Abstract:
An ETC (electronic toll collection) system includes an antenna having a predetermined directivity for providing a limited radio-communication service zone. A vehicle sensor operates for detecting a vehicle which reaches a predetermined position in the limited radio-communication service zone. A radio signal is transmitted via the antenna. A decision is made as to whether or not a radio response to the radio signal is received via the antenna. In cases where a radio response to the radio signal is received, it is judged that there is an ETC vehicle incoming. In cases where the vehicle sensor detects a vehicle while a radio response to the radio signal is not received, it is judged that there is a non-ETC vehicle incoming.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an electronic toll collection system (an ETC system) for a toll road. 
   2. Description of the Related Art 
   In an ETC system for a toll road, when every ETC vehicle passes through a tollgate, an accounting machine in the tollgate and the ETC vehicle communicate with each other by wireless to automatically implement an accounting process. Accordingly, it is unnecessary for the ETC vehicle to pause at the tollgate to pay toll. The ETC vehicle means a vehicle designed for the ETC system. 
   The ETC system can not automatically implement an accounting process with respect to a non-ETC vehicle. The non-ETC vehicle means a vehicle not adapted to the ETC system. It is necessary for the tollgate in the ETC system to discriminate non-ETC vehicles from ETC vehicles, and to guide the non-ETC vehicles to a booth where toll can be manually paid. It is desirable to provide a high accuracy of discrimination of non-ETC vehicles from ETC vehicles. 
   SUMMARY OF THE INVENTION 
   It is an object of this invention to provide an electronic toll collection system (an ETC system) for a toll road which is able to accurately discriminate non-ETC vehicles from ETC vehicles. 
   A first aspect of this invention provides an ETC system comprising an antenna having a predetermined directivity for providing a limited radio-communication service zone; a vehicle sensor for detecting a vehicle which reaches a predetermined position in the limited radio-communication service zone; first means for transmitting a radio signal via the antenna; second means for deciding whether or not a radio response to the radio signal is received via the antenna; third means for, in cases where the second means decides that a radio response to the radio signal is received, judging that there is an ETC vehicle incoming; and fourth means for, in cases where the vehicle sensor detects a vehicle while the second means decides that a radio response to the radio signal is not received, judging that there is a non-ETC vehicle incoming. 
   A second aspect of this invention is based on the first aspect thereof, and provides an ETC system wherein the first means comprises means for continuously transmitting the radio signal via the antenna. 
   A third aspect of this invention is based on the first aspect thereof, and provides an ETC system wherein the limited radio-communication service zone has a length greater than a length of a standard vehicle and smaller than twice the length of the standard vehicle. 
   A fourth aspect of this invention is based on the first aspect thereof, and provides an ETC system wherein the limited radio-communication service zone has a length of about 6.5 m along a lane. 
   A fifth aspect of this invention is based on the first aspect thereof, and provides an ETC system wherein the vehicle sensor is only one in the ETC system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a tollgate in a background-art ETC system for a toll road which is not prior art against this invention. 
       FIG. 2  is a diagrammatic side view of the tollgate in  FIG. 1 . 
       FIG. 3  is a plan view of the tollgate in  FIG. 1 . 
       FIG. 4  is a block diagram of an electronic portion of the background-art ETC system in  FIG. 1 . 
       FIG. 5  is a diagrammatic side view of a tollgate in an ETC system according to an embodiment of this invention. 
       FIG. 6  is a plan view of the tollgate in  FIG. 5 . 
       FIG. 7  is a block diagram of an electronic portion of the ETC system in  FIG. 5 . 
       FIG. 8  is a plan view of an antenna in  FIG. 5 . 
       FIG. 9  is a flowchart of a segment of a control program for a computer in  FIG. 7 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A background-art ETC system for a toll road will be explained below for a better understanding of this invention. 
     FIGS. 1 ,  2 , and  3  show a tollgate in a background-art ETC system for a toll road which is not prior art against this invention. As shown in  FIGS. 1 ,  2 , and  3 , the tollgate includes a first vehicle sensor  91  composed of a photo-transmitter  91 A and a photo-receiver  91 B, and a second vehicle sensor  92  composed of a photo-transmitter  92 A and a photo-receiver  92 B. 
   The photo-transmitter  91 A and the photo-receiver  91 B in the first vehicle sensor  91  are located at the opposite sides of a lane, respectively. The photo-transmitter  91 A emits a light beam toward the photo-receiver  91 B along an optical path perpendicular to the lane. The light beam does not reach the photo-receiver  91 B when a vehicle  95  blocks the optical path. The light beam reaches the photo-receiver  91 B in the absence of a vehicle  95  from the optical path. The photo-receiver  91 B converts the presence and the absence of the received light beam into an electric signal representing whether or not a vehicle  95  is in a lane position corresponding to the position of the first vehicle sensor  91 . The photo-receiver  91 B outputs the electric signal as an output signal of the first vehicle sensor  91 . 
   Similarly, the photo-transmitter  92 A and the photo-receiver  92 B in the second vehicle sensor  92  are located at the opposite sides of the lane, respectively. The second vehicle sensor  92  generates and outputs an electric signal representing whether or not a vehicle  95  is in a lane position corresponding to the position of the second vehicle sensor  92 . The position of the second vehicle sensor  92  relative to the lane precedes the position of the first vehicle sensor  91  by an interval of about 4 m. 
   As shown in  FIGS. 1 ,  2 , and  3 , the tollgate in the background-art ETC system includes an antenna  93  located above the lane. The tollgate also includes a machine box  94  located at one side of the lane. 
   As shown in  FIG. 4 , the background-art ETC system has a computer  94 A contained in the machine box  94  (see  FIG. 1 ). The computer  94 A is electrically connected to the first vehicle sensor  91  and the second vehicle sensor  92 . In addition, the computer  94 A is connected to a radio transceiver  93 A. The radio transceiver  93 A is connected to the antenna  93 . The computer  94 A includes a combination of an input/output port, a CPU, a ROM, and a RAM. The computer  94 A operates in accordance with a control program stored in the ROM. 
   The radio transceiver  93 A is controlled by the computer  94 A, feeding a radio signal to the antenna  93 . The antenna  93  radiates the radio signal toward the lane as a downward radio signal. Every ETC vehicle has an on-vehicle machine including a combination of an antenna and a radio transceiver. The on-vehicle machine can receive the downward radio signal. The on-vehicle machine can transmit an upward radio signal. The upward radio signal is received by the antenna  93 . The received radio signal is fed from the antenna  93  to the radio transceiver  93 A. 
   The control program for the computer  94 A has a segment which is executed for every incoming vehicle. Specifically, a step “ 1 ” in the program segment decides whether or not a vehicle reaches the lane position of the first vehicle sensor  91  by referring to the output signal therefrom. When a vehicle reaches the lane position of the first vehicle sensor  91 , the program advances from the step “ 1 ” to a step “ 2 ”. Otherwise, the step “ 1 ” is repeated. 
   The step “ 2 ” controls the radio transceiver  93 A to start radio communication with the incoming vehicle. Specifically, the radio transceiver  93 A outputs a radio signal to the antenna  93 . The radio signal is radiated from the antenna  93  as a downward radio signal. In the case where the incoming vehicle is an ETC vehicle, the on-vehicle machine of the incoming vehicle receives the downward radio signal and transmits an upward radio signal in response to the received downward radio signal. The upward radio signal is a response to the downward radio signal. The upward radio signal contains ID (identification) information, departure-place information, and information of places through which the vehicle passed. The upward radio signal is received by the antenna  93 . The received radio signal is fed from the antenna  93  to the radio transceiver  93 A. The radio transceiver  93 A extracts the information from the received radio signal. The radio transceiver  93 A outputs the extracted information to the computer  94 A. In this case, the computer  94 A is notified that a response to the downward radio signal has successfully come from the incoming vehicle. On the other hand, in the case where the incoming vehicle is a non-ETC vehicle, any upward radio signal is not received by the antenna  93  and hence the radio transceiver  93 A informs the computer  94 A that a response to the downward radio signal has failed to come from the incoming vehicle. 
   A step “ 3 ” following the step “ 2 ” decides whether or not a response to the downward radio signal has successfully come from the incoming vehicle by referring to the information given by the radio transceiver  93 A. When a response to the downward radio signal has successfully come from the incoming vehicle, the computer  94 A judges the incoming vehicle to be an ETC vehicle. In this case, the program advances from the step “ 3 ” to a step “ 4 ”. When a response to the downward radio signal has failed to come from the incoming vehicle, the computer  94 A judges the incoming vehicle to be a non-ETC vehicle. In this case, the program advances from the step “ 3 ” to a step “ 6 ”. 
   The step “ 4 ” implements an accounting process related to the incoming vehicle. A step “ 5 ” following the step “ 4 ” decides whether or not the incoming vehicle reaches the lane position of the second vehicle sensor  92  by referring to the output signal therefrom. When the incoming vehicle reaches the lane position of the second vehicle sensor  92 , the program advances from the step “ 5 ” to a step “ 8 ”. Otherwise, the step “ 5 ” is repeated. 
   Similarly, the step “ 6 ” decides whether or not the incoming vehicle reaches the lane position of the second vehicle sensor  92  by referring to the output signal therefrom. When the incoming vehicle reaches the lane position of the second vehicle sensor  92 , the program advances from the step “ 6 ” to a step “ 7 ”. Otherwise, the step “ 6 ” is repeated. 
   The step “ 7 ” controls a suitable apparatus (not shown) to guide the incoming vehicle to a tollbooth and to instruct the incoming vehicle to pause at the tollbooth for manually paying toll. After the step “ 7 ”, the program advances to the step “ 8 ”. 
   The step “ 8 ” controls the radio transceiver  93 A to terminate radio communication with the incoming vehicle. After the step “ 8 ”, the program returns to the step “ 1 ”. 
   As best shown in  FIG. 2 , the tollgate of the background-art ETC system has a predetermined radio-communication service zone  97  spreading from the antenna  93  to the surface of the lane. Within the predetermined service zone  97 , the intensity of a downward radio signal which has been radiated from the antenna  93  is equal to or greater than a rating level, for example, −60 dBm. When an ETC vehicle is in the predetermined service zone  97 , radio access thereto (radio communication therewith) can be executed. The predetermined service zone  97  is designed to just cover the region of the lane between the position of the first vehicle sensor  91  and the position of the second vehicle sensor  92 . Specifically, the predetermined service zone  97  extends from a place following the position of the first vehicle sensor  91  by an interval of 2 m to a place substantially coincident with the position of the second vehicle sensor  92 . 
   The predetermined service zone  97  is surrounded by a zone  98  forming a pseudo service zone. Within the pseudo service zone  98 , the intensity of a downward radio signal is equal to or greater than a certain level, for example, −70 dBm at which radio communication with an ETC vehicle may be established. For example, the pseudo service zone  98  extends from a place following the position of the first vehicle sensor  91  by an interval of 5 m to a place preceding the position of the second vehicle sensor  92  by an interval of 1 m. 
   The background-art ETC system tends to erroneously judge a non-ETC vehicle to be an ETC vehicle in conditions mentioned below. When a non-ETC vehicle (a first incoming vehicle) immediately followed by an ETC vehicle (a second incoming vehicle) reaches the lane position of the first vehicle sensor  91 , a downward radio signal is radiated from the antenna  93 . In the case where the ETC vehicle (the second incoming vehicle) has already reached the pseudo service zone  98  at this moment, the ETC vehicle may respond to the downward radio signal while the non-ETC vehicle (the first incoming vehicle) does not respond thereto. The computer  94 A is caused by the response from the second incoming vehicle to erroneously judge the first incoming vehicle to be an ETC vehicle. 
   EMBODIMENT  
     FIGS. 5 and 6  show a tollgate in an ETC system for a toll road according to an embodiment of this invention. As shown in  FIGS. 5 and 6 , the tollgate includes a vehicle sensor  11  of an optical type. The vehicle sensor  11  is composed of a photo-transmitter  11 A and a photo-receiver  11 B. 
   The photo-transmitter  11 A and the photo-receiver  11 B are located at the opposite sides of a lane, respectively. The photo-transmitter  11 A emits a light beam toward the photo-receiver  11 B along an optical path perpendicular to the lane. The light beam does not reach the photo-receiver  11 B when a vehicle  14  blocks the optical path. The light beam reaches the photo-receiver  11 B in the absence of a vehicle  14  from the optical path. The photo-receiver  11 B converts the presence and the absence of the received light beam into an electric signal representing whether or not a vehicle  14  is in a lane position corresponding to the position of the vehicle sensor  11 . The photo-receiver  11 B outputs the electric signal as an output signal of the vehicle sensor  11 . 
   As shown in  FIGS. 5 and 6 , the tollgate includes an antenna  13  located above the lane. Specifically, the antenna  13  is directly above a position on the lane which precedes the position of the vehicle sensor  11  by a predetermined interval, for example, about 1 m. The tollgate also includes a machine box  12  located at one side of the lane. 
   As shown in  FIG. 7 , the ETC system has a computer  12 A contained in the machine box  12  (see  FIG. 5 ). The computer  12 A is electrically connected to the vehicle sensor  11 . In addition, the computer  12 A is connected to a radio transceiver  13 A. The radio transceiver  13 A is connected to the antenna  13 . The computer  12 A is connected to a suitable apparatus (a guiding apparatus)  19  designed to guide an incoming vehicle to a tollbooth and to instruct the incoming vehicle to pause at the tollbooth for manually paying toll. The computer  12 A includes a combination of an input/output port, a CPU, a ROM, and a RAM. The computer  12 A operates in accordance with a control program stored in the ROM. 
   The radio transceiver  13 A is controlled by the computer  12 A, feeding a radio signal to the antenna  13 . The antenna  13  radiates the radio signal toward the lane as a downward radio signal. Every ETC vehicle has an on-vehicle machine including a combination of an antenna and a radio transceiver. The on-vehicle machine can receive the downward radio signal. The on-vehicle machine can transmit an upward radio signal. The upward radio signal is received by the antenna  13 . The received radio signal is fed from the antenna  13  to the radio transceiver  13 A. 
   As shown in  FIG. 5 , the tollgate of the ETC system has a predetermined radio-communication service zone  17  spreading from the antenna  13  to the surface of the lane. Within the predetermined service zone  17 , the intensity of a downward radio signal which has been radiated from the antenna  13  is equal to or greater than a rating level, for example, −60 dBm. When an ETC vehicle is in the predetermined service zone  17 , radio access thereto (radio communication therewith) can be executed. The predetermined service zone  17  is designed to extend in a given region of the lane which contains the position of the vehicle sensor  11 , and which has a length greater than the length of a standard vehicle and smaller than twice the length of the standard vehicle. For example, the predetermined service zone  17  has a length of about 4 m along the lane. For example, the position of the vehicle sensor  11  is rearward separate from the front edge of the predetermined service zone  17  by an interval of about 1 m. 
   The predetermined service zone  17  is surrounded by a zone  18  forming a pseudo service zone. Within the pseudo service zone  18 , the intensity of a downward radio signal is equal to or greater than a certain level, for example, −70 dBm at which radio communication with an ETC vehicle may be established. The antenna  13  is designed to feature a predetermined directivity which causes the pseudo service zone  18  to be relatively narrow. For example, on the surface of the lane, the pseudo service zone  18  extends from a place following the rear edge of the predetermined service zone  17  by an interval of about 1.5 m to a place preceding the front edge of the predetermined service zone  17  by an interval of about 1 m. 
   Preferably, the whole service zone equal to the combination of the predetermined service zone  17  and the pseudo service zone  18  has a length along the lane which is greater than the length of a standard vehicle and smaller than twice the length of the standard vehicle. For example, the length of the whole service zone is equal to about 6.5 m. 
   As shown in  FIG. 8 , the antenna  13  includes an insulating base board (an insulating substrate)  51 , patch antenna elements  52 , and feeder lines  53 . The patch antenna elements  52  are formed on the insulating base board  51 . The patch antenna elements  52  are arranged in a suitable array, for example, a two-dimensional matrix array. Each of the patch antenna elements  52  has a rectangular electrically-conductive plate. The feeder lines  53  are formed on the insulating base board  51 . The feeder lines  53  are connected to the patch antenna elements  52 , respectively. Radio power can be fed from the radio transceiver  13 A (see  FIG. 7 ) to the patch antenna elements  52  via the feeder lines  53 . The number of the patch antenna elements  52  and the array of the patch antenna elements  52  are designed to provide the previously-mentioned predetermined directivity. 
   The control program for the computer  12 A is designed to continuously activate the radio transceiver  13 A. Accordingly, the radio transceiver  13 A continuously outputs a radio signal to the antenna  13 , and the antenna  13  continuously radiates the radio signal as a downward radio signal. In the case where an ETC vehicle comes in, the on-vehicle machine of the ETC vehicle receives the downward radio signal and transmits an upward radio signal in response to the received downward radio signal. The upward radio signal is a response to the downward radio signal. The upward radio signal contains ID (identification) information, departure-place information, and information of places through which the vehicle passed. The upward radio signal is received by the antenna  13 . The received radio signal is fed from the antenna  13  to the radio transceiver  13 A. The radio transceiver  13 A extracts the information from the received radio signal. The radio transceiver  13 A outputs the extracted information to the computer  12 A. In this case, the computer  12 A is notified that a response to the downward radio signal has come from an incoming vehicle. On the other hand, in the case where a non-ETC vehicle comes in, any upward radio signal is not received by the antenna  13  and hence the radio transceiver  13 A continues to inform the computer  12 A that any response to the downward radio signal does not come. 
     FIG. 9  shows a segment of the control program for the computer  12 A which is iterated, and which is executed for every incoming vehicle. As shown in  FIG. 9 , a first step S 1  of the program segment decides whether or not a response to the downward radio signal is received by referring to the information given by the radio transceiver  13 A. When a response to the downward radio signal is received, the computer  12 A judges that there is an ETC vehicle incoming. In this case, the program advances from the step S 1  to a step S 2 . When a response to the downward radio signal is not received, the program advances from the step S 1  to a step S 3 . 
   The step S 2  implements an accounting process related to the incoming ETC vehicle. A step S 4  following the step S 2  decides whether or not the incoming ETC vehicle reaches the lane position of the vehicle sensor  11  by referring to the output signal therefrom. When the incoming ETC vehicle reaches the lane position of the vehicle sensor  11 , the program exists from the step S 4  and then the current execution cycle of the program segment ends. 
   The step S 3  decides whether or not an incoming vehicle reaches the lane position of the vehicle sensor  11  by referring to the output signal therefrom. When an incoming vehicle reaches the lane position of the vehicle sensor  11 , the computer  12 A judges that there is a non-ETC vehicle incoming. In this case, the program advances from the step S 3  to a step S 5 . When any incoming vehicle does not reach the lane position of the vehicle sensor  11 , the program returns from the step S 3  to the step S 1 . 
   The step S 5  controls the guiding apparatus  19  to guide the incoming non-ETC vehicle to a tollbooth and to instruct the incoming non-ETC vehicle to pause at the tollbooth for manually paying toll. After the step S 5 , the current execution cycle of the program segment ends. 
   As previously mentioned, the downward radio signal is continuously radiated from the antenna  13 . When a response to the downward radio signal is received, the computer  12 A judges that there is an ETC vehicle incoming. In the case where an incoming vehicle is detected by the vehicle sensor  11  while any response to the downward radio signal is not received, the computer  12 A judges that there is a non-ETC vehicle incoming. Since only one standard vehicle can be contained in the whole radio-communication service zone (the predetermined service zone  17  plus the pseudo service zone  18 ), an incoming non-ETC vehicle can be correctly detected even when the incoming non-ETC vehicle is immediately followed by an ETC vehicle. 
   The ETC-system tollgate in  FIGS. 5 and 6  has only one vehicle sensor  11 . Therefore, the ETC-system tollgate is relatively inexpensive. 
   The antenna  13  may be replaced by another directional antenna. The vehicle sensor  11  may be of a type different from the optical type.