US2521683A

US2521683A - Traffic detection apparatus

Info

Publication number: US2521683A
Application number: US542729A
Authority: US
Inventors: John L Barker
Original assignee: Eastern Ind Inc
Current assignee: Eastern Ind Inc
Priority date: 1944-06-29
Filing date: 1944-06-29
Publication date: 1950-09-12
Anticipated expiration: 1967-09-12

Description

Se t. 12, 1950 J. L. BARKER mmxc DETECTION APPARATUS UNE OLPEII 6H! EIEI.

2 Sheets-Sheet A INVENTOR. film L flar/fzr Filed June 29, 1944.

pt. 12, 1950 J, BARKER 2,521,683-

TRAFFIC DETECTION APPARATUS Filed June 29, 1944 2 Sheets-Sheet 2 ""1 E9 5 ,w J 1 i} I iaarm mm REL/n 0 B l 007F117 mom T TIM/V6. Rec. am. INVENTOR.

John L. Barker BY M, M V

Patented Sept. 12, 1950 2,521,683 TRAFFIC DETECTION APPARATUS John L. Barker, Nor-walk, Conn., assignor, by

mesne assignments, to Eastern Industries, Incorporated, a corporation of Delaware Application June 29, 1944, Serial No. 542,729

18 Claims. 1

This invention relates to improvements in ultra high frequency signalling apparatus, and particularly to an improved means for using ultra high frequency electro-magnetic or radio waves for periodically examining trafllc conditions along one or more rights of way to detect the presence of vehicles thereon.

The invention is particularly useful in the control of vehicular trafllc at intersections of two or more roadways according to the tramc conditions prevailing thereon, although it will be apparent from the ensuing description that the invention is capable of many other applications.

Automatic trailic control systems may be classifled into two broad groups: flxedtime sequence systems and trafllc-actuated systems. The ordinary stop and go" installations employing signals for street traffic control and regulated by a timing device which exhibits the, signals in a fixed-time sequence irrespective of traffic conditions in the streets, are inefflcient in that the stop signal is frequently displayed against streets having moving trafllc, and right of way is given to an intersecting street on which there are no waiting vehicles. The second broad classification includes systems whereby the time cycle of right of way on a traihc lane is initiated or modified by electrical impulses created by the passage of moving traillc over a contactor or other roadway installation and conveyed by a cable installation or the like to a detecting apparatus wherein the traffic conditions are analyzed and right of way given as most appropriate to the particular condition.

The latter traffic control system has a fault in that the impulse generating stations are best located, to meet an average traiflc condition, at locations relatively distant from the intersection, and may thus fail to provide for local conditions in which an alley or infrequently used driveway enters the street between the position of the actuator and the intersection.

A feature of the present invention resides in the employment of means whereby roadwayembedded signal actuators, or other contactors requiring permanent cable connection with the traflic detection system, are supplanted by-ultra high frequency transmission and detection apparatus which detects vehicle activity over a relatively large zone in as many rights of way as the location requires.

Another feature-of thepresent invention re.- sides in its ability to periodically explore traffic conditions along one. or more of several traffic lanes in a time sequence which may be regulated as desired.

Accordingly. the present invention embodies means for periodically testing traflic conditions along one or more rights of way and utilizing the detected presence or movement of vehicles to institute such traffic control asis desirable for the existing trafl'lc condition in the said right of way.

It is well-known that ultra high frequency or hyper frequency radio waves have quasi-optical characteristics in that such waves may be transmitted from a wave guide along alane of relatively narrow width and will be reflected in substantial measure from metal or other surfaces of an object which comes within the path of the transmitted waves.

The high frequency waves, which are advantageously of a frequency capable of transmission by wave guides, may be suitably generated and projected, by means of a suitable antenna and wave guide, in a relatively narrow directional beam or pattern. The wave reflected from a vehicle in the lane may be intercepted by the same wave guide and antenna, or the transmis sion and reception means may be separated. as desired. In either method of operation, the time spacing between the instant of transmission of a wave and the instant of reception of the reflected' portion of the wave is compared to establish the distance of the reflecting surface from the transmitter, assuming negligible relative distance between transmitter and receiver.

Operational advantages result from the use of a frequency modulated system embodying transmitting a frequency modulated ultra high frequency wave and beating the reflected wave against the transmitted wave, with a resultant beat frequency which is characteristic of the distance of the reflecting surface from the transmitter-receiver unit. The transmission and reception apparatus may be arranged for continuous or intermittent transmission, as desired, it being .understood that the period of transmission along the traffic lane is of such duration as to afford adequate comparison of the transmitter and received-reflected wave for operation of devices responsive to the beat frequency. The output from the transmitter-receiver unit may be amplified and utilized to operate a relay or like device in a frequency selective circuit to actuate apparatus responsive only to ab'eat frequency or beat frequency range corresponding to the desired vehicle detection distance in the trafllc lane.

As previously mentioned, the invention contemplates the periodic testing of traflic conditions in one or more lanes, by the projection of ultra high frequency electromagnetic waves along said trafiic lanes. Operation is simplified by the continuous generation of said ultra high frequency wave and a periodic gating of the wave guides, so that transmission-and reception of a reflected wave-may be accomplished, at a particular instant, only through selected wave guides, the remainder being non-transmitting during such instant. Y

For traflic detection purposes, in which the apparatus is exposed to the elements and must operate under adverse weather conditions and in remote locations, it is desirable to use means for creating an electrical reflecting surface within the wave guide or directional burn from which transmission of the ultra high frequency wave is to be prevented at a particular instant or period.

Accordingly, a preferred form of the present invention contemplates the employment of a twoelectrode gaseous tube disposed within the wave guides or the directional horns thereof. By impressing a voltage across the electrodes of the tube, the gaseous content thereof is ionized, creating a highly effective reflecting surface across the Wave guide. By suitable timing means the wave guide or horns thereof may be so gated that transmission and reception of the radio waves may be had at a particular instant only through preselected horns of the installation.

'By correlating with the gate timing means, means for connectin the amplified resultant of the compared transmitted and reflected waves to an electrical apparatus allocated to the born or horns which are transmitting, the plurality of streets or traffic paths may be periodically examined and the intelligence conveyed by the combined transmitted and received wave may be utilized as desired.

It is therefore an object of the invention to provide apparatus which by means of ultra-high frequency electro-magnetic waves may be used to detect the presence of vehicles in a plurality of trafiic lanes.

It is a further object of the invention to provide improved means whereby an ultra-high frequency wave may be successively projected in different directions by means of a wave guide having appropriately directed horns and gate means which permit transmission from the respective horns of the wave guide according to a predetermined timed sequence.

It is still another object to utilize a common transmitting and reception unit having means for successively projecting an ultra high frequency or hyper frequency wave along predetermined trailic lanes and receiving a reflection of said wave from a vehicle or the like in the trafllc lane along which the wave was projected.

It is another object of the invention to employ a wave uide or equivalent for beaming ultrahigh frequency electromagnetic waves periodically and successively along specified tramc lanes, and to compare the transmitted wave with a wave reflected from a vehicle thereon to determine the distance of such vehicle from the transmitter station and to appropriately operate a relay or the like which is allocated to the trafilc lane from which the reflected wave originated.

In the accompanying drawings, which show various embodiments of means for accomplishing the objectives of the invention:

Fig. 1 is a diagrammatic representation of intersecting highways, at the center of which is disposed ultra high frequency transmitting and detecting equipment embodying the instant invention;

Fig. 2 is a representation of one form of multihorn wave guide, the directional horns of which are individually equipped with gate means; the figure also shows schematicallya mechanically actuated timing switch by means of which the respective gate means'are successively operated and a relay device serving a particular directional horn is connected into the receiver circuit coincident with the periods of transmission of the said horn;

Fig. 3 is a plan section of a horn of the wave guide taken on lines 3-3 of Fig. 2;

Fig. 4 is a similar plan section taken on lines 4-4 of Fig. 2;

Fig. 5 is a schematic representation of a gated transmitter horn and a gated receiver horn arranged as individual units;

Fig. 6 is a representation of the periods of operation and non-operation of the respective gates of a four-horn installation during one complete operative cycle and corresponding operative periods of the output-actuated devices;

Fig. 7 is a circuit diagram of an electronic sequence or timing switch, as applied to a two-gate installation; and

Fig. 8 is a schematic representation of a multihorn wave guide utilizingtwo gates for controlling transmission therefrom.

The following description is illustrative of an application of the invention to vehicular traffic control installations. It is to be understood that the two street interesection of Fig. 1 is not used in a limiting sense; the invention may be applied to traflic intersections of more complex character, and has application to many trafiic control situations not involving intersecting highways.

, Referring to the drawings, the intersecting highways schematically shown in Fig. 1 are designated N, E," S, and W respectively. Disposed at a suitable elevated level at the intersection as by an arm [2 carried by a standard I, is an oscillator-receiver unit In associated with which is a multi-directional wave guide II. It will be understood that Fig. 1 is grossly out of scale, and the depicted angle of equipment with respect to the roadway is not representative of installation practice.

The wave guide II has directional horns HN, H HE, HW, so arranged that an ultra high frequency wave emanating therefrom will be projected along the approaching traffic lane of the respective highways. The height of the wave guide above the intersection and the relative angle of the horns thereof with respect to the roadway will largely determine the distance from the intersection, of a substantially clearly defined zone within which an approaching vehicle will come into the effective field of the high frequency wave projection.

It will be understood that this zone may be selected as demanded by local conditions. For example, where an alley or driveway enters a highway at a relatively short distance from the intersection, it would be most desirable to be able to detect the presence of vehicles entering the highway therefrom, and the ultra high frequency zone would be established to include the point of entry of such alley or driveway. Conversely, and particularly on parkway installations, there may be no points of entry to the highway for a considerable distance. and the average speed of ve- 8 hicular trafllc may be greater. Accordingly. the none of detection may be disposed at a relatively greater distance from the detector unit.

R f rrin now to Fig. 2 an oscillator-detectoramplifler unit it may comprise any suitable apparatus by means of which an utra-high frequency or hyper-frequency oscillation within a range capable of transmission by wave guides may be transmitted and a reflected wave compared therewith. Unit 10 includes an antenna it dis posed within a chamber II at the base or the wave guide it. Said wave guide may comprise a vertically extending rectangular metallic tube ii, at the upper end of which are the directional horns rm, HW, suitably positioned beneath HS and EN. By suitably flaring the ends of the said horns, a narrow beam having desired directional properties may be projected along the approaching right of way of the respective highways. A flare angle of fifty (50) degrees, for example, is known to aflord a good directional pattern for the transmitted waves The horns HN and HS which, in the installation shown, conduct the electromagnetic wave about an angle, may have appropriate configuration, as at 26 and ti, see Fig. 4.

In the four-horn embodiment of Fig. 1, each has a resonance chamber within which is disposed a gaseous tube which functions as gate means for the horn. Said tubes in the East and West horns are designated TE and TW; and it is understood that the North and South directed horns are provided with gate tubes, which may be identified as TN and TS respectively.

It is contemplated that trafllc conditions will be mriodically explored along the individual highways, or simultaneously along pairs of highways, such as NS, or EW. Taking as an example of operation, the testing of the presence of traftie in individual highways, Fig. 6 shows a cycle diagram in which is shown in double line, the periods during which the respective horns are nontransmitting, and in single line the portion of the period of transmission of a horn during which the relay or like device allocated to said transmitting horn is connected into the output circuit of the transmitter receiver.

For energizing selected gates according to the desired time schedule there may be employed a timing or sequence switch, of which 22, Fig. 2, is a schematic representation of a mechanical timer. A motor 23, of adjustable speed, or operating through adjustable speed transmission, is organized to rotate a, shaft 24 at a desired rate of speed. The shaft 2% terminates in a cam 25. desirably of di-electric material, and operatively associated with switches individual to the respective gates. Said switches are designated SE,

-SS, SW, and SN respectively; and each may comprise a movable contact 26 biased toward the cam and functioning as a cam follower, and a fixed contact 2'5. Said switches may be in circuit with the respective gates as shown in Fig 2 with the power source 28 and resistances 29 such as to provide sufllcient ionization of the gate tubes for reflecting the electromagnetic waves.

The cam 25 is so conflgurated that over successive periods of approximately cycle the circuit to each of the gates will be open, the circuit to other of the gates being closed. Hence, assuming a continuously generated ultra high frequency electromagnetic wave. the said wave may be projected through only such of the horns as is desired by closing the circuit to the gates oi the other horns.

A complete cycle of operation of each of the horns may comprehend such time period as is desired. As. an example, a periodic examination at the rate of one cycle per second should be sufllcient for usual vehicle activity. During the interval when an open gate permits of operation of I a horn, it transmits the utra high frequency wave and receives the wave which may be reflected from a vehicle in the tramc lane served thereby.

In the circumstance of using a frequencymodulated transmission system, and the comparison of transmitted and reflected waves" by beating the latter against the former to obtain a beat frequency characteristic of the distance of the reflecting vehicle, the antenna I6 is in circuit with receiver-amplifier means in housing l0, and the amplified signal, converted to audio-frequency range, may be conducted by output leads 30, 3|, through timer 22 to actuate electrical devices individual to the respective horns.

Said output-responsive devices, for purposes of illustration, may be relays RE, RW, RN, RS, in circuit with apparatus (not shown) which utilizes the closing of a relay circuit to operate the trafiic signal or control apparatus, counting apparatus, or warning signal devices, as desired.

The interconnection of a relay and its associated operating horn may be accomplished by a cam 33 rotated by the shaft 2| and cooperating with normally open switches RSE, RSW, RSN, and RSS comprising movable contacts and fixed contacts, arranged in any suitable manner.

The cam has a rise 33 comprehending an are slightly less than A cycle and eilfective to sequentially close the switches serving the respective relays. It is apparent that during the period when one relay switch is closed the gate switch of the corresponding horn is open, and when the horn gate switches of the remaining horns are closed, the relay switches corresponding to said horns are open. By connecting each output-- responsive device into the output circuit of the transmitter-receiver a fraction of a cycle later than transmission commences from its respective horn, and disconnecting the device prior to the changeover of transmission from said horn to the next horn, transient conditions during the changeover instant are not transmitted to the output-responsive device, and possible false" signals to said device are eliminated. In other words, operating conditions at a horn are stable during the period of connection of the relay or like responsive device.

It will be understood that during the fractions of a cycle represented in Fig. 6, the output devices may be in circuit continuously during such period or for such portion or portions thereof as desired.

Fig. 5 schematically illustrates an embodiment of the invention in which the transmitter-oscillator illll is in a unit apart from the receiveramplifler 260; each such unit has an individual wave guide Tit and RIB, and an individual antenna, (not shown). The receiving wave guide RG8 may be served by an antenna RIG, connected by coaxial cable to the unit 200.

The transmitting and the receiving waveguide terminates in a directional horn TA and RA respectively, or, as shown in dotted line, additional horns, such as TB and RB. The respective horns are gated, as shown by GA, GB, GRA and GRB, operation of which is controlled by a sequence switch 220 having cam-operated switches GSA and 688 and GSRA and GSRB, respectively. When mechanically actuated switches are used, they may be as previously described with respect to 2.

'15s: transmitted and reflected-received waves may be combined in the receiver-amplifier 200, and the amplified output from each pair of transmitting' and receiving horns connected through synchronized cam switch RSA or R83 to appropriate relays or other electrical apparatus.

Another form of wave guide, useful in a combined transmitter-receiver unit of the type shown in Fig. 2, may be as shown in Fig. '8, in which the wave guide!!! branches into individual guides IA and BB terminating in paired directional horns HNS and HEW respectively. The said branch guides are gated, and hence a single gate sumces for each pair of horns An arrangement as shown in Fig. 8, or as shown in Fig. when horns TA and TB and RA and RB are used, is useful in exploring north-south trafflc conditions as a group, or east-west traflic conditions as a group, to allocate north-south or east-west right of way as appropriate.

An electronic circuit, employing the familiar multivibrator circuit may advantageously be utilized as the sequence or time switch means for actuating the gates of the respective horns and concomitantly eifecting actuation or non-actuation of the relays or other electrical apparatus allocated to the respective gates.

As shown in Fig. 7, a multiple thermionic tube, MT, has a plate PI interconnected to grid G2: and a plate P2 interconnected to grid GI, through capacitances Cl and C2 respectively, the capacities of which are selected according to the changeover periods desired. Resistances RGI and RPI are in series with. grid GI and plate Pl respectively. Similar resistances RP2 and RG2 are in series with plate P2 and G2.

The output from plate PI is connected to gate B, and to relay A through vacuum tube circuit VTA; the output from plate P2 is connected to gate A, and to relay B through vacuum tube circuit VTB.

The grids of the respective vacuum tubes VTA and VTB are in circuit with the amplified output of the transmitter-receiver unit, in the familiar cathode follower circuit.

As is known to those familiar with the multivibrator circuit, vacuum tube MT, in the circuit shown, operates as a sequence switch, alternately causing flow of current in the respective plate circuits and consequently, in the respective gates A and B.

In the respective relay circuits, current flow in the plate circuit serving gate A makes the plate of tube VTB positive relative to the grid and cathode of tube VTB, and relay B is thereby in circuit with the output from the transmitterreceiver unit during the instant of non-energiza tion of gate B.

The representation in Fig. 2 of the unit Ill mounted at the base of the wave guide It does not preclude the installation of said unit at a location remote from the wave guide, with transmission from the unit it to antenna It by coaxial cable, wave guide, or other suitable means.

From the foregoing, it is apparent that the invention provides for a fully automatic system of systematic examination of trailic conditions on one or several rights of way, and for utilizing the intelligence resulting from such examination for operation of electrical apparatus serving tramc control devices or the like.

Subject matter relating to detection at a particular distance or in a zone corresponding to a particular range of distance per se is disclosed and claimed in my copending application Serial No. 535,937, filed May 17, 1944.

Whereas it is obvious that among the several objects of the invention as specifically afore noted are achieved, it is apparent that numerous changes in construction and rearrangements of the parts might be resorted to without departing from the spirit of the invention as defined by the claims.

I claim:

1. In a traiiic detection system, means for generating an ultra high frequency radio wave; a

wave guide including a plurality of directional horns for transmitting said wave in desired directions; gate means in said wave guide for the respective horns to permit or prevent transmission of said wave from said horns as desired; a sequence switch for sequentially operating said gate means to permit periodic transmission from said horns in a prearranged time sequence; means for receiving a reflection wave from an object in the path of said transmitted wave for combination with a wave of the frequency of the transmitted wave; and electric devices individual to each of said gate means and means coordinated with said sequence switch to connect said electrical devices sequentially for each device to be energized by the combined transmitted and reflected waves only during the period when its respective gate means is permitting transmission of said ultra high frequency wave.

2. In a traffic detection system, means for generating an ultra high frequency radio wave; means comprising a wave guide having a plurality of directional horns for transmitting said ultra high frequency wave in desired directions; timer means for controlling the transmission from said directional horns for transmission from selected horns according to a preestablished time schedule; means for receiving a reflection wave from an object in the path of a transmitted wave for combination with a wave of the frequenc of the transmitted wave; electric devices individual to said horns for actuation by the electrical energy of the combined transmitted and reflected waves when connected; and means synchronized with said'timer means for connecting the electrical device individual to a then transmitting horn to said combined wave energy.

3. Apparatus according to claim 2, in which the timer means includes gaseous tubes for creating across said directional horns, a body of ionized gas capable of reflecting back said waves prior to transmission from said wave guides, and adjustable speed switch means for sequentialLv impressing across said gaseous tubes, a current capable of ionizing the gaseous content thereof.

4. Apparatus according to claim 2, inwhich the timer means includes gaseous tubes for creating across said wave guides a body of ionized gas capable of reflecting said waves prior to transmission from said wave guides, and adjustable speed mechanical switch means for sequentially impressing across said tubes, a current capable of ionizing the gaseous content thereof.

5. Apparatus according to claim 2, in which the means for controlling the transmission of said wave from said wave guide comprises a reflecting surface disposed internally of said wave guide and thermionic means for creating and 9 removing said reflecting surface pursuant to a predetermined time schedule.

6. Apparatus according to claim 2, in which the means for controlling the transmission oi said wave from said wave guide comprises a reflecting surface disposed internally of said wave guide and thermionic means including a multivibrator vacuum tube circuit for creating and removing said reflecting surface pursuant to a predetermined time schedule.

7. Apparatus according to claim 2, in which the period of connection of said electrical device to the electrical energy of the combined transmitter and reflected waves is less than the transmission period of the directional horns associated therewith.

8. Apparatus according to claim 2, in which the period of connection of said electrical device to the electrical energy of the combined transmitted and reflected waves commences after the transmission period of the directional horns associated therewith.

9. Apparatus according to claim 2, in which the period of connection of said electrical device to the electrical energy'of the combined transmitted and reflected waves terminates prior to the end of the transmission period of the directional horns associated therewith.

it. Means for detecting the presence of vehicles or the like in a plurality of intersecting trafllc lanes, comprising means for generating an ultra high frequency radio wave; an antenna for radiating said wave; a waveguide associated with said antenna and disposed at said intersection, and including a directional horn for each trafllc lane for directing a radio wave along said lane in a relatively narrow beam; a second wave guide at said intersection and including a second organization of directional horns of substantially the same wave-dispersion pattern as the first named horns and individual to each said traflic lane for receiving a reflection wave representing the reflection of said transmitted wave from a vehicle in the path thereof a receiver antenna in said second wave guide; an ultra high frequency radio receiver associated with said receiver antenna; means for beating said received reflection wave against the transmitted wave to derive an electrical pulse: output devices individual to each trams lane and interconnected to said heating means to derive an energizing pulse therefrom; electrical gate means associated with each of said directional horns to permit or prevent alternatively the transmission of said wave from said horns as desired; sequence switch means in circuit with each gate means to actuate each pecally into transmission-permitting status for a brief interval in accordance with a predetermined time sequence: and switch means in circuit with each of said output devices and synchronized with said sequence switch means to connect to the output of said heating means only the output device individual to a then transmitting horn.

11. Means for detecting the presence of vehicles or the like in a plurality of tramc lanes, including means for generating an ultra high ireuency radio wave; an antenna for radiating said wave; a wave guide including a plurality of directional horns each individual to a selected traiilc lane to transmit said radio wave in a narrow beam along its selected trafilc lane; means for receiving a, reflection wave from an object in the path of a transmitted wave and for beating said received wave against the transmitted wave 10 to derive a beat frequency wave; output means from said receivingmeans: electrical gate means associated with each of said directional horns to permit or prere; alternatively the transmission of said wave fro T id horns as desired; sequence switch means in circuit with each gate means to actuate the same periodically from transmission permitting to preventing and return in accordance with a pre-determined time sequence providing individual transmitting periods for the respective horns; electric devices individual to each said directional horn and in circuit with the output of said reflection wave receiving means to be energizedthereby', and means synchronized with said sequence switch means to connect only the electrical device individual to a then transmitting horn to the output of said receiving means.

\ wave from an object in the path of a transmitted wave and for beating said received wave against the transmitted wave to derive a beat frequency wave; an electrical circuit energized by the output of said receiving means; gate means associated with said transmitting wave guides, to permit or prevent alternatively the transmission of said wave; switch means in circuit with said gate means to actuate the same individually to so permit transmission for relatively brief time periods, according to a predetermined sequence schedule; electrical devices individual to each said transmitting wave guide and in circuit with the output circuit of said receiving means to be energized thereby; and means. synchronized with said switch means to connect an output means of a wave guide into said receiver output circuit only during the intervals when the gate of said wave guide is in wave-transmitting status. v

13. Apparatus for detecting tramc in two distinct trafflc paths entering a trafllc intersection common to such paths comprising means for directing a beam of ultra-high frequency electromagnetic waves from the vicinity of the intersection successively along each of the paths alternately, means for receiving waves reflected from tramc as a result of encounter of the beam therewith, a plurality of output devices each associated with a diflerent one of said paths for utilizing the received waves, and means for operatively associating said output devices with said receiving means for response to said received waves successively in coordination with the transmitting and receiving of the waves alternately in the respective paths to detect and distinguish tramc in the respective paths.

14. Apparatus for detecting traffic in a plurality of distinct trafilc paths entering a trafllc intersection common to such paths including means for generating ultra-high frequency electromagnetic waves, means for directing such waves along each of said paths, cyclic time controlled means for transmitting and interrupting transmission, of such generated waves via said directing means in a time cycle including separate transmission periods for the respective paths, means for receiving waves reflected from trafflc in such lane, a plurality of translating operatively associating said translating devices with said received waves for response thereto successively in coordinationwith the transmission periods in the respective paths to distinguish trailic in the respective paths.

15. In a tramc detection system employing ultra-high frequency radio waves, wave directing means individual to each of two distinct directions, means for generating such waves and means for receiving such waves reflected from trafllc in such directions, said generating and receiving means being common to said wave directing means for the two directions, means for alternately causing and interrupting transmission of such waves via the respective wave directing means in a cyclic sequence including one period of transmission in one only of such two directions and a separate period of transmission in the other only of such directions, a plurality of output circuits including one for each of such directions and means connecting the output circuits to said receiving means in sequence in coordination with transmission in the corresponding direction to distinguish tramc in the respective directions.

16. In a traillc control system, means for periodically detecting vehicles along a plurality of trafllc lanes, comprising an ultra-high frequency wave generator and ultra-high frequency wave receiver; a wave guide system for said generator and said receiver and having means for directionally transmitting said ultra-high frequency waves along said trams lanes respectively and for receiving a wave reflected from vehicles'in said lane; means for controlling transmission of said wave along said trafllc lanes and the reception of a reflected wave therefrom in substantially synchronized periods according to a pre-determined time sequence for distinguishing traflic in the respective lanes; said wave guide system including directional horns so disposed with respect to the traflic lanes as to provide within each said trailic lane, a substantially clearly defined detection zone in which a vehicle is exposed to said ultra-high-frequency waves.

17. In a tramc control system, means for periodically detecting vehicles along a plurality of tramc lanes, comprising an ultra-high frequency wave generator and ultra-high frequency wave receiver; a wave guide system for said generator and said receiver and having means for directionally transmitting said ultra-high frequency waves along said trafllc lanes respectively and for receiving a wave reflected from vehicles in said lane; means for controlling transmission of said wave along said trafllc lanes and the reception of a reflected wave therefrom in substantially synchronized periods according to a pre-determined time sequence for distinguishing traillc in the respective lanes; said wave guide system including directional horns disposed at an elevated level above said traiilc lanes.

18. In a trafllc detection system as in claim 15, said output circuits including relays individual to said circuits for operation in response to such received waves when the respective output circuits are connected to said receiving means.

JOHN L. BARKER.

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