FIELD OF THE INVENTION

The invention relates to a traffic registration system, comprising vehicle detector means for by visible or invisible light detecting a vehicle while passing therealong, and communication means for through communicating between the registration system and the vehicle effecting a registration of that vehicle. As the case may be, such invisible light could be a radar beam. For better referencing, the following definitions are given for further use hereinafter:

1. Detection: checking the actual presence of a particular vehicle at such position that the same or another camera can subsequently make a useful, in particular, a sharp picture of that vehicle.

2. Registration: making pictures of both front side and rear side of a vehicle with the purpose of checking the identity of the vehicle with respect to legal or other requirements. 3. Tracking: in such manner following the location of a vehicle in time so as to allow matching and/or correlating the detection-registration of the front side with the detection-registration of the rear side of the vehicle in question. 4. Classification: checking the class of a particular vehicle (such as motorcycle, passenger car or van) through an extension of the detection system.

Single-lane traffic registration has been disclosed in several documents, cf. US Patents 5,204,675 and 5,422,473, for various purposes, such as for road toll collecting or for checking access to security areas. The identity of the vehicle can be ascertained by means of an electronic on-board unit that is identified by some kind of roadside communication system.

Various other fields of use can be envisaged, such as finding out traffic offenders, checking the correctness of license plates, and measuring general conditions of actual traffic. Other ways for ascertaining the vehicle identity may use an active or passive tag, or the license plate of the vehicle. As an exemplary embodiment, road toll collection is

O 97/50067 PCMB97/00618

2 considered hereinafter. Now, present trends go to registration systems that are operative on multi-lane highways, and which systems must implement various conflicting requirements, such as:

- the toll amount is non-uniform for various types of vehicle - the system must check slow as well as very fast vehicles

- lateral positioning of the vehicles is not restrained

- the vehicles should remain anonymous viz a viz the system, in that after passage and correct payment the system should "forget" the vehicle in question

The toll amount can be levied beforehand, in that users pay an amount to an appropriate authority, which is then credited to a vehicle-borne device in the manner of an electronic purse. Upon passing the tolling point, a communication dialog will verify the amount to be paid versus the amount present in the electronic purse. If the latter allows subtraction of the toll amount, such will then be effected; this may be done with the vehicle remaining anonymous viz a viz the system. If the amount is not sufficient however, or the electronic purse facility is absent, the vehicle's identity has to be registrated by the system to enable its administration authority to then bill the actual user of the road, or another entity responsible for such using. Alternatively, the toll amount can be levied afterwards, in which case the organization is similar to the one effected with the user who was not or not sufficiently authorized: in such case, all vehicles are registrated. In other fields of use, the financial aspects may of course be totally different; however, the four primitives listed supra have generally corresponding functionality, if present.

SUMMARY OF THE INVENTION

Accordingly, amongst other things, it is an object of the present invention to provide a system according to the preamble, by which the vehicle can be registrated with at least a limited degree of certainty that the pretended identity of the vehicle corresponds to truth. In particular, it should be noticed that various pictures may be taken of the vehicle at different instances in time, which would represent a cause of further uncertainty in the correlation thereamongst. Now, the invention, having recognized that the motion of the vehicle through the detection area could cause such uncertainty, in particular because lateral motion may occur, should be able to match various registrations of a particular vehicle to its effective identification. Therefore, according to one of its aspects, the invention is characterized in that for use with a multilane system, said detector means are multiple and gantry-mounted and are arranged for through successive triggers detecting sequential

locations of a particular vehicle for as based thereon correlating multiple registrations of that vehicle as present on multiple positions that are spaced in time and at those multiple positions viewing the vehicle from respective different angles. The light may be visible or near infrared. The identification, for example by video storage of the vehicle's license plate, can be effected afterwards, conditional to the need proper for the registration. Another procedure is that all license plates are recorded provisionally, but are retained only if the information must be used further, such as for afterbilling, but cancelled otherwise. Through looking at the vehicle from different angles, additional checks can be effected.

Advantageously, the system has tracking means for tracking a vehicle through a change-of-lane when passing the gantry arrangement. Lateral movements are in principle a cause of much uncertainty, for example if various vehicles pass the gantry arrangement quasi-simultaneously. Various other types of mystifications occur, but must be overcome to prove that front side and rear side represent the same vehicle. Through the tracking, the registration and the actual presence of the vehicle can be matched uniquely. Advantageously, the detector means allow classifying said vehicle as based on one or more physical size-related properties thereof as a parameter for ascertaining an access right, and actual registration is conditional on matching between said classifying and a predetermined nonconforming outcome of said communicating. It has been customary to toll vehicles according to their size or weight, for example in that motorcycles pay less than passenger cars, which in turn pay less than minivans and so on. Measuring the size of the vehicles, as expressed in one or more of width, height or length can be a useful, and straightforwardly implementable feature of the invention. In this way the posing as another type of vehicle would often fall through. Methods for fraud would be to install an on-board unit of another vehicle class or attaching a wrong tag. ^' Advantageously, the system is arranged on viewing both a front license plate and a rear license plate of a vehicle in passage with subsequent verification thereamongst. One type of identification is based on the vehicle's license plate. The invention has recognized that the reading of a single license plate from a predetermined side is often inconclusive, inasmuch as motorcycles often have only a rear license plate, whereas many other vehicles have their rear license plate unreadable through dirt, or obscured by loads carried on the vehicle, or by a trailer. Quite often also, the two plates do not match. It is to be noted that the required fault margins are unbalanced. On the one hand, the chance for a vehicle to pass for a too low toll amount, or even toll-free may be in the range of a few percent. On the other hand, the chance for erroneously imposing toll may not be higher than

for example one in ten thousand. The double reading if two license plates are present gives an additional safety margin.

In consequence, the system may have several interactions with the vehicle, in that first an electronic device therein is accessed, and also the license plate and/or shape may be checked. Now, whereas three successive gantries would accommodate subsystems for all types of those interactions, an advantageous arrangement does with only two, or even with only one of such gantries. The cooperation between subsystems on such gantries is of course on a local level, in that the operation of one subsystem is supported or checked by another one. If two gantries are present, the tracking distance is substantially equal to the distance between the two gantries, or larger.

If only one structure is present, the tracking distance may be several times the height of the gantry structure. The latter setup may also be used for measuring overall vehicle behaviour. Particular aspects thereof, such as a slowed speed, excessively frequent change-of-lane could signal actual or impending traffic jams, accident or other. For such case, detecting the license plate would often not be necessary, but colour or shape aspects of a vehicle could help much to correlate its registrations. In such organization, it would often be necessary to do the correlation-based measurement on only a fraction of all vehicles. Various further advantageous aspects are recited in dependent Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the invention will be discussed more in detail with reference to the disclosure of preferred embodiments hereinafter, and in particular with reference to the appended Figures that show:

Figure 1 , a flow chart of the system operation; Figures 2a, 2b, a three-gantry arrangement;

Figure 3, a change-of-lane configuration;

Figure 4, size detection of vehicles;

Figure 5, various beam configurations;

Figures 6a, 6b, a two-gantry arrangement; Figure 7, a change-of-lane in the configuration of Figures 6a, 6b;

Figures 8a, 8b, a one-gantry arrangement;

Figure 9, a change-of-lane in the configuration of Figures 8a, b8.

5

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 is an exemplary flow chart of the system operation according to the invention for use with road tolling. In block 20, the system is set up, tested for correct operation, corrected for such things as environmental light, and finally brought into action. In block 22, a wake-up signal is produced by the system that wakes up an on-board electronic unit of approaching vehicles, so that an associated wireless dialog can be started as soon as the vehicle is in-range for on the basis of this dialog undertaking the financial aspects of the transaction. The on-board unit may or may not contain an electronic purse. This dialog may imply a mutual verification as to the vehicle's identity or class, and the eventual subtracting of the necessary debit amount that has been prescribed for letting the vehicle type in question pass the tolled route. In block 24 a waiting loop is expressed that waits for a signal back from the vehicle. As from this instant, the wireless dialog proceeds in a manner that has not been depicted, and in fact is asynchronous with respect to the subsequent stages in the Figure. The dialog may be effected through a transponder, or through an electromagnetic beam in an applicable frequency range.

In block 26 the position of the vehicle is ascertained with respect to an appropriate camera system. If found, in block 28 the front license plate is read, inter alia, with respect to ascertaining the kind of vehicle, such as passenger car, lorry, motorbike, or other. In block 30, the size of the vehicle is measured, which size in first instance is related to the bounding box of the vehicle as expressed in Cartesian coordinates. One parameter is the width of the vehicle, that may be checked with a granularity of some 10 ^{" 1} meter with video technology or laser radiation. In block 32, which may be executed some time later, it is detected whether the vehicle in question is effectively moving to a new traffic lane. The criterion may be that the eventual lateral displacement of the vehicle is extrapolated to more than one half of the sizing granularity. The extrapolation is effected to the vehicle position where the other license plate will be read. If little or no lateral displacement takes place, or need be considered, the system directly goes to block 36. Otherwise, in block 34 the system tracks down the lateral motion of the vehicle, and correlates or matches the positions at respective blocks 28, 36. In block 36, the other license plate is read, and the two numbers are compared. If the two disagree, an alarm procedure is executed, as governed by the check in block 38. In block 40, the size of the vehicle is ascertained once more. In block 42, it is ascertained whether the two sizes measured are in agreement with each other, and with the size of the vehicle as associated with the information of tag, on-board unit or license plate. If

yes, the data is processed, the financial transfer is effected if applicable, and the system is given free. Various aspects are not given in the Figure, such as the course of action taken when the sizes do not match, or when the license number disagrees with the size. In practice, a video picture can be taken of the license plate, possibly in combination with an image of the vehicle itself in black/white or colour, or a time/location identifier that is displayed inside or outside of the video camera. Finally, the system is given free for detecting a next signal in block 24.

The system may have various extensions or simplifications, such as:

- The system measures at least one deviation between the vehicle size and the bounding box size: this may pertain to the transition between a motor vehicle and its trailer, or a non- uniform height along the vehicle length, which identifies a passenger car versus a mini-bus.

- The number of gantries is reduced to one or two, as will be explained hereinafter.

- The first license plate that is detected in time is taken for granted, if appropriate with other registrated aspects of the vehicle. Figures 2a, 2b, show a three-gantry set-up as seen along the road, and as seen from above, respectively. In Figure 2a, the road 60, and a vehicle 62 have been shown for reasons of scaling. The far end or down-stream gantry 68 carries the camera arrangement for the front license plate of the vehicle through camera field 72. Near end or upstream gantry 64 carries the camera arrangement for the rear license plate of the vehicle through camera field 70. Middle gantry 66 carries antenna 78 that defines the communication area for the dialog with the vehicle through beam 74, and IR-detectors 76 for detecting the vehicle width in a passive manner. Figure 2b shows a top view of the same arrangement, with vehicle 62, and gantries 64, 66, and 68 clearly shown. Moreover, the camera fields of view 70, 72 have been shown to extend in a lateral direction. In fact, these fields of view are relatively flat. Also, three contiguous lanes have been shown. The lateral granularity of the IR-detectors is a fraction of the lane width, for example 0.35 m. The lateral granularity of the two rows of cameras is about one lane. The antenna beam 74 has also been shown in this projection, its footprint is an array of stripes each having the width of one lane, and a length that is somewhat larger than its width. Figure 3 depicts a change-of-lane configuration, with respect to cross-lane moving of vehicle 62. The Figure shows two parallel antenna beams 78, each pertaining to a contiguous lane, and the projection of infrared detector array 76. The further black and white dots in the antenna beam area indicate the center of gravity of vehicle 62 at successive instants in time, the black ones indicating instants at which the transaction, including the

verification of the vehicle identity, takes place, and the white ones subsequent instants of tracking of the vehicle. The five white dots in the detector array indicate the signal difference between the covered and the non-covered detector elements, respectively, that allow measuring the vehicle width at an accuracy level comparable to the granularity of the detector row. In this respect, Figure 4 shows size detection of a vehicle. In the Figure, each line shows the parallel signals of the row of IR detectors, a 1 indicating a "vehicle" signal level, and a 0 a "vehicle absent" signal. Successive rows correspond to successive instants depicted in Figure 3. The measurement indicates the detection of five different vehicles. Three thereof show as rectangles, indicating that they keep their lane: a relatively narrow vehicle, 4x6 dots, a wider vehicle, 5x6 dots, and a smaller vehicle, 2x4 dots, that classifies as a motorcycle. Furthermore, there is a vehicle E that changes from lane 3 to lane 2 to the left, and finally, there is a vehicle D that changes from the edge of lane 4 in the direction of its central axis 2 to the right. If the communication is effected through short-range radio, the antenna reception indicates the lateral location/position of the vehicle. The matching must be effected with respect to the most recently known lateral position and the vehicle detection with optical measures.

Figure 5 shows various beam configurations, in particular for governing the transaction window size for various vehicle categories. Given are the height of the antenna array at 6 metres, and the 5 metres long footprint of the antenna beam. As shown, for a low passenger car the communication area with respect to the on-board-unit is two metres long, which at a speed of 160 km/hr gives a time frame of 90 millisecs to handle the transaction. Likewise, for a high truck having the on-board-unit at 3.6 metres high, and a speed of 80 kms/hr, the time frame is 90 milliseconds as well. As shown in the lower part of the Figure, the antenna sub-beams are 0.7 metres wide. The upper part of the figure shows the quasi footprints of these beams at heights of 1.2 and 3.6 metres, respectively. At intermediate heights, similar data apply as recited above.

LOWERING THE NUMBER OF GANTRY STRUCTURES

For lowering equipment costs, it has been found advantageous to lower the number of gantry structures, at a cost of aggravating the tracking requirements. However, the present inventor has experienced the overcoming of this problem as fully feasible. First, Figures 6a, 6b show a two-gantry arrangement, that for the remainder is rather similar to the set-up of Figures 2a, 2b. In the Figures, various reference numerals, such as beams 70, 72, for effecting the registration, in particular the viewing of the license

plates, have been re-used. These beams have an axis making an angle with the horizontal axis of somewhat less than 45°. Furthermore, the communication beam 84 has been attached to the first gantry, and in consequence, looks back to the vehicle. Looking forward would be a feasible solution as well. Now clearly, the tracking problem is aggravated with respect to the situation in Figures 2a, 2b. In the former, the tracking distance was substantially limited to the vehicle length between front license plate and rear license plate, inasmuch as the two reading beams "meet" at the central gantry. In the newer situation, the tracking distance is comparable to the distance between the first and second gantries. This means that the lateral displacement of a vehicle may be rather more than in the former configuration. Figure 7 effectively shows a change-of-lane in the configuration of

Figures 6a, 6b. As shown, two footprints of the respective vehicle detection beams have a substantial corner part thereof in common. This commonality allows to match the vehicle positions even if, on the relatively short distance separating the two gantries, the vehicle had moved so much as a whole lane's width. Furthermore, if the distance between the two beams is known, the vehicle speed can be measured. In practice, the two gantries are some 6 metres high, so that their distance is in the order of 20 metres. Further, at left in Figure 6a an interval is shown, wherein the front of the vehicle is detected, whereas at the right an interval is shown wherein the rear of the vehicle is detected. In the middle region, the necessary tracking takes place Figure 6b again is a top view. The sequential organization may be viewed as follows:

Detection front ( -(-possibly classification)

Registration front tracking from first gantry

I tracking to second gantry

Detection rear

Registration rear

9

Figures 8a, 8b show a one-gantry arrangement. The rationale for lowering the number of gantries is cost, flexibility, and less required space for building structures. For example, a one-gantry set-up does need no calibrating regarding the distance between the gantries. Further, in tunnels and curves, the usage of three gantries would be a disadvantage with respect to using only two such gantries. To some extent, these advantages are offset by the higher cost of processing viz a viz the tracking procedure. The viewing beams 70, 72 have been indicated again. The tracking distance is now substantially twice as long as in the two-gantry solution, in as much as the two cameras view forwards and rearwards from the same longitudinal position. Beam 92 is the first detecting beam as discussed with reference to Figure 5. For clarity, the second detecting beam has not been shown in figures 8a, 8b, cf. Figure 9. The angles of incidence of the various beams can have different values from those shown in the Figures. Especially, in Figure 8a the registration beams can be directed at regions further away from the gantry structure. Inasmuch as the license plate would then become difficult to read, further aspects of the vehicle, such as colour or size aspects can be taken into account. For example, the tracking of a red or high vehicle might be relatively easy. The set up shown then can be advantageously used to detect various behaviourial aspects of the vehicle, such as for measuring lateral motion, and detecting speed variation patterns in an impending traffic jam situation. It would not be necessary to measure all vehicles, but say, 5 % thereof would be quite sufficient. The fact that the vehicles by themselves may not be a representative selection of the population would not be detrimental, if only their behaviour approaches average behaviour.

Figure 9 shows a change-of-lane in the configuration of Figures 8a, 8b, now with detection beams shown on both sides of the gantry structure. The three intervals highlighted at the bottom are the same as those of Figure 7, but have a lengthwise scale that is larger by about a factor of two. This necessitates a larger amount of tracking, causing the time difference between the first and the second vehicle detection to be larger. As indicated, again the two beam footprints have a corner in common. It may be necessary to have these beams somewhat wider in this organization, or rather, to raise their number above the number of lanes. For measuring traffic behaviour over longer road distances, the angle of incidence of the detection beams may be chosen again at lower values.