GB2300291A

GB2300291A - Traffic analyser system

Info

Publication number: GB2300291A
Application number: GB9511124A
Authority: GB
Inventors: John Keith Hall; Gideon Edmund Roberts; Christopher Paul Waghorn
Original assignee: POWER MAGNETICS AND ELECTRONIC
Current assignee: POWER MAGNETICS AND ELECTRONIC
Priority date: 1995-04-25
Filing date: 1995-06-01
Publication date: 1996-10-30
Also published as: GB9511124D0; GB2300292A; GB9511127D0; GB2300292B; GB9508720D0

Abstract

A traffic analyser systems (10) for detecting the presence, speed and/or kind of vehicle travelling a highway comprises a sensor means (13) comprising first (11) and second (12) magnetic sensors spaced apart and located adjacent to a highway along which vehicles travel with the sensors (11, 12) spaced apart longitudinally of the highway, detection means (14) adapted to receive signals from each of the first (11) and second (12) sensors and to detect changes in the magnetic field sensed by the sensors (11, 12) due to a vehicle travelling along the highway, passing in the vicinity of the sensor means (13).

Description

TITLE: Traffic Analyser System Description of the Invention This invention relates to a traffic analyser system and more particularly but not exclusively to such a system for detecting the speed and/or kind of vehicle travelling along a highway.

Traditionally, traffic analyser systems have utilised a tube or loop sensor which is usually mounted on the road surface and senses when a vehicle wheel passes over the sensor.

Surface mounted sensors are prone to damage due to adverse weather conditions, and have a limited life where traffic is heavy.

More recently it has been proposed to utilise a pair of magnetic sensors embedded in or mounted on the carriageway. Such sensors are adapted to measure local distortions in the earth's magnetic field occurring due to a vehicle having a ferrous content passing over or by such a sensor.

However such systems in which magnetic sensors are mounted in the carriageway have permanently to be installed in the carriageway, whereas it is preferable for a traffic analyser system readily to be portable from place to place where traffic analysis is required. Surface mounted sensors tend to present an obstruction in the road.

According to one aspect of the invention, we provide a traffic analyser system comprising a sensor means comprising first and second magnetic sensors spaced apart and located adjacent to a highway along which vehicles travel with the sensors spaced apart longitudinally of the highway, detection means adapted to receive signals from each of the first and second sensors and to detect changes in the magnetic field sensed by the sensors due to a vehicle travelling along the highway, passing in the vicinity of the sensor means.

Thus the invention provides the advantage that the sensors are mounted adjacent to the carriageway rather than by mounted on the carriageway surface and so provide no obstruction. Also the system may be made portable as the sensor means is not buried in the carriageway, and may be used whenever traffic analysis is required.

Thus there are benefits in road safety, reduced installation costs, and the sensors will tend to have a longer working life than in a conventional system.

Each sensor may comprise a magnetometer, and preferably a multiple axis magnetometer. For example, each sensor means may comprise a ring core second harmonic fluxgate magnetometer sensitive to magnetic fields along two or three generally mutually orthogonal axis. Each such magnetometer may provide a signal indicative of the magnetic field sensed along the two or three generally orthogonal axis.Where the magnetometer is a three axis magnetometer, the magnetometer may generate a signal used by the detection means derived by analogue processing means, according to the following formula namely: VO = 5/(X- y2+ (Z-offset)2) where X and Y represent the mutually orthogonal magnetic field components and Z the vertical magnetic field component of the sensed magnetic field, the "offset" being a scaling factor, to give a means of adjustment which makes a change in magnetic gradient as a vehicle passes in the vicinity of the sensor means, less dependant on the direction of travel of the vehicle.

Preferably each magnetometer includes circuitry for performing such analogue processing, for example substantially as described in GB Patent 2246888.

The detection means may sample the output signal from each magnetometer. The signal from the or each magnetometer or other magnetic sensor will of course change as a vehicle moves into the vicinity of the magnetometer and the detection means may make reference to an algorithm which determines the direction in which a vehicle affects the sensor means, is travelling.

A traffic analyser system in accordance with the invention may be utilised simply to count vehicles to enable the level of traffic to be analysed, but may be utilised to obtain a measure of the speed of a vehicle travelling along a highway past the sensor means and/or to classifying the kinds or types of vehicle.

A measure of vehicle speed may be achieved by comparing the output signals from the first and second sensors and determining the time shift between them. For example, each sensor will generate an output signal in response to a vehicle passing the sensor, which will be a vehicle magnetic signature unique to the kind or type of vehicle. The vehicle magnetic signature from one sensor may be moved by a time increment and the field value samples at each time slot multiplied together and then added to give a measure of the time correlation.

This may be repeated for increasing time increments until a maximum correlation is obtained. The time shift then equates to the time delay between the two vehicle magnetic signatures generated from the two sensors representing the time for the vehicle to travel the distance between the two sensors, which may typically be two metres, but which in any event is a known distance.

The detection means may be adapted to classify vehicles detected by the traffic analyser system from an analysis of the vehicle magnetic signature generated by each sensor and by using the measured vehicle speed.

The sensor means may be provided as a sensor means assembly e.g.

with each sensor provided at or towards either end of a tube, or as individual sensor assemblies, in each case the sensors each being connected to a detection means at the side of the carriageway via cables.

Alternatively, the sensors may communicate with a remote detection means to provide their signals via a radio or other wireless link.

Thus a single detection means may service multiple sensor means at remote locations The invention will now be described with reference to the accompanying drawing which is a purely illustrative view of an embodiment of a traffic analyser system in accordance with the invention.

Referring to the drawing there is shown a traffic analyser system 10 which comprises a first magnetic sensor 11 and a second magnetic sensor 12 together providing a sensor means 13, and a detection means 14.

In the embodiment shown each sensor 11,12, is contained within a housing such as a tube 15 and is located towards either end of the tube 15. The sensor means 13 is mounted by the side of a carriageway 16 of a highway 17 above the surface S of the highway 17. The first and second sensors 11 and 12 may for example be spaced apart longitudinally along the carriageway 16 by about two metres.

In this embodiment, each sensor 11,12, comprises a three axis magnetometer for example of the ring core second harmonic fluxgate type, arranged to produce a measure of magnetic field at the position of the respective sensor 11,12, along three orthogonal axes, utilising conventional analogue processing electronics. A suitable analogue processing means is described in prior GB patent 2246888 and such circuitry may be included for each sensor 11,12, within the sensor means 13.

In any event, each of the first and second sensors 11,12, is arranged to provide a respective d.c. output signal V11, V12 determined by the analogue processing circuitry in accordance with the following formula, namely Vo = 8,/(X2+ y2+ (Z-offset)2) where VO is the d.c. output signal V11 or V12 respectively, X and Y are horizontal components of the sensed earth's magnetic field at the position of the respective sensor.

Z is the vertical component of the earth's magnetic field sensed hv the respective sensor and "the offset" is the scaling factor.

The two signals V11, V12 from the sensor means 13 are fed to the detection means 14 along cables although in another embodiment, the magnitude of the signals V11, V12 may be communicated by wireless means such as à radio link, to a remote detection means 14.

The detection means 14 may be calibrated to ignore the presence of local large metallic structures, but will determine a change in the earth's magnetic field caused for example by a vehicle passing by in the vicinity of the sensor means 13 and locally distorting the earth's magnetic field.

Preferably the detection means 14 is adapted to make reference to an algorithm to determine the direction of a vehicle passing in the vicinity of the sensor means 13.

Whereas in the embodiment described, each sensor 11 and 12 is a ring core second harmonic fluxgate three axis magnetometer, any other suitable kind of magnetic sensor but preferably multi-axis, may be used to provide an input to the detection means 14. Preferably, the system 10 is calibrated when initially powered up, but means are provided to enable some adjustment to the system automatically, to allow for changes in the earth's magnetic field occurring locally due to other than the presence of a vehicle passing near the sensor means 13. For example, the system 10 may be re-calibrated at intervals.

The signals V11 and V12 from the sensors 11 and 12 may be utilised simply to obtain a count of vehicles passing the sensor means. Preferably though, the signals V22 and V12 are utilised to obtain a measure of the speed of the vehicle travelling along the highway 17 and/or to classify the kinds of types of vehicle passing the sensor means 13.

This may be achieved by sampling the output signals V11, V12 and then comparing the sampled signals to determine the time shift in magnetic signature between them. The magnetic signature from one sensor may be moved by a time increment and the field value samples at each time slot multiplied together and then added to give a measure of the time correlation. This may be repeated for increasing time increments until the maximum correlation is obtained. The time shift then equates to the time delay between the two vehicle magnetic signatures generated from the two sensors 11 and 12 representing the time to travel the distance between the two sensors 11 and 12. The detection means 14 would know the distance between the two sensors 11, 12, and thus may calculate the speed of the vehicle passing the sensor means 13.

Furthermore, the traffic analyser system may be utilised to classify kinds or types of vehicle detected by the system 10 from an analysis of the vehicle magnetic signature generated by each sensor 11,12, and by utilising the measured vehicle speed.

This may be achieved because each vehicle kind or type will generate a unique magnetic signature. The detection means 14 may be arranged to determine an effective length of each vehicle passing the sensor means 13, for example by measuring the time increment between two points of the generated magnetic signature of either sensor 11,12, at one fifth of the peak value of magnetic field disturbance in the magnetic signature. This length measurement will in reality be a measurement in time, which may he convened to an actual distance by multiplying by the vehicle speed measured as described above.

This effective length may not equate to the actual vehicle length, but is related to it and may thus be used to classify vehicles by their lengths. Such an arrangement is readily able to classify vehicles according to their lengths regardless of the position of the vehicle relative to the sensor means 13, because the apparent increase in vehicle length due to the vehicle being further away from the sensor will he compensated for by a decreased peak value in the vehicle magnetic signature.

In each arrangement though, the detection means 14 may provide an output 22 usable for traffic analysis.

The sensors 11 and 12 may be powered if necessary, from a mains power source or a battery power source located to the side of or otherwise adjacent to the highway 17.

In another arrangement though, the sensors 11,12, may he powered via an in-road power source such as a device which generates electricity as a vehicle passes over it. One suitable device may comprise piezo electric material which generates electricity in response to stresses imposed upon it. Such a device may be mounted on the surface of the highway 16, or in it, and may be connected to the system 10 by suitable cabling. Another such power generation device may generate electricity due to magnetic induction effects caused as a result of a vehicle passing over the device.

The features disclosed in the foregoing description the following claims or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A traffic analyser system comprising a sensor means comprising first and second magnetic sensors spaced apart and located adjacent to a highway along which vehicles travel with the sensors spaced apart longitudinally of the highway, detection means adapted to receive signals from each of the first and second sensors and to detect changes in the magnetic field sensed by the sensors due to a vehicle travelling along the highway, passing in the vicinity of the sensor means.

2. A system according to claim 1 which is portable.

3. A system according to claim 1 or claim 2 wherein each sensor comprises a magnetometer.

4. A system according to claim 3 wherein each sensor comprises a multiple axis magnetometer.

5. A system according to claim 4 wherein each sensor comprises a ring core second harmonic fluxgate magnetometer sensitive to magnetic fields along two or three generally mutually orthogonal axis.

6. A system according to claim 4 or claim 5 wherein each magnetometer provides a signal indicative of the magnetic field sensed along two or three generally orthogonal axis.

7. A system according to claim 6 wherein the magnetometer is a three axis magnetometer which generates a signal used by the detection means derived by analogue processing means, according to the following formula namely: VO= 2 (X2 + y2 + (Z-offset)3 where X and Y represent the mutually orthogonal magnetic field components and Z the vertical magnetic field component of the sensed magnetic field, the "offset" being a scaling factor, to give a means of adjustment which makes a change in magnetic gradient as a vehicle passes in the vicinity of the sensor means, less dependant on the direction of travel of the vehicle.

8. A system according to claim 7 wherein each magnetometer includes circuitry for performing such analogue processing.

9. A system according to any one of claims 2 to 8 where appendant to claim 2 wherein the detection means samples the output signal from each magnetometer.

10. A system according to any one of the preceding claims which is utilised to count vehicles to enable the level of traffic to be analysed.

11. A system according to any one of claims 1 to 9 wherein the system is adapted to be utilised to obtain a measure of the speed of a vehicle travelling along a highway past the sensor means and/or to classify the kinds of types of vehicle.

12. A system according to claim 11 wherein a measure of vehicle speed is achieved by comparing the output signals from the first and second sensors and determining the time shift between them.

13. A system according to claim 12 wherein each sensor generates an output signal in response to a vehicle passing the sensor, which will be a vehicle magnetic signature unique to the kind or type of vehicle, and the vehicle magnetic signature from one sensor is moved by a time increment and the field value samples at each time slot multiplied together and then added to give a measure of the time correlation.

14. A system according to claim 12 wherein the detection means is adapted to classify vehicles detected by the traffic analyser system from an analysis of the vehicle magnetic signature generated by each sensor and by using measured vehicle speed.

15. A system according to any one of claims 1 to 14 wherein the sensor means is provided as a sensor means assembly.

16. A system according to claim 15 wherein each sensor is provided at or towards either end of a tube, the sensors each being connected to a detection means at the side of the carriageway via cables, or communicating with a remote detection means to provide their signals via a radio or other wireless link.

17. A system according to any one of the preceding claims comprising multiple sensor means at remote locations and a single detection means to receive signals from all of the sensor means.

18. A system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

19. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.