Patent Publication Number: US-2023150506-A1

Title: Notification control apparatus, vehicle, notification control method, and program

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a notification control apparatus, a vehicle, a notification control method, and a program. 
     Description of the Related Art 
     Japanese Patent Application Laid-Open (kokai) No. 2018-173723 discloses a driving assistance apparatus which detects a traffic light ahead of a vehicle on the basis of map data during travel of the vehicle, recognizes the lighting color of the traffic light from an image captured by a camera when the traffic light enters the field of view of the camera, and executes deceleration control for stopping the vehicle before reaching the traffic light when the recognized lighting color of the traffic light is red or yellow. 
     Here, assume the case where the driving assistance apparatus is executing follow-up control for causing the vehicle to follow a preceding vehicle and starts the deceleration control upon detection of a traffic light ahead of the vehicle in the period during which the follow-up control is being executed. In the period during which the follow-up control is being executed, a driver basically entrusts driving operation to the apparatus. However, the driver must monitor the control to determine whether or not the control is performed appropriately, while paying attention to the situation around the vehicle. Therefore, in the case where the apparatus switches the driving assistance control from the follow-up control to the deceleration control upon detection of a traffic light, it is desired for the apparatus to notify the driver that an object which causes the apparatus to decelerate the vehicle (an object which is recognized by the control as one which requires deceleration of the vehicle) has been switched from the preceding vehicle to the traffic light ahead of the vehicle (hereinafter, such an object will be referred to a “deceleration causing object”). 
     However, merely notifying the driver that the deceleration causing object is a traffic light does not enable the driver to grasp whether the deceleration causing object is a traffic light detected on the basis of the map data or a traffic light whose lighting color is recognized by the camera. If the driver places excessive trust in the control in a state in which the driver does not grasp whether the deceleration causing object is the traffic light detected on the basis of the map data or the traffic light whose lighting color is recognized by the camera, there may arise a possibility of failing to secure safety, for example, in the case where the traffic light in the map data does not coincide with the actually existing traffic light or the case where the camera fails to recognize the lighting color of the traffic light. 
     SUMMARY OF THE INVENTION 
     The present disclosure discloses a technique which has been achieved so as to solve the above-described problem. Namely, an object of the technique is to effectively notify a driver of a deceleration causing object during execution of deceleration control. 
     A notification control apparatus ( 10 ) of the present disclosure is applied to a vehicle (V) and controls a notification apparatus ( 61 ) which gives a notice to a driver of the vehicle (V). The vehicle (V) has a driving assistance apparatus ( 1 ) which comprises a first recognition section ( 10 ,  50 ) which recognizes a traffic light (S 1 , S 2 ) present ahead of the vehicle (V) on the basis of map data ( 51 ) including pieces of information of traffic lights on a road on which the vehicle (V) travels, a second recognition section ( 10 ,  40 ) which recognizes the traffic light (S 1 , S 2 ) present ahead of the vehicle (V) and an indication state of the traffic light (S 1 , S 2 ), and a deceleration control section ( 10 ) which executes deceleration control for decelerating the vehicle (V) at a predetermined deceleration rate by using, as a deceleration causing object, a traffic light (S 1 , S 2 ) which is recognized by at least one of the first recognition section ( 10 ,  50 ) and the second recognition section ( 10 ,  40 ) in a period during which the vehicle (V) is traveling. 
     The notification control apparatus ( 10 ) comprises a control section ( 10 ) which controls the notification apparatus ( 61 ) to notify the driver of the deceleration causing object associated with the deceleration control in different manners between the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) and the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the second recognition section ( 10 ,  40 ). 
     The deceleration control section ( 10 ) executes the deceleration control when at least one of the first recognition section ( 10 ,  50 ) and the second recognition section ( 10 ,  40 ) recognizes a traffic light (S 1 , S 2 ) in the period during which the vehicle (V) is traveling, and a predetermined condition is satisfied. The deceleration control section ( 10 ) executes the deceleration control (gentle deceleration control) when the first recognition section ( 10 ,  50 ) recognizes the traffic light (S 1 , S 2 ) in the period during which the vehicle (V) is traveling, and there is satisfied a predetermined condition that the vehicle (V) has reached a deceleration start position (Psd 1 , Psd 2 ) and the vehicle speed (Vs) at that time is higher than a target vehicle speed (V 1 ). The deceleration control section ( 10 ) executes the deceleration control (deceleration and stop control) when the vehicle (V) has reached the recognizable position (Pr 1 , Pr 2 ), the second recognition section ( 10 ,  40 ) recognizes, at that time, the traffic light (S 1 , S 2 ) and the lighting color of the traffic light (S 1 , S 2 ), and there is satisfied a predetermined condition that the recognized lighting color is a color other than green. 
     A notification control method of the present disclosure is applied to a vehicle (V) and controls a notification apparatus ( 61 ) which gives a notice to a driver of the vehicle (V). The vehicle (V) has a driving assistance apparatus ( 1 ) which comprises a first recognition section ( 10 ,  50 ) which recognizes a traffic light (S 1 , S 2 ) present ahead of the vehicle (V) on the basis of map data ( 51 ) including pieces of information of traffic lights on a road on which the vehicle (V) travels, a second recognition section ( 10 ,  40 ) which recognizes the traffic light (S 1 , S 2 ) present ahead of the vehicle (V) and an indication state of the traffic light (S 1 , S 2 ), and a deceleration control section ( 10 ) which executes deceleration control for decelerating the vehicle (V) at a predetermined deceleration rate by using, as a deceleration causing object, a traffic light (S 1 , S 2 ) which is recognized by at least one of the first recognition section ( 10 ,  50 ) and the second recognition section ( 10 ,  40 ) in a period during which the vehicle (V) is traveling. 
     The notification control method controls the notification apparatus ( 61 ) to notify the driver of the deceleration causing object associated with the deceleration control in different manners between the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) and the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the second recognition section ( 10 ,  40 ). 
     A program of the present disclosure is applied to a vehicle (V) and controls a notification apparatus ( 61 ) which gives a notice to a driver of the vehicle (V). The vehicle has a driving assistance apparatus ( 1 ) which comprises a first recognition section ( 10 ,  50 ) which recognizes a traffic light (S 1 , S 2 ) present ahead of the vehicle (V) on the basis of map data ( 51 ) including pieces of information of traffic lights on a road on which the vehicle (V) travels, a second recognition section ( 10 ,  40 ) which recognizes the traffic light (S 1 , S 2 ) present ahead of the vehicle (V) and an indication state of the traffic light (S 1 , S 2 ), and a deceleration control section ( 10 ) which executes deceleration control for decelerating the vehicle (V) at a predetermined deceleration rate by using, as a deceleration causing object, a traffic light (S 1 , S 2 ) which is recognized by at least one of the first recognition section ( 10 ,  50 ) and the second recognition section ( 10 ,  40 ) in a period during which the vehicle (V) is traveling. 
     The program causes a computer to execute a process of controlling the notification apparatus ( 61 ) to notify the driver of the deceleration causing object associated with the deceleration control in different manners between the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) and the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the second recognition section ( 10 ,  40 ). 
     By virtue of the above-described configuration, the notification apparatus ( 61 ) notifies the driver of the deceleration causing object in different manners between the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) and the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the second recognition section ( 10 ,  40 ). Accordingly, the driver can grasp, without fail, whether the deceleration causing object is the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) or the traffic light (S 1 , S 2 ) whose indication state is recognized by the second recognition section ( 10 ,  40 ). 
     The notification apparatus ( 61 ) may be a display apparatus ( 61 ) provided at a position determined such that the driver of the vehicle (V) can view the display apparatus ( 61 ). In this case, the control section ( 10 ) may operate as follows. When the deceleration control is executed by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ), the control section ( 10 ) displays an image ( 80 A) of a traffic light on the display apparatus ( 61 ) in such a manner that none of lighting portions of the traffic light is on. When the deceleration control is executed by using, as the deceleration causing object, the traffic light recognized by the second recognition section ( 10 ,  40 ), the control section ( 10 ) displays an image ( 80 B) of a traffic light on the display apparatus ( 61 ) in such a manner that a lighting portion of the traffic light corresponding to the indication state is on. 
     In this case, different notification images ( 80 A,  80 B) are displayed on the display apparatus ( 61 ) depending on whether the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) or the traffic light (S 1 , S 2 ) recognized by the second recognition section ( 10 ,  40 ) is used as the deceleration causing object associated with the deceleration control. Accordingly, the driver can easily grasp whether the deceleration causing object is the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) or the traffic light (S 1 , S 2 ) whose indication state is recognized by the second recognition section ( 10 ,  40 ), by merely checking the notification image ( 80 A,  80 B) displayed on the display apparatus ( 61 ). 
     The deceleration control section ( 10 ) may be configured to decelerate the vehicle (V) at different deceleration rates between the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) and the case where the deceleration control section ( 10 ) executes the deceleration control by using, as the deceleration causing object, the traffic light (S 1 , S 2 ) recognized by the second recognition section ( 10 ,  40 ). 
     In this case, the deceleration causing objects used in the deceleration control for decelerating the vehicle (V) at different deceleration rates can be notified to the driver in different manners by the notification apparatus ( 61 ). Accordingly, the driver can grasp, without fail, the cause of a change in the deceleration rate of the vehicle (V) during execution of the deceleration control. 
     The second recognition section ( 10 ,  40 ) may be such that it becomes able to recognize the lighting color of the traffic light (S 1 , S 2 ) when the distance between the vehicle and a traffic light ahead of the vehicle becomes a predetermined threshold distance (Lr) or shorter. In this case, the deceleration control section may operate as follows. In case where the speed (Vs) of the vehicle (V) is higher than a predetermined target vehicle speed (V 1 ) when the vehicle (V) reaches a predetermined point (Psd) before a point where the distance between the vehicle (V) and the traffic light (S 1 , S 2 ) recognized by the first recognition section ( 10 ,  50 ) becomes the predetermined threshold distance (Lr) or shorter, the deceleration control section ( 10 ) executes first deceleration control (gentle deceleration control) for decelerating the vehicle (V) at a predetermined first deceleration rate (A 1 ) from a point in time when the vehicle (V) reaches the predetermined point (Psd). In the case where the second recognition section ( 10 ,  40 ) recognizes the lighting color of the traffic light (S 1 , S 2 ) ahead of the vehicle (V) and the recognized lighting color is red or yellow, from a point in time when the lighting color of the traffic light (S 1 , S 2 ) is recognized, the deceleration control section ( 10 ) executes second deceleration control (deceleration and stop control) for decelerating the vehicle (V) at a predetermined second deceleration rate (A 2 ) higher than the first deceleration rate (A 1 ). 
     In this case, when the vehicle (V) reaches the deceleration start point (Psd) before the recognizable point (Pr), the deceleration control section ( 10 ) executes the gentle deceleration control for decelerating the vehicle (V) at the first deceleration rate (A 1 ), and, when the vehicle (V) reaches the recognizable point (Pr) and the second recognition section ( 10 ,  40 ) recognizes at that time that the lighting color of the traffic light (S 1 , S 2 ) is red or yellow, the deceleration control section ( 10 ) executes the deceleration and stop control for decelerating the vehicle (V) at the second deceleration rate (A 2 ) higher than the first deceleration rate (A 1 ). As a result, it becomes possible to stop, without fail, the vehicle (V) at a predetermined stop position (PST 1 , PST 2 ) before the traffic light (S 1 , S 2 ). 
     In the above description, in order to facilitate understanding of the present invention, the constituent elements of the invention corresponding to those of an embodiment of the invention which will be described later are accompanied by parenthesized reference numerals which are used in the embodiment; however, the constituent elements of the invention are not limited to those in the embodiment defined by the reference numerals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic overall diagram of an automatic driving system according to an embodiment; 
         FIG.  2    is an illustration used for describing one example of deceleration control according to the embodiment; 
         FIG.  3    is an illustration used for describing another example of the deceleration control according to the embodiment; 
         FIG.  4    is an illustration used for describing still another example of the deceleration control according to the embodiment; 
         FIG.  5    is an illustration used for describing an example notification image displayed on a display apparatus by an ECU; 
         FIG.  6    is an illustration used for describing another example notification image displayed on the display apparatus by the ECU; 
         FIG.  7    is an illustration used for describing still another example notification image displayed on the display apparatus by the ECU; 
         FIG.  8    is an illustration used for describing still another example notification image displayed on the display apparatus by the ECU; 
         FIG.  9    is a timing chart used for describing a specific flow of display control; 
         FIG.  10    is another timing chart used for describing the specific flow of the display control; and 
         FIG.  11    is a flowchart used for describing a routine (first half) for the deceleration control and the display control according to the embodiment; and 
         FIG.  12    is a flowchart used for describing a routine (second half) for the deceleration control and the display control according to the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A notification control apparatus, a vehicle, a notification control method, and a program according to an embodiment will now be described with reference to the drawings. Notably, throughout the drawings, the same components are denoted by the same reference numerals, and their names and functions are the same. Therefore, their detailed descriptions will not be repeated. 
     [Overall Configuration] 
       FIG.  1    is a schematic overall diagram of an automatic driving system  1  according to the present embodiment. The automatic driving system  1  is mounted on a vehicle V and includes an ECU  10 . The ECU  10  includes a microcomputer as a main component. Notably, ECU is an abbreviation for Electronic Control Unit. The microcomputer includes a CPU, a ROM, a RAM, an interface, etc. The CPU realizes various functions by executing instructions (programs, routines) stored in the ROM. 
     The ECU  10  executes automatic driving control for the vehicle V. Herein, “automatic driving control” is a concept which encompasses driving assistance control. Examples of the driving assistance control include adaptive cruise control (hereinafter referred to as “ACC”), path following control, etc. The ACC is a control for causing the vehicle V to travel in different ways depending on whether or not another preceding vehicle is traveling ahead of the vehicle V. In the case where the preceding vehicle is present, the ACC causes the vehicle V to follow the preceding vehicle while maintaining the distance between the preceding vehicle and the vehicle V at a set inter-vehicle distance. In the case where no preceding vehicle is present, the ACC causes the vehicle V to travel at a set vehicle speed; i.e., travel at a constant speed. The path following control is a control for automatic travel which causes the vehicle V to follow a target track (target path). In the present embodiment, the driving assistance control may be either of the ACC and the path following control. However, in the following description, the ACC will be described as one example of the driving assistance control. 
     The ECU  10  performs the ACC by controlling the operations of a drive apparatus  11 , a steering apparatus  12 , a brake apparatus  13 , etc. on the basis of the travel state of the vehicle V and the circumstances around the vehicle V. Therefore, the drive apparatus  11 , the steering apparatus  12 , the brake apparatus  13 , a vehicle state obtaining apparatus  30 , a surrounding recognition apparatus  40 , a navigation system  50 , an HMI (Human Machine Interface)  60 , an operation switch  70 , etc. are communicably connected to the ECU  10 . 
     The drive apparatus  11  generates drive power which is transmitted to drive wheels of the vehicle V. The drive apparatus  11  is, for example, an electric motor or an engine. The vehicle V may be any of a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), a fuel cell vehicle (FCEV), a battery electric vehicle (BEV), and an engine vehicle. The steering apparatus  12  is, for example, an electric power steering apparatus and applies steering forces to steerable wheels of the vehicle V. The brake apparatus  13  is, for example, a disc-type brake apparatus and applies braking forces to the wheels of the vehicle V. 
     The vehicle state obtaining apparatus  30  is a group of sensors for obtaining the state of the vehicle V. Specifically, the vehicle state obtaining apparatus  30  includes a steering angle sensor  31 , a steering torque sensor  32 , a vehicle speed sensor  33 , an accelerator sensor  34 , a brake sensor  35 , a yaw rate sensor  36 , etc. 
     The steering angle sensor  31  detects the steering angle of an unillustrated steering wheel (or an unillustrated steering shaft). The steering torque sensor  32  detects a steering torque which acts on the steering shaft (not shown) of the vehicle V as a result of operation of the steering wheel. The vehicle speed sensor  33  detects the travel speed of the vehicle V (vehicle speed). The vehicle speed sensor  33  may be a wheel speed sensor. The accelerator sensor  34  detects the operation amount of an unillustrated accelerator pedal. The brake sensor  35  detects the operation amount of an unillustrated brake pedal. The yaw rate sensor  36  detects the yaw rate of the vehicle V. The pieces of information representing the state of the vehicle V and obtained by the vehicle state obtaining apparatus  30  are transmitted to the ECU  10 . 
     The surrounding recognition apparatus  40  is a group of sensors for recognizing objects around the vehicle V and outputting pieces of object information relating to the objects. Specifically, the surrounding recognition apparatus  40  includes a radar sensor  41 , an ultrasonic sensor  42 , a camera  43 , etc. Examples of the pieces of object information include pieces of information relating to vehicles around the vehicle V, pieces of information relating to traffic lights, pieces of information relating to white lines on roads, pieces of information relating to signs, and pieces of information relating to fallen objects. The pieces of object information relating to the objects around the vehicle V and obtained by the surrounding recognition apparatus  40  are transmitted to the ECU  10 . 
     The radar sensor  41  includes a radar transmitting/receiving section and a signal processing section (not shown). The radar transmitting/receiving section radiates a radio wave in the millimeter wave band (hereinafter referred to as “millimeter wave”) to a region around the vehicle V and receives a millimeter wave (i.e., reflection wave) reflected by a three-dimensional object present in the region to which the millimeter wave is radiated. On the basis of the phase difference between the transmitted millimeter wave and the received reflection wave, the level of attenuation of the reflection wave, the time elapsed until the radar transmitting/receiving section received the reflection wave after having transmitted the millimeter wave, etc., the signal processing section obtains pieces of information representing the distance between the vehicle V and the three-dimensional object, the relative speed of the vehicle V in relation to the three-dimensional object, the relative position (direction) of the three-dimensional object in relation to the vehicle V, etc. The signal processing section outputs the pieces of information to the ECU  10 . 
     The ultrasonic sensor  42  transmits an ultrasonic wave in the shape of pulses to a predetermined range around the vehicle V and receives a reflection wave; i.e., the ultrasonic wave reflected by a three-dimensional object. On the basis of the time between transmission of the ultrasonic wave and reception of the reflection wave, the ultrasonic sensor  42  can detect a refection point (i.e., a point on the three-dimensional object at which the transmitted ultrasonic wave is reflected), the distance between the ultrasonic sensor  42  and the three-dimensional object, etc. 
     The camera  43  is disposed, for example, on an upper portion of a front windshield glass of the vehicle V. The camera  43  captures images of scenes around the vehicle V and processes data of the captured images, thereby obtaining pieces of information relating to objects present around the vehicle V (hereinafter referred to as “object information”). The camera  43  is, for example, a stereo camera or a monocular camera, and a digital camera including an imaging device such as CMOS or CCD can be used. 
     In the present embodiment, the camera  43  analyses image data obtained by photographing a scene in front of the vehicle V at a predetermined frame rate, and obtains, from the image of the scene, the lighting color of a traffic light located ahead of the vehicle V in the travel direction of the vehicle V. Notably, the vehicle V must get closer to the traffic light to some extent so as to allow the camera  43  to accurately determine whether or not a group of red, yellow, or green pixels which are contained in the image data and form a circular shape corresponds to the light emitted from the corresponding lighting portion of the traffic light. For example, when the vehicle V approaches a traffic light and the distance between the vehicle V and the traffic light becomes a predetermined distance, the camera  43  becomes able to accurately determine the lighting color of the traffic light. In the following description, the maximum value of the distance (the distance between the vehicle V and the traffic light), below which the camera  43  can accurately determine the lighting color of the traffic light, will be referred to as a “recognizable distance Lr.” Also, a point which is located before the traffic light and at the recognizable distance Lr from the traffic light will be referred to as a “recognizable point Pr.” Notably, the recognizable distance Lr depends on the specifications of the camera  43 . Therefore, the recognizable distance Lr is experimentally obtained in the stage of developing the vehicle V, and the obtained recognizable distance Lr is stored in the ROM of the ECU  10  beforehand. 
     The navigation system  50  receives GPS signals from a plurality of artificial satellites and detects the present position VP (latitude and longitude) of the vehicle V on the basis of the received GPS signals. Also, the navigation system  50  stores map data  51  which represents a map. The map data  51  includes pieces of road information representing roads, and pieces of traffic light position information representing positions where traffic lights are provided, etc. The navigation system  50  transmits to the ECU  10  vehicle position data representing the detected present position VP of the vehicle V. Furthermore, the navigation system  50  has a function of calculating the distance (the distance along a road) between two points. For example, the navigation system  50  computes the distance between the present position VP of the vehicle V and a traffic light (nearest traffic light) which the vehicle V first passes when the vehicle V travels straight along the road on which the vehicle V currently travels. The navigation system  50  transmits data representing the computed distance to the ECU  10 . 
     The HMI  60  is an interface for exchanging pieces of information between the ECU  10  and the driver through input and output of data. Specifically, the HMI  60  has an input apparatus and an output apparatus. Examples of the input apparatus include a touch panel and a switch. Examples of the output apparatus include a display apparatus  61  and a speaker. Examples of the display apparatus  61  include a display of the navigation system  50  disposed on an instrument panel or the like and a head-up display. 
     The operation switch  70  is an operating element (for example, a push-button-type switch operating element) which the driver operates when the driver requests start and end of the ACC. In the case where the driver operates the operation switch  70  (presses the button) in a period during which the ACC is not executed, the operation switch  70  transmits an ACC start signal to the ECU  10 . The ACC start signal represents “that the driver requests start of the ACC (ACC start request).” Meanwhile, in the case where the driver operates the operation switch  70  in a period during which the ACC is being executed, the operation switch  70  transmits an ACC end signal to the ECU  10 . The ACC end signal represents “that the driver requests end of the ACC (ACC end request).” Also, the operation switch  70  includes operation elements for selecting a set inter-vehicle distance Dd between the vehicle V and a preceding vehicle and a set vehicle speed Vd for constant speed travel. The set inter-vehicle distance Dd and the set vehicle speed Vd are used in the ACC, which will be described later. 
     [ACC] 
     Upon reception of the ACC start signal from the operation switch  70 , the ECU  10  executes the ACC. Specifically, on the basis of the information obtained from the surrounding recognition apparatus  40 , the ECU  10  determines whether or not another vehicle (preceding vehicle) to follow is present. In the case where the ECU  10  determines that a preceding vehicle to follow is present, the ECU  10  detects the inter-vehicle distance between the preceding vehicle and the vehicle V (the driver&#39;s vehicle) on the basis of the information obtained from the surrounding recognition apparatus  40  and controls the operations of the drive apparatus  11  and the brake apparatus  13  such that the inter-vehicle distance becomes equal to the set inter-vehicle distance Dd selected as a result of the operation switch  70  being operated. Hereinafter, the control for causing the vehicle V to follow the preceding vehicle will be referred to simply as “follow-up control.” Meanwhile, in the case where the ECU  10  determines that no preceding vehicle to follow is present, the ECU  10  controls the operations of the drive apparatus  11 , the brake apparatus  13 , etc. such that the speed Vs of the vehicle V becomes equal to the set vehicle speed Vd selected as a result of the operation switch  70  being operated. Hereinafter, the control for causing the vehicle V to travel at the set vehicle speed Vd (i.e., travel at a constant speed) will be referred to simply as “constant speed travel control.” Also, when the ECU  10  detects a traffic light as a deceleration causing object in a period during which the ECU  10  is executing the ACC, the ECU  10  performs deceleration control for decelerating the vehicle V even when the preceding vehicle does not start deceleration. The details of the deceleration control will now be described. 
     [Deceleration Control] 
       FIG.  2    is an illustration used for describing one example of the deceleration control according to the present embodiment. During a period during which the ECU  10  is executing the ACC, on the basis of the map data  51  of the navigation system  50  and the present position VP of the vehicle V, the ECU  10  obtains a point PS 1  where a traffic light S 1  located ahead of the vehicle V and closest to the vehicle V is provided and a recognizable point Pr 1  corresponding to the traffic light S 1 . Also, the ECU  10  obtains the present position VP of the vehicle V from the navigation system  50  at predetermined intervals. Furthermore, the ECU  10  obtains the speed Vs of the vehicle V from the vehicle speed sensor  33  at predetermined intervals. 
     The ECU  10  controls the operations of the drive apparatus  11 , the brake apparatus  13 , etc. before the vehicle V reaches the recognizable point Pr 1  such that, at a point in time when the vehicle V reaches the recognizable point Pr 1 , the vehicle speed Vs becomes equal to or lower than a predetermined target vehicle speed V 1 . The target vehicle speed V 1  is set beforehand to be a speed which makes it possible to decelerate the vehicle V from the recognizable point Pr 1  at a deceleration rate which does not give an unpleasant feeling to the driver (hereinafter referred to as the “second deceleration rate A 2 ”) and stop the vehicle Vat a predetermined stop position PST 1  (for example, a stop line associated with the traffic light S 1 ) before the traffic light S 1 . 
     Specifically, in the case where the vehicle speed Vs before the recognizable point Pr 1  is higher than the target vehicle speed V 1 , when the vehicle V reaches a predetermined deceleration start point Psd 1  before the recognizable point Pr 1 , the ECU  10  executes gentle deceleration control for decelerating the vehicle V at a predetermined deceleration rate (hereinafter referred to as the “first deceleration rate A 1 ”) smaller than the second deceleration rate A 2 . The magnitude (absolute value) of the first deceleration rate A 1  is, for example, 0.1 G (G: gravitational acceleration). Notably, the first deceleration rate A 1  may be smaller than 0.1 G. 
     The ECU  10  computes the deceleration start point Psd 1  located before the recognizable point Pr 1  as follows. First, the ECU  10  computes a distance L 1  over which the vehicle V travels until the vehicle speed Vs becomes equal to the target vehicle speed V 1  in the case where the vehicle V decelerates from the current vehicle speed Vs at the first deceleration rate A 1 . Subsequently, the ECU  10  determines, as a deceleration start point Psd 1  corresponding to the current vehicle speed Vs, a point located before the recognizable point Pr 1  and at the distance L 1  from the recognizable point Pr 1 . The ECU  10  repeatedly computes (updates) the deceleration start point Psd 1  at predetermined computation intervals. 
     In the case where the vehicle speed Vs is higher than the target vehicle speed V 1  when the vehicle V reaches the deceleration start point Psd 1  (the present position VP of the vehicle V obtained from the navigation system  50  coincides with the deceleration start point Psd 1 ), the ECU  10  executes the gentle deceleration control for decelerating the vehicle V at the first deceleration rate A 1  from the point in time when the vehicle V reaches the deceleration start point Psd 1 . Meanwhile, in the case where the vehicle speed Vs is equal to or lower than the target vehicle speed V 1  when the vehicle V reaches the deceleration start point Psd 1 , the ECU  10  does not execute the gentle deceleration control. 
     When the vehicle V reaches the recognizable point Pr 1 , the ECU  10  obtains the lighting color of the traffic light S 1  from the camera  43 . In the case where the obtained lighting color is red (R) or yellow (Y), the ECU  10  executes deceleration and stop control for decelerating the vehicle V at the second deceleration rate A 2  and stopping the vehicle V at the stop position PST 1  before the traffic light S 1  (point PS 1 ). 
     Meanwhile, in the case where, as shown in  FIGS.  3  and  4   , the lighting color of the traffic light S 1  obtained from the camera  43  when the vehicle V reaches the recognizable point Pr 1  associated with the closest traffic light S 1  is green (G), on the basis of the map data  51  of the navigation system  50 , the ECU  10  obtains the distance DS between the closest traffic light S 1  and the next traffic light S 2  located ahead of and adjacent to the traffic light S 1 . Also, the ECU  10  determines whether the distance DS is relatively long or relatively short by comparing the obtained distance DS with a predetermined threshold distance DSth. The threshold distance DSth may be set by using, as a reference, for example, a distance determined such that, when the gentle deceleration control and the deceleration and stop control are executed in a state in which the vehicle speed Vs has been increased to the set speed Vd of the ACC, the vehicle V can stop at a predetermined stop position PST 2  (for example, the stop line associated with the traffic light S 2 ) before the next traffic light S 2 . Such distance is equivalent to the sum of the distance L 1  and the recognizable distance Lr. 
     In the case where the distance DS is relatively long as shown in  FIG.  3   ; specifically, the distance DS is longer than the predetermined threshold distance DSth (DS&gt;DSth), the ECU  10  causes the vehicle V to accelerate from the recognizable point Pr 1 , at which the ECU  10  obtains the lighting color (green (G)) of the traffic light S 1  from the camera  43  and pass the traffic light S 1 , and starts computation of a deceleration start point Psd 2  associated with the next traffic light S 2 . Notably, the upper limit of the vehicle speed Vs at that time is the set vehicle speed Vd of the ACC. When the vehicle V reaches the deceleration start point Psd 2 , the ECU  10  executes the gentle deceleration control. When the vehicle V reaches the recognizable point Pr 2  associated with the traffic light S 2 , the ECU  10  obtains the lighting color of the traffic light S 2  from the camera  43 . Subsequently, at the point in time when the ECU  10  succeeds in obtaining the lighting color of the traffic light S 2 , in accordance with the lighting color, the ECU  10  executes control similar to the control performed when the vehicle V passes the traffic light S 1  or stops at the traffic light S 1 . 
     In the case where the distance DS is relatively short as shown in  FIG.  4   ; specifically, the distance DS is equal to or shorter than the threshold distance DSth (DS  5  DSth), the ECU  10  causes the vehicle V to travel at a constant speed and pass the traffic light S 1 . Namely, the vehicle speed Vs at the time when the vehicle V passes the traffic light S 1  is the vehicle speed Vs at the point in time when the vehicle V has reached the recognizable point Pr 1  (namely, the target speed V 1 ). In this case, the vehicle speed Vs has been reduced enough so that, when the lighting color of the next traffic light S 2  becomes red (R) or yellow (Y), the ECU  10  can stop the vehicle V at the stop position PST 2  associated with the traffic light S 2 . Therefore, the ECU  10  omits computation of the deceleration start point Psd 2  associated with the traffic light S 2 . After the vehicle V has passed the traffic light S 1 , the ECU  10  attempts to obtain the lighting color of the traffic light S 2  from the camera  43  at predetermined time intervals. At the point in time when the ECU  10  has succeeded in obtaining the lighting color of the traffic light S 2 , in accordance with the lighting color, the ECU  10  executes control similar to the control performed when the vehicle V passes the traffic light S 1  or stops at the traffic light S 1 . 
     Incidentally, because of a topographical reason, for example, because the road on which the vehicle V is traveling is not a simple straight road but the road contains curved portions before the traffic lights S 1  and S 2 , in some times, the camera  43  fails to recognize the lighting color of the traffic light S 1  or S 2  at a point in time when the vehicle V reaches the recognizable point Pr 1  or Pr 2 . In such a case, the ECU  10  assumes that the lighting color of the traffic light S 1  or S 2  is red or yellow and decelerates the vehicle V at the second deceleration rate A 2  from the recognizable point Pr 1  or Pr 2 . In the case where the camera  43  becomes able to recognize the lighting color of the traffic light S 1  or S 2  as a result of further advancement of the vehicle V and the lighting color of the traffic light S 1  or S 2  at that time is red or yellow, the ECU  10  further decelerates the vehicle V at the second deceleration rate A 2 , and stops the vehicle V at the stop position PST 1  or PST 2  before the traffic light S 1  or S 2 . Meanwhile, in the case where the lighting color of the traffic light S 1  or S 2  at the point in time when the camera  43  becomes able to recognize the lighting color is green, the ECU  10  causes the vehicle V to pass the traffic light S 1  or S 2  while traveling at a constant speed. 
     Here, assume the case where, in the period during which the ACC is being executed, the ECU  10  switches the driving assistance control from the ACC to the deceleration control (the gentle deceleration control or the deceleration and stop control) upon detection of the traffic light S 1  or S 2  located ahead of the vehicle V. The driver basically entrusts the driving operation of the vehicle V to the ECU  10  not only in the period during which the ACC is being executed but also after the driving assistance control has been switched from the ACC to the deceleration control. However, the driver must monitor the control to determine whether or not the control is performed appropriately, while checking the situation around the vehicle V. Therefore, in the case where the ECU  10  switches the driving assistance control from the ACC to the deceleration control, it is desired for the ECU  10  to appropriately notify the driver that the deceleration causing object has been switched from the preceding vehicle to the traffic light S 1  or S 2  ahead of the vehicle V. 
     However, in the case where the ECU  10  merely notifies the driver that the deceleration causing object is the traffic light S 1  or S 2  does not allow the driver to grasp whether the deceleration causing object is the traffic light S 1  or S 2  detected on the basis of the map data  51  of the navigation system  50  or the traffic light S 1  or S 2  whose lighting color (red or yellow) is recognized by the camera  43 . If the driver places excessive trust in the deceleration control in a state in which the driver cannot grasp the deceleration causing object, there may arise a possibility of failing to secure safety, for example, in the case where the traffic light S 1  or S 2  in the map data  51  does not coincide with the actually existing traffic light S 1  or S 2  or the case where the camera  43  fails to recognize the lighting color of the traffic light S 1  or S 2  due to environmental conditions and/or a topographical reason. 
     In order to solve such a problem, during execution of the deceleration control, the ECU  10  of the present embodiment executes display control for displaying the deceleration causing object on the display apparatus  61 , thereby appropriately notifying the driver of the deceleration causing object. The details of the display control will now be described. Notably, for notification to the driver, a sound produced by a speaker can be used additionally. However, in the below, the case where notification to the driver is made by notification images displayed on the display apparatus  61  will be described as one example. 
     [Display Control] 
       FIGS.  5  to  8    are illustrations used for describing notification images displayed on the display apparatus  61  by the ECU  10 . Each of notification images  80 A to  80 D is a graphic image which imitates a traffic light and which has a housing portion  81  (corresponding to the housing of the traffic light) and three light portions  82 ,  83 , and  84 . In the illustrated examples, the three light portions  82 ,  83 , and  84  are provided in the housing portion  81  such that the three light portions  82 ,  83 , and  84  are arranged in series in the horizontal direction. However, the three light portions  82 ,  83 , and  84  may be arranged in the vertical direction. Of these light portions  82 ,  83 , and  84 , the light portion  82  corresponds to green, the light portion  83  corresponds to yellow, and the light portion  84  corresponds to red. 
     The notification image  80 A shown in  FIG.  5    is an image which shows a state in which none of the three light portions  82 ,  83 , and  84  is on by displaying the three light portions  82 ,  83 , and  84  in black, gray, or the same color as the housing portion  81  (hereinafter, the notification image  80 A will be referred to as the “no light portion lighting image  80 A”). The no light portion lighting image  80 A is displayed on the display apparatus  61  by the ECU  10  when the ECU  10  notifies the driver that an object recognized for the deceleration control is the traffic light S 1  or S 2  detected on the basis of the map data  51  of the navigation system  50 . 
     The notification image  80 B shown in  FIG.  6    is an image which shows a state in which a red signal light is on by displaying the light portion  84  in red and displaying the remaining two light portions  82  and  83  in the same color as the housing portion  81  or in a color other than red (hereinafter, the notification image  80 B will be referred to as the “red light portion lighting image  80 B”). The notification image  80 C shown in  FIG.  7    is an image which shows a state in which a yellow signal light is on by displaying the light portion  83  in yellow and displaying the remaining two light portions  82  and  84  in the same color as the housing portion  81  or in a color other than yellow (hereinafter, the notification image  80 C will be referred to as the “yellow light portion lighting image  80 C”). The red light portion lighting image  80 B (or the yellow light portion lighting image  80 C) is displayed on the display apparatus  61  by the ECU  10  when the ECU  10  notifies the driver that the object recognized for the deceleration control is the traffic light S 1  or S 2  which is recognized by the camera  43  to light in red (or yellow). 
     The notification image  80 D shown in  FIG.  8    is an image which shows a state in which a green signal light is on by displaying the light portion  82  in green and displaying the remaining two light portions  83  and  84  in the same color as the housing portion  81  or in a color other than green (hereinafter, the notification image  80 D will be referred to as the “green light portion lighting image  80 D”). The green light portion lighting image  80 D is displayed on the display apparatus  61  by the ECU  10 , when the ECU  10  causes the vehicle V to pass the traffic light S 1  or S 2  while causing the vehicle V to travel at the target speed V 1  (i.e., at a constant speed), so as to notify the driver that an object recognized for the constant speed travel control is the traffic light S 1  or S 2  which is recognized by the camera  43  to light in green. 
     In the case where the ECU  10  executes the gentle deceleration control upon determination that the vehicle V has reached the deceleration start point Psd 1  or Psd 2 , the ECU  10  displays the no light portion lighting image  8 A on the display apparatus  61  over the period during which the gentle deceleration control is executed. Also, in the case where the ECU  10  executes the deceleration and stop control upon determination that the vehicle V has reached the recognizable point Pr 1  or Pr 2  and that the lighting color of the traffic light S 1  or S 2  recognized by the camera  43  is red (R) (or yellow (Y)), the ECU  10  displays the red light portion lighting image  80 B (or the yellow light portion lighting image  80 C) on the display apparatus  61  over the period during which the deceleration and stop control is executed. The specific flow of the display control will now be described on the basis of the timing charts of  FIGS.  9  and  10   . 
     During the period between time t 0  and time t 1  shown in  FIGS.  9  and  10   , the ECU  10  causes the vehicle V to travel by the ACC. In the case where the ACC is the follow-up control, the ECU  10  displays a preceding vehicle follow-up image  86  on the display apparatus  61  as a notification image which shows that the deceleration causing object is a preceding vehicle. In the case where the vehicle V reaches the deceleration start point Psd 1  at time t 1  and the vehicle speed Vs at that time is higher than the target speed V 1 , the ECU  10  starts the gentle deceleration control. 
     When the gentle deceleration control is started, the ECU  10  displays the no light portion lighting image  80 A on the display apparatus  61  from time t 1 . As a result, the driver can grasp that the deceleration causing object has been switched from the preceding vehicle to the traffic light S 1  detected by the navigation system  50 . The no light portion lighting image  80 A displayed on the display apparatus  61  from time t 1  is continuously displayed on the display apparatus  61  over the period between time t 1  and a point in time when the vehicle V reaches the recognizable point Pr 1  and the camera  43  recognizes the lighting color of the traffic light S 1 . 
     When the vehicle V reaches the recognizable point Pr 1  at time t 2 , the ECU  10  obtains the lighting color of the traffic light S 1  from the camera  43 . In the case where the obtained lighting color is red (or yellow), as shown in  FIG.  9   , the ECU  10  executes the deceleration and stop control for stopping the vehicle V at the stop position PST 1  before the traffic light S 1 . The ECU  10  continuously displays the red light portion lighting image  80 B on the display apparatus  61  over the period between time t 2  and time t 3  when the vehicle V stops at the stop position PST 1 . As a result, at or after t 2 , the driver can grasp that the deceleration causing object has been switched to the traffic light S 1  recognized by the camera  43 . The red light portion lighting image  80 B displayed on the display apparatus  61  may be deleted when the vehicle V stops at the stop position PST 1  or immediately when the lighting color of the traffic light S 1  is switched from red to green. 
     Meanwhile, in the case where the lighting color obtained at time t 2  is green, as shown in  FIG.  10   , the ECU  10  causes the vehicle V to pass the traffic light S 1  while causing the vehicle V to travel at the vehicle speed at that time (the target speed V 1 ) (i.e., at a constant speed). The ECU  10  displays the green light portion lighting image  80 D on the display apparatus  61  over the period between time t 2  and time t 4  when the vehicle V passes the traffic light S 1 . As a result, the driver can grasp that the ECU  10  causes the vehicle V to travel at the constant speed while recognizing that the lighting color of the traffic light S 1  is green G by using the camera  43 . The green light portion lighting image  80 D displayed on the display apparatus  61  may be deleted immediately when the vehicle V passes the traffic light S 1 . 
     Next, a routine for the deceleration control and the display control, which is performed by the ECU  10 , will be described on the basis of the flowcharts shown in  FIGS.  11  and  12   . This routine is started when the ECU  10  executes the ACC. 
     In step S 100 , the ECU  10  obtains the recognizable point Pr corresponding to the closest traffic light S located ahead of the vehicle V on the basis of the map data  51  of the navigation system  50  and the present position VP of the vehicle V. 
     Next, in step S 110 , the ECU  10  determines whether or not the vehicle speed Vs obtained by the vehicle speed sensor  33  is equal to or lower than the target speed V 1  determined such that, when the deceleration and stop control is executed from the recognizable point Pr, the vehicle V can be stopped at the stop position PST before the traffic light S. In the case where the vehicle speed Vs is equal to or lower than the target speed V 1  (Yes), it is unnecessary to execute the gentle deceleration control before reaching the recognizable point Pr. In this case, the ECU  10  proceeds to step S 200 . Meanwhile, in the case where the vehicle speed Vs is not equal to or lower than the target speed V 1  (No); namely, in the case where the vehicle speed Vs is higher than the target speed V 1 , the ECU  10  proceeds to step S 120 . 
     In step S 200 , the ECU  10  executes the ACC continuously. Namely, in the case where no preceding vehicle to follow is present, the ECU  10  executes the constant speed travel control, and, in the case where a preceding vehicle to follow is present, the ECU  10  executes the follow-up control. 
     In step S 210 , the ECU  10  determines whether or not the present position VP of the vehicle V coincides with the recognizable point Pr; i.e., whether or not the vehicle V has reached the recognizable point Pr. In the case where the vehicle V has reached the recognizable point Pr (Yes), the ECU  10  proceeds to step S 300  of the deceleration and stop control shown in  FIG.  12   . Meanwhile, in the case where the vehicle V has not yet reached the recognizable point Pr (No), the ECU  10  returns to step S 110 . 
     In the case where the ECU  10  determines in step S 110  that the vehicle speed Vs is not equal to or lower than the target speed V 1  and proceeds to step S 120 , the ECU  10  computes the deceleration start point Psd for starting the gentle deceleration control. Next, in step S 130 , the ECU  10  determines whether or not the present position VP of the vehicle V coincides with the deceleration start point Psd; i.e., whether or not the vehicle V has reached the deceleration start point Psd. In the case where the vehicle V has reached the deceleration start point Psd (Yes), the ECU  10  proceeds to step S 140 . Meanwhile, in the case where the vehicle V has not yet reached the deceleration start point Psd (No), the ECU  10  returns to step S 110 . 
     In step S 140 , the ECU  10  determines whether or not any preceding vehicle to follow by the ACC is present. In the case where a preceding vehicle to follow is present (Yes), the ECU  10  proceeds to step S 160 . Meanwhile, in the case where no preceding vehicle to follow is present (No), the ECU  10  proceeds to step S 150 . 
     In step S 160 , the ECU  10  determines whether or not the deceleration rate A′ (absolute value) of the preceding vehicle is higher than the first deceleration rate A 1  (absolute value) used in the gentle deceleration control. In the case where the deceleration rate A′ of the preceding vehicle is higher than the first deceleration rate A 1 , if the gentle deceleration control is executed, the inter-vehicle distance between the vehicle V and the preceding vehicle becomes shorter than the set inter-vehicle distance Dd. In this case, the ECU  10  proceeds to step S 170  so as to execute the follow-up control by the ACC. At that time, preferably, the ECU  10  displays on the display apparatus  61  the preceding vehicle follow-up image  86  (see  FIGS.  9  and  10   ) which notifies the driver that the deceleration causing object is the preceding vehicle. 
     Next, in step S 190 , the ECU  10  determines whether or not the present position VP of the vehicle V coincides with the recognizable point Pr; i.e., whether or not the vehicle V has reached the recognizable point Pr. In the case where the vehicle V has reached the recognizable point Pr (Yes), the ECU  10  proceeds to step S 300  of the deceleration and stop control shown in  FIG.  12   . Meanwhile, in the case where the vehicle V has not yet reached the recognizable point Pr (No), the ECU  10  returns to step S 140 . 
     In the case where the ECU  10  determines in step S 160  that the deceleration rate A′ of the preceding vehicle is equal to or lower than the first deceleration rate A 1  (No), the ECU  10  must execute the gentle deceleration control even when the preceding vehicle does not decelerate. In this case, the ECU  10  proceeds to step S 150 . 
     In step S 150 , the ECU  10  executes the gentle deceleration control for decelerating the vehicle V at the first deceleration rate A 1  so that the vehicle speed Vs decreases to the target speed V 1 . Also, the ECU  10  displays on the display apparatus  61  the no light portion lighting image  80 A (see  FIG.  5   ) which notifies the driver that the deceleration causing object is the traffic light S detected by the navigation system  50 . Namely, the ECU  10  notifies the driver that the deceleration causing object is the traffic light S detected by the navigation system  50 . 
     In step S 190 , the ECU  10  determines whether or not the present position VP of the vehicle V coincides with the recognizable point Pr; i.e., whether or not the vehicle V has reached the recognizable point Pr. In the case where the vehicle V has reached the recognizable point Pr (Yes), the ECU  10  proceeds to step S 300  of the deceleration and stop control shown in  FIG.  12   . Meanwhile, in the case where the vehicle V has not yet reached the recognizable point Pr (No), the ECU  10  returns to step S 140 . 
     As shown in  FIG.  12   , in step S 300 , the ECU  10  obtains the lighting color of the traffic light S. 
     Next, in step S 305 , the ECU  10  determines whether or not the lighting color of the traffic light S could be obtained. In the case where the lighting color of the traffic light S could not be obtained (No), the ECU  10  proceeds to step S 400 . Meanwhile, in the case where the lighting color of the traffic light S could be obtained (Yes), the ECU  10  proceeds to step S 310 . 
     In step S 400 , the ECU  10  determines whether or not any preceding vehicle to follow is present. In the case where the ECU  10  determines that no preceding vehicle to follow is present (No), the ECU  10  proceeds to step S 410 . In step S 410 , the ECU  10  assumes that the lighting color of the traffic light S is red and executes the deceleration and stop control for causing the vehicle V to decelerate at the second deceleration rate A 2 . Also, the ECU  10  displays the red light portion lighting image  80 B (see  FIG.  6   ) on the display apparatus  61 . At that time, the ECU  10  may additionally display on the display apparatus  61  a message image or the like which notifies the driver that the ECU  10  causes the vehicle V to travel under the assumption that the lighting color of the traffic light S is red. After having executed the deceleration and stop control in step S 410 , the ECU  10  returns to step S 300 . 
     Meanwhile, in the case where the ECU  10  determines in step S 400  that a preceding vehicle to follow is present (Yes), the ECU  10  proceeds to step S 420 . In step S 420 , the ECU  10  determines whether or not the deceleration rate A′ (absolute value) of the preceding vehicle is higher than the second deceleration rate A 2  (absolute value). In the case where the deceleration rate A′ of the preceding vehicle is higher than the second deceleration rate A 2  (Yes), the ECU  10  proceeds to step S 430  and causes the vehicle V to decelerate while following the preceding vehicle by the follow-up control. At that time, preferably, the ECU  10  displays on the display apparatus  61  the preceding vehicle follow-up image  86  (see  FIGS.  9  and  10   ) which notifies the driver that the deceleration causing object is the preceding vehicle. After having caused the vehicle V in step S 430  to decelerate by the follow-up control, the ECU  10  returns to step S 300 . 
     Meanwhile, in the case where the ECU  10  determines in step S 420  that the deceleration rate A′ of the preceding vehicle is equal to or smaller than the second deceleration rate A 2  (No), the ECU  10  proceeds to step S 410 . Namely, the ECU  10  executes the deceleration and stop control for decelerating the vehicle V at the second deceleration rate A 2  without causing the vehicle V to follow the preceding vehicle. 
     In the case where the ECU  10  determines in step S 305  that the lighting color of the traffic light S could be obtained and then proceeds to step S 310 , the ECU  10  determines whether or not the obtained lighting color is green. In the case where the lighting color is green (Yes), the ECU  10  proceeds to step S 500 . Meanwhile, in the case where the lighting color is not green (No); namely, the lighting color is red or yellow, the ECU  10  proceeds to S 320 . 
     In step S 500 , the ECU  10  obtains the distance DS between the closest traffic light S 1  and the next traffic light S 2  located ahead of and adjacent to the traffic light S 1  on the basis of the map data  51  of the navigation system  50  and the present position VP of the vehicle V. Subsequently, in step S 510 , the ECU  10  determines whether the distance DS is equal to or shorter than the predetermined threshold distance DSth. In the case where the distance DS is equal to or shorter than the threshold distance DSth (Yes), the ECU  10  proceeds to step S 520 . Meanwhile, in the case where the distance DS is not equal to or shorter than the threshold distance DSth (No); namely, the distance DS is longer than the threshold distance DSth, the ECU  10  proceeds to step S 570 . 
     In step S 570 , the ECU  10  causes the vehicle V to pass the traffic light S 1  by the ACC. Namely, in the case where the set speed Vd of the ACC is higher than the target speed V 1 , the ECU  10  causes the vehicle V to pass the traffic light S 1  while accelerating the vehicle V such that the vehicle speed Vs increases to the set speed Vd. After that, the ECU  10  ends the current execution of the present routine (returns to an unillustrated original routine). 
     In the case where the ECU  10  determines in step S 510  that the distance DS is equal to or shorter than the threshold distance DSth and then proceeds to step S 520 , the ECU  10  determines whether or not any preceding vehicle to follow is present. In the case where the ECU  10  determines that no preceding vehicle to follow is present (No), the ECU  10  proceeds to step S 530  and executes the constant speed travel control for causing the vehicle V to travel at the target speed V 1 ; i.e., travel at a constant speed. At that time, the ECU  10  displays the green light portion lighting image  80 D (see  FIG.  8   ) on the display apparatus  61 . Namely, the ECU  10  notifies the driver that the ECU  10  causes the vehicle V to travel at a constant speed while recognizing that the lighting color of the traffic light S is green. 
     Meanwhile, in the case where the ECU  10  determines in step S 520  that a preceding vehicle to follow is present (Yes), the ECU  10  proceeds to step S 540  and determines whether or not the speed V′ of the preceding vehicle is higher than the target speed V 1 . In the case where the speed V′ of the preceding vehicle is higher than the target speed V 1  (Yes), if the ECU  10  causes the vehicle V to follow the preceding vehicle, the vehicle speed Vs exceeds the target speed V 1 . In this case, the ECU proceeds to step S 530  so as to execute the constant speed travel control for causing the vehicle V to travel at the target speed V 1 ; i.e., travel at a constant speed. Meanwhile, in the case where the speed V′ of the preceding vehicle is not higher than the target speed V 1  (No); namely, in the case where the speed V′ of the preceding vehicle is equal to or lower than the target speed V 1 , even when the ECU  10  causes the vehicle V to follow the preceding vehicle, the vehicle speed Vs does not exceed the target speed V 1 . In this case, the ECU proceeds to step S 550  and causes the vehicle V to follow the preceding vehicle by the follow-up control. 
     In step S 560 , the ECU  10  determines whether or not the vehicle V has passed the traffic light S 1 . In the case where the vehicle V has not yet passed the traffic light S 1  (No), the ECU  10  returns to step S 520 . Meanwhile, in the case where the vehicle V has passed the traffic light S 1  (Yes), the ECU  10  ends the current execution of the present routine (returns to the original routine). After that, at a point in time when the lighting color of the next traffic light S 2  is obtained, in accordance with the lighting color, the ECU  10  executes control similar to the control performed when the vehicle has passed the traffic light S 1 . 
     In the case where the ECU  10  determines in step S 310  that the lighting color of the traffic light S is not green and then proceeds to step S 320 , the ECU  10  determines whether or not any preceding vehicle to follow by the ACC is present. In the case where the ECU  10  determines that a preceding vehicle to follow is present (Yes), the ECU  10  proceeds step S 350 . Meanwhile, in the case where no preceding vehicle to follow is present (No), the ECU  10  proceeds to step S 330 . 
     In step S 350 , the ECU  10  determines whether or not the deceleration rate A′ (absolute value) of the preceding vehicle is higher than the second deceleration rate A 2  (absolute value) used in the deceleration and stop control. In the case where the deceleration rate A′ of the preceding vehicle is higher than the second deceleration rate A 2 , if the deceleration and stop control is executed, the inter-vehicle distance between the vehicle V and the preceding vehicle becomes shorter than the set inter-vehicle distance Dd. In this case, the ECU  10  proceeds to step S 360  so as to execute the follow-up control by the ACC. At that time, preferably, the ECU  10  displays on the display apparatus  61  the preceding vehicle follow-up image  86  (see  FIGS.  9  and  10   ) which notifies the driver that the deceleration causing object is the preceding vehicle. 
     In the case where the ECU  10  determines in step S 350  that the deceleration rate A′ of the preceding vehicle is equal to or smaller than the second deceleration rate A 2  (No), the ECU  10  must execute the deceleration and stop control even when the preceding vehicle does not decelerate. In this case, the ECU  10  proceeds to step S 330 . 
     In step S 330 , the ECU  10  executes the deceleration and stop control for causing the vehicle V to decelerate at the second deceleration rate A 2  and stop at the stop position PST before the traffic light S. Also, the ECU  10  displays on the display apparatus  61  the red light portion lighting image  80 B (see  FIG.  6   ) which notifies the driver that the deceleration causing object is the traffic light S whose lighting color could be recognized by the camera  43 . Namely, the ECU  10  notifies the driver that the deceleration causing object is the traffic light S recognized by the camera  43 . 
     In step S 370 , the ECU  10  determines whether or not the vehicle V has stopped at the stop position PST before the traffic light S. In the case where the vehicle V has not yet stopped at the stop position PST (No), the ECU  10  returns to step S 320 . Meanwhile, in the case where the vehicle V has stopped at the stop position PST (Yes), the ECU  10  ends the display of the red light portion lighting image  80 B on the display apparatus  61  and ends the current execution of the present routine (returns to the original routine). 
     In the present embodiment having been described in detail above, the ECU  10  detects a traffic light S present ahead of the vehicle Von the basis of the map data  51  of the navigation system  50  and computes the deceleration start point Psd associated with the detected traffic light S. In the case where the vehicle speed Vs at the time when the vehicle V reaches the deceleration start point Psd is higher than the target speed V 1 , the ECU  10  executes the gentle deceleration control for decelerating the vehicle V at the first deceleration rate A 1  to the target speed V 1 . At that time, the ECU  10  displays the no light portion lighting image  80 A on the display apparatus  61 . Also, when the vehicle V reaches the recognizable point Pr, the ECU  10  obtains the lighting color of the traffic light S ahead of the vehicle V by the camera  43 . In the case where the obtained lighting color is red or yellow, the ECU  10  executes the deceleration and stop control for decelerating the vehicle V at the second deceleration rate A 2  higher than the first deceleration rate A 1  and stopping the vehicle V 1  before the traffic light S. At that time, the ECU  10  displays the red light portion lighting image  80 B on the display apparatus  61 . 
     Namely, the ECU  10  is configured to selectively display the different notification images  80 A and  80 B on the display apparatus  61  depending on whether the ECU  10  executes the gentle deceleration control or the deceleration and stop control. As a result, it becomes possible to effectively notify the driver whether the deceleration causing object is the traffic light S detected on the basis of the map data  51  of the navigation system  50  or the traffic light S which is recognized by the camera  43  that its lighting color is red or yellow. Since the driver can grasp the deceleration causing object, it becomes possible for the driver to effectively monitor the deceleration control to determine whether or not the deceleration control is performed appropriately, while paying attention to the situation around the vehicle. Accordingly, it becomes possible to enhance safety without fail. 
     Although the notification control apparatus, the vehicle, the notification control method, and the program according to the present embodiment have been described, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention. 
     For example, in the above-described embodiment, the lighting colors of the traffic lights S 1  and S 2  are obtained by the camera  43 . However, the ECU  10  may be configured to obtain pieces of information representing the signal colors of the traffic lights S 1  and S 2  through data communication with an infrastructure such as a traffic control center.