U.S. patent number 3,629,802 [Application Number 04/749,560] was granted by the patent office on 1971-12-21 for conflicting phase error detector.
This patent grant is currently assigned to Gulf & Western Industries. Invention is credited to Peter G. Bartlett, Larry K. Clark, Frank W. Hill.
United States Patent |
3,629,802 |
Clark , et al. |
December 21, 1971 |
CONFLICTING PHASE ERROR DETECTOR
Abstract
A system for traffic signal controllers is provided to detect
the occurrence of coincident command signals that would cause
right-of-way signals to be displayed for conflicting or
intersecting traffic lanes or traffic paths or courses. For such
detection NOR logic means are provided with input connections to
controller command signal output lines to produce an output when
different right-of-way command signals are coincident. The output
from the NOR logic means is employed to disconnect all right-of-way
traffic lamps and to connect all caution lamps to an energy source
through a flasher.
Inventors: |
Clark; Larry K. (Davenport,
IA), Bartlett; Peter G. (Davenport, IA), Hill; Frank
W. (Moline, IL) |
Assignee: |
Gulf & Western Industries
(New York, NY)
|
Family
ID: |
25014248 |
Appl.
No.: |
04/749,560 |
Filed: |
July 18, 1968 |
Current U.S.
Class: |
340/931 |
Current CPC
Class: |
G08G
1/097 (20130101) |
Current International
Class: |
G08G
1/097 (20060101); G08g 001/097 () |
Field of
Search: |
;340/46 ;307/218 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Cooper; William C.
Claims
We claim:
1. In a traffic control system for controlling traffic flow through
an intersection of at least two conflicting traffic courses and
having signal light means for, upon command by a command signal,
displaying a right-of-way signal in one of said traffic courses and
traffic signal control means for providing a said command signal
for each traffic course for which a right-of-way signal is to be
received; the improvement comprising:
Nor logic means associated with conflicting traffic courses for
providing an output signal indicative that said controller means
has provided coincident command signals for causing right-of-way
signals to be displayed for such conflicting traffic courses;
and,
means associated with the output of said NOR logic means for
providing an error signal whenever said NOR logic means provides
such an output signal.
2. In a traffic control system the improvement as set forth in
claim 1 including error indicating means responsive to a said error
signal for providing an indication thereof.
3. In a traffic control system the improvement as set forth in
claim 2 wherein said error indicating means includes a visual
display means, and means for alternately, energizing and
deenergizing said visual display means for the duration of said
error signal.
4. In a traffic control system the improvement as set forth in
claim 3 wherein said visual display means includes traffic signal
light means for displaying a warning signal for each of said
conflicting traffic courses for the duration of said error
signal.
5. In a traffic control system the improvement as set forth in
claim 2 wherein said error indicating means includes timing means
responsive to a said error signal for timing a predetermined period
of time and then providing a control signal.
6. In a traffic control system the improvement as set forth in
claim 5 including bistable means having a normal first condition
and a second condition in response to a said control signal,
and
error warning signal means responsive to said second condition for
providing a warning signal.
7. In a traffic control system the improvement as set forth in
claim 6 wherein said error warning signal means includes traffic
signal light means for providing a said warning signal in each of
said conflicting traffic courses.
8. In a traffic control system the improvement as set forth in
claim 7 including reset means for resetting said bistable means to
its normal first condition.
9. In a traffic control system for controlling traffic flow through
an intersection of a plurality of pairs of conflicting traffic
courses, each having signal light means associated therewith for,
upon actuation by a command signal, displaying a right-of-way
signal to the associated traffic course, and traffic signal control
means for providing a said command signal for each of said traffic
courses; the improvement comprising:
solid-state NOR logic means associated with each pair of
conflicting traffic courses for providing an output signal
indicative that said controller means has provided coincident
command signals for causing right-of-way signals to be displayed in
both of said conflicting traffic courses; and,
solid state logic means associated with the outputs of each of said
NOR logic means for providing an error signal when any of said NOR
logic means provides a said output signal.
10. In a traffic control system the improvement as set forth in
claim 1, having output logic means adapted activate an indicator,
wherein the NOR logic means comprises a plurality of NOR gates,
each having inputs from controller output lines for causing
conflicting go signals, and NOR gate means having inputs from said
first-mentioned NOR gates with output means to said output logic
means.
Description
This invention relates to the art of traffic control and, more
particularly, to means for detecting whether two or more
conflicting traffic movements, are concurrently being awarded
right-of-way signals.
The invention is particularly applicable for energizing a flashing
warning signal, such as a yellow light of a traffic signal, to all
traffic approaching an intersection where an error has occurred,
although the invention is not limited thereto and may be used
wherever it is desired to prevent conflicting traffic movements
from concurrently receiving right-of-way signals.
In a traffic control system a traffic signal light serves to
provide right-of-way (green), caution (yellow), and stop (red)
visual displays to traffic approaching the intersection. A traffic
controller serves to energize the traffic light to sequentially
provide the green, yellow and red displays in conflicting or
intersecting traffic lanes, such as in a main street and in an
intersecting cross street. The traffic controller normally operates
in successive phases, each corresponding to traffic movement in one
of the intersecting lanes or streets or traffic courses in the case
of left-turn passage of vehicles. Obviously, in the event that both
the main street and cross street green lights are concurrently
energized, there would result a disruption in traffic flow. This
may result, for example, due to a malfunction in the traffic
controller or the associated circuitry used for energizing the
traffic signal lights. Accordingly, it is desirable in the event
the traffic signal lights are commanded to display green signals in
intersecting streets for conflicting traffic movements, such as
main street and cross street in the example given above, that some
means be provided for detecting this condition and in response
thereto providing an error signal, which may be used, for example,
to energize a warning signal.
Error detection circuitry known heretofore for use with traffic
controllers has taken the form of interlocks or interconnecting
contacts on various relays to prevent the conflicting signals from
appearing. With such apparatus should a relay fail to function, or
a contact on a relay weld, the conflicting signals will still
result. These relays are normally the same relays that are used for
switching the AC line voltage directly to the traffic signals.
Hence, such relay mechanisms were not a true error detection
circuit, since they do not serve a separate function with the
single purpose of providing an output indication of an error.
The present invention is directed toward an error detection circuit
which serves the independent function of monitoring traffic signal
commands obtained from a traffic signal controller and then
providing an error signal when the commands are such to
concurrently display right-of-way signals for conflicting traffic
movements.
The present invention contemplates that a traffic control system
serve to control traffic flow through an intersection of at least
two conflicting traffic lanes, and having signal light means for,
upon command by the control signal, displaying a right-of-way
signal in one of the lanes. It is further contemplated that a
traffic signal control means serve to provide the control signal
for each of the traffic lanes.
In accordance with the present invention, the improvement
incorporates solid-state error detector means which is coupled to
the traffic signal control means for developing an error signal in
response to coinciding command signals, commanding the signal means
to display right-of-way signals in conflicting traffic lanes.
In accordance with a more limited aspect of the present invention,
the error signal is used to operate an error indicating means, such
as a flashing yellow light, to provide a warning signal in each of
the conflicting traffic lanes for the duration of the error
signal.
In accordance with a further aspect of the present invention, a
timing means serves to time a predetermined period of time before
the error signal causes a warning signal to be displayed.
The primary object of the present invention is to provide a
conflicting error detection system which is relatively inexpensive
to manufacture and economical to operate.
It is a still further object of the present invention to provide an
error detection system using solid-state logic circuitry to
minimize power requirements, as well as to minimize maintenance
normally attributed to electromechanical systems.
It is a still further object of the present invention to provide a
conflicting error detection circuit which has as its sole purpose
to monitor the command signals from a traffic controller, and then
provide an error signal in the event that conflicting traffic
movements are to receive right-of-way signals.
It is a still further object of the present invention to provide an
error detection system which may be used for both conflicting and
compatible traffic movement, such as in an eight-phase, quad
left-turn traffic control system.
The foregoing objects and advantages of the invention will become
apparent from the following description of the preferred
embodiments of the invention as read in connection with the
accompanying drawings in which:
FIG. 1 illustrates one application of the invention in conjunction
with four conflicting traffic lanes;
FIG. 2 is a combined schematic block diagram illustration of the
preferred embodiment of the invention;
FIG. 3 is a schematic illustration of the error detector circuit
used in FIG. 2;
FIG. 4 is a schematic illustration of another application of the
invention to an eight-phase, quad left-turn traffic control system;
and,
FIG. 5 is a schematic illustration of the error detector circuit to
be used for the eight-phase, quad left-turn traffic control
system.
GENERAL DESCRIPTION
Referring now to the drawings, which are presented for illustrating
preferred embodiments of the invention only and not for limiting
same, FIG. 1 illustrates an intersection of four conflicting
traffic movements; to wit, in traffic paths or courses designated
by reference characters .phi.A, .phi.B, .phi.C and .phi.D. Phases A
and B may be respectively considered as in the main street and
cross street directions of traffic flow. Traffic movement D is a
left-turn from main street A into cross street B and, similarly,
traffic movement C is a left turn from cross street B into main
street A. All of these traffic movements are conflicting. That is,
if any pair of these traffic movements receive right-of-way signals
at the same time, the traffic movements will conflict with each
other, resulting in a disruption of traffic flow through the
intersection. A traffic signal S is provided to display green,
yellow and red signals for each of the traffic movements under
control of command signals received from a four-phase local
controller LC-1.
Reference is now made to FIG. 2 which illustrates a local traffic
controller LC-1 having eight output circuits AG, AY, BG, BY, CG,
CY, DG, and DY, each for carrying a command signal for respectively
actuating load switches LS-1, LS-2, LS-3, LS-4, LS-5, LS-6, LS-7
and LS-8. These load switches serve, when actuated, to respectively
connect an associated load AGL, AYL, BGL, BYL, CGL, CYL, DGL and
DYL, with an alternating current voltage source V. The outputs of
the local traffic controller are applied through a plurality of OR
gates to conflicting traffic error detector circuit ED, which has
its output coupled through a NOR-gate 10 to a timer control circuit
TC. Timer control circuit TC, in turn, is coupled through a memory
circuit M to a triac 12 which, when biased into conduction, serves
to apply alternating current voltage from source V across coil
CR1-C of a relay CR1. Briefly, during operation, the local
controller LC-1 serves to sequentially apply a direct current
control signal on its output terminals for purposes of sequentially
energizing the associated load switches LS-1 through LS-8. The
error detector ED serves to monitor the operation of the output
circuits AG through DY for purposes of detecting whether
conflicting loads are being energized. In the event, for example,
that green light AGL and green light BGL are concurrently energized
due to command signals being present on output terminals AG and BG
of local controller LC-1, the error detector circuit ED applies a
binary "1" signal into the input of NOR-gate 10. This triggers an
operation, as will be described in detail hereinafter, wherein
relay CR1 becomes energized to couple flasher F to each of the
yellow lights AYL, BYL, CYL and DYL so that these lights
alternately flash on and off, providing a warning signal to each of
the conflicting traffic movements.
TRAFFIC CONTROL SYSTEM
In the embodiment illustrated in FIG. 2, the traffic control system
includes traffic signal lights AGL through DYL for traffic
movements A through D. Thus, for example, lights AGL and AYL
respectively serve as the green light for lane A and the yellow
light for lane A. The traffic controller LC-1 provides positive
direct current voltage signals on its output circuits AG through DY
in a sequential fashion so that the associated signal lights AGL
through DYL become sequentially energized. Typically, such traffic
controllers incorporate direct current logic circuitry for
determining when the green and yellow terminals for each of the
traffic courses A, B, C and D are to be energized, and for what
duration. An example of such a traffic controller is found in the
U.S. Pat. to G. D. Hendricks, No. 3,344,398, which is assigned to
the same assignee as the present invention. Load switches LS-1
through LS-8 each incorporate a triac. Thus, switch LS-1 includes a
triac 14 having its gate connected to terminal AG of local
controller LC-1 and its terminal T2 connected through alternating
current voltage source V to ground. Terminal T1 of triac 14 is
connected through normally closed relay contacts CR1-1 of relay CR1
to the traffic course A green light AGL. The remaining load
switches LS-2 to LS-8 are connected in a similar fashion to source
V, as well as to output terminals AY through DY. Also, the outputs
of load switches LS-2 through LS-8 are respectively coupled through
normally closed relay contacts CR1-2 through CR1-8 and then to the
associated signal lights AYL through DYL, as shown in FIG. 2.
Controller output terminals AG and AY are coupled through an
OR-gate 16 having its output connected to input terminal A of the
conflicting traffic detector ED. Similarly, output terminals BG and
BY are coupled through an OR-gate 18 having its output connected to
input terminal B or error detector ED. Also, output terminals CG
and CY are coupled through an OR-gate 20 having its output coupled
to input terminal C of error detector ED. Also, output terminals DG
and DY are coupled through an OR-gate 22 having its output
connected to input terminal D of error detector ED. The outputs of
OR-gates 16 and 18 are also coupled through an OR-gate 24 having
its output connected to input terminal AB of error detector ED.
Similarly, the outputs of OR-gates 20 and 22 are coupled through an
OR-gate 26 having its output connected to input terminal CD of
error detector ED. The output of error detector ED, which is
illustrated in greater detail in FIG. 3, is coupled to the input of
NOR-gate 10 having its output coupled to the timer control circuit
TC. NOR-gate 10, as well as the remaining NOR gates disclosed
herein, preferably take the form of the resistor-transistor logic
RTL NOR gate illustrated in Figure 7.5, at page 178, of General
Electric's Transistor Manual, 7th Edition. The timer control
circuit TC includes a NOR-gate 30, used as a signal inverter,
together with an RC timing circuit 32. This timing circuit may take
various forms, such as a unijunction relaxation oscillator circuit,
as illustrated in Figure 13.18, at page 313, of General Electric's
Transistor Manual, 7th Edition. Briefly, that oscillator circuit
includes a capacitor which is normally short circuited by a binary
"1" signal from NOR-gate 30. However, whenever the output binary
signal of NOR-gate 30 becomes a binary "0" signal this short
circuit is removed whereupon the capacitor charges toward the value
of a direct current voltage source. When the level of the voltage
stored reaches the peak point voltage of the unijunction
transistor, the capacitor discharges through the emitter to base B1
of the transistor and a positive voltage pulse appears across a
load resistor. This positive pulse may be considered as a "1"
signal. Whenever the capacitor has not discharged through the
transistor unijunction, the output of timer control circuit TC is
at a ground or binary "0" level.
The output of the timer control circuit TC is applied to a NOR-gate
34 in memory circuit M. This memory circuit includes an additional
NOR-gate 36 which is coupled to the output of NOR-gate 34 and has a
feedback path for defining a bistable multivibrator circuit. The
output of NOR-gate 36 is also coupled through a normally open
switch S-1 to ground potential. Closure of this switch serves to
reset memory M, as will be described in detail with respect to the
operation of the circuitry.
The output of memory M is coupled to the gate of triac 12 having
its terminal T1 connected to ground and its terminal T2 connected
through relay coil CR1-C to voltage source V, as well as to flasher
F. The other side of flasher F is coupled through the normally open
side of relay contacts CR1-2, CR1-4, CR1-6 and CR1-8. The flasher F
may take any suitable form, such as a motor controlled circuit
interrupter, for alternately opening and closing the circuit
between source V and the above-mentioned normally open relay
contacts. Such a flasher commences operation upon closure of these
relay contacts.
CONFLICTING TRAFFIC ERROR DETECTOR
Reference is now made to FIG. 3 which illustrates the circuitry
within error detector ED of FIG. 2. This error detector includes
six inputs; to wit, terminals A, B, C, D, AB and CD. These input
terminals are connected to various combinations of NOR-gates 40,
42, 44, 46 and 48. Thus, terminal A is connected to one input each
of NOR-gates 40 and 44. Terminal B is connected to one input each
of NOR-gates 42 and 44. Terminal C is connected to one input each
of NOR-gates 40 and 46. Terminal D is connected to one input each
of NOR-gates 42 and 46. Terminal AB is connected to one input each
of NOR-gates 44 and 48. Lastly, terminal CD is connected to one
input each of NOR-gates 46 and 48. The outputs of NOR-gates 40 and
42 are coupled to the input of a NOR-gate 50 having its output
connected to the input of an OR-gate 52. Similarly, the outputs of
NOR-gates 44 and 46 are coupled to the input of a NOR-gate 54
having its output connected to the input of OR-gate 52. Lastly, the
output of NOR-gate 48 is connected to one input of OR-gate 52. The
output of OR-gate 52 is connected to the input of NOR-gate 10 in
FIG. 2.
OPERATION
During the operation of the circuitry illustrated in FIGS. 1, 2 and
3, it may be assumed that initially the local controller LC-1 has
energized its main street A green terminal AG with a positive
direct current signal. This signal is coupled to the gate of triac
14 in load switch LS-1 so as to gate this triac into conduction.
Accordingly, alternating current voltage from source V is applied
through the triac and normally closed relay contacts CR1-1, to
energize the main street A green lamp AGL. The positive signal on
terminal AG is applied through OR-gate 16 to input terminal A of
the error detector ED. This signal is also applied from the output
of OR-gate 16 through OR-gate 24 to the input terminal AB of error
detector ED. Accordingly, binary "1" signals are applied to the
input terminals A and AB of the error detector circuitry shown in
FIG. 3. The binary "1" signal on input terminal A is inverted by
NOR-circuit 40 to apply a binary "0" signal to one input of
NOR-circuit 50. Since, however, the input on terminal B is a binary
"0" signal, which is the normal signal when traffic in cross street
B is not receiving a right-of-way signal, NOR-gate 42 applies a
binary "1" signal to the input of NOR-gate 50. Accordingly, the
output of NOR-gate 50 carries a binary "0" signal which is
reflected to OR-gate 52. Terminals C, D and CD also carry binary
"0" signals and hence the output of NOR-gate 46 carries a binary
"1" signal and the output of NOR-gate 54 carries a binary "0"
signal. Since input terminal AB carries a binary "1" signal, then
the output of NOR-gate 48 carries a binary "0" signal. Since all of
the inputs to OR-gate 52 are binary "0" signals, the output of this
gate is also a binary "0" signal which is the correct indication
for a situation wherein conflicting traffic movements are not
receiving right-of-way signals from the traffic signal S.
With reference to FIG. 1, it can be seen that traffic movements A
and B conflict and accordingly should not be awarded right-of-way
intervals at the same time. Assume now that output terminals AG and
BG are concurrently energized by local controller LC-1. In such
case, input terminals A, B and AB will all carry binary "1" input
signals. Since terminals A and B both carry binary "1" signals, the
outputs of NOR-gates 40 and 42 carry binary "0" signals.
Accordingly, the output of NOR-circuit 50 carries a binary "1"
signal which is reflected through OR-gate 52 and is applied to the
input of NOR-gate 10 in FIG. 2. This is indicative of an error
condition of conflicting traffic movements receiving right-of-way
signal displays.
Since a binary "1" signal has been applied to its input, NOR-gate
10 applies a binary "0" signal to the input of NOR-gate 30, which
in turn, applies a binary "1" signal to the input of the RC timer
32 in the timer control circuit TC. The timing circuit 32 now times
a predetermined period of time and then provides a binary "1"
signal pulse which is applied to the input of NOR-gate 34 in memory
M. This causes the output of NOR-gate 36 to become a binary "1"
signal and this state of the memory M is retained due to the
feedback circuit until switch S-1 is momentarily closed to return
the memory to its normal condition. The binary "1" signal obtained
from the output of NOR-gate 36 serves to gate triac 12 into
conduction to thereby energize relay coil CR1-C and apply power to
start flasher F. This causes all the movable contacts of relay CR1
to move in a downward direction, as viewed in FIG. 2, so that the
previously open side of relay contacts CR1-2, CR1-4, CR1-6 and
CR1-8 become closed so that flasher F can then alternately energize
and deenergize yellow lamps AYL, BYL, CYL and DYL. These yellow
lamps will stay in this flashing condition displaying warning
signals to all conflicting traffic movements A, B, C and D until
switch S-2 is momentarily closed to restore the memory circuit to
the condition where it applies a binary "0" signal to the gate of
triac 12. As the alternating current voltage obtained from source V
crosses through a zero level, the triac will cease to conduct,
deenergizing relay CR1. The operation in conjunction with detecting
conflicting go signal conditions for any of the combinations of
conflicting traffic movements A, B, C and D is the same as that
discussed above with respect to traffic lanes A and B, and no
further description is deemed necessary for a complete
understanding of this invention.
SECOND EMBODIMENT
Reference is now made to FIGS. 4 and 5 which illustrate a second
embodiment of the invention. FIG. 4 schematically illustrates an
eight-phase, quad left-turn traffic control system wherein signal
light S2 is controlled by an eight-phase local controller LC-2.
From an inspection of FIG. 4, it will be noted that there are both
conflicting traffic movements and compatible traffic movements.
Conflicting movements, of course, are movements which, if given
right-of-way signals, will result in a disruption of traffic flow.
Compatible traffic movements are those which may receive
right-of-way signals at the same time without disruption in traffic
flow. Thus, for example, with reference to FIG. 4, traffic courses
A1 and A3 are compatible, traffic courses B1 and B2 are compatible;
left-turn courses T3 and T4 are compatible; left-turn courses T1
and T2 are compatible; course A2 and course T2 are compatible;
phase A1 and phase T1 are compatible; phase B2 and course T4 are
compatible; and, course B1 and course T3 are compatible. Also, with
reference to FIG. 4, it will be noted that the following traffic
courses are conflicting. A1 with T2, A2 with T1, B1 with T4 and B2
with T3. It will further be noted that the group of traffic courses
consisting of A1, A2, T1 and T2 are conflicting with the group of
courses consisting of B1, B2, T3 and T4.
Conflicting traffic course error detector ED-2 serves essentially
the same purpose for an eight-phase, quad left-turn system as the
error detector circuit ED serves for a four-phase conflicting
traffic control system. However, since, as discussed above, an
eight-phase, quad left-turn system has both conflicting phases and
compatible phases, the error detector circuit should recognize
right-of-way signals being displayed to compatible traffic
movements as being proper, but right-of-way signals being displayed
to conflicting traffic movements as being an error condition. This
function is performed by error detector ED-2.
Error detector ED-2, like error detector ED, illustrated in FIG. 3,
has a plurality of input terminals which are energized by local
controller LC-2 by a positive direct current signal, i.e., a binary
"1" signal, when an associated traffic movement is to receive a
right-of-way signal. As shown in FIG. 5, these input terminals are
labeled T1, A2, T2, A1, T3, B2, T4 and B1, each representative of
the like numbered traffic courses shown in FIG. 4. The input
terminals representative of conflicting courses are grouped
together; to wit, terminals T1 and A2, terminals T2 and A1,
terminals T3 and B3, and terminals T4 and B1. These terminals are
coupled to the inputs of NOR-gates 60 through 74 which serve as
signal inverters. More particularly, the inputs of NOR-gates 60
through 74 are coupled to terminals T1, A2, T2, A1, T3, B2, T4 and
B1, respectively. The outputs of NOR-gates 60 and 62 are coupled to
the inputs of a NOR-gate 76 having its output coupled to the input
of an OR-gate 78, the output of which is coupled to the input of a
NOR gate such as NOR-gate 10, of the circuitry shown in FIG. 2.
The outputs of NOR-gates 60 and 62 are also connected to inputs of
an AND-gate 80 having its output connected through a NOR-gate 82 to
the input of OR-gate 78. The outputs of NOR-gates 64 and 66 are
coupled to the inputs of a NOR-gate 84 having its output connected
to one input of OR-gate 78. The outputs of NOR-gates 64 and 66 are
also connected to inputs of AND-gate 80.
The outputs of NOR-gates 68 and 70 are connected to the inputs of
NOR-gate 86 having its output connected to one input of OR-gate 78.
The outputs of NOR-gate 68 and 70 are also connected to two inputs
of AND-gate 88. The outputs of NOR-gates 72 and 74 are applied to
the inputs of NOR-gate 90 having its output connected to one input
of OR-gate 78. The outputs of NOR-gates 72 and 74 are also
connected to inputs of AND-gate 88.
Preferably, the error detector ED-2 is coupled to a traffic
controller in a manner similar to that of error-detector ED in FIG.
2. Thus, the local controller LC-2 may take the form of four,
two-phase controllers or two, four-phase controllers or a single,
eight-phase controller. In any case, the controller circuitry
should have the capability of providing outputs similar to those of
the eight outputs with reference to local controller LC-1 of FIG.
2. Each of these outputs are connected through load switches,
similar to load switches LS-1 through LS-8, to energize traffic
signal lamps as in the case of lamps AGL through DYL of FIG. 2.
This circuitry is not shown with reference to FIG. 5 for purposes
of simplifying the description of the invention.
The operation of error detector ED-2 is substantially similar to
that of error detector ED of FIG. 2. Thus, for example, if input
terminals T1 and A2 receive binary "1" signals representative that
conflicting traffic courses T1 and T2 are being awarded
right-of-way signals, then NOR-gate 76 provides a binary "1" signal
which is reflected through OR-gate 78 as an error signal. As in the
case of FIG. 2, this will cause the operation of triac 12 to
energize a relay CR1, whereupon switches are actuated to display
flashing yellow signals to all approaches to the intersection shown
in FIG. 4. However, in the event compatible traffic courses, such
as turns T1 and T2, are being awarded right-of-way signals, then
NOR-gate 76 and NOR-gate 84 have binary "0" signals on their
outputs which are reflected through OR-gate 78 and no error signal
is provided. Thus, in this case, all terminals carry binary "1"
signals with the exception of terminals T1 and T2. Accordingly, the
outputs of NOR-gates 60 and 64 carry binary "0" signals and the
outputs of NOR-gate 62 and 66 through 74 carry binary "1" signals.
Since one of its inputs has a binary "1" signal, the outputs of
NOR-gate 76 and 84 each carry "0" signals for application to the
input of OR-gate 78. Since the outputs of NOR-gate 60 and 64 carry
binary "0" signals and the outputs of NOR-gates 62 and 66 carry
binary "1" signals, only two of the four inputs of AND-gate 80
carry binary "1" signals and, accordingly, the output of AND-gate
80 carries a binary "0" signal for application to one input of
NOR-gate 82. However, since each of the outputs of NOR-gates 68
through 74 carry binary "1" signals, AND-gate 88 applies a binary
"1" signal to the other input of NOR-gate 82, whereupon all inputs
to OR-gate 78 are binary "0" signals, which is the correct
condition for no error with compatible traffic courses T1 and T2
being awarded right-of-way signals.
The operation that results with another combination of compatible
traffic courses being awarded right-of-way signals and/or
conflicting traffic courses being awarded right-of-way signals is
substantially the same as discussed above and, accordingly, no
further description is deemed necessary for a complete
understanding of the invention.
Although the invention has been shown in connection with preferred
embodiments, it will be readily apparent to those skilled in the
art that various changes in form and arrangements of parts may be
made to suit requirements without departing from the spirit and
scope of the invention as defined by the appended claims.
* * * * *