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Publication numberUS3778762 A
Publication typeGrant
Publication dateDec 11, 1973
Filing dateJul 23, 1971
Priority dateJul 23, 1971
Publication numberUS 3778762 A, US 3778762A, US-A-3778762, US3778762 A, US3778762A
InventorsJarko M, Newmeyer R, Powers A
Original AssigneeSolid State Devices Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Monitor for detecting conflicting traffic control signals
US 3778762 A
Abstract
A monitoring device for use with a traffic control signal system in which the monitor is adapted to detect when a conflict of vehicle or pedestrian proceed signals occurs and switch the system to emergency operation. The monitor may also be employed to detect if the conflict clears and restore the system to normal operation.
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Description  (OCR text may contain errors)

United States Patent Jarko et al.

[ 1 Dec. 11, 1973 MONITOR FOR DETECTING 3,648,233 3/1972 Clark 340/46 CONFLICTING TRAFFIC CONTROL 3,384,871 5/1968 Selzer et al.. 340/37 SIGNALS 3,336,574 8/1967 Selzer 340/46 3,241,113 3/1966 Sobotta et al... 340/78 [75] Inventors: Michael F. .larko; Avery W. Powers, 2,100,313 11/1937 Fitzgerald 340/41 Scmsdale; Reed FOREIGN PATENTS OR APPLICATIONS Newmeyer, Glendale, all of Al'lZ.

1,225,080 9/1966 Germany 340/46 [73] Assignee: Solid State Devices, Inc., Tempe,

Ariz. Primary ExaminerWilliam C. Cooper Assistant ExaminerRandall R. M ers 22 F1 d: 1 23 1971 Y I 1 1 y Y Att0rneyHerbert E. Haynes, Jr.

21 Appl. No.: 165,528

[57] ABSTRACT [52] US. Cl. 340/46 A monitoring device for use with a traffic control sig- [51] Int. Cl G08g 1/97 nal system in which the monitor is adapted to detect [58] Field of Search 340/37, 41, 42, 46, when a conflict of vehicle or pedestrian proceed sig- 340/36, 78, 251 nals occurs and switch the system to emergency operation. The monitor may also be employed to detect if [56] References Cited the conflict clears and restore the system to normal UNITED STATES PATENTS operation- 3,629,802 12/1971 Clark et a1 340/46 10 Claims, 1 Drawing Figure *W Egempmea 51 575149 12;

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----- 1 11 15a ja F l l -Z- l i 17/? i/TJ? 1 i 1 17 i :17 eoaen/w 485/7 16 g l l "77 E l l l :19 19 c'aA/Fucr L0 m 1 c/ecu/r 18 1 l l l 20 g 1 l L I i LO/VFL/CT 22 SIG/VAL)! I r 2 fczsme r 52% T Mrs/l0 cam/r52 amen/'02 25 LflA/FL/L'l' DEL/H U 600N758 T 2? E5557 M005 [Z6 41 SELL-C702 SW. 5 1 f5V ac /.440 LWA/FL/L'f DELAY ll 0 l MONITOR FOR DETECTING CONFLICTING TRAFFIC CONTROL SIGNALS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electronic'devices and more particularly to an electronic monitor for detecting conflicting traffic signals in a traffic control system.

2. Description of the Prior Art Electric signaling systems are in common use at roadway intersections to control the flow of vehicular and pedestrian traffic. These systems, as any electrical apparatus, are subject to failures or malfunctions due to burned out components, worn mechanical relays, electrical interference and the like.

With the ever increasing traffic handling problems, accidents, and legal actions resulting from the latter, it has become essential that a fail-safe traffic signaling system be devised.

Some failures or malfunctions of traffic signaling systems result in conflicting proceed signals appearing at the signal heads or semaphores. A conflicting condition or signal may be defined as one which results in intersecting traffic patterns being signaled to proceed simultaneously. For example, one type of a conflicting condition would be when the semaphores of two or more intersecting roads are simultaneously displaying green lights or any other form of proceed signals such as turn arrows, amber lights, pedestrian walk and the like.

For fail-safe operation of the semaphore system when conflicting conditions occur it is necessary to monitor the proceed signals, detect when a conflict occurs and take appropriate action such as switching the system to a flashing mode of operation.

It is also desirable in some instances to restore the semaphore system to normal operation if the conflict clears. This feature is known to those skilled in the art of traffic engineering as Auto-Scan.

Many problems exist in the development of a semaphore conflict monitor. One of these problems results from random RF. signals or other electrical interference which may cause undesirable operation of the equipment. Another problem is developing a monitor which may be easily modified to handle the variety of signal combinations required to handle differing traffic problems at various intersections.

Monitoring devices have been devised which due to expense, inflexibility and the like have not received wide acceptance.

One particular prior art device has the capability of monitoring four proceed signals, thus multiple road intersections must employ a plurality of these monitors. This same prior art monitor lacks versatility, that is, a different monitor must be employed at each intersection which varies from the normal signaling combinations. The Auto-Scan feature of this prior art monitor is not a fully automatic system. When a conflict occurs, the prior art monitor will switch the semaphore to a flashing mode and trigger an external clock. At the expiration of a predetermined time, the monitor restores normal operation to the system, and if the conflict still exists will switch the semaphore to the flashing mode once again.

In view of the foregoing, the need exists for a new and useful semaphore conflict monitor which is capable of monitoring a complex road intersection, lends itself readily to modification for handling various signaling combinations, is completely isolated from R.F. signals and other electrical noise, and has a completely automatic Auto-Scan feature.

SUMMARY OF THE INVENTION In accordance with the invention, a new and useful semaphore conflict monitor, or monitoring circuit for use in traffic handling systems is disclosed.

The semaphore conflict monitor of the present invention comprises a plurality of optically coupled sensors for sensing the traffic proceed lights. Each of the sensors produce a signal when the proceed light it is monitoring is receiving power. The output signals of the sensors are routed through a program area which is modifiable to adapt the monitor to various signaling combinations. The sensor output signals are routed through the program area to a detector logic circuit. When a conflict is detected by the detector logic circuit an output signal results which is optically coupled to the traffic control system and causes it to switch to emergency operation.

The output signal from the detector logic circuit is also routed to an Auto-Scan circuit of the monitor. The Auto-Scan circuit of the monitor senses when a conflict clears and allows the user to preselect the number of times the traffic control system will be allowed to return to normal operation after a number of conflicts have occurred and cleared.

A lock-up mode of operation is available to the user which will not allow the traffic control system to return to normal operation after an initial conflict has occurred. A first reset mode is also available which allows restoration of normal operation a predetermined number of times after the conflicts have cleared. A second reset mode available to the user is to allow normal operation of the traffic control system to be restored after each conflict that occurs has cleared.

Accordingly, it is an object of this invention to provide a new and useful semaphore conflict monitor.

Another object of this invention is to provide a new and useful semaphore conflict monitor which is completely isolated from random RF. signals and other types of electrical interference.

Another object of this invention is to provide a new and useful semaphore conflict monitor which is easily modified to adapt the monitor to handle different signaling combinations employed in various traffic control systems.

A further object of this invention is to provide a new and useful semaphore conflict monitor which is capable of monitoring the proceed signals of multi-roadway intersections.

A further object of this invention is to provide a new and useful semaphore conflict monitor which is provided with a plurality of preselectable fully automatic operating modes of Auto-Scan circuitry.

'The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE of the drawing is a schematic diagram illustrating the semaphore conflict monitor of the present invention connected to a fragmentary schematic view of the traffic control system.

DESCRIPTION OF THE PREFERRED EMBODIMENT A semaphore system 9 or traffic control system which is normally located at intersections to control vehicular and pedestrian traffic is operated by an a.c. switching device 10, sometimes referred to as a controller. The controller 10 applies power in a predetermined timed sequence to a series of busses 11 connected in the conventional manner to signal heads or semaphores (not shown).

A semaphore conflict monitor 12 of the present invention may be connected to the semaphore system 9 in various ways to sense when the lights of the semaphores are receiving power. As shown in the drawing, a wire 13 is connected to each buss l1 and is routed to a conflict detector means 14.

The conflict detector means 14 may be an analog detector device which would monitor voltage levels. However, a problem of random RF. signals, which may be present at intersections, would require that extensive filtering be employed to prevent the R.F. signals from causing erroneous detections.

In the preferred embodiment of the present invention, the conflict detector means 14 is designed to isolate the inputs to the monitor from random RF. signals or any noise which may be generated within the semaphore system 9.

To accomplish the input isolation, the conflict detector means 14 is provided with a plurality of optically coupled sensors 15a through ln, there being one sensor 15 for each proceed signal of the semaphore to be monitored. In some instances it may be desirable to couple two or more proceed signals from a semaphore through an OR-gate (not shown) to each of the sensors 15. This would reduce the number of sensors required.

Each of the sensors 15 is adapted to produce an output signal when their respective semaphore proceed signals are receiving power.

The sensors 15 are fully disclosed in a copending US. Patent application entitled Optical Coupling Circuit, by Reed A. Newmeyer, filed Sept. 27, 1971, Serial Number 183,965, which issued on Sept. 12, 1972 as U. S. Pat. No. 3,691,403. Therefore the sensors 15 will be only briefly described herein.

The sensors 15 are connected to the busses 11 as previously described and are adapted to operate on a fullwave a.c. input signal or either polarity of half-wave a.c. input. The input signal to the sensors 15 is employed to excite a light emitting device 15'. Radiated light from the light emitting device impinges on a photo-sensitive device 15'' which in response thereto produces a signal. The signal from the photo-sensitive device is coupled to a turn-on delay circuit (not shown) which delays turn-on signals but does not delay turn-off signals. The turn-on delay feature prevents overlapping of signals from causing erroneous conflict signals within the monitor 12.

The output signals from the sensors 15a-15n are routed through a program area 16. The program area 16 is in the form of a wiring matrix which may employ a plurality ofjumper wires 17 which are repositionable for connecting various ones of the input terminals 17 to various ones of the output terminals 17" thereof to allow the monitor 12 to be easily modified by the user to monitor any signaling combinations that he considers could result in a conflict. It should be understood that the jumper wires 17 are only one method of providing the programmable feature. A plug-in printed circuit arrangement in which a different printed circuit (not shown) could be used for the different combinations would be a functional equivalent.

The output signals of the sensors l5a-15n are routed through the program area 16, as previously described, to a conflict logic circuit 18. The conflict logic circuit 18 is adapted to determine if a conflict exists between the output signals of the sensors 15a-l5n. An AND- gate and OR-gate structure is employed for this purpose, and there is one AND-gate for each possible conflicting condition. The gate structure is similar for each condition, therefore only a portion thereof is shown and described.

For descriptive purposes, assume that sensor 15a and sensor 151: simultaneously produce output signals which is a condition indicating that a conflict exists. The respective output signals from the sensors 15a and 15in are coupled to an AND-gate 19 which is adapted to produce an output signal only if both of its inputs are simultaneously presented thereto.

It should be noted that any of the semaphore lights sensed by one of the sensors 15 could be involved in a plurality of possible conflicting situations. Thus one AND-gate 19 is employed for each possible conflicting situation, and the output signal from each sensor 15 may be routed to a plurality of these AND-gates. The output signals from the AND-gates 19 are routed to an OR-gate 20 which is adapted to produce a conflict signal 21 when any single output from any of the AND- gates 19 is presented thereto.

The conflict signal 21 from the conflict logic circuit 18 is routed to an AND-gate 23, whose other input is derived from a clock pulse generator 24. When the signal from the clock generator 24 and the conflict signal 21 are simultaneously presented to the AND-gate 23, the clock pulse is passed through.

In some instances, momentary conflicting signals will be sensed by the conflict detector means 14. These momentary signals may result from worn or slow acting components within the semaphore system such as mechanical relays. To preventthese momentary signals from causing the monitor 12 to indicate a conflict, the output signal from AND-gate 23 is applied to an adjustable conflict delay circuit 25. The conflict delay circuit 25 is adjustable by the user to provide a small time delay (0.25 to 4 seconds) to filter out any momentary signals. When the output signal of AND-gate 23 is of sufficient duration, it will be transmitted through the conflict delay circuit 25 and will set a conflict storage flip-flop 26. When the flip-flop 26 is set its 1 terminal goes high and will remain in that state until reset. The signal present at the 1 terminal of flip-flop 26, when set, is considered the first signal produced thereby.

The output from the conflict storage flip-flop 26 is coupled to an interface circuit 27 which is adapted to react to the high output signal from the flip-flop 26.

When the interface circuit 27 is activated, it produces an optically coupled output signal which is employed to take appropriate action within the semaphore system 9. By way of example, the appropriate action may take the form of bypassing the controller 10 with an emergency flasher unit (not shown).

As seen in the drawing, the optical coupling is accomplished within the interface circuit 27 by a light emitting device 28, the radiation from which impinges on a photo-sensitive device 29. The photo-sensitive device 29 produces an output signal which is suitably coupled to the semaphore system 9.

It should be noted that the optical coupling accomplished by the interface circuit 27 isolates the output circuitry of the monitor 12 from random R.F. signals and any other electrical interference.

The circuitry thus far described will sense a conflicting condition of the semaphore proceed signals and take appropriate action as described. In some instances these conflicting conditions will clear themselves. The types of conflicts which may clear themselves result from malfunctions of the equipment itself, from electrical interference and the like. Therefore it is desirable to be able to detect when a conflict clears as well as when one occurs, and to restore the semaphore system to normal operation when the conflict clears.

To sense if a conflict has cleared, a three input clear AND-gate 31 is employed which produces an output signal when all of the inputs applied thereto are high. The first input to the clear AND-gate 31 is the conflict signal 21 which is routed through an inverter 22 so that a clear signal 30 presented to the AND-gate 31 is low when a conflict exists and will go high when the conflict clears. The second input to the clear AND-gate 31 is derived from the clock pulse generator 24 which provides the timingflhe third input signal to the AND- gate 31 is applied thereto from the 1 terminal of the conflict storage flip-flop 26, which is high when a conflict exists as hereinbefore described. Therefore when a conflict exists, the first signal is low, the second signal alternates since it is the clock pulse, and the third signal is high so the AND-gate 31 will not conduct. When a conflict clears the clear signal 30 will go high and the conditions necessary for conduction through the AND- gate 31 are met.

The output signal from the clear AND-gate 31, which indicates that a conflict has cleared, is routed to control circuitry which includes a clear delay counter 32. The clear delay counter 32 may be adjusted by the user to provide a time delay, which for descriptive purposes may be adjusted within the range of 8.5 seconds to 1,092 seconds. The clear delay counter 32 is provided so that the controller of the semaphore system 9 may cycle through one or more times to insure that it is functioning properly prior to restoring the system to normal operation.

If during the delay provided by the clear delay counter 32 another conflict does not occur, the clear delay counter 32 will produce an output signal which may be employed to restore the semaphore system to normal operation.

Restoration of normal operation to the semaphore is accomplished by resetting the conflict storage flip-flop 26. When reset, the output from the 1 terminal of the conflict storage flip-flop 26 goes low, and is considered the second signal produced thereby which stops the output signal from the interface circuit 27, and thus allows the semaphore system to be restored to normal operation.

In some circumstances it may be desirable to not allow restoration of normal operation. This may be accomplished by complete elimination of the components which sense that a conflict has cleared and elimination of the Auto-Scan or control circuitry so that only the detection and its associated circuitry remains. However, to provide a more versatile monitor and allow the user to select what will be allowed to occur when a conflict clears, a lock-up mode and at least two reset modes of operation are provided.

The lock-up mode will not allow the semaphore system to return to normal operation after an initial conflict has occurred and cleared. To release the semaphore system from the lock-up mode requires manual I restoration by the user as will hereinafter be described.

A first reset mode will allow normal operation to be restored, after a delay, for a predetermined number of times and any conflicts occurring after that will switch the semaphore system to the lock-up mode and further restoration of normal operation is prevented.

A second reset mode allows restoration of normal operation each time a conflict clears with no limit on the number of times this may occur.

To accomplish the lock-up mode or the reset modes, the output signal from the clear delay counter 32 is routed to a monostable multivibrator 33, sometimes referred to as a one-shot. An output signal from the oneshot 33 provides one input to a reset AN D-gate 37. The reset AND-gate 37 is similar to the previously described clear AND-gate 31, that is, it is a three input device that requires that all of its inputs be high in order for it to conduct. The output signal from the oneshot 33 is high, and the other two inputs to the reset AND-gate 37 are provided from various sources depending on the reset mode selected as will be described.

It may be seen in the drawing that when the reset AND-gate 37 conducts the conflict storage flip-flop 26 will be reset and cause normal operation of the semaphore system to be restored. Therefore the number of times which the AND-gate 37 is allowed to conduct determines the reset mode.

The lock-up mode may be accomplished in a number of ways by not allowing the AND-gate 37 to conduct and for descriptive purposes is shown as a lock-up mode selector switch 36 in the output line from the AND-gate 37. When the switch 36 is opened, an open circuit results thus not allowing the output signal from the AND-gate 37 to reset the flip-flop 26.

When the lock-up mode is inactivated (switch 36 closed) the reset modes of operation are available to the user.

When the first reset mode is selected, the first signal is applied to the AND-gate 37 from the one-shot 33 as previously described. The second signal is applied to the AND-gate 37 from the 1 terminal of a second conflict flip-flop 38. The second conflict flip-flop 38 is a normally set device which is manually placed in this state when the monitor 12 is put into operation, or initialized, as will be described. The output signal from the 1 terminal of the second conflictflip-flop 38 is high when the device is in the set state. The third signal applied to the AND-gate 37 is the clear signal 30 which goes high when a conflict clears. Therefore, the AND- gate 37 will conduct under these circumstances and restore normal operation of the semaphore system. The output signal from the AND-gate 37 is also routed through a delay circuit 39 to reset the second conflict flip-flop 38 so that the signal from its 1 terminal goes low which disallows further conduction through the AND-gate 37. The same signal routed through the delay circuit 39 is employed to reset the conflict delay counter 25 and the clear delay counter 32.

It should now be apparent that when the first reset mode is selected, the reset AND-gate 37 will be allowed to conduct once to restore normal operation to the semaphore system 9, and having conducted will not conduct again. Any further conflicts will therefore result in switching of the semaphore system to emergency operation which will require manual restoration.

It may also be seen that the number of times that AND-gate 37 is allowed to conduct prior to its not being allowed to conduct again can be changed to any predetermined number by modifying the circuitry to include such devices as an event counter (not shown), flip-flops in series (not shown), or any other wellknown mechanical or electrical counting device.

The second reset mode is adapted to allow the reset AND-gate 37 to conduct each time a conflict has cleared. This is accomplished by applying a continuously high input signal to the AND-gate 37 in place of the signal previously derived from the second conflict flip-flop 38. This is accomplished by a reset mode selector switch 41 which may be a physical part of the switch 36.

An initialize circuit 42 is provided so that the monitor 12 may be cleared, that is, returned to its original state as if no conflicts have been detected. This is a manually operable device which allows the'user to reset the flipflop 26 and set flip-flop 38 when the problem causing the conflict has been rectified. A predetermined time delay is built into the initialize circuit 42 so that on power-up and manual resets the data from previously detected conflicts will have time to clear and thus not interfere with the newly monitored conditions.

While the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in the art many modifications of structure, arrangements, proportions, the elements, materials, and components, used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operation conditions and requirements without departing from those principles. The appended claims are therefore intended to cover and embrace any such modifications, within the limits only of the true spirit and scope of the invention.

What we claim is:

l. A monitoring circuit for detecting if conflicting traffic proceed signals occur in a traffic control system and for detecting if the conflicting condition clears, said monitoring circuit comprising:

a. a conflict detector coupled to the traffic control system for monitoring the traffic proceed signals and producing a conflict signal upon the occurrence of conflicting traffic proceed signals and a clear signal if the conflicting condition clears;

b. a conflict storage flip-flop coupled to be set by the conflict signal from said conflict detector, said flipflop adapted to produce a first signal when in the set state and a second signal when in the reset state;

c. an interface circuit coupled to said conflict storage flip-flop which upon receipt of the first signal therefrom signals the traffic control system to commence emergency operation and upon receipt of the second signal therefrom interrupts the signal from said interface circuit to allow the traffic control system to restore normal operation;

d. an inverter coupled to receive the conflict and the clear signals from said conflict detector;

e. a clear AND-gate having its input signals applied thereto from said conflict storage flip-flop, and from said inverter, said clear AND-gate adapted to produce an output signal when a conflicting condition clears, said AND-gate output signal coupled to reset said conflict storage flip-flop whereby normal operation of the traffic control system is restored; and

f. control circuitry connected to said clear AND-gate output for selecting if said clear AND-gate output signal will be allowed to reset said conflict storage flip-flop, and if so allowing selection of at least one reset mode.

2. A monitoring circuit as claimed in claim 1 wherein said control circuitry comprises:

a. a one-shot coupled to receive the output from said clear AND-gate and produce an output in response thereto;

b. a first reset mode circuit adapted to allow said clear AND-gate output signal to reset said conflict storage flip-flop a predetermined number of times;

0. a second reset mode circuit adapted to allow said clear AND-gate output signal to reset said conflict storage flip-flop an unlimited number of times;

d. a reset mode selector switch coupled to said first and second reset mode circuits; and

e. a reset AND-gate coupled to receive the output signal from said one shot, to receive the clear signal from said inverter, and to receive an output signal either from said first reset mode circuit or from said second reset mode circuit depending on the preselected position of said reset mode selector switch, said reset AND-gate adapted to produce a reset output signal upon simultaneous presentation of the signals received thereby, the reset output signal thereof is coupled to reset said conflict storage flip-flop.

3. A monitoring circuit as claimed in claim 2 wherein said control circuitry further comprises a clear delay counter coupled to receive said clear AND-gate output signal and delay its being applied to said one-shot for an adjustable predetermined amount of time.

4. A monitoring circuit as claimed in claim 2 wherein said control circuitry further comprises a lockup mode selector means coupled between said reset AND-gate and said conflict storage flip-flop for disallowing resetting of said conflict storage flip-flop.

5. A monitoring circuit as claimed in claim 2 wherein said second reset mode circuit comprises means coupled to said reset mode selector switch for applying a constant signal thereto.

6. A monitoring circuit as claimed in claim 2 wherein said first reset mode circuit allows said reset AND-gate to conduct once and thereafter disallows conduction thereof, said first reset mode circuit comprising:

a. a second conflict flip-flop adapted to produce a first and a second output signal both of which are applied to said reset AND-gate, said second conflict flip-flop preset to produce the first output signal which allows said reset AND-gate to conduct; and

b. delay means coupled to receive the reset output signal from said reset AND-gate and apply a delayed output signal to said second conflict flip-flop which resets said second conflict flip-flop to produce its second output signal which disallows further conduction of said reset AND-gate.

7. A monitoring circuit for use with a traffic control system of the type which produces visual signals in timed sequence for controlling traffic movement through an intersection, said monitoring circuit for sensing the traffic proceed signals and detecting simultaneous occurrence of the proceed signals which could cause conflicts in traffic movement, said monitoring circuit comprising:

a. a plurality of optical couplers connected to the traffic control system for producing an electrically isolated output signal for each of the traffic proceed signals when they are produced by the traffic control system;

b. a modifiable wiring matrix coupled to receive the output signals from said optical couplers for changeable preselecting combinations of these signals which are to be monitored for simultaneous v occurrence;

c. a conflict logic circuit coupled to the output signal combinations from said wiring matrix for producing an output signal upon the simultaneous occurrence of the output signals which form at least one of these combinations; and

d. an optical coupler interface connected to receive the output signal from said conflict logic circuit and upon the occurrence thereof produce an electrically isolated output signal indicative of a conflict of traffic proceed signals.

combinations from said wiring matrix, each of said AND-gates adapted to produce an output signal upon the simultaneous occurrence of the output signals which forms its respective combination; and

b. an OR-gate coupled to receive the output signals from each of said AND-gates for producing an output signal if the output signal from any of said AND-gates is presented thereto.

10. A monitoring circuit as claimed in claim 7 wherein said wiring matrix comprises a plurality of repositionable jumper wires.

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4135145 *Sep 7, 1976Jan 16, 1979Solid State Devices, Inc.Error detecting circuit for a traffic control system
US4383240 *Feb 24, 1981May 10, 1983Solid State DevicesRecorder of the status of a traffic control system
US5073866 *Sep 20, 1989Dec 17, 1991Daeges Michael JTraffic signal control system
US5327123 *Apr 23, 1992Jul 5, 1994Traffic Sensor CorporationTraffic control system failure monitoring
US5986576 *Jan 21, 1998Nov 16, 1999Armstrong; Sheldyn KyleRemote control portable traffic control device and system
US6965322Jul 18, 2003Nov 15, 2005Eric A. MetzTraffic signal operation during power outages
EP0007579A1 *Jul 18, 1979Feb 6, 1980Siemens AktiengesellschaftCircuit arrangement for monitoring the state of signalling systems, especially traffic light signalling systems
Classifications
U.S. Classification340/931
International ClassificationG08G1/097
Cooperative ClassificationG08G1/097
European ClassificationG08G1/097
Legal Events
DateCodeEventDescription
Jun 1, 1998ASAssignment
Owner name: DISPLAY TECHNOLOGIES, INC., GEORGIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:INTERSECTION DEVELOPMENT CORPORATION;REEL/FRAME:009436/0916
Effective date: 19980324
Sep 9, 1992ASAssignment
Owner name: INTERSECTION DEVELOPMENT CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:SOLID STATE DEVICES, INC.;REEL/FRAME:006276/0336
Effective date: 19920217
Sep 9, 1992AS02Assignment of assignor's interest
Owner name: INTERSECTION DEVELOPMENT CORPORATION A CORP. OF CA
Owner name: SOLID STATE DEVICES, INC.
Effective date: 19920217