Patent Publication Number: US-2020298885-A1

Title: Vehicle control apparatus, vehicle control method, vehicle, and storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Japanese Patent Application No. 2019-051451 filed on Mar. 19, 2019, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a vehicle control apparatus, a vehicle control method, a vehicle, and a storage medium, and particularly relates to vehicle control techniques for autonomously-driven vehicles. 
     Description of the Related Art 
     Japanese Patent No. 4193765 discloses a configuration in which an object in the surrounding area of a vehicle is detected by a plurality of sensors, and travel assistance control in the same control state is suppressed when the number of active detection devices decreases. 
     However, depending on the travel state of a self-vehicle, the travel state of a front vehicle traveling in front of the self-vehicle, and so on, there are cases where it is necessary to smoothly transition from the control state for the current vehicle control to a control state having a lower level of autonomy, or a control state where the driver contributes more to the vehicle operations. 
     The present invention provides a vehicle control technique that can smoothly transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, in accordance with changes in a travel state of the vehicle, a travel state of a front vehicle traveling in front of the vehicle, and so on. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a vehicle control apparatus that can control a vehicle on the basis of a plurality of control states, the apparatus comprising: a periphery monitoring unit configured to be capable of detecting a front vehicle traveling in front of the vehicle; and a vehicle control unit configured to be capable of controlling the vehicle on the basis of a travel state of the vehicle or a travel state of the front vehicle, wherein as vehicle control in the plurality of control states, the vehicle control unit can carry out vehicle control in a first control state, as well as vehicle control in a second control state in which a level of autonomy of the vehicle control is higher or the extent to which a driver is required to contribute to vehicle operations is lower than in the first control state; when, during vehicle control in the second control state, a threshold speed serving as an upper limit for carrying out vehicle control in the second control state has been reached or exceeded, the vehicle control unit carries out control to transition from vehicle control in the second control state to vehicle control in the first control state; and a first threshold speed and a second threshold speed are set as threshold speeds, the first threshold speed being for a speed of the vehicle, and the second threshold speed being for the speed of the front vehicle and being faster than the first threshold speed. 
     According to another aspect of the present invention, there is provided a vehicle control method of a vehicle control apparatus that can control a vehicle on the basis of a plurality of control states, the method comprising: an obtainment step of obtaining, from a periphery monitoring unit capable of detecting a front vehicle traveling in front of the vehicle, information of the front vehicle; and a vehicle control step of controlling the vehicle on the basis of a travel state of the vehicle or a travel state of the front vehicle, wherein in the vehicle control step: vehicle control in a first control state, as well as vehicle control in a second control state in which a level of autonomy of the vehicle control is higher or the extent to which a driver is required to contribute to vehicle operations is lower than in the first control state, can be carried out as vehicle control in the plurality of control states; when, during vehicle control in the second control state, a threshold speed serving as an upper limit for carrying out vehicle control in the second control state has been reached or exceeded, control to transition from vehicle control in the second control state to vehicle control in the first control state is carried out in the vehicle control step; and a first threshold speed and a second threshold speed are set as threshold speeds, the first threshold speed being for a speed of the vehicle, and the second threshold speed being for the speed of the front vehicle and being faster than the first threshold speed. 
     According to the present invention, it is possible to smoothly transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, in accordance with changes in a travel state of the vehicle, a travel state of a front vehicle traveling in front of the vehicle, and so on. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram illustrating an example of the configuration of a vehicle control apparatus. 
         FIG. 1B  is a diagram illustrating an example of the configuration of control blocks for controlling a vehicle. 
         FIG. 2  is a diagram illustrating the flow of processing in the vehicle control apparatus when a control state is transitioned from a first control state to a second control state. 
         FIG. 3  is a diagram illustrating the flow of processing in the vehicle control apparatus when the control state is transitioned from the second control state to the first control state. 
         FIG. 4  is a diagram illustrating the flow of processing in the vehicle control apparatus when the control state is transitioned from the second control state to the first control state. 
         FIG. 5  is a diagram schematically illustrating a travel state of a vehicle. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention, and limitation is not made an invention that requires all combinations of features described in the embodiments. Two or more of the multiple features described in the embodiments may be combined as appropriate. Furthermore, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     First Embodiment 
     Configuration of Vehicle Control Apparatus 
       FIG. 1A  is a diagram illustrating an example of the configuration of a travel control system including a vehicle control apparatus  100  that controls automated driving of a vehicle; the vehicle control apparatus  100  includes sensors S, a plurality of cameras CAM, a cabin monitor camera MON, and a computer COM. The sensors S include, for example, a plurality of radar S 1 , a plurality of LIDAR S 2  (Light Detection and Ranging), a gyrosensor S 3 , a GPS sensor S 4 , a speed sensor S 5 , a grip sensor S 6 , and the like. 
     The computer COM includes a CPU (C 1 ) that controls processing pertaining to controlling the automated driving of the vehicle, memory C 2 , a communication apparatus C 3  that is connected to a network NET and that can communicate with a server apparatus located on the network, other vehicles located in the periphery of the vehicle (the self-vehicle), and so on. The sensors S and the cameras CAM obtain various types of information of the vehicle and input that information to the computer COM. 
     The CPU (C 1 ) of the computer COM carries out image processing on image information input from the cameras CAM. On the basis of the camera image information subjected to the image processing and sensor information input from the sensors S (radar S 1  and LIDAR S 2 ), the CPU (C 1 ) extracts an object present in the surrounding area of the self-vehicle, analyzes how the object is arranged in the surrounding area of the self-vehicle, and monitors the object. 
     The gyrosensor S 3  detects rotational movement, the orientation, and so on of the self-vehicle, and the computer COM can determine the path of the self-vehicle on the basis of detection results from the gyrosensor S 3 , a speed detected by the speed sensor S 5 , and so on. The GPS sensor S 4  detects the current position (position information) of the self-vehicle in map information. 
     The grip sensor S 6  is built into a steering wheel of the vehicle, for example, and can detect whether or not a vehicle occupant (a driver) is gripping the steering wheel. The grip sensor S 6  inputs detected steering wheel grip information to the computer COM. On the basis of the steering wheel grip information input from the grip sensor S 6 , the computer COM can determine whether or not a vehicle occupant (the driver) is gripping the steering wheel, i.e., whether the steering wheel is in a hands-on state or a hands-off state. 
     The cabin monitor camera MON is disposed so as to be capable of shooting an image of the interior of the vehicle, and shoots an image of a vehicle occupant. The cabin monitor camera MON inputs appearance information obtained by shooting an image of the vehicle occupant to the computer COM. By carrying out image processing on an image of the occupant of the vehicle input from the cabin monitor camera MON, the computer COM can detect the appearance information of the vehicle occupant, which includes the vehicle occupant&#39;s expression, facial orientation, line of sight, driving posture, how open/closed his/her eyes are, and so on. On the basis of the detected appearance information of the vehicle occupant, the computer COM can determine whether the state of the vehicle occupant (the driver) while driving is an eyes-on state or an eyes-off state. 
     A notification apparatus NTF includes an audio output apparatus and a display apparatus, and the audio output apparatus communicates information to the driver using audio. The display apparatus communicates information to the driver by displaying images. 
     The computer COM of the vehicle control apparatus  100  can control automated driving travel of the vehicle by causing the vehicle to transition among a plurality of control states on the basis of information of the peripheral environment of the vehicle. In other words, the computer COM obtains information of the peripheral environment of the vehicle using the information from the sensors S and the cameras CAM, and controls the automated driving travel of the vehicle by causing the vehicle control state to transition on the basis of the information of the peripheral environment. 
     The CPU (C 1 ) of the computer COM functions as a vehicle control unit C 11  and an image processing unit C 12  by executing programs stored in the memory C 2 . The vehicle control unit C 11  controls the vehicle on the basis of detection results from a detecting unit that detects information of the vehicle and information of the vehicle&#39;s periphery (the sensors S, the cameras CAM, and so on). The automated driving travel of the vehicle is controlled by one of the plurality of control states. 
     When the vehicle control apparatus  100  illustrated in  FIG. 1A  is installed in a vehicle, the computer COM may, for example, be provided in a recognition processing system ECU, an image processing system ECU, or the like that processes information from the sensors S, the cameras CAM, the cabin monitor camera MON, and the like, or may be provided in an ECU that controls the communication apparatus, an input/output device, and the like, or may be provided in an ECU in a control unit, an automated driving ECU, or the like that controls the driving of the vehicle. For example, as illustrated in  FIG. 1B , which will be described below, functions may be distributed among a plurality of ECUs constituting the vehicle control apparatus  100 , such as sensor S ECUs, camera ECUs, input/output device ECUs, and automated driving ECUs. 
       FIG. 1B  is a diagram illustrating an example of the configuration of control blocks in the vehicle control apparatus  100  for controlling a vehicle  1 . An overview of the vehicle  1  is illustrated in  FIG. 1B , both as a plan view and as a side view. The vehicle  1  is, for example, a sedan-type four-wheeled passenger vehicle. 
     A control unit  2  in  FIG. 1B  controls the various units of the vehicle  1 . The control unit  2  includes a plurality of ECUs  20  to  29 , which are communicatively connected over an in-vehicle network. Each ECU (Electronic Control Unit) includes a processor such as a CPU (Central Processing Unit), a storage device such as semiconductor memory, an interface with external devices, and the like. The storage device stores programs executed by the processor, the data used in processing by the processor, and so on. Each ECU may include a plurality of processors, storage devices, interfaces, and so on. 
     Functions and the like handled by the ECUs  20  to  29  will be described hereinafter. Note that the number of ECUs, the functions handled by the ECUs, and so on can be designed as appropriate for the vehicle  1 , and can be set at a finer or broader level than that described in the present embodiment. 
     The ECU  20  executes vehicle control pertaining to the automated driving of the vehicle  1  (the self-vehicle) according to the present embodiment. During automated driving, at least one of the steering and the acceleration/deceleration of the vehicle  1  is automatically controlled. Specific processing pertaining to the control involved in the automated driving will be described in detail later. 
     The ECU  20  controls the travel of the vehicle on the basis of the position of the vehicle  1  (the self-vehicle), the relative position of other vehicles present in the periphery of the vehicle  1 , information of the road the vehicle  1  is traveling on, the map information, and so on, which indicate the surrounding conditions of the vehicle. 
     The ECU  21  controls an electric power steering device  3 . The electric power steering device  3  includes a mechanism for turning the front wheels in response to a driver making a driving operation (turning operation) on a steering wheel  31 . The electric power steering device  3  also includes a motor for assisting the turning operation or for producing drive power for automatically turning the front wheels, a sensor for detecting a steering angle, and the like. When the driving state of the vehicle  1  is automated driving, the travel direction of the vehicle  1  is controlled by the ECU  21  automatically controlling the electric power steering device  3  in accordance with instructions from the ECU  20 . 
     The ECUs  22  and  23  control detecting units  41  to  43 , which detect the surrounding conditions of the vehicle, and process information of detection results. The detecting unit  41  is an element corresponding to the cameras CAM of  FIG. 1A , and is an image capturing device that detects an object in the surrounding area of the vehicle  1  by capturing an image (this may be referred to as cameras  41 A and B hereinafter). The cameras  41  are attached to the windshield, within the vehicle cabin, in an area corresponding to a forward part of the roof of the vehicle  1 , so as to be capable of shooting images of the area in front of the vehicle  1 . By analyzing the images shot by the cameras  41 A and B (image processing), the contours of objects such as a front vehicle traveling in front of the vehicle  1  in the lane in which the vehicle  1  is traveling, lane dividing lines (white lines and the like) on the road, and so on can be extracted, for example. 
     The detecting unit  42  (LIDAR detecting unit) is, for example, Light Detection and Ranging (LIDAR) (also called “LIDAR  42 ” hereinafter), which detects objects in the surrounding area of the vehicle  1 , measures the distances to those objects, and so on by using light. The detecting unit  42  (LIDAR  42 ) is an element corresponding to LIDAR S 2  in  FIG. 1A . In the present embodiment, a plurality of LIDAR  42  are provided around the vehicle. In the example illustrated in  FIG. 1B , five of the LIDAR  42  are provided, for example: one on each front corner of the vehicle  1 , one in the rear center, and one each on the rear sides of the vehicle  1 . 
     The detecting unit  43  (radar detecting unit) is, for example, millimeter wave radar (also called “radar  43 ” hereinafter), which detects objects in the surrounding area of the vehicle  1 , measures the distances to those objects, and so on using millimeter waves. The detecting unit  43  (radar  43 ) is an element corresponding to the radar S 1  in  FIG. 1A . In the present embodiment, a plurality of radar  43  are provided around the vehicle. In the example illustrated in  FIG. 1B , five of the radar  43  are provided, for example: one in the front center of the vehicle  1 , one on each front corner, and one on each rear corner. 
     The ECU  22  controls the one camera  41 A and each LIDAR  42 , and processes information of the detection results therefrom. The ECU  23  controls the other camera  41 B and each radar  43 , and processes information of the detection results therefrom. By providing two sets of devices that detect the surrounding conditions of the vehicle, the reliability of the detection results can be improved; furthermore, by providing different types of detecting units, i.e., cameras, LiDAR, and radar, the peripheral environment of the vehicle can be analyzed in several different ways. Note that the ECU  22  and the ECU  23  may be realized by a single ECU. 
     The ECU  24  controls a gyrosensor  5 , a GPS sensor  24   b,  and a communication apparatus  24   c,  and processes information of detection results or communication results therefrom. The gyrosensor  5  detects rotational movement of the vehicle  1 . The path of the vehicle  1  can be determined from the detection results from the gyrosensor  5 , the wheel speed, and so on. The GPS sensor  24   b  detects the current position of the vehicle  1 . The communication apparatus  24   c  communicates wirelessly with a server apparatus that provides map information, traffic information, and the like, and obtains that information. The ECU  24  can access a map information database  24   a  provided in the storage device, and the ECU  24  searches for routes from the current location to a destination and the like. The database  24   a  can be located on a network, and the communication apparatus  24   c  can access the database  24   a  on the network and obtain the information. The gyrosensor  5 , the GPS sensor  24   b,  and the communication apparatus  24   c  are elements corresponding to the gyrosensor S 3 , the GPS sensor S 4 , and the communication apparatus C 3  of  FIG. 1A , respectively. 
     The ECU  25  includes a communication apparatus  25   a  for vehicle-to-vehicle communication. The communication apparatus  25   a  communicates wirelessly with other vehicles in the periphery, and exchanges information with those vehicles. 
     The ECU  26  controls a power plant  6 . The power plant  6  is a mechanism for outputting drive power that rotates drive wheels of the vehicle  1 , and includes an engine and a transmission, for example. For example, the ECU  26  controls the output of the engine in response to a driving operation (an acceleration operation or a deceleration operation) made by the vehicle occupant (the driver), detected by an operation detecting sensor  7   a  provided in an accelerator pedal  7 A, switches the gear ratio of the transmission on the basis of information such as a speed detected by a speed sensor  7   c  (the speed sensor S 5  of  FIG. 1A ), and the like. When the driving state of the vehicle  1  is automated driving, the ECU  26  automatically controls the power plant  6  in response to instructions from the ECU  20 , and controls the acceleration/deceleration of the vehicle  1 . 
     The ECU  27  controls lights (headlights, taillights, and the like), including directional indicators  8 . In the example illustrated in  FIG. 1B , the directional indicators  8  are provided in a front area, a rear area, and on the door mirrors of the vehicle  1 . 
     The ECU  28  can control an input/output device  9  and carry out image processing on a facial image of the driver input from a cabin monitoring camera  90 . Here, the cabin monitoring camera  90  corresponds to the cabin monitor camera MON of  FIG. 1A . The input/output device  9  outputs information to the vehicle occupant (the driver) and accepts settings from the driver. An audio output apparatus  91  communicates information to the driver through audio. A display apparatus  92  communicates information to the driver by displaying images. The display apparatus  92  is disposed, for example, in front of the driver&#39;s seat, and constitutes an instrument panel and the like, for example. Although audio and a display are mentioned here as examples, information may be communicated through vibrations, lights, or the like. The information may also be communicated using a combination of audio, a display, vibrations, and lights. Furthermore, the combinations may be varied, or the states of the notifications may be varied, in accordance with a level (e.g., a level of urgency) of the information to be communicated. The audio output apparatus  91  and the display apparatus  92  correspond to the notification apparatus NTF of  FIG. 1A  described earlier, for example. 
     An input apparatus  93  is disposed in a position where the device can be operated by the driver, and is a group of switches for making instructions to the vehicle  1 ; however, an audio input apparatus may be included as well. 
     The ECU  29  controls a braking apparatus  10 , a parking brake (not shown), and the like. The braking apparatus  10  is, for example, a disk brake apparatus, provided in each of the wheels of the vehicle  1 , which causes the vehicle  1  to decelerate or stop by applying resistance against the rotation of the wheels. The ECU  29  controls the operations of the braking apparatus  10  in response to a driving operation (a braking operation) made by the driver, detected by an operation detecting sensor  7   b  provided in a brake pedal  7 B, for example. If the driving state of the vehicle  1  is automated driving, the ECU  29  controls the deceleration and stopping of the vehicle  1  by automatically controlling the braking apparatus  10  in response to instructions from the ECU  20 . The braking apparatus  10 , the parking brake, and the like can also be operated in order to keep the vehicle  1  in a stopped state. Furthermore, if the transmission of the power plant  6  is provided with a parking lock mechanism, that parking lock mechanism can also be operated in order to keep the vehicle  1  in a stopped state. 
     Plurality of Control States 
     In the present embodiment, vehicle control pertaining to steering, control, and the like, including vehicle acceleration and deceleration, lane changes, and so on, as well as tasks required of the vehicle occupant (the driver), are set in the plurality of control states. Tasks required of the vehicle occupant include operations required of the vehicle occupant in order to respond to the need to monitor the vehicle periphery, e.g., gripping the steering wheel (hands off or hands on), monitoring the periphery (eyes off or eyes on), handing off driving control, and so on. 
     The plurality of control states are classified into a plurality of stages in accordance with the extent of autonomy in the vehicle control (the level of autonomy), and the extent of the tasks required of the vehicle occupant (the driver) (the extent to which the vehicle occupant contributes to vehicle operations). 
     The vehicle control apparatus  100  can control the vehicle on the basis of the plurality of control states, and the vehicle control unit C 11  can control the automated driving travel of the vehicle through one of the plurality of control states on the basis of periphery monitoring information (outside information) obtained from the LIDAR  42 , the camera  41 A, the radar  43 , the camera  41 B, and the like. For example, the sensors S and the cameras CAM ( FIG. 1A ), the detecting units  41  to  43  (the LIDAR  42 , the camera  41 A, the radar  43 , and the camera  41 B of  FIG. 1B ) function as a periphery monitoring unit capable of detecting a front vehicle traveling in front of the vehicle  1 , and the vehicle control unit C 11  can control the vehicle on the basis of the travel state of the vehicle  1  or the travel state of the front vehicle. 
     First Control State 
     In the present embodiment, the first control state is a control state in which a predetermined extent of autonomy in the vehicle control (the level of autonomy), and a predetermined extent of the tasks required of the vehicle occupant (the driver) (the extent to which the vehicle occupant contributes to vehicle operations), are set. In the first control state, the primary operator of the vehicle is the driver, and although the driver is required to monitor the periphery, the driver is not required to grip the steering wheel. The first control state is a control state that can be executed in, for example, a main lane of an uncongested highway. 
     Second Control State 
     The second control state is a control state in which the level of autonomy (the extent of autonomy) of the vehicle control is higher, or the extent to which the driver is required to contribute to vehicle operations is lower, than in the first control state. In the second control state, the primary operator of the vehicle is the vehicle control apparatus  100  (a vehicle system), and the driver is required neither to monitor the periphery nor grip the steering wheel. However, the driver is required to monitor the vehicle system in preparation for an alert notification from the vehicle system. The second control state is a control state in which vehicle control can be carried out within the lane in which the vehicle  1  is traveling (e.g., L 2 , indicated in ST 51  of  FIG. 5 ), in a predetermined speed range in which vehicle control is active; for example, this control state can be executed in a travel situation where the vehicle  1  (the self-vehicle) follows a front vehicle  501  (ST 1  in  FIG. 5 ) in a main lane of a congested highway (Traffic Jam Pilot; TJP). 
     As control in the plurality of control states, the vehicle control unit C 11  can carry out vehicle control in the first control state, as well as vehicle control in the second control state, in which the level of autonomy of the vehicle control is higher or the extent to which the driver is required to contribute to vehicle operations is lower than in the first control state. 
     Note that the control states are not limited to the foregoing examples, and for example, vehicle control can also be carried out in a control state in which the level of autonomy (the extent of autonomy) of the vehicle control is lower, or the extent to which the driver is required to contribute to vehicle operations is higher, than in the first control state (called a “third control state” hereinafter). In the third control state, the primary operator of the vehicle is the driver, and the driver is required to monitor the periphery. The driver is also required to grip the steering wheel. 
     Furthermore, in addition to the first to third control states, the vehicle control unit C 11  can also control the vehicle in a mode in which no driving assistance is active. 
     Setting Threshold Vehicle Speed in Vehicle Control Apparatus Threshold Vehicle Speed Pertaining to Transition from Second Control State to First Control State 
     When, during vehicle control in the second control state, a threshold speed serving as an upper limit for carrying out vehicle control in the second control state has been reached or exceeded, the vehicle control unit C 11  carries out control to transition from vehicle control in the second control state to vehicle control in the first control state. In the present embodiment, a plurality of threshold vehicle speeds serving as references are set in the vehicle control unit C 11 . In other words, a first threshold speed for the speed of the vehicle  1  (the self-vehicle), and a second threshold speed which is for the front vehicle and is faster than the first threshold speed, are set as threshold speeds. 
     For example, the first threshold speed (e.g., V 1 =40 km/h) is set for the speed of the vehicle  1  (the self-vehicle), and the second threshold speed, which is faster than the first threshold speed (e.g., V 2 =50 km/h) is set for the speed of the front vehicle (e.g.,  501  in  FIG. 5 ), as the threshold vehicle speeds used when starting a transition from the second control state to the first control state. 
     Assuming, for example, the same threshold speed is set for the vehicle  1  (the self-vehicle) and the front vehicle, if the front vehicle accelerates in a state where driving control is required to be handed off to the driver of the vehicle  1  (the self-vehicle) (e.g., a state of standing by to transition from the second control state to the first control state), the inter-vehicle distance will become greater than is necessary, and the transition to the new control state may therefore disrupt the flow of traffic. 
     In the present embodiment, the upper limit vehicle speed at which vehicle control is carried out in the second control state is set to the second threshold speed (V 2 ) pertaining to the speed of the front vehicle. Additionally, the speed threshold for the vehicle  1  (the self-vehicle) is set lower than the second threshold speed so that the driver can respond to a driving handoff request output from the vehicle control apparatus  100  side and a smooth transition can be made from the second control state to the first control state. In other words, a slower vehicle speed than the vehicle speed serving as the upper limit at which vehicle control can be carried out in the second control state is set as the first threshold speed (V 1 ) pertaining to the speed of the vehicle  1  (the self-vehicle). 
     When, during vehicle control in the second control state, a threshold speed serving as an upper limit for carrying out vehicle control in the second control state has been reached or exceeded, the vehicle control unit C 11  carries out control to transition from vehicle control in the second control state to vehicle control in the first control state. In other words, when, during vehicle control in the second control state, the speed of the vehicle  1  (the self-vehicle) has become greater than or equal to the first threshold speed, or the speed of the front vehicle  501  has become greater than or equal to the second threshold speed, the vehicle control unit C 11  transitions from vehicle control in the second control state to vehicle control in the first control state. 
     Note that the speeds indicated as the first threshold speed (V 1 ) and the second threshold speed (V 2 ) are merely examples, and it is sufficient for the relative relationship between the first threshold speed (V 1 ) and the second threshold speed (V 2 ) to be maintained. Additionally, during vehicle control in the second control state, it is also possible for the vehicle control unit C 11  to transition from vehicle control in the second control state to vehicle control in the first control state under the conditions that the speed of the vehicle  1  (the self-vehicle) has become greater than or equal to the first threshold speed, and the speed of the front vehicle  501  has become greater than or equal to the second threshold speed. 
     Threshold Vehicle Speed Pertaining to Transition from First Control State to Second Control State 
     Additionally, a third threshold speed that is slower than the first threshold speed (e.g., V 3 =30 km/h) is set in the vehicle control unit C 11  as a threshold vehicle speed used when starting a transition from the first control state to the second control state. When, during vehicle control in the first control state, the speed of the vehicle  1  (the self-vehicle) or the speed of the front vehicle  501  has become less than the third threshold speed, the vehicle control unit C 11  transitions from vehicle control in the first control state to vehicle control in the second control state. When the speed of the vehicle  1  (the self-vehicle) becomes less than the third threshold speed and the vehicle control transitions from the first control state to the second control state, the control state remains the second control state until the speed of the vehicle  1  (the self-vehicle) becomes greater than or equal to the first threshold speed or the speed of the front vehicle  501  becomes greater than or equal to the second threshold speed. 
     Note that during vehicle control in the first control state, it is also possible for the vehicle control unit C 11  to transition from vehicle control in the first control state to vehicle control in the second control state under the conditions that the speed of the vehicle  1  (the self-vehicle) and the speed of the front vehicle  501  have become less than the third threshold speed. 
     Process for Transitioning from First Control State to Second Control State 
     The flow of a process for transitioning from the first control state to the second control state in the vehicle control apparatus will be described next.  FIG. 2  is a diagram illustrating the flow of processing carried out by the vehicle control apparatus  100  when the control state transitions from the first control state to the second control state, and the vehicle control apparatus  100  repeatedly executes the processing illustrated in  FIG. 2  every predetermined sampling period while vehicle control is being carried out in the first control state. 
     In step S 21 , the vehicle control unit C 11  determines whether or not there is a front vehicle traveling in front of the vehicle  1  on the basis of detection results from the periphery monitoring unit (the sensors S and the cameras CAM ( FIG. 1A ), the detecting units  41  to  43  ( FIG. 1B ), and so on). 
     Note that in the process of step S 21 , the vehicle control unit C 11  can also obtain a degree to which a lane width overlaps with a vehicle width of the front vehicle as vehicle width direction position information of the front vehicle  501  in the lane. For example, if 10% of the vehicle width of the front vehicle is protruding into the adjacent lane, the vehicle control unit C 11  obtains 90% as the degree to which the vehicle width of the front vehicle  501  overlaps in the lane, on the basis of the detection results from the periphery monitoring unit. Likewise, if 30% of the vehicle width of the front vehicle is protruding into the adjacent lane, the vehicle control unit C 11  obtains 70% as the degree to which the vehicle width of the front vehicle  501  overlaps in the lane, on the basis of the detection results from the periphery monitoring unit. 
     The vehicle control unit C 11  can determine changes in the vehicle width direction position information of the front vehicle  501  in the lane (changes in the position information occurring over time) on the basis of the detection results from the periphery monitoring unit. On the basis of changes in the vehicle width direction position information, the vehicle control unit C 11  can determine whether or not the front vehicle  501  is gradually moving sideways toward the adjacent lane, to the right or to the left of the center of the lane. 
     The periphery monitoring unit can obtain dimension information indicating the extent to which the vehicle width of the front vehicle protrudes toward the adjacent lane as an amount of skew between the center of the lane width and the center of the vehicle width of the front vehicle, and can also obtain an amount of skew (offset amount) between the center of the lane width and the center of the vehicle width of the front vehicle, and determine whether or not the front vehicle  501  is in a state of gradually moving sideways from the center of the lane toward the adjacent lane on the basis of changes in the offset amount (changes in the offset amount over time). 
     Furthermore, in order to travel so as to follow the front vehicle, the vehicle control unit C 11  can also determine the degree to which the vehicle width of the front vehicle overlaps with the vehicle width of the vehicle  1  (the self-vehicle) on the basis of the detection results from the periphery monitoring unit, and if there is skew with respect to the vehicle width direction, control the position with respect to the vehicle width direction so as to cancel out the skew. 
     When traffic jam pilot is carried out as the second control state, the presence of the front vehicle  501  (the front vehicle directly in front) traveling ahead of the vehicle  1  (the self-vehicle) in the same lane (e.g., L 2  indicated in ST 51  of  FIG. 5 ) is a requirement for transitioning from the first control state to the second control state. For example, a situation where a front vehicle  502  has made a lane change  500  to an adjacent lane L 3  and there is no longer any front vehicle in the lane L 2  in which the vehicle  1  (the self-vehicle) is traveling, as indicated by ST 52  in  FIG. 5 , does not meet the conditions for the transition. 
     Even if the front vehicle  501  is present within the lane width, the travel trajectory of the front vehicle  501  cannot be traced if the front vehicle  501  changes lanes by gradually moving sideways, to the right or to the left, from the center of the lane. To determine whether or not to change lanes, a threshold pertaining to sideways movement of the front vehicle  501  (a sideways movement reference value) may be set, and the vehicle control unit C 11  may determine whether or not it is possible to follow the front vehicle  501  on the basis of the comparison between the sideways movement reference value and the position information of the front vehicle  501  in the lane. 
     Even if the front vehicle  501  is present within the lane width, the vehicle control unit C 11  determines that the front vehicle will change lanes to an adjacent lane when the position information of the front vehicle  501  within the lane exceeds the sideways movement reference value. In such a case, the vehicle control unit C 11  determines that the conditions for transitioning from the first control state to the second control state are not met. 
     In the determination of step S 21 , if a front vehicle has not been detected, or if a front vehicle has been detected but the position information of the front vehicle  501  in the lane exceeds the sideways movement reference value (step S 21 —No), the process of step S 21  is repeatedly executed in a detection standby state. On the other hand, if a front vehicle has been detected in the determination process of step S 21  (step S 21 —Yes), the vehicle control unit C 11  moves the process to step S 22 . 
     In step S 22 , the vehicle control unit C 11  determines whether the vehicle width of the detected front vehicle is within the range of a threshold vehicle width. In this step, the vehicle control unit C 11  determines whether the front vehicle is a target for following travel, carried out in the vehicle control in the second control state, on the basis of a comparison between the vehicle width of the front vehicle and the threshold vehicle width serving as a reference. If the vehicle width of the front vehicle  501  exceeds an upper limit value of the threshold vehicle width serving as a reference, or is lower than a lower limit value of the threshold vehicle width, the vehicle control unit C 11  determines that the front vehicle  501  is not a target for following travel carried out in the vehicle control in the second control state. In this case, the front vehicle  501  is assumed to be outside the range of the threshold vehicle width (step S 22 —No), and the vehicle control unit C 11  therefore returns the process to step S 21  and repeatedly executes the same process. 
     For example, when the vehicle  1  (the self-vehicle) is a sedan-type four-wheeled passenger vehicle, if a truck or the like that is larger than the vehicle  1  (the self-vehicle) becomes the front vehicle, it may be necessary to stay alert for cargo falling from the truck, for example. Meanwhile, if the front vehicle is a two-wheeled vehicle or the like, that vehicle has a narrower vehicle width than the vehicle  1  (the self-vehicle), and thus even if the front vehicle can travel through a given region, it may not be possible for the vehicle  1  (the self-vehicle) to travel through the same region. In this case, the range of the threshold vehicle width is set, and vehicles outside the range of the threshold vehicle width are excluded from targets for following travel carried out in the vehicle control in the second control state (the front vehicle). 
     On the other hand, if, in the determination process of step S 22 , the vehicle width of the front vehicle  501  is within the range of the threshold vehicle width (less than or equal to the upper limit value for the threshold vehicle width and greater than or equal to the lower limit value for the threshold vehicle width; S 22 —Yes), the vehicle control unit C 11  sets the front vehicle  501  as a target for following travel, and moves the process to step S 23 . 
     In step S 23 , the vehicle control unit C 11  obtains speed information of the vehicle  1  (the self-vehicle) and the front vehicle  501 . 
     The vehicle control unit C 11  can obtain the speed information of the vehicle  1  (the self-vehicle) and the speed information of the front vehicle detected by the periphery monitoring unit (the sensors S and the cameras CAM ( FIG. 1A ), the detecting units  41  to  43  ( FIG. 1B ), and so on). It is also possible for the vehicle control unit C 11  to obtain the speed information of the front vehicle from a change over time in the relative distance to the vehicle (the self-vehicle) obtained in the detection results from the periphery monitoring unit. Alternatively, the vehicle control unit C 11  can obtain the speed information through vehicle-to-vehicle communication with the front vehicle. 
     In step S 24 , the vehicle control unit C 11  compares the speed information obtained in step S 23  with a threshold speed (the third threshold speed). On the basis of the result of the comparison process, if, during vehicle control in the first control state, the speed of the vehicle  1  (the self-vehicle) or the speed of the front vehicle  501  has become less than the third threshold speed (step S 24 —Yes), the vehicle control unit C 11  transitions from vehicle control in the first control state to vehicle control in the second control state (step S 25 ). 
     On the other hand, if, in the comparison process carried out in step S 24 , the speed becomes greater than or equal to the threshold speed (the third threshold) (step S 24 —No), the process returns to step S 23 , where the speed information of the vehicle  1  (the self-vehicle) or the front vehicle  501  is obtained again and the comparison process of step S 24  is carried out. 
     Note that conditions such as the type of the traveled road being a highway can also be included, as a prerequisite, as conditions for transitioning to a different control state. 
     Process for Transitioning from Second Control State to First Control State 
     The flow of a process for transitioning from the second control state to the first control state in the vehicle control apparatus will be described next.  FIGS. 3 and 4  are diagrams illustrating the flow of processing carried out by the vehicle control apparatus  100  when the control state transitions from the second control state to the first control state, and the vehicle control apparatus  100  repeatedly executes the processing illustrated in  FIGS. 3 and 4  every predetermined sampling period while vehicle control is being carried out in the second control state. 
     In step S 31 , the vehicle control unit C 11  confirms the presence of a front vehicle. The vehicle control unit C 11  confirms the presence of the front vehicle  502  traveling in front of the vehicle  1  (the self-vehicle) in the same lane (e.g., L 3  indicated in ST 53  of  FIG. 5 ) on the basis of the detection results from the periphery monitoring unit. 
     The communication apparatus  25   a  can communicate with other vehicles traveling in the periphery of the vehicle  1 , and information can be exchanged with other vehicles in the periphery through wireless communication with those vehicles. On the basis of the information from at least one of the periphery monitoring unit and the communication apparatus  25   a,  the vehicle control unit C 11  determines whether or not a forward front vehicle group  505 , including at least one forward front vehicle ( 503  and  504 ) traveling in front of the front vehicle  502 , is present in the same lane as the lane in which the vehicle  1  (the self-vehicle) is traveling and within a reference inter-vehicle distance from the vehicle  1  (ST 53  in  FIG. 5 ). Here, a vehicle traveling in front of the front vehicle  502  is called a “forward front vehicle”, and a plurality of vehicles including at least one forward front vehicle is called a “forward front vehicle group”. 
     Here, the vehicle control unit C 11  compares inter-vehicle distances L 1  and L 2 , respectively between the vehicle  1  and a first forward front vehicle  503  and a second forward front vehicle  504  included in the forward front vehicle group  505 , with an inter-vehicle distance LS serving as a reference. If the inter-vehicle distances L 1  and L 2  are within the inter-vehicle distance LS serving as a reference, the vehicle control unit C 11  sets the first forward front vehicle  503  and the second forward front vehicle  504  as candidates for targets of following travel. However, if the inter-vehicle distances L 1  and L 2  are greater than the inter-vehicle distance LS serving as a reference, the vehicle control unit C 11  excludes the first forward front vehicle  503  and the second forward front vehicle  504  as candidates for targets of following travel. In this case, the vehicle control unit C 11  determines that the forward front vehicle group  505  is not present in the same lane. In this step, the vehicle control unit C 11  carries out the processes for confirming the presence of the front vehicle  502  and confirming the presence of the forward front vehicle group  505  in parallel. 
     In step S 32 , the vehicle control unit C 11  determines whether the front vehicle  502  has changed lanes to the adjacent lane L 3  and has therefore departed the lane L 2  in which the vehicle  1  is traveling. If, in the determination of step S 32 , the front vehicle has not changed lanes (S 32 —No), the vehicle control unit C 11  moves the process to step S 35 . 
     In step S 32 , the vehicle control unit C 11  obtains the degree to which the lane width overlaps with the vehicle width of the front vehicle (or the amount of skew between the center of the lane width and the center of the vehicle width of the front vehicle) as position information of the front vehicle  501  in the lane, in the same manner as in the process of the earlier step S 21 . Then, the vehicle control unit C 11  determines whether or not it is possible to follow the front vehicle  501  on the basis of a comparison between a threshold pertaining to sideways movement (the sideways movement reference value) and the position information of the front vehicle  501  in the lane. Even if the front vehicle  501  is present within the lane width, the vehicle control unit C 11  determines that the front vehicle will change lanes to an adjacent lane when the position information of the front vehicle  501  within the lane exceeds the sideways movement reference value. 
     On the other hand, if, in the determination of step S 32 , the front vehicle  502  has changed lanes to the adjacent lane L 3  (S 32 —Yes), the vehicle control unit C 11  moves the process to step S 33 . 
     In step S 33 , the vehicle control unit C 11  determines whether or not the forward front vehicle group  505  is present. If the forward front vehicle group  505  is not present in the same lane L 2 , i.e., if the front vehicle  502  has departed the same lane L 2  by making a lane change (S 32 —Yes), and if the forward front vehicle group  505  traveling in front of the front vehicle  502  is not present (S 33 —No), the vehicle control unit C 11  moves the process to step S 37  and transitions from vehicle control in the second control state to vehicle control in the first control state. 
     On the other hand, if, in the determination process of step S 33 , the forward front vehicle group  505  is present (S 33 —Yes), the process moves to step S 34 . 
     In step S 34 , the vehicle control unit C 11  determines whether the vehicle width of the forward front vehicle is within the range of a threshold vehicle width. The vehicle control unit C 11  determines whether the front vehicle is to be a target for following travel, carried out in the vehicle control in the second control state, on the basis of a comparison between the vehicle width of the front vehicle or the vehicle width of a forward front vehicle included in the forward front vehicle group  505  and the threshold vehicle width serving as a reference. 
     For example, if the vehicle width of the first forward front vehicle  503  (a two-wheeled vehicle), which serves as the forward front vehicle included in the forward front vehicle group  505 , exceeds an upper limit value of the threshold vehicle width serving as a reference, or is lower than a lower limit value of the threshold vehicle width, the vehicle control unit C 11  excludes the first forward front vehicle from targets for following travel carried out in the vehicle control in the second control state. In other words, if the vehicle width of the first forward front vehicle  503  (a two-wheeled vehicle) is less than the lower limit value of the threshold vehicle width, the first forward front vehicle  503  is excluded from the targets for following travel. 
     In this case, the vehicle control unit C 11  makes the same determination for the second forward front vehicle  504  (a sedan-type four-wheeled vehicle), which is a forward front vehicle included in the forward front vehicle group  505  and is a candidate for a target for the following travel. If the vehicle width of the second forward front vehicle  504 , which is traveling in front of the first forward front vehicle  503  in the forward front vehicle group  505 , is within the range of the threshold vehicle width, the vehicle control unit C 11  sets the second forward front vehicle  504  as a target for following travel. If the vehicle width of the second forward front vehicle  504  is outside the range of the threshold vehicle width, the second forward front vehicle  504  is excluded from the targets for following travel. 
     The communication apparatus  25   a  can obtain dimension information including the vehicle width of the forward front vehicles included in the forward front vehicle group  505  through vehicle-to-vehicle communication, and the vehicle control unit C 11  carries out the determination process on the basis of the information obtained by the communication apparatus  25   a.    
     In step S 35 , the vehicle control unit C 11  specifies a vehicle for comparison with the second threshold speed. 
     If, in the determination process of step S 32 , the front vehicle  502  is not changing lanes (S 32 —No), the vehicle control unit C 11  specifies the front vehicle  502  as the vehicle for comparison with the second threshold speed. 
     On the other hand, if, in the determination process of step S 32 , the front vehicle  502  is changing lanes (S 32 —Yes), the forward front vehicle, among the forward front vehicle group  505 , that is within the range of the threshold vehicle width is specified as the vehicle for comparison with the second threshold speed. For example, if the first forward front vehicle  503  has been excluded but the vehicle width of the second forward front vehicle  504  is within the range of the threshold vehicle width, the vehicle control unit C 11  specifies the second forward front vehicle  504  as the vehicle for comparison with the second threshold speed. 
     In step S 36 , the vehicle control unit C 11  moves the process to step S 41  of  FIG. 4 . 
     In step S 41  of  FIG. 4 , the vehicle control unit C 11  obtains the speed information of the vehicle  1  (the self-vehicle) and the vehicle specified in step S 35  of  FIG. 3  (e.g., the front vehicle  502  or the second forward front vehicle  504 ). 
     The vehicle control unit C 11  can obtain the speed information of the vehicle  1  (the self-vehicle) and the speed information of the specified vehicle (the front vehicle  502  or the second forward front vehicle  504 ), which are detected by the periphery monitoring unit. 
     It is also possible for the vehicle control unit C 11  to obtain the speed information of the specified vehicle (the front vehicle  502  or the second forward front vehicle  504 ) from a change over time in the relative distance to the specified vehicle obtained in the detection results from the periphery monitoring unit. Alternatively, the vehicle control unit C 11  can obtain the speed information through vehicle-to-vehicle communication with the specified vehicle. 
     In step S 42 , the vehicle control unit C 11  compares the speed information obtained in step S 41  with the threshold speeds (the first threshold speed and the second threshold speed). 
     When, during vehicle control in the second control state, the speed of the vehicle  1  (the self-vehicle) has become greater than or equal to the first threshold speed, or the speed of the front vehicle  502  (the forward front vehicle ( 504  in  FIG. 5 )) has become greater than or equal to the second threshold speed (S 42 —Yes), the vehicle control unit C 11  moves the process to step S 43  and transitions from vehicle control in the second control state to vehicle control in the first control state. 
     On the other hand, when, in the comparison process of step S 42 , the speed of the vehicle  1  (the self-vehicle) is less than the first threshold speed, or the speed of the front vehicle  502  (the forward front vehicle ( 504  in  FIG. 5 )) is less than the second threshold speed, the process returns to step S 41  with the control state remaining the second control state, after which the same processing is repeated. 
     In step S 43 , the vehicle control unit C 11  controls the notification apparatus NTF of  FIG. 1A  (or the audio output apparatus  91  and the display apparatus  92  of  FIG. 1B ) to notify the driver that he or she is to contribute to vehicle operations. In other words, when the speed of the vehicle  1  (the self-vehicle) has become greater than or equal to the first threshold speed, or the speed of the front vehicle  502  (the forward front vehicle ( 504  in  FIG. 5 )) has become greater than or equal to the second threshold speed, the vehicle control unit C 11  controls the notification apparatus NTF to notify the driver that he or she is to contribute to vehicle operations (e.g., gripping the steering wheel), which had been reduced in the second control state. 
     In step S 44 , the vehicle control unit C 11  determines whether or not the driver is operating the vehicle (e.g., gripping the steering wheel) using a contribution detecting unit (e.g., the grip sensor S 6  of  FIG. 1A ). The vehicle control unit C 11  carries out vehicle control in the second control state (step S 47 ) until the contribution detecting unit (the grip sensor S 6 ) detects that the driver is contributing to vehicle operations, and then returns the process to step S 43 , after which the same processing is repeated. 
     On the other hand, when, in the determination process of step S 44 , the contribution detecting unit (e.g., the grip sensor S 6 ) has detected that the driver is contributing to vehicle operations (S 44 —Yes), the vehicle control unit C 11  moves the process to step S 45 , and transitions from vehicle control in the second control state to vehicle control in the first control state. 
     Second Embodiment 
     The first embodiment describes a configuration in which when a front vehicle has made a lane change to an adjacent lane and departed the lane L 2  in which the vehicle  1  is traveling, the speed of the forward front vehicle present in the same lane is compared with the second threshold speed; however, it is also possible to compare that speed with a threshold speed that is slower than the second threshold speed. For example, it is also possible to set a fourth threshold speed (e.g., V 4 =45 km/h), which is faster than the first threshold speed but slower than the second threshold speed, as the threshold speed for transitioning from the second control state to the first control state, and carry out the comparison process of step S 42  in  FIG. 4  on the basis of a comparison between the fourth threshold speed and the speed of the forward front vehicle. 
     The forward front vehicle (e.g., the second forward front vehicle  504  in ST 53  of  FIG. 5 ) is a vehicle that has appeared as a result of the front vehicle  502  changing lanes, and thus using the slower threshold speed in the comparison process makes it possible to transition the control state more smoothly than with the conditions for the front vehicle  502 . 
     Third Embodiment 
     In the first embodiment, in step S 35  of  FIG. 3 , the vehicle control unit C 11  specifies a vehicle for comparison with the second threshold speed. For example, if, in the determination process of step S 32  in  FIG. 3 , the front vehicle  502  is not changing lanes, the vehicle control unit C 11  specifies the front vehicle  502  as the vehicle for comparison with the second threshold speed. Additionally, if the front vehicle  502  is changing lanes, the forward front vehicle, among the forward front vehicle group  505 , that is within the range of the threshold vehicle width (e.g., the second forward front vehicle  504  in ST 53  of  FIG. 5 ) is specified as the vehicle for comparison with the second threshold speed. 
     However, when both speeds are contrary with respect to the second threshold speed, e.g., when the front vehicle  502  is changing lanes while accelerating at a speed greater than or equal to the second threshold speed or when the forward front vehicle (the second forward front vehicle  504 ) is traveling at less than the second threshold speed, preferentially comparing one of the speeds with the second threshold speed may result in a situation where the results of the comparison processes differ from each other. 
     Rather than being limited to specifying one of the vehicles as in the first embodiment, it is also possible to use the speed information of the front vehicle  502  and the second forward front vehicle  504  for the comparison with the second threshold speed, for example. 
     In other words, when, during vehicle control in the second control state, the front vehicle  502  has made a lane change to the adjacent lane and has departed from the lane in which the vehicle is traveling, the vehicle control unit C 11  can also set the speed for comparing with the second threshold speed using the speed of the forward front vehicle (the second forward front vehicle  504 ) included in the forward front vehicle group  505  and the speed of the front vehicle  502  that has made the lane change. 
     The vehicle control unit C 11  can also carry out the comparison process of step S 42  in  FIG. 4  having set the slower speed, obtained by comparing the speed of the forward front vehicle (the second forward front vehicle  504 ) with the speed of the front vehicle  502 , as the speed for comparison with the second threshold speed. 
     In this case, when the speed of the vehicle is less than the first threshold speed and the speed obtained from the comparison (the slower speed) is less than the second threshold speed, the vehicle control unit C 11  keeps the vehicle control in the second control state. 
     However, when the speed of the vehicle is greater than or equal to the first threshold speed or the speed obtained from the comparison (the slower speed) is greater than or equal to the second threshold speed, the vehicle control unit C 11  transitions from vehicle control in the second control state to vehicle control in the first control state. 
     According to the present embodiment, even if both speeds are contrary with respect to the second threshold speed, e.g., when the front vehicle  502  is changing lanes while accelerating at a speed greater than or equal to the second threshold speed or when the forward front vehicle (the second forward front vehicle  504 ) is traveling at less than the second threshold speed, setting the speed for comparison with the second threshold speed using the speed of a forward front vehicle included in the forward front vehicle group and the speed of the front vehicle that has changed lanes makes it possible to apply the speed information of a plurality of vehicles traveling in front of the vehicle  1  in the determination for transitioning the control state. 
     Fourth Embodiment 
     The third embodiment describes an example in which the slower speed, obtained by comparing the speed of the forward front vehicle (the second forward front vehicle  504 ) with the speed of the front vehicle  502 , is set as the speed for comparison with the second threshold speed, but it is also possible to use an average speed. 
     The vehicle control unit C 11  can also set a speed, obtained from the average of the speed of the forward front vehicle (the second forward front vehicle  504 ) and the speed of the front vehicle  502 , as the speed for comparison with the second threshold speed. 
     In this case, when the speed of the vehicle is less than the first threshold speed and the speed obtained from the average is less than the second threshold speed, the vehicle control unit C 11  keeps the vehicle control in the second control state. 
     However, when the speed of the vehicle is greater than or equal to the first threshold speed or the speed obtained from the average is greater than or equal to the second threshold speed, the vehicle control unit C 11  transitions from vehicle control in the second control state to vehicle control in the first control state. 
     Other Embodiments 
     A vehicle control program realizing one or more of the functions described in the embodiments can be supplied to a system or apparatus over a network or through a storage medium, and one or more processors in a computer of the system or apparatus can read out and execute the program. The present invention can be carried out in such a form as well. 
     Summary of Embodiments 
     Configuration 1. A vehicle control apparatus according to the foregoing embodiments is a vehicle control apparatus that can control a vehicle on the basis of a plurality of control states (e.g.,  100  in  FIG. 1A ), the apparatus including: a periphery monitoring unit (e.g., the sensors S and the cameras CAM ( FIG. 1A ), the detecting units  41  to  43  (the LIDAR  42 , the camera  41 A, the radar  43 , and the camera  41 B in  FIG. 1B ), and the like) configured to be capable of detecting a front vehicle traveling in front of the vehicle; and a vehicle control unit (e.g., C 11  in  FIG. 1A , the ECU  20  in  FIG. 1B , and the like) configured to be capable of controlling the vehicle on the basis of a travel state of the vehicle or a travel state of the front vehicle, wherein the vehicle control unit (C 11 , the ECU  20 , and the like) can carry out vehicle control in a first control state, as well as vehicle control in a second control state in which a level of autonomy of the vehicle control is higher or the extent to which a driver is required to contribute to vehicle operations is lower than in the first control state, as vehicle control in the plurality of control states; when, during vehicle control in the second control state, a threshold speed serving as an upper limit for carrying out vehicle control in the second control state has been reached or exceeded, the vehicle control unit carries out control to transition from vehicle control in the second control state to vehicle control in the first control state; and a first threshold speed and a second threshold speed are set as threshold speeds, the first threshold speed being for a speed of the vehicle, and the second threshold speed being for the speed of the front vehicle and being faster than the first threshold speed. 
     According to the vehicle control apparatus of Configuration 1, it is possible to smoothly transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, in accordance with changes in a travel state of the vehicle, a travel state of a front vehicle traveling in front of the vehicle, and so on. 
     Configuration 2. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when the speed of the vehicle has become greater than or equal to the first threshold speed, or the speed of the front vehicle has become greater than or equal to the second threshold speed, the vehicle control unit (C 11 , the ECU  20 , and the like) carries out control so as to transition from vehicle control in the second control state to vehicle control in the first control state. 
     According to the vehicle control apparatus of Configuration 2, it is possible to smoothly transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, when the speed of the vehicle serving as the travel state of the vehicle has become greater than or equal to the first threshold speed, or when the speed of the front vehicle serving as the travel state of the front vehicle traveling in front of the vehicle has become greater than or equal to the second threshold speed. 
     Configuration 3. The vehicle control apparatus ( 100 ) according to the foregoing embodiments, further including: a notification unit (e.g., the notification apparatus NTF in  FIG. 1A , the audio output apparatus  91  and the display apparatus  92  in  FIG. 1B ) configured to notify the driver that they are to contribute to vehicle operations reduced under the second control state, when the speed of the vehicle has become greater than or equal to the first threshold speed or when the speed of the front vehicle has become greater than or equal to the second threshold speed; and a contribution detecting unit (e.g., the grip sensor S 6  in  FIG. 1A ) configured to detect the contribution to the vehicle operations, wherein the vehicle control unit (C 11 , the ECU  20 , and the like) carries out vehicle control in the second control state until the contribution detecting unit (the grip sensor S 6 ) detects that the driver is contributing to the vehicle operations. 
     Configuration 4. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when the contribution detecting unit (the grip sensor S 6 ) detects that the driver is contributing to the vehicle operations, the vehicle control unit (C 11 , the ECU  20 , and the like) transitions from vehicle control in the second control state to vehicle control in the first control state. 
     According to the vehicle control apparatus of Configurations 3 and 4, the second control state, in which vehicle control is carried out at a low speed, can be maintained until it is detected that the driver is contributing to the vehicle operations, and the vehicle control can be carried out in a range defined by the second control state until the contribution to vehicle operations is detected with certainty. 
     Configuration 5. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, a third threshold speed is set as a threshold speed for transitioning from the first control state to the second control state, the third threshold speed being slower than the first threshold speed; and when, during vehicle control in the first control state, the speed of the vehicle or the speed of the front vehicle has become less than the third threshold speed, the vehicle control unit (C 11 , the ECU  20 , and the like) transitions from vehicle control in the first control state to vehicle control in the second control state. 
     According to the vehicle control apparatus of Configuration 5, by setting the third threshold speed, which is slower than the first threshold speed, as the threshold speed for transitioning from the first control state to the second control state, interference among the plurality of control states can be avoided, and the control state transitions can be carried out smoothly. 
     Configuration 6. The vehicle control apparatus ( 100 ) according to the foregoing embodiments, further including a communication unit (e.g., C 3  in  FIG. 1A , the communication apparatus  25   a  in  FIG. 1B ) configured to be capable of communicating with another vehicle traveling in the periphery of the vehicle, wherein on the basis of information from at least one of the periphery monitoring unit and the communication unit, the vehicle control unit (C 11 , the ECU  20 , and the like) determines whether or not a forward front vehicle group (e.g.,  505  in  FIG. 5 ) including at least one forward front vehicle (e.g.,  503  and  504  in  FIG. 5 ) traveling in front of the front vehicle is present in the same lane as a lane in which the vehicle is traveling and within a reference inter-vehicle distance from the vehicle. 
     According to the vehicle control apparatus of Configuration 6, by suppressing the frequency with which control state transitions can occur each time the front vehicle changes lanes and determining whether or not the forward front vehicle is present in parallel, the following travel can be continued in the second control state on the basis of information of the forward front vehicle, even if the front vehicle has made a lane change and departed the lane of travel. 
     Configuration 7. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when, during vehicle control in the second control state, the front vehicle has made a lane change to an adjacent lane and has departed from the lane in which the vehicle is traveling, the vehicle control unit (C 11 , the ECU  20 , and the like) sets a speed for comparing with the second threshold speed using a speed of a forward front vehicle included in the forward front vehicle group and the speed of the front vehicle that has made the lane change. 
     According to the vehicle control apparatus of Configuration 7, setting the speed for comparison with the second threshold speed using the speed of a forward front vehicle included in the forward front vehicle group and the speed of the front vehicle that has changed lanes makes it possible to apply the speed information of a plurality of vehicles traveling in front of the vehicle in the determination for transitioning the control state, which makes it possible to transition the control states more smoothly. 
     Configuration 8. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, the vehicle control unit (C 11 , the ECU  20 , and the like) compares the speed of the forward front vehicle with the speed of the front vehicle and sets the slower of the speeds as the speed for comparison with the second threshold speed. 
     Configuration 9. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when the speed of the vehicle is less than the first threshold speed and the speed obtained from the comparison is less than the second threshold speed, the vehicle control unit (C 11 , the ECU  20 , and the like) keeps the vehicle control in the second control state. 
     Configuration 10. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when the speed of the vehicle is greater than or equal to the first threshold speed, or the speed obtained from the comparison is greater than or equal to the second threshold speed, the vehicle control unit (C 11 , the ECU  20 , and the like) transitions from vehicle control in the second control state to vehicle control in the first control state. 
     According to the vehicle control apparatus of Configurations 8 to 10, setting the speed for comparison with the second threshold speed to the slower speed obtained by comparing the speed of a forward front vehicle included in the forward front vehicle group with the speed of the front vehicle that has changed lanes makes it possible to apply the speed information of a plurality of vehicles traveling in front of the vehicle in the determination for transitioning the control state, which makes it possible to transition the control states more smoothly. 
     Configuration 11. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, the vehicle control unit (C 11 , the ECU  20 , and the like) sets a speed obtained from the average of the speed of the forward front vehicle and the speed of the front vehicle as the speed for comparison with the second threshold speed. 
     Configuration 12. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when the speed of the vehicle is less than the first threshold speed and the speed obtained from the average is less than the second threshold speed, the vehicle control unit (C 11 , the ECU  20 , and the like) keeps the vehicle control in the second control state. 
     Configuration 13. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when the speed of the vehicle is greater than or equal to the first threshold speed, or the speed obtained from the average is greater than or equal to the second threshold speed, the vehicle control unit (C 11 , the ECU  20 , and the like) transitions from vehicle control in the second control state to vehicle control in the first control state. 
     According to the vehicle control apparatuses of Configurations 11 to 13, setting the speed for comparison with the second threshold speed to the speed obtained from the average of the speed of a forward front vehicle included in the forward front vehicle group with the speed of the front vehicle that has changed lanes makes it possible to apply the speed information of a plurality of vehicles traveling in front of the vehicle in the determination for transitioning the control state, which makes it possible to transition the control states more smoothly. 
     Configuration 14. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when, during the vehicle control in the second control state, the front vehicle (e.g.,  502  in ST 53  of  FIG. 5 ) has made a lane change to an adjacent lane and has departed the lane in which the vehicle is traveling, if the forward front vehicle group (e.g.,  505  in ST 53  of  FIG. 5 ) is not present in the lane, the vehicle control unit (C 11 , the ECU  20 , and the like) transitions from vehicle control in the second control state to vehicle control in the first control state. 
     According to the vehicle control apparatus of Configuration 14, no vehicle traveling in front in the lane in which the self-vehicle is traveling means that there is not target for the following travel in the second control state, and thus the control state can transition from the second control state to the first control state regardless of the conditions for the speed of the self-vehicle. 
     Configuration 15. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, the vehicle control unit (C 11 , the ECU  20 , and the like) determines whether the front vehicle (e.g.,  501  in ST 51 , and  502  in ST 52  and ST 53 , of  FIG. 5 ) is to be used for following travel, carried out in the vehicle control in the second control state, on the basis of a comparison between a vehicle width of the front vehicle or a vehicle width of a forward front vehicle (e.g.,  503  and  504  in ST 53  of  FIG. 5 ) included in the forward front vehicle group and a threshold vehicle width serving as a reference. 
     Configuration 16. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when a vehicle width of a first forward front vehicle (e.g.,  503  in ST 53  of  FIG. 5 ) serving as the forward front vehicle included in the forward front vehicle group ( 505 ) exceeds an upper limit value of the threshold vehicle width serving as a reference, or is lower than a lower limit value of the threshold vehicle width, the vehicle control unit (C 11 , the ECU  20 , and the like) excludes the first forward front vehicle as a target for following travel carried out in the vehicle control in the second control state. 
     Configuration 17. In the vehicle control apparatus ( 100 ) according to the foregoing embodiments, when a vehicle width of a second forward front vehicle (e.g.,  504  in ST 53  of  FIG. 5 ) traveling in front of the first forward front vehicle ( 503 ) in the forward front vehicle group ( 505 ) is within a range of the threshold vehicle width, the vehicle control unit (C 11 , the ECU  20 , and the like) sets the second forward front vehicle ( 504 ) as a target for following travel. 
     According to the vehicle control apparatuses of Configurations 15 to 17, a range is set for the threshold vehicle width, and vehicles outside the range of the threshold vehicle width can be excluded from the targets (front vehicles) for the following travel carried out in the vehicle control in the second control state, whereas vehicles within the range of the threshold vehicle width can be set as targets for the following travel carried out in the vehicle control in the second control state. 
     When the vehicle (the self-vehicle) is a sedan-type four-wheeled passenger vehicle, for example, if a truck or the like that is larger than the self-vehicle becomes the front vehicle, it may be necessary to stay alert for cargo falling from the truck, for example. Meanwhile, if the front vehicle is a two-wheeled vehicle or the like, that vehicle has a narrower vehicle width than the self-vehicle, and thus even if the front vehicle (a two-wheeled vehicle or the like) can travel through a given region, it may not be possible for the self-vehicle to travel through the same region. Accordingly, a range is set for the threshold vehicle width, and vehicles outside the range of the threshold vehicle width can be excluded from the targets (front vehicles) for the following travel carried out in the vehicle control in the second control state, whereas vehicles within the range of the threshold vehicle width can be set as targets for the following travel carried out in the vehicle control in the second control state; this makes it possible to transition the control states more smoothly. 
     Configuration 18. A vehicle according to the foregoing embodiments (e.g., the vehicle  1  in  FIG. 1B ) is a vehicle capable of traveling on the basis of control by a vehicle control apparatus, and includes the vehicle control apparatus according to any one of Configurations 1 to 17 (e.g., the vehicle control apparatus  100  in  FIG. 1A ). 
     According to the vehicle of Configuration 18, it is possible to provide a vehicle control technique that can smoothly transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, in accordance with changes in a travel state of the vehicle, a travel state of a front vehicle traveling in front of the vehicle, and so on. 
     Configuration 19. A vehicle control method of the vehicle control apparatus ( 100 ) according to the foregoing embodiments is a vehicle control method of a vehicle control apparatus that can control a vehicle on the basis of a plurality of control states, the method including: an obtainment step of obtaining, from a periphery monitoring unit capable of detecting a front vehicle traveling in front of the vehicle, information of the front vehicle; and a vehicle control step of controlling the vehicle on the basis of a travel state of the vehicle or a travel state of the front vehicle, wherein in the vehicle control step, vehicle control in a first control state, as well as vehicle control in a second control state in which a level of autonomy of the vehicle control is higher or the extent to which a driver is required to contribute to vehicle operations is lower than in the first control state, can be carried out as vehicle control in the plurality of control states; when, during vehicle control in the second control state, a threshold speed serving as an upper limit for carrying out vehicle control in the second control state has been reached or exceeded, control to transition from vehicle control in the second control state to vehicle control in the first control state is carried out in the vehicle control step; and a first threshold speed and a second threshold speed are set as threshold speeds, the first threshold speed being for a speed of the vehicle, and the second threshold speed being for the speed of the front vehicle and being faster than the first threshold speed. 
     According to the vehicle control method of a vehicle control apparatus of Configuration 19, it is possible to smoothly transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, in accordance with changes in a travel state of the vehicle, a travel state of a front vehicle traveling in front of the vehicle, and so on. 
     Configuration 20. A program according to the foregoing embodiments causes a computer (e.g., the CPU in  FIG. 1A ) to execute the steps of the vehicle control method according to Configuration 19. 
     According to the program of Configuration 20, it is possible to provide a program that can smoothly control a transition from the control state for current vehicle control to a control state having a lower level of autonomy, or a control state where a driver contributes more to vehicle operations, in accordance with changes in a travel state of the vehicle, a travel state of a front vehicle traveling in front of the vehicle, and so on. 
     The invention is not limited to the foregoing embodiments, and various variations/changes are possible within the spirit of the invention.