US 3516056 A
Description (OCR text may contain errors)
June 2, 1970 MATTHEWS 3,516,056
TRAFFIC CONTROL SYSTEM Filed Nov. 10, 1966 32 3s 25 n AI RA! 7o 80 24 33) 43 2s TAZ 1 RAZ f2 Tsl zngous FILTERS I -fl 2: 30) 34/ g 2 el RBI' f2N- :1? 23 3| 357 ,24 DATA f4 PROCESSING 92 52 I EQUIPMENT 1 so FIG. 4 22 v T I (RALRAZ) 24( 'T R 2| A|,A2, B 2 T R v \\42 (T T 2) INVENTQR DAVID R. MATTHEWS United States Patent 7 US. Cl. 34038 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an optical system for surveying tratfic conditions along a roadway. Light transmitting and receiving means are positioned above the roadway such that the respective emission and acceptance of predetermined volumes of light energy intercept at a given distance above the surface of the roadway. The interruptions of either the emission, the acceptance or of both volumes of light energy by passing vehicles will be sensed by the receiving means and will thereby provide information regarding the passing vehicles. Specific information obtainable from this system relates to vehicle count, stream acceleration, density, space between vehicles and lane occupancy.
This invention relates to a traflic control system and, more particularly, to an optical trafiic control system for surveying traffic conditions along a roadway.
The detection of vehicles for trafiic control purposes presents an extremely complex problem, particularly when more information is desired than a simple vehicle count. From a technical standpoint, any proposed system must be evaluated in terms of component parts which usually comprise some type of sensor, a data transmission complex and a centralized data processing station. Pertinent evaluation guidelines include the ability to install the system on the roadway without cutting into any existing road surface, the ability to replace units without the destruction of road surfaces, the ability to replace units rapidly with a minimum time of interrupted traffic flow at that point, the ability of the system to operate during both the day and the night, the ability of the system to operate under varying weather conditions, the reliability, maintainability and accuracy of the system and, of course, the initial, installation, replacement and maintenance costs.
A number of systems have been proposed heretofore for'utilization in traffic control environments. These systems can be generically classified as the magnetic field system, the radiometry system, the radar system, the sound system, the nuclear system, the pressure sensor system, the television scanning system and the interrupted carrier system.
Each of the presently available systems suffer from one or more of a number of disadvantages which serve to render their utilization somewhat impractical in a traffic control system. The operating disadvantagesof the various systems are generally hardware oriented, although some of them fail in basic concept. For example, magnetic detection units are customarily embedded in or under the roadway which necessitates destructive installation and, possibly, destructive maintenance. The system is subject to error because of random distribution of iron within the vehicle being counted. Thus, a truck with many 'axle's and a wooden bed may well be detected as a number of cars. Additionally, the increasing tendency to fabricate vehicles from materials such as aluminum and Fiberglas will, in all probability, render this system-of slight utility in the future.
The radiometry system detects vehicles by micrcowave and infrared radiometers. The signals consist of the presence or absence of thermal power and the output produced 3,516,056 Patented June 2, 1970 is dependent on many conditions in the sensed environ ment. Output signals are low and require the use of relatively expensive amplifiers. Additionally, the presence of snow upon the road surface renders this type of system totally inaccurate.
Radar systems can detect vehicles and velocity by Doppler operation. Vehicle length, however, is quite inaccurate for given car-truck counts and velocity measurements are highly inaccurate in low speed, stop-and-go situations. The installations are extremely expensive both with regard to installation and maintenance.
Sound may be utilized for vehicle count and velocity measurements. The pulsing frequency of a sonic detection system, however, does not permit time-headway measurements of desirable accuracy, particularly in the higher speed ranges. When more than one lane is involved, the detection and data discrimination functions become extremely diflicult to execute because of cross talk. While the data transmission from such a system can be accomplished via the utilization of telephone lines, each lane requires a separate line unless the data is processed at the remote station.
The nuclear detector is an integrating device which requires a strong source for the short integrating periods imposed by the flow of traffic. The vehicle modulates detector input by the blocking eflfect of metallic volumes. This, of course, requires that the nuclear source be located in the pavement. The strength of the source required for installations of this type is highly dangerous and, thus, this system has not proved satisfactory.
The pressure sensor system is simple in nature, but must be placed or embedded within the pavement, thus requiring destructive installation and replacement. Snow and ice accumulations on the roadway render sensors of these types inoperative. Further, these sensors are primarily axle counters and are inaccurate, therefore, for unit vehicle counts.
' Television camera scanning systems depend on the differential signal generated by the pavement or roadway and the passing vehicle. This renders the problem of signal detection extremely difiicult. For example, the signal will change fromiplus to minus repeatedly for some arbitrary reference, as the vehicle passes through the scan beam. It will change for the same type of vehicle with variations in paint color, glass, chrome and the amount of dirt on the surface. Likewise, the signal will change in rain, snow, sunlight and darkness. Further complicating the problem is the affect of vehicle headlights when attempting to detect vehicle length and velocity. The energy striking the pavement in front of the vehicle will cause the vehicle to appear extremely long and,in cases of heavy traffic, will cause the detection system to invert headway and vehicle length measurements. In short, the complex techniques required in the operation of the detectors and in signal processing for a system of this type virtually void its use- 7 fulness.
The interrupted carrier system produces a continuouswave signal that is interrupted by the presence of a vehicle.-
rier system appears to possess characteristics which satisfy universal evaluation criteria for traffic monitoring'systems 1 more effectively than any of the other existing systems,
no device has been proposed heretofore which utilizes characteristics of the interrupted carrier technique to maximum advantage.
More particularly, it is an object of this invention to provide a system of the type described which may be installed on an existing roadway or a roadway under construction without embedding any of the operative components into the road surface.
Similarly, it is an object of this invention to provide a system of the type described wherein the sensing units may be removed and replaced without destruction of the road surface and, thus, with a minimum time period of traflic interruption at the sensing point.
It is an object of this invention to provide a traffic surveying and control system whose efliciency will be unaffected by changes from daylight to nighttime operating conditions.
It is an object of this invention to provide a system which is capable of operating effectively despite the presence of snow, water and the like on the road surface.
It is yet another object of this invention to provide a trafiic surveying and control system which may be utilized in conjunction with a central data processing station, thus eliminating the necessity of processing the data at the sensing site.
It is an object of this invention to provide such a system wherein the data may be transmitted from the sensing station to the centralized data processing station via a single conventional telephone line, regardless of the number of lanes on the roadway being monitored.
It is an object of this invention to provide a trafiic surveying system which has a high degree of reliability, is easily maintained and which is capable of furnishing accurate information with regard to vehicle count, vehicle length, car count, truck count, volume, speed, acceleration-deceleration and headway.
It is additionally an object of this invention to provide a system of the type described wherein the initial costs, installation costs, replacement costs and maintenance costs are minimized.
These and other objects of this invention will be readily understood by reference to the following specification and accompanying figures in which:
FIG. 1 is a schematic view illustrating the manner in which the sensing and detecting units are positioned with respect to the roadway for an examplary two-lane traffic surveying system;
FIG. 2 is a schematic, front-elevational view of the sensing and detecting stations;
FIG. 3 is a schematic, side-elevational view of the sensing and detecting stations; and
FIG. 4 is a schematic diagram of the sensing and detecting stations, indicating the manner in which the data therefrom may be transmitted to the centralized data processing center.
Briefly, this invention comprises a light transmitting means for emitting a beam of light energy having a predetermined volume of emission and a receiver means having a predetermined volume of energy acceptance. The transmitting and receiving means are positioned with respect to the pavement such that their emission and acceptance volumes intersect at the surface of the particular lane on the roadway with which they are associated and, additionally, such that either the emission volume, the acceptance volume or both such volumes are interrupted by vehicles passing therealong. Preferably, the light transmitting means comprises a nonlasing optical diode source operating in the infrared region whereby the sensing system will not promulgate hazardous driving conditions during the nighttime.
Depending upon the particular types of information sought it may be desirable to utilize two such transmitters and receivers for each lane being surveyed, the trans-- mitters and receivers being arranged such that the intercept volumes on the surface of the road and the source form a right triangle whereby a vehicle traveling in one upon which it will be assumed, for purposes of illustration, that the traffic is traveling in an identical direction indicated by the arrows 10. A conventional superstructure having standards 21 and a cross member 22 is positioned as indicated to provide an elevated platform upon which various components of the invention may be po itioned. The height of cross member 22 may, for example, be in the range of 15 to 25 feet above the roadway surface.
As indicated in FIG. 4, each of the lanes has operatively associated therewith two infrared laser transmitters and two receivers. Thus, lane A has transmitters T and T and receivers R and R positioned such that their respective volumes of energy emission and energy acceptance intersect at points on the surface of lane A. Likewise, lane B has transmitters T and T and receivers R and R similarly positioned. The Nth lane, as illustrated in FIG. 4, has transmitters T and T and receivers R and R positioned identically with respect thereto. Thus, while only two lanes are illustrated in FIG. 1, it will be apparent to those skilled in the art that the teachings disclosed herein may be applied to a roadway containing any number of lanes. For multi-lane installations, the transmitters and receivers may be located together. Thus, as illustrated in FIGS. 1 and 4, package 23 contains the two transmitters T and T only; package 24 contains transmitters T and T as well as receivers R and R132; and package 25 contains receivers R and R only.
As illustrated in FIG. 1, the transmitter T transmits a predetermined volume of emission energy 30 towards section 34 of the road surface. The field of view or volume of energy acceptance 40 of receiver R is similarly confined and, also, intersects the road surface 50 and the energy emission volume 30 at the positions on the road indicated by the reference numeral 34. Similarly, the energy emission volume 31 of transmitter T and the energy acceptance volume 41 of receiver R intersect at the point on the road surface delineated by the reference numeral 35; the energy emission volume 33 of transmitter T and the energy acceptance volume 43 of receiver R intersect at point 37; and, the energy emission volume 32 of transmitter T and the energy acceptance volume 42 of receiver R intersect at point 36. Beams 31 and 41; 33 and 43 may be vertical the same as 30 and 40; 32 and 42 and displaced upstream a distance D as illustrated by the distance between areas 34 and 35 or 36 and 37.
While the preferred embodiment of this invention will be illustrated utilizing associated transmitter and receiver components having converging fields of view, it will be appreciated readily by those skilled in the art that coaxial systems could also be utilized for single lane operation.
Each of the transmitters consists of an energy source, chopper, optics and an enclosure. The energy source may be a quartz bulb with an IR transmitting filter or an IR injection laser diode which emits radiation at approximately 9000 angstroms with a 200 angstrom bandwidth. Other suitable types of light sources such as a spontaneous emission diode or more conventional light-generating device may also be utilized. The laser sources are preferable since they inherently permit the energy emission volume to be confined within relatively small limits.
If a quartz bulb is utilized, the chopper may be a mechanical rotating disc or a vibrating reed. In the case of an injection diode, modulation will be obtained by varying the input power. The purpose of operating in the IR regions of the electromagnetic spectrum is to prevent visual identification of the detection system during the nighttime. Any beam of visible light, however dim, would produce a lighted spot on the pavement which might lead to evasive or cautionary maneuvers by motorists, resulting at best, in a disruption of the traffic flow. The transmitted beam is collimated to approximately a one-degree beamwidth by the optical section. Conveniently, an index mark may be provided on the external package to indicate the beam centerline as an aid to installation since the energy emitted is not visible.
The receiver sections of the detection unit may comprise a suitable solid state detector, receiving optics and a signal amplifier. The receiver optics may also have approximately a one-degree field of view or energy acceptance. The volume of energy acceptance of a particular receiver will be directed, as pointed out previously, to intersect the volume of energy emission from the associated transmitter at a specified area on the road surface.
Since the transmitters and their associated receivers are permanently directed such that the road surface 50 lies within the intercept volumes, the receivers will constantly detect a signal from their associated transmitters when the system is in operation except during periods when either one or both of the associated energy transmission and acceptance volumes are interrupted by the passage of a vehicle through the sensing station. The frequency of the received signal will depend, of course, on the frequency of the signal transmitted from the associated transmitter.
The presence of an object within the intercept areas of a particular emission volume and its associated acceptance volume causes the signal to disappear at the associated receiver.
Referring now additionally to FIGS. 2 and 3, it will be noted that the positioning of the transmitters and receivers positively prevents a vehicle traveling in one lane from interrupting the carrier waves of another lane regardless of its height. As illustrated in FIG. 2, assume that the phantom lines 51, 52 and 53 represent the heights of a car hood, a car top and a truck top, respectively. It will be noted that line 51 representing the car hood falls above the crossover point of emission volume 32 and acceptance volume '42 (similarly with volumes 30 and 40). If a reflective surface of a vehicle were below this crossover point, the signal would be reflected from the vehicle rather than the roadway and give an erroneous indication. The increased height of the vehicle results only in the interruption of the associated emission and reception volumes at points closer to the transmitters and receivers.
If it were necessary only to count the number of vehicles passing a given point, only one set of energy emission and acceptance volumes would be necessary for each lane. Thus, the system, as illustrated in FIG. 2, would suflice for this purpose. Information could not be computed with desired accuracy from this system, however,
pertaining to vehicle speed, length and the like, at least not without assuming a typical vehicle length. In order to resolve such information with the present system, it is necessary that each of the lanes be provided with two intercept areas. With the arrangement shown in FIG. 3, which schematically represents lane B of the roadway shown in FIG. 1, the bumper of an approaching vehicle will initially intercept emission volume 33 and acceptance volume 43. The second intercept (with emission volume 32 and acceptance volume 42) will also occur at the bumper because of the vertical orientation of this intercept line. As pointed out previously, each of these intercepts will blank the signal being received by the associated receiver and, thus, indicate that a vehicle has passed over the particular intercept point. The speed of the vehicle may be calculated from the time differential of intercept with the two sets of emission and acceptance volumes as indicated by the receiver output. Minor varianal discrimination networks.
tion 56 which exists in bumper height between varying types of vehicles will cause little error because of the vertical orientation of emission volume 321 and acceptance volume 42. Of course, the transmitter-receiver components for each lane could be mounted on separate spaced platforms and have both sets of beams oriented vertically as beams 32, 42.
A large truck, having a height 57 as indicated in FIG. 3, will continue to intercept volumes 33 and 43 until the rear of the truck is a distance D from the initial bumper intercept point. The angle 6 should be chosen such as to make D equal to the shortest distance a vehicle might possibly be following a truck. This, of course, prevents missing the second vehicle in the data processing scheme. The time difference between initial intercepts of volumes 33 and 43, coupled with the derived velocity information, will provide a relatively accurate indication of vehicle headway. The time that a particular vehicle intersects volume 32, 42 coupled with the vehicles speed, as computed from the intercept time differential, will be a relatively accurate indication of the length of the vehicle. From the length, it may be easily determined whether the passing vehicle was a car or a truck. Acceleration and deceleration will be determined, of course, by the relative speeds of the passing vehicles.
Referring now specifically to FIG. 4, the chopping frequencies of the transmitters should be chosen for simultaneous transmission on a single telephone line to the data processing center 90. This, of course, requires that 2f f so that harmonic generation due to signal distortion will have no effect on the data detection and sig- With crystal-controlled choppers such as the injection diode, more than six lanes of data can easily be transmitted over a single class 3 telephone circuit without multiplexing or synchronizing circuits.
After transmission along telephone line 70 to the central processing center, the data is fed into a filter network where it is again resolved into frequencies f through jf From filter 80, the data is fed into a suitably programmed computer, indicated generally by the reference numeral 90. By way of example, if energy emission volume 32 and energy acceptance volume 42, generated by transmitter T and receiver R respectively, are not interrupted by a vehicle passing on lane A, the computer will receive a signal of frequency f The moment, however, that a vehicle passes adjacent intercept area 36 and, thus, interrupts energy emission volume 32 and/or energy acceptance volume 42 such that the two no longer intersect, receiver R will cease receiving signal f and the absence of this signal will be transmitted via telephone line 70 and filters 80 to the computer 90. Within the data processing and computing equipment 90, the continuance and discontinuance of the signals on the various lines is continually processed according to a predetermined program to determine the vehicle conditions on the various lanes of theroadway being monitored. From the resultant data, highway engineers can determine the advisability of opening lanes to travel in the opposite direction, building new roads and new interchanges and the like.
As noted previously, the embodiment of the invention illustrated in FIG. 1 assumes traffic to be traveling in the same direction in both lanes A and B. It will be obvious, however, to those skilled in the artthat the information relative to trafiic traveling along the lanes in the opposite direction may be provided by merely rotating the transmitters and receiversv associated with the particular lane such that the vehicle initially intercepts those energy acceptance and transmission volumes which are slanted with respect to the direction of vehicle travel 10. Thus, a single overhead cross member 22 may span six lanes of trafiic traveling in opposite directions and the equipment positioned on them arranged such as to provide the desired trafiic information accurately with respect to trafiic traveling in both directions.
The area of the roadway 50 which the transmitter illuminates with infrared radiation should be somewhat smaller than the receiver field of view in order to receive a signal from 100% of the transmitter power and to obviate somewhat the critical alignment features of both fields of view. For example, the receiving field of View or, volume of energy acceptance may be approximately 12 inches in diameter at the roadway surface. With such an arrangement it will be readily apparent that the presence of snow, ice or merely bare pavement at the intercept area of the associated transmission and acceptance volumes will not materially interfere with signal transmission from-transmitter to receiver. There will be, of course, some noise but the signal-to-noise ratio may be kept at acceptable standards by the choice of components. Under extreme conditions of fog or other causes of low visibility, the desired signal path from transmitter to roadway and back to receiver may be augmented by double scattering in the atmosphere, Some of this power will be effected by the vehicles to be detected and some not. This eflFect, however, will be present only under severe limitation of visibility wherein the system may be inoperative due to the low signal-to-noise ratio or the vehicle data will not be useful due to low trafiic velocity. This will occur only, however, under extreme conditions and, therefore, it does not present a major system drawback since few vehicles -will be traveling on the roadway. While a preferred embodiment of this invention has beenvdescribed in detail, it will be readily apparent to those skilled in the art that other embodiments may be implemented without departing from the spirit of the teachings set forth in this specification and the accompanying drawings. Such other embodiments are to be deemed as included within the scope of the following claims unless these claims, by their language, expressly state otherwise.
I claim: 1. Apparatus for optically surveying trafiic along a roadway comprising:
first light transmitting means for emitting a beam of light energy having a predetermined volume of emission; first receiver means having a predetermined volume of energy acceptance, said transmitting and receiving means angularly positioned above said roadway such that the light energy will be reflected from said roadway into said receiver means with the cross-over point of the volumes of emission and acceptance located below the reflective surfaces of a vehicle, said receiver means differentiating between the continuous and the interrupted passage of said beam of light energy from said transmitting means; and means responsive to the interruption of said volumes for indicating information regarding vehicles passing along said roadway. 2. The apparatus as set forth in claim 1 which further 8 comprises second light transmitting and receiver means having their volumes of energy emission and acceptance directed to intersect at a point on said roadway removed from the point of intersection of the energy volumes of said first transmitting and receiver means.
3. The apparatus as set forth in claim 2 wherein said point of intersection of the energy volumes of said first transmitting and receiver means and said remote point are in the same lane of said roadway.
4. The apparatus as set forth in claim 3 wherein said energy volumes of said first transmitting and receiver means are directed toward said lane-in a direction ap proximately perpendicular to the path of travel of traflic therealong and wherein said remote point lies rearwardly therefrom.
5. The apparatus as set forth in claim 4 wherein said first and second transmitting means are positioned adjacent each other above the roadway at one side thereof and wherein said first and second receiver means are positioned above the roadway-and to the other side thereof.
6. The apparatus as set forth in claim 3 wherein the volumes of emission of said first and second transmitting means are chopped at differing frequencies whereby the signals emitted by said first and second receiver means may be discriminated.
7. The apparatus as set forth in claim 2 wherein the volumes of emission of said first and second transmitting means are chopped at differing frequencies whereby the signals emitted by said first and second receiver means may be discriminated.
8. The apparatus as set forth in claim 6 wherein said roadway comprises a plurality of lanes and wherein each said lane has associated therewith separate first and second transmitting means and first and second receiving means, the chopping frequencies of all of said transmitting means differing whereby the signals emitted by all said receiving means may be discriminated.
9. The apparatus as set forth in claim 7, which further comprises a remote data processing center and wherein said chopping frequencies are within the audible frequency range whereby said signals may be transmitted to said center over the same telephone line.
10. The apparatus as set forth in claim 1 wherein said light transmitting means comprises an optical diode source adapted to emit energy within the infrared spectrum.
References Cited UNITED STATES PATENTS THOMAS B. HABECKER, Primary Examiner C. M. MARMELSTEIN, Assistant Examiner U.S. Cl. X.R. 250222