Traffic monitoring and control system

Sept. 27, 1966

Original Filed Feb.

j. L. BARKER 3,275,984

TRAFFIC MONITORING AND CONTROL SYSTEM 5, 1959

Sheets-Sheet 1

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Sept. 27, 1966

J. L. BARKER

3,275,984

TRAFFIC MONITORING AND CONTROL SYSTEM

Original Filed Feb. 5, 1959

Sheets-Sheet 2

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ATTORNEY

Sept. 27, 1966

Original Filed Feb.

J· L. BARKER 3,275,984

TRAFFIC MONITORING AND CONTROL SYSTEM 5, 1959

Sheets-Sheet 3

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ATTORNEY

3,275,984

Patented Sept. 27, 1966

United. States Patent Office traffic changes by deriving the rate of change of the average speed and/or the rate of change of the traffic volume.

Some aspects of the invention may be applicable to fields other than traffic, as in the determination of rate of 5 change of a varying average over an adjustable range or beyond a selectable limit or critical value.

The great increase in the volume of vehicular traffic on streets and highways in recent years has resulted in many of such roads becoming overloaded or congested at jq times despite the continued building of new road facilities. In this connection, the term “traffic volume” is used in its generally accepted sense of the rate of traffic flow past a given point in number of vehicles per unit of time, such as vehicles per hour for example.

Modern high type traffic road facilities such as expressways, freeways, parkways and the like, generally limit access to widely spaced entrance ramps and exit ramps, avoid cross traffic by over-passes or under-passes, and provide multiple traffic lanes and easy curves and are 20 designed for heavy traffic at relatively high speeds. Such high type highway facilities are very costly to build and are involved in the transport of essential goods and the transport of people to and from work, in many cases, as well as for pleasure.

Even in the best of such high type facilities, most or all of the roadway may be blocked in one direction by a major accident, and in periods of heavy traffic volume, a relatively small· accident or minor breakdown in one lane or some local change in road or visibility conditions may 30 so impede traffic that the flow of traffic is suddenly slowed down to a very low level and the effective capacity of the roadway is so reduced that long lines of traffic may accumulate with large numbers of vehicles stopped or waves of stopping and starting and moving at very low 35 speeds may move back along the line of traffic.

The accumulation of such stopped or very slow moving traffic, may extend back several miles from the obstruction before traffic authorities are aware of the situation, and in many cases, because of hills or curves in the road, ⁴⁰ other drivers approaching the trailing end of the line of slow moving traffic will not realize the situation until they have passed a possible exit or other alternate route.

Certain sections of the roadway may be more susceptible to such conditions than others, but in any event, it has 45 been a serious problem to notify traffic authorities or the traffic itself, or both, of such congested traffic conditions as soon as possible, both from the viewpoint of getting aid to accident victims promptly and from the viewpoint of expediting traffic and diverting it if necessary as soon ⁵⁰ as possible.

The sensing of sustained low speed alone below a preselected critical speed as by a succession of such speeds of vehicles, may give indication of traffic obstruction or the like in some instances. Apparatus for responding to a 55 succession of below critical low speeds of vehicles in traffic, and operating an indicating device or alarm device therefrom, is disclosed and claimed in a copending patent application Serial Number 777,711, entitled, Traffic Speed Monitor, filed December 2, 1958, now U.S. Patent 3,024,60 443, issued March 6, 1962, in which I am a joint inventor with Bernard J. Midlock. Such apparatus may be used as a means for determining sustained low speeds in certain traffic control systems as some aspects of the present invention as appears below.

However, speed alone may also decrease with increasing traffic volume before the latter reaches a critical level approximating the practical capacity of the road. It is known to traffic authorities that if more traffic then arrives on the road tending to exceed this critical level, the • 70 actual traffic volume and speed will both drop sharply, and the effective capacity will be much reduced. En; vironmental factors also such as weather and road condi1

3,275,984

TRAFFIC MONITORING AND CONTROL SYSTEM John L. Barker, Norwalk, Conn., assignor to Laboratory for Electronics, Inc., Waltham, Mass., a corporation of Delaware

Continuation of application Ser. No. 791,460, Feb. 5, 1959, now Patent No. 3,237,154, dated Feb. 22, 1966. This application May 27, 1965, Ser. No. 459,284

Claims. (Cl. 340—31)

This invention relates to a system for monitoring traffic and responding to particular changes in conditions of traffic flow such as volume and speed, to indicate such changes, and to operate alarm devices and remote changeable signs, signals or other devices to guide or control ; traffic in relation to entrance to and exit from highways or expressways, or to one or more of these features.

This application is a continuation of my copending patent application, Serial No. 791,460, filed February 5, 1959, now U.S. Patent 3,237,154, issued February 22, ! 1966. The present application is directed more particularly to certain aspects of the subject matter disclosed in said parent application but not claimed in said Patent 3,237,154, as more fully set forth below.

Certain aspects of the disclosure of the present application, particularly relating to response to concurrent rates of change in traffic volume and traffic speed of predetermined amounts and directions of change, for example, are repeated to some extent from said parent application for convenience of reference and understanding in the present application, but are claimed in said Patent 3,237,154. Reference may be had to the aforesaid patent for further features and details of response to concurrent changes in speed and volume.

The present application is more particularly directed to aspects of the invention relating to sensing or determining and responding to the rate of change of a traffic flow characteristic such as traffic volume or traffic speed alone.

In a preferred form of one aspect of the invention, the present application provides means for sensing vehicles in a stream of traffic and producing an electrical signal, such as a voltage, representing a varying characteristic of traffic flow as averaged over a period of time or number of vehicles, producing therefrom a further electrical signal or voltage as an output representative of the rate of change of the first electrical signal, and representative of the rate of change of said traffic flow characteristic. Such output or a predetermined such output may be used for operating an indicator, alarm or traffic control device. In one preferred form such further electrical signal (for rate of change) is compared with a reference to provide an output in response to such further electrical signal having a predetermined amount or value representing a rate of change of predetermined amount and direction, which output may be used to operate the indicator, alarm, or traffic control device.

From further aspects, the invention relates to electrical apparatus for determining the rate of change of traffic volume and the rate of change of traffic speed and indicating or responding to selected such changes of predetermined degree, which may be adjustable. Thus the apparatus may be arranged to respond to decreasing traffic volume alone, or to decreasing speed alone, or to increasing speed or volume, or to a combination of increasing speed and increasing volume, or to a combination of increasing. speed and decreasing volume, or to a combination of decreasing speed and increasing volume, or to concurrent decrease in both speed and volume, where response to or indication of such individual conditions or combination of conditions is desired.

In its preferred form, the present apparatus senses the

3,275,984 tions such as ice, snow, wet pavement or fog Will often cause marked shifts in a critical level of volume or of speed.

Thus, the impedance or congestion of traffic popularly known as a “traffic jam,” may arise because of an accident, road conditions, or other factors at moderate or relatively low traffic volume as well as arising at times of high traffic volume, and the problem has been to identify automatically by some means the congestion or substantial impedance of traffic over a wide range of traffic volumes and speeds.

Most people are familiar with the fluctuations normally encountered in normal traffic flow over any given time period, and thus decreasing traffic volume alone would not necessarily indicate traffic congestion.

It is an object of the invention to determine and indicate the rate of change of traffic volume with respect to time and the rate of change of traffic speed with respect to time in relation to running averages of such volume and speed.

It is another object of the invention to sense a predetermined minimum or threshold value of rate of change of traffic volume or traffic speed in a predetermined direction of change for indicating, alarm or control purposes.

It is a further object of the invention to provide a meth°^d °^{r means} traffic control by sensing restriction of traffic flow by sensing substantial reduction in traffic speed and/or traffic volume at a point on a roadway and to operate or control a traffic sign and/or signal to warn of and/or to relieve such restriction.

It is also an object of the invention to provide a method or means for monitoring traffic along a highway or expressway by sampling traffic speed and traffic volume at one or more points thereon, computing running averages of traffic speed and traffic volume, and determining therefrom at a remote or central monitoring point the rate of change of speed and the rate of change of volume over a scale from negative to positive values, and providing indications or alarms or both at such remote point.

Other objects of the invention may be apparent in the following description and appended claims with reference to the accompanying drawings in which:

FIG. 1 shows a plan view of spaced sections of a roadway such as an expressway or freeway, illustrating one application of speed and volume change sensing equipment tor remote monitoring and control of traffic signs and related devices.

FIG. 2, comprising the SUB-FIGURES 2a, 2b, and 2c illustrates in block diagram form a preferred form of traffic monitoring and control system for sensing particular changes m traffic speed and volume and responding to such changes.

FIG. 3 shows in schematic form a preferred circuit dia?ram of a Volume and Speed Rate of Change Unit an?earing in part FIG. 2b of FIG. 2 and of certain associated ilarm and control products of part FIG. 2c of FIG. 2

Πθ· 4 illustrates the indicating, adjustment and control &gt;anel of a preferred form of Volume and Speed Rate of .flange Unit for responding to concurrently decreasing Olume and speed, of the type shown in FIG. 2b and 1G. 3.

FIG. 5 shows another form of exit ramp arrangement mploymg detection of traffic congestion on the ramp to perate a warning sign on the expressway approaching tie ramp, or other traffic control device.

Referring now to FIG. 1, .there is shown a part of an xpressway or freeway of the usual divided roadway type f which only about one half is shown for convenience of lustration. The outer and inner edges 11 and 12 of the ladway for the one direction of traffic indicated by the rrow 13 extend through the three sections of roadway idicated as spaced some distance apart along the roadway y the breaks 14 and 15, introduced merely for conveniice in the drawing. The central divider strip is indicated y the edges 12 and 16, the latter edge also representin;

the inner edge of the companion roadway (not shown) for the opposite direction of traffic.

A detector 17 for sensing vehicle passage and speed is illustrated 'at the right side of the FIG. 1 at a desired point for sampling vehicular traffic passing along the roadway in one of traffic lanes on the roadway. The detector 17 is illustrated over the outer lane, for example, and may be of the type known as Model RSI Radar Speed and Impulse Unit, manufactured by Automatic Signal Division of Eastern Industries, Incorporated, the assignee of the present application for patent, and more fully described and illustrated in my copending application Serial Number 732,248, filed May 1, 1958, for Traffic Monitoring System, now U.S. Patent 3,059,232 issued October 16,1962.

.This speed and passage detector 17 develops an electrical signal representing passage of a vehicle and its speed m the associated traffic lane, this signal being transmitted by a two-wire line 22, such as a telephone line, for example, to the remote monitoring and control center 23, where this signal is .translated into separate channels for computing traffic volume and traffic speed on a running average basis, and particular rates of change of speed and volume are sensed for indicating and alarm purposes and to control automatic or changeable signs or other control devices as more fully explained later herein. The blocks withm block 23 are numbered to correspond to their respective counterparts in FIGS. 2a and 2b, for example

The monitoring and control center 23 may control via line 24 an electrically operated changeable sign 25, for example, in advance of exit ramp 26 to direct traffic to mis exit m case of sensing traffic congestion or impending congestion at the sampling point by a combination of decreasing average speed and decreasing volume. Simi^{center 23 may 0}P^erate another changeable sign 27 via line 28 to direct traffic from entering the expressway on entrance ramp 29. A traffic barrier or gate 32 of the remotely controlled or automatic type may be operated as a supplement to sign 27, if desired.

Other speed and passage sensing directors may be located over other lanes as indicated by such detectors 18 ^{and 19}· These may be in addition to detector 17 or one or the other may be connected to the remote center 23 instead of detector 17. If only one detector such as 17 is used, it will be in whichever lane is most representative of changes in traffic volume and speed on the roadway particularly in case of congested traffic conditions.

For continuous monitoring on all lanes, the several detectors 17, 18 and 19 would be individually connected to the monitoring center 23 by additional channels or lines not shown, and the center 23 would have individual translating, computing and rate of change response units preferably, although their outputs might be combined for alarm control circuitry.

FIGS. 2a, 2b and 2c are arranged to be connected together, as indicated by the corresponding numbered lines and together represent a complete traffic speed and volume sensing and concurrent rates of change sensing, indicating and control system, although certain features may be omitted m some instances, as desired. For example the ?^{r contl}'°I featured on FIG. 2c may be omitted if it is desired to use the monitoring, indicating or alarm features as one aspect of the invention, as in FIGS. 2a plus 2b, or as in FIG. 2b, where average speed and volume inputs are available.

FIG. 2a shows in block diagram form the vehicle passage and speed sensing detector 17 and its connection 22 to a speed and impulse translator 31, which is preferably, but not necessarily, located in the remote monitoring and control center 23 of FIG. 1. This translator separates the combined speed and passage signal into its speed pulse or signal on line 32 and passage pulse or signal on line 33. This translator 31 is more fully disclosed in my copending application Serial Number 732,248, above referred to, and its details are not material tq the present invention.

3,275,984

The speed signal pulses from individual passing vehicles are in the form of a direct current voltage substantially proportional to speed and are fed into the speed average computer 34 which is also disclosed in my said copending application, Serial Number 732,248, and provides an 5 electrical voltage output on line 36 representing a running average of the latest, adjustably predetermined number of vehicles.

The volume or passage pulses for the individual vehicles are of the voltage change type, as provided by operation ₁₀of a relay contact, for example, and are fed to the volume computer 35, which is also disclosed in my said copending application, Serial Number 732,248. This volume computer provides an output voltage on line 37, representative of a running average of .the average number 15 of vehicles passing the sampling point per unit of time over the latest adjustably predetermined time period, which may be of the order of several minutes, for example.

Thus the details of the components and connections of FIG. 2a are all the subject of prior patent applications, 20 and are illustrated here as examples of means for sensing vehicle passing and speed and providing an average speed output signal voltage and a traffic volume output voltage which also serves as an averaged value as contrasted with an instantaneous value. 2a

The respective output voltages representing. average speed on line 36 and average volume on line 37 serve as inputs to differentiating circuits 38 and 39 respectively, in FIG. 2b, to determine the rate of change of speed as a voltage output abbreviated ds/dt on line 41 and the rate 30 of change of volume as a voltage output abbreviated dv/dt on line 42. These rates of change are indicated on the respective meters 43 and 44, each of which is calibrated in percent between negative and positive scale limits with a center zero. Different ratios of the rate of change to 35 the scale and to the output voltage on line 41 or on line 42 respectively may be obtained by the range adjustments indicated at 45 and 46 for the respective rate circuits. Similarly, the blocks 47 and 48 indicate resets for the respective rate circuits. These may be manually op- 40 erated or by remote controlled relays, for example, to reset the rate circuits to zero, if desired.

The rate output lines 41 and 42 extend as lines 41' and 42' respectively and feed into the negative change coincidence unit 52 and may also extend into a positive change coincidence unit 53, on lines 41 and 42 as ⁴³branches of lines 41' and 42' respectively.

These change response units operate as more fully disclosed in connection with the circuit diagram of FIG. 3, but serve to respond to concurrent rates of change beyond predetermined minimum limits in the stated direction, ⁵⁰with such predetermined limits for speed and volume rates individually adjustable as indicated by the block 54 for the negative, change response unit 52 and by the block 55 for. the positive change response unit 53. Considering further, the negative change coincidence unit 52, it will be ⁵⁵noted that it is indicated that this responds to concurrent negative values of rates of change of both speed and volume by releasing relay VSL to close its associated contacts to provide an output on line 56. These relay contacts are of the normally closed type, i.e., they are closed 60 only when the relay is deenergized, but these contacts are normally held open by energization of the relay through the action of the associated circuit shown in FIG. 3, in absence of concurrent negative rates, characterizing decreasing speed and volume, beyond the limits set by the 65 dual individual adjustments 54.

The output line 56 is connected by a branch to an instantaneous indicator or alarm 57, and by another branch to a time delay device 58, which after a predetermined time of persistence of its input provides an output to line 60 70 and also via line 61 to the “Hold/Release Selector” 62. The output on line 60 may be used for generation of other devices, such as remotely located indicators, alarms, or traffic warning or control signs or devices.

The hold-release selector 62, as shown more fully in 75

FIG. 3, controls the action of the delayed alarm or indicator 63 and the associated output line 66' by determining whether the delayed alarm 63 and the output on line 66' will be maintained only as long as the concurrent negative change indicating output on line 56 continues or will be held or maintained after such indicating output on line 56 ends, as when the traffic volume and speed are no longer decreasing sufficiently.

In the hold condition, the output on line 66 and 66' and the operation of the alarm or indicator 63 is sustained until release by manual switching of this selector 62 to a release or non-hold position, or by manual operation of a remote release switch 64, or by automatic remote release via line 65, for example. Any other or remote devices which may be connected to line 66' will also be held in activated condition by the hold-release selector 62 when the latter is set to the hold condition and until released in a manner similar to that described above in relation to delayed alarm or indicator 63.

The other or remote devices may alternatively be connected to line 60, so that they will release automatically upon ending of output on line 56, and consequent reset of the time delay unit 58. The latter provides its time delay between the start of active output on line 56 and the start of output on lines 60 and 61, and after such output on line 56 has persisted for such time period, but this unit 58 is immediately resettable to terminate its output on 60, 61 if there is any interruption of output on line 56, which serves as the input to this time delay unit 58. This unit 58 acts as a slow-operate, quick release time delay relay.

The part of FIG. 2b described above corresponds in general to the circuit diagram of FIG. 3 presenting a speed and volume rate of change unit which responds to concurrent negative rates of change exceeding the limits set. There is also shown in FIG. 2b a speed and volume rate of change unit for responding to concurrent positive rates of change exceeding set limits as briefly mentioned above.

The latter unit is shown in the lower right part of FIG. 2b. Thus branches 41 and 42 of the rate of change output lines for speed and volume respectively extend downward to feed these outputs into a positive change coincidence unit 53. This unit 53 is the same as the corresponding negative change coincidence unit 52 above except that the diodes shown in FIG. 3 associated with the input circuits 41 and 42 would be reversed in unit 53 to respond to positive coincidence or concurrence of inputs instead of negative concurrence of inputs, and in connection with unit 53 the limits adjustment 55 for response would be set as desired for the minimum positive rates of change to which it is desired to respond.

The concurrence of positive rates of change of both volume and speed beyond the set limits releases the relay VSH in unit 53 in the same manner as concurrence of negative rates of change releases the corresponding relay VSL in unit 52. The release of relay VSH closes its contact shown in FIG. 2b to provide an output on line 70 in response to concurrence of positive rates of changes beyond the limits set by adjustor 55 and thus representing concurrent substantial increase in both traffic volume and speed.

This output on line 7® operates an instantaneous indicator 71 and a time delay untit 72 which, after a sufficiently long continued such output on line 70, will operate the delayed indicator 73 via line 74. A further output line 65 is shown from the time delay unit 72 and serves as an automatic remote reset or release of any previously set up delayed alarm 63 or associated devices which may be held operated after initial actuation by the time delay unit 58 and the hold-release selector 62 when the latter is set to its “Hold-Remote Reset” position as indicated on the control panel of the assembly shown in one preferred form in FIG. 4, for example but without limitation thereto.

The two outputs 74 and 65 from delay unit 72 are

3,375,984 shown to illustrate both make contact and break contact operations, since the delayed indicator 73 and other such devices would ordinarily operate from make contacts and since the reset or release through the hold-release selector is illustrated in the circuit diagram as of the series type employing the opening at least momentarily of a normally closed contact, such as shown in the box marked “remote reset” in the lower right corner of FIG. 3. This contact may be of the manually operated pushbutton or momentary opened contact type or may be a break contact on the output relay of the time delay unit, represented by the designation “64 or 65.” A corresponding such break contact 65' is illustrated on the output relay TL in the time delay unit 58 of FIG. 3 for example, and it will be understood that a corresponding break contact on the output relay (not shown) may be provided in time delay relay 72. It will be appreciated that electrical devices may readily be arranged to operate from either make contacts or from break contacts as desired, and the circuit arrangements are for purposes of illustration.

It will also be understood that other indicator, alarm or control devices may be connected to line 74 to be operated thereby, and that if desired to use the positive change unit 53 as an independent indication of positive change coincidence instead of for reset of the negative change coincidence alarm, the positive change may have a hold-release selector for control of indicator 73 or the like for example.

FIG. 2c illustrates in more detail several types of traffic control or warning devices which may be operated by one of the outputs 56', 60 or 66' derived from the output 56 of the negative change coincidence unit 52. Thus in FIG. 2c all three lines 56', 60 and 66' are shown with a switch for selecting among them for the type of control desired. The line 56' would provide instantaneous control, the line 60 would provide delayed control and the line 66' would provide delayed control subject to the action of the hold-release selector 62. The switch in FIG. 2c is shown in position connecting the latter line 66' to operate the electrical illuminated or changeable signs 25 and 27, as well as the barrier or gate 32, these reference numbers corresponding to the same devices in FIG. 1.

It will be noted in FIG. 2c that sign 27 is indicated as part of a larger sign and signal assembly, including a red or stop signal R which is operated with the sign, and a cautionary or flashing signal F operated when the sign is not operated, the operation or non-operation being under the control of the relay indicated. It will be appreciated that these signs and other devices are illustrative and other forms may be used or the signals or some of the other features might be omitted in some instances.

The circuit diagram comprising FIG. 3 illustrates a preferred form of electrical apparatus corresponding to the block diagram of FIG. 2b, but illustrating particularly the upper part of FIG. 2b involving response to concurrently decreasing speed and volume and the associated alarm circuitry, without the positive change response unit 53 and its associated indicators 71 and 73 and time delay unit 72.

The positive change response unit 53 and such associated elements of FIG. 2b relate to the response to concurrently increasing speed and volume, and may be used alone in some instances as a suppliement to the concurrent decrease response part above if desired in accordance with the types of response desired for the intended use.

As mentioned above, however, if the rectifier pairs associated with input lines 41' and 42' at the left in the broken line 52 of FIG. 3 are all reversed from the manner shown, and the relay designation VSL changed VSH, then the part of FIG. 3 designated 52 will serve to illustrate the positive change response unit 53, it being assumed in such case that the limit or threshold adjustments or 54(s) and 54(v) also will be set to the desired higher positive voltage value equivalent to a meter reading substantially above zero on its scale, which zero in turn may be equivalent to some convenient intermediate voltage value on a scale of positive voltage values of the same polarity, as positive for example in the preferred form illustrated.

Operation of the speed rate of change measuring circuit, including differentiating circuit 38, range adjust 45 and reset 47 will now be described more fully with reference to FIG. 3. It should be noted that the volume rate of change measuring circuit is an exact duplicate of the speed rate of change measuring circuit, therefore the circuitry details of the volume rate of change measuring circuit are not shown within the block 87, but the detailed circuitry above in the corresponding speed rate of change measuring block 88 serves to illustrate both. The procedure of calibration and setting as will be discussed below, as well as operation of the circuitry, apply to both the speed rate of change measuring circuit and the volume rate of change measuring circuit.

Input speed information, in the form of a direct current voltage, from zero, with respect to ground, to plus 100 volts above ground for example, is applied via lead 36, from the speed averaging computer, through a potential divider including resistors 101, 102, 103 and 104 to ground. The input applied via lead 36 represents the detected running average vehicle speed of the desired last number of vehicles of from zero to 100 miles per hour.

Input volume information, in the form of a direct current voltage, from zero, with respect to ground, to plus 100 volts above ground for example, is applied via lead 37 from the volume computer to a similar potential divider, not shown, in the circuitry of the volume rate of change measuring circuit 87.

The input applied via lead 37 represents the running average volume of traffic with 100 volts representing the upper end of the range of traffic volume anticipated, for example. This may for example, be of the order of 2000 vehicles per hour for a typical traffic lane in a roadway having free running traffic, although some lanes might have a lower volume corresponding to the 100 volts. For convenience 100 volts are considered to equal 100% for the upper end of the desired range of traffic volume.

A multiposition ganged selector switch 76, including sections 76a and 76b, in conjunction with the associated resistors comprise the “range adjust” 45, which serves to adjust the sensitivity of the rate measuring circuit, that is, the speed change per unit of time to produce full scale reading on the rate of change meter 43.

A corresponding selector switch and associated circui-. try serve as “range adjust” 46 for the control of sensitivity of the volume rate measuring circuit 39.

The selector switch 76 of range adjustor 45 is illus-. trated in FIGS. 3 and 4 in its second position, which may for example correspond to a rate of change of speed of 10 miles per hour per minute for a 100% indication on the meter 43. The rate of change of speed may be expressed as m.p.h. per minute for example for convenience and as a reminder that this is the rate of change of the average speed and is not employed in the frequently used sense of acceleration.

The scale of values of range adjustor 45 shown in FIG. 4 are given as one example of such values in m.p.h. change per minute, but without limitation thereto.

With range adjustor 45 so set for 10 m.p.h. per minute the speed rate of change meter 43 will indicate minus 100% for a decrease in the running average speed of 10 m.p.h. per minute, and will indicate plus 100% for an increase in the running average speed of 10 m.p.h. per minute, the meter having a central zero indication for no change in speed and being linear for intermediate readings as well.

The signal from selector switch section 76a is chan3,275,984 junction 133 with respect to ground in cooperation with similar rectifier 114' and the “limit adjust” 54(f), and thus to provide a threshold control for operation of the amplifier tube 135 in response to a differentiated signal of sufficiently low positive D.C. voltage, corresponding to a sufficiently large negative rate of change of speed, as set by the threshold or limit adjuster 54(j), as more fully described below in connection with the clamping and unclamping of the input to tube 135 under control of the impedance at junction 133.

FIG. 2b illustrates in block form a “limit adjust (dual) (%)” 54. This illustrates, functionally, two limit adjusting units, shown in FIG. 3: 54(f) associated with rate of change of speed and 54(v) associated with rate of change of volume.

The limit adjusting units 54(f) and 54(v) are similar to each other and limit adjust 54(f) is in the form of a potential divider including resistors 128 and 129 in series with potentiometer 130 between a positive D.C. supply and ground, and this limit adjust 54(s) serves to set the desired limit or threshold of negative rate of change of speed required for operation of the negative change coincidence unit.

To set the desired decrease as a limit on the limit adjust 54(f), the potentiometer arm 130' may be adjusted so that the positive voltage between arm 130' and ground is of the same value as the positive voltage between line 41 and ground when the meter 43 reads a value of minus 10%, for example. This setting would provide one of the two inputs required for operation of the negative change coincidence unit when a rate of decrease of 10% or more occurs in the average speed.

The negative change coincidence unit provides an indication when both the average speed decreases at a rate exceeding the preset limit as adjusted by the limit adjust 54(f) and the average volume decreases at a rate exceeding the preset limit as adjusted by the limit adjust 54(v). The individual rates of decrease, represented in a percentage, will appear on the respective meters 43 and 44, as for example minus 10%. The speed and volume rate of change signals for operation of the negative change coincidence gate are applied on leads 41' and 42 to rectifiers 114 and 114' and to rectifiers 115 and 15' respectively. When the positive voltage applied via lead 41' at point 133 is less than the positive voltage applied via arm 130' of limit adjust 54(f) and the positive voltage applied via lead 42' at point 133' is less than the positive voltage applied via the arm of the potentiometer of limit adjust 54(v), an unclamping of the grid 132 occurs and the negative change coincidence unit produces an output.

Operation of the clamping action at the input circuit to the negative change coincidence unit will now be explained more fully with, respect to the rate of change of speed circuit, which operation is similar to that of the rate of change of volume circuit.

Sixty cycle alternating current (A.C.) of a very low value, 3 volts for example, is connected via high resistance 134 to the grid 132 of triode 135. With the negative change coincidence unit held clamped, the A.C. is prevented from acting on the grid 132 by capacitor 138, in combination with diodes 114 and 114' and/or by capacitor 137, in combination with diodes 115 and 115'. With the voltage at lead 41', of a higher value than the voltage at the arm 130' of potentiometer 130, current flows through diodes 114 and 114' of sufficient magnitude to hold the voltage at junction 133. This effectively provides an A.C. ground at junction 133 and via capacitor 138 to the grid 132.

It has been found that satisfactory operation is provided with the following typical values of components associated with the circuits producing the clamping, but without limitation to such values; resistance 134, 10 megohms; capacitor 138, 1 microfarad; resistance 128, neled through resistor 108 to capacitor 109, the combination of which serves as a smoothing filter for the signal and to substantially eliminate any sharp changes in voltage that may occur in the signal due to any A.C. pickup or extraneous noise.

The filtered signal is fed through the differentiating network 38 including capacitor 110 and resistor 111, with the differentiated voltage appearing across resistor 111. Selector switch section 766 is ganged to section 76α as previously described and provides a 100% increase in the sensitivity of the unit in the maximum sensitivity or top position as compared to the second position by connection of resistor 112 in series with resistor 111, and resistor 112 is shunted out in all positions except the top position.

The differentiated input voltage, corresponding to the rate of change of the speed is applied to the grid of triode 81· Triode sections 81 and 82 are a balanced type voltmeter through which is obtained stability for accurate reading of low voltages. The meter 43 is connected via resistor 113 between the cathodes of triode sections 81 and 82. It will be noted that terminal 85 is connected to terminal 83 via line 86. This connection includes resistor 113 in the circuit between the two cathodes of the two triodes.

It may be desired to by-pass the resistor 113 via terminal 84 and to connect a recorder or remote meter between terminal 84 and terminal 83. In such case the resistance of such recorder or remote meter should approximate the value of resistor 113 which may be of 30 the order of 2000 ohms, for example, to maintain the calibration of the unit.

The differentiated signal is available in voltage form at the cathode of triode 81 and is fed via line 41 and 41' to crystal rectifier 114 in the negative change coincidence 35 unit 52.

. The differentiating circuit 38 may be reset by operation of reset 47, which is illustrated as a push-button controlling contacts 118 and 119. Closure of contact 118 shunts out the input series resistance 108 in the filter ⁴θ network to provide a low impedance path for rapidly charging capacitors 109 and 110 while contact 119 shunts out the resistor 111 to provide another low impedance path. . The combined low impedance paths insure that capacitor 110 rapidly assumes the potential of the input 45 voltage from the speed averaging computer as applied via line 36 as tapped by switch 76α, and thereby, upon release of . the reset pushbutton 47, the unit will read the differentiated input signal from this point on.

Calibration of meter 43 is made by adjustment of two 50 potential dividers, one potential divider including potentiometer 121 and resistor 120 between the cathode of triode 81 and ground, the second potential divider including resistor 125 and potentiometer 126 between the D.C. supply and ground. With tap 127 adjusted to its 55 ground extremity the minus 100% rate indication is calibrated by adjustment of tap 122 on potentiometer 121. The zero or center point may then be set by adjustment of. tap 127 on potentiometer 126. The latter adjustment in effect determines the voltage about which 60 the circuit will differentiate the input signal. Calibration of the circuit would be made with the reset button 47 held closed. After calibration is completed, the reset button 47 serves to reestablish a proper reading more quickly after any change in adjustment 45 for example or 65 when the unit is first turned on.

The output of the differentiating circuit is biased in a positive direction with respect to ground by the potentiometer 126-127, and is applied to the grid of the cathode follower triode 81, and the output of this tube 70 on line 41 is always positive above ground for all indications of meter 43 from minus 100% reading through zero to plus 100% reading of rate of change.

The differentiated signal on line 41 is applied via lead 41' to crystal rectifier 114 to control the impedance at 75

3,275,984 ¹¹

82,000 ohms; resistance 129, 3000 ohms; potentiometer 130, 3000 ohms; resistance 136, 100,000 ohms.

Resistors 128, 129 may be reduced or omitted and the value of 130 increased if desired to extend the range of adjustment. Similarly the fixed resistors in limit adjust 54( v) may also be reduced or omitted if so desired.

Thus the output voltage, via leads 41' and 42' of the rate of change of speed circuit and the rate of change of volume circuit respectively, must fall below the voltage set on the respective limit adjust circuits 54(j) and 54(v) in order that the unclamping effect occur and thus provide a clipped A.C. or a chopped D.C. for amplification by the tubes 135 and 140.

This action results from the change from low impedance to high impedance at both junctions 133 and 133'. The increased impedance in the A.C. circuit reduces the current and consequent voltage drop across resistor 134 and allows the A.C. to act on the grid 132.

The applied 60 cycle A.C. is amplified by two high gain stages of conventional resistance capacity coupled amplifiers. The amplified A.C. is then rectified at the anode circuit of triode 140 by means of diode doubler combination 141 and 142. This combination produces a negative D.C. voltage (with respect to ground), which voltage is applied to the parallel connected grids of dual triode 144, which is connected to react as one tube. The applied negative voltage on the grids of dual triode 144 increases the bias of the triode to cut-off. The triode, which is in the energizing circuit for relay VSL materially reduces the plate current and deenergizes relay VSL.

This combination of a high gain amplifier and the clamping-unclamping action described above on the A.C. signal at its input and a rectified output operating the control circuit for relay VSL, provides the sensitivity required to sense the small D.C. rate signals with a high degree of accuracy at the threshold points, and to respond only beyond the desired threshold or thresholds as set by the limit adjustors.

With both inputs from 41' and 42' sufficient for unclamping, relay VSL is deenergized and closes its contacts 151 and 152 and opens its contact 153^;. Closure of contact 151 supplies A.C. power, of the order of 110 volts for example, to the “instant alarm” 57 and to output lead 56'. Closure of contact 152 supplies D.C. positive power to time delay unit 58, while the opening of contact 153 opens the discharge circuit to ground for the timing capacitor 154 in the time delay unit.

The time delay unit, illustrated in the circuit diagram in FIG. 3, blocked off by a broken line box 58 includes a timer which may, by way of example, be of the type illustrated, or may be any conventional timer or delay action relay. The timer illustrated in FIG. 3, in time delay unit 58, is one type of electronic timer that may be employed in the time delay unit. The illustrated timer is of the type disclosed and claimed by Peter C. Brockett in his copending application Serial Number 677,993 filed August 13, 1957, under the name, Electronic Timing Circuit, now U.S. Patent 2,964,625 and assigned to the assignee of the present invention.

Normally, with relay VSL energized, contact 153 is closed and supplied a ground connection to the upper side of timing capacitor 154 to keep the capacitor substantially at ground potential. This maintains the grid in the left side of triode 170 at ground potential and keeps the left side of the triode 170 biased to cut off while the right side of triode 170 is conducting.

The switch 77 is a multiposition selector switch for selection, as desired, of one or more of the resistors 155 to 161 for inclusion in the charging circuit between the D.C. supply and timing capacitor 154, to determine the timing interval.

Upon completion of the charging circuit and opening of the ground connection to the upper side of ca ¹² pacitor 154 the charge on the capacitor 154 is increased and the potential applied to the grid in the left side of tube 170 is likewise increased.

When the potential applied to the grid in the left side of triode 170 increases to an amount as determined by the setting of arm 171 on the potential divider associated with the grid in the right side of the triode 170, the left side of the triode 170 will begin to pass current and the right side of triode 170 will become nonconductive. When the left side of triode 170 becomes conductive a surge of current will pass through the coil of relay TL to energize this relay.

Energization of relay TL reverses its contacts from the normal position shown, thus providing activation of an alarm 175 and a ground connection to selector switch section 78c.

Selector switch section 78c is ganged with switch section 78d in multi-position switch 78, and in its rightmost position as illustrated and in its center position, provides a ground connection for relay RS through contacts of relay TL and line 61 when relay TL is energized. Thus relay RS is energized after the time delay of unit 58, and thus in response to sustained rate of charge beyond the threshold as described above.

Energization of relay RS provides illumination of the delayed alarm 63 as well as an output via lead 66' for control of other devices. Relay RS and selector switch 78 are included in the Hold/Release Selector 62 which is illustrated in block form in FIG. 2b and also shown on the control panel in FIG. 4. Adjustment of switch section 73d to its rightmost position provides a lockin circuit for relay RS via its upper contact which is connected to ground through a remote reset switch 64. Adjustment of switch 78 to its center position opens the lock-in circuit for relay RS but maintains the operating circuit under control of relay TL to be operated and released directly with the latter. Adjustment of switch 78 to its leftmost position disconnects relay RS. Thus switch 78 may be changed from its rightmost position momentarily if desired for local reset.

The relay RS is provided in the preferred circuit illustrated to give greater flexibility of output control and to permit heavier duty contacts to be employed on relay RS while leaving relay TL as a lighter duty relay for example, If desired, however, the functions of these relays might be combined in relay TL by adding contacts and conventional circuitry.

Referring again to the time delay unit 58 and its control by the coincidence threshold response unit 52 as shown in FIG. 3, it will be noted that the time delay unit 58 is controlled via two input circuits from contacts of relay VSL as part of the output of unit 52. These two circuits are 56(a) from make contact 152 and 56(6) from break contact 153. It will be appreciated that if desired the functions of these contacts in supplying D.C. for charging the time capacitor 154 and opening tbe discharge or reset circuit therefor could be transferred to a separate relay which might be added in unit 58 and controlled by a single lead 56 or 56'. The circuits 56(a) and 56(b) in FIG. 3 may be considered a part of control line 56 or 56' in FIG. 2b.

It will also be appreciated that the time delay unit 58 may be controlled by the circuit 56(b) from contact 153 alone if the circuit 56(a) were shunted around the contact 152 to connect directly with the D.C. power supply which serves unit 58 via lead 69.

Although for convenience the D.C. power supply for time delay unit 58 is drawn from that available in unit 52 below in FIG. 3, the unit 58 may have its own power supply if desired.

Although the above description with reference to the circuit diagram of FIG. 3 and the block diagrams of FIG. 2, has set forth certain preferred aspects of the invention and certain modifications of the invention, other aspects of the invention include cooperation of either

3,275.984 of the rate of change circuits with either of the “coint^^nCfh ^thresh°^Id response units, as well as cooperation of both rate of change circuits with both coincidence or response units for response to rates of change of traffic volume and traffic speed in opposite directions.

n ^UnZ ^{52 and 53 have been} referred to in part above as change coincidence units, particularly in responding to concurrent conditions of changing speed and volume it will be appreciated that either unit may serve as a threshold response unit either for the rate of of thFra°t^f Th^{d al}°^Dep^{by the om}ission or disconnection to Ftr Z ^{f Chang}^ °^{f volume unit}&gt; blocks 87 and 54(v) “Γθ· J Z^{mp e}’ °^{Γ f0r the rate of} change of volume unit,alone by the omission or disconnection of the rate of change of speed unit blocks 88 and 54(j) in FIG 3 15 oZuSfro ^AS-Z ^aIZ^natiVe’ ^f°^{r 8}elective operSon οί ho h⁵² Zb ^{e her} Z ^{speed unit} °^{r the} volume unit or both, switches may be placed in the lines above and 138 to FIG 3ⁿto n’ ° °^{f capacitors} «⁷ and as desired in nnb 5?^βΠ&lt;?·^{Γ C} °^{SS theSe clrcuits} individually 20 uni? Iff Teshed. · ^{&amp;milar Pr}°^{VisiOn may be made}

Various combinations of units include the speed rate change unit alone cooperating either with coincidence cmaXTeedZ ^{52 al0ne}/^di-^^d for response toT 25 53 aloneTd t Z °^{Γ W1± coin}cidence or response unit thtvni ^adjusted/^ΟΓ response to increase speed alone Zh Z^mV^{a Of change unit alone} cooperating either XonleX T ^Or.^respOn,^{se unit 52} alone adjusted fm respond unit «^eT^ID8 Γ ™ °^{r with} coincidence or 30 S volume ^{for response t0} increasrpnt Γ °^th combinations for response to differof snX^CUrX ^condltions «dude both the rate of change iZg wfih TIT⁸ -n^te °^{f Change Of V01ume units} cooperatbe m response to concurrently increasing sXd anTde 114and U^’show inHG. ““““, ™^{th diod}« STS· ume ^CUrrently decreasing speed and increasing volarraneedⁱⁿfor°^rr ^^{31 te}™^{S the circuits ma}Y be readily amo'w ώ ^predetermined⁶ dlrXV directions ^Y^Same dictions or opposite ssas a--?response to a 10% decrZ&gt;0» · λ ^{t0 obtain} coincidence speed and a 15% decreXln ZX X ^Change °^fume, with the diodes as shown ‘in°^{f Vo1}' or a 2% increase in th» . ⁿ m FIG. 3, for example, 5% decrease n L“ate ofXnlA⁸? °^{f Speed and a}n_t._r nr _f = «Xis «« similarly !a_Meil, „ _{f0I mmpfe m} °_r“₃“^d_n™· alarm”M ^Steh- t^{5 and} Z^{limit indicator 57} and “remote alarm 63 which may be an alarm itself or an indicator s operated⁶ 'tSF ^{3 remOtely 10Cated alarm} amn ms' ™ Z ^{delay ad}J^ustment ⁷⁷ and indicator Sated in^OrFIG^O3 ‘° ^slmiIarly WM components adjuster 77 ^ Γ?’ ?' ^{The SCale above the time dela}y adjuster 77 may be in minutes for example.

lowthX?¹⁰^^{11 the C}°^{ntro1 panel :are} expanded bethe face of the panel for convenience in the drawing to make the legend appearing thereon legible. Thus for pXe’ Z^{660 C}°^{mputer Change} in M.P.H./Minute for Full Scale on Meter” refers to the scale of figures luster 45 ΓΪ Z f^{djuSting knob of} speed range adjustor 45 and the large horizontal arrow identifies the legend‘νοίΓ^Ζ¹⁶ °^{f Change meter 43}‘ Similarly the legend Volume Computer Change in %/Minute for Full Scale on the Meter” associates the range of values o rate n°fT^{e raDSe adiUStOr 46 above} * with the volume XsX^Cra!m^eeX^ter a Z ^{The ranges of vaIues for}

Neither of the limit adjustors 54(s) or 54(v) compris sh^inZyrT? ^{54 appear} °^{n tbe cont}rol Panel as 54(i) and 54ivl ^{18 anticipated} that the limit adjustors 4(s) and 54(v) will be varied much less often than the tb« appear „„ _lhe « an ta

SS “a”,??^1, '“·« ’» or » .te .p!

above.⁸ The^xkXnZ26°^fA ?^{Xpressway as in FIG}tion of n j ¹ . ^{mp 26} terminates at the intersecbridve 29 “^{dicated by} hues 30 and 30'. The &amp; . indicates that the roadway 30-30' is illustrated .a paaarns under rhe expms.w.y „I_{12 fo}SS λ.

in mr’ c λλ ana ot tne exit ramn ience of Xstation° °^{Γ f}°^resbortened convenes corresponding labeteTdeVctorX“icA‘° trated over the exit ramp in FIG 5 τη -?’J^{S lUuS}’ be suspended over the roadway^/meanl of ηΙοΓ'Α ₌,,._g or by means „( ’ inSmedfateLAdsHtoT? ^{the exit ramp} lengths in advance of theΐηηΓΚ ^{M Car} in the normally relativelv 4» ⁵° ® to sense vehicles the ramp rather Ihan X f^ret J^{g traffic zone along}ing down t the en“raj⁸ to th ^St°^Pping °^{r slow}example. France to the lower road 30-30' for ae™: st^a_o?s_e^{bc imm} «r m mlnme section ^γ “ujacent to the interSsSS'ss “ a. .« war.

lane of the condition of fhe exit rXn τη^{eCe eratlon}is illustrated by way of examnte λ Γ ? ^{The Slgn 25}' desired may be used in its stead ^f°^r °^{ther signs as}the sign 25'. ^{1 1 ad or} cooperatively with

3,275,984

Although a number of aspects of the invention and modifications of the form thereof have been described above, it will be understood by those skilled in the art that various other modifications might be made or rearrangements or substitution of parts and the like without departing from the spirit of the invention within the scope of the claims.