EP0494815B1 - Motor vehicles traffic measuring system - Google Patents

Description

The present invention relates to a system for measuring the traffic of motor vehicles on a traffic lane, comprising at least two measurement stations, spaced along said lane.

We are looking for information on automobile traffic. The time taken by a vehicle to travel a stretch of urban or road lane is the main element that defines "traffic flow".

Currently the flow of a lane is measured using a vehicle counter (magnetic loop placed in the roadway).

It has been imagined to equip a fleet of vehicles (so-called tracer vehicles) with a measurement device and a device for transmitting data to beacons installed at crossroads. A significant percentage (5 to 10%) of the vehicle fleet must be equipped to obtain valid information from the system, which requires a high initial investment.

The present invention aims to achieve a device for measuring automobile traffic requiring no special equipment on motor vehicles.

The motor vehicle traffic measurement system according to the invention is characterized in that each measurement station comprises a trigger detector operating by transmission / reception of a beam infrared laser and providing a trigger signal for each vehicle identified, an infra-red light projector directing a beam on vehicles in circulation and a camera whose shooting is triggered by the signal of the trigger detector and providing a video signal to an image analysis and data processing system that analyzes vehicle license plates to identify them and calculates vehicle travel time.

According to one characteristic, the measuring stations are located in height relative to the roadway, at the edge or above the track.

According to one characteristic, the projector consists of a discharge lamp associated with a reflector and an infrared filter, an electronic control unit and an electronic supply for the discharge lamp.

According to one characteristic, the trigger detector is constituted by a triangulation measurement system the transmitter of which is an infrared laser diode and the receiver of which is a photoelement associated with a lens fitted with an infrared filter and with a electronic detection of the signal received by reflection on the road or on vehicles.

According to one characteristic, the system comprises means of synchronization between the lightning of the infrared projector, the shooting by the CCD camera, acquisition and computer processing of images and arrival of the vehicle in the field of the camera.

• La figure 1 est une vue d'ensemble montrant les deux postes de mesure du système selon l'invention.
• La figure 2 est un schéma synoptique d'une tête de prise de vues et du dispositif de traitement des formations associé .
• La figure 3 est un schéma de principe du dispositif de détection automatique des véhicules équipant chaque poste de mesure.
• La figure 4 est une vue de détail du capteur utilisé dans ce dispositif de détection.
• La figure 5 est un schéma synoptique du projecteur d'éclairage équipant chaque poste de mesure.
• La figure 6 est un schéma d'une disposition en chaîne de postes de mesure dans une ville.
• La figure 7 est un schéma d'une disposition en étoile des postes de mesure dans une ville.
• La figure 8 est un schéma d'une disposition en réseau multiple des postes de mesure dans une ville.

The invention will now be described in more detail with reference to an embodiment given by way of example and represented by the accompanying drawings in which:

• Figure 1 is an overview showing the two measuring stations of the system according to the invention.
• Figure 2 is a block diagram of a shooting head and the associated training processing device.
• Figure 3 is a block diagram of the automatic detection device for vehicles fitted to each measuring station.
• Figure 4 is a detail view of the sensor used in this detection device.
• Figure 5 is a block diagram of the lighting projector fitted to each measuring station.
• FIG. 6 is a diagram of a chain arrangement of measurement stations in a city.
• Figure 7 is a diagram of a star arrangement of measurement stations in a city.
• Figure 8 is a diagram of a multiple network layout of measurement stations in a city.

The system according to the invention comprises two measuring stations A and B located along a traffic lane 1 and spaced apart from one another in the direction of traffic. Each station includes a shooting head 2 situated in height relative to the track, on the edge or above this track, integrating or associated with an image processing system 8.

Measuring stations A and B are located high above the road, at the edge or above the track.

Each shooting head 2 comprises a trigger detector 3, a light projector 4, and a CCD camera 5.

The trigger detector 3 has the function of detecting each vehicle 9 in the flow of traffic and triggering a shooting. It is placed next to camera 5 and observes the way in the same way as the camera.

The trigger detector 3 illustrated in FIG. 3 is based on a distance measurement by telemetry, by means of the emission of an infrared laser beam modulated in amplitude and the detection by appropriate optics and electronics of the beam reflected by the roadway or a vehicle.

The trigger detector 3 operates on a triangulation principle. It is constituted by an infrared laser emitter 31 giving a focused beam 36 and amplitude modulated and by a light receiver 32 receiving the reflected beam 37 on the vehicle 5. The axes of the beams 36 and 37 make a non-zero angle between them. The transmitter 31 is constituted by a laser diode. The light receiver 32 is constituted by a lens 33, associated with a filter 35 and by a detector 34 constituted by a photodiode with two sensitive surfaces 341 and 342. An electronics controls the laser diode and processes the signal coming from photodiode 34. Au rest, the reflected beam 37, marked 37 A in FIG. 3 gives a light spot which is evenly distributed between the two sensitive surfaces 341 and 342 (FIG. 4a). The system is then in equilibrium. When a vehicle 9 arrives, the beam marked 37 B in FIG. 3 moves. As a result, the surface 341 or 342 unbalances the system (FIG. 4 b) which is detected by the electronics which then emits the trigger signal.

The light projector 4 illustrated in FIG. 5 is of the infrared projector type. It comprises a discharge lamp 41 mounted on a support 42, a parabolic or spherical focusing reflector 43 and an infrared filter 44 associated with at least one lens. This projector 4 emits a flash of light in the near infrared which is focused on the front of the vehicles by the reflector 43. This light emission aims to compensate for a lack of light due to the nocturnal situations and the short time d integration of the measurement chain associated with the shooting head. The emitted power is concentrated in space thanks to good focusing, and in time thanks to an impulse type emission. It also has the advantage of being almost completely invisible and therefore meets the criterion of discretion. The lamp is controlled by an electronic assembly comprising power electronics 45, control electronics 46 and interface electronics 47.

The camera 5 makes it possible to take the image of the front of the moving vehicles, detected by the trigger 3. Reading license plates requires a precise image when the front of the vehicle is in the field of the camera.

Camera 5 is of the CCD type with electronic shutter. It has a low integration time and preferably works with frame transfer to obtain a better quality image. The integration time (time during which the image is formed on the CCD) is low. To this end, the camera includes a mechanical or optical shutter or an equivalent electronic function.

The video signal supplied by the camera 5 is sent by a link 61 to an image acquisition card 71 included in a microcomputer 8. This card 71 is composed of an analog-digital converter, of one or more memory plans for image storage and possibly specialized processors providing part of the processing on the card. The associated software includes a specific license plate recognition software, which provides (if possible) an alphanumeric character string representing the license plate and an operating software which ensures the running of all shooting, detection operations and reading the license plate, communicating with the other station (s), or measuring and storing journey time (and other traffic information: vehicle counting, hourly statistics, etc.)

The projector 4, the detector 3 and the camera 5 are synchronized by a synchronization card 72 mounted in the microcomputer and connected by a link 62 to a synchronization circuit 63 of the shooting head connected to the various elements 4, 3, 5.

Other cards 73 and 74 respectively allow the optional connection with a screen-keyboard interface and inter-station communication.

The system works as follows:

When the vehicle arrives near the station, the infrared beam from the vehicle detector 3 is cut off. The latter triggers the infrared projector 4, the camera shoots 5 and acquires the image by the image analysis system. This identifies the vehicle by its registration number and enters the time of passage of the vehicle. It transmits this information to station B which stores it.

Only a part of the mineralogical number can be read or communicated between stations, while ensuring sufficient identification of the vehicles in the traffic flow.

Other information entered in the image taken by the camera can be associated with the registration number to reinforce the identification of the vehicles.

When the vehicle arrives at station B, the previous operations are repeated. The vehicle is re-identified by its registration number and the passage time is entered. The vehicle is then searched for in the list stored by station B, from which it is extracted. It is thus possible by difference of hours, to measure the journey time of the vehicle and to deduce from it an average journey time (by time slot, ...).

It is sufficient to recognize at station B part of the vehicles detected and identified at station A to measure the journey time and therefore the average speed between A and B.

Travel time measurement systems can be implemented in a city no longer as a series of pairs of stations A and B but as a complete network. In this case, the stations can be organized either in a chain (figure. 6), each transmitting information to the next and receiving the previous one, or in a star (fig. 7), the information for each station being concentrated in the same common system , or again any configuration associating these two modes of organization (fig. 8).

Claims (6)

1. System for measuring automotive vehicle traffic on a traffic route, comprising at least two measuring stations (A and B), spaced along said route, characterised in that each measuring station comprises a trigger sensor (3) emitting an infra-red laser beam, detecting the reflected beam and supplying a trigger signal for each vehicle registered, an infra-red light projector (4) triggered by said trigger signal and directing a beam onto the vehicles in the traffic, a camera (5), in which the taking of images is controlled by the signal of the trigger sensor (3) and providing a video signal to an image analysing and data processing system (8) which analyses the licence plates of the vehicles such as to identify them and calculates the time taken by the vehicles to travel a distance.
2. System according to claim 1, characterised by the fact that the measuring stations (A and B) are located above the height of the carriageway, at the edge of or over the road.
3. System according to claim 1 or 2, characterised by the fact that the projector (4) triggered by the trigger sensor (3) comprises a discharge lamp (41) combined with a reflector (43) and with an infra-red filter (44), of control electronics (45, 46, 47) and supply electronics for the discharge lamp.
4. System according to any one of the preceding claims, characterised by the fact that the trigger sensor (3) comprises a triangulation measurement system, the emitter (31) of which is an infra-red laser diode, and the receiver (32) of which is a photo-element combined with a lens equipped with an infra-red filter and with electronics for sensing the signal received by reflection off of the carriageway or off the vehicles.
5. System according to any one of the preceding claims, characterised by the fact that the camera (5) is a CCD type camera with an electronic shutter.
6. System according to any one of the preceding claims, characterised by the fact that it comprises means (72, 63) for synchronisation between the light discharge of the infra-red projector (4), the image taking by the CCD camera (5), the capture and the computer processing of the images and the arrival of the vehicle in the field of vision of the camera.

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