EP0654774A1 - Traffic control system - Google Patents

Abstract

A traffic control system comprising video cameras, being positioned above or along a traffic roadway for monitoring a predetermined road or lane segment, is provided with means for continuously recording road images and with selection means for selectively recording images when a vehicle is within sight.

The road segment to be monitored is provided with a cross strip, contrasting clearly with the road surface within the viewing sight of the camera(s), and the video cameras are connected to a processor capable of distinguishing this cross strip even when a shadow or light from the headlights of a vehicle is incident on it. A blocking function blocks the selection means when the cross strip is distinguishable, and releases them only when the cross strip, for at least across a section of its length, is indistinguishable. In this manner it is ensured the only images recorded are of an actual vehicle.

Description

• The invention relates to a traffic control system comprising one or several video cameras, being positioned above or along a traffic roadway for monitoring a predetermined road or lane segment, and provided with means for continuously recording road images, and selection means for selectively recording images, when a vehicle is within sight.
• Such systems are known and are widely used for monitoring traffic lights, enforcement of speed regulations on highways and such. The video camera(s) is/are directed on the road section to be monitored; in the case of multiple cameras the recording angles of adjacent cameras overlap partly, and record images of the road e.g. 5 to 50 times per second. In this an image is to be registered and stored for further processing only when a vehicle is properly within sight.
• However, such a video camera system has a problem with respect to shadow effects. When a video camera system monitors a road section with the sun low on the horizon or during darkness, during which the headlights of vehicles are lit, then shadows cast forward or light emanating from the headlights cause selective registration of an image at an instance when the vehicle itself is not within camera range. Under certain circumstances particularly during heavy traffic on a roadway which is being monitored, this can lead to many faulty recordings nevertheless being registered, thereby substantially increasing the costs of using such a system, while moreover there is a probability that the vehicle in violation will not be registered due to such an early recording.
• The purpose of the invention is to eliminate this objection and to provide a traffic control system which records images of vehicles only when there indeed is the case of such a vehicle.
• To that end the invention provides a traffic control system, as described in the preamble, characterized in that the road or track segment to be monitored is provided with at least one cross strip, contrasting clearly with the road surface within the viewing sight of the camera(s), and in that the video cameras are connected to a processor capable of distinguishing this cross strip even when a shadow or light from the headlights of a vehicle is incident on it, and being provided with a blocking function, which blocks the selection means when the cross strip is distinguishable, and enables them only when the cross strip, at least across a section of its length, is indistinguishable.
• Essential to the invention is that unless the contrasting cross strip is screened off by a vehicle, it must always be visible to the camera. In order to enable this, the video camera is effectively connected to a processor, which is capable of comparing the recorded road images with a stored image of the contrast strip. By this it is possible to recognize the contrast strip even under bad lighting or when it is covered by a shadow. The same holds true for the case in which observation is hampered by bright lights emanating from vehicle headlights. As long as the camera(s) is (or are) able to observe the cross strip uninterruptedly, a blocking function is in operation for blocking the selective recording of images. Thus, when, for example, a car shadow falls across the cross strip, the camera will still be able to observe the cross strip and block the recording of the image. The blocking is eliminated only in the case in which the camera cannot observe the cross strip across a length thereof, which is the case when it (the cross strip) is covered by an approaching vehicle, and an image of the vehicle can be recorded. In this way the recording of deceptive images resulting from shadow effects is effectively eliminated.
• The cross strip, which needs not to be visible to the naked eye, but does have to be visible for the camera, can, for example, be formed by a row of contrasting patterns. These patterns may include, for example, white or coloured elements, such as stripes, arrows, diamond shapes, blocks and stones. In order to achieve very accurate images, and particularly when operating in light-deficient surroundings, the embodiment may be such that the contrasting patterns comprise light-emitting elements. This may relate to passive elements, such as reflectors, but also bulbs or light-emitting diodes (LED's) can actually be used.
• Further, an advantage of such a strip is that it can be positioned on the road surface in such a way, that an approaching vehicle finds itself exactly in the ideal position for imaging. Through this the probability that registration plates of cars on video prints derived from the recorded images are illegible, is reduced to a minimum.
• Further, the invention can effectively be such that the road or lane section to be monitored is provided with contrasting cross strips both near its beginning and at the end thereof. In this way the velocity of a vehicle can be determined accurately, in case the camera records a sufficient number of road images per second. Additionally, the use of a cross strip offers the advantage that not only can the position of a vehicle be determined in the longitudinal direction of the road, but it can also be determined in the transverse direction, depending on the section of the strip being screened by the vehicle. Through this the possibility of determining both the forward and the lateral velocities of a vehicle is also created.
• The invention is further explained in the following by way of an embodiment with reference to the figures. Illustrated in the figures are:
• In Fig. 1 a top view of a road segment of a traffic road monitored by a traffic control system according to the invention; and
• In Fig. 2 a side-elevational view of the same road segment.
• Depicted in the figures is a section of aroad 1, which may be a roadway, throughfare or the like, intended for motorized traffic. Positioned on this road is a camera assembly which is positoned under an angle α at an elevation H above the road, schematically represented byvideocamera 2. Thiscamera 2 monitors aroad segment 3, of which the length is determined by the viewing angle γ of the camera. A cross strip 4, of material contrasting with respect to the road way, is positioned on the road in this monitored road section, which, in the case shown, is a zig-zag strip. Further depicted is acar 5, which is approaching with a velocity V. In the case illustrated thiscar 5 casts a shadow 6 forward obliquely, for example as a result of sunlight obliquely incident from the rear.
• Videocamera 2 continuously records road images at a frequency of, for example, 50 (images) per second. If the car now comes within camera view, a selection circuit ensures that an image of the car is recorded. The shadow cast forward obliquely might nonetheless trigger a false image, and to prevent such an occurrence the camera is adjusted such that this shadow image can be eliminated.
• This occurs as follows: aided by a suitable processor (not shown) the camera is capable of recognizing the contrasting cross strip 4 as long as the latter is not screened by a car or other vehicle. As long as this is the case, a blocking function is in operation for blocking the recording of video images for photographs. However, as soon ascar 5 screens the cross strip 4, this blocking is cancelled, and the camera is capable of selectively recording images of the vehicle.
• In this manner it is achieved that images are recorded only when there actually is the case of a car, and it is prevented that an image taken too early is recorded by an image taken too early as a result of shadow or illumination by headlights (which may form mirror images on the road) on which the car is not well visible, and moreover the probability is eliminated that through it, for example, a car being driven too fast, might elude the camera check.
• Such a cross strip may consist of simple contrasting material, for example a row of white or coloured symbols or elements, but it may also consist of light-emitting elements, which latter offer the advantage that an even more accurate observation is enabled. Further, the cross strip offers the advantage that through this an excellent determination of the position of the car is made possible, so that as much as possible of the car and its registration plate is visible, while furthermore the position, both in the longitudinal and the lateral directions, is determined with the aid of the discontinued section of the cross strip.
• Further, this system offers an excellent possibility for accurate determinations of velocities. This accuracy can be enhanced further if a plurality of such cross strips is used, for example, with one at the beginning and at the end of the roadway monitored.
• The system, according to the invention, with the contrasting cross strips or patterns offers, amongst others, the following advantages:
• Since in fact it is the cross strip, and not the vehicle itself, that determines the moment of imaging, less illumination is necessary than otherwise would be the case. This holds true especially when using infra-red cameras, because in general these are slightly less photosensitive in the infra-red spectrum.
• Further, an accurate determination of the position of vehicles is possible.
• Inherent to this point is that also a more accurate determination of the velocity is possible.
• The invention has been elucidated in the foregoing by way of a practical embodiment.
• It will be clear that numerous variations, all within the scope of the invention, are possible. For example, the road segment may be provided with obliquely intersecting strips, with the intersections signifying markings, instead of being provided with one or several cross strips. Other possibilities will be apparent to the man skilled in the art after studying the foregoing.

Claims (8)

1. Traffic control system, comprising
      one or several video cameras, being positioned above or along a traffic roadway for monitoring a predetermined road or lane segment, and provided with means for continuously recording road images, and selection means for selectively recording images, when a vehicle is within sight,
      characterized in that
   the road or track segment to be monitored is provided with at least one cross strip, contrasting clearly with the road surface within the viewing sight of the camera(s), and in that the video cameras are connected to a processor capable of distinguishing this cross strip even when a shadow or light from the headlights of a vehicle is incident on it, and being provided with a blocking function, which blocks the selection means when the cross strip is distinguishable, and enables them only when the cross strip, at least across a section of its length, is indistinguishable.
2. Traffic control system according to Claim 1,characterized in that the cross strip is formed by a row of contrasting patterns.
3. Traffic control system according to Claim 2,characterized in that the contrasting patterns consist of white or coloured elements such as stripes, arrows, diamond shapes, blocks and stones.
4. Traffic control system according to Claim 2,characterized in that the contrasting patterns consist of lightemitting elements.
5. Traffic control system according to Claim 4,characterized in that the light-emitting elements are reflectors.
6. Traffic control system according to Claim 4,characterized in that the light-emitting elements are bulbs.
7. Traffic control system according to Claim 4,characterized in that the light-emitting elements are light-emitting diodes (LED's).
8. Traffic control system according to any of the foregoing Claims,characterized in that that the road or lane section to be monitored is provided with contrasting cross strips both near its beginning as well at the end thereof.

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