustrating an example of processing executed by a controller in  FIG.  2   ; 
         FIG.  5    is a block-diagram showing a modification of  FIG.  2   ; and 
         FIG.  6    is a block-diagram showing another modification of  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention is explained with reference to  FIGS.  1  to  6   . The driving assistance apparatus according to an embodiment of the present invention is configured to assist driving of a driver of a vehicle on a road on which a railway vehicle travels along a railroad track laid on a road, i.e., on the road which a tram travels. In such a road on which the tram travels, a driving assistance suitable for the situation is required. 
       FIG.  1    is diagrams showing an example of travel scene to which the driving assistance apparatus according to the embodiment of the present invention is applied.  FIG.  1    shows an intersection  103  where a road  101  and a road  102  intersect. A railroad track  200  is laid at a central portion LN 0  in a width direction (referred to as a central lane for convenience) of the road  101 . A tram  201  travels along the railroad track  200 . The road  101  includes a first lane LN 1  and a second lane LN 2  adjoining each other. The first lane LN 1  is a lane for straight travel and left turn of the intersection  103 , and the second lane LN 2  is a lane for right turn. The second lane LN 2  extends adjacently to the central lane LN 0 . 
     The subject vehicle  110  is located in the second lane LN 2 . In the first lane LN 1 , another vehicle  111  is located behind the subject vehicle  110 . The configurations of the roads  101  and  102  are not limited to those described above. For example, the road  101  may be one lane or three lanes or more, rather than two lanes on one side. The second lane LN 2  may be a right-turn enabled lane instead of a right-turn dedicated lane. 
     At the intersection  103 , a traffic light  120  is installed. A plurality of traffic lights  120  are installed at the intersection  103  in association with vehicles entering the intersection  103  from the respective directions, but for convenience, a single traffic light  120  is illustrated in  FIG.  1   . The traffic light  120  includes a main traffic light  121  configured to be capable of switching between a red light indicating a stop command, a green light indicating that traveling is possible, and a yellow light indicating that traveling is possible but safe stop is difficult, and an auxiliary traffic light  122  attached to the main traffic light  121 . 
     The auxiliary traffic light  122  is an arrow traffic light indicating a direction in which a vehicle can travel by using an arrow. More specifically, the auxiliary traffic light  122  includes arrows indicating a straight direction, a left-turn direction, and a right-turn direction and makes notification of a direction in which the vehicle can travel by turning on the arrows. In  FIG.  1   , a main traffic light  121  is red, the arrows indicating the straight direction and the left-turn direction are turned on, and the arrow indicating the right-turn direction is turned off. Therefore, the subject vehicle  110  located in the second lane LN 2  stops at a stop line  104  before the intersection  103  while causing a turn signal lamp to blink. The other vehicle  111  located in the first lane LN 1  passes by the subject vehicle  110  and passes through the intersection  103  or turns left. 
     The traffic light  120  includes not only the traffic lights  121  and  122  for vehicles but also a traffic light  123  for trams. The traffic light  123  is an arrow traffic light indicating a direction in which the tram  201  can travel by using an arrow. The auxiliary traffic light  122  for vehicles is turned on with green arrows, whereas the traffic light  123  is turned on with, for example, a yellow arrow. In  FIG.  1   , the arrow of the traffic light  123  is turned on, and the tram  201  can travel without stopping at the intersection  103 . 
     In such a traveling scene, a driver of the subject vehicle  110  may feel unexpected when the tram  201  approaches from the diagonally back side of the subject vehicle  110  stopped in the second lane LN 2  and passes by the subject vehicle  110 . In particular, when a driver is unfamiliar with driving on a road on which the tram  201  travels, the driver does not expect that the tram  201  passes by the subject vehicle  110 , in particular, passes on the right side thereof, and thus is greatly surprised. In such a situation, for example, in order to notify the driver of the approach of the tram  201  by road-to-vehicle communication, it is necessary to install communication facilities such as an optical beacon and a radio beacon on the road. This leads to an increase in cost. In view of this, the present embodiment provides a driving assistance apparatus as described below in order to favorably notify the driver of the approach of the tram  201  while suppressing the increase in cost. 
       FIG.  2    is a block-diagram schematically illustrating a configuration of a main part of the driving assistance apparatus  100  according to the embodiment of the present invention. As shown in  FIG.  2   , the driving assistance apparatus  100  includes a controller  20 , and a radar sensor  1 , a vehicle speed sensor  2 , a positioning sensor  3 , a turn signal switch  4  and a display portion  5  which are communicably connected to the controller  20 , respectively. 
     The radar sensor  1  is attached to the left and right rear end portions (for example, in the rear bumper) of the subject vehicle, and detects the position of the object around the subject vehicle (in particular, obliquely behind) by the reflected wave from the object. Specifically, the radar sensor  1  includes a radar that detects the presence or absence of an object on the left and right rear sides of the subject vehicle and the distance to the object by emitting electromagnetic waves and detecting reflected waves, and a LIDAR that detects the position of the object on the left and right rear sides of the subject vehicle and the distance to the object by emitting laser light, which is a kind of electromagnetic waves, and detecting reflected light. 
     The vehicle speed sensor  2  detects the vehicle speed of the subject vehicle. The positioning sensor  3  receives positioning signals transmitted from positioning satellites such as GPS satellites and quasi-zenith satellites. The current position of the subject vehicle can be calculated using the position information received by the positioning sensor  3 . The turn signal switch  4  detects an operation of a direction indicator by the driver. The direction indicator is a device for indicating the direction to the surroundings at the time of the right-left turn or the course change of the subject vehicle, and is constituted by a turn signal lever or the like. 
     A display portion  5  includes indicator lamps provided on left and right side-view mirrors. More specifically, the display portion  5  is provided around or on a mirror surface of each of the left and right side-view mirrors. When an object on the back right side of the subject vehicle is detected, the display portion  5  of the right side-view mirror is turned on or blinks, whereas, when an object on the back left side is detected, the display portion  5  of the left side-view mirror is turned on or blinks. Therefore, in a case where the driver cannot recognize existence of another vehicle via the side-view mirrors due to poor visibility or the like, the driver can recognize the existence of the other vehicle via the display portions  5  and thus can safely change lanes, for example. The display portions  5  may be provided at any positions as long as the driver can visually recognize the display portions  5  at the same time when the driver checks whether or not an object exists on the back left or right side of the subject vehicle. Thus, the display portions  5  may be provided at positions other than the side-view mirrors. For example, the display portions  5  may be provided at positions in a vehicle interior (e.g. left and right A-pillars of the subject vehicle) near the side-view mirrors. 
     The controller  20  includes an electronic control unit having a microprocessor and a memory connecting the microprocessor. More specifically, the controller  20  includes a computer including a CPU, a ROM, a RAM, and other peripheral circuits such as an I/O interface. The controller  20  includes, as functional components, an approach recognition unit  21 , a direction estimation unit  22  and a display control unit  23 . The memory of the controller  20  stores road information in advance. The road information includes information on lanes in which the tram ( FIG.  1   ) travels. 
     The approach recognition unit  21  determines whether or not an object such as another vehicle or a tram exists around the subject vehicle within a predetermined distance from the subject vehicle on the basis of a signal from the radar sensor  1 . That is, the approach recognition unit recognizes an approach operation of an object approaching the subject vehicle from the diagonally back side of the subject vehicle. 
     The direction estimation unit  22  estimates a direction in which the subject vehicle travels on the basis of a signal from the turn signal switch  4 . For example, the direction estimation unit estimates that the subject vehicle is to change lanes or turn right or left. 
     The display control unit  23  first determines whether or not the subject vehicle is located on the side of the center lane LN 0  ( FIG.  1   ) on which the tram  201  travels on the basis of road map information stored in the memory and a signal from the positioning sensor  3 . The display control unit may determine whether or not the subject vehicle is located on the side of the center lane LN 0  on the basis of an image captured by an in-vehicle camera. The display control unit may determine whether or not the subject vehicle is located on the side of the center lane LN 0  when a position of the subject vehicle detected by the positioning sensor  3  is within a predetermined distance from the center lane LN 0 . 
       FIG.  3    illustrates an example of a traveling scene where there is no lane for trams on the side of a traveling lane (second lane LN 2 ) on which the subject vehicle  110  travels, that is, where the subject vehicle is not located on the side of the center lane LN 0  on which the tram  201  travels. In this case, the display control unit  23  controls the display portions  5  as follows. When a vehicle speed v of the subject vehicle  110  detected by the vehicle speed sensor  2  is equal to or larger than a predetermined value v1 and the approach recognition unit  21  recognizes an approach operation of the other vehicle  111  from the diagonally back side of the subject vehicle  110  as illustrated in  FIG.  3   , the display control unit  23  turns on the display portion  5  on the side (left side) on which the other vehicle  111  is detected between the left and right display portions  5 . The predetermined value v1 is set to a value larger than zero (e.g. 20 km/h). Therefore, the display portions  5  are turned on when the subject vehicle  110  is traveling. Accordingly, the driver can recognize the existence of the other vehicle  111  even when the other vehicle  111  diagonally behind the subject vehicle  110  does not appear in the side-view mirrors. 
     Thereafter, when the direction estimation unit  22  estimates that the subject vehicle  110  moves to the side (left side) on which the other vehicle  111  is detected, the display control unit  23  causes the display portion  5  to blink. Therefore, the driver can change lanes safely, while recognizing the existence of the other vehicle  111  behind. At the same time when the display portion  5  blinks, a warning sound may be emitted from a speaker in the vehicle interior. In a case where the vehicle speed detected by the vehicle speed sensor  2  is smaller than the predetermined value v1 (e.g. while the vehicle is stopped), the display portion  5  is not turned on or does not blink even if the other vehicle  111  is detected on the diagonally back side. 
     Meanwhile, as illustrated in  FIG.  1   , when the subject vehicle  110  is located on the side of the center lane LN 0  and the approach recognition unit  21  recognizes an approach operation of the tram  201  from the diagonally back side of the subject vehicle  110 , the display control unit  23  controls the display portions  5  as follows. In this case, when the vehicle speed v detected by the vehicle speed sensor  2  is equal to or smaller than a predetermined value v2 (e.g. 3 km/h) and the direction estimation unit  22  estimates that the subject vehicle  110  moves to cross a railroad track  200  after the signal light turns green, the display control unit  23  turns on the display portion  5  or causes the display portion  5  to blink. Therefore, the driver who has stopped the subject vehicle to wait for the traffic light to change in front of the intersection  103  can easily recognize that the tram  201  approaches from the diagonally back side. At the same time when the display portion  5  is displayed, a warning sound may be emitted from the speaker in the vehicle interior. The predetermined value v2 may be 0 km/h. 
     Even when the approach recognition unit  21  recognizes the approach operation of the tram  201 , the display control unit  23  does not turn on the display portion  5  or cause the display portion  5  to blink while the subject vehicle is travelling at the vehicle speed v detected by the vehicle speed sensor  2  larger than the predetermined value v2. Even when the vehicle speed v is equal to or smaller than the predetermined value v2, the display control unit  23  does not turn on the display portion  5  or cause the display portion  5  to blink in a case where the direction estimation unit  22  does not estimate that the subject vehicle  110  moves to cross the railroad track  200  ( FIG.  1   ) (e.g. turns right), that is, in a case where the direction estimation unit estimates that the subject vehicle  110  travels straight or turns left at the intersection  103 . 
       FIG.  4    is a flowchart showing an example of processing executed by the controller  20  (microprocessor) in  FIG.  2   . The processing shown in the flowchart starts when, for example, a power key switch is turned on and is repeated at predetermined cycles. 
     First, In S 1 , the controller refers to the road map information stored in the memory, and determines whether or not the subject vehicle  110  is located on the side of the railroad track  200  for the road surface train based on the signal from the positioning sensor  3 . If a negative decision is made in S 1 , the processing proceeds to S 2 , and the controller determines whether or not the vehicle speed v of the subject vehicle  110  detected by the vehicle speed sensor  2  is equal to or larger than the predetermined v1, that is, whether or not the subject vehicle  110  is traveling at the predetermined vehicle speed V1 or larger. If a negative decision in S 2  is made, the processing proceeds to S 3 , and the controller outputs a control signal to the display portions  5  so as to turn off the display portions  5 . 
     If an affirmative decision in S 2  is made, the processing proceeds to S 4 , and the controller determines whether or not the other vehicle  111  is recognized obliquely behind the subject vehicle  110  based on a signal from the radar sensor  1 . If an affirmative decision in S 4  is made, the processing proceeds to S 5 , and if a negative decision is made, the processing proceeds to S 3 . In S 5 , the controller determines whether or not the turn signal switch  4  is turned on. If a negative decision in S 5  is made, the processing proceeds to S 6 , and the controller makes the display portion  5  in the side-view mirror on the side on which the other vehicle  111  is recognized turn on. On the other hand, if an affirmative decision in S 5  is made, the processing proceeds to S 7 , and the controller makes the display portion  5  in the side-view mirror on the side on which the other vehicle  111  is recognized blink. The warning sound may be output simultaneously with the blinking of the display portion  5 . 
     If the controller determines in S 1  that the subject vehicle  110  is located on the side of the railroad track  200  for the tram, the processing proceeds to S 8 . In S 8 , the controller determines whether or not the vehicle speed v of the subject vehicle  110  detected by the vehicle speed sensor  2  is equal to or smaller than the predetermined v2, that is, whether or not the subject vehicle  110  is stopped. If an affirmative decision in S 8  is made, the processing proceeds to S 9 , and if a negative decision is made, the processing proceeds to S 3 . In S 9 , the controller determines whether or not the tram  201  is recognized diagonally behind the subject vehicle  110  (on the railroad track side) on the basis of a signal from the radar sensor  1 . If an affirmative decision in S 9  is made, the processing proceeds to S 10 , and if a negative decision is made, the processing proceeds to S 3 . 
     In S 10 , the controller determines whether or not the turn signal switch  4  on the right side, that is, on the railroad track side is turned on. If an affirmative decision in S 10  is made, the processing proceeds to S 11 , and if a negative decision is made, the processing proceeds to S 3 . In S 11 , the controller makes the display portion  5  in the side-view mirror on the right side turn on. The display portion  5  on the right side may be made to blink. The warning sound may be output at the same time as the display portion  5  is turned on or blinks. 
     An operation of the driving assistance apparatus  100  according to the present embodiment is summarized as follows. When the other vehicle  111  approaches from the diagonally back left side of the subject vehicle  110  while the subject vehicle  110  is traveling on a normal road on the side of which the railroad track  200  for the tram  201  is not located as illustrated in  FIG.  3   , the display portion  5  of the left side-view mirror is turned on (S 6 ). Thereafter, when the left turn signal switch  4  is turned on and the subject vehicle  110  attempts to change the second lane LN 2  to the first lane LN 1 , the display portion  5  blinks (S 7 ). Therefore, even in a case where the other vehicle  111  does not appear in the side-view mirror when the driver changes lanes, the driver can recognize the existence of the other vehicle  111  and can change lanes safely. 
     When the subject vehicle  110  crosses the railroad track  200  for the tram  201 , the subject vehicle  110  stops on the side of the railroad track  200  while the turn signal lamp for turning right is on as illustrated in  FIG.  1   . At this time, when the tram  201  approaches from the diagonally back right side of the subject vehicle  110 , the display portion  5  of the right side-view mirror is turned on or blinks (S 11 ). Therefore, the driver who has stopped the subject vehicle to wait for the traffic light to change can recognize that the tram  201  approaches from behind. Accordingly, the driver expects the passage of the tram  201 , and thus is less surprised in a case where the tram  201  passes by the subject vehicle  110 . This makes the driver more comfortable. 
     The display portion  5  originally notifies the driver of the approach of the other vehicle  111  during traveling, and the driver is accustomed to visually recognizing the display portion  5 . Therefore, the driver can easily recognize the approach of the tram  201  by turning on or blinking of the display portion  5 . The display portion  5  for notifying the driver of the approach of the traveling another vehicle  111  is used to notify the driver of the approach of the tram  201 . Thus, it is unnecessary to separately provide a notification part, thereby suppressing an increase in cost. Facilities such as a communication beacon are unnecessary. Also in this respect, the increase in cost can be suppressed. 
     According to the present embodiment, the following operations and effects are achievable. 
     (1) A driving assistance apparatus  100  is configured to assist a driver in driving a subject vehicle  110  located on the side of a railroad track  200  on which a tram  201  serving as a railway vehicle travels. The driving assistance apparatus  100  includes: an approach recognition unit  21  that recognizes approach of the tram  201  along the railroad track  200  to the subject vehicle  110  from the diagonally back side of the subject vehicle  110  on the basis of a signal from a radar sensor  1 , without using road-to-vehicle communication; a direction estimation unit  22  that estimates a traveling direction of the subject vehicle  110  at an intersection  103 ; and a display control unit  23  (a notification control unit) that controls a display portion  5  so as to notify the driver of the approach of the tram  201  when the direction estimation unit  22  estimates that the subject vehicle travels to cross the railroad track  200  and the approach recognition unit  21  detects (recognizes) the approach of the tram  201  to the subject vehicle  110  ( FIG.  2   ). 
     With this configuration, it is possible to notify the driver of the subject vehicle  110  that stops for crossing the railroad track  200 , that is, the driver who is waiting for the tram  201  to pass, of the approach of the tram  201  with an inexpensive configuration, without performing road-to-vehicle communication using a communication beacon. 
     (2) When another vehicle  111  travels along a lane LN 1  adjacent to a lane LN 2  while the subject vehicle  110  is traveling in the lane LN 2 , the approach recognition unit  21  further recognizes approach of the other vehicle  111  to the subject vehicle  110  from the diagonally back side of the subject vehicle  110  ( FIGS.  3  and  4   ). When the approach recognition unit  21  detects the approach of the other vehicle  111  to the subject vehicle  110  while the subject vehicle  110  is traveling, the display control unit  23  controls the display portion  5  to further notify the driver of the approach of the other vehicle  111  ( FIG.  4   ). Therefore, the display portion  5  for notifying the driver of the approach of the other vehicle  111  from the diagonally back side can be used to notify the driver of the approach of the tram  201 . Therefore, it is unnecessary to separately provide a device for notifying the driver of the approach of the tram  201 , which can reduce a cost. 
     (3) When the approach recognition unit  21  recognizes the approach of the other vehicle  111  while the subject vehicle  110  is stopped, the display control unit  23  controls the display portion  5  so as not to notify the driver of the approach of the other vehicle  111 , whereas, when the approach recognition unit  21  detects the approach of the tram  201  while the subject vehicle  110  is stopped, the display control unit  23  controls the display portion  5  so as to notify the driver of the approach of the tram  201  ( FIG.  4   ). The subject vehicle  110  does not change lanes while stopped, and thus it is unnecessary to notify the driver of the approach of the other vehicle  111 . Meanwhile, the driver is surprised when the tram  201  passes by the subject vehicle  110  unexpectedly for the driver. Therefore, it is preferable to notify the driver of the approach of the tram  201  even while the subject vehicle  110  is stopped. The driving assistance apparatus  100  is configured in consideration of this point in the present embodiment, which makes the driver more comfortable. 
     (4) The driving assistance apparatus  100  includes the radar sensor  1  that is provided at the back of the subject vehicle  110  to detect a position of an object located on the diagonally back side of the subject vehicle  110 . The approach recognition unit  21  detects the approach of the tram  201  on the basis of a signal from the radar sensor  1  ( FIG.  2   ). Using the radar sensor  1  in this manner makes it possible to detect the approach of the tram  201  inexpensively. 
     In the above embodiment, the approach of the tram  201  (a railway vehicle) to the subject vehicle  110  along the railroad track  200  (a travel path) is detected using the radar sensor  1 , but the configuration of an approach detection unit is not limited to this.  FIG.  5    is a diagram illustrating a modification of  FIG.  2   . In  FIG.  5   , a communication unit  6  is provided in place of the radar sensor  1 . The communication unit  6  is connected to a communication network such as a wireless communication network, an Internet network, or a telephone line network, and is configured to be capable of performing wireless communication with an external server device  202  via the communication network. 
     The server device  202  is a management server that manages an operation of the tram  201 . The controller  20  acquires, from the server device  202  via the communication unit  6 , operation information of the tram  201  corresponding to the position of the subject vehicle  110  obtained by the positioning sensor  3 . The approach recognition unit  21  recognizes the approach of the tram  201  to the subject vehicle  110  based on the operation information of the tram  201 . Accordingly, it is not necessary to use the radar sensor  1  to detect the approach of the tram  201 , and the entire apparatus can be configured at a lower cost. 
     The driving assistance apparatus  100  may include a situation recognition part that detects a situation around the subject vehicle  110 . In this case, when the situation recognition unit recognizes a traffic light  123  for railway vehicles ahead of the subject vehicle  110 , the direction estimation unit  22  may estimate a traveling direction of the subject vehicle  110 .  FIG.  6    is a block diagram illustrating a configuration of main parts of the driving assistance apparatus  100  in that case. As illustrated in  FIG.  6   , the situation recognition part can include, for example, a camera  7  provided in the subject vehicle  110  to capture an image of the front of the subject vehicle  110 . The traffic light  123  for trams looks different from the traffic lights  121  and  122  for vehicles, and thus the traffic light  123  can be easily identified on the basis of the camera image. The direction estimation unit  22  is configured to estimate the traveling direction of the subject vehicle  110  when the traffic light  123  is recognized. This makes it possible to reduce a processing load in the controller  20 . 
     The above embodiment can be modified in various forms. Several modifications will be described below. In the above embodiment, the tram  201  travels at the center in the width direction of the road  101  (center lane LN 0 ), but may travel at a location other than the center of the road. In the above embodiment, the approach recognition unit  21  recognizes the approach of the tram  201  based on the signal from the radar sensor  1 , thereby detecting the approach of the tram  201 , or the controller  20  acquires the operation information of the tram  201  via the communication unit  6  serving as an information acquisition unit, and the approach recognition unit  21  recognizes the approach of the tram  201  based on the operation information, thereby detecting the approach of the tram  201 , but the configuration of an approach detection part is not limited to the above configuration. 
     In the above embodiment, the direction estimation unit  22  estimates the traveling direction of the subject vehicle  110  at the intersection  103  based on the signal from the turn signal switch  4 , but for example, the traveling direction may be estimated based on a route information to a destination set by a navigation device, and the configuration of a direction estimation unit is not limited to the above configuration. In the above embodiment, the driver is notified of the approach of the tram  201  provided that the vehicle speed v of the subject vehicle  110  is equal to or smaller than the predetermined value v2 (for example, 0), but the predetermined value v2 may be larger than 0. 
     In the above embodiment, the driver is notified of the approach of the tram  201  by turning on or blinking the display portions  5  of the side-view mirrors (a pair of left and right display portions) that is a kind of side mirrors provided on the left and right sides of the subject vehicle. However, the configuration of a notification part is not limited to this. In addition to the notification part for notifying of detection of the approach of the other vehicle, a notification part for notifying of detection of the approach of the tram may be provided. In the above embodiment, the position of the subject vehicle  110  is detected by the signal from the positioning sensor  3 . However, the configuration of a position detection part is not limited to this. In the above embodiment ( FIG.  3   ), the configuration of the driving assistance apparatus  100  is described by way of example in which the other vehicle  111  travels in the lane LN 1  (a second lane) on the left side in the lane LN 2  while the subject vehicle  110  travels in the right lane LN 2  (a first lane). However, the first lane may be on the left side of the second lane. 
     The present invention can also be used as a driving assistance method configured to assist a driving by a driver of a subject vehicle, the subject vehicle locating on a side of a travel path on which a railway vehicle travels, the driving assistance method including detecting an approach of the railway vehicle along the travel path from a diagonally backward of the subject vehicle to the subject vehicle without using a road-to-vehicle communication, estimating a traveling direction of the subject vehicle at an intersection, and notifying the driver of the approach of the railway vehicle when the traveling direction crossing the travel path is estimated and the approach of the railway vehicle to the subject vehicle is detected. 
     The above embodiment can be combined as desired with one or more of the above modifications. The modifications can also be combined with one another. 
     According to the present invention, it is possible to provide a driver of a vehicle crossing a travel path of a railway vehicle with a useful information in a low-cost configuration. 
     Above, while the present invention has been described with reference to the preferred embodiments thereof, it will be understood, by those skilled in the art, that various changes and modifications may be made thereto without departing from the scope of the appended claims.