US3911390A

US3911390A - Traffic sensor strip

Info

Publication number: US3911390A
Application number: US413538A
Authority: US
Inventors: Richard H Myers
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-11-07
Filing date: 1973-11-07
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07

Abstract

An elongated traffic sensor strip having a plurality of separate segments each appropriately spaced along the sensor to monitor traffic in separate lanes of a multi-lane roadway. A sealed envelope encloses segmented pressure-sensitive elements and a plurality of conductors connected to the individual elements. Metallic plates are positioned in the envelope along the length of the strip for attaching the strip to the surface of the roadway. In one embodiment, the elements have a pair of conductor plates normally held in spaced parallel relationship and movable to contact each other upon compression of the elements. In another embodiment, the elements have a coaxial cable which produces an electrical effect when subjected to pressure.

Description

mem -ant: 35 l States Patent i 1 T, j

Mym

I mmc SENSOR mm I76 sw mp Richardll. Myers, 170a Woods,

15:} m. cl. t;08(; 1/00 {58} Field of Search 340/38 R; 177/136 T561 p References Cited UNITED STATES PATEN'IS 7 1.83655 12/193: Dunford s. 340/38 R 7 2305.327 7/z939 Cooperr..- Mm 340/38 R 2.181318 1:939 Greentrce .M 340/38R 292mm 1/:960 340/32 R FOREIGN PATENTS OR APPLICATIONS 70,229 7/1952 ;Netherlands...l M... 340/38 R 1500120 9/[967 France 340/38 R 1221 Bled:

1 Arlington, Tex. 76010 Nov. 7, 1973 an Ap'pl. M0,: 413.538 1 {521 US. Cl. 340/38 R; 174/113 A 2.004.271? "969 France m 340/38 R Primary Examiner-Thomas B. Habecker Attorney, Agent, or Firm-Richards, Harris 8:

. Medlock 71" ABSTRACT An elongated traffic sensor strip having a plurality of separate segments each appropriately spaced along the sensor to monitor traffic in separate lanes of a multi-lane roadway. A sealed envelope encloses segmerited pressure-sensitive elements and a plurality of conductors connected to the individual elements. Me-

tallic plates are positioned in the envelope along the;

length of the strip for attaching the strip to the surface of the roadway. In one embodiment, the elements have a pair of conductor plates normally held in spaced parallel relationship and movable to contact each other upon compression of the elements. In art'- other embodiment, the elements have a coaxial cable which produces an electrical effect when subjected to pressure.

10 Chin's, '12 Drawing Figures 1 v .QRMQ

mmamum 12a kill 4.4. .7.

2 5% NM 4m 3 Sheet l0f2 us. Pat ent [0. 1,1915

p TRAFFIC'SENSORSI'RIP. BACKGROUND oFnramvENnoN.

The present invention relates. to traflic sensors for use in separately and simultaneously monitoring the traffic moving in a plurality of different lanes of a roadway In the design of roads, highways, bridges; and other structures and facilities',data oonceming trafiic speed and density; vehicle size,loading and type; and vehicle condition is used by traffic engineers. The complexity of the data required for complete evaluation and planfeet of a coaxial cable as it is comprwed by a vehicle ning of these structures at times requires the monitoring of many roadways simultaneously. including multi lane roadways. The volume and complexity of the data matic traffic recorders have been devised for recording data in a form which can ultimately be used with a computer in the design of these structures.

necemary to make a complete evaluation renders man- Y ual traffic counting impractical. Accordingly, auto- To provide the information for these automatic traflic recorders, sensors are placed across the roadway. These sensors must be able to monitor traffic in multilane roadways with complete lane isolation while sensing the variety of the data required. In addition, the

sensors should have a low profile so that they are not rows;

FIG. 3 is a sectional view similar to H6. 2 illustrating an alternate embodiment of the present invention;

FIG. 4 is a graphical illustration of the tire patch contact as a function of time; 7

FIG. 5 is a graphical illustration of the electrical efpassing thereover; y I

FIG. 6 is a graphical illustration of a differentiated output of a cablei FlGS. 7 through 9 illustrate plan views of other embodiments of :n improved traflic sensor element of th present invention; and a FIGS. 10 through 12 are sectional views of various I embodiments of the present invention.

oEscRn rroN or "me PREFERRED EMBODIMENTS Referring now to the Drawings, wherein like refer ence characters designate like or corresponding parts throughout the several views, the tralfic analyzer sysreadily visible by the motorists and have a gradual taporing profile to provide a smooth tire transition thereover. The sensors should be durable to resist wear and the possibility of damage from dirt or moisture. in addition, it is desirable that the sensors be provided with means for anchoring in'the roadway so that they will remain in position over a prolonged period of time.

Therefore, according to one embodiment of the prescnt invention, an improved trafiic sensor is provided having a pressure-sensitive element enclosed in a sealed envelope. The envelope is formed between a pair of polyethylene sheets attached at their edges. The v element is segmented along its length corresponding to the number of lanes of the roadway. A plurality of conductors are located in the envelope at the sides of the element. A pair of metallic strips are sealed in the envelope on the outsides ofthe-conductor to provide tabs for anchoring the sensor to the roadway.

It has also been discovered that when compressed, a

coaxial cable will produce an'electrical effect by generatinga iltage between the conductor and the-shield of g the cable. It is believed that the amplitude of the voltage is proportional to pressure on the cable and the frequency is a function of the speed and the tire patch length of the vehicle comprcsing the cable.

Therefore, according to another embodiment of the present invention, an improved sensor-is provided having a coaxial cable generating an electrical effect upon compression thereof. i

r The objects and advantages of the present invention tern 10 with the improved sensor of the present invention is illustrated in FlG.- l. Trafiic amlyaer system 10 is illustrated with a sensor strip 12 positioned transversely across a rnultidane roadway l6. Roadway 16 is divided into

lanes

16a, 16b, 16c and 16d. Strip 12 is connected by shielded cable 20 to an electrical assembly 21 for recording the electrical efi'ects generated by strip 12 as a vehicle passes over the strip. Assembly 21 is sclficontained and can be located a safe distance from roadwayl6 out of view of the motorists. Assembly 2! is provided with means for recording theelectrical effects generated by strip 12. I A control unit 22 may also be provided and selectively connected by cable 24 to initiate the operation of assembly 21 and provide identifying inputs to assembly 21 as desired. Unit 22 can then bedisconnected and y removed allowing assembly 21 to record the flow of r trafiic information desired. Strip :2 has-individual sensor segments 12a, 1%, 12

' and 12d spaced to correspond to

lanes

16d, 16b, 16c

and 16:1. The individual segments are independently connected to assembly 21 to record vehicle data for each particular lane. In FIG. 2, the details of construction of one embodiment.of strip 12 are illustrated. in this embodiment.

segment l2a is illustrated enclosed in a sealed envelope v25 formed by a pair of strips of

polyethylene material

26 and 28.

Strips

26 and 28 extend the le'hgth of strip I I2 and are sealed at their edges 30 and 32. Segment will be readily appreciated by those of ordinary skill in s the art as the same becomes better understood by referf can: to the following Detailed Description when coni a j sidered in connection with the accompanying Drawings in which: I v f y r BRIEF onscnn nonor'me DRAWINGS- 7 FIG. 1 illustrates-a plan view of an improved trafiic" i sensor element of the present invention shown sche-,

matically connected to a recorder in position on a four- 'lane roadw ayrj, "1 J 12a is constructed from a commcrcialiy available resil ient envelope 34 defining a chamber 36 in which are mounted a pair of parallel spaced conducting

plates

38 and 40.

Plates

38 and 40 are normally resiliently held in the position-illustrated in FIG. Zby a pair of cornpressible spacers 42 integrally moulded into the interior of envelope 34 to extend from the sides thereof.

Upon compression of envelope 34,

plates

38 and 40 will contact. Suitable electrical conductors are connected to

plates

38 and 40 and are connected through cable 2i!" to. amemhly 21. To assist in the compression of envelope 34 an extending portion-$4 protrudes from l 1 thulupper surface thereof.

Positioned on either side of segmcntlza six eon- E l 1 ductors 45 50. Conductors 45-50 can be appropriately 1 FIG. 2 is anenlarged section ofthe device taken on line 2-2 of FIG. I, looking in the direction of the ar- 3 connected to the plates of segments I212, 12tand 12d.

J More or less conductors can be provided :srequired by the number of lanes in a given roadway to be monitored. y

A pair of plates 52 are bonded between strips 26 and through plates 52 at spaced locations along the length of strip 12. l a

In addition to edges 30 and 32. an 1235 completely sealed at its ends. A connector may be provided in the 1 end of strip 12 adjacent to segment 12a to attach cable l 28 adjacent to sealed edges 30 and 32. To anchor strip I 12 to roadway l6, suitable fasteners 54 can be driven to the conductors for the pressure-sensitive elements of segments 12a, 12b, i2tand I211. Alternalively, cable 2.0 could be fixed to strip 12 and a connector provided at assembly 2i. p

Assembly 21 is provided with means for sensing and recording contact between the plates of segments 12a,

12b. 12c and 12d, caused by the passage of an automobile thereover.

An alternate embodiment of the invention illus tratcd in FIG. 3. This alternate embodiment 58 is iden-.

tical to strip r2 illustrated in no- 2 except that a coaxhas been found to P1} duce a distinct and identifiable signal upon passage of a vehicle thereover.

In the embodiment illustrated in FIG- 3, cable 60 is divided into a plurality of segments corresponding to the lanes to be monitored. These individual segments are connected through conductors in cable 20 to unit The operation of the coaxial cable when generating the electrical cheer '5 not completely understood. It is believed that the mirage in the conductor is created. ei-

ther through friction generated by shield element 66 i rubbing on the adiacent dielectric as cable 60 produces a static charge or by an effect similar to a piezoelectric 1 device caused by the molecular arrangement when the dielectric is extruded.

By using the cable as a variable current generator, recording electronics can be used with a low input impedance. These electronics can be what is generally known as a charge amplifier, which partially integrates the cable signal which is differentiated to some degree by the cable. This output of this amplifier can be used insystems to mcaure dynamic local road loading. in l addition, the output can be connected to a threshold detector to produce signals from only these vehicles which exceed a desired road loading. This system minimizes the effects of environmental factors such as temperature and moisture. 1

It may also be desirable to detect just the leading or trailing edge of the patch. This can be accomplished by differentiating the signal produced by the cable. An example of the resultant signal from this differentiation is illustrated in FIG. 6. The leading and trailing edges of y I the patch produce sharp indications on the graph.

In FIG. 7, a third embodiment is illustrated using coaxial cable as a transducer providing lane segregation.

On this embodiment two closely spaced cables 80 and 82 are placed acm a roadway 84. in this illustration,

roadway 84 has trafiic lanes 84:: and 8412. Cable extends completely across

lanes

84a and 84b while cable 82 extends only across lane 84a.

Cable 80 is connected to an AND gate 86 while cable 82 is connected to gate 86 and amplifier 88'. The output l'of amplifier 88 will represent the traffic in lane 84a while the output of AND gate 86 will represent the traf- Zl-as previously described with respect to strip 12.

l 7 Cable 60 has central conductor 62 which is surrounded by dielectric insulation 64. Shield element 66 surrounds insulation 63 and shield element 66 issurrounded by a second layer ofhigli wearresistant insula- 7 tion 68.

In use. central conductor 62 shield element 66 l are connected to unit 22 throdgh eahlelll. Ar! electri' cal effect in the form of voltage is generated betweenthe conductor and shield when avehicle passes over andc0mpressescable60. ln HO. 4, a time history of a tire patch presence on the cable is graphically illustrated. At the tire first touches the sensor. During period A (from I to and therefore, the greatest change in forces on the cable occur. During the .B" (I: to 1 the force a on the cable is relatively constant and is approximately the maximum acceleration of the tire mbber occurs fic lane 84b. y I 7 By designing the sensor in this manner the trafiic in more than two lanes can be separated and recorded. in addition, the lanes can be segregated by placing a small rigid tubular member around the cable in the lanes in which a signal is not desired. I I

7 in FIG. 8, another embodiment isillustrated using coaxial cable as a lransfilcer providing lane segregation.

in this embodirnan lanes 84:: and 84!; have three

cables

90, 91 and 92 extending completely thereacross.

Cables 90 and 91 intersect at a point between the lanes. I I

Cables 91 and 92 are positioned transverse to the trai fie flow. By differentiating the signal from the cables 1

l

90, 91 and 92 asdescribed above. lane segregation and speed can be determined. Vehicles in lane 84a would be indicated by signals in order from cables 99, .91 and 92. Vehicles in lane 84b would be indicated by signals in order from 9!,90 and 92. In both instances the time proportional to the pressure in the tire and the acceler ation of the rubber away from the road at the sensor." 1

in the C" (1,10 :4). the tire is leaning the sensor with complex dynamics occuring in the tire.

in no. 5, a graphicillustrafion ofthe voltage gem ated in an 80-foot length of cable is shown as plot 70. The ordinate of the graph is voltageand the abscissa is timcs'l'he amplitude A is believedto be proportional to vehicle speed and patch length; 1 g I the weight of the vehicle or exerted on theca--' ble. The period B is believed to be proportional to the lapse between cablesQl and 92 would be proportional r l to speed. r j a In FIG. 9, anembodimentusing cables 94, 95and 96 is shown whichprevents coincidence at the cable cross 1 overofeables 9439x195. ln thisembodiment, cable 94 I r l is protected by arigid metal tube 97 or the like to prea vent a coincident at the crossover point. By using the logic of the E6. 8. embodiment lane segregation and speed can be determined.

H I In FIG. 10, anembodirnent for irstalling'a cable 100 i on a road bed mlisshovm. in this embodiment tempo- 7 my mounting of cable 100 is accomplished by use of an adhesive tape 104. r

. in H6. 11, cable 100 is permanently attached by means of an adhesivecompound 106 which is shaped to cozcr cable 100 and adhere to roadway 102. A suitable adhesive compound 106 has been found to be Miracle Seal Mfg. by Revere Chemical Corp., 12407 Wootfiand Ave; Cleveland. Ohio 44120.

p In HG- 12, an additional embodiment is illustrated wherein the cable 100 is inserted into a groove 108 in the roadbed 102. This groove extends completely I across the lane to be monitored. A suitable adhesive compound 110 can be used to adhere the cable to the roadway.

7 Thus, it can be seen that the present invention prosicles a traffic sensor element which is portable and easy to install with lane isolatiomln addition, the profile of the sensor has a gradual buildup for smooth transition making the sensor practically invisible to the mowrists. The sensor is scaled to reduce the possibility of damage from dirt and moisture, and flanges are provided to easily attach the sensor to the road.

In addition, the strip 58 can provide an inexpensive element which functions even through the near lane is compressed. It is' believed that by use of strip 58,

. speeds weights, patch lengths and axle counting can be accomplished. In addition, the strip 58 can be utilized to sense compression by other than the passage of vehicles thereover. V V

Hating thus described the invention, it is to be understood, of course, that the present invention may be practiced otherwise than as described and thatnumerous modifications and alterations may be made therein without departing from the spirit and scope of the ini vcntion as set forth in the appended claims.

in the claims: v I. A trafiic sensor which comprises:

' a. an elongated element which produces an electrical effect when compressed;

b. a pair of insulating strips enveloping said element with faces of said strips confronting; c. a plurality of parallel insulated electricalconduc- [tors positioned between said strips and alongside said element, and v -d. a pair of rigid metallic strips bonded to said insulating strips at each edge thereof. 1 a 3 2.1he sensor of claim 1 in which said element comprises a pair of conductive plates normally spaced apart which make electrical contact when compressed.

3. The sensor of claim} wherein said clement comprises a coaxial cable having a central insulatedcondoctor, a shield around said insulator and a second in- 'sulator around said shield.

4. The sensor of claim 1 wherein said element is segmented along its length.

- 5. A traffic sensor which comprises:

a. an elongated element which produces an electrical 7 effect when compressed; v t b. an elongated insulating envelope housing said element centrally thereof;

c. a pair of rigid metallic strips of thickness substan i m tiaily less than the thickness of said element and bonded to the inner faces of opposite sides of said insulating envelope, and

d. a plurality of insulatedelectrica] conductors positioned between said strips and extending parallel L t5 alongside said element.

6. The sensor of claim 5 inwhich said strips hav holes therethrough at spaced points along the length for receiving hold down anchors.

7. The sensor of claim. 6 wherein said element comprises a compression frictionresponsive coaxial cable having a central insulated conductona shield around i said insulator and asecond insulator around said shield forming an elongated cylinder, bodies of filler material on opposite sides of said cable having sides which slope 25 from a thickness of said cable to a thickness of said strips.

8. A traffic sensor which comprises:

a. an elongated compression-friction responsive co- 7 axial cable which produces an electrical effect 39 when compressed,

bl a wide thin insulating body enveloping and intimately adhered to said cableforming a profile of gradual buildup for smooth transition of an auto- I mobile tire thereover, and i c. a pair of metallic members bonded to said insulating body at opposite sides of said cable for securing said body to a roadway. 9. A trafiic sensor which comprises: I

40 axial cable having a central conductor, an insulator surrounding said conductor, and a coaxial conductive shield clement intimately secured to and surrounding said insulator over its length wherein said cable produces an electrical signal when com- V pressed, and

1 b. a wide thin insulating body enveloping and adhera ing said cable to a vehicle path and forming a profile of gradual buildup for smooth transition of an I automobile tire 'thereover.

5n 10. The sensor of-claim 9- inwhich said body is ad- V hered to said path by adhesive material. g

fss

a. an elongated compression-friction responsive co-

Claims

1. A traffic sensor which comprises: a. an elongated element which produces an electrical effect when compressed; b. a pair of insulating strips enveloping said element with faces of said strips confronting; c. a plurality of parallel insulated electrical conductors positioned between said strips and alongside said element, and d. a pair of rigid metallic strips bonded to said insulating strips at each edge thereof.

2. The sensor of claim 1 in which said element comprises a pair of conductive plates normally spaced apart which make electrical contact when compressed.

3. The sensor of claim 1 wherein said element comprises a coaxial cable having a central insulated conductor, a shield around said insulator and a second insulator around said shield.

4. The sensor of claim 1 wherein said element is segmented along its length.

5. A traffic sensor which comprises: a. an elongated element which produces an electrical effect when compressed; b. an elongated insulating envelope housing said element centrally thereof; c. a pair of rigid metallic strips of thickness substantially less than the thickness of said element and bonded to the inner faces of opposite sides of said insulating envelope, and d. a plurality of insulated electrical conductors positioned between said strips and extending parallel alongside said element.

6. The sensor of claim 5 in which said strips have holes therethrough at spaced points along the length for receiving hold down anchors.

7. The sensor of claim 6 wherein said element comprises a compression friction responsive coaxial cable having a central insulated conductor, a shield around said insulator and a second insulator around said shield forming an elongated cylinder, bodies of filler material on opposite sides of said cable having sides which slope from a thickness of said cable to a thickness of said strips.

8. A traffic sensor which comprises: a. an elongated compression-friction responsive coaxial cable which produces an electrical effect when compressed, b. a wide thin insulating body envoloping and intimately adhered to said cable forming a profile of gradual buildup for smooth transition of an automobile tire thereover, and c. a pair of metallic members bonded to said insulating body at opposite sides of said cable for securing said body to a roadway.

9. A traffic sensor which comprises: a. an elongated compression-friction responsive coaxial cable having a central conductor, an insulator surrounding said conductor, and a coaxial conductive shield element intimately secured to and surrounding said insulator over its length wherein said cable produces an electrical signal when compressed, and b. a wide thin insulating body enveloping and adhering said cable to a vehicle path and forming a profile of gradual buildup for smooth transition of an automobile tire thereover.

10. The sensor of claim 9 in which said body is adhered to said path by adhesive material.