U.S. patent number 3,774,147 [Application Number 04/534,603] was granted by the patent office on 1973-11-20 for traffic cycle split selectors.
This patent grant is currently assigned to Gulf & Western Industries. Invention is credited to George Donald Hendricks.
United States Patent |
3,774,147 |
Hendricks |
November 20, 1973 |
TRAFFIC CYCLE SPLIT SELECTORS
Abstract
1. In a traffic cycle split control system for two intersecting
highways, traffic detector means for said highways for detecting
the passage of substantially all vehicular traffic thereon, main
highway traffic density computer means to which all said detector
means for the main highway are connected, cross highway traffic
density computer means to which all said detector means for the
cross highway are connected, the outputs of said computer means
being proportional to traffic density on their respective highways,
balance detector means for receiving and comparing the outputs of
said computer means to determine the higher output, a plurality of
adjustable impedances, a plurality of ratio detector means
connected to said impedances, said balance detector means applying
the higher output of said computer means through said impedances to
said plurality of ratio detector means, said balance detector means
applying the lower output of said computer means directly to said
ratio detector means, said plurality of ratio detector means being
responsive to said computer outputs to represent a ratio of main
highway traffic to cross highway traffic, a plurality of local
controllers, and a control circuit between said controllers and
said ratio detector means for actuating one of a group of
presettable traffic cycle splits dependent on said represented
ratio.
Inventors: |
Hendricks; George Donald
(Davenport, IA) |
Assignee: |
Gulf & Western Industries
(New York, NY)
|
Family
ID: |
24130769 |
Appl.
No.: |
04/534,603 |
Filed: |
February 10, 1966 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
343182 |
Feb 3, 1964 |
|
|
|
|
742160 |
Jun 16, 1958 |
|
|
|
|
Current U.S.
Class: |
340/910;
701/118 |
Current CPC
Class: |
G08G
1/07 (20130101) |
Current International
Class: |
G08G
1/07 (20060101); G08j 001/00 () |
Field of
Search: |
;340/35,36,40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Habecker; Thomas B.
Parent Case Text
This application is a continuation application of my copending
application, Ser. No. 343,182, now abandoned filed Feb. 3, 1964,
which is a continuation of my application, Ser. No. 742,160, now
abandoned filed June 16, 1958.
Claims
Having thus described my invention, I claim:
1. In a traffic cycle split control system for two intersecting
highways, traffic detector means for said highways for detecting
the passage of substantially all vehicular traffic threon, main
highway traffic density computer means to which all said detector
means for the main highway are connected, cross highway traffic
density computer means to which all said detector means for the
cross highway are connected, the outputs of said computer means
being proportional to traffic density on their respective highways,
balance detector means for receiving and comparing the outputs of
said computer means to determine the higher output, a plurality of
adjustable impedances, a plurality of ratio detector means
connected to said impedances, said balance detector means applying
the higher output of said computer means through said impedances to
said plurality of ratio detector means, said balance detector means
applying the lower output of said computer means directly to said
ratio detector means, said plurality of ratio detector means being
responsive to said computer outputs to represent a ratio of main
highway traffic to cross highway traffic, a plurality of local
controllers, and a control circuit between said controllers and
said ratio detector means for actuating one of a group of
presettable traffic cycle splits dependent on said represented
ratio.
2. In a traffic cycle split control system as in claim 1, a
plurality of relays energizable by said ratio detector means, a
plirality of local controllers, means within said local controllers
for changing the traffic cycle split between said streets according
to a plurality of splits, an interconnection between said relays
and said local controllers, and means within said local controllers
responsive to energization of said relays to change said
splits.
3. In a split control system for a major street and a group of
streets intersecting said major street, traffic detector means at
at least one intersection, a main street traffic density computer
means, an intersecting street traffic density computer means,
balance detector means for receiving the out-puts of said computer
means to dicern which direction of traffic flow exhibits the
heavier traffic density, ratio detector means coupled to said
balanced detector means to discern the ratio of heavier to lighter
traffic density, split selector means energized by said ratio
detector means, a plurality of local street intersection
controllers, an electric cable connecting said local controllers
with said split selector means, traffic cycle timers in said local
controllers, a plurality of cycle split means in said timers for
dividing the cycle time between main street and cross street, and
relays in said local controllers controlled by said cycle split
selector for selection of one of said cycle split means.
4. In a split control system for a grid of intersecting streets,
traffic signals at a plurality of intersections, local traffic
signal controllers controlling said traffic signals, a timer within
each said controller for timing a cycle of signal change, split
control means on said timer for controlling allocation of a
plurality of percentage splits of right-of-way time between the two
intersecting directions; a master traffic controller including a
split selector, a plurality of ratio detector means, balance
detector means, an east-west traffic computer means, a north-south
traffic computer means, traffic detector means for a plurality of
streets in each direction, said detector means for all east-west
streets connected to one computer means, said detector means for
all north-south streets connected to the other computer means, each
said computer means developing an output signal proportional to a
characteristic of traffic in that direction, said balance detector
means determining which output signal is higher, said ratio
detector means determining by what ratio one output signal exceeds
the other, said split selector means being controlled by said ratio
detector means for in turn energizing one of said split control
means at each said controller.
5. In a traffic control system, means for developing an electric
potential for a first direction of traffic flow in accordance with
a characteristic of traffic in said first direction, means for
developing an electric potential for a second direction of traffic
flow in accordance with a characteristic of traffic in said second
direction, electrical potential balance detector means for
determining the higher of said two potentials, ratio detector relay
means, a plurality of potential dividers having outputs connected
to said ratio detector relays, and switching means controlled by
said detector means for applying said higher potential across said
potential dividers.
6. In a traffic control system, electric potential developing means
for developing an electric potential for a first direction of
traffic flow in accordance with a characteristic of traffic in said
first direction, means for developing an electric potential for a
second direction of traffic flow in accordance with a
characteristic of traffic in said second direction, electric
potential balance detector means for determining the higher and
lower of said potentials, a plurality of voltage dividers, a
plurality of ratio detector means each connected to one of said
voltage dividers, a pair of balance detector relay means connected
to said balance detector means for respectively applying said
higher potential across said voltage dividers and said lower
potential to said ratio detector means, and a function selector
relay connected to each of said ratio detector means.
7. A traffic control apparatus for controlling traffic flow in at
least two directions, means for providing output signals
representative of a characteristic of traffic in each of said two
directions, reference ratio means, means for comparing said output
signals and applying on of said signals to said reference ratio
means to attenuate said one signal by said reference ratio, second
means for comparing said attenuate one signal to the other signal,
and traffic control means coupled to and controlled by said second
comprising means for controlling traffic flow in said two
directions in accordance with said comparison.
8. A traffic cycle split selector apparatus for controlling
allocation of traffic cycle splits to a roadway intersection having
two intersecting directions of traffic flow, means for providing
output signals representative of a characteristic of traffic in
each of said two directions, means for fixing a reference ratio,
means for comparing said output signals and applying the greater to
said reference ratio means to reduce said greater signal by said
reference ratio, second means for comparing said reduced greater
signal to the lesser signal, and traffic control means coupled to
said second comparing means for controlling allocation of a
particular traffic cycle split to said intersection.
9. A traffic cycle split selector apparatus for controlling
allocation of traffic cycle splits to a roadway intersection having
two intersecting directions of traffic flow, means for providing
output signals representative of a characteristic of traffic in
each of said two directions, means for fixing a reference ratio,
means for comparing said output signals and applying the greater to
said reference ratio means, second means for comparing said greater
signal to the lesser signal, said reference ratio means coupled to
said second comparing means, and traffic control means coupled to
said second comparing means for controlling allocation of a
particular traffic cycle split to said intersection.
10. A traffic cycle split selector apparatus for controlling
allocation of traffic cycle splits to a roadway intersection having
two intersecting directions of traffic flow, means for providing
signals representative of a characteristic of traffic in each of
said two directions, balance detector means responsive to said
characteristic signals to determine which characteristic signal is
representative of the greater characteristic of traffic, means for
fixing a reference preset ratio representing a ratio of
characteristics of traffic in said two directions, ratio detector
means coupled to said balance detector means and said reference
ratio means for detecting whether the ratio of the greater
characteristic signal to the lesser characteristic signal is
greater than said reference preset ratio, and traffic control means
coupled to said ratio detector means for controlling allocation of
a particular traffic cycle split to said intersection.
Description
This invention relates to a traffic control system and more
particularly to a traffic control system of the computer type able
to select the most expeditious balance between main street and
cross street use of a group of intersections.
The invention comprises part of a traffic control system which
changes the traffic signals at various intersections according to a
pattern. The pattern includes a right-of-way interval, a caution
interval, and a stop interval for each street and is called a
cycle. The invention provides means for apportioning the cycle
between two or more intersecting directions. The division of the
cycle between the intersecting directions of travel is here
referred to as the split. When expressed as a percent division of
the cycle between main street and cross street it is defined as a
percentage split.
Heretofore, the percentage split of time available to main street
and to cross street has been preset by hand or by time clock.
Single dial pretimed controllers are normally set by hand to allow
the most efficient flow of traffic across the intersection. An
interconnected group on single dial controllers, all with the same
cycle length, usually employed the same cycle split to allow most
efficient progression along the main thoroughfare. Little
flexibility was possible with this type of equipment.
Multiple dial pretimed controllers were developed to overcome this
lack of flexibility. With the usual three dials, three different
percentage splits were available, set in many cases to favor cross
street traffic on one dial, to favor main street traffic on another
dial, and balanced traffic on a third dial. Other common settings
favored both streets equally on one dial, main street on a second
dial, and main street more on a third dial. Dial changes were made
at predetermined times usually by a time clock arrangement
energizing control conductors and effecting remote dial change.
Another form of split change device in use today is shown in U.S.
Pat. No. 2,815,410 and consists of a number of contact assemblies
associated with and positioned above a dial unit. Keys are
positioned around the dial periphery, one key for each split
percent desired. A remotely controlled transfer device makes one
contact assembly and key effective at one time and another contact
assembly and key effective at another time. The number of split
percentages available is limited by the size of the contact
assemblies to three or four splits. A master programming device
determines which split is effective at various hours of the
day.
Still another form of split change device is incorporated in and
made a part of a cycle length change device and disclosed in U.S.
Pat. No. 2,761,119. Two adjustable frequencies are employed to vary
the main street and cross street right-of-way periods. By
increasing one frequency the right-of way period for the street is
lengthened. In order not to change the total cycle length the other
frequency must be decreased to shorten the right-of-way period on
the opposite street. This system is costly to produce and maintain
because in addition to the normal amount of equipment required, two
variable frequency generators are required at the master, an
amplifier is required at each local controller, and a three
conductor cable is required to connect the master with each local
controller.
The invention does not require variable frequency generators or
amplifiers and does not need more than two conductors to each
controller.
Traffic actuated controllers are not concerned with percentage
split except under certain circumstances. A two street controller
with traffic detectors in the cross street normally dwells in main
street green and goes to cross street green only on call. If cross
street traffic is heavy or if the recall switch is closed, the
controller will operate as a cyclic controller with the cross
street green interval being timed by its maximum timer and the main
street green interval being timed by its minimum timer. The setting
of these timers determines the split at one intersection.
A two street controller with traffic detectors in both streets may
likewise time as a cyclic controller if traffic from both
directions is heavy or if both recall switches are closed. Isolated
actuated controllers find their own best solution to the split
problem, and are not primarily concerned with this invention.
The full value of the invention is most evident when used in
conjunction with a system of pretimed controllers. However, the
invention operates equally well when used with a system containing
both pretimed and traffic actuated controllers.
The principal feature of the invention is automatic control of the
traffic cycle split at a group of intersection traffic signal
controllers on a grid or along a thoroughfare according to the
density of traffic in intersecting directions as measured at one or
more representative intersections. Methods have been described
above to remotely change the split at a number of intersections but
none makes use of traffic density in the two intersecting
directions as measured at one or representative intersections
during a number of traffic signal cycles.
What is believed to be new is a traffic density comparator device
able to compare the ratio of measured traffic volumes in two
intersecting directions against a plurality of preset, adjustable
ratios and select one of a plurality of splits for the heavier
direction of traffic dependent upon which of the present ratios the
measured ratio exceeds. The invention selects the most efficient
split of the cycle without varying the overall duration of the
cycle. The duration of the cycle may be determined by factors other
than the ratio of traffic densities in intersecting directions.
Traffic density is here defined as the number of vehicles passing a
given point during a predetermined interval. Control of traffic
cycle split according to traffic density has a decided advantage
over preset controls because the former system is related to actual
rather than predicted traffic conditions. For this use a novel
traffic density computer has been designed. The system for
computing traffic density, herein described, is considered superior
to known systems.
One traffic computer and control system known in the prior art
determines traffic density during a discrete interval, then selects
the cycle length at the end of the interval, and operates on that
cycle length for at least one interval. At the end of each interval
the count is erased. Actuations are then totaled during the ensuing
interval. The density thus computed is referred to as a discrete
density or average. A device for determining such a discrete
average is disclosed in U.S. Pats. Nos. 2,288,601 and
2,834,001.
A computer device is herein described which appears to be more
accurate for control work than any known device. It consists of a
traffic density computer which integrates traffic actuations over a
running interval so that the most recent actuations are given more
weight than past actuations. The count is not erased all at once
but is allowed to drain off as time transpires. This count
approximates actual traffic conditions as nearly as is practical.
An integrator and controller which approximates traffic conditions
more closely than this would tend to over control or to hunt.
Since the running average of traffic density is based on signals
originating from passing vehicles it is essential that the signals
created by each passing vehicle be modified to be identical
regardless of the speed of the vehicle or the condition of
individual detectors in different lanes. One of the features of the
invention is a novel circuit which converts the signals received
from several detectors into uniform signals. The uniform signals
are applied to the traffic density computers which consist of a
capacitor charging circuit which permits the running average of
traffic density in each direction to be represented by electrical
potentials.
The potentials indicative of traffic in intersecting directions are
applied to a balance detector. Here the higher potential determines
which direction of traffic is to be favored. A potential divider
reduces the high potential by several preset ratios and then
compares these reduced values with the lower potential. This
comparison determines the extent to which the direction of traffic
selected by the balance detector is to be favored in the split.
The present invention, in accordance with one aspect, is directed
toward a traffic control apparatus for controlling traffic flow in
at least two directions and comprises: means for providing signals
representative of a characteristic of traffic in each of two
directions; means for fixing a reference ratio; means for
developing a signal when a given ratio relationship of the
characteristic signals is different from the reference ratio; and,
traffic signal control means coupled to the developing means and
responsive to a developed signal for controlling traffic flow in
the two directions.
The principal object of the invention is to provide a system for
the control of traffic cycle split at a plurality of intersections
according to relative traffic densities measured at one or more
representative intersections.
It is another object of the invention to provide traffic density
computers for main street and for cross street, and a cycle split
selector consisting of a balance detector to determine which street
is to be favored, and a group of ratio detectors to determine the
ratio of traffic in the two directions.
It is another object of the invention to provide a local split
selector device able to select four splits at each intersection and
operable over a two conductor cable.
It is another object of the invention to provide a split selector
apparatus able to select various splits relative to traffic density
on two intersecting roadways.
It is another object of the invention to select one of a series of
splits to obtain most expeditious traffic flow on both the cross
street and the main thoroughfare.
It is another object of the invention to provide a split selector
device compatible for use with other devices of similar design
which select cycle lengths and offsets.
The apparatus will be explained in detail with reference to the
following figures, in which like symbols are carried throughout the
drawings:
FIG. 1 is a diagram showing a series of intersections along a
thoroughfare, traffic detectors in each street at one intersection,
a main street computer, a cross street computer, a split selector,
slave relays, and an interconnecting circuit to local
controllers;
FIG. 2 is a diagram showing a grid of intersecting traffic lanes,
traffic detectors in representative lanes, a north-south traffic
density computer, an east-west density computer, a split selector,
traffic signals at each intersection, and local traffic signal
controllers connected to the split selector by slave relays and an
electric cable;
FIG. 3 is a block diagram of a computer showing a number of
blocking oscillators, a bistable multi-vibrator, a monostable
multivibrator, an instantaneous integrator, a long time integrator,
percent traffic density meter, and an output terminal, approximate
wave shape at each stage is shown;
FIG. 4 is a block diagram of a balance detector and ratio detectors
for the thoroughfare system shown in FIG. 1;
FIG. 5 is a wiring diagram of the apparatus shown in FIG. 4;
FIG. 6 is a block diagram of a balance detector and ratio detectors
for a grid system;
FIG. 7 is a block diagram of a balance detector and ratio detectors
for a balanced grid system as shown in FIG. 2;
FIG. 8 is a wiring diagram of a split selector apparatus in a local
controller; and,
FIG. 9 is an isometric view of a two dial local controller.
GENERAL DESCRIPTION
The main street and cross street traffic density computers are
disclosed fully in U.S. Patent application, Serial No. 738,327,
filed May 28, 1958, now abandoned, entitled "Traffic Lane Control,"
but will be described here in block diagram form for the sake of
completeness. In the application named above, the computers are
associated with detectors in the inbound and the outbound lanes of
main thoroughfare for detecting characteristics of traffic, such as
traffic density, and are used to compute inbound and outbound
traffic density. Here, the computers are associated with main
street and a cross street and are used to compute traffic density
in the two intersecting directions.
Each traffic density computer develops a direct current output
potential substantially proportional to the running average of
traffic density on that street. Each computer contains an
integrator circuit which averages traffic flow over a running
interval of time. Heretofore, computers counted the traffic flow
over a discrete interval, totaled the count after a fixed time, and
erased the total at the end of the interval. This invention
utilizes a running average which appears to approximate average
traffic conditions more accurately, and leads to more accurate
control of traffic.
The output of each computer, a DC potential substantially
proportional to traffic density on that street, is fed to a
comparator device which comsists of a balance detector and a group
of ratio detectors. A stage of preamplification may be inserted
ahead of the balance detector to reduce the back effect on the
computers.
When the balance detector senses an unbalanced condition it
energizes a relay that switches the input potentials to a group of
ratio detectors. The higher potential is reduced by a plurality of
potential dividers and the resulting reduced potentials compared
with the lower input potential.
Each ratio detector, when unbalanced by the higher potential
representing a certain ratio of main street to cross street
traffic, energizes a split selector device representing the best
percentage split for that ratio of traffic. The split selector in
turn energizes a control conductor leading to each local
intersection controller to effect the proper split at each
intersection.
MAIN THOROUGHFARE CONTROLLED SYSTEM
One application of the invention is shown by FIG. 1. A series of
street or highway intersections are shown along a main
thoroughfare. The local traffic signal controllers at each
intersection are electrically interconnected with a control circuit
to permit control of the cycle split for most efficient flow of
traffic on both the main thoroughfare and on the cross streets.
At one representative intersection traffic actuated detector
devices are located in, on, above, or along the lanes in both
streets. In this description pressure sensitive traffic detectors
are used because they are easy to represent and describe. However,
any of the well known types of detectors may be used without
departing from the spirit of the invention.
A representative intersection is chosen for most efficient
operation of the system. The intersection may not be the one along
the controlled thoroughfare which has the most traffic; it would
preferably be the intersection where traffic conditions most nearly
approximate those at other intersections during most intervals of
the day.
It is important to the accuracy of the system that detectors be
located in all heavily traveled lanes at the representative
intersection and preferably in any other lanes frequently used.
Lanes not detected reduce the accuracy of the traffic density
computers.
As shown in FIG. 1, the main street MS is provided with detectors
D1, D2, and the representative cross street RCS is provided with
detectors D3, D4. Each detector D1 to D4 consists of two plates
mounted in the pavement, the bottom plate being electrically and
mechanically grounded, and the upper plate insulated from fround.
Upon passage of a vehicle over the upper plate of detector D1, for
example, a circuit is established to ground over conductor 1.
Passage of a vehicle over either main street detector D1, D2
grounds a circuit in the main street traffic density computer MC
through conductors 1, 2. Passage of a vehicle over either cross
street detector D3, D4 grounds a circuit in the cross street
traffic density computer CC through conductors 3, 4.
Both traffic density computers MC, CC receive signals from their
respective detectors, amplify the signals, reduce the number of
signals by a factor of two, give the remaining signals a definite
duration, integrate the number of signals over a short interval,
again integrate the number of signals over a long interval, and
develop a direct current potential proportional to the running
average of traffic density on that street. The function of the
integrators is explained more fully in another section.
The output of the traffic density computers is available for a
variety of purposes. In the present invention, the outputs are used
to select the proper division of traffic cycle time to main street
and to cross street. In another system the outputs might be used to
determine traffic cycle length; in another application they might
be used to provide a progression; or any combination of these
functions.
In this invention the computer outputs are applied to a split
selector SS comprised of balance and ratio detectors which compare
the values of the potentials and permit the higher potential to
energize a switching device. The switching device routes the higher
potential to the ratio detectors through one or more potential
dividers. It also routes the lower potential to the other side of
the ratio detectors. The ratio detectors compare the higher
potential, reduced by the potential dividers, with the lower
potential to determine the ratio of main street to cross street
traffic density.
A ratio detector will become energized if the reduced higher
potential is greater than the lower potential. The ratio detector
carries contacts which switch power to slave relays SR which
translate the information received over three or four conductors to
information capable of being sent over two conductors IC to the
local controllers LC. It is necessary to reduce the number of
control conductors required so that the cost of interconnecting
cable will be kept to a minimum. In most installations a cable
already interconnects the various local controllers with a master
controller located at a central station. The split control function
is assigned to two of the conductors or its control signal is
superimposed on one or more of the conductors being used by a
non-interferring control function. A radio or other link might be
employed to transmit the information to the local controller.
GRID SYSTEM
The usual layout of a city may include a number of streets lying in
an east-west direction with a number of intersecting streets lying
in a north-south direction. To adjust the traffic cycle split at
all the intersections to the average densities of traffic at all of
the many intersections, a few intersections that seem most typical
are selected. Vehicular traffic moving east and west at these few
intersections is used to determine one density. Vehicular traffic
moving north and south at these few intersections is used to
determine the other density.
In FIG. 2 any street bearing eastbound traffic is designated ES;
any street bearing westbound traffic is designated WS. Streets
normal to ES and WS streets are designated NS and SS. The streets
are shown as one-way thoroughfares but may be the more common
two-way streets or any combination thereof.
Each signalized intersections is equipped with a local traffic
signal controller LC which may be either pretimed or traffic
actuated or any combination thereof. For purposes of illustration,
pretimed controllers are used. To simplify nomenclature, streets
running one direction will be termed east-west streets and those
running at right angles will be termed north-south streets.
On one or more representative streets in each direction traffic
actuated detector devices D1 to D8 are located in, on, above, or
along the lanes of travel. Pressure sensitive traffic detectors are
used by way of illustration but any of the well known types of
detectors may be used.
The streets chosen for traffic sampling purposes must preferably be
representative of the major portion of streets running in that
direction. In FIG. 2, one-way streets are illustrated with traffic
detectors in each lane of eastbound ES, westbound WS, northbound
NS, and southbound SS streets. To count most accurately and to
anticipate changing traffic conditions it is preferred that the
traffic detectors be located at the entry points to the grid.
Each of the east-west traffic detectors D1 to D4 feed into
individual circuits of the east-west traffic density computer MC.
Each of the north-south traffic detectors D5 to D8 feed into
dividual circuits of the north-south traffic density computer CC.
It is important to the accuracy of the system that detectors be
located in all heavily traveled lanes and preferably in all other
lanes frequently used in the representative streets. Lanes not
detected reduce the accurcay of the traffic density computers.
Passage of a vehicle over any east-west street detector D1 to D4
grounds a circuit in the east-west traffic density computer MC over
conductor 1 to 4. Passage of a vehicle over any north-south street
detector D5 to D8 grounds a circuit in the north-south traffic
density computer CC over conductor 5 to 8.
The function of the traffic density computers MC, CC Is identical
to that described above. The output of each computer is
substantially proportional to traffic density for that direction of
travel averaged over the integrating interval.
In this form of the invention, the balance and ratio detectors may
be designed to include one or more split selections for each main
direction of travel. For instance, two splits may be available
favoring east-west travel and two splits may also be available
favoring north-south travel. One balanced split would favor each
direction equally. In the first form of the invention, as shown in
FIG. 1, two splits are available favoring main street traffic and
one balanced split is available favoring each direction equally. In
the first form of the invention the cross sections are of only
secondary importance, and no split is provided to favor them. The
design and layout of the ratio detector circuits is slightly
different for the two forms of the invention.
LIkewise, the design of the split selector slave relay circuit is
slightly different in that it must select one of two splits for
each direction of traffic, or a total of four splits. If traffic
density is relatively balanced, a fifth split favoring each
direction equally is selected. Information received over four
conductors is translated to information transmittable over two
conductors and an existing ground conductor to local
controllers.
TRAFFIC DENSITY COMPUTER
In both forms of the invention a traffic density computer is
provided for each direction of traffic. That is, one computer is
provided to measure traffic density on main street and another is
used to measure traffic density on cross street, as in FIG. 1. Or,
one may be provided to measure traffic density on two one-way
east-west streets, and another to measure density on two one-way
north-south streets, as in FIG. 2. Or, any combination may be used
so long as density in the two intersecting directions is
measured.
A block diagram of the units associated with each traffic density
computer is shown in FIG. 3. A plurality of detectors D1, D2 are
installed in the highway, one in each lane of traffic. The
detectors may be placed at the approaches to the intersection as
shown in FIG. 1, or in the various lanes of one-way streets as
shown in FIG. 2, or in any configuration to count all the traffic
in that direction.
To assure maximum accuracy of the counter, each detector feeds into
a respective blocking oscillator circuit as indicated by BO1-BO5,
which receives the signal from the detector and emits a pulse of
uniform wave shape and substantially uniform amplitude.
The noisy output of the detectors, which has been noted on a
cathode ray oscilloscope to include up to 14 impulses per
actuation, is fed into the block oscillators, which accept the
first pulse and block out the remaining signal for 6 to 7
milliseconds. This wipes out the chatter.
The signal is next fed into a bistable multi-vibrator MV1 whose
purpose it is to reduce two pulses to one. Each vehicle passing
over a pressure sensitive detector puts out two pulses, one for
each set of wheels. Since the purpose of the computer is to count
vehicles per unit of time, it is desirable it reduce the two pulses
to one so that the count will be accurate.
Another reason for supplying both the blocking oscillators BO1 to
BO5 and the bistable multivibrator MV1 is to reduce each actuation
to as short a pulse as possible for preventing loss of one by
overlapping of two pulses arriving almost simultaneously from
different detectors.
The bistable multi-vibrator puts out a sharp pulse of short
duration. This pulse is fed into a monostable multi-vibrator MV2
for which it emerges with a constant duration or width. It is
desirable to send to the integrator 11 pulses of uniform duration
so that the integrator will give each pulse equal weight.
Pulses of uniform duration, one for each two axle vehicle, are fed
into the next stage, an instantaneous integrator 11. The time
constant of the RC combination is 20 seconds, which is
instantaneous only by comparison to the long time integrator 12.
The incoming pulses charge a capacitor which is allowed to drain
off through a high resistance. The potential of the capacitor is
applied to the grid of a triode. A cathode follower provides a
potential across its cathode resistor proportional to the running
average of the number of vehicles counted during the previous 20
seconds.
The short time integrator is provided for at least three reasons.
First, a linear charging circuit is more easily applied to a short
time integrator than a long time integrator. Second, a RC circuit
with a short time constant is more accurately charged from a short
duration pulse than is an RC circuit with a long time constant.
Third, in some types of traffic control application it is desired
to know the instantaneous density. An example of this application
is a single intersection traffic control.
The potential from the short term integrator is applied to the long
time integrator 12 which is an RC circuit with a longer time
constant. One novel feature of this circuit is that its charging
circuit is different from and independent of its discharge circuit
and each may be set with a different time constant. In this
embodiment its charging circuit may be set from 1 to 9 minutes in 1
minute increments.
The potential from the long-time integrator is applied to the grid
of a triode. A cathode follower circuit provides a potential across
its cathode resistor proportional to the running average of the
number of vehicles counted during the running interval. It will be
understood that no definitely timed interval, as such, is used
here; the average is a running average. As time transpires, new
counts are added and old counts allowed to drain off so that the
most current average is used. This is a distinct improvement over
present equipment.
The long time integrator is required for control of a system of
intersections. A sufficient number of vehicles must be included in
the sample to obtain an accurate picture of traffic conditions.
Short time changes must not be allowed to effect a split change.
But short time changes must still be allowed to exert their
influence on the long time total. Density from the long time
integrator is useful in determining cycle length, split, and
offset.
The output potential from the long time integrator is applied to a
"Percent Traffic Density" meter VM which registers traffic density
as a percent of the setting on an adjustment dial entitled
"Vehicles per hour per lane at 100%". This latter adjustment
permits the computer to be used on highways with widely different
traffic densities.
Output is provided at output terminal OT for use by the split
selector, or by a cycle length selector, an offset selector, a lane
selector, or any of a variety of purposes.
A more detailed disclosure of the traffic density computer will be
found in U.S. Patent application, Ser. No. 738,327, entitled
"Traffic Lane Control," filed May 28, 1958.
BLOCK DIAGRAM OF RATIO DETECTOR
The potential from the two computers is applied to a balance and
ratio detector shown in block diagram in FIG. 4. The output
potentials of the main street and cross street traffic density
computers MC, CC are applied to the input terminals M, C of the
generator FG. The potentials from the generator are then applied to
the valance detector BD where the higher potential may energize a
relay to switch said higher potential to a plurality of voltage
dividers. The lower potential is switched to one side of each ratio
detector RD1 to RD3.
Voltage dividers VD1 to VD3 reduce the higher potential by three
differently reduced adjustable ratios. Each different potential is
applied to the grid of a ratio detector tube, the lower potential
having been applied to the other grid in each ratio detector tube.
If any reduced higher potential is sufficently high to outbalance
the lower potential it energizes a relay which switches power to a
control conductor. The control conductor in turn energizes the
proper relay in the slave relay circuit SR.
The relative position of the three ratio detector relays determines
which of four splits is energized at the local controller. Power to
select the proper split at the local controllers flows over lines
M', C' from slave relay circuit SR.
The purpose of the slave relay circuit is to permit energization of
the split selector relays in a number of local controllers. The
slave relays act as current amplification devices to reduce the
load on the ratio detector relays which are necessarily small
becuase they are plate circuit relays.
A plurality of contact assembly and keys on a cycle timing dial at
each local controller effects the cycle split. A split selector
relay makes effective the proper contact assembly and dial key. A
more detailed explanation of the local split selector is found in
another section.
BALANCE AND RATIO DETECTOR
A circuit diagram of the balance and ratio detector shown in block
diagram in FIG. 4 is shown in FIG. 5. A five tube unit is employed
in this embodiment with three of the tubes used as ratio detectors.
In another embodiment more or fewer ratio detectors may be employed
without departing from the spirit of the invention.
One ratio detector stage is employed for each independently
adjustable ratio desired. For instance, tube V3 detects the ratio
of cross street to main street traffic. When traffic exceeds the
preset ratio, tube V3 energizes relay CR4. Contacts on relay CR4
actuate a control function -- in this case, a 50-50 split favoring
cross street equally with main street.
A second ratio detector V2 is employed to detect the ratio of main
street to cross street traffic. When traffic exceeds the preset
ratio, tube V2 energizes relay CR1 which actuates a control
function, here a 60-40 split favoring main street.
A third ratio detector V5 is utilized to detect a higher ratio of
main street to cross street traffic. When traffic exceeds a second,
greater preset ratio, tube V5 energizes relay CR5 which actuates
another control function, here a 70-30 split favoring main
street.
Thus the unit serves two functions: it discerns which direction of
traffic is heavier, and it compares the ratio of heavy to light
flow against one or two adjustable ratios to determine how much of
the traffic cycle shall be allocated to main street traffic.
Referring to FIG. 5 in greater detail, the output of the main
street traffic density computer MC is fed in on pin P4, through
potentiometer R1 and resistor R2 to the grid V4G1 of tube V4A. The
output of the cross street traffic density computer CC is fed in on
pin P7, through potentiometer R3 and resistor R4 to the grid V4G2
of the tube V4B.
Tube V4 serves as a generator. The tube half which has the higher
potential impressed on its grid conducts more heavily. The cathode
to plate current flowing through tube V4A increases the voltage
rise across resistor R5 and increases the bias voltage on grid V1G1
of tube V1A. The current flowing through tube V4B increases the
voltage rise across resistor R6 and increases the bias voltage on
grid V1G2 of tube V1B.
The tube half V1A, V1B which has the higher positive potential
impressed on its grid conducts more heavily and pull in relay CR2
or CR3 in its plate circuit. If traffic is sufficiently heavier on
main street than cross street, for example, relay CR2 will pull in
closing contacts CR2-1 and -2 and contacts CR2-4 and -5. L2 power
is fed in on pin L2, through the contacts CR3-6 and -5, through
contacts CR2-5 and -4, through line 51 to contacts CR5-3, CR1-3,
CR4-3. Now closed contacts CR2-1 and -2 apply the potential
arriving from the cross street computer CC through pin P7 to the
grids V5G2, V2G1, and V3G2 of the ratio detector tubes through grid
resistors R7, R8, R9 associated with tubes V5B, V2A, V3B,
respectively.
The output of the main street computer MC arriving through pin P4
is now being fed through contacts CR3-3 and -2, through conductor
52 to the potential dividers PD2, PD1 and PD3 associated with tubes
V5A, V2B, V3A, respectively. The tap on each potential divider
applies a reduced voltage to the grids V5G1, V2G2, V3G1,
respectively. The taps may be set for the various ratios desired
for split change. To illustrate further conditions enumerated in
the first part of this section, potential divider PD1 associated
with tube V2 may be set for any ratio between 1 to 1 and 2.5 to 1.
When the ratio of the main street to cross street traffic exceeds
the ratio set on potential divider PD1, relay CR1 is energized
pulling in split 60/40, for example. Note that the ratio set on the
potential divider need not be the same as the split.
Potential divider PD3 associated with tube V3 may also be set for
any ratio between 1 to 1 and 2.5 to 1. When the ratio of cross
street to main street traffic exceeds the ratio set on potential
divider PD3, relay CR4 is energized pulling in split 50/50, for
example. That is, even though cross street traffic is heavier than
main, the split is awarded evenly, which actually gives main street
an advantage and allows main street traffic free movement.
Potential divider PD2 associated with tube V5 may be set for any
ratio between 1.5 to 1 and 2.5 to 1. When the ratio of main street
to cross street traffic exceeds the ratio set on potential divider
PD2, relay CR5 is energized pulling in split 70/30, for
example.
Assume now that traffic is relatively heavy and that main street
traffic exceeds cross street traffic by the ratio 1.25 to 1, for
instance. The left half of balance detector tube V1 conducts
pulling in relay CR2. Contacts CR2-1 and -2 close and apply across
street computer potential to grids of V5G2, V2G1, V3G2, of ratio
detector tubes V5, V2, V3. Contacts CR3-2 and -3 apply main street
computer potential through potential dividers PD2, PD1, PD3 to the
other grids V5G1, V2G2, V3G1 of tubes V5, V2, V3, respectively,
where the resultant ratios are compared. Tube halves V2B and V3A
will both conduct sufficiently to energize relays CR1 and CR4,
respectively, because the ratios of higher to lower potential are
within the ratios set on potential dividers PD1, PD3. With the
energization of relay CR1, contacts CR1-3 and -4 close feeding L2
power through conductor 55 onto output terminal M' associated with
the 60/40 split selector. Closure of contacts CR1-1 and -2 has no
effect because contacts CR5-1 and -2 and contacts CR3-4 and -5 are
open preventing L2 power from reaching output terminal C' on
conductor 58.
Since relay CR4 is also energized, contacts CR4-3 and -4 are closed
feeding L2 power through conductor 57 onto terminal IB which is
vacant in this application. Closure of contacts CR4-1 and -2 has no
effect because line 56 is not energized because contacts CR5-1 and
-2 are open, and because line 54 is not energized because contacts
CR3-4 and -5 are open. Thus, no power is fed over line 58 to
terminal C'. No power is fed over line 59 to terminal OB because
contacts CR5-3 and -4 are also open. Terminals IB, OB are used for
inbound and outbound favoring offsets in another application.
If cross street traffic had exceeded main street traffic, output
terminal C' and not M' would have been energized. Contacts CR3-4
and -5 would have been closed allowing L2 power to energize output
terminal C' over conductor 58. Also, output terminal M' would not
have been energized because contacts CR2-4 and -5 would have been
open.
If now main street traffic builds up heavier than cross street
traffic until the ratio of main to cross street traffic reaches 2
to 1, for example, relay CR5 will also be energized. Conduction
through tube half V5A will result from the increased potential
developed by the main street computer and fed in on pin P4, and
applied through contacts CR3-3 and -2, conductor 52, and potential
divider PD2, to grid V5G1. The increase in potential causes tube
half V5A to conduct, energizing relay CR5.
Relays CR1 and CR4, and therefore M', were already energized as
traffic increased so that now all three ratio detector relays are
energized.
With relays CR5, CR1, and CR4 energized, power is fed from line L2,
through contacts CR5-1 and -2, conductor 56, contacts CR1-1 and -2,
contacts CR4-2 and -1, conductor 58, to output terminal C'. With
both termials C' and M' thus energized, they make the fourth split
effective at the local controllers. This split may be set 70/30 in
favor of main street.
Output terminals IB and OB are also energized but they are vacant
in this application.
OTHER BALANCE AND RATIO DETECTOR CIRCUITS
Variou combinations of balance and ratio detectors may be assembled
by one skilled in the art of electronics. For example, two
combinations are shown in FIGS. 6 and 7. The type designed depends
on highway requirements and the number of splits required for each
direction of traffic.
FIG. 6 illustrates a type of balance and ratio detector for a grid
system. Two adjustable split changes are provided for each
direction of traffic in addition to a balanced split favoring each
direction equally. An independently adjustable greater and lesser
voltage divider and ratio detector is provided for each direction
of traffic. With only slight change in wiring, three of the
adjustable ratios could be used for one street, and one for the
other street.
If traffic and geographic conditions are such that the same setting
could be used for both streets, a simplified version of the ratio
detectors could be assembled as shown in FIG. 7. Only two
adjustable settings are provided and are used for both streets.
That is, if the lesser voltage divider is set to effect a split
change when the ratio of traffic density on the two streets is 1.25
to 1, the split change will favor main street when its traffic is
1.25 times heavier than cross street, or the split change will
favor cross street when its traffic is 1.25 times heavier than main
street. Likewise, when the greater voltage divider is set to effect
a second split change when the ratio of traffic density on the two
streets is 1.75 to 1, the split change will favor the busier street
when its traffic is 1.75 times greater than the less busy street.
This simplified system could be used advantageously with a grid
system when the two groups of intersecting streets are of equal
dignity.
LOCAL CYCLE SPLIT CONTROLLERS
The split selector disclosed in this invention is designed for use
in traffic control systems using local traffic signal controllers
of the type described in pending U.S. Patent application, Ser. No.
642,469, filed Feb. 26, 1957, entitled "Multiple Program Traffic
Control Systems." However, the selector is not limited to use with
one specific type of local traffic signal controller but may be
used with any type which allows for the utilization of information
or electrical energy furnished by the selector. Many controllers
now in use may be adapted to permit the master controller to vary
their cycle split.
In one version of a split control mechanism, power is fed out on
terminals M' and/or C' of the split selector shown in FIG. 5. In
the slave relay circuit SR shown in FIGS. 1 and 2 the current may
be amplified so that a large number of local controllers may be
controlled. Power flows over one or more conductors in the
interconnecting cable IC to each local controller LC connected into
the system. The relay circuit SR is employed also to permit the
transmission of four items of information over a two conductor
cable. The table below shows which conductors are energized for the
following conditions:
Con- Split Condition of Traffic Split, per- Con- di- Desig- cent
Main/ ductor tion nation Cross energi- zed 1 S1 Cross street less
than main st. 60/40 None 1 S1 Cross st. equal with main st. 60/40
None 2 S2 Cross street more than main st. 50/50 C' 3 S3 Main st.
1.25 times cross st. 60/40 M' 4 S4 Main st. 1.5 times cross st.
65/35 C' and M'
within each local controller is a decoding network which utilizes
the information received on two conductors to energize the selected
cycle split. The relative position of two relay armatures and
contacts determines which split is effective. A wiring diagram of
one such relay circuit is shown in FIG. 8. FIG. 8 is a reproduction
of part of FIG. 7 of application, Ser. No. 642,469 noted above.
Relay positions will be explained with reference to conditions
shown in the table above and with reference to FIGS. 5 and 8.
Under condition 1 when cross street traffic is equal to or less
than main street traffic, neither control relay CR2 nor CR3 is
energized and neither conductor C' nor M' is energized. Power is
fed in on conductor L2, through contacts 108, 118, 103S, conductor
58, switch 70S, to motor 37 making split S1 effective.
In condition 2 when cross street traffic exceeds main street
traffic by a ratio greater than that preset on adjustable potential
divider PD3, as previously explained, power is fed onto conductor
C', which at the local controller is wire 24, energizing local
relay coil 10. This switches local power from line L2 through
contacts 10S, 11S', 101S, conductor 58, switch 70S, to motor 37
making split S2 effective.
Under condition 3 when main street traffic exceeds cross street
traffic by a ratio greater than that present on adjustable
potential divider PD1, but not as great as that preset on potential
divider PD2, control relays CR2, CR1, and possibly CR4 are
energized. (CR4 has no effect under this condition because CR3 is
de-energized preventing L2 power from reaching the movable contact
member, CR4-2.) Power is fed onto conductor M', which at the local
controller is wire 25, energizing local relay coil 11. This
switches local power from line L2 through contacts 10S, 11S, 102S,
conductor 58, switch 70S, to motor 37 making split S3
effective.
In condition 4 when main street traffic exceeds cross street
traffic by a ratio greater than that preset on adjustable potential
divider PD2, control relays CR2, CR1, CR4 and CR5 are energized.
Power is fed onto conductors C' and M', which at the local
controller are designated 24, 25, energizing local relay coils 10
and 11. This switches local power from line L2 through contacts
10S, 11S', 101S', conductor 58, switch 70S, to motor 37 making
split S4 effective.
The above description shows how the master cycle split selector
chooses and energizes the proper split at the local controllers. A
typical local controller will be explained more fully in the
following section to illustrate its complete split function. The
remainder of the circuit shown in FIG. 8 will also be
described.
TWO DIAL CONTROLLER
A very thorough description of a local split selector will be found
in U.S. Pat. application, Ser. No. 642,469, noted above. A short
explanation will be made here to supplement the teaching of the
present invention.
FIG. 9 represents part of a two dial local traffic signal
controller and is identical in function to the device shown in FIG.
1 of application, Ser. No. 642,469 noted above. The same numerical
designations are used to avoid confusion. Dial 3 is the amber
timing dial and is driven by synchronous motor 37 which is powered
directly from 60 cycle alternating current. Dial 3 carries on its
surface 100 slots each representing 1 percent of the periphery and
1 percent of a revolution of the dial. Dial 3 is geared to motor 37
so that it makes half a revolution in less time than the shortest
split of the shortest cycle for which the equipment is
designed.
Into the slots in the face of dial 3 fit keys which may be
displaced at any percent point in the cycle. Four types of keys are
available, each with a projection located at one of four different
locations measured from the front of the slot. Four contact pairs
are located above the dial, each pair operated by only one of the
four key projections. When the front contact pair is to be closed,
for example, a key with a projection in the front position is used.
The table below shows the function of each dial key, its
designation, and a sample dial setting.
DIAL 3
Key Setting Function Percent 32 2 Stops Dial 3 in Cross Street
Green. 78 40 Begins Cross Street Amber. Ends C.S. Green. 80 50
Begins Main Street Green. Ends C.S. Amber. 33 52 Stops Dial 3 in
Main Street Green. 31 90 Begins Main Street Amber. Ends M.S. Green
74 0 Begins Cross Street Green. Ends M.S. Amber.
In the example illustrated in FIG. 9, six keys are fitted into
slots on dial 3, four keys having projections near the front of the
dial, and two keys having projections near the rear of the dial.
The former keys are located at percentage times in the cycle at
which it is desired to step the step switch and change the traffic
signal indications. The keys carry projections which close contacts
which step the step switch once for each contact closure. The three
keys 74, 78, 80, with projections in the front position are impulse
keys. The key 31 with a projection in the second position is a
release key. Their interaction is explained in greater detail
below.
Two keys, 32, 33, with projections located near the rear of dial 3
serve to open motor control contacts 32S, 33S. As soon as the
projection on key 33, for example, opens contacts 33S, motor 37 is
deenergized, dial drum 3 stalls, and contacts 33S remain open.
Closure of one of contact pairs 101S, 101S', 102S, or 103S on dial
2 is requied to energize the motor 37 momentarily to rotate dial
drum 3 and cause the motor control contacts 33S to close,
energizing motor 37 for another half revolution of the dial 3.
In like manner, the projection on key 32 opens the contact pair
32S, deenergizing motor 37, which stalls dial drum 3 allowing
contacts 32S to remain open. Dial 2 must then rotate until the
projection on key 100 momentarily closes the contact pair 100S
energizing motor 37 through line 57 and now-closed contacts 70S.
When motor 37 rotates dial 3 a few degrees contacts 32S again close
permitting motor 37 to be energized directly from line L2 for
another half revolution of dial 3. Contacts 70S are closed at the
proper time by relay 70 being energized from line L2 through
contacts 49S closed by cam 49.
As noted above, two types of keys have projections near the front
of the dial: impulse and release keys. Although neither is
important to the present invention, they are included in the
description. Impulse keys 74, 78, 80, are developed around the dial
at each point in the cycle at which the step switch is to be
stepped to change the traffic signal indication. The front contact
30S is closed by impulse keys 74, 78, 80 to cause such stepping
action.
To keep the camshaft 46 in step with dial 3 a release key 31 is
used. Release key 31 closes contact pair 31S located adjacent to
impulse contacts 30S. The release key's projection is to the rear
of the impulse key's projection. Release key 31 closes contacts 31S
energizing ratchet solenoid 48 which rotates camshaft 46 out of the
main street green interval. The release key is used to terminate
the main street green interval so that if camshaft 46 and dial 3
get out of step camshaft 46 will remain in the main street green
interval until dial 3 makes up to one revolution to again step the
camshaft.
The camshaft 46 shown in part in FIG. 9, carries cams 49, 59, and
additional cams (not shown) to operate switches to energize traffic
signal lights S, as in FIGS. 1 and 2.
Cam 59 allows closure of contacts 59S admiting L2 power to one
contact of front contact pair 30S. Closure of contacts 30S thus
energizes the ratchet solenoid 48 only when contacts 59S are
closed. Contacts 59S are controlled by the action of cam 59 and are
closed by the low section on cam 59. The low section of cam 59
corresponds to all of the cycle except the main street green
interval. During the main street green interval the high portion of
cam 59 opens contacts 59S and makes impulse contacts 30S
ineffective. Closure of release contacts 31S by key 31 energizes
ratchet solenoid 48 because one contact of contact pair 31S is
continuously connected to L2 power. The dial 2 and camshaft 46 are
thus kept in step.
SPLIT DIAL
Dial 2 is constructed similarly to dial 3. Five keys 100, 101,
101', 102, 103, have projections located in unique positions from
front to rear, one projection on each key. Key 100 located in slot
0 may momentarily energize motor 37 out of its stalled condition
during the cross street green interval. Any one of the keys 101,
101', 102, 103 may momentarily energize motor 37 out of its stalled
position during the main street green interval. Which of the latter
keys is made effective depends upon which contact 101S, 101S',
102S, 103S is energized which in turn depends upon the position of
relay contacts 10S, 11S, and 11S'.
Relay contact is maintained in the position shown by its own spring
pressure and is urged into its other position when coil 10 is
energized through conductor 24 from interconnecting conductor C'.
Relay contacts 11S, 11S', are maintained in the position shown by
their own spring pressure and are urged into their other position
when coil 11 is energized through conductor 25 from interconnecting
conductor M'.
Dial 2 rotates continuously at a uniform speed determined by
synchronous motor 60, energized by an alternating voltage VF which
may vary in frequency from 40 to 120 cycles per second. The
frequency is constant over a period and is varied by or from a
master controller to effectively change the length of cycle of
traffic signal change. This feature is covered in U.S. Patent
application, Ser. No. 642,469, noted above.
The purpose of dial 2 is to time the termination of the cross
street green interval near the zero point in the cycle, and to time
the termination of the main street green interval at the percentage
split in the cycle as selected by the Master Controller. Keys on
dial 3 actually initiate and terminate the intervals while the keys
on dial 2 time the start of dial 3. The table below shows the
function of each key on dial 2, its designation, and a sample dial
setting. The keys on dial 2 actually time the beginning of the end
of their interval.
DIAL 2
Key Setting Function Percent 100 0 Releases Dial 3 in Cross Street
Green. 101 50 Split S2. Releases Dial 3 in Main Street Green. 103
59 Split S1. Releases Dial 3 in Main Street Green. 102 60 Split S3.
Releases Dial 3 in Main Street Green. 101' 70 Split S4. Releases
Dial 3 in Main Street Green.
One rotation of dial 2 times one rotation of dial 3 and one
complete change of traffic signals. The first key on dial 2, key
100, closes contacts 100S momentarily which energize motor 37 out
of its deenergized condition caused by the opening of contacts 32S.
The latter four keys on dial 2, keys 101, 101', 102, 103, close
contacts 101S, 101S', 102S, 103S, momentarily, one of which
energizes motor 37 out of its deenergized condition caused by the
opening of contacts 33S. At any time, only one of the four latter
contacts is energized and is effective to start dial 3 into the
second half of its cycle. The effective contact determines how the
cycle will be split and is energized through relay contacts
controlled by the split control conductors C', M'.
If the cycle is to be split 50-50, for example, key 101 located in
slot 50 must be effective. Key 101 is made effective when contact
101S is energized from an L2 source through contacts 10S and 11S'.
This condition exists when relay coil 10 is energized and coil 11
is not energized. Thus, to make split S2 effective, control
conductor C' must be energized causing the traffic cycle to be
divided 50 percent to main street and 50 percent to cross
street.
Energizing control conductor M' and not C' makes split S3
effective. Power flows from conductor L2 through contacts 10S,
contacts 11S, contacts 102S, line 58, contacts 70S, to motor
37.
Solenoid coil 70 is energized only during the cross street green
interval to close contacts 70S and make line 57 and contacts 100S
effective. This circuit permits contacts 100S to start motor 37 out
of its stalled condition during the cross street green
interval.
Energizing control conductors C' and M' energizes both relay coils
10 and 11 and makes split S4 effective. Power flows from conductor
L2, through contacts 10S, contacts 11S', through contacts 101S',
line 58, contacts 70S, to motor 37.
Split S1 is effective with neither control conductor C' nor M'
energized. Power flows from conductor L2, through contacts 10S,
contacts 11S', through contacts 101S', line 58, contacts 70S, to
motor 37.
Latch relays may be used instead of the normal relays 10, 11 used
to energize one or another split contact. When the interconnecting
conductors C' or M' are energized they energize the main coil of
their associated relays 10, 11. Contacts 10S, 11S, or 11S' do not
close until the release coils (not shown) are energized, pulling a
latch away from themain armature, permitting the main armature to
act on its contacts.
The release coils are energized during a portion of the cycle when
a transfer in splits would be least disruptive of normal operation.
The release coils may be energized by contacts 49S which are closed
only during the cross street green interval. This prevents
disruption of the traffic signal cycle during switching of the
splits.
FUNCTION SELECTOR
Broadly, the invention provides means for selecting a particular
mode of operation of an apparatus capable of operating in several
different manners. The use of the balance and ratio detectors
disclosed in this invention is not limited to split selection or to
traffic control. As stated in a prior section, the output of the
traffic density computers can be used for a variety of purposes
such as split selection, offset selection, cycle length selection,
lane control, or any other purpose. Likewise, the ability of the
balance and ratio detectors to discern which of two potentials is
higher and by what ratio is useful for split selection, offset
selection, cycle length selection, lane control, or any other
purpose. Therefore, the balance and ratio detector assembly may
well serve as a function selector for a variety of apparatus.
Having described the invention in one or more forms or
arrangements, it will be evident to one skilled in the art that
modifications or changes may be made without departing from the
spirit of the invention.
* * * * *