U.S. patent number 3,613,073 [Application Number 04/824,520] was granted by the patent office on 1971-10-12 for traffic control system.
Invention is credited to Eugene Emerson Clift.
United States Patent |
3,613,073 |
Clift |
October 12, 1971 |
TRAFFIC CONTROL SYSTEM
Abstract
A traffic control system for regulating the movement of traffic
at an intersection, including magnetic sensors at the entrance and
exit ends of each lane leaving said intersection for producing
vehicle count signals for each vehicle entering and leaving the
lane, and traffic lights at said intersection having controllers
for varying the cycles, offsets and splits thereof for regulating
flow of traffic across the intersection into each of said lanes.
Counters respond to the count signals for determining the number of
vehicles in each selected street block and logic means respond to
the counters for determining the direction of the greatest traffic
flow and applying control signals to said traffic signal light
controllers to control the same in response to the sensed traffic
conditions.
Inventors: |
Clift; Eugene Emerson (Daytona
Beach, FL) |
Family
ID: |
25241609 |
Appl.
No.: |
04/824,520 |
Filed: |
May 14, 1969 |
Current U.S.
Class: |
340/920 |
Current CPC
Class: |
G08G
1/08 (20130101) |
Current International
Class: |
G08G
1/08 (20060101); G08G 1/07 (20060101); G08g
001/065 () |
Field of
Search: |
;340/31,31A,35 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
436,883 |
|
Oct 1935 |
|
GB |
|
985,427 |
|
Mar 1965 |
|
GB |
|
Primary Examiner: Cooper; William C.
Claims
I claim:
1. In a traffic control system for regulating the movement of
traffic into the leaving lanes of four street sections of selected
length leaving in four directions from a roadway intersection, each
leaving lane having an entrance end at said intersection and an
exit end at the end of said selected length of the street section,
a first vehicle detector at the entrance end of each lane leaving
said intersection for producing a counter advance signal for each
vehicle entering the associated lane, a second vehicle detector at
the exit end of each of said lanes for generating a counter
subtract signal for each of the vehicles leaving the associated
street section for each of said lanes, traffic signal lights at
said intersection including traffic light controller means for
operating the signal lights in a plurality of different time
duration cycles to regulate flow of traffic across said
intersection into each of said lanes, plural counting means
including a counter for each respective street section for
continuously counting the vehicles collectively in all of the
leaving lanes of the associated street section responsive to the
advance and subtract signals from the detectors for the leaving
lanes of the associated street section, each counter having an
array or contacts controlled in accordance with the counts for
establishing combinations of open and closed contact conditions
indicating the collective count of the number of vehicles in the
leaving lanes of the associated street section, and logic means
responsive to said contact conditions for determining the direction
of the greatest traffic flow and applying control signals to said
traffic light controller means to control the cycles of said
traffic signal lights in selected relation to the sensed traffic
conditions.
2. A traffic control system as defined in claim 1, wherein said
logic means includes saturation control means coupled to said
counting means and responsive to selected contact conditions
thereof to determine existence of a vehicle saturation level in any
of said street sections and activate said traffic signal lights to
halt traffic flow into the lanes of the saturated street section as
long as the saturation level persists.
3. A traffic control system as defined in claim 2, wherein said
logic means includes route control means to select the next highest
count below the saturation level signified by the contact
conditions of said counters and control the traffic signal lights
in selected relation to said next highest count to permit a
continued flow of traffic to unsaturated street sections.
4. A traffic control system as defined in claim 1, wherein said
logic means includes means to halt traffic flow into the lanes of a
street section having a vehicle saturation level and means for
controlling the traffic signal light to maintain traffic flow into
the nonsaturated street sections.
5. A traffic control system as defined in claim 1, wherein said
counter for each respective street section includes a counter
circuit and said array of contacts controlled thereby is arranged
in a numerical series and regulated thereby to produce closure of
contacts whose position signifies the number of vehicles in the
associated street section, said contacts of such array being
grouped in a plurality of serially arranged sets of plural contacts
each signifying progressively increasing traffic density levels,
and said logic means including a relay coupled to each respective
set of contacts to be activated when contacts of its associated set
are closed, and the relays associated with said array are coupled
to said controller means to respectively establish progressively
longer duration traffic signal light cycles for contact closures
signifying progressively higher numbers of vehicles.
6. A traffic control system as defined in claim 2, wherein said
counter for each respective street section includes a counter
circuit and said array of contacts controlled thereby is arranged
in a numerical series and regulated thereby to produce closure of
contacts whose position signifies the number of vehicles in the
associated street section, said contacts of such array being
grouped in a plurality of serially arranged sets of plural contacts
each signifying progressively increasing traffic density levels,
and said logic means including a relay coupled to each respective
set of contacts to be activated when contacts of its associated set
are closed, and the relays associated with said array are coupled
to said controller means to respectively establish progressively
longer duration traffic signal light cycles for contact closures
signifying progressively higher numbers of vehicles.
7. A traffic control system as defined in claim 3, wherein said
counter for each respective street section includes a counter
circuit and said array of contacts controlled thereby is arranged
in a numerical series and regulated thereby to produce closure of
contacts whose position signifies the number of vehicles in the
associated street section, said contacts of such array being
grouped in a plurality of serially arranged sets of plural contacts
each signifying progressively increasing traffic density levels,
and said logic means including a relay coupled to each respective
set of contacts to be activated when contacts of its associated set
are closed, and the relays associated with said array are coupled
to said controller means to respectively establish progressively
longer duration traffic signal light cycles for contact closures
signifying progressively higher numbers of vehicles.
8. A traffic control system as defined in claim 4, wherein said
counter for each respective street section includes a counter
circuit and said array of contacts controlled thereby is arranged
in a numerical series and regulated thereby to produce closure of
contacts whose position signifies the number of vehicles in the
associated street section, said contacts of such array being
grouped in a plurality of serially arranged sets of plural contacts
each signifying progressively increasing traffic density levels,
and said logic means including a relay coupled to each respective
set of contacts to be activated when contacts of its associated set
are closed, and the relays associated with said array are coupled
to said controller means to respectively establish progressively
longer duration traffic signal light cycles for contact closures
signifying progressively higher numbers of vehicles.
9. A traffic control system as defined in claim 1, wherein said
logic means includes means responsive to different count levels of
said counting means to provide different offset and split control
signals for application to said controller means which vary in
selected relation to the count levels.
10. A traffic control system as defined in claim 2, wherein said
logic means includes means responsive to different count levels of
said counting means to provide different offset and split control
signals for application to said controller means which vary in
selected relation to the count levels.
11. A traffic control system as defined in claim 3, wherein said
logic means includes means responsive to different count levels of
said counting means to provide different offset and split control
signals for application to said controller means which vary in
selected relation to the count levels.
12. A traffic control system as defined in claim 5, wherein said
logic means includes means responsive to different count levels of
said counting means to provide different offset and split control
signals for application to said controller means which vary in
selected relation to the count level.
13. A traffic control system as defined in claim 5, wherein each of
said relays associated with each said array includes relay contact
means for establishing offset and split control signals for said
controller means which differ for respective sets of said
contacts.
14. A traffic control system as defined in claim 6, wherein each of
said relays associated with each said array includes relay contact
means for establishing offset and split control signals for said
controller means which differ for respective sets of said
contacts.
15. A traffic control system as defined in claim 7, wherein each of
said relays associated with each said array includes relay contact
means for establishing offset and split control signals for said
controller means which differ for respective sets of said
contacts.
16. A traffic control system as defined in claim 1, including
timing means to reset said counting means at least once every 24
hours.
17. A traffic control system as defined in claim 1, including relay
means activated responsive to selected failure conditions in said
logic means to produce signals for activating the associated
traffic signal light in a flashing yellow condition.
18. A traffic control system as defined in claim 1, wherein said
logic means includes means for providing control signals for a
plurality of different cycles, offsets and splits to apply control
signals to said controller means establishing multiple cycles,
offsets and splits which differ in selected relation to the count
levels of said counting means.
19. A traffic control system as defined in claim 2, wherein said
logic means includes means for providing control signals for a
plurality of different cycles, offsets and splits to apply control
signals to said controller means establishing multiple cycles,
offsets and splits which differ in selected relation to the count
levels of said counting means.
20. A traffic control system as defined in claim 13 wherein said
relay contact means for establishing offset and split control
signals are associated with said relays in such relation to provide
multiple offsets and splits having multiple settings which vary in
preselected relation to the traffic density levels signified by
said sets of contacts.
21. A traffic control system as defined in claim 14 wherein said
relay contact means for establishing offset and split control
signals are associated with said relays in such relation to provide
multiple offsets and splits having multiple settings which vary in
preselected relation to the traffic density levels signified by
said sets of contacts.
Description
BACKGROUND AND OBJECTS OF THE INVENTION
The present invention relates in general to traffic control systems
for automatically regulating vehicular traffic, and more
particularly to traffic control systems employing means for sensing
the forward flow and density of vehicular traffic along each lane
of roadways leaving an intersection and automatically regulating
traffic lights in accordance with the actual traffic conditions
sensed.
Heretofore, many efforts have been made to provide devices which
will automatically regulate traffic lights at roadway intersections
in a manner related to the amount of traffic in the lanes
approaching the intersection to provide efficient flow of traffic.
These devices, for the most part, have involved expensive computers
and other complex devices as well as expensive wiring installations
from a central computer to each vehicle sensor device or equally
expensive multiplex hookup costs.
The present invention provides a traffic control system employing
magnetic sensors placed under the pavement in each lane of traffic
leaving an intersection and connected by a cable to a logic package
wherein the number of vehicles entering a given block or section of
the roadway is counted, the number of vehicles departing from the
same block or section is counted, which results in a running total
of vehicles in each control area, and logic means determine the
direction of the greatest traffic flow and activates selection
means to set the proper timing for offsets, splits and cycles of
traffic lights for efficient flow of traffic through the
intersection.
The present system is completely automatic and all control
decisions are made by the logic package installed separately at the
various intersections in the highway or roadway system. The
electronic logic controls at each intersection are isolated
decision-making packages so that failure of traffic lights at any
one intersection would not effect the other controls in the system.
Also, the use of separate decision-making logic controls at each
intersection permits the system to be enlarged or its location
changed without the usual problems and costs involved in a
centralized system. By the use of magnetic sensing devices placed
under the pavement in each lane of traffic leaving the
intersection, the operation of the device will not be affected by
ice, snow, sludge, or temperature extremes. The system maintains a
running total of traffic volume information from each of the four
roadways or blocks immediately ahead of (i.e., in the leaving lanes
from) a normal intersection and makes a positive determination of
which of the various traffic flows through the intersection is
heaviest for appropriate regulation of the traffic lights. Also, on
the basis of the stored information as to vehicle density in the
blocks immediately beyond the intersection, the system is capable
of making a positive decision not to permit additional vehicles to
enter this traffic flow when it approaches a saturation level and
as long as the saturation level exists, and regulate traffic lights
accordingly.
Because the present traffic control system continuously senses and
responds to traffic flow volume through its own associated
intersection, it is readily able to automatically adjust to the
many varied traffic flow changes which occur throughout the day and
night to appropriately regulate the traffic lights.
A principle object of the present invention, therefore, is the
provision of a novel traffic control system which includes logic
means associated with a particular intersection and sensing means
for monitoring vehicular traffic flow through the intersection over
a selected block or section of roadway to make traffic flow
decisions from such sensed information and automatically operate
traffic light signals accordingly, and which system is less complex
and expensive than automatic traffic control systems heretofore
provided.
Other objects, advantages, and capabilities of the present
invention will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings
illustrating a preferred embodiment thereof.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a diagrammatic illustration of a roadway intersection and
the connecting roadway blocks, showing the location of the vehicle
sensors of the present invention;
FIGS. 2A and 2B collectively form a schematic diagram of the logic
package providing traffic control at one of the individual
intersections;
FIG. 3 is a schematic diagram of an example of the circuit that may
be used for the pulse generator PG-1; and
FIG. 4 is a schematic diagram of the circuitry immediately
associated with the sensors at the downstream end of the lanes of
traffic monitored by sensors MS-1 and MS-2.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to the drawings, wherein like reference characters
designate corresponding parts throughout the several figures the
automatic traffic control system of the present invention involves
an equipment package, hereinafter frequently referred to as a logic
package, indicated generally by the reference character 10,
associated with a particular roadway intersection, for example, the
intersection 11 illustrated in FIG. 1. The reference character 12
indicates the northbound roadway, 13 the westbound roadway, 14 the
southbound roadway, and 15 the eastbound roadway, associated with
this intersection 11. Embedded beneath the pavement at the upstream
end of each of the traffic lanes leaving this intersection 11 is a
magnetic sensor for each respective departing lane, and at the exit
or downstream end of each of the corresponding lanes is another
similar sensor, each designed to produce a pulse signal of selected
duration responsive to passage of a vehicle over the location of
that particular sensor. For example, referring to the two
northbound traffic lanes of the northbound roadway 12, indicated as
left-hand or inner northbound lane 12A and right-hand or outer
northbound lane 12B, sensor units MD-1 and MD-2 are located at the
entrance or upstream ends of lanes 12A and 12B, respectively, and
sensors MS-3 and MS-4 are located at the exit or downstream ends of
these respective lanes. These sensors are commercially available
magnetic sensing devices, such as those designated as "magnetic
field sensors" and manufactured by Research Associates, Inc.,
Linden, N.J., which are buried under the pavement and result in the
closure of relay contacts, as indicated schematically in FIGS. 2
and 4, responsive to passage of a vehicle over the sensor to
provide an encoding input to the logic package 10, to which the
sensors MS-1 and MS-2 are connected by cables, and to which the
sensors MS-3 and MS-4 are coupled by radio links as later
described.
Referring, for example, to the sensor MS-1 monitoring the entrance
end of the lane 12A, it will be noted that its contact is connected
through the normally closed contact B of reed relay RE-1 to what
may be referred to as open contacts BB and A of latching relay LR-1
and also to the input Z of pulse generator PG-1 designed to scan or
oscillate the latching relay LR-1 back and forth. Assuming that a
vehicle activates the magnetic sensor MS-1 resulting in closure of
the relay contact indicated at MS-1, power is applied from the
closed relay contacts of MS-1 through the closed contact B of reed
relay RE-1 to the contact BB and A of the latch relay LR-1, which
will be assumed to be in open condition at this point, and also
through the diode D-2 to the input Z of the pulse generator PG-1, a
schematic circuit for which is illustrated in FIG. 3. The encoding
pulse from the contact of sensing device MS-1 which is applied to
the input Z of pulse generator PG-1 is sent through the closed
contact B of the pulse generator and through the resistor R1 to the
coil of the reed relay RE-5. The power applied through the closed
contact B to the coil of reed relay RE-5 instantaneously switches
the contact A of relay RE-5 to closed condition applying power to
the X coil of the latching relay LR-1, closing the contacts BB and
A of latching relay LR-1 (if they were open) and applying power
through the last-mentioned contacts BB and the closed contact B of
reed relay RE-4 to the advance terminal CA of counter C-1 to
advance the counter one count. When the shunted capacitor 5-C
across the coil of relay RE-5 discharges, the relay RE-5 drops out
and power is switched back to its closed contacts B and BB, the
latter applying power to the coil Y of the latching relay SR-1 to
switch the latter back to the illustrated position wherein contacts
B and AA are closed and contact BB and A are open.
It will be noted that it is immaterial which position the latching
relay LR-1 is in when the pulse generator is activated. For
example, assume that the latching relay is in the position
established by energization of the Y coil (which may be referred to
as the Y coil or open position) wherein the contacts BB and A are
closed and the contacts B and AA are open. In this condition, the
input pulse from the magnetic MD-1 is fed through the BB contact of
LR-1, which immediately triggers the count advance circuit of the
counter C-1, and is also fed through the A contact of LR-1 and the
capacitor 1-C to the coil of relay RE-1 when the capacitor 1-C is
charged. This result in transferring the encoding power from the B
contact of RE-1 to its A contact to hold in the coil of relay RE-1
as long as the vehicle which initiated activation of the magnetic
sensor MS-1 continues activation of that sensor. The blocking diode
D-3 prevents a feedback from the A contact of relay RE-1 during the
hold-in period of the coil. The time cycle of the pulse generator
PG-1 is slightly longer than the time required to activate the coil
of relay RE-1 so that the coil of RE-1 is pulled in and then held
in by the closure of its contact A before the pulse generator
switches the latch relay LR-1 back to the other state. The
capacitor 1-C is provided to insure a make-before-break action of
the coil of relay RE-1 and the diodes D-1 and D-2 are provided to
block feedbacks from the input point Z of the pulse generator
PG-1.
If the latch relay LR-1 is assumed to be in the X coil or closed
position, wherein the condition of its contacts are as illustrated
in FIG. 2, the power supplied by the sensor MS-1 through the closed
contact B of relay RE-1 activates only the pulse generator PG-1,
which, after one cycle, will then trigger the Y coil of latch relay
LR-1, closing the contacts BB and A and thus resulting in
application of an advance pulse to the contact CA of counter C-1 as
well as causing energization of the relay RE-1 when the capacitor
1-C is charged.
It will observed from FIG. 2 that the magnetic sensor MS-2 connects
through contact B of reed relay RE-2 with the contacts B and AA of
the latch relay LR-1 (which are closed in the X coil position) as
well as to the input Z of the pulse generator PG-1. Thus, if the
latch relay LR-1 is in the X coil position, the pulse from the
sensor MS-2 monitoring the lane 12B will be applied through contact
AA of the latch relay LR-1 to the count advance contact CA of the
counter C-1 to register another count, and will also be applied
through the closed contact B of latch relay LR-1 and through the
capacitor 2-C to the coil of reed relay RE-2 effecting actuation of
this relay in the same manner as relay RE-1 was activated
responsive to sensor MS-1.
If both sensors MS-1 and MS-2 are activated at exactly the same
moment, the position of the latching relay LR-1 would determine
which sensor input pulse would be counted first. Thus, if the
latching relay were in the X position, the input pulse from MS-2
would be counted first, while the pulse from sensor MS-1 would be
counted first if the latching relay were in the Y position. It will
be apparent that the input pulses from the sensors MS-1 and MS-2
are terminated as far as the balance of the encoding circuits is
concerned by the action of the reed relays RE-1 and RE-2 as
previously explained. The hold-in action of relays RE-1 and RE-2
positively prevents a vehicle from being counted more than once, as
might otherwise be the case where traffic is held up momentarily by
a traffic signal or for any other reason. For example, if a vehicle
is stalled over sensor MS-1, the closure of the contact of MS-1
which persists so long as the vehicle remains over the sensor
cannot affect other than the first activation of the pulse
generator PT-1, due to the opening of the contact B of relay RE-1
upon energizing of that relay coil and the holding of that coil in
the energized state by its closed contact A for the remainder of
the period the vehicle remains over the sensor MS-1. This applies
to all sensors used in this invention.
The use of the pulse generator PG-1 to switch the latching relay
LR-1 alternately from the X coil to the Y coil positions permits
the counting of vehicles moving in both lanes 12A and 12B
regardless if one lane has been stalled. Where more than two lanes
of traffic are moving in the same direction, the latching relay
LR-1 would be replaced by a ring counter formed from commercially
available hybred reed flip-flops having a single input and parallel
output, which in effect would scan the inputs from the plural
magnetic sensors monitoring the more-than-two lanes. Of course,
additional control relays similar to the relays RE-1 and RE-2 would
be added for each additional lane in the control system.
The magnetic sensors MS-3 and MS-4 at the exit or downstream ends
of the lanes 12A and 12B are provided to count vehicles leaving the
block 12 in the respective lanes and subtract the counts from the
counter C-1, which is a bidirectional integrated circuit binary
counter which drives its integrated circuit decoder-driver. The
encoding circuitry for the magnetic sensors MS-3 and MS-4 is shown
schematically in FIG. 4 and incorporates the pulse generator PG-2
which is identical to the pulse generator PG-1 for the purpose of
scanning or cycling the latching relay LR-2 for the same purpose
that the latching relay LR-1 is cycled. This block exit or
downstream portion of the system is located in a package at the end
of the block 12 remote from the intersection 11, and only the pulse
signal from each count applied through the contact BB or the
contact AA of the latching relay LR-2 is sent back to the base
package 10 by any convenient means, such as by cable, or by radio,
as indicated schematically in the drawings, and a single cable or
radio transmitter-receiver is all that is required in the way of
signal connections from the exit end package to the base control
package for each counter.
It will be observed from FIG. 2B that count pulses from the sensors
MS-1 and MS-2 are also applied to the coil of reed relay RE-3 in
addition to the circuit through the closed contact B of reed relay
RE-4 to the count advance contact of counter C-1 and that signals
from the encoding sensors MS-3 and MS-4 and their immediately
associated circuitry 16 are coupled by radio or by cable, or other
convenient means, to the coil of reed relay RE-4 and then in a
circuit through the closed contact B of relay RE-3 to the subtract
contact CR of counter C-1. The purpose of these two relays RE-3 and
RE-4 is to prevent both count advance and count subtract pulses
being received at the same time by the counter C-1. It should be
apparent that if this occurs, both the coil of RE-3 and RE-4 will
be activated, thus blocking both circuits to the counter C-1. Since
these two counts cancel each other, the correct setting of the
counter C-1 is maintained.
Also, it should be mentioned that the speed of the pulse generator
PG-1 is such that in the event of a slightly staggered relation of
encoding pulses reaching the latching relay LR-1, the information
(i.e., the pulse signifying detection of a vehicle at the sensor)
would be retained until terminated by the appropriate control relay
RE-1 or RE-2. The moving vehicle must clear the magnetic sensor
before the encoding pulse is terminated, thus creating a lengthy
pulse in relation to the high-speed action of the other components
of the system. It will be noted that one-shot multivibrators OS-1
and OS-2 are provided in the leads to the count advance and count
subtract terminals CA, CR, of the counter C-1, these being
high-speed, integrated circuits used to insure the proper pulse
width to drive the binary counter C-1. The counter C-1 is
preferably an integrated circuit up-down binary counter of
conventional construction having an associated integrated circuit
decoder-driver DD-1 indicated schematically as a series of open
contacts.
It will be noted that the contacts of the decoder-driver DD-1
associated with the counter C-1 are group connected in series of
five contacts in each group. Counting from the top, the contact
group 1 to 5 will pull in the coil of reed relay RR-1, the A
contact of which connects directly to the 40-second control contact
of the traffic signal, for example, the traffic signal 12C in FIG.
1, commanding the northbound traffic flow pattern toward the lanes
12A and 12B in the example shown in FIG. 1. Thus, the counting
sensors MS-1 and MS-2 and cooperating sensors MS-3 and MS-4
monitoring the traffic flow in the next block along the lanes 12A
and 12B control the counter C-1 and thus the contact condition of
the decoder driver DD-1 so that if the count during the selected
count period in the lanes 12A and 12B totals 1 to 5, the traffic
light 12C will operate on the 40-second cycle (program duration).
The next group of five contacts of the decoder driver DD-1 will
pull the coil of reed relay RR-2, the third group of five contacts
pulls in the coil of reed relays RR-3, the fourth group of five
contacts activates the coil of reed relay RR-4, and the fifth group
of contacts activates the coil of the saturation flow control relay
RR-5. The A contact of relay RR-2 connects to the 52-second control
contact of the traffic signal 12C, the A contact of RR-3 connects
to the 70-second contact of this traffic signal, and the A contact
of RR-4 connects with the 90-second contact of this traffic signal.
The multiple offset command signals (time on green or delay in
signal change between successive intersections) are provided by the
open relay contacts in FIG. 2A labeled OS-1, OS-2, OS-3 and OS-4.
The signal light settings for multiple splits (cycles from green to
yellow to red) are provided by the open relay contacts labeled
SP-1, SP-2, SP-3 and SP-4. It will be understood that the traffic
signals used with this system are of the types now manufactured
incorporating switching devices to regulate the cycles, splits and
offsets, which require only command signals for proper
selections.
It will be appreciated that the number of contacts and groupings in
the decoder-driver will depend on the length of the block or the
distance to the next signal installation, and whether or not
parking is permitted in the block. Any major outlet, such as a
parking garage, should be treated the same as an intersection.
Driveways and similar outlets should be treated the same as
on-street parking and be added before the saturation total level is
reached.
The fifth group of contacts of the decoder-driver DD-1 controls the
saturation flow control relay RR-5, the A contact of which connects
to the red light control contact (labeled R) of the signal light
installation 12C, commanding the northbound flow of traffic. This
"red" light will remain on until the subtract sensors MS-3 and MS-4
cause the counter C-1 and decoder-driver D-1 to step off the block
of contacts controlling the relay RR-5, and thus indicate that the
saturation level in the relevant block no longer exists. The B
contact of the relay RR-5, which is normally closed, is connected
to the right-hand green turn arrow control contact of the traffic
13C, so that when relay RR-5 is pulled in, it will break the power
supply to the right-hand arrow in the westbound lane until the
traffic saturation in the northbound lanes of the block 12 clears.
The BB contact of relay RR-5 connects directly to the left-hand
turn arrow control contact (labeled AL) of the traffic signal 15C
controlling the eastbound lanes of block 15.
It will be appreciated that counters C-2, C-3 and C-4 and
associated decoder drivers DD-2, DD-3 and DD-4 are provided for
each of the other blocks 13, 14 and 15, each of these counters
having similar separate count circuits responsive to magnetic
sensors and including pulse generators and latching relays similar
to those described in connection with the block 12 and counter
C-1.
A time-delay TD-1 is provided in association with the saturation
flow control relay RR-5 to activate a "fail safe" latching relay
LR-1A in the event of the failure of the counters C-1 to step back
off the saturation contact group that controls relay RR-5 after a
predetermined time period. Relay LR-1A, when activated, will break
the power circuit to the contacts of relay RR-5 and provide power
through a normally open contact to a yellow flashing circuit,
labeled YF in the signal light installation, to continue activating
the yellow flashing circuit until the counter C-1 corrects itself
or the basic control package is repaired or replaced. This action
permits traffic flow to continue under caution unless an obvious
traffic jam exists.
Inspection of the schematic diagram of FIGS. 2A and 2B will reveal
that the counters C-2, C-3 and C-4 and their associated decoder
drivers DD-2, DD-3 and DD-4, having reed relays RR-6 to RR-20,
associated with groups of five contacts each control their
associated traffic signals in a manner similar to the decoder
driver DD-1, and halt traffic flow into the respective blocks they
control until the traffic congestion has cleared.
It will be noted that the normally closed B contacts of relays
RR-2, RR-3 and RR-4 are linked in a series hookup involving their
counterparts in the decoder drivers driven by the counters C-3,
C-2, and C-4. By means of this circuit, the highest block of
contacts will control the traffic light control settings and is
established by the heaviest traffic tallied by the sensors and
counters. In the event the flow is evenly divided, the relays
driven by counters C-1 would prevail, then C-3, followed by C-2 and
C-4. The higher decision capacity will go to the counters
controlling the major artery at the intersection. It will also be
observed that the power out of these closed contacts also controls
the common side of the next lower relay in the counter block chain.
The saturation flow control relay RR-5, and its counterparts RR-10,
RR-15 and RR-20, are not involved in this circuit since they halt
all traffic flow into a congested block. This permits the system to
select the next highest traffic level and permit a continued
traffic flow in other available directions. Tracing these circuits
involving the B contacts of the relays of the decoder drivers, it
will be noted that one branch lead from the B contact of relay RR-4
connects to the coil of relay RR-3 and the other branch lead
therefrom connects to the backside of the B contact of relay RR-9.
Similarly, one branch lead from the other side of the B contact of
relay RR-9 connects to the coil of RR-8 and the other branch lead
connects to the backside of the B contact of relay RR-14. Again,
one lead from this contact connects to the coil of RR-13 and the
other lead connects to the backside of the B contact of relay
RR-19, one lead from which goes to the coil of RR-18 and the other
lead proceeds to the backside of the B contact of relay RR-3.
It will also be noted from FIGS. 2A and 2B that a timing device
TD-2 is included in the power supply circuit to the decoder drivers
to reset all counter one or more times every 24 hours. This
time-delay action will compensate for possible accumulative
counting errors that could result from vehicles pulling out of
driveways in the opposite direction they entered the block without
clearing the subtract sensors, such as sensors MS-3 and MS-4.
Although this description calls for the operation of this system on
the basis of the running traffic volume in the immediate blocks
adjacent to the intersection or between the next traffic signals,
it should be obvious that the control area could be any distance
and other signal lights within the control areas could operate as
slaves of the controlled intersection. This would be of particular
advantage in areas with few major cross traffic intersections.
* * * * *