Emergency Vehicle Control Of Traffic Signals

Abstract

The present system provides a traffic light control system which enables an emergency vehicle such as a fire engine, ambulance or the like to control all traffic lights at each intersection through which it will pass in the course of its intended travel. The traffic lights can be rendered one green and three red at each said intersection along the route with the green light facing the oncoming emergency vehicle. In the alternative the system provides a means for rendering the traffic lights all red at each intersection thereby stopping the traffic in all directions and enabling the emergency vehicle to weave in and out of the stopped traffic.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a traffic light control system which can change from a normal-traffic mode of operation to an emergency mode of operation in response to the command of an emergency vehicle.

2. Description of the Prior Art

When an emergency vehicle, such as fire engine, police car, ambulance or the like, is summoned to a place where an emergency is in effect, the vehicle, of course, attempts to get there in the shortest period of time. Accordingly over the years there have been numerous accidents between emergency vehicles passing through intersections against red lights and non-emergency or emergency vehicles entering these intersections with the green lights. In such cases, the driver of the vehicle entering the intersection usually did not hear the siren nor see the flashing light of the emergency vehicle. On the other hand, in some of these accidents, the vehicle entering the intersection was another emergency vehicle whose operator thought that he had the right of way because of his siren or flashing red light as well as the green light facing him at the intersection.

The numerous incidents of this kind of motor vehicle accident have given rise to some attempts to solve the problem. One such attempt is to have all of the traffic lights wired from a central console, very often located in the police radio room, or the municipal building, of the city in which the system is located. At the console of this centrally controlled traffic light system, there is stationed a dispatcher who is equipped with a two-way communication system. Each of the emergency vehicles is also equipped with a two-way radio communication system and hence, the operator of an emergency vehicle system can be in communication with the dispatcher. The procedure has been to have the operator of the emergency vehicle call the dispatcher and designate what his route might be or what his destination might be. The dispatcher accordingly acts to cause the traffic lights, at the intersections lying along the route of the emergency vehicle and facing the oncoming vehicle, to turn green, with the traffic lights facing the other three directions at these intersections being illuminated red, thereby enabling the emergency vehicle to pass on through.

A problem with this particular system is that all the lights must be controlled by a central control means and the wiring thereof is extremely costly. In addition, there is the problem of human error. The dispatcher has to understand and act upon the message of an operator who is in an extreme hurry to get to his destination and who is apt to provide a "hurried" set of directions. In addition, the dispatcher has to make a sound and quick judgment as to what traffic lights he should control if the route is not a straight line route from the place at which the emergency vehicle is located, at the time the operator has notified the dispatcher, to the place where the emergency vehicle is destined to go. In addition, since the traffic lights are turned on for a long period of time prior to the emergency vehicle arriving at any particular intersection, other emergency vehicles cannot pass therethrough which is inefficient and long traffic jams of normal traffic are created.

Another system which has been employed to deal with the general problem is the clock timer system. In this system, the traffic lights of the entire city are once again wired to a central control and there is either a verbal request, as in the above described system, or the crew, or the operator, of the emergency vehicle sets the system into operation when they leave their particular location. In accordance with this system, the lights along a certain route are turned green for a predetermined amount of time and then are returned to their normal operating system. This system, of course, has the undesirable aspects of the first described system which include the element of human error, the costs of complete wiring and the failure to take into account the problems of other emergency vehicles approaching the intersections along the route of the first request vehicle.

A third system has been used, one in which each of the traffic light facilities at each intersection is equipped with a radio receiver. In this system there is also a dispatcher who has a two-way radio communication setup with each emergency vehicle and will accept requests. When a request has been given by an emergency vehicle operator, the dispatcher through his radio control transmitter causes each of the traffic lights, at the intersections which lie along the intended route of the emergency vehicle, to be changed to green with the traffic lights of the other three directions being red. After a sufficient period of time, in the dispatcher's judgment or in the alternative after the operator of the emergency vehicle has told him to do so, he will cause the traffic lights at the respective intersections to return to a normal operation. Here again there is the element of human error to be considered as well as the inefficiency which is inherent in having the operator of the emergency vehicle continually describing his location so that the dispatcher can turn off the emergency control at the proper lights. The last mentioned operation undoubtedly interferes with other emergency vehicles and normal traffic in general will be snarled.

SUMMARY OF THE INVENTION

The present system provides that each traffic light device at each intersection in the system is equipped with a radio receiver that can distinguish between the four directions, i.e., north, east, south and west. That is to say the radio receiver will receive a signal on the proper channel only, indicating whether the vehicle is approaching from the north, south, east or west. The system provides the option of having the system render the traffic lights one green and three red or alternatively, all four red. The system takes into account that the traffic at each intersection along the intended route of the emergency vehicle is moving in some fashion and gives sufficient time for that traffic to complete its movement before the emergency operation goes into effect. The emergency operation stays in effect only so long as the emergency vehicle is approaching the intersection and immediately thereafter the system returns to a normal operation. The system further takes into account that more than one emergency vehicle may be attempting to take command of the traffic lights at a particular intersection and provides circuitry to handle only one request at a time with leave to hand over to some other vehicle, requesting the command, immediately after the vehicle in command has passed through the intersection.

BRIEF DESCRIPTION OF THE DRAWING

The features and objects of the present invention will be better understood in the course of studying the following description in conjunction with the figures, in which:

FIG. 1 is a block diagram of the system,

FIG. 2 is a circuit schematic of a circuit for changing an RF signal into a DC signal;

FIG. 3 shows how to arrange FIGS. 4A, 4B, 4C and 4D;

FIGS. 4A, 4B, 4C and 4D taken together represent a circuit schematic of the admit one circuit, the flasher circuit, the master transfer safety circuit, 7 -second time delay circuit and the 4-second amber timer circuit;

FIG. 5 shows how to arrange FIGS. 6A, 6B and 6C;

FIGS. 6A, 6B and 6C taken together represent the emergency amber lamp control, emergency lamp control, red lamp monitor, green lamp monitor, emergency green lamp control and the emergency master transfer;

FIG. 7 shows how to arrange FIGS. 8A and 8B;

FIGS. 8A and 8B when taken together represent the terminal board wiring arrangement;

FIG. 9 shows the arrangement for FIGS. 10A and 10B;

FIGS. 10A and 10B when taken together represent the circuit paths through the changeover relays, the green control relays, the amber control relays, the master transfer relay and the flasher relay;

FIG. 11 shows a schematic circuit of one possible combination of relay points as exemplary of all such paths;

FIG. 12 shows the arrangement of FIGS. 13A, 13B and 13C;

FIGS. 13A, 13B and 13C when taken together represent a typical superheterodyne radio receiver which can be employed in the present system;

FIG. 14 shows the arrangement of FIGS. 15A, 15B and 15C;

FIGS. 15A, 15B and 15C when taken together represent two typical tone channel circuits;

FIG. 16 depicts a typical power supply circuit.

It should, of course, be understood that the description and drawings herein are illustrative merely, and that various modifications and changes can be made in the structure disclosed without departing from the spirit of the invention.

Like numerals refer to like parts throughout the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Consider a situation in which there is a main thoroughfare running through a community and along this main thoroughfare there are a number of intersections which have traffic lights, of the kind taught by the present invention, located thereat. These traffic lights are operating to control traffic in the normal fashion. These traffic lights each have a green light for advance, a yellow light for caution and a red light for stop. In all probability, they have been set to be green for a predetermined period of time such that if the operator of a regular vehicle is driving his vehicle along this main thoroughfare at a speed above a certain minimum but within the speed limit, these lights will automatically be green so as to allow the traffic to flow in the most expeditious manner up and down the thoroughfare.

Now consider that there has been a call to the police department of the community which call indicates that there is a fire of a very serious nature at the northern end of the town and in the opinion of the caller, there is a high likelihood of injury. The police department immediately notifies the fire department (which dispatches at least one fire engine) as well as the local hospital (which dispatches an ambulance) to the scene. Now let us further assume that our hypothetical thoroughfare runs north and south and that the fire company which has been notified lies directly south of the location of the fire. We will further assume that the police department lies east of the thoroughfare, while the hospital lies west of the thoroughfare. Further assume that the police station lies some 15 blocks north of the location of the fire station while the hospital lies only three blocks north of the location of the first station. Finally, assume that all the emergency vehicles, that is, the fire engines, the ambulance and the police car will attempt to use the main thoroughfare as the most direct way to get to the scene of the fire.

The fire engine will leave almost immediately after having received the call since its people are ready for this sort of action at all times. The fire engine will leave the fire house and move onto the main thoroughfare at which time the operator of the engine will set his radio transmitter on N, indicating that he is travelling north on the thoroughfare and therefore, wants to seize control of all of the traffic light installations as he approaches them along the thoroughfare.

If we consider FIG. 1 which is a block diagram of the system and study this block diagram in view of the hypothetical just set forth, the general operation of the system becomes better understood. In FIG. 1 we find that there is an emergency admit one circuit 101 with four input lines thereto labeled W, E, S and N. These input lines obviously stand for west, east, south and north. At each of the intersections of the thoroughfare having a traffic light installation, the circuitry represented by the block diagram of FIG. 1 will be installed. At each of these installations, there is a radio receiver which can receive signals of at least four different frequencies or four channels, each of which respectively represents west, east, south and north. The signal which is received by the radio receiver is ultimately changed into a DC signal and transmitted to the emergency admit one circuit. In FIG. 1, and considering the hypothetical set forth, we find that the signal from the fire engine would be received and after proper modulation it would be transmitted along the line 100, which is labeled "N." The emergency admit one circuit 101 accepts the signal on line 100 and transmits it via line 102 to the actuation and reset control circuit 103. At the same time there is a feedback signal from the emergency admit one circuit 101 back to certain gates within that circuit, which feedback signal inhibits those gates so that no further demand signals may be handled until the demand signal in control is no longer active, i.e., the emergency vehicle has passed through the intersection. In other words, if the ambulance leaving the hospital and traveling east toward the thoroughfare had arrived or approached the thoroughfare in some given time after the fire engine had started up the thoroughfare, the signal which the ambulance would have sent and which would have been received on line 104 would have no effect on the emergency admit one circuit because the gates through which that signal would have had to pass would have been blocked by the feedback signal on line 105.

Now the signal from the emergency admit one circuit is transmitted to the actuation and reset control circuit, which circuit only serves to transmit the signal received to the alarm memory and reset actuator circuit 106 at this time. Actually the reset circuit acts to reset the memory circuit under proper conditions. However, thus far this signal would simply be transmitted to the alarm memory circuit to cause the memory circuit to remember that a request has been received and to remember the direction from whence that request came.

However, there are certain conditions which must be met before the signal from the emergency admit one circuit can be transmitted to its memory circuit and that is, that sufficient time must be given for the normal traffic which has been operating under normal (preemergency) conditions to be cleared thereout, or at least to have the operators of such vehicles have sufficient time to manipulate their vehicles in accordance with what will probably be a shortened time cycle for the normal operation. In this particular system, it has been found that if a green light which has been actuated during a normal operation is permitted to stay on for at least 7 seconds, the operators of motor vehicles which are moving through the intersection under consideration have sufficient time to manipulate their motor vehicles across the intersection rather than be startled by a quick change of the traffic light which may cause some confusion. The 7-second delay is somewhat arbitrary and the circuitry provides for changing this period of time if such a period of time should be found to be unnecessarily long or on the other hand too short.

The 7-second delay circuit operates each time the system under normal operating conditions changes to a green light and it insures that the green light will remain on for at least 7 seconds even though there has been a demand for an emergency take over sometime within that 7 seconds. After the 7 seconds has elapsed, the proper gates within the actuation and reset control circuit 103 are permitted or allowed to become actuated and accordingly the signal on the line 102 can be passed through those gates. Next the signal from the actuation and reset control circuit 103 is transmitted on line 107 to the alarm memory circuit 106 so that the system is now conditioned to remember that a demand for control has been made.

Once the memory has been set to remember that a demand for control has been made, there is a signal transmitted on line 108 to the emergency amber timer circuit 109. Now the purpose of the emergency amber timer circuit 109 is threefold. First of all, it is through this circuit 109 that any lights which have been green at the intersection coming under the control of the emergency vehicle, are changed to amber for a 4-second period with one exception. The exception being that if a green light is already facing the oncoming emergency vehicle in control it will remain green. In other words, in our case if the light facing south (which would of course permit the vehicle to travel north) were in fact green at the time that the demand was made this light would remain green and not be subjected to a 4 -second amber period. However, as indicated if the direction for the control is not green, then the other two directions which were green would be changed to an amber color for 4 seconds.

The emergency amber timer circuit 109 has a second role and that is of transmitting a signal to reset the memory if in fact the current demand is following a previous demand and the normal operation monitor has not operated to reset the memory. In other words, in our hypothetical, assuming that the fire engine has seized control of the lights along the thoroughfare prior to the ambulance arriving at the intersection, then once the fire engine has passed the intersection at which the ambulance is waiting, the ambulance's demand will be received at the emergency admit one circuit. The same electronic manipulations will be experienced as just described above and on this occasion, the emergency amber timer will transmit a signal on line 110 to reset the north memory so that the circuit will now remember that there has been a demand by a vehicle traveling in an eastward direction.

After the 4 seconds has elapsed, the emergency amber timer 109 transmits a signal on line 111 to the master transfer safety circuit 113 to permit that circuit to be actuated for the purpose of having the system cause the traffic lights, at the various intersections along the thoroughfare, to provide a green light facing south and a red light facing east, north and west. Actually, the system has the option of providing red lights in all four directions, but for the main part of our description we will consider a "one-green, three-red" system. At the same time and as an option at each of the traffic lights there is a flasher light which flashes during an emergency situation.

Returning now to the block diagram, we find that once the alarm memory has been set, (in addition to activating the emergency amber timer), it activates the emergency master transfer circuit 112. The role of the emergency master transfer circuit 112 is the role of handing over the control of the system from the normal operation to the emergency operation. The emergency master transfer circuit 112 is not fully activated until it receives a signal from the master transfer safety circuit 113. In effect, the emergency master transfer circuit can be considered a coincidence type device, which requires a signal from the alarm memory circuit 106 as well as the master transfer safety circuit 113. It will be recalled that the master transfer safety circuit 113 did not come into operation until after the 4 seconds required by the emergency amber timer 109 had elapsed. Therefore the coincidence occurs 4 seconds after the memory has been set.

Once the emergency master transfer circuit 113 has been energized, it in turn transmits a signal on line 117 to the emergency changeover relays 118. Actually, the energizing of the emergency changeover relays is the final step in taking over the system from a normal operation by the emergency operation.

Returning now to the block diagram and in particular the alarm memory 106, we find that the output therefrom on line 119 is transmitted to the emergency lamp control relays 120. It should be understood that the memory remembers the particular direction channel that has been activated, (in our case of the fire engine it was the north channel), and hence is capable of providing a signal to specifically initiate the turning on of the green lamps (advance as go lamps) to allow a northerly traffic flow. The emergency changeover relays are arranged in relay-point logic such that the proper signal from a voltage source, through the particularly chosen emergency lamp control relay, will find a path through the emergency changeover relays to the proper direction green light circuit. In other words, in our example the memory will choose the north green light drive control circuit which will energize the north green emergency lamp control relay, whose relay points are so connected that, in conjunction with the emergency changeover relay points, a signal will be transmitted to turn on a light permitting northerly traffic flow for the oncoming fire engine. This latter step is depicted by the signal being transmitted from the emergency changeover relays 118 along the line 121 to the emergency green lamp control 122. It should be understood that reference to directions is made with respect to the desired traffic flow and not necessarily to the physical location of a traffic light. For instance, a north control will eventually cause a light facing south to be energized because such a light permits northerly flow.

Before discussing the operation of the present invention in greater detail, let us consider certain ground rules or circuit particulars so that the description is more readily understood. The system encompasses a binary concept and for the particular system discussed herein, a voltage in the range of 0 volts (or ground condition) to +1 volts will be considered a "ZERO" condition while a signal in the range of +2 to +4 volts will be considered a "ONE" condition. Further, let it be understood that throughout the circuitry there will be shown NAND gates depicted by the normal configuration of a half moon with input lines thereto and a circular output line indicating an inversion. It will be understood that these NAND gates are positive NAND gates following the TRUTH TABLE below.

Input Output A B C 0 0 1 0 1 1 1 0 1 1 1 0

it should be understood that while the "ONES" and "ZEROS" in this particular description are for the voltages outlined, other voltage levels could be used and in like manner it should be understood that other forms of logic other than the positive NAND gates which have been employed could be used, both of these changes still being within the spirit of the present invention.

CHANNEL DESIGNATED SIGNALS

It will be recalled that in our hypothetical the fire engine was traveling along the thoroughfare in a northerly direction. It will further be recalled that the operator of the fire engine had set his transmitter to north. The transmitter sends out a keyed signal. The keyed signal is received by a radio amplifier which is part of the equipment of the present invention located at the intersection being approached by the fire engine. This keyed signal is properly amplified, passed through a mixer whereat the signal is refined by a local oscillator, passed through the normal stages of IF amplification and finally is received at four filter circuits. The four filter circuits respectively represent the north filter, the south filter, the east filter and the west filter. Depending upon which frequency is being transmitted, as determined by the operator of a motor vehicle, a signal will be transmitted through the proper filter circuit. In our case, the filter circuit representing the north direction is the one which will accept and pass the signal. After the signal leaves the filter circuit it is further amplified and modulated by subcarriers until finally this particular signal is tone detected and rectified to become a DC input signal. Equipment for accomplishing the foregoing transition of changing a radio frequency signal into a DC signal is well known and can be accomplished in a number of ways. A radio receiver and filter circuits are shown in FIG. 13, by way of example, and will be discussed subsequently, while tone detector circuits are depicted, by way of example in FIG. 15.

The transition of the R.F. signal into a DC signal is not unique to the invention at hand and therefore at this juncture of the description we will simply consider that a DC signal is generated in response to the transmission of a signal from a vehicle and this particular DC signal is further channeled to represent the direction, either north, south, east or west, from whence it came.

Having established the foregoing, let us examine FIG. 2 which depicts two tone channel circuits i.e., the circuitry necessary to transform a varying signal resulting from the radio frequency transmitted signal into a stable DC signal, i.e., binary signal representing either a "ONE" or a "ZERO."

In FIG. 2, there are shown two channels, channel A and channel B. Actually, the system contains four such channels, one each being assigned to the direction north, south, east and west.

Initially, let us assume that no signal is being transmitted by a vehicle and therefore each of the channels is in its quiescent state. Further assume that from the terminal 222 of terminal board 223, there is a DC voltage of +15 volts supplied. The +15 volts is an arbitrary selection and obviously could be another value. Also assume that from the terminals 212 and 211, there is ground potential supplied as depicted in the figure. Under these circumstances, we find that there is current flowing from the terminal 222, along line 229, through the resistor 224, through the Zener diode 225, along lines 226, 227 and 228 back to the ground terminals 212 and 211. In addition, there is current flowing from the terminal 222 along the line 229, through the resistor 230, through the resistor 231, along the lines 226, 227 and 228 back to the ground terminals 212 and 211. The first current flow mentioned above provides a positive voltage of approximately +3 volts at terminal 232 and hence there is a 3 volt back bias across the base-emitter junction of the transistor 233. The foregoing is true because the emitter of the transistor 233 experiences approximately 3 volts at the point 232, through the diode 234, while the base of the transistor 233 is tied to ground through the capacitor 235. The second current flow through the resistors 230 and 231 develops a potential of approximately +4.5 volts at terminal 236.

Accordingly we find that in the quiescent state, that is, without any radio signals being transmitted from a vehicle, the channel B output is a binary ONE (i.e., +4.5 v.) developed at the collector of the transistor 237 and appearing at the terminal 218 of the terminal board 223.

Now consider that the channel B shown in FIG. 2 is the circuitry to which the amplified and rectified radio signal defining the northerly movement of the fire engine is transmitted. Such a signal would be received at terminal 216. In other words, as indicated earlier, as the fire engine commences traveling north, the operator turned the switch on its transmitter to the "north" (N) frequency which transmitted a signal to the traffic light system. After proper amplification, modulation, and rectification, the signal would appear on terminals 216 of the terminal board 223. The diode 238 along with the capacitors 239 and 235 as well as the resistor 240 represent the last portion of the circuitry employed in the rectification, or "smoothing out" of the varying signal.

The positive DC signal would be applied to the base of the transistor 233, thereby providing current flow from the terminal 222, through the resistor 242, through the transistor 233, through the diode 234, in a reverse direction through the Zener diode 225 to the ground side of the circuit. This last mentioned current flow would cause the collector of the transistor 233 to experience a drop in potential since there is now heavy current flow across the resistor 242. The potential drop at the collector of transistor 233 turns on the PNP-transistor 243, thereby providing current flow from the terminal 222, through the diode 244, through the transistor 243, and through the resistor 245 to the ground side of the circuit.

In response to turning on of the resistor 243, as just described, there is a relatively large potential developed across the resistor 245 which in turn has two effects. The first effect is to forward bias the base to emitter junction of the transistor 237 thereby causing this last mentioned transistor to turn on and provide current flow from the terminal 222 along the line 229, through the resistor 230, through the transistor 237, to the terminal 246, the last terminal being on the ground potential side of the circuit. It should be recognized that this last activated circuit substitutes a low impedance in the form of transistor 237 for a relatively high impedance in the form of resistor 231. The effect is to cause a greater loss of voltage across the resistor 230 and hence the terminal 236 experiences a drop in potential to somewhere in the range of between 0 and +2 volts. Hence, the output signal of the channel B circuit is now a ZERO in a binary sense.

The second effect of developing a high potential across the resistor 245 is to charge up the capacitor 247. Capacitor 247 is a relatively large capacitor and is introduced into the circuit to block a DC and pass an AC signal. A charging of the capacitor 247 provides current to the base of the transistor 248 thereby turning on that transistor. When transistor 248 conducts, it in turn causes transistor 249 to conduct. When transistor 249 is turned on, its circuit path provides a shunt to the current passing through transistor 233 and accordingly, the value of the back bias across transistor 233 is reduced. In other words, transistor 249 even though it is series connected to the diodes 250 and 251 provides only approximately a 2 volt drop and hence the threshold value necessary to cause the transistor 233 to conduct has been changed from +3 volts to +2 volts. This change in sensitivity of the threshold which would be required to fire the transistor 233 eliminates the condition of having a noise signal, whose voltage swing is around 3 volts, to cause the circuit to oscillate. Such a condition is made possible by the location of the vehicle being in a critical position after once having turned on the circuit. When the value of the input signal as received on the terminal 216 falls below the 2 volt level, transistor 233 turns off, thereby turning off the rest of the circuit and returning it to the quiescent state. Meantime the capacitor 247 is able to discharge through the resistor 252, through the base to emitter junction of the transistor 237, and through the resistor 253 back to the other side of the capacitor 247.

Accordingly, it becomes apparent that when there is an input signal from the radio receiver which is transformed into a positive DC signal on the input to tone channels, this signal results in a binary ZERO being present at the output signal line of the channel.

ADMIT ONE CIRCUIT

Consider FIGS. 4A through 4D in conjunction with FIGS. 6A through 6C, FIGS. 8A and 8B, and FIGS. 10A and 10B. It will be noted that in these figures there are terminal boards such as the terminal board 223 shown in FIG. 2. The terminal locations on these boards will be numbered such that the first number identifies the figure for which it is most meaningful. In FIGS. 8A and 8B which show the wiring of the terminal boards, the terminals are identified as they are in the separate figures but without the figure identifying number, e.g., terminal 22 in FIGS. 8A and 8B might be 622 in FIG. 6B.

Examine first FIGS. 4A through 4D, which show the logic of the "admit one" circuit. Bearing in mind that the vehicle in our hypothetical is a fire engine traveling north, and further bearing in mind that we have studied how to generate a binary ZERO signal, in response to a radio signal being transmitted on the "north" frequency, we find that we have a ZERO signal present on the terminal board at terminal 4R. This signal came from the North tone channel, such as channel B in FIG. 2. The ZERO signal at 4R will be transmitted to the gate 424. It will be recalled that the gates are positive NAND gates (i.e., there must be two ONE signals at the input to provide a ZERO output) and hence with a ZERO-ONE condition respectively present on the two inputs to the gate 424 there will be a ONE signal transmitted therefrom. The ONE signal from the gate 424 will be transmitted along line 425 to the input 426 of the NAND-gate 427. In order to determine the output of the gate 427 examine the nature of the input signals on the input lines 428, 429 and 430.

The nature of the input signal to gate 427 on line 428 is determined by the output of the gate 431. We need look no further than the input on line 432 of the gate 431 because that input is a ZERO which is developed at the input gate 433 representing the south demand signal. In other words, there is no demand from the south at this moment and hence the gate 433 has two ONE signals applied thereto providing (in accordance with our TRUTH TABLE) a ZERO signal on line 432. In further accordance with our TRUTH TABLE, one ZERO input to the NAND gate will provide a ONE output signal therefrom, hence there is a ONE signal present on the line 428 of the gate 427. The input signal on line 429 is determined by the output signal of the gate 434 and we need look no further than the input signal on the line 435 to determine the nature of that output signal. The signal on line 435 emanates from the input gate 436 which represents a demand signal from an easterly direction and since there is no easterly demand signal at this time, there is a ZERO signal present on line 435. In accordance with the TRUTH TABLE a ZERO signal on line 435 will provide a ONE signal from gate 434 which signal will be found present on the input 429 to the gate 427. Finally the input signal on input line 430 is determined by the output signal of gate 437. The output signal of gate 437 can readily be determined by considering the signal on line 438. The signal on line 438 comes from the input gate 439 which represents a west demand signal. Since at this time there is no west demand signal, the signal on line 438 is ZERO and hence there is a ONE output signal from gate 437. The ONE output signal from gate 437 appears on line 430. It follows then that the signals on each of the lines 426, 428, 429 and 430 are all ONE signals and hence there is a ZERO output signal from gate 427 on line 440.

It should be noted before we continue with the description that each of the gates 427, 431, 434 and 437 are similar gates handling the initial input signal from the demand gates and having further input signals from the respective counterpart gates.

The output signal from gate 427 on line 440, which we have determined is a ZERO at this time, is transmitted to the gates 441, 442, 431, 434 and 437. Now the transmission of this ZERO signal to the gates 431, 434 and 437 effectively blocks those gates, or inhibits those gates, so that if in fact there is a demand signal from one of the other directions the gate handling that demand signal will be inhibited and will not be able to pass the signal on. Hence it becomes evident why this circuit is referred to as an "admit one" circuit. Only one demand signal at a time is permitted to pass through the circuit. In our example if the ambulance had arrived at the intersection and its transmitter was demanding attention, the fire engine would already have taken over the admit one circuit and the signal from the ambulance would not have been accepted.

The gate 441 receiving the ZERO signal from gate 427 provides a "ONE" signal therefrom which is transmitted to gate 443. Now it should be recalled that in the general description it was indicated that the alarm memory would not be set until the system had been assured that the green lights which were turned on, under the normal operation, had in fact been on for at least 7 seconds. Without discussing the detailed operation of the 7-second green light timer 444 at this time, it can be seen that the output signal from gate 445 of the 7-Second Green Light Delay Timer circuit 444 provides a signal which is the second input to gate 443 on input line 446. Assume for this portion of the discussion that the 7-second period has passed and that there is a ONE signal being transmitted from gate 445 to the input line 446. Accordingly, there will be two ONE input signals to gate 443 which will provide a ZERO output signal therefrom. The ZERO output signal is transmitted to the gate 447.

The gates 447 and 448 make up a flip-flop which is the memory of the system. The flip-flop will be considered set when the output of gate 447 is a ONE and the output of gate 448 is a ZERO and will be considered reset when the output signal of gate 447 is a ZERO and the output signal of gate 448 is a ONE.

Returning momentarily to the output signal of gate 427 (which is a ZERO at this time), this signal is also transmitted to the gate 442. The second input signal to gate 442 is the output signal of the gate 449 found in the controller green monitor section. The normal controller green monitor devices are set up such that when the system is operating in the normal mode of operation, and there is a green light, for instance in the north-south direction, the relay coil 450 will be energized transferring the points 451. When the points 451 are transferred there is ground potential or a ZERO input applied through capacitor 452 to the gate 449 which assures that a ONE signal will be transmitted from gate 449 to the gate 442. The reason for transmitting a ONE to gate 442 is to reset the flip-flop, as will be explained. At the time that the demand signal passes away and the admit one circuit refers to its quiescent state, the output from gate 427 will also be a ONE and hence there will be a ZERO signal emanating from the gate 442. The ZERO signal from the gate 442 under these last conditions will provide a ZERO input signal to the flip-flop gate 448, which will provide a ONE output signal therefrom. The ONE output signal from the gate 448 will be transmitted to the flip-flop gate 447 and in conjunction with the quiescent state ONE signal from the gate 443 will provide a ZERO output from gate 447. Hence the flip-flop will reset. It becomes apparent that when the demand signal terminates and normal operation is resumed and attempting to provide a green light in a north-south direction, the north green flip-flop will be reset.

In partial summary of our present consideration, we have set the flip-flop indicating that there is a north demand in effect and accordingly provided a ONE signal from gate 447 and a ZERO signal from gate 448.

EMERGENCY AMBER TIMER

It will be recalled from the general discussion that after the system was satisfied that the green lights had been illuminated for at least 7 seconds, it next provided for a 4 second amber period by energizing the emergency amber timer. The signal which initiates the energization of the emergency amber timer is a signal from the gate 448 transmitted along line 453 to the line 454. This will be a ZERO signal which is transmitted through the capacitor 455 to the gate 456. Accordingly, there results a ONE output signal from gate 456 which is transmitted to the gate 457. The ONE input signal from gate 457 in conjunction with the ever present ONE signal on line 458 provides a ZERO output signal therefrom which is transmitted to the gate 459. The ZERO input signal to gate 459 provides a ONE signal therefrom which is transmitted to gate 460 and back to the cathode of the diode 462 as well as to the resistor 463. The resistors 463, 464 in conjunction with the capacitor 465 provide an RC time constant which consumes some 4 seconds before the transistor 466 is turned on. When transistor 466 turns on, it turns on transistor 467 which in turn turns on transistor 468 to provide a ZERO input signal on line 469 through the gate 460.

It will be recalled that one of the functions which the emergency amber timer accomplishes is the function of resetting the memory if in fact the actuation of the emergency amber timer is the result of one demand signal following another, i.e., with no normal operation in between demand signals. This is accomplished by transmitting the signal from the gate 460 along the line 470 to the gates 449 and 471. It will be recalled that when we discussed the gate 449 it was indicated that if there were a ONE signal provided therefrom at the time that the demand signal had died, the memory would be reset. Now during the 4 second amber timer interval, the signal on line 469 as well as the signal on line 472 are both in a ONE state and hence there is a ZERO output from the gate 460. The ZERO output signal from the gate 460 will cause each of the gates 449 and 471 to provide a ONE output signal. Hence if there previously had been a demand signal which had terminated and allowed the admit one circuit to accept another demand signal, the memory of the first demand signal would be erased, i.e., the memory would be reset.

It will also be recalled from the general description that the emergency amber timer provided a signal to turn each of the green lights to an amber state unless the green light faced the direction in demand. This is accomplished by the output signal from gate 459. The output from gate 459 is transmitted along the line 473 to the terminal 4U of the terminal board 423.

Examine terminal board 423 as shown in FIG. 8. We find that the 4U line takes the signal along line 801 to the terminal 6A of terminal board 623. Examine then FIG. 6A whereat we find the signal coming from the terminal 6A on line 624 to each of the gates 625 through 628. Hence it follows that each of the gates 625 through 628 has received a ONE signal on at least one of its input lines. Each of the further input lines to the gates 625 through 628 comes from the red lamp monitor circuits, each of which is energized when its particular direction has a red lamp illuminated. In other words, assume in our case that the east-west direction of a particular intersection has red lights illuminated thereat. This condition would respectively energize the relay coils 629 and 630. The energization of those relay coils would respectively transfer the relay points 631 and 632 to provide a ZERO input signal to the gates 625 and 626. Since the north-south directions in the last example would have green lights, the gates 627 and 628 each would have a ONE signal transmitted thereto from their respective red lamp monitor relays. Hence the gates 627 and 628 would each have two ONE signal inputs thereto. Accordingly, there would be a ONE output signal from each of the gates 625 and 626, and a ZERO output signal from each of the gates 627 and 628. These last-mentioned output signals are transmitted to the gates 633 through 636.

Accordingly, the gates 633 and 634 would each have two ONE input signals thereto, while the gates 635 and 636 would each have a ZERO-ONE combination of input signals. In response to this last set of signals there would be provided ZERO output signals from the gates 633 and 634 and ONE output signals from the gates 635 and 636.

The ZERO output signals from the gates 633 and 634 would be transmitted to the respective cathodes of the diodes 637 and 638.

The ZERO signals thereat would provide a ZERO input signal to the base elements of the respective transistors 639 and 640 and hence render those transistor nonconducting. On the other hand, the ONE signal which would be transmitted from the gates 635 and 636 respectively to the cathodes of the diodes 641 and 642 would render those diodes nonconducting thereby providing a ONE signal to the base elements of the respective transistors 643 and 644. A ONE signal to an NPN-transistor will turn on such a transistor and hence, the transistors 643 and 644 would be conducting.

When transistor 643 conducts the current supplied thereto comes from the terminal 6D of the terminal board 623. This can be determined by tracing the line 645. If we examine FIG. 8 we find that terminal 6D is connected to the south amber point -2 relay terminal.

The south amber point -2 relay terminal can be seen in FIG. 10 at point 1001. The line from the terminal 6D in FIG. 8 is line 1002 in FIG. 10. The power to energize relay coil 1003 is connected from the terminal -2 identified as 1004 along the line 1005 from the 12volt supply 1006.

It follows without repetitive detailed explanation that the signal from transistor 644 can be traced in a manner similar to that just described through the terminal boards to eventually energize the relay 1007 in FIG. 10. However, it will be remembered that in the general explanation it was pointed out that if the light which was in demand was already green, it would not be turned amber. This is accomplished in accordance with the selection of both the north green relay 1008 at the same time that the relay 1007 is energized. When both relays are energized simultaneously, the path through the relay points simply energizes the amber lamp for the south but permits the green lamp to be continued in operation. This will become more apparent hereinafter when we describe the operation of the circuitry shown in FIG. 12.

Returning to the operation of the emergency amber timer it will be recalled from the general description that the emergency amber timer in its third function energizes the master transfer safety circuit.

This last mentioned function is accomplished by the output signal from gate 460. The output from gate 460 is transmitted along the line 474, which if followed out will terminate at the terminal 4L on terminal board 423. Examining FIG. 8, we find that 4L is further connected to 6J. Examine FIGS. 6 and it is found that 6J provides one input signal to the gate 646. Now it will be recalled that the output signal from gate 460 during the amber timer 4-second period is a ZERO output signal and at the end of the 4-second period is a ONE output signal. It is this ONE output signal that is effective at the gate 646. Assume that the input signal on the line 647 is a ZERO which input signal will be explained in more detail hereinafter. The input signal on line 647 comes from the beacon flasher circuit and for the most part is a ZERO. Accordingly, then gate 646 has a ONE input signal and a ZERO input signal which causes a ONE output signal on line 648. Line 648, if traced, will be found connected to the terminal 6K. If we go to FIGS. 8 we find that 6K is connected to terminal 416. FIG. 4 reveals that 416 is connected to the cathode of diode 475. A ONE signal to the cathode of diode 475 renders that diode nonconductive and causes a ONE signal to be applied to the base of transistor 476. Accordingly, transistor 476 will conduct providing a low voltage signal to the base of transistor 477 thereby cutting off that transistor. With transistor 477 cut off, the collector thereof will provide a high-voltage signal to the base of transistor 478 thereby rendering that transistor conductive, assuming, of course, that the proper voltages are applied to the collector and emitter thereof. The application of the proper voltages represents further control conditions.

EMERGENCY MASTER TRANSFER

If we follow the line connected to the collector of transistor 478, we find it is connected to terminal 419. Turning to FIG. 8, it becomes apparent that 419 is connected to the master transfer relay 1010 at point 2. If we examine FIG. 10, we find that line 1009 is a line coming from terminal 419 and the other side of relay coil 1010 is connected to terminal 1006 and hence there is a 12volt supply provided to the relay 1010. We need only consider now whether the emitter terminal of transistor 478 is connected for electrical continuity to the relay power supply. If we trace out the emitter line of transistor 478, we find it is connected to terminal 418 of terminal board 423. In FIG. 8, terminal 418 is connected to terminal 613 of terminal board 623. In FIG. 6, terminal 613 is found to be connected to the collector of transistor 649. Accordingly, then if transistor 649 is turned on, we find that we have connected the relay 1010 between a 12-volt supply and ground, thus providing sufficient power to energize the master transfer relay 1010 as shown in FIG. 10.

If we examine the connection to the cathode of diode 650, we find that this line is connected to terminal 622. FIG. 8 reveals that terminal 622 is connected to 4T. In FIG. 4 we find that terminal 4T is connected to the output of gate 479. The gate 479 is connected to the same input signal on line 453 that was transmitted to start the emergency amber timer circuit in operation. It will be recalled that that signal came from gate 448 and it was a ZERO signal. Irrespective then of what the other input signals are to the gate 479, the ZERO signal on line 454 will render the gate 479 with a ONE output signal and that ONE output signal will be transmitted therefrom to the terminal 4T, further to the terminal 622 and finally to the cathode of the diode 650. A ONE signal at the cathode of diode 650 will render that diode nonconducting and hence will cause a ONE signal to be applied to the base of transistor 649 thereby causing that transistor to be conductive. We now find that we have completed electrical continuity as well as provided power to energize the master transfer relay 1010. As will be seen subsequently the energization of the master transfer relay 1010 acts to energize and transfer all of the changeover relays.

PARTIAL SUMMARY

Thus far in keeping with the general description, we have considered the detailed description; of the emergency admit one circuit; of the actuation and reset control circuits; of the setting up of the memory and the possible resetting thereof; as well as the operation of the emergency amber timer circuit and the functions that it accomplishes. We have not considered how the green light remains energized when it is the light in demand, i.e., doesn't turn amber. That consideration will come when we have considered how to energize the north green relay.

ENERGIZATION OF NORTH GREEN RELAY

Energization of the north green relay is initiated by the signal from gate 447. It will be recalled that gate 447 is that part of the flip-flop which remembers whether or not there has been a demand and in our example a demand by a vehicle traveling in the northerly direction. In our example there has been a demand and accordingly (as explained earlier) there is a ONE signal emanating from gate 447. This ONE signal is transmitted to the gate 480. Consider for the moment that the inputs on lines 481 and 482 are ONES (we will consider these inputs hereinafter) and therefore there is a ZERO output signal from gate 480 which ZERO output signal is transmitted to the gate 483. The input signal on line 482 is always a 4.5 v. as can be determined by tracing it to terminal 6W of terminal board 623. With a ZERO output signal present at gate 483 there is a ONE output signal on the line 484. If the line 484 is traced, it will be found to be connected to the terminal 4E. FIGS. 8 indicate that terminal 4E is connected to terminal 621. In FIG. 6 the line connected to terminal 621 is connected to the cathode of diode 651. Now it will be recalled that there is a ONE signal on the line from terminal 621 and hence a ONE signal is applied to the cathode of diode 651 which renders that diode nonconducting. The nonconducting diode 651 enables a high-voltage signal to be applied to the base of the transistor 652. Accordingly then transistor 652 is ready to conduct if the proper voltages are present on its collector and emitter. It will be noted that the transistor 652 is labeled the "north green coil driver." If we trace out the connection to the collector of transistor 652 we find that it is connected to terminal 612. FIG. 8 reveals that terminal 612 is connected to the north green two relay terminal. If we examine FIG. 10 we find that line 1011 is the line from terminal 612 and that terminal 10 on the other side of the relay coil 1008 is connected to the 12-volt terminal 1006. Accordingly, when the transistor 652 has a ONE signal applied to its base the north green relay 1008 is energized.

Before we proceed with the discussion of the relay point path to effect the illumination we should consider whether or not we can energize the north green relay if all the conditions that we have around are not present. For instance, we assumed that the signal on line 481 had a ONE signal thereon. If we trace line 481 we find it is connected to terminal 4Z which from FIG. 8 is found to be connected to terminal 6R of terminal board 623. The line from 623 on FIG. 6 goes to switch 654 of the North Green Lamp Monitor. If the north lamp is already green relay 653 will be energized thereby removing the ground clamp from line 656 so that a ONE signal (4.5 v. from the source shown at switch 654) is present on line 481. Hence it becomes apparent that if a direction has a green light and the demand is for a green light in that direction the green coil driver will be energized which in turn will switch the associated green relay.

Let us digress for a moment and consider FIG. 11 since at this point of the discussion we have traced the circuitry to energize the north amber relay, the north green relay and the south amber relay. In FIG. 11 it will be noted that there is an option switch 1101 located in the left-hand side of the figure. The option switch is set to the "three red--one green" mode of operation. Also note in FIG. 11 that when the north green relay has been energized the point 1102 is connected to the transfer strap, point 1103 is connected to its transfer strap and the point 1104 is connected to its transfer strap. The connecting of points 1103 and 1104 to their respective transfer straps has no effect on the particular operation at this time because point 1103 is related to a "four red" option and with respect to point 1104 we have not discussed any means for transferring the flasher relay circuit points.

We have discussed the energization of the north amber relay which would connect the point 1105 to its transfer strap. As was mentioned earlier, it should be recognized that when the master transfer relay was energized by the energization of the relay coil 1010 (FIG. 10), each of the emergency changeover relays was also energized and hence the emergency relays A, B, C, D, E and F have had their points transferred. Accordingly, then, in FIG. 11, each of the emergency changeover relays A, E, and B has transferred the straps, respectively, to the points 1106 through 1108. Having discussed the proper energization of the relays we find that a signal transmitted along the line 1109 passes through the "three red--one green" option switch, through the point 1102, through the point 1106 to energize the north green lamp even though the north amber relay has been energized. Let us consider this circuitry as though it were labeled "South Green Relay" and "South Amber Relay," understanding of course that there is such circuitry provided for all the directions. If we consider that the south amber relay has been transferred while the south green relay has not been transferred (according to the last example) we find that there is a signal along line 1109, along line 1110, through the point 1112 of the south green relay, through the point 1105 of the south amber relay through the emergency changeover relay E point 1102 to energize the south amber lamp. It follows then that we have discussed how to keep the green lamp for the North Light, which is in demand, energized while illuminating an amber lamp for the South Light.

It should also become apparent at this point that as long as the memory flip-flop made up of the gates 447 and 448 (FIG. 4) is set there will be a signal provided to the north green coil driver (FIG. 6) to keep the north green relay coil 1008 (FIG. 10) energized and hence to keep the green light on.

SEVEN SECOND DELAY

Earlier it was mentioned that when a green light was turned on the 7 second delay circuit provided an inhibit signal for at least 7 seconds. During a normal operation (or emergency operation) if the north green light is illuminated the relay 653 is energized. The relay 653 is energized through the control socket (CS) terminal 1020, terminal 617 and diode 675.

With the relay coil 653 energized, the strap 654 will be transferred and there will be a ZERO signal on line 655, and a ONE signal on line 656. It should be understood that the green lamp monitors are not a particular part of the emergency circuitry but are in operation whether the emergency circuitry is on or whether the normal mode circuitry is on. Accordingly, the ZERO signal on line 755 is found connected to the terminal 6S. FIG. 8 reveals that terminal 6S is connected to terminal 415. FIG. 4 reveals that terminal 415 is connected to input line 485 of gate 486. Hence there is a ZERO signal from line 655 to input line 485. The ZERO signal on line 485 provides a ONE output signal from gate 486. The ONE signal from gate 486 is fed back to the cathode of diode 487 as well as to the resistor 488. The resistors 488, 489 and capacitor 490 provide an RC time constant which is approximately 7 seconds long and hence it is 7 seconds before transistor 491 gets turned on. When the transistor 491 gets turned on, it in turn causes transistor 492 to conduct, which in turn causes the transistor 493 to conduct. When the transistor 493 conducts it provides a ZERO signal to gate 445 thereby providing a ONE output signal therefrom which enables the admit one circuitry to advance the demand signal to set the memory. At the same time the ZERO signal from gate 445 is transmitted to gate 486 and effectively resets the flip-flop which is made up of the gates 486 and 445.

Let us consider what happens with the operation of the lights when there is not a green signal in effect in the demand direction. In particular let us consider an example of when north-south are red and east-west are green and the fire engine is traveling in a north direction making a demand to control for this north direction light. In this situation we would find that both the east-west lights would be turned amber in accordance with the circuit shown in FIG. 11. After the 4 second time period the east and west coil drivers, respectively transistors 640 and 639, would become deenergized and hence the amber relays analogous to the north amber relays shown in FIG. 11 would permit their points analogous to the points 1105 to drop out. Thereafter then the signal on 1109 would be transmitted through the normally closed points 1112 through the normally closed points 1113 and through the normally open points of the red lamp signals. This is true because the emergency changeover relay B would have been energized and hence the relay points 1111 would be transferred. Accordingly then all directions would be red and hence all the red lamp monitors would be energized. With each of the red lamp monitors energized there are ONE signals provided to the gate 660 and since the north direction has been selected there is a ONE signal transmitted thereto on line 661. Accordingly, gate 660 provides a ZERO output signal which is transmitted to gate 483 through the proper terminal wire connections and hence the ONE signal which would be transmitted from the gate 480 in our present example combines with the ZERO signal to provide a ONE signal from the gate 483. Hence the north green coil driver is energized to turn the north green light on.

HOLD CIRCUIT

Thus far we have considered the operation of the circuitry without considering a hold circuit to keep the master transfer relay 1010 transferred when the system is under the emergency control circuitry. It will be recalled that the master transfer circuit was initially energized by applying a ONE signal to the cathode of diode 475, and this ONE signal was the output of gate 646. It was possible initially to supply ONE signals from the output of gate 646 because the input signal on line 662 was a ZERO signal which came from the gate 460 of the emergency amber timer circuit. The output of gate 460 is ZERO until the transistor 468 is turned on which is at the end of the 4 second time interval. Accordingly then we have a signal on 648 which energizes the master transfer relay 1010 for the 4-second period that the amber timer is in operation.

At the end of the 4-second period as previously described all of the lamps are turned red and there will be a demand on one system to turn that light green. In our hypothetical the demand is on the north green light. The system provides for a check to see that the proper pattern is in effect. This is accomplished by the circuitry shown in FIG. 6C, the emergency lamp control circuitry. If there has been no demand on the south green lamp then there will be a ZERO signal on line 666 which signal comes from the gate 495 and which is transmitted to the gate 663. The gate 663 in turn provides a ONE output signal on line 667 which is transmitted through the terminals 609 on terminal board 623 and 4B on terminal board 423 to the line 496 of gate 497 (FIG. 4). In like manner, if there has been no demand for an east green signal there is a ZERO signal on the line 668 which is transmitted to the gate 664. In turn, the gate 664 provides a ONE output signal on line 669 which is also transmitted through the terminal board to the gate 497. Finally, if there is no demand for a west green lamp condition there will be a ZERO signal on line 670 which is transmitted to the gate 665. The gate 665 in turn provides a ONE signal on the line 671 which in turn is transmitted through the terminal board to the gate 497. Hence there are ONE signals on the lines 496, 498 and 499 of the gate 497 (FIG. 4).

Now during this time the gate 660 has been experiencing three ONE input signals on the lines from the red lamp monitors since all the lamps had been turned momentarily red. Since there has been a demand on the north green light there is a ONE signal from gate 447 transmitted to gate 660 and accordingly there will be a ZERO signal from the gate 660. The ZERO signal from gate 660 is transmitted through the terminal board to the gate 483 (FIG. 4) to provide a ONE signal therefrom to the gate 497. As previously described the ONE signal from gate 483 renders the diode 651 nonconducting to turn on the north green coil driver of transistor 652. On the other hand, the ZERO signal transmitted to the line 4100 (FIG. 4) of gate 497 causes the gate 497 to provide a ONE output signal therefrom. The ONE output signal from the gate 497 in conjunction with the constant ONE signal to the gate 4102 causes a ZERO output signal from the gate 4102 which is transmitted through the terminal boards 423 and 623 to line 647 of the gate 646.

Now it becomes apparent that the signal on line 662 may become a ONE while the signal on line 647 is still a ONE and hence there is some possibility that the output signal at the gate 647 could become a ZERO in the transition time between the end of the 4second amber time, i.e., the changing over of all the lamps to the red condition and the final selection of the green lamp in demand. If this were to happen then the master transfer relay would drop out. The master transfer relay is held up during this period by the action of resistor 4103 in conjunction with the capacitor 4104 in the master transfer safety circuit.

Prior to the 4second amber timer being turned on there has been current flow through resistor 4105, resistor 4103 to the capacitor 4104 and this capacitor is fully charge. Now when the ONE signal is transmitted to the diode 475 in response to the 4second amber timer being turned on, the transistor 476 will be turned on as described earlier, and hence there will be current flow through the resistor 4105 and the transistor 476 to ground. At the same time the capacitor 4104 will discharge through the transistor 476. Now during the transition period when the gate 646 is subject to having two ONE input signals and therefore providing a ZERO output signal therefrom if the transistor 476 should be turned off, the capacitor 4104 must become fully charged before transistor 477 commences to conduct. The RC time constant is chosen to assure that the time required for the capacitor 4104 to become fully charged is sufficiently long so that the ZERO signal on line 647 will be in effect before the transistor 477 gets turned on. Hence the master transfer safety circuit operates to keep the transistor 478 conducting until such time as the emergency control is over.

Now if it should happen that the proper pattern of the lights is not developed so that at the end of the 4second amber timer there are all ONE signals transmitted to the gate 497 then there will be a ONE signal transmitted from the gate 4102 and there will be two ONE signals present at the gate 646. Accordingly, there will be a ZERO signal transmitted to the diode 476 thereby cutting off the transistor 476. After the capacitor 4104 has charged, the transistor 477 will commence conducting thereby cutting off the transistor 478 and causing the emergency changeover relays to fall out.

Finally, there is one further action which results from providing a ONE output signal from the gate 497. It will recalled that as part of the equipment at each intersection there is a beacon flasher mounted on top of the normal red-amber green light device. When a ONE signal is developed as the output of gate 497, this ONE signal serves to cut off the diode 4106 which in turn causes the transistor 4107 to conduct. When the transistor 4107 conducts, the flasher oscillator is activated and this alternately opens and closes the ground connection to the flasher relay coil through the transistors 4107 and 4108. It follows then that if the pattern of lights has been properly selected and the master transfer relay is to continue in operation indicating that the emergency control has been selected, the beacon flashers will also commence to operate indicating to the drivers of motor vehicles which are coming into the intersections that there is an emergency condition in effect.

As was indicated earlier, the radio frequency receiver and tone amplifier used with the present system in and of themselves are not considered unique, but indeed some such device must be employed to make the overall system operable. An example of the kind of radio receiver which might be employed is shown in FIGS. 13A, 13B and 13C. The schematic of the receiver shown in these last-mentioned figures depicts a superheterodyne radio receiver and will be described in some detail hereinafter. FIGS. 15A, 15B and 15C depict a tone amplifier circuit configuration which is more complete than the circuit shown in FIG. 2.

In FIG. 13A there is shown an antenna jack 1324. Radio frequency signals from the transmitter on the emergency vehicle are received at the antenna of this set and subsequently transmitted to the jack and to ground via the terminals 1322 and 1512 (FIG. 15). The radio frequency signal is first coupled to an impedance matching circuit 1325 which includes a rejection choke, a bypass filter and a bias (resistance) circuit. Thereafter the radio frequency signal is amplified via amplifier 1526. The local oscillator 1327 meanwhile provides a signal to be mixed with the radio frequency signal at the mixing circuit 1328. The mixer circuit 1328 provides an intermediate frequency signal to be amplified by the amplifier 1329. Further coupled to this circuit is an automatic gain control stage 1330 to provide automatic gain control. The intermediate frequency signal is transmitted to the detector circuit 1331 whereat the information signal is bypassed to the north filter circuit 1332, the south filter circuit 1333, the east filter circuit 1334, and the west filter circuit 1335. The foregoing filter circuits are properly tuned to pass only the frequency representing the associated direction. That is to say the north filter circuit will only pass a signal representing a north frequency transmitted from the emergency vehicle. After the signal has been transmitted through the proper filter circuit it is transmitted to the correct direction terminal (i.e., w, e, s, n), on terminal board 1323.

After the signal has been transmitted to the proper direction terminal it is transmitted to one of four tone amplifier channels two of which are shown in the FIGS. 15A, 15B and 15C. Since we have been dealing throughout with a northerly direction consider for the moment that the terminal 701 represents the north input and therefore the signal passing through the north filter is received at the terminal 701. The signal received at terminal 1501 is transmitted along the line 1524 to the base of transistor 1525. The signal is passed through a series of filtering circuits 1526, 1527 and 1528 and further amplified by the transistors 1529, 1530 and 1531. The signal is then AC coupled through the transformer 1532 into the rectifier circuit 1533 from whence it becomes a DC signal. The description of the signal thereafter was covered in the description of FIG. 2.

Claims

We claim:

1. In an arrangement of traffic lights having go, caution and stop lamps for directing the flow of vehicle traffic on streets and highways, an emergency regulating system for enabling an emergency vehicle to control said traffic lights comprising in combination:

first circuit means to receive a plurality of different direction-indicating direct-current signals, each of which is generated in response to direction-indicating signals transmitted from an emergency vehicle;

second circuit means connected to said first circuit means to receive said plurality of different direction-indicating direct-current signals, said second circuit means including a plurality of first type logical circuits each of which has a plurality of input channels and an output means and each of said first type logical circuits connected to receive a different one of said direction-indicating direct-current signals;

third circuit means interconnecting said plurality of first type logical circuits such that when any one of said first type logical circuits receives its associated direction-indicating direct-current signal said last-mentioned first type logical circuit will generate signals which will inhibit the remainder of said first type logical circuits from being response to their respective associated direction-indicating direct-current signals;

a plurality of second type logical circuits, each of said second type logical circuits having a plurality of input channels and an output means, each of said second type logical circuits connected to a different assigned one of said first type logical circuits to receive output signals therefrom and to generate first type control signals in response thereto;

go light timing circuit means for generating a second type control signal to inhibit said second type logical circuits from generating said first type control signals for a first predetermined time;

caution light timing circuit means for generating third type control signals for a second predetermined time, said caution light timing circuit means connected to said second type logical circuits to receive some of said first type control signals therefrom and to transmit at least one third type control signal to turn on at least some of said caution lamps for said second predetermined time;

fourth circuit means connected to said second type logical circuits and to said caution light timing circuit means to illuminate said go lamps and said stop lamps in a predetermined pattern, after said second predetermined time has elapsed, to accommodate an emergency vehicle whose related direction-indicating signal is being processed by said first and second type logical circuits.

2. An emergency regulating system according to claim 1 wherein each of said second type logical circuits includes a memory circuit, each memory circuit being assigned to a different one of said direction-indicating signals to store an indication of the direction of the particular direction-indicating signal being processed.

3. An emergency regulating system according to claim 2 wherein said caution light timing circuit means is connected to said second type logical circuits to erase from each of said memory circuits an indication of a previously received direction-indicating signal after said second predetermined time if such memory circuits were storing the same.

4. An emergency regulating system according to claim 1 wherein there are further included go lamp monitors connected to said go light timing circuit means to cause said go light timing circuit means to commence clocking said first predetermine time on each occasion that a go lamp is newly illuminated.

5. An emergency regulating system according to claim 1 wherein there is further included, at each traffic light location, a flasher lamp and wherein there is circuitry means connected from said second type logical circuits to said flasher lamp to cause said flasher lamp to flash in response to some of said first type control signals from said second type logical circuits.

6. An emergency regulating system according to claim 1 wherein there is further included a normal controller monitor circuit connected to said first type logical circuits which transmits a signal thereto to continually test whether or not said first type logical circuits are processing a direction-indicating signal and which acts to return said arrangement of traffic lights to a nonemergency mode of operation when said first type logical circuits are no longer processing a direction-indicating signal.

7. An emergency regulating system according to claim 1 wherein there is further included stop light monitoring circuit means connected to said second type logical circuits and to said caution light timing circuit to condition said second type logic circuits so that if a go lamp facing the emergency vehicle's approach were illuminated it would remain illuminated and all other directions would have stop lamps illuminated and alternatively if a stop lamp facing the emergency vehicle's approach were illuminated all directions would first be illuminated with a stop lamp and then said go lamp facing the said emergency vehicle's approach would be illuminated.

8. An emergency regulating system according to claim 1 wherein there is further included a caution lamp control unit connected to said caution light timing circuit and wherein there is further included a stop lamp monitoring circuit means connected to said caution lamp control unit to condition said caution lamp control unit so that any caution lamps facing the direction where go lamps are illuminated at the time of an emergency are conditioned to be illuminated prior to their associated stop lamps becoming illuminated excepting if the illuminated go lamp is facing the emergency vehicle's approach.