United States Patent 3663937

An electronic detection circuit identifies several traffic paths through an intersection as a vehicle passes over a predetermined sequence of discrete separated positions identifying a path. A television camera can view the intersection and the paths be identified on a receiving cathode ray tube screen by placing a series of light detectors over desired patterns. A switching circuit responsive to the detectors then identifies and counts only those vehicles passing one complete sequence of the positions identifying a particular path.

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International Classes:
G08G1/04; (IPC1-7): G08G1/04
Field of Search:
340/38R,38L,38P,22,23,24,39,38S 178
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Primary Examiner:
Claffy, Kathleen H.
Assistant Examiner:
Myers, Randall P.
What is claimed is

1. An electronic system for determining traffic patterns comprising in combination, a series of electronic position detectors arranged in the form of at least one predetermined traffic path on an electronic image receiving screen and so spaced as to detect the position of a vehicle at predetermined sequential positions in a pattern in said path, an electrical switching circuit with a plurality of switching stages connected to operate in sequence to actuate a final switch stage only in response to said detectors when said vehicle travels through said traffic path in said pattern in the predetermined sequence of positions, and an egress counter-circuit connected for counting the number of switching operations, at said final switch stage.

2. The system defined in claim 1 including an ingress counter coupled for response to an initial one of the switching stages.

3. The system defined in claim 1 wherein the traffic path is of an intersection to identify a vehicle making a turn.

4. A system as defined in claim 1 wherein the electronic position detectors comprise a series of light detectors placed on a television screen displaying traffic moving through said pattern.

5. A system as defined in claim 1 wherein each switching stage in said sequence comprises a prior relay with a contact connected for enabling the next sequential switching stage only when a vehicle passes through said sequence of positions to energize said prior relay.

6. An electronic traffic pattern determining system for analyzing a plurality of traffic patterns at an intersection comprising in combination, a television camera directed to view traffic at said intersection, a television receiver with a cathode ray tube screen displaying a view of the traffic at said intersection in response to the camera signals, a set of light discriminating devices located at discrete separated sequential positions in a multiplicity of traffic patterns on said screen to detect at least two discrete paths a vehicle may take through said intersection, a switching circuit responsive to said devices to identify traffic patterns of a vehicle encompassing a full sequence of said devices responding to a particular one of said vehicle paths, and a counting circuit actuated by said switching circuit only when a vehicle passes each sequential position identifying said particular one path.

7. A system as defined in claim 6 wherein said light discriminating devices comprise means for temporarily locating and holding them on said screen but permitting them to be moved to other positions when desired.

8. An electronic traffic pattern determining system for displaying a plurality of traffic patterns at an intersection comprising in combination means for producing an image of said intersection and means for displaying said image, electronic vehicle path detection means on said image displaying means identifying a set of discrete sequential detector positions in at least two paths vehicles may take through said intersection, means converting each of said detector positions into an electrical signal, a switching circuit responsive to only a sequence of said electrical signals identifying a vehicle path through each possible discrete position in one of said paths, and egress counting means connected for totalling each response of said switching circuit.

The present invention relates generally to traffic monitoring systems and more particularly it relates to an electronic system for tracing vehicles through a plurality of optional paths at an intersection.

Traffic control has increased in complexity to the extent that most cities, with a population of 30,000 or greater, engage the services of a Traffic Engineer to establish and maintain a program for controlling vehicular movement on the city's streets. In pursuit of these objectives, the Traffic Engineer makes use of "traffic surveys" which, among other things, tell him what the traffic density and turning movements are at various intersections. He is interested in the number of vehicles which pass through an intersection; their direction of ingress and egress; and, variation in traffic flow patterns during the day.

Manual counting is the current technique for establishing these traffic flow patterns at intersections. One man can count the 12 basic movements of a single intersection at off hours (a vehicle can enter from one of four directions and execute one of three movements on egress). More complex intersections, or high density traffic at peak hours, can require as many as four or more men to count the vehicles and record their movement through the intersection. Normally, a survey is conducted for 12 continuous hours, and this requires relief personnel. The man-hour costs for these surveys is a basic problem confronting all Traffic Engineers.

Current state-of-the-art traffic systems record only the number of vehicles or axles passing through a sensing zone or over a pneumatic tube. These devices can be used to indicate the number of ingress and egress vehicles at an intersection, but they can not record turning movements in the intersection. In order to record turning movements the system must be capable of sensing the ingressing vehicle, trace it through the intersection, and record its egress direction.

Accordingly, it is a main object of this invention to provide an improved traffic monitoring system which can trace the path of a vehicle through an intersection.

Another object of this invention is to provide traffic monitoring equipment which is capable of tracing a multiplicity of vehicle paths through a complex intersection.

A still further object of the invention is to provide versatile and efficient equipment that will provide automatic traffic counts and be capable of simple adaption to different traffic patterns and different intersections.

Other objects, features and advantages of the invention will be found throughout the following description and accompanying drawings illustrating the embodiment wherein:

FIG. 1 is a sketch illustrating vehicle traffic at a typical intersection;

FIG. 2 is a block diagram of an electronic television automatic traffic monitoring system afforded by the invention;

FIG. 3 is a side view partially in section of a rubber cup assembly that may hold a light detecting device on the screen of a television tube in accordance with the teachings of this invention; and

FIG. 4 is a schematic switching circuit diagram, of a portion of the switching system of FIG. 2, partly in block, for identifying a particular sequence of vehicle positions in a predetermined traffic path.

FIG. 1 indicates the movements which vehicle "A" can make at a simple intersection. A zone counter at each point of egress for vehicle "A" (N, E, or S exit lane) could discriminate the movement of vehicle "A" if this were the only vehicle entering the intersection. Also, these zone counters could discriminate the total vehicular movement of the east bound ingress lane if this were the only ingressing lane for the intersection. However, if vehicles "A", "B", "C" and "D" each executed a right turn through the intersection, zone egress counters at each point of exit could not discriminate this movement from a left turn or a straight through movement for each vehicle.

In order to discriminate the movement of each vehicle, that vehicle must be "tracked" through the intersection and counted upon egress. (This assumes there is no lane control, such as a left turn lane, where all vehicles entering the lane must execute a specific movement). Tracking and counting the vehicle through the intersection will be accomplished with an "Ingress-Egress Sequential Counter Circuit" as later described in connection with FIG. 4 functioning on radiant energy from the face of a cathode ray tube in a television receiver as shown in FIG. 2.

The television camera and receiver are state-of-the-art systems which will function under natural lighting conditions or where the field of view is lighted with infra-red or other mono-wave band light.

The sequential counter circuit of FIG. 4 is composed of solid state switches 12 which are secured to the face of the cathode ray tube 11 in FIG. 2 and activated by light energy emitted from the tube. These solid state switches can be individually secured to the face of the tube with vacuum cups 13 as shown in FIG. 3 or preassembled in the form of flexible strips which can be secured to the face of the tube. This structure permits the system to be readily adapted to identify different types of paths and different types of intersections or traffic patterns without any change in the system; since each switch 12 can be temporarily held in a location identifying a position in one traffic path until the system is moved to another intersection or the path through the intersection is changed, whereupon the switch 12 can be moved to another position on the screen 14 of cathode ray tube 11.

Each switch 12 may be simply a standard photo-resistive device that is responsive to a change from a normal null-setting that identifies a cleared intersection picture on the screen 14 to change its resistance when the image of a vehicle enters that position and changes the light level.

FIG. 1 illustrates the positioning of detectors at sequential discrete positions for two ingressing lanes at the typical intersection shown. (The north and east ingressing lane detectors are not shown for purposes of clarity). Assume Vehicle A is in the process of turning left and Vehicle B is in the process of passing north. Counters are diagrammatically shown by notation C-Wi which indicates the west ingress and C-WSE which shows the west to south egress path of the vehicle, etc. Thus if Vehicle A is considered, the ingress from west into the intersection will be recorded on Counter C-Wi when detector 1 is encountered. As the vehicle passes into position A' it will sequentially pass detectors 1 through 5, and when it completes the turn it will sequentially pass detectors 1 through 10.

If Vehicle A is waiting at position A' for Vehicle B to pass through position B', it may be seen that detector position 6 is not yet encountered by any car even though Vehicle B encounters and passes detector positions 7 through 10 in sequence while Vehicle A is waiting at position 5. Thus the detector positions are placed logically in a pattern to identify uniquely by their sequence the different paths under observation. In this respect a special switching system for identifying sequential positions (15, FIG. 2) is provided for each traffic path to be observed. Each path may have a switching circuit of the nature shown in FIG. 4.

In the sequential switching circuit embodiment illustrated it may be seen from FIG. 1 that positioning the detectors so that at least two are encompassed at one time by the vehicle will prevent any problems of timing in releasing an energization contact 21 etc., before the next sequential position is entered.

Improper traffic movement such as one vehicle passing another in the intersection will result in that vehicle not being counted. Also, an improper turning movement, such as vehicle "A" turning left into the north ingress lane, will result in his egress not being counted.

As seen in FIG. 4, blocks 1-9 represent the sequentially numbered position detectors of FIG. 1, which may be for example the light detectors 12 positioned on the television screen 14 of FIG. 2. As the initial detector 1 is energized then the battery 18 may be connected to both ingress counter 17 for one count and to relay 19 serving to close contact 20 and connect detector 2 to the battery 18. Thus detector 2 can only be energized in sequence after detector 1 shows entry of a vehicle. The same action progresses until, as the vehicle enters the position of the tenth detector 10 in sequence, then the egress counter 16 is counted once, identifying the number of vehicles taking the designated path of detector positions 1 through 10 in sequence.

As may be seen from FIG. 1, if position 6 is missed, then detector 7 will not be connected to battery 18 and Vehicle B passing position B' will not serve to operate egress counter 16 (C - W NE). It is clear that other equivalent switching circuits can be used to perform the necessary function of identifying the sequence of adjacent positions.

As seen in FIG. 2, a technician may mount the camera 21 above the intersection to view a field 22 including the portion of the intersection identified in FIG. 1. The camera could be mounted on a boom, telephone pole, at an upper story window overlooking the intersection, or any convenient overhead structure. After the camera and, if required, special light source is mounted the sequential counting circuits would be attached where required to the screen 14 of the tube 11 operated by television receiver 23 by means of appropriate wires 24 or radio link. The technician would then connect the counting circuits to their appropriate counters and visually check the output of the counters against the observed traffic pattern.

Hourly counts or any predetermined periodic counts could be recorded electrically or photographically. Also, if it were desirable to count more than one intersection at any given time, a televised tape could be made of each intersection and this could be played back (at high speed) to the counter.

Of particular importance in the television system embodiment shown is the ability to remove detector positions 12 easily and replace in different paths or patterns, and to conform to differently shaped intersections or traffic paths if desired.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same and that various changes may be resorted to without departure from the spirit of the invention or the scope of the subjoined claims.