Communications: electrical – Vehicle detectors – Photoelectric
Reexamination Certificate
2001-03-13
2004-06-15
Wu, Daniel J. (Department: 2652)
Communications: electrical
Vehicle detectors
Photoelectric
C340S933000, C340S935000, C340S936000, C701S119000
Reexamination Certificate
active
06750787
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the measurement and recording of vehicle traffic and, more specifically, to the count of vehicles moving on a street, measuring the velocity of the vehicles, and determining the relative direction of travel of the vehicles. The present invention is referred to herein as an Optronic System because it integrates an optical light beam emitting and sensor system, sensing light beam interruptions with current state-of-the-art electronics, and digital processing of the vehicle traffic measurements into useful engineering data form. The Optronic System does not sacrifice accuracy for portability, and the system can be moved from one location to another traffic measurement location and set-up quite easily in 15 minutes or less. The Optronic System eliminates the need for embedding inductance type sensors in the pavement of a street, especially at a busy intersection, or taping “hoses” to a street surface.
2. Description of the Related Art
The measurement of vehicle traffic (the number of vehicles passing a location on a street, the direction in which the individual vehicles are traveling, and most importantly the velocity at which individual vehicles are moving on the street) is vital to the traffic engineers and law enforcement personnel of large communities as part of their traffic engineering and public safety responsibilities and activities. Accurate measurements of traffic are necessary at locations where vehicle and pedestrian traffic conditions are hazardous to vehicle operators and/or pedestrians, and the measured vehicle traffic data must be properly analyzed to identify effective solutions for resolving the safety problem or abating the unsafe conditions.
The present traffic measurement system used primarily by traffic engineering personnel is referred to herein as a pneumoelectronic system, since the system is a combination of pneumatic and electronic components and functions to measure the vehicle traffic. The pneumoelectronic system employs one or more pneumatic tubes (often referred to as “hoses”) stretched across the street at the location where the measurement of the vehicular traffic is desired to be made. A functional description of the generic type of pneumoelectronic system presently in use is shown schematically in FIG.
1
. The schematic in
FIG. 1
(and all other Figures included in this document) is not to any dimensional scale, and the size/shape of the hardware units in the system cannot be determined from this functional schematic.
Also at present, vehicle traffic law enforcement personnel use radar equipment for measuring the velocity of moving vehicles, and using the results to control excessive vehicle speeding (as defined in the Motor Vehicle Code) which endangers other vehicles and pedestrians. Radar equipment improvements are constantly being made to improve the accuracy of the measured vehicle velocities, particularly in the moving mode of operation, but the other important aspects of vehicle traffic (counting the number of vehicles and determining their direction of travel at a specific location on a street for traffic engineering use) is not possible with present radar equipment.
The need for an improved traffic measurement system, which can be of more effective use, for example, to both traffic engineering and law enforcement personnel, becomes apparent after considering the limitations and shortcomings of the present traffic measurement systems (pneumoelectronic and radar).
Pneumoelectronic Counting of Vehicles
The measurement of vehicle traffic presently is done with a one- or two-pneumatic tube (each tube sealed at one end) system stretched generally parallel across a street surface in a near-orthogonal orientation to vehicle traffic, as indicated schematically in FIG.
1
. The tube system (one or two non-metallic “hoses” of substantial length) is fastened by an installation technician to the street surface, typically with multiple, wide, long strips of an adhesive tape. The unsealed end of the tube(s) are then attached to an electronic box (referred to herein as the data unit), which is typically located in a median strip or on the sidewalk adjacent to the street (or on the shoulder of the street when no sidewalk exists). The data unit is normally not physically located in the traveled portion of the street, as passing vehicles could roll over the data unit and incur crushing damage to the data unit and/or cutting damage to the tires of the vehicle.
The pneumatic tube system is connected through an attachment port on the data unit exterior so as to pass pressure pulses generated in the tube(s) into a pulse sensor (typically an electromechanical pressure transducer) in the data unit. When the front wheels of a vehicle pass over a tube, a pressure pulse is transmitted pneumatically to the pulse sensor which senses the increase in pressure of the pulse. When the pressure pulse is first sensed, the pulse sensor (which functions essentially as a pressure-activated electrical switch) outputs an electrical signal indicating the traffic event (i.e., that a vehicle wheel has passed over and compressed a tube) has taken place. When a count of the number of vehicles passing a selected location on a street is the only traffic parameter of interest to traffic engineering, it is necessary to install only a single detector capable of sensing the passing of the vehicles at that location. Each vehicle wheel passing over a tube compresses the tube and creates a pressure wave traversing through the tube. Two pulses in pressure will be introduced into the single tube by the wheels on the first two axles of a multi-axle vehicle passing over the tube and with a short time interval between the two pulses.
When activated by each pressure pulse, the pulse sensor in the data unit transmits an electronic signal to a multi-function processor, one function being to count the passing of each axle (since all wheels on one axle simultaneously passing over the single tube will result in only one pulse) of each vehicle. Two pulses in rapid sequence are interpreted by the processor as having been generated by the first and second axle of one passing multi-axle vehicle. The sensing logic in the signal processor typically has a “processing pause” after the initial two pulses so as not to count vehicles with more than two axles as being more than one vehicle. The processor then causes a simple counter device to add a unit count into a cumulative count of the number of vehicles passing over the tube(s) in the vehicle traffic volume measurement time period. The cumulative count is typically stored on a recording device also within the data unit, along with the essential date and time of each vehicle passing event to describe the numerical flow of traffic on a time-line basis. These traffic data recordings (referred to herein as line data) are electronically down-loaded from the data unit at the end of the measurement session and printed in hard copy for subsequent analysis by traffic engineering.
The velocity of the passing vehicles is also a traffic parameter of high interest to traffic engineers to study the rate of flow and individual speed of the vehicle traffic passing along a street. When it is desired to both count the number of vehicles passing a location on a street and to also record at what velocity the individual vehicles are traveling, more than one sensor is needed. In order to determine the velocity of vehicles using the pneumoelectronic system, two separated parallel tubes must be installed across the lane(s) of traffic to measure the time interval elapsed by a vehicle passing between the two tubes. As indicated in
FIG. 1
, the second tube is stretched across the street parallel to and at some pre-selected reference distance, D
Ref
(typically 8 feet), from the first tube. The second tube is typically fastened to the street surface in the same manner as was done for a single tube (vehicle count only) installation. The second tube also is typically connected to the first tube with
Afshar Maymanat S.
Hutchinson Keith D.
Tang Son
Wu Daniel J.
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