US3739333A

US3739333A - Vehicle lane occupancy computer for traffic controller

Info

Publication number: US3739333A
Application number: US00150337A
Authority: US
Inventors: G Meredith
Original assignee: Tamar Electronics Industries Inc
Current assignee: Tamar Electronics Industries Inc
Priority date: 1971-06-07
Filing date: 1971-06-07
Publication date: 1973-06-12
Anticipated expiration: 1990-06-12

Abstract

The invention is concerned with computing the percentage of a total time period that a particular point on a roadway is occupied by vehicles. Pulses generated by a clock generator are fed to a gating circuit, the gate of this circuit being controlled by the output of a vehicle presence detector which is installed on the roadway being monitored. The output of the gating circuit is fed to a scaling counter where a particular desired scale factor is selected. The output of the scaling counter is fed through an appropriate commutator to an accumulator, where a digital count in accordance with the road occupancy conditions as taken on successive samples is accumulated. The digital output of the accumulator is fed to an output register from which digital readings in accordance with the road occupancy conditions is provided to computing and display circuitry for appropriate utilization.

Description

111 3,739,333 1 June 12, 1973 VEHICLE LANE OCCUPANCY COMPUTER FOR TRAFFIC CONTROLLER 75 Inventor: Gary L. Meredith, Anaheim Calif. [73] Assignee: Tamar Electronics, Inc., Anaheim,

Calif.

[22] Filed: June 7, 1971 [21] Appl. No.: 150,337

' [52] U.S. Cl 340/31 A [51] Int. Cl G08g 1/01 [58] Field of Search 340/31 A, 31 R, 36,

[56] References Cited UNITED STATES PATENTS 3,397,306 8/1968 Auer, Jr 340/31 A 3,602,882 8/1971 Hill 340/38 L 3,536,900 10/1970 Iwamoto et al... 235/l50.24 3,397,304 8/1968 Auer, Jr 340/38 R 3,397,305 8/1968 Auer, Jr 340/38 R 3,315,065 4/1967 Auer, Jr 235/150 24 3,414,876 12/1968 Cress, Jr. et al. 340/36 PARALLEL SHIFT Primary ExaminerKathleen H. Claffy Assistant Examiner-Randall P. Myers Att0rneySokolski & Wohlgemuth 57] ABSTRACT The invention is concerned with computing the percentage of a total time period that a particular point on a roadway is occupied by vehicles. Pulses generated by a clock generator are fed to a gating circuit, the gate of this circuit being controlled by the output of a vehicle presence detector which is installed on the roadway being monitored. The output of the gating circuit is fed to a scaling counter where a particular desired scale factor is selected. The output of the scaling counter is fed through an appropriate commutator to an accumulator, where a digital count in accordance with the road occupancy conditions as taken on successive samples is accumulated. The digital output of the accumulator is fed to an output register from which digital readings in accordance with the road occupancy conditions is provided to computing and display circuitry for appropriate utilization.

8 Claims, 3 Drawing Figures RESET pfi' k z i l DETECTOR 2] a) OUTPUT ACCUMULATOR REG'STER E08 1 I z I I2 I a,\ b UNITS TENS l 70 DECODER DECODER 1 CLOCK i F9 GENERATOR i l Patented June 12, 1973 3 Sheets-Sheet 3 CLOCKS MARK CENTER WWW EOS (f) (3) FF-l OUTPUT h GENERAL RESET SIGNAL/ 1 FF-l REsT f| (CLOCK 3) COUNTER (DINCIDENCE (K) SET SIGNAL FOR FF-2 (l) FF-2 OUTPUT (m) ADVANCE TO ACCUMULATOR\ (n) SCALE FACTOR DIVIDER Man (O) FF-Z RESET SIGNAL DQCUMU ATOR INPUk H (q) SAMPLQH FIG. 3

I JILI I: L-

LT n INVENTOR GARY L. M EREDITH SOQSKI 8 \MDHLGEMUTH ATTCRNEYS VEHICLE LANE OCCUPANCY COMPUTER FOR TRAFFIC CONTROLLER This invention relates to digital traffic control equipment, and more particularly to such equipment for computing the vehicle occupancy of a roadway over a predetermined time period.

In traffic control systems, information as to the flow of traffic along the roadway is often computed to provide information for use in adapting the control of the traffic signals in accordance with the measured traffic conditions. Such information is also useful for statistical purposes for use in the design of systems for particular locations and for designing modifications to existing installations to meet changes in conditions.

In a self-adaptive traffic controller timing system such as described in U.S. Pat. No. 3,414,876, as part of the control information, the traffic density is computed, this measurement representing the number of vehicles passing during a given period of time. Such a density measurement has its limitations in analyzing traffic flow in that it does not provide information as to the speed of movement of the traffic, that is to say, it could give a very low density reading with the traffic moving very slowly, yet jammed up bumper to bumper, or with the traffic at a complete standstill. In order to provide more accurate information as to traffic flow, computing devices have been developed which measure the total amount of time that a point on a road surface is occupied by vehicles during a given period of time. Prior art implementations, however, have generally been analog rather than digital and have not been readily adaptable to digital circuitry used in modern traffic control equipment. Further, such analog implementations generally do not have the accuracy that digital circuitry can afford.

It has been found that under normal conditions the actual occupancy by vehicles of a point on a roadway over a given period of time is a relatively low percentage ranging to a maximum of about 25 percent of the total time. It is therefore desirable in order to increase resolution in the low ranges of interest to set the maximum percentage of occupancy to be expected into the system as 100 percent by means of an appropriate scaling device. It is also desirable to provide some variation in this maximum 100 percent range to provide a control for selecting any one of a number of different maximum occupancy settings into the system.

The system of this invention provides a fully digital implementation for providing continuous successive measurements of the occupancy of a point on the roadway during a given time period. The system further provides means for adjusting the scale factor of the measurement so that any one of a number of portions of the total measurement period can be utilized to represent 100 percent occupancy. The system of the invention thus is capable of providing highly accurate occupancy measurements in digital form which are suitable for immediate readout or indication, recording for future reference, or for use in computing circuitry of a traffic controller to automatically adjust the traffic control timing cycles in accordance with these measurements.

It is therefore an object of this invention to provide continuous accurate measurements as to the occupancy of a roadway by vehicles.

It is another object of this invention to provide a more accurate technique for providing continuous readout as to vehicle occupancy of a roadway.

It is still, another object of this invention to facilitate the control of traffic by providing continuous and accurate information as to traffic occupancy of a roadway.

Other objects of this invention will become apparent as the description proceeds in connection with the accompanying drawings, of which:

FIG. 1 is a functional block diagram illustrating the basic features of the system of the invention;

FIG. 2 is a functional block diagram illustrating a preferred embodiment of the system of the invention; and

FIG. 3 is a series of wave forms graphically illustrating the operation of the embodiment of FIG. 2.

Briefly described, the system of the invention is as follows: The presence of vehicles at the road location to be monitored is sensed by a presence detector which provides an enabling signal to a gating circuit whenever vehicles are present. Clock pulses at a predetermined repetition rate are fed to the gate throughout a sampling period and are fed through the gate to a scaling counter whenever the enabling signal from the vehicle detector is present. Thus, the scaling counter receives a train of pulses during the sampling period, the number of such pulses received being in accordance with the portion of the total period during which vehicles are in the detection zone of the presence detector. The digital signals are appropriately scaled in a scaling counter to a selected scale factor. The scaled digital signals are stored in an accumulator and at the end of the sampling period, shifted to an output register for appropriate display or use for computation. At the completion of each sampling period, a new similar sampling period is initiated to provide continuous monitoring of the occupancy conditions. Updated readout in accordance with road occupancy are thus continuously provided.

Referring now to FIG. 1, the general features of the system of the invention are illustrated in a functional block diagram. Vehicle presence detector 11 is located on the roadway and provides a TRUE signal to AND gate 15 whenever vehicles are within the detection range of the detector. Clock generator 12 provides a continuous train of clock pulses to gate 15. Typically, there may be 10,000 clock pulses for each predetermined sampling period. Thus, clock pulses are fed through gate 15 whenever a TRUE or enabling signal is received thereby from presence detector 11, the number of such pulses fed through the gate being in accordance with the portion of the total sampling period during which vehicle presence detector is detecting vehicles.

The output of AND gate 15 is fed to scaling counter 17, which, as to be explained in connection with FIG. 2, includes a manual control for setting into the system any one of a number of scale factors representing percentages between 2 and 98 percent of the total sampling period. The output of scaling counter 17 is fed to commutator 25 which operates in response to a series of clock signals fed thereto from clock generator 12 to provide various control functions in a predetermined order as follows: When the scaling counter reaches the count set on its selector switches, the commutator first operates to pass one of the clock pulses received thereby through to accumulator 21 to provide a count thereto. Then a subsequent clock pulse is fed from the commutator through OR gate 30 to the scaling counter to reset the counter to zero. This operation is repeated throughout the sampling period to provide counts to accumulator 21 whenever the scaling counter reaches the selected count. Accumulator 21 thus accumulates a count during the sampling period which is directly in accordance with the output of presence detector 11, and is scaled in accordance with the selective setting on scaling counter 17.

The end of the sampling period is signaled by the arrival of an end-of-sampling pulse from clock generator 12 (EOS Pulse) at EOS gating circuit 13. The EOS pulse performs two functions. First, a parallel shift signal is fed from gating circuit 13 to output register 20 to shift the count in the accumulator into the output register. Output gating 22 outputs the contents of register 20 to computer 23 and display 24, thus providing a readout thereof. Output control lines (not shown) control the output gating. Secondly, the gating signal provides a reset signal which resets accumulator 21 to zero and passes through OR gate 30 to reset scaling counter 17 to zero. With the completion of the sampling period, a new sampling period is started, and so on, to provide a continuously updated occupancy readout.

Referring now to FIGS. 2 and 3, a preferred embodiment of the system of the invention and wave forms associated therewith are respectively illustrated. The various wave forms of FIG. 3 are identified by a letter which is indicated on the lines where they appear in FIG. 2.

Clock generator 12 has a series of successive output pulses designated clocks 1-10. These clock pulses may be generated by means of appropriate counter circuitry from a pulse train of mark pulses, as shown in FIG. 3, immediately below clock 10. An end-of-sample pulse (EOS) is generated between the th and 1st clock pulse from a center pulse train which is in interlacing time relationship with the mark pulse train, i.e., phase shifted with respect to the mark pulses, as indicated so that its positive going portions are half-way in between the positive going portions of the pulses of the mark pulse train. Typically there is one EOS pulse for each 10,000 of each of the sampling clock pulses, that is to say, the EOS pulse appears between 10th and 1st clock pulse after each 10,000th sampling clock pulses. As already noted, the EOS pulses signify the end of the sampling period. Therefore as will soon be seen, each sampling period is defined by 10,000 sampling clock pulses.

The output of vehicle presence detector 11 is fed to AND gate 15, this gate also receiving each sampling clock pulse (q). The sampling clock pulses are synchronized with the second clock pulses but are generally at a lower rate, this rate defining the duration of the sampling period. The output of AND gate is fed to divider 40 which divides by 5, the output of which in turn is fed to divider 41 which divides by 10. The outputs of

dividers

40 and 41 are fed to units and tens decoders 43 and 44 respectively to convert the signals from the binary stages of the counters to decimal form. A selector switch 45 is connected to units decoder 43 by means of which any one of the five divider outputs can be selected. Similarly, switch 46 is provided to select any one of the 10 outputs of decoder 44. It is to be noted at this point that switches 45 and 46, as shown in FIG. 2, are designated with numerals that indicate twice their dividing capacity, this in view of the fact that an additional divide by two factor is provided by means of divider 52, which is located in the signal line to accumulator 21. The outputs of

switches

45 and 46 are fed to AND gate 49. Also fed to AND gate 49 is clock pulse 3 (b). Thus whenever the count reaches the setting on

switches

45 and 46, the next succeeding third clock pulse (b) will be gated through gate 49 to provide a set signal (k) for flip-flop 53 (FF-2).

The output of flip-flop 53 (I) is fed to AND gate 60, this gate also receiving the 5th clock pulse (d). Thus, with flip-flop 53 in its set condition, the fifth clock pulse (d) is fed through AND gate 60, the output of which is inverted by means of inverter 61 to provide an input (n) to OR gate 30'. The sixth clock pulse (e) is inverted by means of inverter 55 to provide a reset signal (0) for flip-flop 53. The output of OR gate 30 is used as a reset signal for

dividers

40 and 41. Thus, whenever the count set on switches 45 and 46 is reached,

dividers

40 and 41 are reset to zero and resume a new count. The output of flip-flop 53 is also fed to AND gate 65 to provide an enabling signal therefor to permit the passage of the fourth clock pulse (0) therethrough to OR gate 67. The output of OR gate 67 is fed to divider 52 where it is divided by two, the output of the divider being fed to accumulator 21.

Thus it can be seen, for example, that with switch 45 set to O and switch 46 set to 40, as shown in FIG. 2, one pulse will be fed to accumulator 21 for each 40 pulses at the output of AND gate 15. The accumulator 21 has a capacity of 199, which represents 199 percent occupancy. To save one switch and a small amount of logic, switches 45 and 46 are set up to provide a maximum scale factor of 98 percent which provides no significant detriment to the operation of the device. Thus,

with switch 46 set at 90 and switch 45 set at 8, the accu- I mulator 21 will have a count of 100 during every sampling period that AND gate 15 has a pulse output of 9800 pulses. It should be immediately apparent that the setting of

switches

45 and 46 determines the number of output pulses from AND gate 15 required to completely fill accumulator 21, and in this manner any portion of a full true occupancy of the monitored location during the sampling period can be made to provide up to 199 percent output from accumulator 21. To prevent inputs to the accumulator if and when a count is ever reached which represents 199 as scaled, a decoder 70 which responds to such an output from the accumulator is utilized to provide an inhibit signal to AND gate 67 in the event that this count is reached. That is to say, decoder 70 has a NOT 199 output at all times except when the equivalent of a 199 count is reached.

When the '199 count is reached, the accumulator is effectively locked up" by the provision of the inhibit signal to gate 67. This indicates an error has been made in the selection of a scale factor. That is to say, the scale factor used is too small in view of the fact that the count has reached or gone over the capacity of the accumulator, thus making it difficult or impossible to make an accurate measurement. The inhibit signal prevents the accumulator from triggering back to zero and continuing to count.

When the end of the sampling period is reached, i.e., for the illustrative example after 10,000 clock pulses, an end of sampling pulse (EOS) is generated. This signal as shown in FIG. 3 at (f) occurs between a 10th and 1st clock pulse. The signal is fed from clock generator 12 through inverter to provide a set signal for flipflop 77. The output of this flip-flop (g) is fed to AND gate 78. Also fed to AND gate 78 is clock pulse 1 (a).

With flip-flop 77 set, AND gate 78 will pass clock pulse 1 therethrough, this pulse providing a reset signal for setting accumulator 21 to zero. The reset signal also is passed through OR gate 30 to reset

dividers

40 and 41 to prepare them for a new sampling. Immediately prior to the generation of the reset signal (1'), which as already noted is synchronized with the first clock pulse, the EOS signal 0) is fed as a parallel shift signal to output register to shift the reading of the accumulated count in accumulator 21 into output gating 20. Output gating 22 outputs the contents of register 20 to computer 2 3 'and display 24 for appropriate utilization.

An indicator 80 which may be a pilot lamp is connected to receive the output of vehicle presence detector 11 to provide an indication whenever this gage is receiving a vehicle actuation.

The system of this invention thus provides a highly accurate indication of the occupancy condition along a roadway, readouts being available in digital form for successive continuous sampling periods. Means are provided in this system to scale the measurements over a wide range so that measurements can be limited and thus more accurately provided over any limited range of interest.

While the system of this invention has been described and illustrated in detail, it is to be clearly understood that this is intended by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the following claims.

I claim:

1. In a system for providing a digital signal indicating the degree of occupancy by vehicles of a portion of a roadway over a predetermined sampling period,

means for generating a gating signal having a time duration corresponding to the presence time of vehicles in said roadway portion, means for generating a train of clock pulses defining said sampling period and a pulse signaling the end of said sampling period, I

gating circuit means receiving said gating signal and said clock pulses for gating a number of said clock pulses therethrough corresponding to the duration of said gating signal,

scaling counter means for decoding the output of said gating circuit means and scaling the decoded output to a selected percentage value, said counter means including switch means for manually selecting an occupancy scaling factor as a percentage of true occupancy,

said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator means to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero an accumulator for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, and

readout means for receiving the count signal in said accumulator at the end of each sampling period.

2. The system of claim 1 wherein said scaling counter means further includes a binary divider and decoder means for converting the outputs of said divider to decimal form, said switch means being connected to select any one of the outputs of said decoder.

I 3. The system of claim 2 and further including means connected to receive the selected output of said switch means for providing a signal for resetting said divider to zero in response to the selected output.

4. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway,

detector means for providing a signal throughout any periods during which vehicles are present at said location, means for generating a train of clock pulses which define a sampling period,

gating means for passing said clock pulses therethrough in response to said detector means signal,

scaling counter means for scaling the output of said gating means to a selected percentage of the actual occupancy of said roadway location, said scaling counter means comprising first and second dividers, first and second decoder means connected to each of said dividers for decoding the outputs thereof to decimal form, first and second switch means connected to said first and second decoder means, respectively, for selecting the outputs thereof representing percentages of full roadway occupancy, and means for generating a reset signal for said dividers when the count represented by the settings of said switch means is reached,

accumulator means for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, and

an output register connected to said accumulator means,

said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator means to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero.

5. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway,

detector means for providing a signal throughout any periods during which vehicles are present at said location,

means for generating a train of clock pulses which define a sampling period, gating means for passing said clock pulses therethrough in response to said detector means signal,

scaling counter means for decoding the output of said gating means and scaling the decoded output to a selected percentage of the actual occupancy of said roadway location, said scaling counter means including switch means for selecting one of a plurality of percentages of the actual occupancy to represent full occupancy,

an output register connected to said accumulator means,

said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero. 6. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway,

scaling counter means for scaling the output of said gating means to a preselected percentage of the actual occupancy of said roadway location, said scaling counter means including a binary divider, decoder means for decoding the outputs of said divider to decimal form and selector switch means for selecting an output of said decoder to represent a percentage of .true occupancy as occupancy,

accumulator means for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby and,

an output register connected to said accumulator means,

7; In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway,

detector means for providing a signal throughout any period during which vehicles are present at said location, means for generating a train of clock pulses which define a sampling period, said clock pulse generating means further providing a series of trains of pulses on separate control lines, pulses on each of said lines being utilized sequentially to implement a separate control function,

scaling counter means for decoding the output of said gating means and scaling the decoded output to a selected percentage of the actual occupancy of said roadway location,

an output register connected to said accumulator means,

8. In a system for providing a digital signal indicating the degree of occupancy by vehicles of a portion of a roadway over a predetermined sampling period,

means for generating a gating signal having a time duration corresponding to the presence time of vehicles in said roadway portion,

means for generating a train of clock pulses defining said sampling period and a pulse signaling the end of said sampling period,

scaling counter means for decoding the output of said gating circuit means and scaling the decoded output to a selected percentage value,

an accumulator for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby,

readout means for receiving the count signal in said accumulator at the end of each sampling period,

said means for generating clock pulses providing a series of sequential control pulses on separate lines, and

commutator means for switching the pulse output of said scaling counter means to said accumulator for providing reset signals to said counter means and said accumulator in an ordered sequence in response to successive ones of said control pulses.

Claims

1. In a system for providing a digital signal indicating the degree of occupancy by vehicles of a portion of a roadway over a predetermined sampling period, means for generating a gating signal having a time duration corresponding to the presence time of vehicles in said roadway portion, means for generating a train of clock pulses defining said sampling period and a pulse signaling the end of said sampling period, gating circuit means receiving said gating signal and said clock pulses for gating a number of said clock pulses therethrough corresponding to the duration of said gating signal, scaling counter means for decoding the output of said gating circuit means and scaling the decoded output to a selected percentage value, said counter means including switch means for manually selecting an occupancy scaling factor as a percentage of true occupancy, said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator means to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero an accumulator for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, and readout means for receiving the count signal in said accumulator at the end of each sampling period.

3. The system of claim 2 and further including means connected to receive the selected output of said switch means for providing a signal for resetting said divider to zero in response to the selected output.

4. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway, detector means for providing a signal throughout any periods during which vehicles are present at said location, means for generating a train of clock pulses which define a sampling period, gating means for passing said clock pulses therethrough in response to said detector means signal, scaling couNter means for scaling the output of said gating means to a selected percentage of the actual occupancy of said roadway location, said scaling counter means comprising first and second dividers, first and second decoder means connected to each of said dividers for decoding the outputs thereof to decimal form, first and second switch means connected to said first and second decoder means, respectively, for selecting the outputs thereof representing percentages of full roadway occupancy, and means for generating a reset signal for said dividers when the count represented by the settings of said switch means is reached, accumulator means for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, and an output register connected to said accumulator means, said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator means to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero.

5. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway, detector means for providing a signal throughout any periods during which vehicles are present at said location, means for generating a train of clock pulses which define a sampling period, gating means for passing said clock pulses therethrough in response to said detector means signal, scaling counter means for decoding the output of said gating means and scaling the decoded output to a selected percentage of the actual occupancy of said roadway location, said scaling counter means including switch means for selecting one of a plurality of percentages of the actual occupancy to represent full occupancy, accumulator means for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, and an output register connected to said accumulator means, said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero.

6. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway, detector means for providing a signal throughout any periods during which vehicles are present at said location, means for generating a train of clock pulses which define a sampling period, gating means for passing said clock pulses therethrough in response to said detector means signal, scaling counter means for scaling the output of said gating means to a preselected percentage of the actual occupancy of said roadway location, said scaling counter means including a binary divider, decoder means for decoding the outputs of said divider to decimal form and selector switch means for selecting an output of said decoder to represent a percentage of true occupancy as occupancy, accumulator means for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby and, an output register connected to said accumulator means, said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator means to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero.

7. In a system for providing continuous successive measurements of the vehicle occupancy at a location on a roadway, detector means for providing a signal throughout any period during which vehicles are present at said location, means for generating a train of clock pulses which define a sampling period, said clock pulse generating means further providing a series of trains of pulses on separate control lines, pulses on each of said lines being utilized sequentially to implement a separate control function, gating means for passing said clock pulses therethrough in response to said detector means signal, scaling counter means for decoding the output of said gating means and scaling the decoded output to a selected percentage of the actual occupancy of said roadway location, accumulator means for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, and an output register connected to said accumulator means, said clock pulse generating means generating a pulse at the end of the sampling period for actuating said output register to shift the signal in said accumulator means to said output register and then subsequently resetting said accumulator means and said scaling counter means to zero.

8. In a system for providing a digital signal indicating the degree of occupancy by vehicles of a portion of a roadway over a predetermined sampling period, means for generating a gating signal having a time duration corresponding to the presence time of vehicles in said roadway portion, means for generating a train of clock pulses defining said sampling period and a pulse signaling the end of said sampling period, gating circuit means receiving said gating signal and said clock pulses for gating a number of said clock pulses therethrough corresponding to the duration of said gating signal, scaling counter means for decoding the output of said gating circuit means and scaling the decoded output to a selected percentage value, an accumulator for receiving the pulse output of said scaling counter means and providing a count signal in accordance with the number of pulses received thereby, readout means for receiving the count signal in said accumulator at the end of each sampling period, said means for generating clock pulses providing a series of sequential control pulses on separate lines, and commutator means for switching the pulse output of said scaling counter means to said accumulator for providing reset signals to said counter means and said accumulator in an ordered sequence in response to successive ones of said control pulses.