Optronic system for the measurement of vehicle traffic
Contents
1. wheelbases of almost all vehicles are more than 10 15 20 25 30 35 40 45 50 55 60 65 4 96 inches This distance of 8 feet assures that the first axle of virtually all motor vehicles will pass over both tubes before the second axle encounters a tube Bicycles occa sionally passing over the two tubes cannot be discerned by the pneumoelectronic system as not being motor vehicles and they will be included in the vehicle traffic count made with the tube type system The equation for calculating the velocity of an object traveling at near constant speed for a known short time duration through a known short distance is found in the Laws of Motion stated in any standard Laws of Physics reference book as Velocity V Distance S Time t Table 1 was constructed using the equation t S V to find the time lapsed when the object has a known velocity and passes through a known distance TABLE 1 Time To Travel Time To Travel Vehicle Between 2 Tubes Vehicle Between 2 Tubes Velocity 8 feet apart Velocity 8 feet apart mph seconds mph seconds 0 trivial 35 0 156 5 1 091 40 0 136 10 0 545 45 0 121 15 0 364 50 0 109 20 0 273 55 0 099 25 0 218 60 0 091 30 0 182 65 0 084 If the time increment is measured for the time it takes for a vehicle to travel between two tubes a known distance apart the average velocity of the vehicle can then be calculated using the equation from the Laws of Moti2. 20 25 50 55 60 65 22 tion of the arithmetic is provided which is commonly easier to understand than using hexadecimal arithmetic The accu racy of a Pulse Oscillator 3f in counting the total pulses for a vehicle traffic event is approximately 3 pulses such that at an actual At of 0 1 seconds 62 500 3 pulses the accuracy of the calculated time interval would be 0 1 0 000048 seconds The corresponding calculated veloc ity e g actual 6 818 mph for 0 1 seconds through a 1 foot reference distance would be 6 818 0 0003272 mph If the actual time for a vehicle to travel through the 1 foot reference distance DREF was accomplished in 0 01 seconds there would be 6 2503 pulses counted and the true velocity of 68 18 mph would be calculated as being 68 18 0 032726 mph This level of high accuracy less than 0 04 inaccuracy achievable with the present Optronic System invention in measuring the velocity of a moving vehicle is not achievable in the art of existing vehicle traffic measurement systems Several measurements of traffic in actual street environ ments were made using the Optronic System and the resulting CDV data Line Data were tabulated and analyzed for accuracy and correctness One such set of Line Data is printed in tabulation form as shown in Table 4 The vehicles measured during this measurement session were a mix of various length vehicles ranging from small size two axle passenger vehicles with wheelbas
3. 1h which are all assembled and operatively interconnected within the Beam Emitter Unit Assembly Box 1a and col lectively comprise the Beam Emitter Unit 1 FIG 2 also shows a Sensor Control Unit 2 which is installed on the opposite side of the street from the Beam Emitter Unit 1 The Sensor Control Unit Assembly Box 2a contains a Left Beam Sensor 2d and a Right Beam Sensor 2e these two sensors utilize current state of the art photoelec tric transistors The Control Display Subunit 3 in FIG 2 is detachably interconnected by a Sensor Control Unit Inter connect Cable 2f to the Sensor Control Unit 2 in order to facilitate removal of the Control Display Subunit 3 therefrom and enables the detached Control Display Sub unit 3 to be transported to a suitable remote computer facility for extraction of the traffic measurement data processed and recorded therein The Control Display Subunit Assembly Box 3a contains a Control Display Subunit Input Connector US 6 750 787 B2 11 3b female a Control Display Subunit Power Source 3c a Control Display Micro Processor 3d a Beam Status Dis criminator a Pulse Oscillator 3f an electronic Timer amp Clock Chip 3g an associated Data Recorder 3h utilizing a current state of the art EEPROM Electronic Erasable Pro grammable Read Only Memory and a Control amp Display Panel 3i which are all integrated for the purpose of enabling the Sensor Control Unit 2 and Control Display Subunit 3 t
4. ments to the road surface loses adhesion allowing the loose tube to move apart laterally with respect to the other tube a change in Drep distance of 4 5 inches could result in a velocity inaccuracy of 3 to 4 mph As another source of velocity inaccuracy if both tubes become very loose in a two tube installation and separate even further than 5 inches this will generally cause the vehicle velocity to be calculated in an even more inaccurate manner 5 to 7 mph If the two tubes are installed at a Drep much closer than 8 feet separation distance the same lateral change due to looseness in distance between the two tubes is a greater percentage of the smaller separation distance reference distance The inaccuracy of the calculated vehicle velocity if Drep is 4 feet will be even greater 10 to 14 mph It is also for this accuracy reason that tubes are installed with the largest distance between them 8 feet but not larger than the wheelbase of the smallest vehicles which as stated earlier is generally at least 96 inches 20 35 40 45 6 Depending on the combination of the several sources of inaccuracy vehicle velocity data especially that at the portion of the traffic velocity spectrum near or above the posted speed limit on the street being measured potentially has a measured velocity inaccuracy of 8 to 10 mph using the two tube technique This is clearly not adequate for law enforcement purposes and also m
5. which if both were activated ON at the same time would be coincident with each other The two center align ment beams 1j and 2h also form the axis of rotation of the large alignment rectangle and it is about this axis of rotation that the two major units the Beam Emitter Unit 1 and the Sensor Control Unit 2 are rotated using the Alignment Screwposts located at the four corners of the two major units to bring the four corners of the alignment rectangle into the same plane The alignment procedure for the Optronic System is analogous to that of turning the adjusting screwfeet at the four bottom corners of a residential refrigerator range or washing machine to bring it into level The six orifice tubes three on the Beam Emitter Unit 1 and three on the Sensor Control Unit 2 perform four important functions 1 to extend a distance from the face of the Unit assembly box and minimize the entry of splashed water or foreign objects from being thrown by passing vehicles into the interior of the Unit and adversely affecting the functional performance of the component at the interior end of the orifice tube into the Unit 2 to serve as a visual guide in pointing the two Units so that they directly face each other in preparation for the finer alignment using the emitted laser beams 3 to provide a means for capping the orifices when those orifices are not in use and 4 to hold the four larger diameter loose fitting screw on caps which have l
6. 3 DB9 Connector 6 1 6 6 M F 9 9 F M 6 Pin Connector Pinout MC MEM Power 2 Signal Beam R Source and 3 Unused 4 Power 5 Signal Beam L DB9 Connector 6 Ground Pinout 1 Data Carrier Detect DCD 2 Transmit Data TX 3 Receive Data RX 4 Data Terminal Ready DTR 5 Signal Ground 6 Data Set Ready DSR 7 Request to Send RTS 8 Clear to Send CTS 3k 9 Ring Indicator RI DB9 Serial Cable Data Download to PC US 6 750 787 B2 1 OPTRONIC SYSTEM FOR THE MEASUREMENT OF VEHICLE TRAFFIC CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority from U S Provisional Application No 60 190 080 filed Mar 17 2000 which is incorporated by reference in its entirety 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
7. Sensor Control Unit Orifice Tube 2c Right Sensor Control Unit Orifice Tube 2d Left Beam Sensor 2e Right Beam Sensor 2f Sensor Control Unit Interconnect Cable 2g Sensor Control Unit Alignment Beam Emitter 2h Sensor Control Unit Center Alignment Beam 2i Center Orifice Tube 2j Alignment Installation Angle Indicator 2k Sensor Control Unit Alignment Screwpost 21 Beam L Sensor Status Output Terminal 2m Beam L Sensor Ground Termina 2n Beam L Sensor Power Terminal 20 Beam R Sensor Power Terminal 2p Beam R Sensor Ground Termina 2q Beam R Sensor Status Output Terminal 3 Control Display Subunit 3a Control Display Subunit Assembly Box 3b Control Display Subunit Input Connector 3c Control Display Subunit Power Source 3d Control Display Micro Processor 3e Beam Status Discriminator 3f Pulse Oscillator 3g Timer amp Clock Chip 3h Data Recorder 3i Control amp Display Panel 3j Control Display Subunit Download Connector 3k Download Interconnect Cable 3l Data Transmitter Data Transmittal RF Wave FIG 2 presents a functional schematic of the preferred installation arrangement of an embodiment of the Optronic System for the measurement of vehicle traffic parameters The Beam Emitter Unit 1 is installed on one side of a street where traffic is to be measured The Beam Emitter Unit 1 includes a Beam Emitter Unit Power Source 15 a Left Beam Emitter 1c which produces a Left Light Beam 1g and a Right Beam Emitter 1d which produces a Right Light Beam
8. The remainder of the installation and initialization of the Optronic System is done with the Control Display Subunit 3 attached on the long cable 2f and the traffic measurement session con ducted At the completion of the traffic measurement session the two Beam Emitter Units 1e and 1f are switched OFF and the four caps are replaced on the ends of the four Orifice Tubes 1e 1f 2b and 2c When the Optronic System is in the alignment and traffic measurement modes the status ON or OFF of the two Light Beams 1g and 1 entering through the two Sensor Control Unit Orifice Tubes 2b and 2c are sensed ON or OFF by photoelectric transistors within the respective Sen sor Control Unit Beam Sensors 2d and 2e and are converted by the photoelectric transistors into electrical signals for discrimination processing non interrupted ON and inter rupted OFF status by a Beam Status Discriminator 3e in the Control Display Subunit 3 The Beam Sensors 2d and 2e perform the light beam sensing function as electric eyes which are more technically correct to be referred to as photoelectric transistors The economic and proven tech nology of photoelectric transistors such as in the Left Beam Sensor 2d and the Right Beam Sensor 2e is found com monly in residential uses e g to cause an automatic closing garage door to reverse its closing motion if the beam of light across the door opening is interrupted by an object person or animal Photoelec
9. 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 mea surement 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 US 6 750 787 B2 3 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 Dy typically 8 feet from the first tube The second tu
10. obvious uses e g when used as a more accurate substitute for stationary radar type velocity measurements of speeding vehicles For example in a preferred embodiment of the invention the Control amp Display Panel 3i of the Optronic System enables law enforcement officer to set a Threshold Velocity which if exceeded by a vehicle will cause the velocity and direction as well as date time location etc of the vehicle to be transmitted ahead to a remote location for example to camera taking a photograph of the vehicle license plate 10 15 20 25 30 35 40 45 50 55 60 65 20 number and of the driver s face This photographic tech nique is currently in use by several cities as a means of identifying vehicle operators who a red light signal at dangerous intersection The velocity of a vehicle may also be transmitted ahead to a mobile speed display unit to indicate to the vehicle operator the velocity measured when the vehicle passed through the Optronic System measure ment beams FIG 8 is a preferred arrangement representation of the Control amp Display Panel 3i located immediately below the top cover of the Control Display Subunit 3 in the Optronic System The switches display windows test buttons and status lights red or green light emitting diodes LEDs are arranged generally in the order starting at the top left of the Control amp Display Panel 32 as one reads a wri
11. placed as near to the curb on the sidewalk next to the street as is possible to reduce the number of pedestrians interrupting the beams If the beams are traversed and interrupted by a walking pedestrian the walking pace of a human is generally less than 5 mph and the velocity calcu lated less than five mph should again cause the traffic data analyst to regard the line of data as being non vehicle caused and to subtract that line of data from the total vehicle count C The logic flow and the processing steps which are used in generating processing displaying recording and optionally transmitting the traffic measurements collected with the Optronic System is described hereafter FIG 7 also shows those logic paths and processing steps in graphical form The logic for processing the sensed beam interruptions of the Light Beams 1g and 1 into traffic measurements follows one of two basic flow paths depending on the mode of operation of the Optronic System When only the count of traffic volume C is desired to be measured the Optronic System will need only one light beam the left Light Beam 1g to be operative and the Number of Beams NB to be entered through the Control amp Display Panel 3i on the Control Display Subunit 3 at the time of the measurement system initialization will be entered by the installing technician as unity NB 1 The logic used for this Count Only mode of operation is that each interruption of Light Beam 1g durin
12. the presence of an object in the beam path of the radar system for indicated angle from the zero azimuth angle axis of the radar emitter to the detected object and for estimating the distance from the radar emitter to the object Ground based stationary radar systems were also used to estimate the altitude of aircraft through simple trigonometric calculations performed with the radar estima tions of slant distance and angle of inclination from the radar US 6 750 787 B2 7 to the aircraft Radar was not initially developed to be an accurate velocity measuring technique because it used broad bandwidth radio wavelength radiation which does also sense the motion of secondary objects in the periphery of the primary moving target Narrow bandwidth radar equipment with laser pointers to target and measure the velocity of a specific vehicle among a group of moving vehicles is only recently coming into availability to law enforcement personnel for more accurate vehicle velocity measurements Radar equipment does have the unique advantage of being able to be operated while in motion such as in the vehicle of a law enforcement officer and achieve an acceptable level of accuracy of velocity measurement while accounting for the relative motion between the vehicle based radar and the target vehicle Additional corrections are mathematically applied to the moving radar detections to account for the difference in relative velocities between the radar an
13. to obtain only a vehicle count a loose tube does not affect the accuracy of the vehicle count This same problem of the adhesive tape losing adhesion and allowing the tube to move laterally is encountered with a two tube installation If the objective of the traffic measure ment is to obtain the vehicle count and the direction of travel of each measured vehicle two loose tubes also do not affect either the count of the vehicles or the determination of their US 6 750 787 B2 5 direction of travel However if the measurement objective is to obtain reasonably accurate vehicle velocity measurements as well as obtaining the count and direction of travel of the vehicles a loose tube one or both in a two tube installation is unacceptable for accurate velocity determination There are several ifs which individually or in combi nation can severely affect the accuracy of traffic measure ments with the pneumoelectronic system If the vehicle velocity is constant as the vehicle passes over the two tubes if the two tubes are reasonably parallel across the street and reasonably orthogonal to the passing traffic if the two tubes fastened to the street surface maintain the pre selected reference distance D within reasonable accuracy if the passing vehicle is the only vehicle introducing the first two pulses into the two tubes a second vehicle passing over the two tubes in the opposite direction at the same approximate time as the first v
14. to said second power source a data recorder operatively interconnected to said second power source and a display panel operatively inter connected to said second power source and a sensor control unit comprising at least two laser beam sensors operatively interconnected to said second power source There is also provided according to the invention a method of counting individual moving vehicles comprising the steps of generating at least one laser beam from a first unit to a second unit interrupting said laser beam s with a moving vehicle sensing said interruption s of said laser beam s processing said sensed interruptions into electronic count data recording said electronic count data and for matting and generating a list of said electronic count data into a usable format There is also provided according to the invention a method of determining individual vehicle velocity and direc tion of travel comprising the steps of generating at least two laser beams from a first unit to a second unit interrupting said laser beams with a moving vehicle sensing said inter ruptions of said laser beams processing said sensed inter ruptions into electronic velocity and direction of travel data recording said electronic velocity and direction of travel data and formatting and generating a list of said electronic velocity and direction of travel data into a usable format There is further provided according to the invention a method of count
15. 1 on the Beam Emitter Unit 1 Once in alignment the center cap with a target imprinted on it should be replaced on the center Orifice Tube 2i and the center Beam Emitter 2g switched OFF 2 Proceed to the Beam Emitter Unit 1 remove all three caps on the three Orifice Tubes 1e 1f and 11 and switch ON all three Beam Emitters 1c 1d and 11 The alignment elevation and angle of the Beam Emitter Unit 1 should be adjusted using the four Alignment Screwposts 1k on the four corners of the Beam Emitter Unit 1 until all three emitted Beams 1g 1h and 1j impinge on the respective three target caps on the Orifice Tubes 2b 2c and 2i on the Sensor Control Unit 2 When aligned accurately the center Beam Emitter is then switched OFF and the cap with target replaced on the end of center Orifice Tube 11 3 Return to the Sensor Control Unit 2 closely observe the targets on the two caps on the two Orifice Tubes 2b and 2c 10 15 20 25 30 35 40 45 50 55 60 65 14 to assure that the two active Beams 1g and 1 from the Beam Emitter Unit 1 are impinging at the target cross hairs on both target caps on Orifice Tubes 2b and 2c The two target caps may then be removed using care not to disrupt the align ment of the Sensor Control Unit 2 from the Orifice Tubes 2b and 2c and the Beams 1g and 1 should then be impinging on the face of the photoelectric transistors at the interior end of Orifice Tube 2b and 2c 4
16. 1f and 17 Since the laser Light Beams 1g and 1 are typically positioned less than 10 inches above the street surface a person would have to place his her head on the street surface to stare into the Beam Emitter Unit 1 Further the laser Light Beams 1g and 1A are confined to the region between the faces of the two main components Beam Emitter Unit 1 and Sensor Control Unit 2 of the Optronic System The Light Beams 1g and 1h are not likely to be propagated significantly elsewhere than in that short confined corridor between the Beam Emitter Unit 1 and the Sensor Control Unit 2 barring tampering or vandalism causing the Beam Emitter Unit 1 to radiate the laser beams along spurious paths The placement and careful alignment of the Beam Emitter Unit 1 and the Sensor Control Unit 2 of the Optronic System during installation at a desired street location has been shown to be crucial to obtaining accurate vehicle velocity measurements at that location As shown in FIG 2 installers and monitors of the Optronic System do not have to perform any installation or beam monitoring activity in the vehicle traveled portion of the street thus avoiding the hazardous exposure of the installers of the Optronic System to passing vehicles FIG 5 shows a preferred installation of the Sensor Con trol Unit 2 installed in the preferred orthogonal orientation to the passing traffic The two Light Beams 1g and 1h emitted from the Beam Emitter Unit 1 propagate ab
17. 5 from the Sensor Control Unit 2 and taken to computer facility where the Line Data resident in the Data Recorder 34 is downloaded through the serial port of a computer into the computer for analysis print out in a well documented and useful form and for further use by traffic engineers and or law enforcement personnel Radiating laser light beams such as Light Beams 1g and 1h of any power level in a populated area obviously has environmental safety considerations where humans and or animals may be exposed to the lasers Low power 1 having an electromagnetic energy level not capable of causing the ignition of any flammable material and not capable of causing physical damage to external skin of humans or animals visible wavelength lasers used in wide spread public use in commercial and residential applications as well as by surveyors in mapping and by construction personnel in aligning structural components or excavations are installed with appropriate safety cautions clearly marked thereon A warning plate on the top of each ofthe Beam Emitter Unit 1 and Sensor Control Unit 2 on the sidewalk or shoulder of the street cautions pedestrian passers by not to stare into the low power laser Light Beams 10 15 20 25 30 35 40 45 50 55 60 65 16 1g and 1 crossing the street which although being of visible wavelength they are invisible to the unaided human eye or into the Emitter Orifice Tubes 1e
18. OFF first interrupted OFF first interrupted OFF Beam R is ON Beam L is ON By Pass Timer Excite Pulse Oscillator 3f Excite Pulse Oscillator 3f activation logic immediately when Beam L immediately when Beam R Timer 0 is interrupted OFF is interrupted OFF Set Direction Code Set Direction Code D 1 L R Set Direction Code 2 R L zi i A JJ D 0 Unknown Store Velocity as V 0 3g Stop Pulse Oscillator 31 when the second Unknown Ti beam either Beam L or R is interrupted OFF Pause Beam Status mer Calculate At from Pulse Count and store At Discriminator 3e 1 sec Pause Beam Status Discriminator 3e 1 sec Processor 3d Calculate Velocity V Calculated Velocity Store calculated V lL V 0 6818 x DRetg At Return To m Reset Timer 0 where Dretg DRefgo BeamStatus cos 90 9 Discriminator 3e Add 1 Count to Counter C is the measured angle between beams Display Data on Control Unit Display Panel 3i and vehicle path vector Send Line Data to Recorder 3h Recorder EEPROM Resume processing after Line Data sent Record data per Line Data format Option Send Transmit Data to Transmitter DB9 Download Connector HH Resume processing after Transmit Data sent 7 k Return to Beam Status Transmit data 5 p Discriminator for the next Transmit Data format traffic event measurement Enable the Beam Status am Enabling of Discriminator Discriminator per NB Mod
19. United States Patent US006750787B2 12 10 Patent No US 6 750 787 B2 Hutchinson 45 Date of Patent Jun 15 2004 54 SYSTEM FOR THE 5 392 034 A 2 1995 Kuwagaki 340 933 MEASUREMENT OF VEHICLE TRAFFIC 5 446 291 A 8 1995 Becker et al 250 559 24 5 748 108 5 1998 Sampey et al 340 933 76 Inventor Herbert A Hutchinson 2075 5 T al Mr 812 ohnson et al USE Rd Westlake Village CA 5 942 993 8 1999 Mio et al 340 033 6 084 533 7 2000 Morgan et al 340 935 Notice Subject to any disclaimer the term of this 6 188 469 B1 2 2001 Liou et al 100 257 patent is extended or adjusted under 35 OTHER PUBLICATIONS U S C 154 b by 191 days JAMAR Technologies Inc TRAX II TrafficCounter amp Classifier User s Manual 1997 all pages 21 Appl No 09 805 691 GK Instruments 5000 Series date unknown all pages 22 Filed Mar 13 2001 Peek Traffic Inc Internet website printouts www peektraf ficinc com printed on Feb 6 2001 12 pages 65 Prior Publication Data xs cited by examiner US 2002 0000921 A1 Jan 3 2002 Primary Examiner Daniel 1 Wu Related U S Application Data Assistant Examiner Son Tang 60 Provisional application No 60 190 080 filed on Mar 17 74 Attorney Agent or Firm Keith D Hutchinson 2000 Maymanat S Afshar 51 Int C
20. adar 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 s
21. al current to pass when the pressure input reaches a pressure level at which the switch has been designed to activate When the first electrical signal is generated from a pressure pulse event i e when the front wheels of a moving vehicle pass over the first tube is received from the pulse sensor at the processor within the data unit a timer device is started When the second elec trical signal is generated from the next pressure pulse event i e when the wheels on the first axle of the moving vehicle also pass over the second tube is received at the processor the timer device is stopped The time interval At between the first and second pressure pulses At t 2 tpuise 1 is measured to the nearest 0 01 seconds using the timer device much like a stop watch at a sport racing event The elapsed time it takes for the wheels on the front axle of a vehicle to sequentially pass over each of two tubes fastened near orthogonal to the vehicle path vector and parallel to each other is a function of the vehicle velocity and the distance between the two tubes Table 1 indicates the length of time measured in seconds taken by a vehicle moving at various constant velocities to travel through a reference distance Dz Typically in pneumoelectronic sys tem installations Dz is selected at 8 feet between the two tubes because the distance wheelbase between the front and rear axles of small automobiles is generally more than 8 feet 1
22. all the possible equivalents nor to limit the invention defined by the claims to any particular equivalent or com bination thereof A person skilled in the art would realize that there may be other equivalent components presently known or to be developed which could be used within the spirit and scope of the invention defined by the claims What is claimed is 1 An apparatus for measuring the speed direction of travel and cumulative count of one or more moving vehicles in a stream of traffic comprising a beam emitter unit comprising at least two visible wavelength laser beam emitters wherein said laser beam emitters are mounted to generate two visible 10 20 25 35 40 45 50 55 24 wavelength laser beams coplanar and parallel to each other and having a lateral separation distance between said laser beams of approximately one foot and b a beam sensor unit comprising i at least two laser beam sensors wherein said laser beam sensors are mounted to receive and distinguish the on off status of said laser beams and ii a beam status discriminator and a timer means for electronically pausing said beam status discriminator and electrical processing for a one second period after said status of said laser beams is interrupted off wherein said beam emitter unit and said beam sensor unit are each positioned to emanate said laser beams between about 4 8 inches above the surface of a roadway 2 An apparatu
23. aser target cross hairs imprinted with a reflecting paint on their face directly over the center of the orifices Four of the Orifice Tubes 1 and 2b 2c and 2i are of circular cross section approximately 5 in diameter and extend approxi mately away from the exterior face of the Unit assembly box Orifice Tubes 1e and 1f are of smaller diameter and the caps for these two Orifice Tubes le and 1f do not require any target imprint on their face The six caps should be in place on the ends of the six orifice tubes whenever the two Units 1 and 2 are in storage awaiting use in a street traffic measurement and or when transporting the Units to a measurement location During the alignment process the sequence of removing and replacing the caps after the two Units 1 and 2 are placed on opposing sides of the street and have been visually pointed to face each other in coarse alignment is recommended to be 1 Remove and place aside for later use the cap on the center Orifice Tube 2i on the Sensor Control Unit 2 and activate the center Alignment Beam Emitter 2g on the Sensor Con trol Unit 2 The center Alignment Beam 2 should impinge somewhere close to the target imprinted on the opposing cap on the center Orifice Tube 1 on the Beam Emitter Unit 1 The four Alignment Screwposts 2k should then be adjusted to bring the center Alignment Beam 2 1 to impinge on the intersection of the cross hairs on the center target of Orifice Tube
24. at the location where the measurement of the vehicular traffic is desired to be made A functional description of the generic type of pneumoelec tronic 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 loca 10 15 20 25 30 35 40 45 50 55 60 65 2 tion 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 trafic measurement systems pneumoelectronic and r
25. be 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 a tee connection at some location where the tee connector will also not be crushed by a passing vehicle a short distance before the single tube entry port on the same data unit as previously described to count the number of passing vehicles In this two tube arrangement the passing of each set of the vehicle wheels on an axle over either tube produces a characteristic single pressure pulse generally of semisinusoidal waveform transmitted into the pulse sensor within the data unit After sensing the first two pulse signals in a passing vehicle traffic event the processor then locks out the remaining pulse signals from the vehicle pulse set a two axle vehicle passing over the two tubes will cause four pulses to be transmitted and a 3 axle vehicle passing over the two tubes will cause six pulses to be transmitted the number of vehicle axles multiplied by the number of tubes After approximately one second from the time of lock out the system resets itself in preparation for the detection and processing of the next set of pressure pulses generated by the next vehicle passing over the two tubes As indicated earlier in this description of the pneumo electronic system the pulse sensor serves as an electrical switch and causes an electric
26. 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 induc tance 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 hazard ous to vehicle operators and or pedestrians and the mea sured 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
27. d and 12 In a preferred embodiment the Beam Emitter Unit Power Source 1b is a typical off the shelf commercial quality rechargeable nickel cadmium cell battery but a hard wired Power Source 1b may alternatively be used in the invention In a preferred embodiment the Beam Emitter Unit 1 may be permanently mounted at a location for example at the drive in window of a restaurant to count the 10 15 20 25 30 35 40 45 50 55 60 65 12 vehicles and control the velocity of the vehicles patronizing the establishment In this preferred embodiment the Beam Emitter Unit Power Source 1b is hard wired from within the location instead of being a rechargeable type battery Inas much as the three BeamEmitters 1c 1d and 1i are designed to operate with 6V DC source current a transformer rectifier is also installed in this preferred embodiment in the Beam Emitter Unit 1 to convert the hard wire source 120V AC current entering the Beam Emitter Unit Power Source 1b electrical circuit into 6V DC current so as not to damage by over voltage the three Beam Emitters 1c 14 and 1i The Beam Emitter Unit Left and Right Beam Emitters 1c and 1d are mounted in the Beam Emitter Unit Assembly Box 1a at the time of manufacture to be precisely coplanar and parallel at a known reference distance DREF of for example 1 foot apart The Left and Right Light Beams 1g and 1 generated within the Beam Emitter Unit 1 exit the cor
28. d and displayed may have the Control Display Subunit 3 with him her in a parked vehicle US 6 750 787 B2 21 Also as shown in FIG 9 the Control Display Subunit Download Connector 3j a DB9 Connector female is affixed on the side of the Control Display Subunit 3 which internally interfaces to the Data Recorder through the Control Display Micro Processor 3d When taken to a computer facility for downloading and further processing of the measured traffic data a Download Interconnect Cable which is a standard DB9 serial cable with standard 9 pin male female connectors is connected from the Control Display Subunit 3 to the Serial Port on a PC compatible computer The necessary downloading program is available on a standard 1 MB floppy disk System Accuracy The interruption of a laser light beam used in the Optronic System is discerned by the Beam Status Discriminator 3e as being virtually a cut off signal traveling at the speed of light The flat face instantaneous cut off time of the first interrupted laser beam signal measured to the flat face of the second interrupted laser beam signal is able to be determined with essentially no rise time The accuracy of the Optronic System in determining a calculated vehicle velocity which is virtually identical to the actual vehicle velocity is also superior to that of measuring vehicle velocity by present radar type instruments which are prone to mis calibration and wh
29. d the target which must be done to convert the radar information into an absolute velocity of the target vehicle i e miles per hour mph relative to the stationary road surface This introduces further sources of inaccuracies into the measure ment and measurement processing If the indicated velocity displayed on the operator s dashboard speedometer and input into the radar processor of the law enforcement vehicle is not accurately calibrated for use in the calculation an error will be introduced into the relative velocity between the two moving vehicles This error will manifest itself in the radar equipment displaying an inaccurate velocity for the target vehicle Currently only the radar system has this capability of measuring the relative velocity of another moving vehicle while itself is in motion Existing and emerging fixed base traffic measurement systems pneumoelectronic and embedded inductance loops cannot practically incorporate any technology that would permit their use in a motion mode One disadvantage of the use of radar speed measurement equipment is that it requires a human operator with atten dant personnel costs but more importantly with the atten dant possibility of human error to operate the radar system in field locations and to interpret real time what the indi cated velocity displayed means Law enforcement personnel cannot be present everywhere to assess with radar equip ment whether the speed of an ind
30. e Transmitter fedis the Sensor Control NB 1 Only Beam L Active Optional Feature Processor for next event NB 2 Both Beams Active U S Patent Jun 15 2004 Sheet 8 of 9 US 6 750 787 B2 Figure 8 Upper Security Cover Hinge Line SYSTEM RESET SENSOR BATTERY ALL DISPLAYS CONTROL VOLTAGE Q ERASE EEPROM UNIT POWER RECHARGE IF RED DATE INSTALLATION ID START FILE NUMBER YY MM DD TIME CLOCK HOUR MINS NUMBER OF ANGLE OF BEAMS xx xx ACTIVE BEAMS TO VEHICLE TRAFFIC NB dor 90 IF PERPENDICULAR DEGS 00 23 00 59 DATA ENTRY KEYBOARD PUSH TO SET CLEAR HOES E TIT NEXT Limit SL MPH 5 THRESHHOLD ENTER SPEED TS MPH BEAM SENSORS RESET RECORDER COUNTER EEPROM e Q Q TO ZERO SYSTEM L R MODE PUSH TO TEST PUSH TO ERASE Lower Monitor Cover Hinge Line VEHICLE VEHICLE VEHICLE count DIRECTION D vELOCITY V 1 L R 2 R L MPH EXCESSIVE SPEED TRANSMIT DATA TO SYSTEM V MPH EXCEEDS REMOTE LOCATION MODEL NO XXXXXXXXX STATUS THRESHHOLD MPH SERIAL NO XXXXXXXXX Q e AUTO 1 000 FT Q PUSH TO SEND orel LASTCDV amp t U S Patent Jun 15 2004 Sheet 9 of 9 US 6 750 787 B2 Figure 9 4 19 2 Traffic Direction 1h 2 Traffic Direction A Right To Left Y 2 Left To Right A 2h 2 3 Alignment X Only 2 ES 2 aso Sensor Right Ground To Pin 6 j 48V DC From Pin 4
31. e vehicle velocity computation has been derived as Dg Dp 90 cos 90 9 The non orthogonal angle 9 in degrees is obtained during the Optronic System instal lation and alignment process using a protractor type device Alignment Angle Indicator 2j affixed on the upper surface of the Sensor Control Unit 2 as shown in FIG 4 The angle 0 is estimated with the aid of the Alignment Angle Indicator 2j and is input directly into the Control Display Subunit 3 through the Control amp Display Panel 3i to be described later in more detail with FIG 8 For most installations the angle 9 will be within a few degrees of 90 orthogonal and the cosine correction factor will be unity for accuracy purposes US 6 750 787 B2 17 Accordingly a default alignment angle of 90 for is programmed into the Control Display Processor 3d and unless changed by a direct input for the alignment angle other than 90 a correction to D is unnecessary FIG 6 shows the geometric basis for the installation requirement on beam elevation distance above the street surface The large rectangular pattern formed by the two co planar and parallel laser Light Beams 1g and 1 and with the two major system components Beam Emitter Unit 1 and Sensor Control Unit 2 at each end of the rectangle is not required to be perfectly horizontal but should be as parallel to the plane of the road surface as the terrain permits under practical street conditions If the road s
32. eam is interrupted before the right beam the vehicle is traveling from left to right Conversely if the right beam is interrupted before the left beam is interrupted the vehicle must be traveling from right to left The output signals beam interruption signals from the Beam Status Discriminator 3e are used most importantly in US 6 750 787 B2 15 determining the velocity of the vehicle passing through the measurement system To accomplish this portion of the vehicle traffic data measurement the output signal from the Beam Status Discriminator 3e when either one of the Light Beams 1g or 1 is interrupted causes a Timer amp Clock Chip 3g to electrically excite a Pulse Oscillator 3f co resident with the Control Display Micro Processor to start oscillating The preferred Pulse Oscillator 3f pulses at the rate of 625 pulses per millisecond and has an accuracy of 3 pulses independent of the length of pulse oscillation time One example of a preferred Pulse Oscillator 3f used in the Optronic System is a PIC16F877 Microcontroller manufac tured by Microchip Technology Inc When the second Light Beam either 1g or 1 is discerned by the Beam Status Discriminator 3e to have been interrupted by a passing vehicle the signal is relayed instantaneously to the Timer amp Clock Chip 3g which in turn removes the electrical exci tation from the Pulse Oscillator 3f causing it to stop oscillating One example of a preferred Timer amp Cloc
33. ee standing on a sidewalk or street shoulder surface but are at risk of being vibrated out of alignment by heavy vehicles such as trucks passing along the street Free standing com 30 40 45 55 18 ponents are also at risk of being tampered with or stolen unless securely attached to the concrete or ground and or chained to a pole or tree It is foreseen that the Light Beams 1g and 1 may be interrupted also by a pedestrian walking jogging or bicycling or more infrequently by a stray animal a bird or a large flying insect passing through the beams The Optronic System counts each interruption of the left Light Beam 1g as a passing vehicle regardless of the nature of the body interrupting the beam The Optronic System also calculates a velocity V for and determines a direction D of the interrupting body if both Light Beams 1g and 1 are interrupted The recorded count direction of travel and velocity data CDV data should be visually scanned on a line by line basis by the data analyst or by the computer itself at the end of the traffic measurement recording session and those line records indicating a velocity below five mph should be disregarded in the count i e subtracting the number of apparently non vehicle caused interruptions from the vehicle total count C If the street to be measured has a large amount of pedestrian travel on the adjacent sidewalks the two components of the Optronic System should be
34. ehicle could contaminate the pulse data sensed and if the timer measurement of the time interval between the first two sensed pulses was more accurate 1 measuring At to 20 001 seconds the two tubes pneumo electronic traffic measurement system would provide veloc ity measurements of sufficient accuracy for traffic engineer ing purposes In a field environment many of these ifs are not always achieved and normally this causes concern over the accuracy of the data In any case for law enforcement purposes an accuracy of 0 01 seconds for the timer mea suring the time between pulses is not acceptable 1 a speeding violation could be challenged in a traffic court with near 10046 success Table 2 indicates the range in calculated velocities for a timer which can measure a time increment At between pressure pulses to an accuracy of 0 01 seconds and with Dre feet TABLE 2 Actual Velocity mph Calculated Velocity mph Calculated Velocity mph 100 Accuracy At error 0 01 sec error 40 01 sec 25 0 26 2 23 9 35 0 374 32 9 45 0 49 1 41 6 55 0 61 3 50 0 If the tubes are installed and maintain a Drep accuracy of 8 feet 96 inches 0 1 inch there will be no significant reduction in the accuracy of the calculated velocity However if the two tubes are not installed at the same Dy distance as used in the velocity calculation and or are not installed with parallelism and or one of the tube attach
35. elocity Vector Sensor Control Unit Beams Orthogonal To Beams Not Orthogonal Vehicie Velocity Vector To Vehicle Velocity Vector 0 90 45 lt lt 135 U S Patent Jun 15 2004 Sheet 6 of 9 US 6 750 787 B2 Figure 6 Cut In Plane Of Wheel Motion Left Meses Road Surface Plane Of Beams Must Be Minimum 4 Height Parallel To Plane Of Road Above Road Surface Surface Height Of Axle 7 8 Is Preferred Height For Plane Of Beams Above Road Surface if The Road Surface 1 At Grade The Plane Of Beams Must Be At The Same Grade And Minimum Of 4 Above Road Surface Cut Perpendicular To Plane Of Light Beams 1 Plane Of Beams Minimum 4 Clearance If The Road Surface Has A Crown Curvature The Plane Of Beams Must Clear The Highest Point Of The Surface Crown By A Minimum Of 4 U S Patent Jun 15 2004 Sheet 7 of 9 US 6 750 787 B2 Figure 7 1g 3 Sth a M 3 x A Beam L Beam R N NB is the Number of Beams 3 Active it either OFF if NB 1 X active for measurements NB 1 or NB 2 Active if NB 2 input to Control amp Display t Sensor Panel 3i at initialization A Control E DRetso X A 90 Unit 2 2d 211222 2e Control Beam L E Beam Status i Beam R Display Sensor Discriminator Sensor Subunit NB 1 NB 2 or NB 1 Beam R is OFF NB 2 and Beam L is NB 2 and Beam R is and Beam L is interrupted
36. ensor which functions essentially as a pressure activated electrical switch outputs an electrical signal indicating the traffic event 1 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
37. es all known to be between 98 and 113 inches to medium size three axle trucks some with a boat trailer being towed by the truck TABLE 4 SPEED TIME DATE PULSES 28 99242 20 27 33 Jun 06 2000 050135 13 01148 20 29 45 Jun 06 1960 112150 14 779 20 30 11 Jun 06 2000 099031 18 4874 20 30 77 Jun 06 2000 079061 38 62571 20 31 35 Jun 06 2000 037237 40 mph accuracy check 16 8746 20 31 48 Jun 06 2000 088098 26 68364 20 33 19 Jun 06 2000 055043 33 29837 20 33 49 Jun 06 2000 043255 18 14042 20 34 41 Jun 06 2000 080193 9 489297 20 38 34 Jun 06 2000 154096 10 mph accuracy check 17 47618 20 38 49 Jun 06 2000 083212 18 81846 20 37 32 Jun 06 2000 094105 The street widths where the measurements for Table 3 were made varied from approximately 70 feet wide to approximately 160 feet wide and showed that the width of the street does not affect the operation or accuracy of the Optronic System The street width may be more than 500 feet wide in terms of the distance through which the laser beams would travel from the Beam Emitter Unit 1 and still have sufficient light energy content to activate the photo electric transistors of Beam Sensors 2d and 2e in the Sensor Control Unit 2 In general the greater the distance between the Beam Emitter Unit 1 and the Sensor Control Unit 2 only requires finer adjustments in the adjustable Alignment Screwposts 1k and 2k to bring the components into proper mutual alignment This should n
38. g a one second time increment will be counted as the passing of one vehicle regardless of the number of axles on the vehicle and regardless if there are other vehicles passing through the measurement gate at precisely the same time The left Light Beam 1g interruption will be sensed by the left Beam Sensor 2d and the normally ON electrical signal will be changed to OFF and passed from the Beam Sensor 2d to the Beam Status Discriminator 3e With the NB set as 1 the Beam Status Discriminator 3e will cause the Control Dis play Micro Processor 3d to by pass the logic to determine direction of the vehicle and the velocity of the vehicle and the processing logic will pause further Beam Discrimina tor signals for one second using the Timer 3g to allow the remaining axles of the vehicle and any other co passing vehicles to pass through the system At the end of the one second pause the processing flow will then proceed directly to the adding of a unit count into the accumulating Counter logic on the Control Display Micro Processor 3d circuit US 6 750 787 B2 19 board and the Count C will be relayed to both the Data Recorder and to the display portion of the Control amp Display Panel 3i The Control Display Micro Processor 3d will then pass the processing control back to the Beam Status Discriminator for the next traffic event 1 the counting of another vehicle passing through the system When the Optron
39. heet 1 of 9 US 6 750 787 B2 Figure 1 Sidewalk Or Shoulder Of Street Traffic Direction Right To Left Distance Right Tube Traffic Direction Left To Right Sidewalk Or Shoulder Of Street Pulse Sensor U S Patent Jun 15 2004 Sheet 2 of 9 US 6 750 787 B2 Figure 2 Sidewalk Or Shoulder f Street E Traffic Direction Left To Right Sidewalk Or Shoulder Of Street 3k U S Patent Jun 15 2004 Sheet 3 of 9 US 6 750 787 B2 Figure 3 EHE v Y 2 X 2 2 2 2 a 2 ai 1f 2 2 7 E 5 Dna 2 7 4 Traffic Direction 2 Right To Left To Sensor Control Unit Center Target A Traffic Direction For Alignment Only 2 Left To Right a gt x a E VAN XN 19 1h U S Patent Jun 15 2004 Sheet 4 of 9 US 6 750 787 B2 Figure 4 1q x th g 2 M t a 2 Dret Y A 2 X Traffic Direction 2 To Beam Unit x Right To Left 4 Center Target X nme 2 For Allgament Only Y 5 Traffic Direction 2 on Left To Right 2 A x v A N 2b 2 Dret 2 S 2 Y 2c 2 3 2 E Y 2 x 2 A X MES SEE peat US we el ME x ux X UM U S Patent Jun 15 2004 Sheet 5 of 9 US 6 750 787 B2 Figure 5 DRefgo Sidewalk Or Shoulder Of Street Vehicle V
40. ic System is installed and both Light Beams 1g and 1 are aligned to function in the two beams 2 mode the logic to process the beam interruption signals into direction of vehicle travel D and velocity of the vehicle V is slightly more complex than that employed for only the counting C of the vehicles When NB 2 the Beam Discriminator 3e will sense both Light Beams 1g and 1A interruptions in the sequence in which they are inter rupted OFF The logic for determining the vehicle direction of travel is simply that if the Left Light Beam lg is interrupted before the Right Light Beam 1 the direction of vehicle is determined as being from left to right L R Direction Code D 1 relative to the face of the Sensor Control Unit 2 If the Right Light Beam 1 is interrupted before the Left Light Beam 1g the direction of travel is determined as being from right to left R L Direction Code D 2 The logic in determining the velocity V of the passing vehicle is more computational than comparative and is performed after one second following the second light beam interruption The Beam Status Discriminator 3e initiates the Timer 3g to pause the Beam Status Discriminator 3e for one second to allow the vehicle being measured and any other co passing vehicles to completely pass through the measurement gate without additional interruption signals Immediately after the vehicle direction of travel has been determined a determination
41. ich often erroneously detect the velocity for false targets in the background of the prime target There are known sources of inaccuracy in the counting of vehicles and in the measurement of vehicle velocity which are unavoidable with the Optronic System when the beams CNT Uno ROO T2 traverse a street and there are vehicles traveling in both directions through the beams One primary source of inac curacy is the uncommon occurrence of a vehicle interrupting beam in one direction and a second vehicle traveling in the opposite direction interrupting the second beam before the first vehicle does so The falsely shortened time increment At measured by the interruption of the two beams by two different vehicles will be discerned by the Optronic System as being caused by one vehicle traveling faster than its actual velocity One means of avoiding this source of inaccuracy is to emit the beams only across the lanes of traffic moving in the same direction and streets having a center island or median area offer this opportunity If it is critical that the traffic mea surements include data for vehicles moving in both direc tions during the same measurement time period a second traffic measurement Optronic System may be installed across those lanes of the street having vehicular motion in the opposite direction To describe the accuracy of the Pulse Oscillator 3f pulse counting process a conventional decimal base 10 descrip 10 15
42. ing and law enforcement purposes than when traffic measure ment equipment such as 1 inch diameter hoses across street surface or a law enforcement marked vehicle is visible to vehicle operators The diameter of the Light Beams 1g and 1 is larger than the diameter of a large raindrop so that operating the Optronic System in rainy weather or heavy fog conditions will not result in beam interruptions 1 resulting in rain drops being counted and recorded as passing vehicles A large diameter beam also allows better tolerance of the system to small installation misalignments of the path of the beam from the Beam Emitter Unit 1 through a relatively small orifice approximately diameter on the Sensor Control Unit 2 many yards away and onto the small circular approximately 74 diameter sensing area on the face of the photoelectric transistor in each Beam Sensor 2d and 2e To keep each component secure to the surface of the sidewalk a long wide strip of adhesive tape or other bonding adhesive material may be attached over the foot of each Alignment Screwpost of the component and fastened down to the surface For installations on the roadside which may not be of concrete or some other form of firm pavement there are holes in the bottom pad of each Alignment Screw post 1k and 2k a total of 8 per installed system through which small stakes may be driven into the ground to anchor the component The components may be placed fr
43. ing determining the velocity and direction of travel of individual vehicles comprising the steps of generating at least two laser beams from a first unit to a second unit interrupting said laser beams with a moving vehicle sensing said interruptions of said laser beams processing said sensed interruptions into electronic count velocity and direction of travel data and formatting and generating a list of said electronic count velocity and direction of travel data into a usable format BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 illustrates a functional schematic of the prior art pneumoelectronic vehicle traffic measurement system pres ently being used by traffic engineering departments in many large cities US 6 750 787 B2 9 FIG 2 schematically shows the preferred functional arrangement of the major components of the Optronic System used for measuring the traffic at a street location FIG 3 illustrates the preferred components comprising the Beam Emitter Unit of the Optronic System and briefly indicates the functional relationship of the components to the overall performance of the Optronic System FIG 4 illustrates the preferred Control Display Subunit and components comprising the Sensor Control Unit of the Optronic System and briefly indicates the functional rela tionship of the components to the overall performance of the Optronic System FIG 5 schematically presents the geometric reason dic tating that a trigonomet
44. is made by the Timer 3g of the number of pulses which the Pulse Oscillator 3f has per formed during the time interval between the interruptions of the two Light Beams 1g and 1h and that time interval At in milliseconds is calculated and stored for subsequent use in a velocity computation The Control Display Micro Processor 3d then performs the velocity computation using the equation from the Laws of Motion described earlier in conjunction with Table 1 and uses the At from immediately above the of 1 foot or that Drep which is calculated should the installation angle of the light beams be other than orthogonal to traffic as described for FIG 5 and the conversion factor k 0 6818 mph fps to convert the result ing calculated velocity to V in miles per hour mph The processing flow then follows the same logic and flow path from the point where a unit count of the vehicle event is added into the accumulated vehicle Count C and the return of processing flow 1 returned to the Beam Status Discrimi nator 3e for the next vehicle passing traffic event An option to transmit data from the Optronic System Control Display Subunit 3 to a remote site arises from the optional inclusion of a Data Transmitter 3 within the Control Display Subunit 3 The Sensor Control Unit 2 and Control Display Subunit 3 perform their basic functions with or without the optional Data Transmitter 37 Selected data transmitted to a law enforcement officer has
45. ividual vehicle is danger ously above the safe speed for the conditions existing at that location on a street e g in a school zone at a crosswalk or near a park or relative to other moving vehicles on that street Returning to the description of the present pneumoelec tronic traffic measurement system to determine the direction of travel 1 from left to right or from right to left relative to the data unit of a moving vehicle requires being able to distinguish which of the two pulses in a two pulse set was created in which tube first Vehicle direction cannot be determined with a single tube or any single detector installation The two tubes pneumoelectronic system most frequently merges the input pulses from the individual tubes prior to the pulses entering the data unit and the pulse sensor interprets these as being two sequential pulses from a single vehicle passing over one tube The processor function within the data unit is capable of calculating the velocity of the passing vehicle but is unable to discern which pulse was produced in the left or right tube and therefore is unable to determine the direction of travel of that vehicle To obtain more accurate measurements of a vehicle veloc ity for both traffic engineering and law enforcement pur poses than 1 possible with most present pneumoelectronic 10 15 20 25 30 35 40 45 50 55 60 65 8 traffic measurement systems to obtain a measu
46. k Chip 3g used in the Optronic System is a DS1302 Trickle Charge Timekeeping Chip manufactured by Dallas Semiconductor Corporation The Timer portion of the Timer amp Clock Chip 3g determines the total number of pulse oscillations which the Pulse Oscillator 3f has performed during the time interval At it was oscillating and converts that total number of pulses into the number of milliseconds lapsed by dividing the total number of pulses by 625 pulses per millisecond the characteristic oscillating frequency for the Pulse Oscillator 3f This timing technique provides a highly accurate time interval At in milliseconds The Control Display Micro Processor 3d then processes the measured time interval At milliseconds and the known 1 foot into an accurate vehicle velocity using the mathematical equation from the Laws of Motion described in Table 2 earlier in this docu ment With the count of the vehicles C the direction of travel of the vehicles D and the velocity of the vehicles V determined the Control Display Micro Processor 3d sends that collective information CDV data and the other variable data e g time of day to the Data Recorder 3 in a Line Data format The Data Recorder is a commercially available state of the art EEPROM type device used exten sively in electronic devices world wide At the end of a vehicle traffic measurement recording session the Control Display Subunit 3 is detached at Connector 3
47. l G08G 1 04 57 ABSTRACT 52 3o eee 340 942 340 933 340 935 NT 340 936 701 119 The present invention is a vehicle traffic measurement 58 Field of Search 340 933 934 system designed to accurately count and record the numiper 340 935 936 942 330 701 117 118 of vehicles passing through a selected location to more aub dU gt 119 accurately determine and record the velocity at which the individual vehicles travel through that location and to 56 References Cited accurately determine and record in which relative direction the vehicles are traveling as they pass that location The U S PATENT DOCUMENTS basic physical principle is of a moving object interrupting 3 872 283 3 1975 Smith et al ss 701 207 Wo parallel light beams a known reference distance apart 4 201 908 377 9 and information extracted from the interruptions sensed and 4 493 103 A 1 1985 Yamashita et al 382 104 electronically processed into count direction and velocity 4 549 182 A 10 1985 Gillet 340 942 being recorded for subsequent data analysis 4 947 353 A 8 1990 Quinlan 702 158 5 298 738 A 3 1994 Gebert et al 250 222 1 4 Claims 9 Drawing Sheets Traftic Direction Left To Right 2f Sidewalk Or Shoulder Of Street Traffic Direction Right To Left Sidewalk Or Shoulder Street 3k U S Patent Jun 15 2004 S
48. m interruption processing the electronic events corresponding to the sequence of and the time interval between said first and second laser beam interruptions via an electronic com puter processor chip into the vehicle direction of travel and vehicle speed and producing an electronic data readout in chronological sequence from said apparatus
49. mitter Unit the Sensor Con trol Unit and the detachable Control Display Subunit are the three major components which comprise the Optronic Sys tem and are described first in greater detail The logic used in processing the vehicle traffic measurements into accurate and useful engineering data and a description of the controls and displays necessary for operating the Optronic System properly and efficiently are also presented A schematic description of the electrical wiring paths used to intercon nect the electronic components of the system and thus enable the processing of the raw field vehicle traffic mea surements into accurate and useful data is then described and discussed Table 3 below presents a summary list of items and their associated reference numbers denoted in FIGS 2 through 9 TABLE 3 Reference Item Number Description 1 Beam Emitter Unit la Beam Emitter Unit Assembly Box 10 15 20 25 30 35 40 45 50 55 60 65 10 TABLE 3 continued Reference Item Number Description 1b Beam Emitter Unit Power Source 1c Left Beam Emitter 14 Right Beam Emitter le Left Beam Emitter Orifice Tube 1f Right Beam Emitter Orifice Tube 1g Left Light Beam 1h Right Light Beam li Beam Emitter Unit Center Beam Emitter 1j Beam Emitter Unit Center Alignment Beam 1k Beam Emitter Unit Alignment Screwpost 11 Beam Emitter Unit Center Orifice Tube 2 Sensor Control Uni 2a Sensor Control Unit Assembly Box 2b Left
50. o functionally perform as designed In a preferred embodiment the Control Display Subunit Power Source 3c comprises a typical off the shelf commercial quality rechargeable nickel cadmium cell battery and such Power Source 3c may alternatively comprise a removable battery In a preferred embodiment the Control Display Subunit 3 may be permanently mounted at a location for example at the drive in window of a restaurant to count the vehicles and control the velocity of the vehicles patronizing the establishment In this second preferred embodiment the Control Display Subunit Power Source 3c is hard wired from within the location instead of being a rechargeable type battery Inasmuch as all of the electrical components of the Sensor Control Unit 2 and the Control Display Subunit 3 are designed to operate with 6V DC source current a trans former rectifier is also installed in this second preferred embodiment in the Control Display Subunit 3 to convert the hard wire source 120V AC current entering the Control Display Subunit Power Source 3c electrical circuit into 6V DC current so as not to damage by over voltage any of the electrical components of the Sensor Control Unit 2 and the Control Display Subunit 3 A Control amp Display Panel 3i under the top cover of the detachable Control Display Subunit 3 of the Optronic System permits the installing technician to define the installation details unique to each system installation and therewi
51. on V mph kxDpe ft At secs where k 0 6818 mph per fps As can be seen in the equation the accuracy of the calculated velocity V is dependent on the accuracy of the measured lapsed time At as well as on the accuracy of the reference distance Dg The conversion factor is math ematically derived to be accurate to the significant places of the number shown A timer having an accuracy of At 0 01 seconds is seen to produce a measured and recorded time between two pulses with marginal accuracy at the lower speeds below 35 mph primarily of interest to traffic engi neers in studying traffic flow At speeds above about 35 mph the region of primary interest to law enforcement personnel a timer having At 0 01 seconds accuracy is not adequate for measuring the time interval At for a vehicle moving between two tubes spaced 8 feet apart For the latter reason law enforcement personnel almost exclusively rely on radar type equipment to directly measure the speed of the higher speed vehicles with much better but certainly not extreme accuracy compared to the velocity indirectly determined with a pneumoelectronic system Frequently one of the shortcomings of the tube type installation is the adhesive tape being peeled back from the road surface by the traction of a vehicle s wheels passing over the tape allowing the tube to move significant distances sometimes as much as 5 laterally If the objective of the traffic measurement is
52. ot be construed to mean that the Optronic System requires a calibration of any type 1 alignment of components does not constitute a calibration per se it does not An important but not a very detrimental consideration of street width would become the number of lanes of traffic traveling in both directions in a very wide street measurement scenario With multiple US 6 750 787 B2 23 vehicles traveling in both directions through the region between the two beams the probability of two vehicles interrupting the two beams from a different direction at nearly the same time is increased This would cause an erroneous measurement of the time increment At between the interruption of the two beams for one of those vehicles and the Optronic System would calculate an apparent veloc ity which is erroneous for whichever vehicle interrupted whichever of the beams first Velocity calculations shown in the print out of the data would likely be so very improbable such as 140 mph in a 25 mph speed limit zone that the traffic data shown in that line of data should be deleted or at least ignored in the traffic data analysis The traffic measurements made with the Optronic System were processed into accurate data descriptions of the traffic and motion of each of the measured vehicles The data were downloaded using conventional computer procedures and converted into data print outs as representative examples More sophisticated data analysis routine
53. ove the surface of the street in parallelism and are co planar every where including at the face of the Sensor Control Unit 2 The reference distance through which vehicle traffic passes between the parallel Light Beams 1g and 1h is referred to herein as This is selected as nominally 1 foot partly for ease of mathematical calculations More importantly a Dres of 1 foot is also less than the diameter of a vehicle wheel usually 14 or 15 inches in diameter such that both Light Beams 1g and 1 will be simultaneously interrupted as a vehicle wheel passes through the light beams When possible the two Light Beams 1g and 1 are installed orthogonal 90 to the vehicle path vector as it moves though the two beams in the measurement system The two parallel Light Beams 1g and 1h across the street are interrupted but cannot be damaged by passing vehicles traveling in either direction For those uncommon occur rences when the two Light Beams 1g and 1 physically cannot be installed orthogonal to the vehicle traffic vector i e they must be installed at a diagonal angle across the street the Drep must be adjusted before use in the vehicle velocity computation because of the geometric lengthening of the actual Drep To account for an installation of the Optronic System requiring a non orthogonal angle 6 ranging anywhere from 45 to 135 relative to the vehicle path vector a trigonometric correction to the actual used in th
54. preferred embodiment the Sensor Control Unit 2 has the Control Display Subunit 3 in a detachable box so that it can be detached after the traffic measurement session is completed and taken to a computer facility for downloading of the traffic measurement data stored therein on a standard EEPROM The attachment interface is a standard Intercon nect Cable 2f having a 6 pin male connector affixed on the free end which attaches to the female Input Connector 35 on the left side of the Control Display Subunit 3 The embed ded end of the cable separates into individual wires which are soldered onto the pins on the pair of photoelectric transistors in the Beam Sensor Unit 2 as shown in FIG 4 The matching 6 pin female Input Connector 3b is assembled on the left side of the Control Display Subunit 3 as shown in FIG 9 and when connected transmits the laser beam interrupt signals from the Left and Right Beam Sensors 2d and 2e in the Sensor Control Unit 2 into the Control Display Subunit 3 for discernment and processing In a preferred embodiment the length of the 6 pin Inter connect Cable 2f is approximately 12 feet long to allow the Control Display Subunit 3 to be remotely positioned from the Sensor Control Unit 2 which will be near the side of a street surface For example the Sensor Control Unit 2 may be installed beneath a parked vehicle to conceal it from passing motorists and a person optionally monitoring the traffic data being recorde
55. rement of the vehicle direction on the street not always possible with the present pneumoelectronic system and to avoid the several real world problems being experienced with the present pneumoelectronic system 1 tubes having to be fastened on a street surface with vehicles moving by in close prox imity to the installing technician and being damaged by traversing vehicles or their reference separation distance being changed by vehicles passing over them requiring maintenance of the tube installation an improved and accurate measurement system is needed BRIEF SUMMARY OF THE INVENTION It is therefore an object of the present invention to wit an Optronic System to provide a vehicle traffic measure ment system in which more than one of the disadvantages of the prior art are overcome In accordance with this objective there is provided according to the invention a vehicle traffic measuring system comprising a beam emitter unit compris ing a first power source and at least two laser beam emitters operatively interconnected to said first power source a detachable control display subunit comprising a second power source a beam status discriminator operatively inter connected to said second power source a pulse oscillator operatively interconnected to said second power source an electronic chip comprising an electronic timer and clock operatively interconnected to said second power source a processor operatively interconnected
56. responding Beam Emitters 1c and 1d through the respective Beam Emitter Unit Orifice Tubes 1 and 1f and propagate across the street towards the Sensor Control Unit 2 The two Left and Right Light Beams 1g and 1 are generally orthogonal to passing vehicle traffic A manual switch not shown atop each of the three Beam Emitter Unit Beam Emitters Left 1c Right 14 and Center 17 will allow the installing technician to activate the Beam Emitter Unit Center Beam Emitter 1i when performing the alignment mode of the Optronic System installation as well as to activate the two primary Beam Emitter Unit Beam Emitters 1c and 1d in the subsequent vehicle traffic measurement mode of operation If the measurement only of vehicle traffic count is planned only the Left Beam Emitter 1c will be activated ON The Right Beam Emitter 1d need not be activated in order to minimize the Beam Emitter Unit Power Source 1b energy consump tion for a potentially lengthy traffic measurement session Careful alignment of the Beam Emitter Unit 1 and the Sensor Control Unit 2 shown schematically in FIG 4 is crucial to the obtaining of the traffic measurement data In its preferred configuration the Optronic System has four laser beam emitters three on the Beam Emitter Unit 1 and one on the Sensor Control Unit 2 The reason for the alignment being crucial is that if the two primary emitted laser beams Left Light Beam 1g and Right Light Beam 1 from the Beam Emit
57. ric correction factor be applied to the reference distance actually traversed by vehicles passing through the Optronic System when the system cannot be installed orthogonal to the vehicle traffic vector This cor rection is required in order to maximize the accuracy of vehicle velocity measurements processed within the Optronic System FIG 6 schematically indicates the preferred elevation of the installed light beams above the street surface to maxi mize the accuracy of vehicle velocity measurements col lected with the Optronic System FIG 7 schematically presents the preferred elements of the System Processor logic in the Optronic System for converting the raw sensed traffic signals beam interruptions into useful traffic data measurements count of vehicles C velocity of each vehicle V and direction of travel D FIG 8 schematically presents one embodiment of the interactive Control amp Display Panel for the control and display functions on the upper face of the Control Display Subunit in the Optronic System enabling the installing technician to interact with the controls and displays FIG 9 schematically shows the preferred electrical wiring paths interconnecting the electrically powered components of the Optronic System DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention and its use for measuring vehicle traffic 1 described hereafter in more detail with reference to the foregoing figures The Beam E
58. s e g calculating and displaying the vehicle velocity spectrum during a selected time period and or during the total measuring period calculating and displaying the volume of traffic flow on a time line basis calculating and displaying the direc tional flow of traffic in a graphically animated manner for the time setting of signal lights etc may optionally be employed by traffic engineering and law enforcement per sonnel in large communities to suit their particular needs and computer resource capabilities and availabilities The Optronic System provides them with the opportunity to do so A Data Transmitter 31 is optionally incorporated in the Optronic System The transmittal for example by radio frequency RF or hard wire means of vehicle traffic code violations to remote locations such as to a remote camera to an existing mobile vehicle speed display or to a law enforcement officer in a vehicle is an optional feature It will be understood that the above described embodi ments of the present invention are susceptible to various modifications changes and adaptations and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims Further although a number of equivalent components may have been mentioned herein which could be used in place of the components illustrated and described with reference to the described embodiment this is not meant to be an exhaustive treatment of
59. s according to claim 1 wherein said beam emitter unit comprises a a first visible wavelength laser beam emitter b a second visible wavelength laser beam emitter and c a third visible wavelength laser beam emitter means for aligning said visible wavelength laser beams between said beam emitter unit and said beam sensor control unit 3 A method of cumulatively counting a plurality of moving vehicles in a stream of traffic comprising the steps of providing an apparatus of claim 1 interrupting either of two said visible wavelength laser beams generated across a roadway and sensed by said apparatus of claim 1 and electronically recording the sensed laser beam interruption processing the sequence and timing of the electronic events corresponding to said laser beam interruption via an electronic computer processor chip into a cumu lative count of said moving vehicles and producing an electronic data readout in chronological sequence from said apparatus 4 A method of determining the speed and direction of travel of one or more moving vehicles in a stream of traffic comprising the steps of providing an apparatus of claim 1 interrupting a first visible wavelength laser beam gener ated by said apparatus of claim 1 and electronically recording said first laser beam interruption interrupting a second visible wavelength laser beam gen erated by said apparatus of claim 1 and electronically recording said second laser bea
60. set the two tubes at an erroneous Da distance apart or at some angle other than 90 to the travel path of the vehicle However this adverse event occurs most often in the installation of a pneumoelectronic type system when the adhesive strips attaching the tubes to the street surface lose their adhesion and allows the tubes to laterally move increasing or decreasing the D as the wheels of a vehicle pass over the tubes The shortcomings of the present pneumoelectronic equip ment to accurately and safely measure vehicle direction and velocity as described heretofore dictates the need for an improved ie more accurate means of simultaneously measuring the three primary vehicle traffic parameters espe cially vehicle velocity Because law enforcement personnel require a much more accurate measurement of vehicle velocity than is available with a pneumoelectronic system radar type equipment is employed by law enforcement personnel to measure the velocity of individual vehicles Radar Measurement of Vehicle Velocity For completeness in describing the techniques presently in use for measuring traffic parameters the attributes of measuring vehicle velocity with radar equipment is included herein The acronym RADAR which has become the noun radar in common usage is derived from its original title RAdio Detection And Ranging Radar was developed by allied military countries during the early 1940s into a practical means for detecting
61. ter Unit 1 do not impinge on the photoelectric transistors within the two Beam Sensors 2d and 2e the laser beams will not provide the laser beam ON or OFF signals associated with passing vehicles interrupting the beams and the traffic measurements will not be properly collected The two Center Alignment Beam Emitters 1i and 2g positioned very accurately on the center line of the Beam Emitter Unit 1 and the Sensor Control Unit 2 respectively have been added to facilitate the alignment of the two primary laser beams passing between the Beam Emitter Unit 1 and Sensor Control Unit 2 During the alignment procedure all four Beam Emitters 1c 1d 1i and 22 when activated ON will emanate the four beams which will all be coplanar and which will all be mutually parallel The two center align ment beams 1j and 2h are precisely half way between 1 everywhere equidistant from the outer two primary beams 1g and 1 which are Drep distance apart It is helpful in understanding the crucial alignment requirement if one envisions a large rectangle on the plane of the beams extending across the street and between the Beam Emitter Unit 1 and the Sensor Control Unit 2 The two corners of the rectangle at the Beam Emitter Unit 1 are the Beam Emitters 1c and 1d and the two corners at the Sensor Control Unit 2 are the Beam Sensor Units 2d and 2e Bisecting this rect US 6 750 787 B2 13 angle longitudinally are the two center alignment beams 1j and 2h
62. th to maximize the accuracy of the vehicle traffic measurements to be made The Control Display Subunit 3 also contains a Control Display Subunit Download Connector 3j female DB9 an accessory Down load Interconnect Cable 3k male female DB9 compatible with the DB9 pin out configuration on the serial port of PC IBM compatible computer equipment and an optional Data Transmitter 37 which optionally transmits selected data from the Data Recorder 3 on the Data Transmittal RF Wave 3m to a remote location FIG 3 presents a slightly more detailed internal arrange ment of preferred subcomponents within the Beam Emitter Unit 1 than was shown in FIG 2 Standard electronic hardware subcomponents of current commercially available state of the art electronic technology are used as Beam Emitters designated as the Left Beam Emitter 1 the Right Beam Emitter 1d and the Center Beam Emitter Li which is used only for system installation alignment purposes to generate the respective low power visible wavelength laser Light Beams 1g 1 and 1j Low power lasers avoid the safety problems to humans and animals associated with higher power lasers It should also be noted that visible wavelength laser beams are not truly visible to the unaided human eye and become visible only when striking a particle having mass in its path The Beam Emitter Unit Assembly Box 1a contains a Beam Emitter Unit Power Source 1b to power the three laser Beam Emitters 1c 1
63. tric transistors are still more widely used in many commercial applications in controlling and safety proofing the operation of manufacturing machinery The Beam Status Discriminator 3e serves as a sub Processor at the interface between the two Beam Sensors 2d and 2e and the Control Display Micro Processor 3d The Beam Status Discriminator 3e discerns which of the two Light Beams 1g and 1h entering the Sensor Control Unit 2 was interrupted first and therefore identifies whether the vehicle was traveling from left to right or right to left relative to the Light Beams 1g and 1 entering the face of the Sensor Control Unit 2 Whenever the left Light Beam 1g is interrupted OFF the Control Display Micro Processor 3d adds a unit count to the cumulative total counter of the vehicle traffic being mea sured So as not to count each axle on a passing multi axle vehicle as one vehicle the programmed logic in the Control Display Micro Processor 3d does not count any further interruptions of the Left Light Beam 1g for one second after the first axle is counted thus allowing ample time for multi axle vehicles to pass through the measurement system and be counted properly as only one vehicle Secondly the beam interruption signals received by the Beam Status Discriminator 3e are converted most simply in determining in which direction the measured vehicle is traveling at the time of the measurement Using the simple comparison logic that if the left b
64. tten page The switches windows buttons status lights and displays pro vide the person installing and aligning the Optronic System with the means of control for activating and initializing the system for identifying the measurements to be performed for testing the functionality of the system after the system has been installed at a measurement location for diagnosing installation errors for monitoring the traffic data as it is being measured for recording data at each set of individual vehicle measurements and at points of special interest and for optionally causing the measured data to be transmitted to a remote location e g to a camera or mobile speed display for further use such as by law enforcement officials FIG 9 shows the general arrangement of the wiring system within and between the elements and units in the Sensor Control Unit 2 which enables the sensing processing displaying and downloading of the traffic mea surements which can be made with the Optronic System The electrical interfaces between the functional elements within the units comprising the Sensor Control Unit 2 are conducted through the wires within the units and wire cables between the units The wiring components are standard state of the art insulated wires and multi strand wiring cables with connectors and are of sufficient quality off the shelf to assure the accuracy of the electrical signals gener ated by sensors within the Optronic System In a
65. urface is at a grade the plane of the beams must be at the same grade It is relatively important that the height of the two parallel Light Beams 1g 1 are equidistant above the street surface so that whatever physical feature of the passing vehicle e g the front bumper a front fender the leading edge of a wheel the manufacturer s hood ornament the bolt head on the front license plate holder etc interrupts the first beam will be the same physical feature of the passing vehicle which interrupts the second beam The height of a vehicle axle typically about seven to eight inches above the road surface is the preferred height for the plane of the Light Beams 1g and 1h above the road surface A typical minimum height for the plane of Light Beams 1g and 1h above the road surface is about four inches If the road surface between the placement of the Beam Emitter Unit 1 and the Sensor Control Unit 2 has a crown curvature then the plane of Light Beams 1g and 1h preferably clears the surface curvature crown by a minimum of about four inches Because the Light Beams 1g and 1 are not visible to vehicle operators without having eye optical aids approaching the Optronic System installed at the sides of a street the vehicle operators will pass through the measuring location without prior knowledge of their motion being detected and recorded This will produce much more unin fluenced traffic measurement data for traffic engineer
66. ust be considered by traffic engineers in their analysis of the measured vehicle velocity data The placement of two tubes physically across a street is recognized to have several other undesirable features some of which are 1 affixing the tubes on the street surface is a hazardous operation for the installing technician when the vehicle traffic is not safely detoured around the installation 2 the tubes are at times dislodged from their attachment to the street surface and lose their reference distance and parallelism calibration 3 the tubes are damaged too often by passing vehicles especially by some speeding motorists who maliciously apply heavy braking or skidding as the wheels of their vehicles pass over the tubes 4 the visual detection of two tubes across the street often causes vehicle operators detecting the tubes from a distance to slow down before passing over the tubes which influences the veloc ity data measurement and 5 there are several possible error sources in the pneumoelectronic hardware components and pressure sensing interpretation producing data of ques tionable accuracy Another source of inaccuracy in the measured and calcu lated velocity of a vehicle occurs when the two tubes are installed across the street such that the Drep through which the vehicle passes is not the same as the used in the calculation of the vehicle velocity Human error is always possible and the installing technician may
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