US3609678A

US3609678A - Magnetized means for providing control information to moving vehicles

Info

Publication number: US3609678A
Application number: US819836A
Authority: US
Inventors: Richard E Fayling
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1969-04-28
Filing date: 1969-04-28
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28

Abstract

Magnet installations on roadways and methods for providing control information to vehicles traveling on the roadways. The magnets are polymer-based magnets, which comprise a tough organic polymeric matrix and particles of magnetic material uniformly distributed through the matrix. The magnets are often installed in the form of a sheet or tape in a channel formed in the roadway surface, and are arranged in geometries or magnetized in patterns to develop information-providing signals in magnetic-flux-sensors in vehicles traveling over the magnets.

Description

United States Patent inventor Richard E. Fayling White Bear Lake, Minn.

Appi. No. 819,836

Filed Apr. 28, 1969 Patented Sept. 28, 1971 Assignee Minnesota Mining and Manufacturing Company St. Paul, Minn.

MAGNETIZED MEANS FOR PROVIDING CONTROL INFORMATION TO MOVING VEHICLES 15 Claims, 7 Drawing Figs.

U.S. CI

Int. Cl

Field of Search 340/32, 94/l.5, 180/98 G08g1/09, EOlf 11/00 340/32; 94/ 1.5

[56] References Cited UNITED STATES PATENTS 3,493,923 2/1970 Stevens et al. 340/32 3,179,918 4/1965 Hoeppel 340/32 Primary Examiner-William C. Cooper Att0rneyi(inney, Alexander, Sell, Steidt & Delahunt ABSTRACT: Magnet installations on roadways and methods for providing control infonnation to vehicles traveling on the roadways. The magnets are polymer-based magnets, which comprise a tough organic polymeric matrix and particles of magnetic material uniformly distributed through the matrix. The magnets are often installed in the form of a sheet or tape in a channel formed in the roadway surface, and are arranged in geometries or magnetized in patterns to develop information-providing signals in magnetic-flux-sensors in vehicles traveling over the magnets.

MAGNETIZED MEANS FOR PROVIDING CONTROL INFORMATION TO MOVING VEHICLES BACKGROUND OF THE INVENTION It has been suggested in the past that control information be supplied to automobiles traveling on a roadway with magnets carried on or embedded in the roadway. For example, in Ferrill, US. Pat. No. 2,493,755, it was suggested to embed permanent .bar magnets over the length of a roadway to form a signal track of magnetic fields that could be used to guide and control the speed of vehicles traveling on the roadway. In five patents of Adler, U.S. Pat. Nos. l,803,288-l,803,292, it was also suggested to embed permanent bar magnets in the roadway, with the magnets-actuating mechanism in autos traveling over them either to automatically reduce the speed of the auto at points of danger ('288-29l) or to warn its driver of changes in the roadway ahead ('292).

Insofar as is known, none of these previous systems has ever been commercially practiced with success. One principal reason for this lack of successful practice is that it would be highly expensive and difiicult to install the systems of magnets called for in the patents. Each of the patents teaches embedding rows of individual bar magnets beneath the surface of roadways, and, as noted, Ferrill teaches a sequence of closely spaced rows of magnets over the whole length of the roadways. The substantial labor required to set these individual magnets in place before the pouring of new cement roadways would add greatly to the cost of the roadways, and the installation of individual magnets in existing roadways-requiring drilling rather extensive cavities in the roadways, inserting the magnets, and then covering them-would be even more expensive. Thus, though the use of magnets on roadways is a promising method for providing control information to vehicles travelling on the roadwaysoperating, for example, without electric power to energize the system, the cost and difficulty in installing the previously suggested systems has contributed significantly to the lack of use of such a method.

SUMMARY OF THE INVENTION The present invention makes installation of magnets on roadways much less expensive and much more convenient than was the case for installation of the earlier suggested systems. This improvement is accomplished through use of a magnet material that is uniquely adapted for installation on a roadway, namely a polymer-based magnet material that is readily formed into a wide variety of shapes. In general, this polymer-based magnet material comprises a tough organic polymeric matrix and particles of a magnetic material such as barium ferrite uniformly distributed throughout the matrix. A preferred polymer-based magnet material producing desirable high magnetic forces is described in several US. patents of Blume, including U.S. Pat. Nos. 2,999,275 and 3,359,152. As taught in those patents, substantially domain-size anisotropic magnetic particles are oriented during the process of manufacture, placing their preferred magnetic axes in substantially parallel alignment so that the magnet material is itself anisotropic. When subjected to a magnetizing force, this preferred magnet material becomes a permanent magnet of high magnetic power; for example, a cube of one commercial variety, one-fourth inch on a side, produces a field of 800 gauss at the surface of the cube.

The wide variety of shapes and forms into which polymerbased magnet material can be preformed permits it to be conveniently handled and conveniently installed on roadways. For example, continuous lengths of narrow sheets or tapes can be used to provide the whole magnetic field across one or more lanes of a roadway. These sheets or tapes may be installed edgewise in a narrow channel or flat in a more shallow channel conveniently cut in the pavement with an abrasive tool. In one preferred system of the invention, polymer-based magnet material in tape form is unwound from a roll on one moving truck and installed in achannel or channels cut by abrasive toolscarried on one or more preceding trucks.

A further important advantage of the present invention is the high resistance to fracture exhibited by polymer-based magnet materials, especially in preferred, somewhat resilient and elastic forms. The stresses that are caused within pavement by daily and seasonal temperature changes or other shifting of the pavement will not degrade polymer-based magnets of the present invention, and such magnets will last at least for the life of the pavement. Another important advantage of the present invention is that the described ploymerbased magnets are much less expensive than the previously suggested permanent bar magnets. For example, ceramic or Alnico magnets generally cost more than twice as much as commercial varieties of polymer-based magnet material used in this invention.

The invention has application to control a wide variety of types of traffic on a wide variety of roadways; for purposes of this specification, the term roadway includes all land surfaces on which vehicles travel, including streets and highways,

driveways, parking lots, airport runways, corridors or open 7 v floors within buildings, and the like. Taken all together, the advantages of the novel installations of the present invention on such roadways take the art a significant step toward commercially practical use of magnets to provide control information to vehicles traveling on the roadways. Through operation of travel-controlling apparatus within the vehiclessuch as visual or audible devices presenting infonnation to drivers or such as mechanisms automatically operating the vehiclesapplication of the invention will make traffic on roadways more convenient and safe.

In the drawings,

FIGS. 1, 3, 4, and 5 are schematic perspectives of roadways of this invention;

FIG. 2 is a section through the installation illustrated in FIG. 1, taken along the lines 22 in FIG. 1;

FIG. 6 is a schematic wiring diagram of a circuit including the magnetic-flux-sensor and associated mechanism in a vehicle adapted to receive control information from an exemplary magnet installation of the invention;

FIG. 7 is a schematic elevation of a roadway and vehicle of the invention.

DETAILED DESCRIPTION As previously indicated, magnets useful in the invention are prepared from tough organic polymers that enable the magnet to resist fracture under the stresses that normally occur within roadways. Elastomers and other polymers that make the magnet somewhat resilient and flexible are preferred, and elastomers such as nitrile and silicone rubbers are especially preferred because of their excellent resistance to oils and other highway environmental conditions. Other polymers, such as polyvinyl chloride, especially such polymers plasticized or otherwise modified so as to exhibit elastomeric properties, can also be used.

The particles are generally dispersed in the polymeric matrix at a high loading; for purposes of this invention, the particles generally constitute at least 50 volume-percent of the magnet material, while it is difficult to include particles in an amount constituting more than about volume-percent of the material. To obtain the highest magnetic forces, the particles should be substantially domain-size, anisotropic particles, and there should be substantially parallel alignment of preferred magnetic axes of a sufficient number of the particles so as to make the magnet material itself anisotropic. The mechanical processes described in the previously mentioned Blume patents for working the particle-loaded matrix material gave a preferred high degree of orientation. Ferrites, especially barium ferrite but also lead and strontium ferrites, generally ina roughly platelike form'having preferred magnetic axes perpendicular to the general planes of the plates, are preferred as the particulate materials, but other materials having permanent magnetic properties, such as iron oxide particles or such as particles of manganese-bismuth or iron protected against oxidation, can also be used.

As previously mentioned, polymer-based magnets can be formed in a wide variety of shapes. Often in the present invention, they are made in sheet form, and most often as narrow sheets or tapes that are either inserted edgewise in a narrow channel or slot or laid flat in a more shallow channel cut in the roadway. Polymer-based magnets are also used in the form of cylinders, blocks, or a variety of special shapes designed to provide visual information to drivers as well as to provide configured magnetic fields that induce a characteristic electric signal in a flux-sensor passed through the field.

The magnets, are generally installed in a channel so that their top surface is somewhat below the top surface of the roadway, and then are generally adhered into the channel with a composition that seals the opening formed in the roadway and often covers the top surface of the magnet; this adhesive or potting composition preferably dries or cures to a tough, somewhat flexible and resilient form. An edgewise installation of a sheet or tape in a channel is preferred for the added durability it possesses. In such an edgewise installation, the sheet or tape is more fully restrained in the roadway whereby traffic or stresses within the pavement will not readily loosen or displace it, and the sheet or tape is less susceptible to wear by traffic or to removal by highway maintenance equipment such as snowplow blades or power sweepers; in addition, an edgewise application is preferred because it permits forming the channel with a rapid-cutting abrasive saw. As previously indicated, the polymer-based magnet material is itself extremely durable, and installations of the invention will be substantially maintenance-free and permanently useful for the life of the roadway.

Magnets of the invention may also be embedded within the pavement of the roadway instead of in an open channel. Or on other roadways where there is not a great deal of fast-moving traffic or where installation of the magnet is temporary, the magnet is simply adhered to the top of the roadway; such installations occur on roadways within factories, for example, on which small trucks, powered carts, and the like are guided. Magnets of the invention are especially adapted to surface installations, since they bear traffic well and are easily installed; thin sheets or tapes coated on one surface with pressure-sensitive adhesive, for example, are conveniently laid out and adhered to the roadway surface.

Magnets are generally installed according to this invention centrally within the lane or lanes of travel that are to be controlled. However, the magnets may also be installed at the side of or adjacent the lane of travel, whereupon magnetic-fluxsensors are mounted near or extend from the side of vehicles being controlled. For convenience in the claims of this specification, any magnet that provides a field in position to be traversed by a magnetic-flux-sensor mounted on a vehicle traveling within a lane of a roadway is regarded as being in that lane.

Some of the variety of useful installations of polymer-based magnets on roadways of this invention are illustrated in the drawings. FIGS. 1, 3, and 4 schematically show installations that are useful in combination with apparatus in a vehicle to warn a driver when he drives in the wrong direction. In FIG. I a polymer-based sheet magnet is inserted edgewise in a channel that is transverse to the direction of travel on a roadway ll. Anisotropic particles in the sheet magnet 10 are oriented so that their preferred magnetic axes are parallel to the surface of the roadway, with the magnet exhibiting a north pole on one of its large-area faces and a south pole on the opposite face. The installation of FIG. 1 is shown in enlarged cross section in FIG. 2. As shown, the magnet 10 is placed within a channel 12 in the pavement and then sealed into the slot with a potting compound 13.

In FIG. 3 a sheet magnet 15 of this invention is laid flat in a shallow channel that is transverse to the direction of travel in a roadway l6. Anisotropic particles in the sheet magnet 15 are oriented so that their preferred magnetic axes are parallel to the surface of the roadway, with a north pole at one edge of the sheet and a south pole at the opposite edge. In FIG. 4, a rather large triangular sheet 17 of magnet material is laid flat in a recess cut in a roadway 18, with anisotropic particles in the sheet oriented so that their preferred magnetic axes are perpendicular to the roadway.

For the wrong-way warning installations illustrated in FIGS. 1 and 3, the sign of the signal initially generated in a suitable flux-sensor mounted on a vehicle will be different for each direction of travel of the vehicle over the installations. The flux-sensor is connected to a sensing electrical circuit that is capable of detecting the signal associated with the wrong direction of travel. When the wrong-way signal is detected, a warning buzzer, horn or the like within the vehicle is actuated, or the automobile engine stopped.

An illustrative sensing circuit useful with either of the installations shown in FIGS. 1 or 3 is illustrated in FIG. 6. This illustrative circuit is supplied from a l2-volt battery in the vehicle through a voltage-dividing

network comprising resistors

20, 21, 22, and 23. The circuit includes the coil 24 of the flux-sensor in the vehicle, two

operational amplifiers

25 and 26, and an RC circuit branch 27. The amplifiers and RC circuit branch in combination amplify and integrate any signal pulse generated in the coil 24. The amplified and integrated signal pulse travels to a gate switch 29, such as a programmable unijunction transistor, silicon-controlled rectifier, gas discharge lamp, and the like which is biased so as to be triggered only by a pulse of one sign, for example, a negative pulse. When the pulse of appropriate sign triggers the gate switch 29, a current flows through an alarm device 30 to actuate the alarm device. The alarm device continues to operate until a reset switch 31 is opened, whereupon the gate switch 29 closes.

FIG. 5 illustrates an installation of a polymer-based magnet on a roadway useful to control the speed and course of vehicles traveling on the roadway. In this installation, a polymerbased magnet 32 in continuous tape form is inserted edgewise in a narrow channel running the length of the roadway 33. The tape is magnetized in a segmental pattern, with adjacent segments 32a, 32b, etc. (which may be regarded as a sequence of individual magnets) being of opposite polarity. Anisotropic particles in the tape are oriented so that their preferred magnetic axes are parallel to the surface of the roadway and transverse to the length of the roadway; thus the segment 32a exhibits a north pole on the large-area side facing out of the drawing in FIG. 5, while the segment 32b exhibits a south pole on that side. The tape magnet 32 may also be laid flat in a recess in the roadway, and while such a repositioning of the tape will change the direction of the field above the roadway and require use of a difierently oriented flux-sensor, the magnitude of the field will remain about the same. In another variation of the invention, the speed and course of vehicles traveling on a roadway are controlled with an essentially continuous path of magnetic fields formed by separate segments of sheeting spaced along the length of the roadway.

In general, for installations of the described magnetic-field paths useful to provide control of the speed and course of vehicles traveling on a roadway, segments of the same polarity are spaced at least as far apart as the distance between the flux-sensor and the roadway to permit adequate resolution of the induced signal pulses. But segments of the same polarity should on the average be spaced not more than about inches apart and preferably on the average not more than about 20 inches apart, so that the signal induced in the fluxsensor, which increases with the rate of traversal of the fields, will have adequate strength and so that the number of signals received in the flux-sensor per unit of time will be sufficient to provide a close control of speed and course. The most standard height for a flux sensor will be 10 inches, but it may be mounted on a movable support on the car so as to be lowered close to the surface of a smooth-surfaced roadway. In general, segments of the same polarity will be spaced between about 3 and 20 inches apart.

Adequate electric signals will be generated in flux-sensors on vehicles traveling on roadways of this invention, if the magnetic fields provided have an intensity at the surface of the roadways of at least 2 gauss, preferably at least gauss. More flexibility is possible in the choice and location of flux-sensors on vehicles, and an ultimate reliability irrespective of road conditions, such as packed snow which raises vehicles away from a roadway, is giventhe system if the field intensity at the surface of the roadway is 100 gauss or more. The latter field can readily be provided with rather small preferred polymerbased magnets, but larger magnets are generally used to provide an extensive field that won't be missed by vehicles traveling on the roadway. For example, in the wrong-way warning installations described above, sheets or tapes of polymerbased magnets preferably extend across substantially the whole lane or lanes being controlled. If the traffic must travel over the central part of a lane, the magnets installed may be smaller, but generally they are at least 24 inches long; they are also generally at least 1 inch wide. in the case of installations of a sequence of separate, spaced magnets to control speed and course, the individual magnets are generally at least 3 inches long and 1 inch wide.

For ease of manufacture, for handling purposes, and to provide a strong field, sheets or tapes of the polymer-based magnets are generally at least 25 mils in thickness and more often at least 50 mils in thickness. Magnets to be installed edgewise within a pavement are generally at least 100 mils in thickness so as to have sufficient stiffness and handleability. Thinner polymer-based magnets can be adhered to metal plates or sheets, such as steel sheets, to increase the strength of the field and strengthen the magnet. I

The invention may be further illustrated by the following example of a wrong-way warning system using a roadway of this invention. A 3-inch-wide, 24-inch-long, %-inch-thick sheet of Plastiform brand magnet (having a nitrile rubber matrix loaded with about 65 volume-percent of barium ferrite particles and an energy product of about one megagauss-oersted and exhibiting a compressive yield strength of 3,750 pounds per square inch, 21 modulus of elasticity in compression of about 30,700 pounds per square inch, a Shore D hardness of 65, an ultimate tensile strength of 640 pounds per square inch, a modulus of elasticity in tension of 65,800 pounds per square inch, an ultimate elongation of 3.25 percent, and an ultimate shear strength of 1,560 pounds per square inch) was embedded edgewise in a transverse channel in an asphalt roadway in the manner illustrated in FIGS. 1 and 2. The channel had been formed in the roadway by an abrasive saw, and the magnet was sealed in the channel with a potting compound that comprised 50 weight-percent of a diglycidyl ether of bisphenol A having an epoxide-equivalent weight of 190 (Epon 828) and 50 weight-percent of the reaction product of a polyamine and a dimerized acid, the reaction product having an amine value of 345 and a viscosity at 75 C. of 8 poises (Versamid 125). The magnet exhibited a field of over 500 gauss at the surface of the roadway and a field of about 0.5 gauss 10 inches above the roadway.

An automobile was equipped with a flux-sensor in the form of a coil having about 4,000 rectangular turns (12.5 inches by 1.5 inches) of No. 49 gauge copper wire; the coil had a height of about 0.4 inch, and was arranged with its axis perpendicular to the surface of the roadway and it was spaced about 10 inches from the roadway. The coil was connected to an alarm through the circuit illustrated in FIG. 6 in which the operational amplifiers were DC amplifiers supplied by RCA as Model No. CA 3000, the programmable transistor was a D l3T2 transistor supplied by General Electric, the alarm was a Mallory SC628 Sonalert," the resistors 33 and 34 both had resistances of 10,000 ohms, the resistor 35 had a resistance of l0 megaohms, the capacitor 36 had a capacitance of 0.5 microfarad, the resistor 37 had a resistance of 1,000 ohms, and a potentiometer 38 used to adjust the voltage fed to the operational amplifier 25 had a resistance of 1,000 ohms. The

resistors

20, 21, 22, and 23 had resistances of 22, 5.6, 33, and 33 ohms respectively. When the auto was driven along the roadway in a first direction at various speeds ranging from 15 to 50 miles per hour, the alarm did not sound as the auto crossed the magnet; but when the auto was driven at the same speeds in the opposite direction along the roadway, the alarm sounded each time the auto crossed the magnet.

The magnet was installed in the roadway and tested in the general manner described in early August. Periodically during the following winter through late April, a vehicle having the apparatus described was driven over the installation. Each time, the alarm was silent for travel of the flux-sensor in the correct" direction and each time the alarm sounded for travel of the flux-sensor in the wrong direction. Though the installation was at St. Paul, Minn., where there was a heavy snowfall during the winter, requiring plowing of the roadway numerous times, there was no visible deterioration to the installation.

The last figure in the drawings, FIG. 7, shows a vehicle on a roadway ready to receive control information from a magnet installation of the invention. The vehicle 40 includes a magnetic-flux-sensor 41 electrically connected to travel-controlling apparatus 42. When the fiux-sensor 41 passes over the magnet installation 43, an electrical signal is developed that operates the travel-controlling apparatus 42 in the manner described above.

What we claim is:

l. A magnet installation on a roadway for providing control information to vehicles traveling on the roadway comprising at least one preformed polymer-based magnet that is installed in a lane of travel of the roadway and that comprises (a) a tough organic polymeric matrix that has a thickness of at least about 25 mils and (b) particles of magnetic material uniformly distributed through the matrix.

2. A magnet installation as in claim 1 in which the organic polymeric matrix exhibits elastomeric properties.

3. A magnet installation as in claim 1 in which the particles are roughly platelike substantially domain-size particles of ferrites selected from barium, strontium, and lead ferrites that have preferred magnetic axes generally perpendicular to the planes of the plates and are oriented to make the magnet anisotropic.

4. A magnet installation as in claim 1 in which the magnet is installed in a channel formed in the roadway.

5. A magnet installation as in claim 4 in which the magnet is in sheet form and is installed edgewise in the channel.

6. A magnet installation as in claim 5 in which the preferred magnetic axes of the particles in the magnet are aligned parallel to the surface of the roadway.

7. A magnet installation as in claim 5 in which the magnet is at least 1 inch wide, 3 inches long, and mils thick.

8. A magnet installation as in claim 4 in which the magnet is in sheet form, is installed flat in the channel, and is at least 1 inch wide, and 3 inches long.

9. A magnet installation as in claim 1 in which a sequence of magnets is installed in the lane of travel in a path extending parallel to the direction of travel on the roadway, with adjacent magnets being of opposite polarity and magnets of the same polarity being spaced at least as far apart as a predetermined distance that flux-sensors on vehicles using the roadway -are spaced above the roadway but not more than about 100 inches apart.

10. A magnet installation as in claim 1 in which the roadway is a one-way roadway, the magnet extends transverse to the direction of travel on the roadway, and the magnet exhibits north and south poles spaced along the length of the roadway.

11. A magnet installation as in claim 10 in which the magnet is a sheet at least 24 inches long, 1 inch wide and 100 mils thick and is installed edgewise in a channel in the roadway.

12. A magnet installation as in claim 1 in which the magnet is shaped in a configuration that is asymmetrical with respect to a line transverse to the length of the roadway.

A. a roadway having a magnet installation for providing control information to an automobile traveling on the roadway comprising at lease one preformed polymerbased magnet that is installed in a lane of travel of the roadway and that comprises (a) a tough organic polymerie matrix that has a thickness of at least about 25 mils and (b) particles of magnetic material uniformly distributed through the matrix; and

B. a vehicle equipped with (a) a magnetic-flux-sensor adapted to develop an electric signal by travel through the magnetic field produced above said highway and (b) travel-controlling apparatus within the vehicle actuated by said electric signal.

14. A magnet 'mstallation of claim 1 in which the preferred magnetic axes of the particles in the magnet are aligned perpendicular to the surface of the roadway.

15. A magnet installation on a roadway for providing control information to vehicles traveling on the roadway comprising at least one preformed polymer-based magnet in narrow elongated sheet form installed in a channel formed in a lane of travel of the roadway and providing a field of at least gauss at the surface of the roadway, the magnet comprising (a) a tough organic polymeric matrix that has a thickness of at least about 25 mils and (b) a high loading of substantially domain-size particles of anisotropic magnetic material uniformly distributed through the matrix and oriented to make the magnet anisotropic, the particles being oriented so that their preferred magnetic axes are perpendicular to the length of the magnet.

Patent No. 3,609,678 Dated September 28, 1971 lnve t Richard E. Fayling It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 13, first line, should read --In combination,--

The patent includes two additional claims, reading as follows l6 A magnet installation as in claim 9 in which magnets of the same polarity are spaced between about 3 and 20 inches apart.

1?. A magnet installation on a roadway for providing control information to vehicles traveling on the roadway comprising at least one preformed polymer-based mag net in sheet form installed edgewise in a channel formed in a lane of travel of the roadway and providing a field of at least 100 gauss at the surface of the roadway, the magnet comprising a) a tough organic polymeric matrix that has a thickness of at least about 25 mils and b) a high loading of substantially domain-size particles of anisotropic magnetic material uniformly distributed through the matrix and oriented to make the magnet anisotropic On the cover sheet, in the heading, "15 Claims" should read 17 Claims Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents ORM PC4050 HO'GQ) USCOMM-DC 60376-P59 Q U 5, GCVERNMENT PP -T|NG OFFICE I969 U3G5-]J4

Claims

2. A magnet installation as in claim 1 in which the organic polymeric matrix exhibits elastomeric properties.
3. A magnet installation as in claim 1 in which the particles are roughly platelike substantially domain-size particles of ferrites selected from barium, strontium, and lead ferrites that have preferred magnetic axes generally perpendicular to the planes of the plates and are oriented to make the magnet anisotropic.
4. A magnet installation as in claim 1 in which the magnet is installed in a channel formed in the roadway.
5. A magnet installation as in claim 4 in which the magnet is in sheet form and is installed edgewise in the channel.
6. A magnet installation as in claim 5 in which the preferred magnetic axes of the particles in the magnet are aligned parallel to the surface of the roadway.
7. A magnet installation as in claim 5 in which the magnet is at least 1 inch wide, 3 inches long, and 100 mils thick.
8. A magnet installation as in claim 4 in which the magnet is in sheet form, is installed flat in the channel, and is at least 1 inch wide, and 3 inches long.
9. A magnet installation as in claim 1 in which a sequence of magnets is installed in the lane of travel in a path extending parallel to the direction of travel on the roadway, with adjacent magnets being of opposite polarity and magnets of the same polarity being spaced at least as far apart as a predetermined distance that flux-sensors on vehicles using the roadway are spaced above the roadway but not more than about 100 inches apart.
10. A magnet installation as in claim 1 in which the roadway is a one-way roadway, the magnet extends transverse to the direction of travel on the roadway, and the magnet exhibits north and south poles spaced along the length of the roadway.
11. A magnet installation as in claim 10 in which the magnet is a sheet at least 24 inches long, 1 inch wide and 100 mils thick and is installed edgewise in a channel in the roadway.
12. A magnet installation as in claim 1 in which the magnet is shaped in a configuration that is asymmetrical with respect to a line transverse to the length of the roadway.
13. In combination, A. a roadway having a magnet installation for providing control information to an automobile traveling on the roadway comprising at lease one preformed polymer-based magnet that is installed in a lane of travel of the roadway and that comprises (a) a tough organic polymeric matrix that has a thickness of at least about 25 mils and (b) particles of magnetic material uniformly distributed through the matrix; and B. a vehicle equipped with (a) a magnetic-flux-sensor adapted to develop an electric signal by travel through the magnetic field produced above said highway and (b) travel-controlling apparatus within the vehicle actuated by said electric signal.
14. A magnet installation of claim 1 in which the preferred magnetic axes of the particles in the magnet are aligned perpendicular to the surface of the roadway.
15. A magnet installation on a roadway for providing control information to vehicles traveling on the roadway comprising at least one preformed polymer-based magnet in narrow elongated sheet form installed in a channel formed in a lane of travel of the roadway and providing a field of at least 100 gauss at the surface of the roadway, the magnet comprising (a) a tough organic polymeric matrix that has a thickness of at least about 25 mils and (b) a high loading of substantially domain-size particles of anisotropic magnetic material uNiformly distributed through the matrix and oriented to make the magnet anisotropic, the particles being oriented so that their preferred magnetic axes are perpendicular to the length of the magnet.