Electronic toll collection system for toll road

An ETC system for a toll road includes a road-side device. The road-side device transmitting a polling signal. The road-side device receives a response of an on-vehicle device to the transmitted polling signal. A decision is made as to whether or not the response is received a plural number of times. In cases where it is decided that the response is received a plural number of times, next radio communications with the on-vehicle device are started.

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. In addition, this invention relates to a method in an ETC system for a toll road. Furthermore, this invention relates to an on-vehicle device in an ETC system for a toll road.

1. 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. Generally, it is desirable to stabilize wireless communications between the ETC vehicle and the accounting machine in the tollgate.

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 or to urge the drivers of the non-ETC vehicles to manually pay toll. It is desirable to provide a high accuracy of discrimination of non-ETC vehicles from ETC vehicles.

SUMMARY OF THE INVENTION

It is a first object of this invention to provide an electronic toll collection system (an ETC system) for a toll road which is able to provide stable wireless communications between an ETC vehicle and a tollgate.

It is a second object of this invention to provide an improved method in an ETC system for a toll road.

It is a third object of this invention to provide an improved on-vehicle device in an ETC system for a toll road.

A first aspect of this invention provides an ETC system for a toll road. The ETC system comprises a road-side device; first means provided in the road-side device for transmitting a polling signal; second means provided in the road-side device for receiving a response of an on-vehicle device to the polling signal transmitted by the first means; third means provided in the road-side device for deciding whether or not the second means receives the response a plural number of times; and fourth means provided in the road-side device for starting next radio communications with the on-vehicle device in cases where the third means decides that the second means receives the response a plural number of times.

A second aspect of this invention provides an ETC system for a toll road. The ETC system comprises a first vehicle sensor for detecting a vehicle at a first position on a lane; a second vehicle sensor for detecting a vehicle at a second position on the lane which is adjacently ahead of the first position; first means for transmitting a polling signal when the first vehicle sensor detects a vehicle; second means for receiving a response of an on-vehicle device to the polling signal transmitted by the first means; and third means for, after the second means receives the response, starting next radio communications with the on-vehicle device in cases where both the first and second vehicle sensors detect a vehicle.

A third aspect of this invention is based on the second aspect thereof, and provides an ETC system wherein the second vehicle sensor is spaced from the first vehicle sensor at an interval of about 80 cm.

A fourth aspect of this invention provides an ETC system for a toll road. The ETC system comprises a road-side device; first means provided in the road-side device for implementing communications with an on-vehicle device; second means provided in the road-side device for measuring a lapse of time from a moment at which the first means starts implementing the communications with the on-vehicle device; third means provided in the road-side device for deciding whether or not the lapse of time which is measured by the second means reaches a prescribed time interval; and fourth means provided in the road-side device for maintaining the communications with the on-vehicle device which are implemented by the first means in cases where the third means decides that the lapse of time does not reach the prescribed time interval, and terminating the communications with the on-vehicle device after the third means decides that the lapse of time reaches the prescribed time interval.

A fifth aspect of this invention provides an ETC system for a toll road. The ETC system comprises an on-vehicle device; first means provided in the on-vehicle device for receiving data from a road-side device; second means provided in the on-vehicle device for receiving a communication end signal from the road-side device after the first means receives the data therefrom; and third means provided in the on-vehicle device for handling the data received by the first means as effective data regardless of whether or not the second means successfully receives the communication end signal.

A sixth aspect of this invention is based on the fifth aspect thereof, and provides an ETC system further comprising means provided in the road-side device for transmitting the communication end signal a plural number of times.

A seventh aspect of this invention provides an ETC system for a toll road. The ETC system comprises a road-side device; first means provided in the road-side device for receiving data from an on-vehicle device; second means provided in the road-side device for receiving a communication end signal from the on-vehicle device after the first means receives the data therefrom; and third means provided in the road-side device for handling the data received by the first means as effective data regardless of whether or not the second means successfully receives the communication end signal.

An eighth aspect of this invention is based on the seventh aspect thereof, and provides an ETC system further comprising means provided in the on-vehicle side device for transmitting the communication end signal a plural number of times.

A ninth aspect of this invention provides an ETC system for a toll road. The ETC system comprises a first road-side antenna for providing a first radio-communication service area; first means for implementing radio communications with an on-vehicle device via the first road-side antenna; a second road-side antenna for providing a second radio-communication service area different from the first radio-communication service area; second means for implementing radio communications with an on-vehicle device via the second road-side antenna; and third means for controlling the first means and the second means to execute the radio communications via the first road-side antenna and the radio communications via the second road-side antenna in a way selected from plural ways including a time sharing way.

A tenth aspect of this invention is based on the ninth aspect thereof, and provides an ETC system wherein the plural ways includes a frequency division way in which a frequency of a radio signal used in the radio communications via the first road-side antenna differs from a frequency of a radio signal used in the radio communications via the second road-side antenna.

An eleventh aspect of this invention provides an ETC system for a toll road. The ETC system comprises a first road-side antenna for providing a first radio-communication service area; first means for implementing radio communications with an on-vehicle device via the first road-side antenna; a second road-side antenna for providing a second radio-communication service area different from the first radio-communication service area; second means for implementing radio communications with an on-vehicle device via the second road-side antenna; third means for writing information related to the first road-side antenna into a memory within an on-vehicle device through the radio communications implemented by the first means; fourth means for accessing a memory within an on-vehicle device through the radio communications implemented by the second means, and deciding whether or not the information related to the first road-side antenna is in the accessed memory; and fifth means for halting the radio communications implemented by the second means when the fourth means decides that the information related to the first road-side antenna is not in the accessed memory.

A twelfth aspect of this invention is based on the eleventh aspect thereof, and provides an ETC system further comprising sixth means for preventing reflection of a radio wave with respect to first radio-communication service area.

A thirteenth aspect of this invention provides a method in an ETC system for a toll road. The method comprises the steps of transmitting a polling signal from a road-side device; enabling the road-side device to receive a response of an on-vehicle device to the polling signal; deciding whether or not the road-side device receives the response a plural number of times; and enabling the road-side device to start next radio communications with the on-vehicle device in cases where it is decided that the road-side device receives the response a plural number of times.

A fourteenth aspect of this invention provides a method in an ETC system for a toll road. The method comprises the steps of detecting a vehicle is at a first position on a lane; detecting a vehicle at a second position on the lane which is adjacently ahead of the first position; transmitting a polling signal when a vehicle at the first position is detected; receiving a response of an on-vehicle device to the polling signal; and after the response is received, starting next radio communications with the on-vehicle device in cases where both a vehicle at the first position and a vehicle at the second position are detected.

A fifteenth aspect of this invention provides a method in an ETC system for a toll road. The method comprises the steps of enabling a road-side device to implement communications with an on-vehicle device; measuring a lapse of time from a moment at which implementing the communications with the on-vehicle device is started; deciding whether or not the measured lapse of time reaches a prescribed time interval; and maintaining the communications with the on-vehicle device in cases where it is decided that the measured lapse of time does not reach the prescribed time interval, and terminating the communications with the on-vehicle device after it is decided that the measured lapse of time reaches the prescribed time interval.

A sixteenth aspect of this invention provides a method in an ETC system for a toll road. The method comprises the steps of receiving data from an on-vehicle device; receiving a communication end signal from the on-vehicle device after the data are received therefrom; and handling the received data as effective data regardless of whether or not the communication end signal is successfully received.

A seventeenth aspect of this invention provides an on-vehicle device in an ETC system for a toll road. The on-vehicle device comprises first means for receiving data from a road-side device; second means for receiving a communication end signal from the road-side device after the first means receives the data therefrom; and third means for handling the data received by the first means as effective data regardless of whether or not the second means successfully receives the communication end signal.

DETAILED DESCRIPTION OF THE INVENTION

Prior-art ETC systems for toll roads will be explained below for a better understanding of this invention.

FIGS. 1 and 2show a tollgate in a first prior-art ETC system. As shown inFIGS. 1 and 2, the tollgate includes a road-side antenna10, a road-side indicator11, a drive machine12, a road-side radio communication unit13, a control apparatus14, and vehicle sensors S1, S2, and S4.

The road-side antenna10is located above a lane. The road-side antenna10is connected to the road-side radio communication unit13. The load-side indicator11is located on an island15extending along a side of the lane. The drive machine12is connected to a gate member associated with the lane. The drive machine12moves the gate member between an open position and a closed position. The control apparatus14is connected to the road-side indicator11, the drive machine12, the road-side radio communication unit13, and the vehicle sensors S1, S2, and S4.

The vehicle sensors S1, S2, and S4are sequentially arranged along the lane in a vehicle forward direction. The vehicle sensor S4is ahead of the gate member connected with the drive machine12.

Each of the vehicle sensors S1, S2, and S4includes a photo-transmitter and a photo-receiver which are located at the opposite sides of the lane, respectively. The photo-transmitter emits a light beam toward the photo-receiver along an optical path perpendicular to the lane. The light beam does not reach the photo-receiver when a vehicle blocks the optical path. The light beam reaches the photo-receiver in the absence of a vehicle from the optical path. The photo-receiver converts the presence and the absence of the received light beam into an electric signal representing whether or not a vehicle is in a lane position corresponding to the position of the vehicle sensor. The photo-receiver outputs the electric signal to the control apparatus14as an output signal of the vehicle sensor.

The road-side radio communication unit13is controlled by the control apparatus14, feeding a radio signal to the road-side antenna10. The road-side antenna10radiates the radio signal toward the lane as a downward radio signal. Every ETC vehicle has an on-vehicle device including a combination of an antenna and a radio communication unit. The on-vehicle device can receive the downward radio signal. The on-vehicle device can transmit an upward radio signal. The upward radio signal is received by the road-side antenna10. The received radio signal is fed from the road-side antenna10to the road-side radio communication unit13. The road-side radio communication unit13derives information from the received radio signal. The road-side radio communication unit13outputs a signal representative of the derived information to the control apparatus14.

The control apparatus14decides whether a vehicle “A” in question is of an ETC type or a non-ETC type, and whether the vehicle “A” should be permitted to pass or be inhibited from passing on the basis of the output signals from the vehicle sensors S1, S2, and S4and the road-side radio communication unit13. In addition, the control apparatus14controls the road-side indicator11and the drive machine12on the basis of the output signals from the vehicle sensors S1, S2, and S4and the road-side radio communication unit13. Specifically, when it is decided that the vehicle “A” should be permitted to pass, the road-side indicator11is controlled to display “go ahead” to the vehicle “A”. At the same time, the drive machine12is controlled to open the gate member. When it is decided that the vehicle “A” should be inhibited from passing, the road-side indicator11is controlled to display “stop” to the vehicle “A”. At the same time, the drive machine12is controlled to maintain the gate member at its closed position or to move the gate member to its closed position.

The interval between the vehicle sensors S1and S2is set to about 4 m. The road-side antenna10provides a radio-communication service area18. The directivity of the road-side antenna10is designed so that the related radio-communication service area18will be limited to the range of the lane between the vehicle sensors S1and S2.

An incoming vehicle traveling along the lane is successively detected by the vehicle sensors S1, S2, and S4. When the vehicle sensor S1detects the front of the present vehicle, the vehicle sensor S1informs the control apparatus14of the vehicle-front detection. The control apparatus14starts the road-side radio communication unit13in response to the information of the vehicle-front detection so that the road-side radio communication unit13feeds a radio signal to the road-side antenna10. The road-side antenna10radiates the radio signal into the radio-communication service area18as a downward radio signal.

In the case where the present vehicle is of the ETC type, the on-vehicle device thereon transmits an upward radio signal in response to the downward radio signal. The upward radio signal (the response radio signal) is received by the road-side antenna10. The received radio signal is fed from the road-side antenna10to the road-side radio communication unit13. In this way, the road-side radio communication unit13receives the response radio signal. The response reception causes subsequent radio communications to be carried out between the road-side radio communication unit13and the on-vehicle device of the present vehicle. The road-side radio communication unit13informs the control apparatus14of the response reception. The control apparatus14decides the present vehicle to be of the ETC type on the basis of the information of the response reception, and automatically implements an accounting process. In addition, the control apparatus14drives the road-side indicator11to display “go ahead”. Furthermore, the control apparatus14commands the drive machine12to open the gate member.

When the vehicle sensor S2detects the front of the present vehicle, the vehicle sensor S2informs the control apparatus14of the vehicle-front detection. The control apparatus14deactivates the road-side radio communication unit13in response to the information of the vehicle-front detection, thereby terminating radio communications between the road-side radio communication unit13and the on-vehicle device of the present vehicle.

When the vehicle sensor S4detects the tail of the present vehicle, the vehicle sensor S4informs the control apparatus14of the vehicle-tail detection. The control apparatus14commands the drive machine12in response to the information of the vehicle-tail detection to close the gate member.

In the case where the present vehicle which has been detected by the vehicle sensor S1is of the non-ETC type, the present vehicle does not transmit any upward radio signal in response to the downward radio signal. Therefore, the control apparatus14is informed of the absence of the response. When the vehicle sensor S2detects the front of the present vehicle, the vehicle sensor S2informs the control apparatus14of the vehicle-front detection. The control apparatus14decides the present vehicle to be of the non-ETC type provided that the response remains absent until the vehicle-front detection is notified from the vehicle sensor S2. In this case, the control apparatus14deactivates the road-side radio communication unit13to interrupt the transmission of the radio signal. In addition, the control apparatus14drives the road-side indicator11to display “stop”. After the present vehicle completes paying toll, the control apparatus14commands the drive machine12to open the gate member.

The first prior-art ETC system (seeFIGS. 1 and 2) has problems indicated below. As shown inFIG. 3, the tollgate has constructions such as a roof16and a gantry (not shown). A consideration is given of the case where a non-ETC vehicle is in the present lane below the road-side antenna10while an ETC vehicle is in a lane adjacent to the present lane. As shown inFIG. 3, there is a chance that radio wave is propagated from the road-side antenna10to the ETC vehicle after being reflected by the roof16and the island15. When radio communications are successfully implemented between the road-side radio communication unit13(seeFIG. 2) and the on-vehicle device of the ETC vehicle, the control apparatus14(seeFIG. 2) erroneously decides that the non-ETC vehicle in the present lane is of the ETC type.

According to the prescription, every on-vehicle device is required to transmit a response radio signal when the strength of the electric field of received radio wave is equal to or greater than −60 dBm, and not to transmit any response radio signal when the electric field strength is equal to or smaller than −70 dBm. Therefore, every on-vehicle device is designed to start radio communications with a tollgate when the strength of the electric field of received radio wave is equal to a value between −60 dBm and −70 dBm.

With reference toFIG. 2, the tollgate is designed in accordance with the prescription so that the strength of the electric field of radio wave radiated by the road-side antenna10will be equal to or greater than −60 dBm only in the radio-communication service area (the standard radio-communication service area)18over the lane between the vehicle sensors S1and S2. Around the standard radio-communication service area18, there is a quasi radio-communication service area in which the strength of the electric field of radio wave radiated by the road-side antenna10is between −60 dBm and −70 dBm. Some of on-vehicle devices in the quasi radio-communication service area can communicate with the tollgate by radio, while the others can not. Reflection of radio wave by the roof16and the island15(seeFIG. 3) may cause an on-vehicle device in the quasi radio-communication service area to be capable of communicating with the tollgate by radio. In an outer portion of the standard radio-communication service area, interference between radio waves may decrease the electric-field strength below −70 dBm.

The road-side antenna10starts radiating a downward radio signal when the vehicle sensor S1detects the front of an incoming vehicle. In the case where the incoming vehicle travels at a low speed or has a long nose and an on-vehicle device is mounted on a dashboard of the vehicle, the on-vehicle device may not reach the standard radio-communication service area at a moment when a polling stage of radio communications should be executed.

Radio communications between the road-side radio communication unit13(seeFIG. 2) and an on-vehicle device of an incoming vehicle are terminated when the vehicle sensor S2detects the front of the vehicle. In the case where the present vehicle has a long nose as shown inFIG. 4, the distance L traveled by the on-vehicle device in the standard radio-communication service area18is relatively short at the moment when the front of the vehicle reaches the position of the vehicle sensor S2. Accordingly, there is a chance that the road-side radio communication unit13and the on-vehicle device are disconnected from each other before necessary radio communications therebetween have not been completed yet.

FIG. 5shows a tollgate in a second prior-art ETC system. In the tollgate ofFIG. 5, there are a first radio-communication service area18and a second radio-communication service area19extending over separate regions of a lane. The first and second radio-communication service areas18and19are provided by first and second separate road-side antennas, respectively. The second prior-art ETC system is similar to the first prior-art ETC system (seeFIGS. 1 and 2) except for additional system elements including a vehicle-type detection device20, a vehicle sensor S3, the second road-side antenna (not shown), and a second road-side radio communication unit (not shown). The vehicle-type detection device20acts to detect the type of a vehicle passing through the first radio-communication service area18. The vehicle sensor S3is located between vehicle sensors S2and S4. The output signal from the vehicle sensor S3is used in deciding a timing of opening the gate member. The second road-side antenna provides the second radio-communication service area19. The second radio-communication service area19extends ahead of the vehicle sensor S4. The second road-side radio communication unit is connected to the second road-side antenna and a control apparatus14(seeFIG. 2).

The second prior-art ETC system (seeFIG. 5) decides whether an incoming vehicle in the first radio-communication service area18is of the ETC type or the non-ETC type as the first prior-art ETC system (seeFIGS. 1 and 2) does. When the present vehicle is decided to be of the ETC type, the second prior-art ETC system automatically implements an accounting process as the first prior-art ETC system does.

In the second prior-art ETC system (seeFIG. 5), the vehicle-type detection device20senses the number of axles of a vehicle passing through the first radio-communication service area18. The vehicle-type detection device20detects the type of the present vehicle on the basis of the sensed number of the axles thereof. The vehicle-type detection device20outputs a signal representative of the detected vehicle type to the control apparatus14(seeFIG. 2). In the case where the present vehicle is of the ETC type, radio communications are carried out between a first road-side radio communication unit13(seeFIG. 2) and an on-vehicle device of the present vehicle. From the radio communications, the first road-side radio communication unit13gets information of the type of the present vehicle. The first road-side radio communication unit13outputs the information of the type of the present vehicle to the control apparatus14. The control apparatus14decides whether or not the vehicle type detected by the vehicle-type detection device20is equal to the vehicle type notified by the first road-side radio communication unit13. During the radio communications, the first road-side radio communication unit13transmits accounting information to the on-vehicle device of the present vehicle. The accounting information is written into a memory within the on-vehicle device.

When the vehicle sensor S3detects an incoming vehicle, the vehicle sensor S3informs the control apparatus14(seeFIG. 2) of the vehicle detection. At this time, the control apparatus14commands a drive machine12(seeFIG. 2) to open or close a gate member in response to a result of the decision as to whether the present vehicle is of the ETC type or the non-ETC type.

When the vehicle sensor S4detects the front of the present vehicle, the vehicle sensor S4informs the control apparatus14(seeFIG. 2) of the vehicle-front detection. In the case where the vehicle type detected by the vehicle-type detection device20is different from the vehicle type notified by the first road-side radio communication unit13, the control apparatus14starts the second road-side radio communication unit in response to the information of the vehicle-front detection from the vehicle sensor S4so that radio communications are carried out between the second road-side radio communication unit and the on-vehicle device of the present vehicle. During the radio communications, the control apparatus14accesses the memory within the on-vehicle device of the present vehicle via the second road-side radio communication unit. The control apparatus14corrects the previously-mentioned accounting information in the on-vehicle device memory in response to the vehicle type detected by the vehicle-type detection device20.

When the vehicle sensor S4detects the tail of the present vehicle, the vehicle sensor S4informs the control apparatus14(seeFIG. 2) of the vehicle-tail detection. The control apparatus14commands the drive machine12in response to the information of the vehicle-tail detection to close the gate member. In addition, the control apparatus14deactivates the second road-side radio communication unit in response to the information of the vehicle-tail detection, thereby terminating the radio communications between the second road-side radio communication unit and the on-vehicle device of the present vehicle if they are implemented.

In the second prior-art ETC system (seeFIG. 5), radio communications with an on-vehicle device in the first radio-communication service area18and radio communications with an on-vehicle device in the second radio-communication service area19can be simultaneously executed on a time sharing basis to prevent interference therebetween.

The second prior-art ETC system (seeFIG. 5) has problems indicated below. Radio communications between the second road-side radio communication unit and an on-vehicle device of a vehicle are terminated when the vehicle sensor S4detects the tail of the vehicle. There is a chance that the second road-side radio communication unit and the on-vehicle device are disconnected from each other before necessary radio communications therebetween have not been completed yet.

The simultaneous execution of first radio communications with an on-vehicle device in the first radio-communication service area18and second radio communications with an on-vehicle device in the second radio-communication service area19on a time sharing basis shortens the total time assigned to the first radio communications and the total time assigned to the second radio communication. Accordingly, there is a chance that the first road-side radio communication unit and the related on-vehicle device are disconnected from each other before necessary radio communications therebetween have not been completed yet, and that the second road-side radio communication unit and the related on-vehicle device are disconnected from each other before necessary radio communications therebetween have not been completed yet.

In the case where the tollgate ofFIG. 5is provided with a countermeasure against reflection of radio waves, the related cost is relatively high.

First Embodiment

FIGS. 6,7, and8show a tollgate in an ETC system (an electronic toll collection system) according to a first embodiment of this invention. With reference toFIGS. 6,7, and8, the tollgate includes a road-side antenna110, a road-side indicator111, a drive machine112, a road-side radio communication unit113, a control apparatus114, and vehicle sensors AS2and AS4. Here, “road-side” means “tollgate-side” opposite to “vehicle-side”.

The road-side antenna110is located above a lane. The road-side antenna110is connected to the road-side radio communication unit113. There are islands115extending along the opposite sides of the lane. The load-side indicator111is located on one of the islands115. The drive machine112is connected to a gate member associated with the lane. The drive machine112moves the gate member between an open position and a closed position. The control apparatus114is connected to the road-side indicator111, the drive machine112, the road-side radio communication unit113, and the vehicle sensors AS2and AS4.

The vehicle sensor AS2and AS4are sequentially arranged along the lane in a vehicle forward direction. The gate member associated with the drive machine112extends ahead of the vehicle sensor AS2. The vehicle sensor AS4extends ahead of the gate member connected to the drive machine112. The road-side indicator111is located near the gate member and the vehicle sensor AS4.

Each of the vehicle sensors AS2and AS4includes a photo-transmitter and a photo-receiver which are located at the opposite sides of the lane, respectively. The photo-transmitter emits a light beam toward the photo-receiver along an optical path perpendicular to the lane. The light beam does not reach the photo-receiver when a vehicle blocks the optical path. The light beam reaches the photo-receiver in the absence of a vehicle from the optical path. The photo-receiver converts the presence and the absence of the received light beam into an electric signal representing whether or not a vehicle is in a lane position corresponding to the position of the vehicle sensor. The photo-receiver outputs the electric signal to the control apparatus114as an output signal of the vehicle sensor.

The road-side radio communication unit113includes a radio communication transceiver. The road-side radio communication unit113is controlled by the control apparatus114, feeding a radio signal to the road-side antenna110. The road-side antenna110radiates the radio signal toward the lane as a downward radio signal. Every ETC vehicle has an on-vehicle device including a combination of an antenna and a radio communication unit (a radio communication transceiver). The on-vehicle device can receive the downward radio signal. The on-vehicle device can transmit an upward radio signal. The upward radio signal is received by the road-side antenna110. The received radio signal is fed from the road-side antenna110to the road-side radio communication unit113. The road-side radio communication unit113derives information from the received radio signal. The road-side radio communication unit113outputs a signal representative of the derived information to the control apparatus114. Also, the road-side radio communication unit113informs the control apparatus114of the presence of the received radio signal.

The control apparatus114includes a computer150having a combination of an input/output port, a CPU, a ROM, and a RAM. The computer150is connected to the vehicle sensors AS2and AS4, the road-side indicator111, the drive machine112, and the road-side radio communication unit113. The control apparatus114(the computer150) operates in accordance with a program stored in the ROM. The program is designed to enable the control apparatus114to execute steps of operation which will be mentioned later.

The control apparatus114decides whether a vehicle “A” in question is of an ETC type or a non-ETC type, and whether the vehicle “A” should be permitted to pass or be inhibited from passing on the basis of the output signals from the vehicle sensors AS2and AS4and the road-side radio communication unit113. In addition, the control apparatus114controls the road-side indicator111and the drive machine112on the basis of the output signals from the vehicle sensors AS2and AS4and the road-side radio communication unit113. Specifically, when it is decided that the vehicle “A” should be permitted to pass, the road-side indicator111is controlled to display “go ahead” to the vehicle “A”. At the same time, the drive machine112is controlled to open the gate member. When it is decided that the vehicle “A” should be inhibited from passing, the road-side indicator111is controlled to display “stop” to the vehicle “A”. At the same time, the drive machine112is controlled to maintain the gate member at its closed position or to move the gate member to its closed position.

The position and directivity of the road-side antenna110are chosen to provide a standard radio-communication service area118extending over a region of the lane in the rear of the vehicle sensor AS2and having a length of about 4 m along the longitudinal direction of the lane. The front edge of the standard radio-communication service area118is positionally equal to the vehicle sensor AS2. The strength of the electric field of radio wave radiated by the road-side antenna110is basically equal to or greater than −60 dBm only in the standard radio-communication service area118. Around the standard radio-communication service area118, there is a quasi radio-communication service area in which the strength of the electric field of radio wave radiated by the road-side antenna110is between −60 dBm and −70 dBm.

The road-side antenna110continuously, substantially continuously, or repetitively radiates a downward polling radio signal into the standard radio-communication service area118. An incoming vehicle passes through the standard radio-communication service area118before being successively detected by the vehicle sensors AS2and AS4.

In the case where an incoming vehicle of the ETC type enters the standard radio-communication service area118, an on-vehicle device thereon transmits an upward radio signal (a response radio signal) in response to the downward polling radio signal. The response radio signal is caught by the road-side antenna110, being fed to and received by the road-side radio communication unit113. The road-side radio communication unit113informs the control apparatus114of the response reception. The control apparatus114decides that an ETC vehicle has come on the basis of the information of the reception of the response radio signal. Then, the control apparatus114controls the road-side radio communication unit113to implement regular radio communications with the on-vehicle device of the present ETC vehicle. The control apparatus114automatically implements an accounting process through the regular radio communications with the present ETC vehicle. In addition, the control apparatus114drives the road-side indicator111to display “go ahead”. Furthermore, the control apparatus114commands the drive machine112to open the gate member.

When the vehicle sensor AS2detects the present ETC vehicle, the vehicle sensor AS2informs the control apparatus114of the ETC-vehicle detection. The control apparatus114controls the road-side radio communication unit113in response to the information of the ETC-vehicle detection, thereby terminating the regular radio communications between the road-side radio communication unit113and the on-vehicle device of the present ETC vehicle.

When the vehicle sensor AS4detects the present ETC vehicle, the vehicle sensor AS4informs the control apparatus114of the ETC-vehicle detection. The control apparatus114commands the drive machine112in response to the information of the ETC-vehicle detection to close the gate member.

On the other hand, in the case where an incoming vehicle of the non-ETC type enters the standard radio-communication service area118, a response radio signal remains absent. When the vehicle sensor AS2detects the present non-ETC vehicle, the vehicle sensor AS2informs the control apparatus114of the vehicle detection. The control apparatus114recognizes that a response radio signal remains absent before the vehicle detection is notified by the vehicle sensor AS2. In this case, the control apparatus114decides that the present vehicle is of the non-ETC type. Then, the control apparatus114drives the road-side indicator111to display “stop”. After the present non-ETC vehicle completes paying toll, the control apparatus114commands the drive machine112to open the gate member. When the vehicle sensor AS4detects the present non-ETC vehicle, the vehicle sensor AS4informs the control apparatus114of the vehicle detection. The control apparatus114commands the drive machine112in response to the information of the vehicle detection to close the gate member.

As previously mentioned, the control apparatus114(the computer150) operates in accordance with a program.FIG. 9shows a segment of the program.

With reference toFIG. 9, a first step ST1of the program segment controls the road-side radio communication unit113to transmit a polling radio signal. The polling radio signal is continuously, substantially continuously, or repetitively radiated by the road-side antenna110into the standard radio-communication service area118.

A step ST2following the step ST1decides whether or not at least one response to the polling radio signal is received by referring to the output signal of the road-side radio communication unit113. When at least one response to the polling radio signal is received, the program advances from the step ST2to a step ST3. Otherwise, the program advances from the step ST2to a step ST8.

The step ST3decides whether or not “n” responses to the polling radio signal are received at a time interval or time intervals shorter than a predetermined reference. Here, “n” denotes a preset natural number equal to or greater than 2. Preferably, the number “n” is equal to 2 or 3. When “n” responses to the polling radio signal are received, the program advances from the step ST3to a step ST4. Otherwise, the program advances from the step ST3to the step ST8.

The step ST4decides that the present vehicle is of the ETC type. The step ST4sets a vehicle-related flag to a state corresponding to the ETC type.

A step ST5following the step ST4controls the road-side radio communication unit113to implement regular radio communications with the on-vehicle device of the present ETC vehicle. The step ST5implements an accounting process. After the step ST5, the program advances to a step ST6.

The step ST6decides whether or not a vehicle is detected by the vehicle sensor AS2on the basis of the output signal therefrom. When a vehicle is not detected, the step ST6is repeated. When a vehicle is detected, the program advances from the step ST6to a step ST7.

The step ST7controls the road-side radio communication unit113to terminate the regular radio communications with the present ETC vehicle. After the step ST7, the program returns to the step ST1.

The step ST8decides whether or not a vehicle is detected by the vehicle sensor AS2on the basis of the output signal therefrom. When a vehicle is not detected, the program returns from the step ST8to the step ST1. When a vehicle is detected, the program advances from the step ST8to a step ST9.

The step ST9decides that the present vehicle is of the non-ETC type. The step ST9sets the vehicle-related flag to a state corresponding to the non-ETC type. After the step ST9, the program returns to the step ST1.

Second Embodiment

FIGS. 10 and 11show a tollgate in an ETC system according to a second embodiment of this invention. The tollgate inFIGS. 10 and 11is similar to the tollgate inFIGS. 6,7, and8except for additional designs mentioned later.

The tollgate inFIGS. 10 and 11includes a vehicle sensor AS1which is positionally equal to the rear edge of the standard radio-communication service area118. The tollgate inFIGS. 10 and 11includes a control apparatus114A and a computer150A instead of the control apparatus114and the computer150(seeFIG. 8) respectively. The vehicle sensor AS1is connected to the computer150A within the control apparatus114A.

FIG. 12shows a segment of a program for the computer150A (the control apparatus114A). The program segment inFIG. 12is similar to the program segment inFIG. 9except that a step ST3A replaces the step ST3(seeFIG. 9).

The step ST3A decides whether or not “n” responses to the polling radio signal are received at a time interval or time intervals shorter than a predetermined reference. Here, “n” denotes a preset natural number equal to or greater than 2. Preferably, the number “n” is equal to 2 or 3. In addition, the step ST3A decides whether or not a vehicle is detected by the vehicle sensor AS1on the basis of the output signal therefrom. In the case where “n” responses to the polling radio signal are received and a vehicle is detected by the vehicle sensor AS1, the program advances from the step ST3A to the step ST4. Otherwise, the program advances from the step ST3A to the step ST8.

Third Embodiment

FIGS. 13,14, and15show a tollgate in an ETC system according to a third embodiment of this invention. The tollgate inFIGS. 13,14, and15is similar to the tollgate inFIGS. 6,7, and8except for additional designs mentioned later.

The tollgate inFIGS. 13,14, and15includes vehicle sensors AS1and AS1A. The vehicle sensor AS1is positionally equal to the rear edge of the standard radio-communication service area118. The vehicle sensor AS1A extends ahead of the vehicle sensor AS1by an interval of about 80 cm along the longitudinal direction of the lane. Thus, the position of the vehicle sensor AS1A corresponds to a position within the standard radio-communication service area118. The tollgate inFIGS. 13,14, and15includes a control apparatus114B and a computer150B instead of the control apparatus114and the computer150(seeFIG. 8) respectively. The vehicle sensors AS1and AS1A are connected to the computer150B within the control apparatus114B.

FIG. 16shows a segment of a program for the computer150B (the control apparatus114B). As shown inFIG. 16, a first step ST11of the program segment decides whether or not a vehicle is detected by the vehicle sensor AS1on the basis of the output signal therefrom. When a vehicle is not detected, the step ST11is repeated. When a vehicle is detected, the program advances from the step ST11to a step ST12.

The step ST12controls the road-side radio communication unit113to transmit a polling radio signal. The polling radio signal is radiated by the road-side antenna110into the standard radio-communication service area118.

A step ST13following the step ST12decides whether or not a vehicle is detected by both the vehicle sensors AS1and AS1A on the basis of the output signals therefrom. When a vehicle is detected by both the vehicle sensors AS1and AS1A, the program advances from the step ST13to a step ST14. Otherwise, the program returns from the step ST13to the step ST12.

The step ST14decides whether or not a response to the polling radio signal is received by referring to the output signal of the road-side radio communication unit113. When a response to the polling radio signal is received, the program advances from the step ST14to a step ST15. Otherwise, the program advances from the step ST14to a step ST19.

The step ST15decides that the present vehicle is of the ETC type. The step ST15sets a vehicle-related flag to a state corresponding to the ETC type.

A step ST16following the step ST15controls the road-side radio communication unit113to implement regular radio communications with the on-vehicle device of the present ETC vehicle. The step ST16implements an accounting process. After the step ST16, the program advances to a step ST17.

The step ST17decides whether or not a vehicle is detected by the vehicle sensor AS2on the basis of the output signal therefrom. When a vehicle is not detected, the step ST17is repeated. When a vehicle is detected, the program advances from the step ST17to a step ST18.

The step ST18controls the road-side radio communication unit113to terminate the regular radio communications with the present ETC vehicle. After the step ST18, the current execution cycle of the program segment ends and then the program segment restarts from the step ST11.

The step ST19controls the road-side radio communication unit113to continue the transmission of the polling radio signal.

A step ST20following the step ST19decides whether or not a response to the polling radio signal is received by referring to the output signal of the road-side radio communication unit113. When a response to the polling radio signal is received, the program advances from the step ST20to the step ST15. Otherwise, the program advances from the step ST20to a step ST21.

The step ST21decides whether or not a vehicle is detected by the vehicle sensor AS2on the basis of the output signal therefrom. When a vehicle is not detected, the program returns from the step ST21to the step ST19. When a vehicle is detected, the program advances from the step ST21to a step ST22.

The step ST22decides that the present vehicle is of the non-ETC type. The step ST22sets the vehicle-related flag to a state corresponding to the non-ETC type.

A step ST23following the step ST22controls the road-side radio communication unit113to terminate the transmission of the polling radio signal. After the step ST23, the current execution cycle of the program segment ends and then the program segment restarts from the step ST11.

Fourth Embodiment

FIGS. 17 and 18show a tollgate in an ETC system according to a fourth embodiment of this invention. The tollgate inFIGS. 17 and 18is similar to the tollgate inFIGS. 6,7, and8except for additional designs mentioned later.

The tollgate inFIGS. 17 and 18includes vehicle sensors AS1and AS3. The vehicle sensor AS1is positionally equal to the rear edge of the standard radio-communication service area118. The vehicle sensor AS3is located between the vehicle sensors AS2and AS4. The output signal from the vehicle sensor AS3is used in deciding a timing of opening the gate member.

The tollgate ofFIGS. 17 and 18has a second radio-communication service area119in addition to the standard radio-communication service area118. The second radio-communication service area119extends over a region of the lane ahead of the vehicle sensor AS4. The second radio-communication service area119is provided by a second road-side antenna152located above the lane. The second road-side antenna152is connected to a second road-side radio communication unit154. The second road-side radio communication unit154includes a radio communication transceiver. The second road-side radio communication unit154can feed a radio signal to the second road-side antenna152. The second road-side antenna152radiates the fed radio signal into the second radio-communication service area119. The second road-side antenna152can catch a radio signal. The second road-side antenna152feeds the caught radio signal to the second road-side radio communication unit154.

The tollgate ofFIGS. 17 and 18includes a vehicle-type detection device120. The vehicle-type detection device120acts to detect the type of a vehicle passing through the standard radio-communication service area118.

The tollgate inFIGS. 17 and 18includes a control apparatus114C and a computer150C instead of the control apparatus114and the computer150(seeFIG. 8) respectively. The vehicle sensors AS1and AS3, the second road-side radio communication unit154, and the vehicle-type detection device120are connected to the computer150C within the control apparatus114B. The control apparatus114C (the computer150C) operates in accordance with a program stored in an internal ROM. The program is designed to enable the control apparatus114C to execute steps of operation which will be mentioned later.

The control apparatus114C decides whether an incoming vehicle in the standard radio-communication service area118is of the ETC type or the non-ETC type. When the present vehicle is decided to be of the ETC type, the control apparatus114C automatically implements an accounting process.

The vehicle-type detection device120senses the number of axles of a vehicle passing through the standard radio-communication service area118. The vehicle-type detection device120detects the type of the present vehicle on the basis of the sensed number of the axles thereof. The vehicle-type detection device120outputs a signal representative of the detected vehicle type to the control apparatus114C. In the case where the present vehicle is of the ETC type, radio communications are carried out between the road-side radio communication unit113and the on-vehicle device of the present vehicle. From the radio communications, the road-side radio communication unit113gets information of the type of the present vehicle. The road-side radio communication unit113outputs the information of the type of the present vehicle to the control apparatus114C. The control apparatus114decides whether or not the vehicle type detected by the vehicle-type detection device120is equal to the vehicle type notified by the road-side radio communication unit113. During the radio communications, the road-side radio communication unit113transmits accounting information to the on-vehicle device of the present vehicle. The accounting information is written into a memory within the on-vehicle device.

When the vehicle sensor AS3detects an incoming vehicle, the vehicle sensor AS3informs the control apparatus114C of the vehicle detection. At this time, the control apparatus114C commands the drive machine112to open or close the gate member in response to a result of the decision as to whether the present vehicle is of the ETC type or the non-ETC type.

When the vehicle sensor AS4detects the front of the present vehicle, the vehicle sensor AS4informs the control apparatus114C of the vehicle-front detection. In the case where the vehicle type detected by the vehicle-type detection device120is different from the vehicle type notified by the road-side radio communication unit113, the control apparatus114C starts the second road-side radio communication unit154in response to the information of the vehicle-front detection from the vehicle sensor AS4so that radio communications are carried out between the second road-side radio communication unit154and the on-vehicle device of the present vehicle. During the radio communications, the control apparatus114C accesses the memory within the on-vehicle device of the present vehicle via the second road-side radio communication unit154. The control apparatus114C corrects the previously-mentioned accounting information in the on-vehicle device memory in response to the vehicle type detected by the vehicle-type detection device120.

When the vehicle sensor AS4detects the tail of the present vehicle, the vehicle sensor AS4informs the control apparatus114C of the vehicle-tail detection. The control apparatus114C commands the drive machine112in response to the information of the vehicle-tail detection to close the gate member. In addition, the control apparatus114C deactivates the second road-side radio communication unit154in response to the information of the vehicle-tail detection, thereby terminating the radio communications between the second road-side radio communication unit154and the on-vehicle device of the present vehicle if they are implemented.

As previously mentioned, the control apparatus114C (the computer150C) operates in accordance with a program.FIG. 19shows a first segment of the program. As shown inFIG. 19, a first step ST31A of the program segment controls the road-side radio communication unit113to start regular radio communications with the on-vehicle device of the present vehicle in the standard radio-communication service area118. In addition, the step ST31A starts a timer for indicating the lapse of time from the start of the regular radio communications. After the step ST31A, the program advances to a step ST32A.

The step ST32A decides whether or not the front of a vehicle is detected by the vehicle sensor AS2on the basis of the output signal therefrom. When the front of a vehicle is not detected, the step ST32A is repeated. When the front of a vehicle is detected, the program advances from the step ST32A to a step ST33A.

The step ST33A accesses the road-side radio communication unit113, and decides whether or not the regular radio communications with the on-vehicle device of the present vehicle are going on now (that is, whether or not the regular radio communications with the on-vehicle device of the present vehicle have been completed). When the regular radio communications are going on now, that is, when the regular radio communications have not been completed yet, the program advances from the step ST33A to a step ST34A. Otherwise, the program jumps from the step ST33A to a step ST35A.

The step ST34A accesses the timer, and decides whether or not the lapse of time from the start of the regular radio communications reaches a predetermined time interval. When the lapse of time reaches the predetermined time interval, the program advances from the step ST34A to the step ST35A. Otherwise, the program returns from the step ST34A to the step ST33A. The predetermined time interval is equal to, for example, 100 ms.

The step ST35A controls the road-side radio communication unit113to terminate the regular radio communications with the on-vehicle device of the present vehicle in the standard radio-communication service area118.

FIG. 20shows a second segment of the program. As shown inFIG. 20, a first step ST31B of the program segment controls the second road-side radio communication unit154to start radio communications with the on-vehicle device of the present vehicle in the second radio-communication service area119. In addition, the step ST31B starts a timer for indicating the lapse of time from the start of the radio communications. After the step ST31B, the program advances to a step ST32B.

The step ST32B decides whether or not the tail of a vehicle is detected by the vehicle sensor AS4on the basis of the output signal therefrom. When the tail of a vehicle is not detected, the step ST32B is repeated. When the tail of a vehicle is detected, the program advances from the step ST32B to a step ST33B.

The step ST33B accesses the second road-side radio communication unit154, and decides whether or not the radio communications with the on-vehicle device of the present vehicle are going on now (that is, whether or not the radio communications with the on-vehicle device of the present vehicle have been completed). When the radio communications are going on now, that is, when the radio communications have not been completed yet, the program advances from the step ST33B to a step ST34B. Otherwise, the program jumps from the step ST33B to a step ST35B.

The step ST34B accesses the timer, and decides whether or not the lapse of time from the start of the radio communications reaches a predetermined time interval. When the lapse of time reaches the predetermined time interval, the program advances from the step ST34B to the step ST35B. Otherwise, the program returns from the step ST34B to the step ST33B. The predetermined time interval is equal to, for example, 100 ms.

The step ST35B controls the second road-side radio communication unit154to terminate the radio communications with the on-vehicle device of the present vehicle in the second radio-communication service area119.

FIGS. 21 and 22show a first example of the sequence of radio communications between an on-vehicle device and the road-side device (the tollgate-side device, that is, the road-side radio communication unit113or the second road-side radio communication unit154).

With reference toFIGS. 21 and 22, at a stage “1” of the radio communications, the road-side device sends an ENQ signal representing the presence of data to be transmitted to the communication opposite party (the on-vehicle device).

At a stage “2” of the radio communications, the on-vehicle device receives the ENQ signal. At a stage “3” following the stage “2”, the on-vehicle device recognizes the road-side device in response to the received ENQ signal. The on-vehicle device transmits an ACK signal as a positive response signal which represents an acknowledgment message, and which requires the communication opposite party to send a data block.

At a stage “4” of the radio communications, the road-side device receives the ACK signal. At a stage “5” following the stage “4”, the road-side device transmits a signal of a data block. The data block contains a BCC (block check character) signal being a parity signal for enabling a receiver side to decide whether a data error (data errors) is present or absent.

At a stage “6” of the radio communications, the on-vehicle device receives the signal of the data block. The on-vehicle device decides whether or not the data block has an error in response to the BCC signal contained therein. When the data block is free from an error, the stage “6” is followed by a stage “8”. When the data block has an error, the on-vehicle device transmits a NAK signal as a negative response signal which requires the communication opposite party to retransmit the signal of the data block.

At a stage “7” of the radio communications, the road-side device receives the NAK signal. The road-side device retransmits the signal of the data block in response to the received NAK signal.

At the stage “8”, the on-vehicle device transmits an ACK signal as a positive response signal which represents an acknowledgment message, and which requires the communication opposite party to send a next data block.

At a stage “9” of the radio communications, the road-side device receives the ACK signal. The road-side device transmits a signal of a next data block. In the absence of a next data block, the road-side device transmits an EOT signal representing “end-of-transmission”.

At a stage “10”, the on-vehicle device receives the EOT signal. Then, the radio communications end.

FIG. 23shows a second example of the sequence of radio communications which is similar to that inFIGS. 21 and 22except for the following point. With reference toFIG. 23, at the stage “9”, a trouble occurs so that the road-side device fails to transmit an EOT signal. Thus, in this case, at the stage “10”, the on-vehicle device does not receive any EOT signal. Even in the event that any EOT signal is not received, the on-vehicle device handles the data blocks, which have been received at the stage “6” and the similar stage or stages, as effective data blocks. In other words, the on-vehicle device handles the previously-received data blocks as effective data blocks regardless of whether or not an EOT signal is successfully received. Thus, it is possible to prevent the occurrence of a disagreement in phase of signal processing between the road-side device and the on-vehicle device.

Fifth Embodiment

A fifth embodiment of this invention is similar to the fourth embodiment thereof except for a design change mentioned later.FIG. 24shows an example of the sequence of radio communications between the on-vehicle device and the road-side device in the fifth embodiment of this invention.

With reference toFIG. 24, at a stage “9” of the radio communications, the road-side device receives the ACK signal. The road-side device transmits a signal of a next data block. In the absence of a next data block, the road-side device transmits an EOT signal representing “end-of-transmission”. Specifically, the road-side device repetitively transmits the EOT signal. In other words, the road-side device transmits the EOT signal twice or more.

Sixth Embodiment

A sixth embodiment of this invention is similar to the fourth or fifth embodiment thereof except for design changes mentioned later. In the sixth embodiment of this invention, the on-vehicle device transmits an EOT signal to the road-side device once or more during radio communications therebetween. Even in the event that any EOT signal is not received, the road-side device handles data blocks, which have been received at a previous stage or stages, as effective data blocks. In other words, the road-side device handles the previously-received data blocks as effective data blocks regardless of whether or not an EOT signal is successfully received.

Seventh Embodiment

A seventh embodiment of this invention is similar to one of the fourth, fifth, and sixth embodiments thereof except for design changes mentioned later. In the seventh embodiment of this invention, a program for the computer150C (seeFIG. 18) is designed so that the mode of operation of the control apparatus114C (seeFIG. 18) can be selected from first and second types.

During the operation of the control apparatus114C in the mode of the first type, radio communications with an on-vehicle device in the standard radio-communication service area118(seeFIG. 17) and radio communications with an on-vehicle device in the second radio-communication service area119(seeFIG. 17) can be simultaneously executed on a time sharing basis to prevent interference therebetween.

During the operation of the control apparatus114C in the mode of the second type, radio communications with an on-vehicle device in the standard radio-communication service area118and radio communications with an on-vehicle device in the second radio-communication service area119are executed in a way different from the time sharing method. During the operation of the control apparatus114C in the mode of the second type, radio communications with an on-vehicle device in the standard radio-communication service area118and radio communications with an on-vehicle device in the second radio-communication service area119may be executed on a frequency division basis. In the frequency division method, the radio-signal frequency used by the radio communications with the on-vehicle device in the standard radio-communication service area118differs from that used by the radio communications with the on-vehicle device in the second radio-communication service area119.

In the seventh embodiment of this invention, during the radio communications with the on-vehicle device in the standard radio-communication service area118, the control apparatus114C writes information related to the first road-side antenna110(seeFIG. 18) into a memory within the on-vehicle device. During a former stage of the radio communications with the on-vehicle device via the second road-side radio communication unit154, the control apparatus114C accesses the memory within the on-vehicle device and decides whether or not the information related to the first road-side antenna110is contained in the latest written information in the accessed memory. When the information related to the first road-side antenna110is contained in the latest written information in the memory within the on-vehicle device, the control apparatus114C determines that the vehicle in question is of the ETC type traveling along the present lane and differs from an ETC vehicle in a lane adjacent to the present lane. Only in this case, the control apparatus114C executes a later stage of the radio communications with the on-vehicle device via the second road-side radio communication unit154. When the information related to the first road-side antenna110is absent from the latest written information in the memory within the on-vehicle device, the control apparatus114C determines that the vehicle in question is an ETC vehicle traveling along a lane adjacent to the present lane. In this case, the control apparatus114C halts or terminates the radio communications with the on-vehicle device via the second road-side radio communication unit154.

FIG. 25shows a segment of the program for the control apparatus114C (the computer150C) in the seventh embodiment of this invention. With reference toFIG. 25, the program segment includes a step ST41executed during radio communications with an on-vehicle device via the first road-side radio communication unit113. The step ST41accesses a memory within the on-vehicle device via the road-side radio communication unit113, and writes ID (identification) information of the first road-side antenna110into the accessed memory.

A step ST42following the step ST41is executed during radio communications with an on-vehicle device via the second road-side radio communication unit154. The step ST42accesses a memory within the on-vehicle device via the second road-side radio communication unit154, and reads out the latest written information from the accessed memory.

A step ST43subsequent to the step ST42decides whether or not the ID information of the first road-side antenna110is contained in the read-out latest written information. When the ID information of the first road-side antenna110is contained in the read-out latest written information, the step ST43determines that the vehicle in question is of the ETC type traveling along the present lane and differs from an ETC vehicle in a lane adjacent to the present lane. In this case, the step ST43sets a vehicle-related flag to a state representing that the vehicle in question is of the ETC type traveling along the present lane. Then, the program advances from the step ST43to a step ST44. On the other hand, when the ID information of the first road-side antenna110is absent from the read-out latest written information, the step ST43determines that the vehicle in question differs from an ETC vehicle traveling along the present lane. In this case, the step ST43sets the vehicle-related flag to a state representing that the vehicle in question is not of the ETC type traveling along the present lane. Then, the program exits from the step ST43and then the current execution cycle of the program segment ends.

The step ST44implements a remaining stage of the radio communications with the on-vehicle device via the second road-side radio communication unit154. The step ST44may execute a given communication process such as a process of rewriting vehicle-type information. After the step ST44, the current execution cycle of the program segment ends.

Preferably, with respect to the standard radio-communication service area118, constructions such as a roof and a gantry are coated with members for absorbing radio waves or members for preventing reflection of radio waves. On the other hand, with respect to the second radio-communication service area119, it is unnecessary to coat constructions with members for absorbing radio waves or members for preventing reflection of radio waves.