Roadway sensors and method of installing same

A linear roadway sensor in which a distributed weight member has a weight per unit length which is sufficient to maintain the sensor on the roadway and substantially immune to air effects generated by vehicular traffic on the roadway. A method of safely installing the sensor is to pivot one end at the edge of the roadway and then swing the sensor on an arc then allowing the weight to maintain the sensor on the roadway.

BACKGROUND OF THE INVENTION AND DISCLOSURE STATEMENT: 
Currently there are four major types of traffic or roadway sensors being 
employed to monitor vehicle traffic i.e., volume, speed, classification 
and weight-in-motion. The most common, the road tube, which generates an 
air pulse, is used for classification, volume and speed studies. The 
inductive loop is used for volume, speed and length classification 
studies. The capacitance mat is used for volume and weight-in-motion 
studies. Piezoelectric rod is used for volume, speed, classification and 
weight-in-motion studies. These sensors, and others, such as resistance 
strips, are used in conjunction with electronic traffic counters which 
establishes the monitoring parameters and stores results for generating 
traffic engineering reports. 
A paper entitled "A Review of Current Traffic Sensor Technology" by the 
inventor hereof sets out and details the general constructions, methods of 
installation and advantages and disadvantages of these various systems and 
is incorporated herein by reference. 
Roadway sensors which use the piezoelectric effect are known in the art as, 
for example, see Robert U.S. Pat. No. 4,383,239 wherein a piezoelectric 
sensor is isolated from roadway pressure waves by means of a system of 
roadway channel embedments. Surface mounting of switch plates or coaxial 
sensing cables to produce an electrical effect when subjected to pressure 
is disclosed in Myers U.S. Pat. No. 3,911,390. In the Myers patent, there 
is disclosed a multilane coaxial cable sensor in which individual sensor 
segments corresponding to lanes are connected to a recording unit. The 
traffic sensor is contained in a sealed envelope. A pair of spaced 
metallic plates are positioned in the envelope along the length thereof 
for nailing the sensor to the roadway. As an alternative, the sensor could 
be secured to the roadway by an adhesive material. Use of adhesive to 
secure roadway sensor switches to the pavement is also shown in Paver U.S. 
Pat. No. 2,067,336 wherein a rubber cement carried in a cloth tape secures 
a switch tube to the pavement. Adhesive tape has also been used for this 
purpose. The invention is applicable to all these various kind of roadway 
sensors where movement of the sensor caused by vehicle air turbulence can 
cause extraneous and/or ambiguous output signals. 
The object of the present invention is to provide an improved roadway 
sensor, and method of attachment to the pavement of a roadway, 
particularly a roadway sensor fitted or equiped with a linear weight 
roadway sensor which is sufficient to itself maintain the sensor on road, 
and more particularly, to a flat roadway sensor which is fitted with a 
distributed linear weight of sufficient weight per unit length to maintain 
the flat sensor on the roadway at selected roadway speeds. For a high 
speed roadway where heavy trucks and the like travel at 75 mph a 
relatively heavy distributed weight is required, greater than one pound 
per foot and for speeds where the air flow effects are lower, a lower 
distributed weight is used. 
A further object of the invention is to provide a roadway sensor, where if 
broken, (by being snagged by a dragging muffler, for example) is safer 
than prior art roadway sensors. A further object of the invention is to 
provide a safe method of installing roadway sensors. In a preferred 
embodiment of the invention, a roadway sensor is constructed of a thin 
flat piezo film strip having a system of sensing electrode patterns 
metallized on opposing surfaces thereof and signal conductors connected to 
the electrode patterns sandwiched or enveloped between two elastomeric 
strips with a flat linear weighting member embedded in or on one of the 
elastomeric strips so as to maintain the sensor on the roadway despite 
having loaded truck-trailer travel at high speeds generating a trailing 
air turbulence having the effect of sweeping the roadway. The weight 
member is uniformly distributed along the roadway portions of the sensor 
strip to maintain the sensor on the roadway and substantially immune to 
air effects generated by vehicular traffic on the roadway, a loaded 
truck-trailer traveling at high speeds, a flat malliable metal such as 
lead, strip having a weight greater than one pound per linear foot is 
required. For example, a lower speed and/or smaller lighter vehicles 
(which cause less air flow effects), a lower distributed weight can be 
used for example 1/2 pound per linear foot of sensor. 
The invention provides a low cost, rugged and roadway sensor which is 
compact, easy to install and can be safely installed in a few minutes by 
one person without stopping traffic. It has a low profile providing 
multilane output signals with one sensor. Moreover, it is portable and 
reuseable. It is capable of wide temperature range of operation and has 
reliable consistent output pulses. It can generate axle pulses and provide 
voltage signals with no external power supply being required. Moreover, if 
it is broken, it is safer than previous roadway sensors because the 
distributed weight in its preferred form holds the portions to the roadway 
so the sensor does not flap around with air currents caused by vehicles on 
the roadway. 
While the invention is applicable to all forms of road sensors fixed to a 
roadway surface, in a preferred embodiment, piezoelectric film such as 
PVDF referred to above, is provided with separate discrete electrodes in 
predetermined metallized patterns for each lane of the roadway. An 
insulating coating or film is applied to the film and electrodes and an 
conductive electrostatic shield is applied or formed over the insulating 
coating. In the preferred embodiment, this piezoelectric film is then 
laminated and sealed between two elastomeric or rubber strips to form a 
sensor envelope. In a specific embodiment, a high weight linear weighting 
strip, such as 13/4 inch wide, 1/8 inch thick lead is affixed to or 
incorporated into the sensor envelope or otherwise incorporated in the 
construction to maintain the sensor in contact with the roadway along the 
length thereof so that only compressive loading caused by vehicle wheels 
cause voltage signals to be generated in the electrodes on the 
piezoelectric film. 
Moreover, static electricity generated by movement of a body in air, for 
example, which can create false signals and/or ambiguous signals, can be 
discharged into conductive elements, which can constitute at least a part 
of the high weight linear weighting strip and serve as an electrostatic 
shield which is incorporated in the sensor. 
In one embodiment, the conductive electrostatic shield is a foil of 
mallable metal such as lead. 
As disclosed in my above-identified application, the manner of installation 
of the sensor to the roadway is critical to its operation. At high speeds, 
such as on interstate highways, vehicular traffic, heavy trucks, for 
example, can create air flow and negative pressure effects of sufficient 
force on the roadway sensor to lift and move it and create ambiguous 
signals. This form of error or ambigupis signal can be generated in other 
varieties of roadway sensors. The uniform adherence of the flat envelope 
to the roadway aids in avoiding stretching along the length of the 
piezoelectric film. In one preferred embodiment, a PVDF piezoelectric film 
strip with metallized electrode patterns and signal conductors connected 
thereto is laminated between two pieces of flat roadway grade rubber or 
plastic strips with a linear weight member in the lower rubber strip. For 
example, a 13/4 inch wide, 1/8 inch thick lead strip about 28 feet long 
weighs about 32 pounds. A thin piezoelectric film strip of the type 
disclosed in my above application for a dual lane roadway is preferred. 
For lower speed highways, a lower weight can be used. For example, for 35 
mph a lead strip 1/16 inch thick and 13/4 inch wide (greater than one-half 
pound per linear foot) could be used. Steel lead shot sand and liquids 
could also be used. 
Electrical connections to the metallizations can be made in a number of 
ways, but in the preferred embodiment, separate electrical connections are 
made to each lane metallization and discrete wires or conductors carry the 
signal voltages which are generated due to compression stressing of the 
piezoelectric film. These discrete wires or conductors can be fine 
multistrand insulated wires individually connected to each metallization 
or conductors printed on a common non-conductive, inert substrate which is 
discrete or non-piezoelectric with respect to the piezoelectric film. For 
single lane roadways, the piezoelectric film strip can be made wider and 
the signal conductor leads printed on the film with the metallization of 
the sensor electrodes. 
The pattern of electrodes for the piezoelectric film can be designed to 
detect the number of tires and axles for a given vehicle. A particularly 
useful application of the invention is in connection with intersection 
data capture systems in which multiple lane roadways meet at intersections 
wherein vehicles traversing the different lanes can turn in different 
directions at the intersection and it is desired to know the various 
turnings and vehicle traffic in the different roadways of the multilane 
highways. 
In the preferred embodiment, the piezoelectric film strip and its electrode 
metallizations have an insulative conformal coating thereon to prevent 
moisture or other material from adversely affecting operation. The 
electrostatic shield can be a conductive coating applied at least to the 
upper external surfaces of the conformed coating, and/or a separate or 
discrete conductive grid sealed in the envelope and/or as conductive 
material, such as carbon granules embedded in the rubber or plastic 
envelope elements. As noted above, in one embodiment the electrostatic 
shield is a strip of lead foil weight to cause an adherence of the sensor 
to the roadway when heavy vehicles, such as trucks, create trailing 
turbulences and air currents tending to lift and drag the sensor. The 
weight distributed along the roadway portion of the sensor prevents this 
and thus prevents stretching along the length (axial stretch) of the 
sensor material. In a further embodiment, the electrostatic shield is a 
conductive epoxy which eliminates voids and secures the upper outer 
roadway rubber layer of the outer protective envelope to the insulating 
conformal coating. Where the electrostatic shield is within the envelope 
it is electrically connected by a separate conductor to earth ground, as 
distinct from the electrical ground or return of the piezoelectric sensor 
elements. 
In a further embodiment, the piezoelectric film sensor is positioned over a 
flat lead strip and a latex layer is between the lead layer and the 
piezoelectric film. This layered assembly is enclosed in an envelope.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIGS. 1a and 1b, a very thin piezoelectric film or piezo 
film 10 is flexible with upper electrode array 11-1, 11-2, and lower 
electrode array 12-1, 12-2, which are metallized areas on the opposing 
surfaces 13, 14, respectively, of piezo film 10 and corresponds to the 
span of each roadway lane to be monitored. Piezo film 10 is a film ranging 
in thickness from a few micrometers upward, reference being made to the 
"KYNAR.TM." "Piezo Film Technical Manual" published (1987) by Pennwalt and 
identified above. In the accompanying drawings, the film thickness and 
metallizations thereon are greatly exaggerated to show physical 
construction. Typically, the film 10 can have a width of about one half to 
three inches, for example, and a length for spanning all of the lanes of 
the roadway with corresponding lane metallizations. 
Electrical connections are made to the electrode metallizations on the 
upper surfaces and by means of electrode Tabs 11T1, 11T2, which include 
conductive eyelets 15 and 16 for metallized electrode areas 11-1 and 11-2, 
and on the lower surfaces by conductive eyelets 17 and 18 for connecting 
metallization tabs 19 and 20 to insulated conductors 21 and 22, 
respectively. Eyelets 15 and 16 connect the upper electrodes to insulated 
conductors 23 and 24 respectively, and any compressive load in the 
direction C1 or C2 will produce a voltage signal S1 between conductors 21 
and 24 and a voltage signal S2 between conductors 22, 23. In the case of 
the more remote sensing electrode pair 11-2 and 12-2, a field effect 
device (not shown) may be connected to amplify the signals from that pair 
of metallizations. The entire assembly may be protected from moisture by 
an insulating coating 25. 
Vehicle electrical ignitions and other high intensity electrostatic fields 
can induce voltages in the piezoelectric film strip and to avoid this 
effect, an electrostatic shield 26 is applied over at least over the upper 
surface and, if desired, over the underside. This electrostatic shield is 
connected by a separate individual conductor 27 for connection to earth 
ground 28 so that any electrostatic fields which could tend to induce 
noise in the metallization electrodes are shielded and grounded separately 
by the electrostatic shield. The electrostatic shield is shielded from the 
electrodes and conductors by the conformal moisture-proof insulating 
coating 25. In one embodiment shown in FIG. 4 of the invention, the 
electrostatic shield 26' is a heavy metal foil, such as lead, to add 
weight to the sensor to constitute a linear weight distributed along the 
sensor and either alone or in conjunction with a further weight strip 50 
the total distributed weight per unit length is sufficient to maintain the 
sensor on the roadway and make it substantially immune to lifting from the 
roadway due to air flow effects and turbulences of traveling at high 
speeds of, for example, 75 mph and avoids erroneous or ambiguous signals 
being generated. 
Even if the sensor strip, whether it be a piezoelectric film or any one of 
the prior art sensors referred to earlier herein (inductive, 
precumulative, capacitance, resistance, etc.) is snagged or broken by 
vehicular traffic it will still hug the road and not be as dangerous to 
moving traffic and pedestrians as a roadway sensor not equiped with this 
invention. 
As shown in FIG. 1b, the piezo film strip 10' is made wide enough so that 
the sensing electrodes E1, E2 . . . EN may be provided with integral 
metallization conductors on both the upper and lower surfaces 13', 14' of 
the piezo film strip and conveyed to one lateral edge 30 where 
metallization pads 31, 32, 33, 34, 35, and 36 are formed for securement by 
means of conductive eyelets to conductors leading to a recording device or 
a counter. Alternatively, a stiffener or rigid edge connector member EC 
may be secured to the end 30 with the metallization formed therein so that 
the end of the strip may be plugged into a conventional strip connector 
(not shown) for leading to the counter. 
Referring now to FIG. 2 which is a cross-sectional isometric view of a 
roadway sensor incorporating the invention, the piezoelectric film strip 
and electrode with metallized electrode and conductors 40, of the type 
shown in FIG. 1a or 1b is encased or enclosed in an elastomeric or rubber 
molded hermetic enclosure 41. Enclosure 41 includes a lower rubber portion 
42 which has embedded therein a flat, distributed weight metal or member 
43 which runs the complete length of the sensor and thereby provides a 
uniformly distributed linear weight for maintaining the sensor on the 
roadway. In this embodiment, the upper strip 44 of the molded rubber 
enclosure 41 is curved or shaped such that the vehicle's air stream is 
used in a positive way to minimize the movement of the sensor in the 
longitudinal direction and further prevent stretch in the piezo film 10, 
10', etc. This embodiment has a height of about 1/4 inch, about half of 
which is constituted by the thickness of the weight member 43. 
The top plan view of FIG. 3 shows the electrical connection of the 
conductors connected to the electrodes to a coupling unit which includes a 
strain relief member. In this view, each of the conductors carrying signal 
currents is coupled via a shielded wire 45S to an electrical connector 50. 
A heat shrinkable tubular member HS is shrunk and secured by means of an 
epoxy adhesive EA to the external surfaces of the envelope, the heat 
shrinking tubing conforming to the shape of the envelope and in 
conjunction with the epoxy, forming a rugged water-tight connection. Other 
forms of seal/securement may be used. The area indicated by the numeral 45 
may be filled with a flexible epoxy to serve as a strain relief. Shielded 
wires 45S couple the signals to pins 49 of the connector. The outer tube 
of the connector has a threaded coupling 46 so that the female connector 
portion 48 mates with the male projection pins 49 (in connector 46). A 
corresponding strain relief portion 50 is provided on the male connector 
element 44 and leads to the recorder 51. The recorder 51 may be of the 
type shown in my U.S. Pat. No. 4,258,430. 
FIG. 4 is a sectional isometric view showing an outer molded enclosure 41' 
in which the flat piezoelectric sensor assembly SA such as shown in FIGS. 
1a and 1b, incorporates a first lead foil weight member 26', which is thin 
enough to transmit the vehicle wheel loadings to the piezo strip, and 
which is adapted to serve as the electrostatic shield for the sensor 
assembly SA, and a heavier lower lead metal layer 50. These two lead 
layers constitute a linear weight distributed along the sensor such that 
the total distributed weight per unit length is sufficient to maintain the 
sensor on the roadway and make it substantially immune to lifting from the 
roadway due to air flow effects caused by vehicular traffic on the 
roadway. With the flat configuration illustrated in FIG. 4, the surface 
roadway air currents are insufficient to cause a lifting or movement due 
to these effects of the sensor and hence reduces or eliminates any 
erroneous or ambiguous signals. Should the roadway sensor be broken, it 
still lay safely on the roadway and does not dangerously flap and fly 
around as vehicular traffic moves by. 
In the arrangement shown in FIG. 5, the piezo film strip assembly 10" has a 
relatively hard under-surface constituted by the lead metal layer 56 
therebeneath it so that the signals induced by the loading or weight of 
vehicles traveling thereover are diminished slightly. 
So that the "KYNAR.TM." can stretch locally due to compression loading, a 
latex layer 55 positioned beneath the piezoelectric film strip causes the 
signals to be greatly enhanced and this is believed to be due to the local 
stretching of the piezoelectric film strip due to the compression loading 
of vehicles traversing thereover. When added, the signal-to-noise ratio 
increases greatly. Thus, the envelope 41' contains as an upper layer the 
piezoelectric film strip 10" as illustrated in FIG. 16b with a 
electrostatic screen thereover and a latex layer 55 beneath the 
piezoelectric sensor strip 10". The lead layer 56 provides the distributed 
weight according to the present invention. In the embodiment shown in FIG. 
5, for a two-lane roadway, the lead strip is approximately 1/8 inch thick, 
13/4 inches wide and approximately 28 feet long and has a weight of 
approximately 32 pounds. This provides a weight per unit per foot of over 
one pound. For roadways where it is known that the traffic speeds will be 
substantially less, less distributed weight can be employed. 
In the embodiment shown in FIG. 6, the envelope 41'" encases a 
piezoelectric sensor strip assembly 10'" with the electrostatic shield 
thereon as illustrated in FIG. 1b, and a lead strip 56' which has been 
secured to the lower face LF of envelope 41'" by a double-faced adhesive 
layer 57. Double-faced adhesive layer 57 is similar to the double-faced 
adhesive layer 42 shown in FIG. 2 and described in greater detail in my 
above-identified application. Video observations thereof confirm that 
there is no movement and electrical signals are more faithful and less 
ambiguous to the observed traffic. 
Referring now to FIGS. 7 and 8, FIG. 7 discloses a sensor unit in which the 
envelope 41' encases a sensor strip assembly 10' similar to as described 
in connection with FIG. 6. In this case, steel or lead shot 60 is encased 
in a separate envelope 61 which may be formed as a part of or secured to 
the lower face LF of envelope 41' by a double-Faced adhesive layer 57'. 
The steel or lead shot can be sand, or any heavy fluent material and 
including liquid such as water having the prescribed weight 
characteristics. However, the key requirement is that the weight have the 
characteristic of being sufficient per unit length without increasing the 
overall height of the strip and reducing its flatness. In a preferred 
embodiment, the roadway strip is less than 3/8 inch high and, in a typical 
embodiment, is approximately 1/4 inch thick, or from the surface engaging 
the roadway to the top surface thereof. 
In FIG. 8, the weight is in the form of steel or lead shot which has been 
embodied in the lower elastomeric layer 62. In this case rupturing of the 
weight envelope may release the shot, sand, or liquid, which is still 
softer that conventional or prior art construction since the envelope is 
light and flexible. 
As shown in FIG. 10, a trailer truck TT has four-wheel axles and, as 
illustrated in the waveform trace of the output of the sensor, each axle 
produces a pulse. It should be noted that the higher the weight on the 
wheel and hence the sensor, the larger the pulse and, the higher the 
speed, more energy is transferred to the sensor to create a larger pulse. 
Thus, as indicated in FIG. 10, the front wheels of the tractor itself 
produces relatively smaller pulses than the rear wheels of a loaded 
trailer which produces substantially larger output pulses. This 
information can be used by the computer to analyze the vehicular traffic 
on the roadway. Cars, for example, will have substantially smaller pulses, 
and the unit can even discriminate cars with front wheel drive as opposed 
to cars with rear wheel drive. 
METHOD OF INSTALLING 
The novel method of installing the sensor, according to the invention, on 
the roadway is illustrated in FIGS. 9a and 9b. This provides a method of 
safely and quickly installing this linear roadway sensor LRS on a roadway. 
A pivot pad PP is attached to one end of the linear roadway sensor LRS 
with a pivot P secured to the pivot pad PP which is secured to the 
roadway. Pivot pad PP is constituted by a base B which may be nailed to 
the edge of the road, and a pivot P secured to one end of the envelope of 
sensor LRS. The pivot secured to one end of the linear roadway sensor LRS 
is freely pivotted thereon and the opposite end OE is grabbed by the 
installer I. Installer I looks in the direction of travel of oncoming 
vehicles on the roadway lanes 1 and 2 and waits for a clearing and when a 
clearing appears, the installer I runs on an arc holding the end OE of 
linear roadway sensor LRS and swings it on an arc across the roadway to 
where it is substantially orthogonal to lanes 1 and 2. The installer I 
simply releases the end OE and allows the linearly distributed weight to 
cause the sensor to maintain direct contact with the roadway. The roadway 
sensor LRS will remain stationary because of the weighting and roadway 
currents and air flow effects, positive and/or negative, do not affect the 
position of the sensor on the roadway. However, to avoid theft and the 
like problems, it is desirable to secure the end OE by other standard 
securement means to the roadway such as a clamp or the like (not shown) by 
the installer I, who, as shown in FIG. 9b is kneeling by the side of the 
roadway waiting for a clearance in vehicle traffic to secure the end OE to 
the roadway. 
In addition, the envelope may be secured to the roadway by means of a 
double-faced adhesive tape as disclosed in my above-identified 
application. This arrangement can be utilized where it is desired to 
provide quick installation of the roadway sensor on non-porous roadways 
and is adapted for reuse. In this case, an example of a double-faced 
adhesive tape useful with this invention is the 3M Company NPE2546 
double-faced adhesive tape. This tape contains a nylon scrim which has a 
loose weave or mesh with approximately 1/8" between interstices or 
intersections to thereby permit the adhesive to be on both sides of the 
scrim to be generally integral or one. 
While the preferred embodiments of the invention have been described, it is 
to be understood that the disclosure is for the purpose of illustration 
and to enable those skilled in the art to practice the invention, and it 
is intended that other embodiments and modifications of the invention can 
be made without departing from the spirit and scope of the invention as 
set forth in the appended claims.