US3015802A - Remote control of traffic signals - Google Patents

Description

Jan. 2, 1962 :R. R. NEWSOM 3,015,802

REMOTE CONTROL OF TRAFFIC SIGNALS Filed April 7 1953 4 Sheets-Sheet 11 SUB-CARRIER TAPE gg fl OSCILLATOR l2 AMPLIFIER TRANSDUCER nu ,4 TRANSMITTER 2a 16;, MODULATOR x:

RA D/O CON TROL'L E175 INVENT OR no I R. NEWSOM ATTORNEY Jan. 2, 1962 R. R. NEWSOM REMOTE CONTROL OF TRAFFIC SIGNALS Filed April 7, 1953 4 Sheets-Sheet 2 RELAYS FIG. 3. 5:9 60

F. M. RECEIVER 056005? INVENTOR ROY R. IVEWSOM ATTORNEY 4 sheets-sheet a R. R. NEWSOM REMOTE CONTROL CF TRAFFIC SIGNALS Jan. 2, 1962 Filed April 7, 1953 INVENTOR R 0 Y R IVEWSOM ATTORNEY gs mmum vm mm m 2 u Q NQ \Q 5 I E m mqmmmmsu Q T Q Q? k 6 m 3 NC" sm :2}: 6 i s R e & J m i Jan. 2, 1962 R. R. NEWSOM 3,015,802

REMOTE CONTROL CF TRAFFIC SIGNALS Filed April 7, 1953 4 Sheets-Sheet 4 FIG. 7.

INVENTOR R0 Y R NEWSOM ATTORNEY Unite This invention pertains to methods and systems of radio communication and control, particularly but not exclusively adapted for controlling traflic through the synchronization of trafiic signal lights by radio transmission. An additional feature of the invention pertains to use of radio sub-carrier techniques for control and communication.

Referring first to traffic control, as is well known, it is often desirable to synchronize traffic lights and for this purpose there are presently required long and expensive underground or overhead cables for carrying several conductors on which necessary power and control currents are transmitted from point to point. By means of the present invention, the same or better synchronization can be obtained, but without the cost of these long power and control cables. Thus, the method and system pertaining thereto of the present invention offer municipalities a close flexible control over the flow of automobile trafiic, with important savings in the costs of initial construction and maintenance of control equipment.

According to the present invention radiations from a radio transmitter at a central control station are employed to actuate the changing of traffic signal lights over an entire town, city or other area. A receiver and associated equipment is installed at each intersection or other trafiic control point to receive the radiated signals and apply control voltages derived from the signals to the light changing equipment. Only one receiver is required for each traffic control point, though numbers of lights at each intersection may be controlled. The control voltages are so established that lights may be equalized along the entire length of an avenue to provide continuous flow of all traflic travelling at the predetermined speed fixed by traflic authorities. Adjacent avenues may be synchronized for identical light timing or for a completely different timing sequence. Lights of crossing or convenging avenues may be synchronized with one of the streets or avenues involved or may be independently cycled. Synchronization may be provided to route trafiic downtown during morning rush hours or out of town at business closing hours. The system is designed to operate efficiently regardless of electrical storms, radio broadcasts, television signals and other signals which might interfere with other types of radio communications.

An auxiliary mechanism may be included in the installation at each traffic control point to provide continued light cycling in the event of failure of a transmitter or receiver. Such auxiliary mechanism may come into operation automatically upon failure of the radio circuits and may automatically be cut out when the radio circuits are again operating.

Needless to say, there are many advantages of the new method and system according to this invention. To enumerate a few, there is elimination of the previous wire control cables, there is lower installation cost, reduced maintenance cost, greater dependability, conservation of critical materials, and increased traffic safety. It may be mentioned that the last advantage results primarily because the low cost of the wireless traffic controls means that more traffic control equipment is available for installation under a specified budget. Additionally, the radio system which is installed may be adapted to also provide a relatively inexpensive public address system which would be of tremendous value for use in civilian defense functions.

States atent A further advantage is that a maximum degree of flexibility is obtained by the system. With the use of known control systems it is often difficult or impossible to change, for example, truck routes or to reroute main trafiic arteries within a city. Such changes may be very easily effected in the present wireless system by simply changing the location of plug-in units.

Referring to the use of radio sub-carrier techniques, I provide by my invention novel circuits for generating and separating modulated sub-carrier frequencies, whereby a single main carrier frequency may be relied upon to carry several control or communication signals.

The primary objects of the invention are to carry out the aforementioned advantages and techniques by use of radio circuits.

It is a further object of the invention to provide in traffic systems, or separately in communication systems, a transmission technique including the modulation of a subcarrier by relatively low frequencies such as audio tones, the thus modulated sub-carrier being further modulated upon a high frequency radio carrier.

It is a further object of the invention to create modulations as aforesaid by recording same on magnetic tape and reading such tape at predetermined times.

It is a further object of the invention to provide a plurality of tape reading units each carrying tape having different recorded signals with means for selecting the desired tape at any given time.

It is a further object to provide a traffic light control system as aforesaid with receiving equipment for separating the modulation frequencies from the carrier and subcarrier and with means provided for selecting among a plurality of modulation frequencies for controlling preselected lights.

Further objects and the entire scope of the invention will be in part obvious and in part expressly set forth in the following detailed description and in the appended claims.

The invention may be best understood with reference to the accompanying drawings, in which:

FIGURE 1 shows an exemplary central transmitting station.

FIGURE 2 shows an exemplary traflic control station with traffic lights and radio controller unit.

FIGURE 3 shows a block diagram of a radio controller unit for use at a traffic control point as in FIG- URE 2.

FIGURE 4 shows a decoder and relay unit for use in the circuit of FIGURE 3.

FIGURE 5 shows diagrammatically a grid of streets having intersections.

FIGURE 6 shows graphically how controller pulses may be time spaced to control a predetermined number of traffic lights in time sequence.

FIGURE 7 shows a circuit for generating and modulating a radio sub-carrier frequency, and

FIGURE 8 shows a circuit for filtering and demodulating a modulated radio sub-carrier frequency.

Referring now to FIGURE 1 there is shown diagrammatically a tape reading mechanism 10 having three sets of tape reading units 12, 14 and 16. Each of the units 12, 14 and 16 may consist of a magnetic tape take-up reel 18, a let-off reel 20' and a transducer 22 for reading signals previously recorded on tape 24. A selector switch 26 is provided for selectively connecting one of the reading units 12, 14 or 16 to a line 28 leading to a modulator unit 30. There is provided a sub-carrier oscillator and amplifier 32 connected by line 34 to the modulator unit 30. The output of the modulator unit appears on line 36, which is connected with a transmitter 38 which preferably will be a frequency modulation transmitter. The output of transmitter 38 is at radiating antenna 40 which may be directional or non-directional as desired.

It may be mentioned that the switch 26 can be either manually operable or automatically operable. For example, each of the tapes 24 and units 12, 14 and 16 may be sufiiciently long to provide eight hours continuous service, and by automatic switching at 26, a full day or twenty-four hours of service is available. Of course, a single tape, perhaps of the endless variety, could be employed, but it will be observed that by the use of two or more tapes while one is operating the other may be removed and replaced with a tape having different signals thereon.

Preferably, the recordings on the tapes 24 consist of short pulses or bursts of a reasonably low frequency such as an audio tone. Each pulse or burst may be of one-fourth second duration. The recording of the tapes forms no part of the present invention. However, it may be mentioned that the audio tones may be recorded through use of synchronous timing motors operating cams for recording transducers, so that the pulses are spaced to coincide with a pre-conceived plan. Therefore, control of the recording process provides maximum flexibility of pulse spacing. Assuming one of the tapes 24 is operating and has recorded thereon the aforesaid pulses or bursts of audio tones, these pulses or bursts of tones will be available on line 28 and will amplitude modulate the sub-carrier frequency on line 34 generated by the oscillator 32. The sub-carrier frequency may be, for example, of the order of 7 to 17 kilocycles. The oscillator 32 may be of any conventional design, as may also the modulator unit 30. The combination of signals from lines 28. and 34 will result in an amplitude modulation of the sub-carrier frequency and this will, therefore, appear on line 36 as an amplitude modulated envelope containing the audio tone frequency. This amplitude modulated signal is then frequency modulated onto preferably an ultra high frequency carrier (or whatever high frequency will be allotted by the communication authorities) for transmission at antenna 40 as a frequency modulated carrier.

In FIGURE 2 there is shown a typical street intersection having the usual trafiiclights 50 and 52 and with a radio controller unit 54 at one of the lamp posts with a suitable power cable 56 interconnecting the lights at the intersection.

FIGURE 3 shows a block diagram of the radio control unit 54. This consists of a frequency modulation receiver 58 connected with a decoder unit 69, this unit in turn being connected to a relay unit 62 for further connection to the trafiic light 50, for example.

Each of the traffic lights 50, 53 may comprise the usual red light at the top, amber in the middle and a green light at the bottom, in the directions of both of the intersecting streets.

It will become apparent as the description proceeds, that additional lights, as are customarily employed for indicating right and left-hand turns, etc., may also be provided and controlled.

In FIGURE 4 there is shown in detail a circuit suitable for the decoder unit 60 and the relay unit 62 as shown in FIGURE 3. In this figure the amplitude or pulse modulated sub-carrier frequency as separated from the carrier in receiver 58 is applied to line '70. This pulse modulated sub-carrier is filtered once at filter unit 72 and again at filter unit 74 and is then detected so that the contents of each pulse are available as bursts of various audio tones at output transformer 76, all as is thought apparent from the drawing. It may be further noted that a voltage is made available for application to a relay coil 78 so that the relay arm 80 associated with coil 78 may be maintained in a given position while proper radio transmission is taking place, but will be placed in an alternate position of radio reception should fail.

The audio tones available from transformer 76 are connected in parallel to the coils of sensitive frequency response tuned reed relays 82, 84, 86 and 33. A suitable direct control voltage may be made available on a line hi) and current from this source may be drawn through the contacts of the tuned reed relays 82, etc. whenever a particular burst of audio tone coming from the transformer 76 is of the correct frequency to excite a given one of the relays. In FIGURE 4 there are four tuned reed relays shown with only 82 and 34 connected. It should be understood that the additional relays (and there may be more) are for flexibility in the system, as will be explained further below.

The relays 82 and 84 are shown connected to further relays 92 and 94 which are employed to change the lights of the traffic light units 50. There is also provided a motor 96 and associated cams 98 and 1% for providing con tinuous local cycling of the traflic lights in case the radio transmission should fail.

In a typical system the tape 24 (FIG. 1) may be prerecorded with the aforementioned bursts of a given audio tone, say 300 cycles per second, intended to cause the red and green lights to shift at the intersections to be controlled. Additionally, the tape 24 may have other pulses of another audio tone, say 400 cycles per second, for causing the turning on of the amber light to indicate that the green light is about to change to the red light at the various intersections. A typical sequence may be to have the red and green lights interchange at 30 second intervals. In other words, at a given intersection to have the red light on in one direction for 30 seconds and then to have the other red light in the other direction on for the next 30 seconds. Additionally, it is customary to have an amber light come on following the green light and before the red light, in a given direction, to apprize the on-coming drivers of an impending change. To follow this typical light schedule, the tape 24 (FIG. 1) may have the bursts of 300 cycles per second audio tone spaced apart along the tape and the tape run at such speed that a burst of this tone will be transmitted at antenna 40 (FIG. 1) every 30 seconds. interposed between the burst of the 300 cycle tone may be the amber controlling tone of 400 cycles per second, about 5 seconds or any other predetermined time in advance of the other bursts.

At the receiving end as shown in FIGURE 4, the tuned reed relay 84- may be tuned to the 400 cycle per second amber tone. Operation of this relay will cause coil 94' of relay ea to be energized by reason of the voltage on line being applied through the coil to the ground. This Will cause the operation of relay arms Wm and 9412 associated with the relay 94. Operation of arm 94b will close a circuit from one side of an A.C. power line to line 112 for energizing a coil 116 of relay 116, which operates relay arm H641 and 1116b to change the green light to an amber light in the direction which happens to be green. The operation of relay arm 94a completes a holding circuit from line 90 through a relay arm 92a of relay 92 to ground. Thus, once relay 94 is energized by reason of energization of relay 84 by a short burst of 400 cycle tone, the relay 94 will remain energized by reason of the holding circuit through relay arrn 94a.

The tuned reed relay 82 may be tuned to the 300 cycle tone and when this relay is energized by a burst of such tone, the relay 92 will be energized, operating relay arms 592a and 9212. Operation of relay arm 92a will open the previously mentioned holding circuit, cutting off the amber light and turning on the green light. Operation of relay arm 92b will connect side 11b of the AC power line through line 118 to energize relay 12h. Relay 120 is of a step by step type having a pawl 122 and ratchet 124 for driving an elongated or double lobe cam 1126. Associated with cam 126 are a first set of leaf contacts 128 and a second set 130, the sets being at 90 to one another. As the cam 126 is stepped about 90 at a time upon each energization of relay 120, first spring contacts 128 will be engaged and then contacts 130. One contact of each set 128 and 130 are connected to the 'side 110 of the A.C. power line and the second contact of set 128 is connected over lines 132 and 134, respectively, to a double-pole, double-throw switch 136. Depending on the position of switch 136 lines 132 and 134 are applied to lines 138 and 140 or vice versa. Lines 138 and 140 are connected to the two red lights of the traffic light unit 50.

From the foregoing it was thought apparent that when the relay 92 is briefly energized the amber light holding circuit will be opened, permitting relay 94 to be deenergized and remain in such deenergized condition. Additionally, operation of relay arm 92]) will step the cam 126 90, shifting the voltage from line 132 to line 134 or vice versa. It will be noted that relay arms 116a and 1161) are connected to lines 138 and 140, respectively, for supplying power through switches 128 and 130 to the green and amber lights. 1

While the radio equipment is in proper working order, a voltage will be available in relay 78 (FIG. 4) to hold down relay arm 80 so that no power is available on line 150 leading to motor 96. It may be noted at this point that the other side of motor 96, as well as the relay coils 116 and 120 and the lights of traffic light unit 50 are connected to the remaining side 152 of the A.C. power line. Failure of voltage at relay coil 78 will cause the relay arm 80 to connect the side 110 of power line to the line 150. This will set the motor 96 in operation and will also energize relay coil 154 for operating relay arm 154a and 154k. Cams 98 and 100 will be driven by motor 96. Cam 9% may have a lobe 98 for providing a dwell period of desired length for operating leaf contacts 156 for applying a voltage from side 110 of the A.C. line to relay arm 154a and thence over line 158 to the amber control relay 116. The cam 100 may havve a short lobe 100' positioned to just follow the lobe 98 so as to provide an impulse of 7 power from side 1110 of the A.C. line through leaf contacts 160 to relay arm 1541). Further connection is made over line 162 to relay 120 for stepping switch 126 90 to shift the red lights.

The purpose of relay 154 is to prevent interference of the auxiliary equipment with the automatic equipment, if the motor 96 should stop so as to leave the earns 98 or 100 holding leaf contacts 156 or 160 closed.

FIGURES 5 and 6 illustrate a method of planning or scheduling the pulse sequences so as to provide a desired traflic flow. In FIGURE 5 streets 1, 2, 3, 4, 5, 6 and 7 run at right angles to streets x, y and z, providing the resulting intersections. It may be assumed that it is desired to provide each intersection along street x, for example, with a 60 second light cycle, 25 seconds green, 5 seconds amber and 30 seconds red and that the local speed limit requires that the lights at each corner change color 10 seconds after the preceding light in a given direction. Referring now to FIGURE 6, pulses may be recorded as designated between indicia on the circle designated 200. In this instance the red light shifting tones, which were above described as bursts of 300 cycle tone, may be again spaced apart 30 seconds, which is the equivalent of 180 on the 60 cycle diagram of FIGURE 6. Now, however, there may be interposed between these 300 cycle tones, bursts of other tones. For example, at 60 or 10 seconds there may be a burst of 325 cycle tone and at 120 or 40 seconds there may be a 350 cycle burst. The only requirement for the frequency of these tones is that the tune reed relays 82, etc. (FIG. 4) will discriminate among the tones. These three phases, so to speak, of distinct shifting tones, willthen appear along the length of the tape 24. Interposed among the three phases of shifting bursts may be additional distinct tones for operating the amber lights. In other words, there will be three phases of amber light control burst available.

With the aforementioned sequence of pulses of the tape 24 it is thought apparent that these'pulses of distinct audio tones may serve to switch the lights at inter- 6 section 2, 10 seconds later than the lights of intersection 1 and similarly for intersection 3, travelling for instance from left to right along avenues x, y or z in FIGURE 5.

It will, of course, be understood that a typical decoding unit 60 will have a complete set of, for example, six tuned reed relays such as the relays 82, 84, 86 and 88 shown in FIGURE 4. Each one of the relays is tuned to react to one of the several audio tones which may be conceivably involved in the operation of the system. Furthermore, space may be provided in the decoding units for adding additional relays for other tones.

Referring again to FIGURE 5, at intersection 4, the tones used for intersection 1 may be applied, but with the switch 136 (FIG. 4) moved so as to reverse the leads from switches 128 and 130 to the red lamps. In other words, to change the connection between lines 132, 134 and 138, 140. Intersections 5 and 6 may be operated by reversal of leads in the same manner. At intersection 7 the pulses from intersection 1 would be properly timed. Obviously, the process may be repeated to control traffic lights to the end of the system.

Where the spacing of traflic control points does not permit the repetitive use of a basic group of pulses, it is clear that additional pulse patterns may be scheduled and recorded to time the light switching according to the desired trafiic plan. In each street pulse recording becomes available for use at any traffic control point since all pulses are present at all control points.

Further extension of the system may be effected through use of more than one sub-carrier frequency. For example, pulse patterns imposed upon a seven kilocycle subcarrier do not interfere with pulses occurring at the same time and of the same audio tone on a fifteen kilocycle sub-carrier. In other Words, for example, a pulse of 325 cycles per second tone may be employed on both the sub-carriers without interference. All that is necessary is to arrange the decoding unit as shown in FIGURE 4 to be sensitive to one sub-carrier and not others. From the foregoing it will be understood that there may be a large number of control transmissions available all on one carrier frequency, the latter frequency being the critical one insofar as frequency allocation by communication authorities is concerned.

It will be further appreciated that under emergency conditions, it is possible to hold the trafl'lc signals in any one of three conditions, that is, red, amber or green. 'In such emergency conditions the tape can be stopped and the control applied by manually controlled switches to impose bursts of particular tones as desired.

Referring now to FIGURE 7, there is shown an alternative circuit for developing a sub-carrier frequency useful in the above described traffic control system, or separately useful for effectively separating communications such as in taxicab and police radio systems. In FIGURE 7 a vacuum tube 210 is provided, which may be of the type known in the trade as a 6U8. This type of tube comprises two sections, one a triode section 212 at the lefthand side of the diagram as viewed in FIGURE 7, and a pentode section 214 at the right-hand side. The triode section 212 of tube 210 is connected to receive on its grid over line 216, the output of a microphone, or the tape recording as in the traflic system described above. The triode section 212 serves as an audio amplifier. The pentode section 214 of tube 210 is connected to serve as a sub-carrier oscillator, modulator and amplifier. The sub-carrier is generated between the control grid 218 and cathode 220, thereby placing the sub-carrier frequency at grid 218. The plate of the triode section 212 supplies the modulating potential to the pentode screen grid 222, thereby modulating the sub-carrier with the audio signal. The modulated sub-carrier output is taken from the plate of the pentode section 214 through a CL coupling circuit comprising the capacitor 224 and coil 226, this output being available on line 228. The modulated sub-carrier on line 228 may be inserted into the audio amplifier of a transmitter section (not shown) so as to be modulated upon the main radio frequency carrier. By this arrangement of triode and pentode sections, which may be found in a single tube of the 6U8 type, there is provided a very compact and economical sub-carrier generator and modulator which is belived to be a marked improvement over any such circuits now known.

Referring now to FIGURE 8, there is shown an alternative circuit for receiving and demodulating sub-carriers. Again, this circuit may be employed in the hereinabove described traffic system, or may be used separately in other types of communication systems, as for example, the systems mentioned in the preceding paragraph. It will be further understood that the circuits of FIGURE 7 and FlGURE 8 may be joined together to use the same power supplies and as such may form an adapter as a unit for simple connection to an existing transmitter-receiver unit as in a mobile radio station.

In FIGURE 8, the output of a receiver audio amplifier in the main carrier frequency receiver (not shown) may be connected over line 24 9 and is first applied across a filter section 242 consisting of inductances L L L and L and capacitors C C and C As will be well understood by those skilled in the art this filter will reject any signal excepting the sub-carrier to which it is tuned. The subcarrier appearing on lines 244, 246 and 248 is demodulated by a detector comprising the two diode sections of a type 6AQ6 tube 25%. This type of tube consists of a plate 252, a grid 254, cathode 255 and diode electrodes 258 and 26%. The sub-carrier is applied to electrodes 258 and 26d by connection to the ends of inductance L and the mid-tap of inductance L is connected over line 248 through a resistance capacitance circuit 262 to the grounded cathode 256. There is also a connection from line 248 over line 264 to the grid 254. This arrange- 'rnent constitutes a balanced detector, with the detector output being applied to the grid 254- of tube 250. The plate 252, grid 254 and cathode 256 of tube 25!) serve as a triode and this by virtue of plate resistor 266 serves as an audio amplifier to provide the audio modulation of the line 268 for application to a suitable audio power output tube in the receiver proper.

The circuits of FEGURES 7 and 8, considered separately or in combination, constitute an appreciable improvement in the art to which they pertain. In the past it has been considered unfeasible to use sub-carriers in such applications because convertor units to modify existing mobile equipment have been too expensive and required prohibitive power drain, particularly when used in automobile electrical systems or other systems remote from conventional power supplies. It has also been thought necessary or at least desirable that sub-carrier frequencies be maintained at a frequency level comparable to the audio frequencies involved, which has made detection difficult. The units described above are capable of performing all the necessary functions at negligible current rating and operate with sub-carriers as low as seven kilocycles and as high as may be desirable.

Additionally, in present-day equipment Where the voice is used to modulate the carrier, in PM transmissions input signals of high amplitude, intensity or frequency tend to cause the carrier deviation to exceed the bandwidth assigned by the FCC. Accordingly, manufacturers are required by F.C.C. regulation to provide limiter circuits which limit the signal amplitude and frequency before the modulation process. When voice is placed upon a sub-carrier as in the present invention, variations in amplitude or frequency of the voice do not affect carrier deviation because the sub-carrier amplitude is fixed. This eliminates the need for the limiter circuitry and permits a wider signal frequency band without excess carrier deviation.

It Should e unders o that the foregoing description of the detailed embodiment of the invention is given for purposes of illustration only and is not intended to limit the scope of the invention. Clearly, there will be many other specific arrangements of circuits and the like which will occur to others for carrying out the invention once the invention is understood by reading the foregoing specification. Accordingly, it is intended that the scope of the invention be limited only by the scope of the appended claims.

What is claimed is:

1. In a traffic light system for controlling trafiic at a multiplicity of control points, a plurality of traific light units each having selectively enengizable lights and being located at a respective control point, a central radio transmitting station for controlling said plurality of trafiic light units in accordance with a predetermined trafiic program, the transmitting station including means for modulating repeated series of bursts of different relatively low control frequencies representing the trafiic program onto a sub-carrier frequency, means for modulating said modulated sub-carrier onto a higher carrier frequency, each of said units including a receiver and switching means dependent upon a predetermined control frequency in said series for energizing selected lights of the unit, and means for transmitting said modulated higher carrier frequency for reception and use by said units.

2. A system as in claim 1 wherein said receiver and switching means of each traffic light unit includes; means for receiving the carrier frequency and side bands thereof, means for separating the sub-carrier from the carrier, means for separating bursts of relatively low control frequencies from the sub-carrier, and at least two frequency sensitive selection means responsive to predetermined ones of the relatively low frequencies.

3. A system as in claim 2 wherein the frequency sensitive means at the receiving means are tuned reed vibratory relays.

4. In a traffic light system for controlling traific at a multiplicity of control points, a plurality of trafiic light units each having selectively energizable lights and being located at a respective control point, a central radio transmitting station for controlling said plurality of trafi'ic light units in accordance with a predetermined traffic program, the transmitting station including means for amplitude modulating bursts of relatively low control frequencies onto a sub-carrier frequency, means for frequency modulating said modulated sub-carrier onto a high carrier frequency, each of said units including a receiver and switching means dependent upon a predetermined control frequency in said series for energizing selected lights of the unit, and means for transmitting said modulated higher carrier frequency for reception and use by said units.

5. A system as in claim 4 wherein said receiver and switching means of each of said traffic light units includes; means for receiving the carrier frequency and side bands thereof, means for separating the sub-carrier from the carrier, means for separating bursts of relatively low frequencies from the sub-carrier, and at least two frequency sensitive selection means responsive to predetermined ones of the relatively low frequencies.

6. A trafiic light system for controlling the operation of signal lights at a multiplicity of control points, said system comprising means including a central station for generating and transmitting a main carrier wave, means for generating a sub-carrier wave at a lower frequency than that of said carrier, means for generating a signal pulse pattern comprising repeated series of bursts of energy at discrete low frequencies, means for modulating said pattern onto said sub-carrier, means for modulating said sub-carrier modulated by said pattern onto said main carrier, a receiving means for each of said control points for demodulating said main carrier wave and for demodulating said sub-carrier wave, said receiving means also including means responsive to the low frequency bursts of said pattern for controlling the signal lights at the control points, said last-mentioned means including means at each control point responsive to respective ones of said low frequency bursts for effecting individual control of the respective signal light in accordance with said pattern.

7. A trafiic light system for controlling the operation of signal lights at a multiplicity of control points, said system comprising means including a central station for generating and transmitting a main carrier wave, means for generating a plurality of sub-carrier waves each at a different frequency lower than that of said carrier, means for generating a plurality of signal pulse patterns each comprising bursts of energy at discrete low frequencies, means for modulating each of said patterns onto a different one of said sub-carriers, means for modulating all of said sub-carriers modulated by said patterns onto said main carrier, a receiving means for each of said control points for demodulating said main carrier wave, and for selecting and demodulating a respective one of said subcarrier waves, each of said receiving means also including means responsive to the ones of said low frequency bursts on the respective sub-carriers for controlling the signal lights at the respective control point whereby certain of said control points are controlled in accordance with the signal patterns modulated on one of said sub-carriers and others of said points are controlled in accordance with the low frequency patterns modulated on another of said sub-carriers.

8. A traffic light system as set forth in claim 7 wherein said sub-carriers are frequency modulated onto said main carrier and said signal pulse patterns comprise groups of discrete audio tones.

9. A traffic light system for controlling the operation of signal lights at a multiplicity of control points, said system comprising means including a central radio station for generating and transmitting a carrier wave, means at said central station for generating a signal pulse pattern conforming to a coordinated trafl ic control program for said multiplicity of points and comprising repeated series of bursts of energy at discrete low frequencies, means for modulating said pattern onto said carrier wave, a radio receiving means for each of said control points for demodulating said carrier wave, said receiving means also including means responsive to the individual series of low frequency bursts of said pattern for controlling the signal lights at the respective control points, said last mentioned means including means at each control point responsive only to respective ones of said low frequency bursts for effecting each of the changes in the energization and de-energization of each individual signal light solely in response to the reception of the respective low frequency bursts.

10. A traffic light system as set forth in claim 9 wherein said means for generating said signal pulse pattern includes a pre-recorded record member and transducer means for generating said pattern of low frequency bursts from said member.

11 A traflic light system as set forth in claim 9 including auxiliary cycling means for the signal lights at each of said control points, and automatic means for effecting operation of said auxiliary cycling means upon failure of radio transmission.

12. A trafiic light system for controlling the operation of signal lights at a multiplicity of control points, said system comprising means including a central radio transmitting station for generating and transmitting a carrier wave, means at said central station for generating a signal pulse pattern conforming to a coordinated traffic control program for said multiplicity of points and comprising concurrent and repeated series of bursts of energy at distinctive low frequencies, means for modulating said pattern onto said carrier Wave, traffic light units one at each of said control points and including switching means for selectively energizing the lights thereof, a radio receiving means for each of said units for receiving and demodulating said carrier wave, said receiving means also including means responsive to the individual series of low frequency bursts of said pattern for controlling said switching means, said last mentioned means including means for each of said units responsive only to respective ones of said low frequencies for effecting each of the changes in the energization and de-energization of each individual signal light solely in response to the reception of the respective low frequency bursts.

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