Patent Publication Number: US-11639174-B2

Title: Automated speed control system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 15/695,585, filed Sep. 5, 2017, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD OF INVENTION 
     This disclosure generally relates to a speed control system, and more particularly relates to an automated speed control system that includes situational awareness. 
     BACKGROUND OF INVENTION 
     It is known to employ perception systems on autonomous vehicles. Safety issues may arise when other vehicles that do not have vehicle-to-vehicle communication capabilities block a view of the roadway and reduce the effectiveness of on-board perception-sensors. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment, an automated speed control system for use on an automated vehicle is provided. The automated speed control system includes a ranging-sensor, a camera, and a controller. The ranging-sensor detects a lead-speed of a lead-vehicle traveling ahead of a host-vehicle. The camera detects an object in a field-of-view. The controller is in communication with the ranging-sensor and the camera. The controller is operable to control the host-vehicle. The controller determines a change in the lead-speed based on the ranging-sensor and reduces a host-speed of the host-vehicle when the lead-speed is decreasing, no object is detected by the camera, and while a portion of the field-of-view is obscured by the lead-vehicle. 
     In another embodiment, an automated speed control system for use on an automated vehicle is provided. The automated speed control system includes a ranging-sensor, a camera, and a controller. The ranging-sensor detects an obstruction on a roadway and a lead-speed of a lead-vehicle traveling on the roadway ahead of a host-vehicle. The camera detects objects in a field-of-view. The controller is in communication with the ranging-sensor and the camera. The controller determines a change in the lead-speed based on the ranging-sensor and reduces a host-speed of the host-vehicle when the lead-speed is decreasing, the obstruction is detected, and the obstruction is not one of the objects detected by the camera. 
     In yet another embodiment, a method of operating an automated speed control system is provided. The method includes the steps of detecting a lead-speed, detecting an object, determining a change in the lead-speed, and reducing a host-speed. The step of detecting the lead-speed includes detecting, with a ranging-sensor, the lead-speed of a lead-vehicle traveling ahead of a host-vehicle. The step of detecting the object includes detecting, with a camera, the object in a field-of-view. The step of determining the change in the lead-speed includes determining, with a controller in communication with the ranging-sensor and the camera wherein the controller is operable to control the host-vehicle, the change in the lead-speed based on the ranging-sensor. The step of reducing the host-speed includes reducing, with the controller, the host-speed of the host-vehicle when the lead-speed is decreasing, no object is detected by the camera, and while a portion of the field-of-view is obscured by the lead-vehicle. 
     In yet another embodiment, a method of operating an automated speed control system is provided. The method includes the steps of detecting an obstruction, detecting a lead-speed, detecting objects, determining a change in the lead-speed, and reducing a host-speed. The step of detecting the obstruction includes detecting, with a ranging-sensor, the obstruction on a roadway. The step of detecting the lead-speed includes detecting, with the ranging-sensor, the lead-speed of a lead-vehicle traveling on the roadway ahead of a host-vehicle. The step of detecting objects includes detecting, with a camera, objects in a field-of-view. The step of determining a change in the lead-speed includes determining, with a controller in communication with the ranging-sensor and the camera, the change in the lead-speed based on the ranging-sensor. The step of reducing the host-speed includes reducing, with the controller, the host-speed of the host-vehicle when the lead-speed is decreasing, the obstruction is detected, and the obstruction is not one of the objects detected by the camera. 
     Further features and advantages will appear more clearly on a reading of the following detailed description of the preferred embodiment, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG.  1    is an illustration of an automated speed control system in accordance with one embodiment; 
         FIG.  2    is an illustration of a host-vehicle equipped with the automated speed control system of  FIG.  1    in accordance with another embodiment; 
         FIG.  3    is an illustration of an automated speed control system in accordance with another embodiment; 
         FIG.  4    is an illustration of a host-vehicle equipped with the automated speed control system of  FIG.  3    in accordance with another embodiment; 
         FIG.  5    is an illustration of a method of operating the automated speed control system of  FIG.  1    in accordance with yet another embodiment; and 
         FIG.  6    is an illustration of a method of operating the automated speed control system of  FIG.  3    in accordance with yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates a non-limiting example of an automated speed control system  10 , hereafter referred to as the system  10 , for use on an automated vehicle  12 , hereafter referred to as a host-vehicle  12 . As will be described in more detail below, the system  10  is an improvement over prior speed control systems because the system  10  is configured to use situational awareness when controlling the host-vehicle  12 . As used herein, the term ‘automated vehicle’ is not meant to suggest that fully automated or autonomous operation of the host-vehicle  12  is required. It is contemplated that the teachings presented herein are applicable to instances where the host-vehicle  12  is entirely manually operated by a human and the automation is merely providing emergency vehicle controls to the human. 
     The system  10  includes a ranging-sensor  14  that detects a lead-speed  16  of a lead-vehicle  18  traveling ahead of a host-vehicle  12 . The ranging-sensor  14  may be any of the known ranging-sensors  14 , and may include a radar, a lidar, or any combination thereof. The ranging-sensor  14  may be configured to output a continuous or periodic data stream that includes a variety of signal characteristics associated with each target detected. The signal characteristics may include or be indicative of, but are not limited to, the range (not shown) to the detected-target from the host-vehicle  12 , the azimuth-angle (not shown) to the detected-target relative to a host-vehicle-longitudinal-axis (not shown), an amplitude (not shown) of the ranging-signal (not shown), and a relative-velocity (not shown) of closure relative to the detected-target. A target is generally detected because the ranging-signal from the detected-target has sufficient signal strength to meet some predetermined threshold. That is, there may be targets that reflect the ranging-signal, but the strength of the ranging-signal is insufficient to be characterized as one of the detected-targets. Data that corresponds to a strong-target will generally be from consistent, non-intermittent signals. However, data that corresponds to a weak-target may be intermittent or have some substantial variability due to a low signal-to-noise ratio. 
     The system  10  includes a camera  20  that detects an object  22  in a field-of-view  24 . The camera  20  may be any of the commercially available cameras  20  suitable for use on the host-vehicle  12 . The camera  20  may be mounted on the front of the host-vehicle  12 , or mounted in the interior of the host-vehicle  12  at a location suitable for the camera  20  to view the area around the host-vehicle  12  through a windshield of the host-vehicle  12 . The camera  20  is preferably a video-type camera  20  or camera  20  that can capture images of a roadway  26  and surrounding area at a sufficient frame-rate, of ten frames per second, for example. 
     The system  10  also includes a controller  28  in communication with the ranging-sensor  14  and the camera  20 , wherein the controller  28  is operable to control the host-vehicle  12 . The controller  28  may control vehicle-controls (not specifically shown) such as steering, brakes, and an accelerator. The controller  28  may include a processor (not shown) such as a microprocessor or other control circuitry such as analog and/or digital control circuitry including an application specific integrated circuit (ASIC) for processing data as should be evident to those in the art. The controller  28  may include a memory (not specifically shown), including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The one or more routines may be executed by the processor to perform steps for determining if a detected instance of the lead-vehicle  18  and object  22  exist based on signals received by the controller  28  from the ranging-sensor  14  and the camera  20 , as described herein. 
     The controller  28  may analyze a signal from the ranging-sensor  14  to categorize the data from each detected target with respect to a list of previously detected targets having established tracks. As used herein, a track refers to one or more data sets that have been associated with a particular one of the detected targets. By way of example and not limitation, if the amplitude of the signal is above a predetermined amplitude threshold, then the controller  28  determines if the data corresponds to a previously detected target or if a new-target has been detected. If the data corresponds to a previously detected target, the data is added to or combined with prior data to update the track of the previously detected target. If the data does not correspond to any previously detected target because, for example, it is located too far away from any previously detected target, then it may be characterized as a new-target and assigned a unique track identification number. The identification number may be assigned according to the order that data for a new detected target is received, or may be assigned an identification number according to a grid-location (not shown) in a field-of-view  24  of the ranging-sensor  14 . 
     The controller  28  may determine a region-of-interest (not shown) within the field-of-view  24 . As illustrated in  FIG.  2   , the region-of-interest may represent the area directly ahead of the host-vehicle  12  that extends from a left-corner and from a right-corner of the host-vehicle  12 . The objects  22  in the region-of-interest and the host-vehicle  12  will collide if the host-vehicle  12  continues to move in the direction of the objects  22 . The field-of-view  24  also has a known vertical-angle (not shown) and a known horizontal-angle (not specifically shown) that are design features of the ranging-sensor  14  and determine how close to the host-vehicle  12  the objects  22  may be detected. 
     The controller  28  may define an occupancy-grid (not shown) that segregates the field-of-view  24  into an array of grid-cells (not shown). As mentioned previously, the controller  28  may assign the identification number to the detected target in the grid-location that is associated with unique grid-cells. A dimension of the individual grid-cell may be of any size and is advantageously not greater than five centimeters (5 cm) on each side. 
     The controller  28  periodically updates the detections within the grid-cells and determines a repeatability-of-detection of each of the grid-cells based on the reflections detected by the ranging-sensor  14 . The repeatability-of-detection corresponds to a history of detections within the grid-cells, where a larger number of detections (i.e. more persistent detections) increases the certainty that the target resides in the occupancy-grid. 
     The controller  28  may determine that an obstruction  30  (i.e. the guard rail, the tree, a lamp post, a slow or non-moving vehicle, etc.) is present in the field-of-view  24  when each of a string of the grid-cells are characterized by the repeatability-of-detection greater than a repeatability-threshold. Experimentation by the inventors has discovered that the repeatability-threshold of two detections in a grid-cell may be indicative of the presence of the obstruction  30 . 
       FIG.  2    is a top-view of the roadway  26  and illustrates a traffic scenario where the host-vehicle  12  is following the lead-vehicle  18  in an adjacent-lane  32 , and the object  22  is a pedestrian that is approaching the roadway  26 , as if to cross the roadway  26  at a cross-walk  34 . The lead-vehicle  18  is reducing the lead-speed  16  due to the proximity of the pedestrian (i.e. the object  22 ) to the roadway  26 . A portion  36  of the field-of-view  24  is obscured  38  by the lead-vehicle  18 . That is, the host-vehicle  12  cannot “see” the pedestrian due to the lead-vehicle  18  blocking a line-of-sight  40  of the system  10 . As used herein, obscured  38  includes a partial or a complete blockage of the line-of-site  40  in the field-of-view  24  of the ranging-sensor  14  and/or of the camera  20  and inhibits the ranging-sensor  14  and/or the camera  20  from detecting targets and/or objects  22 , and will be understood by those in the art. 
     The controller  28  determines a change in the lead-speed  16  based on the ranging-sensor  14  and reduces a host-speed  42  of the host-vehicle  12  when the lead-speed  16  is decreasing, no object  22  is detected by the camera  20 , and while a portion  36  of the field-of-view  24  is obscured  38  by the lead-vehicle  18 , as illustrated in  FIG.  2   . That is, host-vehicle  12  reduces the host-speed  42  when the system  10  detects that the lead-vehicle  18  is reducing the lead-speed  16  and the pedestrian is not detected by the camera  20  while the lead-vehicle  18  is blocking part of the field-of-view  24 . 
     The system  10  may be particularly beneficial when the lead-vehicle  18  may be traveling in the adjacent-lane  32  of the roadway  26 . In the specific example illustrated in  FIG.  2   , the prior art system would have no reason to reduce the host-speed  42  based on the signals received from the camera  20  and the ranging-sensor  14 . In the event that the pedestrian enters the roadway  26  and emerges from the obscured  38  portion  36  of the field-of-view  24 , the prior art system will have a reduced time window in which to reduce the host-speed  42 , potentially endangering the pedestrian and any surrounding-vehicles. By reducing the host-speed  42  in response to the reduction in the lead-speed  16 , the system  10  may increase the time required to react to the pedestrian. 
     The controller  28  may reduce the host-speed  42  by activating a braking-actuator  44  of the host-vehicle  12 , and/or may reduce the host-speed  42  by adjusting a throttle-position  46  of the host-vehicle  12 . The controller  28  may further reduce the host-speed  42  when the lead-speed  16  is decreasing by greater than a change-threshold  48 . The change-threshold  48  may be user defined and is preferably at least eight kilometers-per-hour (8 kph). The controller  28  may also reduce the host-speed  42  to a value equivalent to the lead-speed  16 , or may bring the host-vehicle  12  to a complete stop. 
     The camera  20  may also detect a marking of the cross-walk  34  on the roadway  26  and the controller  28  may further determine that the marking is the cross-walk  34  using any of the known image-analysis methods (not specifically shown). The marking may be any of the United States Department of Transportation Federal Highway Administration known cross-walk  34  markings, including, but not limited to Solid, Standard, Continental, Dashed, Zebra, and Ladder markings. The cross-walk  34  may also be accompanied by a road-sign (not shown) that may also be detected by the camera  20  as an indication of the presence of the cross-walk  34 . 
     The ranging-sensor  14  may also detect the obstruction  30  on the roadway  26  ahead of the lead-vehicle  18  that may be the slow or non-moving vehicle, as illustrated in  FIG.  2   . The controller  28  may determine the change in the lead-speed  16  based on the ranging-sensor  14  and reduces the host-speed  42  of the host-vehicle  12  when the lead-speed  16  is decreasing, no object  22  is detected by the camera  20 , and while the portion  36  of the field-of-view  24  is obscured  38  by the lead-vehicle  18 . 
       FIG.  3    is a non-limiting example of another embodiment of an automated speed control system  110 , hereafter referred to as the system  110 , for use on an automated vehicle  112 , hereafter referred to as a host-vehicle  112 . The system  110  includes a ranging-sensor  114  that detects an obstruction  130  on a roadway  126  and a lead-speed  116  of a lead-vehicle  118  traveling on the roadway  126  ahead of the host-vehicle  112 . The ranging-sensor  114  may be any of the known ranging-sensors  114 , and may include a radar, a lidar, or any combination thereof. The ranging-sensor  114  may be configured to output a continuous or periodic data stream that includes a variety of signal characteristics associated with each target detected. The signal characteristics may include or be indicative of, but are not limited to, the range (not shown) to the detected-target from the host-vehicle  112 , the azimuth-angle (not shown) to the detected-target relative to a host-vehicle-longitudinal-axis (not shown), an amplitude (not shown) of the ranging-signal (not shown), and a relative-velocity (not shown) of closure relative to the detected-target. A target is generally detected because the ranging-signal from the detected-target has sufficient signal strength to meet some predetermined threshold. That is, there may be targets that reflect the ranging-signal, but the strength of the ranging-signal is insufficient to be characterized as one of the detected-targets. Data that corresponds to a strong-target will generally be from consistent, non-intermittent signals. However, data that corresponds to a weak-target may be intermittent or have some substantial variability due to a low signal-to-noise ratio. 
     The system  110  includes a camera  120  that detects objects  122  in a field-of-view  124 . The camera  120  may be any of the commercially available cameras  120  suitable for use on the host-vehicle  112 . The camera  120  may be mounted on the front of the host-vehicle  112 , or mounted in the interior of the host-vehicle  112  at a location suitable for the camera  120  to view the area around the host-vehicle  112  through a windshield of the host-vehicle  112 . The camera  120  is preferably a video-type camera  120  or camera  120  that can capture images of a roadway  126  and surrounding area at a sufficient frame-rate, of ten frames per second, for example. 
     The system  110  also includes a controller  128  in communication with the ranging-sensor  114  and the camera  120 , wherein the controller  128  is operable to control the host-vehicle  112 . The controller  128  may control vehicle-controls (not specifically shown) such as steering, brakes, and an accelerator. The controller  128  may include a processor (not shown) such as a microprocessor or other control circuitry such as analog and/or digital control circuitry including an application specific integrated circuit (ASIC) for processing data as should be evident to those in the art. The controller  128  may include a memory (not specifically shown), including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The one or more routines may be executed by the processor to perform steps for determining if a detected instance of the lead-vehicle  118 , the object  122 , and the obstruction  130  exist based on signals received by the controller  128  from the ranging-sensor  114  and the camera  120 , as described herein. 
     The controller  128  may analyze a signal from the ranging-sensor  114  to categorize the data from each detected target with respect to a list of previously detected targets having established tracks. As used herein, a track refers to one or more data sets that have been associated with a particular one of the detected targets. By way of example and not limitation, if the amplitude of the signal is above a predetermined amplitude threshold, then the controller  128  determines if the data corresponds to a previously detected target or if a new-target has been detected. If the data corresponds to a previously detected target, the data is added to or combined with prior data to update the track of the previously detected target. If the data does not correspond to any previously detected target because, for example, it is located too far away from any previously detected target, then it may be characterized as a new-target and assigned a unique track identification number. The identification number may be assigned according to the order that data for a new detected target is received, or may be assigned an identification number according to a grid-location (not shown) in a field-of-view  124  of the ranging-sensor  114 . 
     The controller  128  may determine a region-of-interest (not shown) within the field-of-view  124 . As illustrated in  FIG.  4   , the region-of-interest may represent the area directly ahead of the host-vehicle  112  that extends from a left-corner and from a right-corner of the host-vehicle  112 . The objects  122  in the region-of-interest and the host-vehicle  112  will collide if the host-vehicle  112  continues to move in the direction of the objects  122 . The field-of-view  124  also has a known vertical-angle (not shown) and a known horizontal-angle (not specifically shown) that are design features of the ranging-sensor  114  and determine how close to the host-vehicle  112  the objects  122  may be detected. 
     The controller  128  may define an occupancy-grid (not shown) that segregates the field-of-view  124  into an array of grid-cells (not shown). As mentioned previously, the controller  128  may assign the identification number to the detected target in the grid-location that is associated with unique grid-cells. A dimension of the individual grid-cell may be of any size and is advantageously not greater than five centimeters (5 cm) on each side. 
     The controller  128  periodically updates the detections within the grid-cells and determines a repeatability-of-detection of each of the grid-cells based on the reflections detected by the ranging-sensor  114 . The repeatability-of-detection corresponds to a history of detections within the grid-cells, where a larger number of detections (i.e. more persistent detections) increases the certainty that the target resides in the occupancy-grid. 
     The controller  128  may determine that an obstruction  130  (i.e. a slow or non-moving vehicle) is present in the field-of-view  124  when each of a string of the grid-cells are characterized by the repeatability-of-detection greater than a repeatability-threshold. Experimentation by the inventors has discovered that the repeatability-threshold of two detections in a grid-cell may be indicative of the presence of the obstruction  130 . 
       FIG.  4    is a top-view of the roadway  126  and illustrates a traffic scenario where the host-vehicle  112  is following the lead-vehicle  118  in an adjacent-lane  132 , and the objects  122  are a guard rail beside the roadway  126  and the lead-vehicle  118  that are detected by the camera  120  and the ranging-sensor  114 . The obstruction  130  is illustrated as a truck that is detected by the ranging-sensor  114  and not detected by the camera  120 . Without subscribing to any particular theory, it is believed that camera  120  is unable to detect the obstruction  130  due to the camera&#39;s  120  inability to distinguish the truck from a background. That is, the camera  120  may not “see” the truck because there is not sufficient contrast between the image of the truck and the image of the horizon as detected by the camera  120 . The truck is also blocking a portion  136  of the roadway  126  and the lead-vehicle  118  is reducing the lead-speed  116  due to its proximity to the truck (i.e. the obstruction  130 ) on the roadway  126 . 
     The controller  128  determines a change in the lead-speed  116  based on the ranging-sensor  114  and reduces a host-speed  142  of the host-vehicle  112  when the lead-speed  116  is decreasing, the obstruction  130  is detected, and the obstruction  130  is not one of the objects  122  detected by the camera  120 , as illustrated in  FIG.  4   . 
     The system  110  is particularly beneficial when the lead-vehicle  118  may be traveling in the adjacent-lane  132  of the roadway  126 . In the specific example illustrated in  FIG.  4   , the prior art system would typically not reduce the host-speed  142  based on the conflicting signals received from the camera  120  and the ranging-sensor  114 . If the obstruction  130  does not clear the roadway  126 , the prior art system will have a reduced time window in which to reduce the host-speed  142 , potentially endangering the host-vehicle  112 , the obstruction  130 , and any surrounding-vehicles. By reducing the host-speed  142  in response to the reduction in the lead-speed  116 , the system  110  may increase the time required to react to the obstruction  130 , and may avoid a collision with the obstruction  130 . 
     The controller  128  may reduce the host-speed  142  by activating a braking-actuator  144  of the host-vehicle  112 , and/or may reduce the host-speed  142  by adjusting a throttle-position  146  of the host-vehicle  112 . The controller  128  may further reduce the host-speed  142  when the lead-speed  116  is decreasing by greater than a change-threshold  148 . The change-threshold  148  may be user defined and is preferably at least eight kilometers-per-hour (8 kph). The controller  128  may also reduce the host-speed  142  to a value equivalent to the lead-speed  116 , or may bring the host-vehicle  112  to a complete stop. 
       FIG.  5    illustrates a non-limiting example of yet another embodiment of a method  200  of operating an automated speed control system  10 , hereafter referred to as the system  10 , for use on an automated vehicle  12 , hereafter referred to as a host-vehicle  12 . 
     Step  202 , DETECT LEAD-SPEED, may include detecting, with a ranging-sensor  14 , a lead-speed  16  of a lead-vehicle  18  traveling ahead of a host-vehicle  12 . The ranging-sensor  14  may be any of the known ranging-sensors  14 , and may include a radar, a lidar, or any combination thereof. The ranging-sensor  14  may be configured to output a continuous or periodic data stream that includes a variety of signal characteristics associated with each target detected. The signal characteristics may include or be indicative of, but are not limited to, the range (not shown) to the detected-target from the host-vehicle  12 , the azimuth-angle (not shown) to the detected-target relative to a host-vehicle-longitudinal-axis (not shown), an amplitude (not shown) of the ranging-signal (not shown), and a relative-velocity (not shown) of closure relative to the detected-target. A target is generally detected because the ranging-signal from the detected-target has sufficient signal strength to meet some predetermined threshold. That is, there may be targets that reflect the ranging-signal, but the strength of the ranging-signal is insufficient to be characterized as one of the detected-targets. Data that corresponds to a strong-target will generally be from consistent, non-intermittent signals. However, data that corresponds to a weak-target may be intermittent or have some substantial variability due to a low signal-to-noise ratio. 
     Step  204 , DETECT OBJECT, may include detecting, with a camera  20 , an object  22  in a field-of-view  24 . The camera  20  may be any of the commercially available cameras  20  suitable for use on the host-vehicle  12 . The camera  20  may be mounted on the front of the host-vehicle  12 , or mounted in the interior of the host-vehicle  12  at a location suitable for the camera  20  to view the area around the host-vehicle  12  through a windshield of the host-vehicle  12 . The camera  20  is preferably a video-type camera  20  or camera  20  that can capture images of a roadway  26  and surrounding area at a sufficient frame-rate, of ten frames per second, for example. 
     Step  206 , DETERMINE CHANGE IN LEAD-SPEED, may include determining, with a controller  28  in communication with the ranging-sensor  14  and the camera  20 , wherein the controller  28  is operable to control the host-vehicle  12 , a change in the lead-speed  16  based on the ranging-sensor  14 . The controller  28  may control vehicle-controls (not specifically shown) such as steering, brakes, and an accelerator. The controller  28  may include a processor (not shown) such as a microprocessor or other control circuitry such as analog and/or digital control circuitry including an application specific integrated circuit (ASIC) for processing data as should be evident to those in the art. The controller  28  may include a memory (not specifically shown), including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The one or more routines may be executed by the processor to perform steps for determining if a detected instance of the lead-vehicle  18  and object  22  exist based on signals received by the controller  28  from the ranging-sensor  14  and the camera  20 , as described herein. 
     The controller  28  may analyze a signal from the ranging-sensor  14  to categorize the data from each detected target with respect to a list of previously detected targets having established tracks. As used herein, a track refers to one or more data sets that have been associated with a particular one of the detected targets. By way of example and not limitation, if the amplitude of the signal is above a predetermined amplitude threshold, then the controller  28  determines if the data corresponds to a previously detected target or if a new-target has been detected. If the data corresponds to a previously detected target, the data is added to or combined with prior data to update the track of the previously detected target. If the data does not correspond to any previously detected target because, for example, it is located too far away from any previously detected target, then it may be characterized as a new-target and assigned a unique track identification number. The identification number may be assigned according to the order that data for a new detected target is received, or may be assigned an identification number according to a grid-location (not shown) in a field-of-view  24  of the ranging-sensor  14 . 
     The controller  28  may determine a region-of-interest (not shown) within the field-of-view  24 . As illustrated in  FIG.  2   , the region-of-interest may represent the area directly ahead of the host-vehicle  12  that extends from a left-corner and from a right-corner of the host-vehicle  12 . The objects  22  in the region-of-interest and the host-vehicle  12  will collide if the host-vehicle  12  continues to move in the direction of the objects  22 . The field-of-view  24  also has a known vertical-angle (not shown) and a known horizontal-angle (not specifically shown) that are design features of the ranging-sensor  14  and determine how close to the host-vehicle  12  the objects  22  may be detected. 
     The controller  28  may define an occupancy-grid (not shown) that segregates the field-of-view  24  into an array of grid-cells (not shown). As mentioned previously, the controller  28  may assign the identification number to the detected target in the grid-location that is associated with unique grid-cells. A dimension of the individual grid-cell may be of any size and is advantageously not greater than five centimeters (5 cm) on each side. 
     The controller  28  periodically updates the detections within the grid-cells and determines a repeatability-of-detection of each of the grid-cells based on the reflections detected by the ranging-sensor  14 . The repeatability-of-detection corresponds to a history of detections within the grid-cells, where a larger number of detections (i.e. more persistent detections) increases the certainty that the target resides in the occupancy-grid. 
     The controller  28  may determine that an obstruction  30  (i.e. the guard rail, the tree, a lamp post, a slow or non-moving vehicle, etc.) is present in the field-of-view  24  when each of a string of the grid-cells are characterized by the repeatability-of-detection greater than a repeatability-threshold. Experimentation by the inventors has discovered that the repeatability-threshold of two detections in a grid-cell may be indicative of the presence of the obstruction  30 . 
       FIG.  2    is a top-view of the roadway  26  and illustrates a traffic scenario where the host-vehicle  12  is following the lead-vehicle  18  in an adjacent-lane  32 , and the object  22  is a pedestrian that is approaching the roadway  26 , as if to cross the roadway  26  at a cross-walk  34 . The lead-vehicle  18  is reducing the lead-speed  16  due to the proximity of the pedestrian (i.e. the object  22 ) to the roadway  26 . A portion  36  of the field-of-view  24  is obscured  38  by the lead-vehicle  18 . That is, the host-vehicle  12  cannot “see” the pedestrian due to the lead-vehicle  18  blocking a line-of-sight  40  of the system  10 . As used herein, obscured  38  includes a partial or a complete blockage of the line-of-site  40  in the field-of-view  24  of the ranging-sensor  14  and/or the camera  20  and inhibits the ranging-sensor  14  and the camera  20  from detecting targets and/or objects  22 , and will be understood by those in the art. 
     Step  208 , REDUCE HOST-SPEED, may include reducing, with the controller  28 , a host-speed  42  of the host-vehicle  12  when the lead-speed  16  is decreasing, no object  22  is detected by the camera  20 , and while a portion  36  of the field-of-view  24  is obscured  38  by the lead-vehicle  18 , as illustrated in  FIG.  2   . That is, host-vehicle  12  reduces the host-speed  42  when the system  10  detects that the lead-vehicle  18  is reducing the lead-speed  16  and the pedestrian is not detected by the camera  20  while the lead-vehicle  18  is blocking part of the field-of-view  24 . 
     The system  10  may be particularly beneficial when the lead-vehicle  18  may be traveling in the adjacent-lane  32  of the roadway  26 . In the specific example illustrated in  FIG.  2   , the prior art system would have no reason to reduce the host-speed  42  based on the signals received from the camera  20  and the ranging-sensor  14 . In the event that the pedestrian enters the roadway  26  and emerges from the obscured  38  portion  36  of the field-of-view  24 , the prior art system will have a reduced time window in which to reduce the host-speed  42 , potentially endangering the pedestrian and any surrounding-vehicles (not shown). By reducing the host-speed  42  in response to the reduction in the lead-speed  16 , the system  10  may increase the time required to react to the pedestrian. 
     The controller  28  may reduce the host-speed  42  by activating a braking-actuator  44  of the host-vehicle  12 , and/or may reduce the host-speed  42  by adjusting a throttle-position  46  of the host-vehicle  12 . The controller  28  may further reduce the host-speed  42  when the lead-speed  16  is decreasing by greater than a change-threshold  48 . The change-threshold  48  may be user defined and is preferably at least eight kilometers-per-hour (8 kph). The controller  28  may also reduce the host-speed  42  to a value equivalent to the lead-speed  16 , or may bring the host-vehicle  12  to a complete stop. 
     The camera  20  may also detect a marking of the cross-walk  34  on the roadway  26  and the controller  28  may further determine that the marking is the cross-walk  34  using any of the known image-analysis methods (not specifically shown). The marking may be any of the United States Department of Transportation Federal Highway Administration known cross-walk  34  markings, including, but not limited to Solid, Standard, Continental, Dashed, Zebra, and Ladder markings. The cross-walk  34  may also be accompanied by a road-sign (not shown) that may also be detected by the camera  20  as an indication of the presence of the cross-walk  34 . 
     The ranging-sensor  14  may also detect the obstruction  30  on the roadway  26  ahead of the lead-vehicle  18  that may be the slow or non-moving vehicle, as illustrated in  FIG.  2   . The controller  28  may determine the change in the lead-speed  16  based on the ranging-sensor  14  and reduces the host-speed  42  of the host-vehicle  12  when the lead-speed  16  is decreasing, no object  22  is detected by the camera  20 , and while the portion  36  of the field-of-view  24  is obscured  38  by the lead-vehicle  18 . 
       FIG.  6    illustrates a non-limiting example of yet another embodiment of a method  300  of operating an automated speed control system  110 , hereafter referred to as the system  110 , for use on an automated vehicle  112 , hereafter referred to as a host-vehicle  112 . 
     Step  302 , DETECT OBSTRUCTION, may include detecting, with a ranging-sensor  114 , an obstruction  130  on a roadway  126  ahead of the host-vehicle  112 . The ranging-sensor  114  may be any of the known ranging-sensors  114 , and may include a radar, a lidar, or any combination thereof. The ranging-sensor  114  may be configured to output a continuous or periodic data stream that includes a variety of signal characteristics associated with each target detected. The signal characteristics may include or be indicative of, but are not limited to, the range (not shown) to the detected-target from the host-vehicle  112 , the azimuth-angle (not shown) to the detected-target relative to a host-vehicle-longitudinal-axis (not shown), an amplitude (not shown) of the ranging-signal (not shown), and a relative-velocity (not shown) of closure relative to the detected-target. A target is generally detected because the ranging-signal from the detected-target has sufficient signal strength to meet some predetermined threshold. That is, there may be targets that reflect the ranging-signal, but the strength of the ranging-signal is insufficient to be characterized as one of the detected-targets. Data that corresponds to a strong-target will generally be from consistent, non-intermittent signals. However, data that corresponds to a weak-target may be intermittent or have some substantial variability due to a low signal-to-noise ratio. 
     Step  304 , DETECT LEAD-SPEED, may include detecting, with the ranging-sensor  114 , a lead-speed  116  of the lead-vehicle  118  traveling on the roadway  126  ahead of the host-vehicle  112 . 
     Step  306 , DETECT OBJECTS, may include detecting, with a camera  120 , objects  122  in a field-of-view  124 . The camera  120  may be any of the commercially available cameras  120  suitable for use on the host-vehicle  112 . The camera  120  may be mounted on the front of the host-vehicle  112 , or mounted in the interior of the host-vehicle  112  at a location suitable for the camera  120  to view the area around the host-vehicle  112  through a windshield of the host-vehicle  112 . The camera  120  is preferably a video-type camera  120  or camera  120  that can capture images of a roadway  126  and surrounding area at a sufficient frame-rate, of ten frames per second, for example. 
     Step  308 , DETERMINE CHANGE IN LEAD-SPEED, may include determining, with a controller  128  in communication with the ranging-sensor  114  and the camera  120 , wherein the controller  128  is operable to control the host-vehicle  112 , a change in the lead-speed  116  based on the ranging-sensor  114 . The controller  128  may control vehicle-controls (not specifically shown) such as steering, brakes, and an accelerator. The controller  128  may include a processor (not shown) such as a microprocessor or other control circuitry such as analog and/or digital control circuitry including an application specific integrated circuit (ASIC) for processing data as should be evident to those in the art. The controller  128  may include a memory (not specifically shown), including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The one or more routines may be executed by the processor to perform steps for determining if a detected instance of the lead-vehicle  118 , the object  122 , and the obstruction  130  exist based on signals received by the controller  128  from the ranging-sensor  114  and the camera  120 , as described herein. 
     The controller  128  may analyze a signal from the ranging-sensor  114  to categorize the data from each detected target with respect to a list of previously detected targets having established tracks. As used herein, a track refers to one or more data sets that have been associated with a particular one of the detected targets. By way of example and not limitation, if the amplitude of the signal is above a predetermined amplitude threshold, then the controller  128  determines if the data corresponds to a previously detected target or if a new-target has been detected. If the data corresponds to a previously detected target, the data is added to or combined with prior data to update the track of the previously detected target. If the data does not correspond to any previously detected target because, for example, it is located too far away from any previously detected target, then it may be characterized as a new-target and assigned a unique track identification number. The identification number may be assigned according to the order that data for a new detected target is received, or may be assigned an identification number according to a grid-location (not shown) in a field-of-view  124  of the ranging-sensor  114 . 
     The controller  128  may determine a region-of-interest (not shown) within the field-of-view  124 . As illustrated in  FIG.  4   , the region-of-interest may represent the area directly ahead of the host-vehicle  112  that extends from a left-corner and from a right-corner of the host-vehicle  112 . The objects  122  in the region-of-interest and the host-vehicle  112  will collide if the host-vehicle  112  continues to move in the direction of the objects  122 . The field-of-view  124  also has a known vertical-angle (not shown) and a known horizontal-angle (not specifically shown) that are design features of the ranging-sensor  114  and determine how close to the host-vehicle  112  the objects  122  may be detected. 
     The controller  128  may define an occupancy-grid (not shown) that segregates the field-of-view  124  into an array of grid-cells (not shown). As mentioned previously, the controller  128  may assign the identification number to the detected target in the grid-location that is associated with unique grid-cells. A dimension of the individual grid-cell may be of any size and is advantageously not greater than five centimeters (5 cm) on each side. 
     The controller  128  periodically updates the detections within the grid-cells and determines a repeatability-of-detection of each of the grid-cells based on the reflections detected by the ranging-sensor  114 . The repeatability-of-detection corresponds to a history of detections within the grid-cells, where a larger number of detections (i.e. more persistent detections) increases the certainty that the target resides in the occupancy-grid. 
     The controller  128  may determine that an obstruction  130  (i.e. a slow or non-moving vehicle) is present in the field-of-view  124  when each of a string of the grid-cells are characterized by the repeatability-of-detection greater than a repeatability-threshold. Experimentation by the inventors has discovered that the repeatability-threshold of two detections in a grid-cell may be indicative of the presence of the obstruction  130 . 
       FIG.  4    is a top-view of the roadway  126  and illustrates a traffic scenario where the host-vehicle  112  is following the lead-vehicle  118  in an adjacent-lane  132 , and the objects  122  are a guard rail beside the roadway  126  and the lead-vehicle  118  that are detected by the camera  120  and the ranging-sensor  114 . The obstruction  130  is illustrated as a truck that is detected by the ranging-sensor  114  and not detected by the camera  120 . Without subscribing to any particular theory, it is believed that camera  120  is unable to detect the obstruction  130  due to the camera&#39;s  120  inability to distinguish the truck from a background. That is, the camera  120  may not “see” the truck because there is not sufficient contrast between the image of the truck and the image of the horizon as detected by the camera  120 . The truck is also blocking a portion  136  of the roadway  126  and the lead-vehicle  118  is reducing the lead-speed  116  due to its proximity to the truck (i.e. the obstruction  130 ) on the roadway  126 . 
     Step  310 , REDUCE HOST-SPEED, may include reducing, with the controller  128 , a host-speed  142  of the host-vehicle  112  when the lead-speed  116  is decreasing, the obstruction  130  is detected, and the obstruction  130  is not one of the objects  122  detected by the camera  120 , as illustrated in  FIG.  4   . 
     The system  110  is particularly beneficial when the lead-vehicle  118  may be traveling in the adjacent-lane  132  of the roadway  126 . In the specific example illustrated in  FIG.  4   , the prior art system would typically not reduce the host-speed  142  based on the conflicting signals received from the camera  120  and the ranging-sensor  114 . If the obstruction  130  does not clear the roadway  126 , the prior art system will have a reduced time window in which to reduce the host-speed  142 , potentially endangering the host-vehicle  112 , the obstruction  130 , and any surrounding-vehicles. By reducing the host-speed  142  in response to the reduction in the lead-speed  116 , the system  110  may increase the time required to react to the obstruction  130 , and may avoid a collision with the obstruction  130 . 
     The controller  128  may reduce the host-speed  142  by activating a braking-actuator  144  of the host-vehicle  112 , and/or may reduce the host-speed  142  by adjusting a throttle-position  146  of the host-vehicle  112 . The controller  128  may further reduce the host-speed  142  when the lead-speed  116  is decreasing by greater than a change-threshold  148 . The change-threshold  148  may be user defined and is preferably at least eight kilometers-per-hour (8 kph). The controller  128  may also reduce the host-speed  142  to a value equivalent to the lead-speed  116 , or may bring the host-vehicle  112  to a complete stop. 
     Accordingly, an automated speed control system  10  (the system  10 ), a controller  28  for the system  10 , and a method  200  of operating the system  10  are provided. The system  10  is an improvement over the prior art systems because the system  10  detects when the lead-vehicle  18  is reducing the lead-speed  16  and reduces the host-speed  42  when the object  22  is obscured  36  in the field-of-view  24 . 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.