GB2469648A

GB2469648A - Traffic counting device

Info

Publication number: GB2469648A
Application number: GB0906824A
Authority: GB
Inventors: Steven Richard Teal
Original assignee: Clearview Traffic Group Ltd
Current assignee: Clearview Traffic Group Ltd
Priority date: 2009-04-21
Filing date: 2009-04-21
Publication date: 2010-10-27
Also published as: GB0906824D0; WO2010122284A1; EP2422331A1

Abstract

A traffic counting device comprises a housing (10), a power supply (40), a vehicle sensor (60), a data storage device (50), a wireless receiver (34), and a wireless transmitter (32). The housing will preferably be disposed in a road surface and may resemble a conventional road stud. The power supply may be a battery (42) chargeable by a solar cell (46). The vehicle sensor (60) is disposed within the housing and is operable to sense the passage of vehicles along the road surface and may be a magnetometer. An environmental sensor, such as a temperature sensor (70) may also be used to calibrate the magnetometer. The data storage device is operable to store sensed vehicle data. Preferably, the storage device may be a non volatile memory with the capacity to store several months of data. A radio clock such as a GPS receiver (80) may be used to associate a time with the sensed data. The wireless receiver (34) is operable to listen for the presence of a nearby external communication device and transmit using the transmitter (32) at least a portion of the stored vehicle data in response to a data request from a nearby external communication device. A corresponding method of collecting traffic data using a traffic counting device disposed in the road surface is also described.

Description

INTELLECTUAL

. .... PROPERTY OFFICE Application No. GB0906824.8 RTM Date:24 July 2009 The following terms are registered trademarks and should be read as such wherever they occur in this document: Bluetooth Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk

TRAFFIC COUNTING DEVICE

FIELD OF THE INVENTION

The present invention relates to a traffic counting device and to a method of collecting traffic data using a traffic counting device.

BACKGROUND OF THE INVENTION

There is a constant demand for information on road traffic flows from a variety of sources. These include national traffic authorities, local authorities and consultants undertaking traffic studies in connection with congestion reduction, local traffic management plans and development proposals, etc. Traffic counters are therefore used to count, classify, and/or measure the speed of vehicular traffic passing along a given road. Traffic counters may provide information on the volume of traffic by hour of day and vehicle class, (e.g. motorcycle, car, goods vehicles distinguished by number of axles, etc.). It is possible from the data collected to establish the vehicle profiles and the various vehicle classes involved.

A variety of traffic counters are currently available to detect the passing vehicles, as described below.

**. o One of the simplest traffic counters that is currently available involves the use of pneumatic rubber tubes laid across the road. The rubber tubes are attached to the road by means of U-clamps, or similar. As a car passes over a...

each rubber tube, a pulse of air is created that can then be detected and logged using connected circuitry which is generally located at the roadside, perhaps in a box chained to a nearby lamppost. The data may then be retrieved from the *"J roadside box at intervals as required. Rubber tube counters are often deployed only temporarily at a particular site. However, rubber tube counters are not easy to deploy and are very susceptible to traffic damage. In addition, rubber tube counters can damage the road surface due to the nails and/or U-clamps used to fix them in place. The roadside box housing the circuitry and data storage may be subject to vandalism. Also, children often cycle back and forth across rubber tube counters, which can lead to false traffic counts.

Vehicles may alternatively be detected by inductive loop sensors embedded in the road surface. Examples of loop sensor systems are the Marksman 68x range or the Marksman 660 range available from Golden River Traffic Limited, 6 Talisman Business Centre, Talisman Road, Bicester, Oxfordshire, 0X26 6HR, United Kingdom. A loop sensor is a system whereby a coil of wire, typically about 2 metres by 2 metres, is placed in the road surface and connected to an oscillator in a box at the roadside. When a vehicle passes over the coil, the phase or frequency of the oscillation is affected, thereby indicating the passage or presence of the vehicle. By counting the number of times a vehicle is detected, the loop sensor is able to determine the vehicle counts over a particular time interval, according to the needs of the user. Signals from the loops are transmitted via feeder cables to a measurement and control unit in the roadside box. Power may be provided by means of the roadside box.

However, loop sensors are difficult to install since the road must be cut to allow the insertion of the loops and wiring. The extensive cutting of the road surface during installation means that loop sensors tend only to be installed as a permanent traffic counting measure. Furthermore, it is not possible to install loop sensors in some road surfaces which have been heavily reinforced such that there is a significant amount of metal in the road surface itself. Also, loop I...

**. o sensors are relatively easily damaged. The use of roadside components again * SS* makes the system susceptible to vandalism. In addition, loop sensors are relatively expensive and are therefore not appropriate in all circumstances. ****

Another known traffic counting system uses magnetometer sensors mounted inset in the road surface to detect the presence and movement of *:**. vehicles. An example of such a system uses the M100 sensor available from Golden River Traffic Limited in the United Kingdom. This system provides a reliable, lower cost and easier to install alternative to traditional inductive loops.

The magnetometer sensor is typically flush mounted in the road surface in the centre of a traffic lane and detects the surrounding ambient magnetic field. This magnetic field is altered by the passage of vehicles so that vehicle detection is therefore possible. The magnetometer sensor then wirelessly transmits detection data in real time via low power secure radio technology to a nearby access point which is fed in to one or more local or remote traffic management controllers or systems using an interface card. To measure vehicle speeds two sensors are located in the same lane with the distance between them measured and configured in the software during the installation. Two or more sensors can be used and configured to replicate extended loops if required eliminating the need for expensive and time consuming slot cutting and trenching/ducting. US 7,388,517 and US 6,662,099 provide further details regarding specific in-road magnetometer sensor systems. In each of these known systems, the use of road side access points makes the systems susceptible to vandalism and may limit where the system can be easily installed.

In the interest of worker safety and ease of installation, non-intrusive traffic-counting technologies have been developed. These devices generally use some sort of transmitted energy such as radar waves or infra-red beams to detect vehicles passing over the roadway. For example, the Marksman 500 available from Golden River Traffic Limited in the United Kingdom is an above ground vehicle count and classifier based on radar technology. The main disadvantage of such systems is the possibility of obscuration (e.g. a lorry parked in the line of site between the road and the radar sensor). In addition, such systems are typically more expensive than magnetometer based systems and draw more o power leading to reduced battery life. For example, the Marksman 500 has its own internal power supply which is derived from a 6V battery which provides around 30 days of data recording.

* The present invention seeks to provide an alternative traffic counting S..

device and method which provide various advantages over those of the prior art. ** * * .2. * 4_s

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a traffic counting device comprising a housing, a power supply, a vehicle sensor, a data storage device, a wireless transmitter, and a wireless receiver. The housing is suitable for disposal in a road surface. The power supply is disposed within the housing for powering the traffic counting device. The vehicle sensor is disposed within the housing and is operable to sense the passage of vehicles along the road surface. The data storage device is disposed within the housing and is operable to store sensed vehicle data. The wireless receiver is operable to listen for the presence of a nearby external communication device. The wireless transmitter is operable to transmit at least a portion of the stored vehicle data in response to a data request from a nearby external communication device.

Due to the presence of the integral data storage device, there is no need for the traffic counting device of the present invention to constantly transmit data to an external roadside box, for example. Thus, the traffic counting device of the present invention draws significantly less power than prior art devices which do constantly transmit. This reduces the power requirements of the device, thereby increasing design freedom and/or enabling a longer battery life. Furthermore, since no permanent roadside box is required in conjunction with the traffic counting device of the present invention, it is much less likely that it will be subject to vandalism.

The internally stored vehicle data is downloaded on demand to an external communication device such as a PC, laptop or handheld computer. The external communication device need not be permanently located at the roadside. Thus the same (portable) external communication device may be used to download data from a number of traffic counting devices of the present invention. This a...

a..' O reduces the hardware requirements per site of interest. a S.S

Since the traffic counting device of the present invention is an in-road : device, there are not the problems with obscuration which may be experienced a..' when using known roadside radar devices and the like. Furthermore, the traffic a counting device of the present invention is a relatively compact device which may *.s be disposed discreetly in the centre of a lane of traffic (or in the centre of a carriageway) so that damage of the device by passing traffic is significantly less likely. In addition, the traffic counting device of the present invention is relatively cheap and easy to install.

Thus, the traffic counting device of the present invention may be cheaply and easily installed in many roads by a Local Authority, for example, and data need only be downloaded from specific ones of these devices as the need arises.

The lifetime of each device may be up to 10 years, or perhaps more, so the need for continuous installation and removal of prior art devices from sites of interest is negated.

Advantageously, the data storage device comprises a non-volatile memory. Advantageously, the data storage device has sufficient memory to store vehicle data sensed over a period of about three months, or more depending on memory capabilities at the time of manufacture. Advantageously, the data storage device comprises a memory having a size of 128kB or more.

Advantageously, the vehicle sensor comprises a magnetometer. More advantageously, the traffic counting device further comprises an environmental sensor for calibrating the magnetometer. In one embodiment, the environmental sensor comprises a temperature sensor.

Advantageously, the power supply comprises a rechargeable battery and a solar cell operable to charge the battery.

Advantageously, the housing is formed to look like a conventional road stud. For example, the housing may be substantially cylindrical having an approximate diameter of 100mm and an approximate depth of 50mm.

Advantageously, the traffic counting device further comprises a radio clock operable to receive a time signal so as to determine times associated with the sensed vehicle data. More advantageously, the radio clock comprises a GPS * * . ** O receiver. ** S

Advantageously, the transmitter and the receiver are each arranged to communicate with external devices using a wireless communication technology S...

or protocol comprising one of radio-frequency, infra-red, Bluetooth, ZigBee and Wi-Fi.

* 5 According to a second aspect of the present invention, there is provided a traffic counting device of the first aspect in combination with an external communication device.

According to a third aspect of the present invention, there is provided a method of collecting traffic data using a traffic counting device disposed in the road surface. The traffic counting device comprises a vehicle sensor, a data storage device, a wireless transmitter and a wireless receiver. The method comprising the steps of: sensing the passage of vehicles along the road surface using the vehicle sensor; storing the sensed vehicle data in the data storage device; using the wireless receiver to listen for the presence of a nearby external communication device; using the wireless transmitter to transmit at least a portion of the stored vehicle data in response to a data request from a nearby external communication device.

Advantageously, the wireless receiver intermittently listens for the presence of a nearby external communication device. More advantageously, the wireless receiver listens at regular time intervals for the presence of a nearby external communication device. Still more advantageously, the regular time interval is of the order of 30 seconds. In one embodiment, the wireless receiver listens for the presence of a nearby external communication device at time intervals that vary depending on the time of day. Advantageously, the time of day is determined by a solar clock that is provided as part of the traffic counting device, the solar clock comprising a solar cell.

Advantageously, the method further comprises the step of determining times associated with the sensed vehicle data. More advantageously, the determining step comprises wirelessly receiving an external time signal. In one embodiment, the storing step further comprises storing the times associated with the sensed vehicle data. *...

**. 0 Advantageously, once the data storage device is full, the oldest stored *...

vehicle data is overwritten with new sensed vehicle data such that the data r storage device always contains the sensed vehicle data for the most recent time S...

* period.

Advantageously, the storing step occurs at regular predetermined time ** intervals, and the storing step comprises storing the vehicle data sensed since the previous storing step. More advantageously, the predetermined time interval is of the order of 1 minute.

Other preferred features of the present invention are set out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a block diagram schematically illustrating the components of a traffic counting device according to one embodiment of the present invention; and Figure 2 is a schematic representation of the traffic counting device of Figure 1 disposed in a road surface.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Figure 1 is a block diagram showing a traffic counting device 10 according to one embodiment of the present invention. The device 10 is intended to be disposed in the surface of a road 12 as shown schematically in Figure 2.

The device 10 has a hard-wearing rigid housing 12 to safely enclose a number of components of the device 10. The housing 12 is designed so that the device 10 appears very similar (in terms of size and shape) to a conventional road stud or cats' eye when disposed in the road surface. Thus, the device 10 is relatively compact compared to traffic counting systems of the prior art, such as loop sensor systems. In addition, by forming the housing 12 of the device 10 similarly to a conventional road stud, the device 10 may be easily installed in a **.* o road surface in a similar way as a conventional road stud is installed. This S...

negates the requirement for new installation equipment for the device 10.

Furthermore, if the device looks like a conventional road stud, it is less likely to be 0SSS * vandalised or abused since road studs are so commonplace.

In one embodiment, the housing 12 of the device 10 is based on the * .5 housing of the Astucia SolarLite F Series Flush Stud available from Clearview Traffic Group Limited of 6 Talisman Business Centre, Talisman Road, Bicester, Oxfordshire, 0X26 6HR, United Kingdom. These SolarLite studs have a substantially cylindrical housing with a maximum diameter of 112 mm and a depth of 52mm, and are intended to be disposed in a road surface such that the axis of the cylindrical housing is perpendicular to the road surface with 4mm of the housing projecting above the road surface. Thus, once installed, each SolarLite stud appears to be circular when viewed from above. Similarly, a traffic counting device 10 having a housing 12 corresponding to an SolarLite stud housing will also appear to be circular once in stalled in the road surface.

However, it will be appreciated that other geometries and sizes of the housing 12 would also be within the scope of the invention. For compactness, the housing 12 preferably has a dimension of about 100mm in the plane of the road surface, and a depth of about 50mm, like the SolarLite stud housing described above.

Within the housing 12, the device 10 comprises a transmitter/receiver assembly 30, a power supply 40, a memory 50, a vehicle sensor 60, a temperature sensor 70, a GPS receiver 80 and a microcontroller 90. Each of these components will be described in more detail below.

The vehicle sensor 60 is operable to sense the passage of a vehicle 14 along the road 12. In a preferred embodiment, the vehicle sensor 60 comprises a magnetometer. Magnetometers sense changes in the ambient magnetic field.

Since road vehicles are at least partially metallic, magnetometers are able to sense related changes in the ambient magnetic field as a vehicle passes nearby.

Magnetometers have the advantages that they are compact, relatively cheap, and very reliable. One example of a magnetometer suitable for use as the vehicle sensor 60 in the present device 10 is the magnetometer used in the M100 Wireless Vehicle Detector available from Golden River Traffic Limited in the I...

United Kingdom (see also the VSN24O-F and VSN24O-T magnetometers available from Sensys Networks, Inc. of 2560 Ninth Street, Suite 219, Berkeley, CA 94710, United States of America). This magnetometer is a 3-axis magnetometer having magneto-resistive sensing devices to measure the x-, y-, and z-axis components of the Earth's magnetic field at a 128Hz sampling rate.

**? Alternatively, a simpler 1-axis magnetometer could be used. Furthermore, the sampling rate need not be 128Hz, but may be higher or lower depending on the desired application and location of the device 10.

In alternative embodiments, the vehicle sensor 60 may comprise an infra-red sensor, an ultrasonic sensor, a pulse inductive sensor, a radar sensor, or a visible light sensor. In the case of the visible light sensor, for example, the sensor would be operable to detect reduced light (i.e. shadowing) during the passage of a vehicle over the device 10. Thus, it may be advantageous to locate the device 10 near a streetlamp or the like to ensure a uniform level of overnight illumination in the absence of any vehicles.

The transmitter/receiver assembly 30 comprises a wireless transmitter 32 and a wireless receiver 34. In one embodiment, the transmitter 32 and the receiver 34 share some common circuitry such that the transmitter/receiver assembly 30 may be considered as a transceiver. This configuration reduces number of components required due to the use of common circuitry components.

As shown schematically in Figure 2, the transmitter 32 and the receiver 34 of the device 10 are each arranged to communicate 22 with one or more external communication devices 18. The transmitter 32 and the receiver 34 both use a wireless communication technology or protocol such as radio-frequency transmission, infra-red transmission, Bluetooth, ZigBee and/or Wi-Fi for these external communications. Wireless communication technologies of this sort are all reliable readily available, and each has its own advantages. For example, Bluetooth allows a connection to be established between a number of devices so as to avoid synchronisation problems. ZigBee may be considered as a simpler version of BlueTooth which is particularly advantageous in the present invention since it draws less power leading to extended battery life. In a preferred embodiment, the transmitter 32 is a radio frequency (RF) transmitter and the o receiver 34 is an RF receiver which communicate using radio frequency *.

communication. In this case an RF antenna 36 may be provided as part of the device 10. The antenna may protrude at least partially from the housing 12.

* Alternatively/additionally, the antenna 36 may form part of the housing 12.

The memory 50 is operable to store sensed vehicle data. In a preferred embodiment, the memory 50 comprises a non-volatile memory such as a flash memory. This ensures that the stored vehicle data is retained in the memory 50 even after the power supply 40 has failed. Advantageously, the memory 50 is a re-writable memory such as random access memory (RAM) (of. read-only memory, ROM). Typically, the memory 50 might be expected to store around I byte of sensed vehicle data per minute. In one embodiment, the memory 50 can store 128kB of data. Assuming data storage of 1 byte per minute, a 128kB memory would be sufficient memory to store vehicle data sensed over a period of -10-about three months on a typically busy road. However, such a memory size may in fact be suitable for storing around six months worth of data depending on the specific data stored and the business of the road 12. Of course, other memory sizes are envisaged within the scope of the invention. In order for the device 10 to be practicably useful, sufficient memory is required such that the device 10 is able to store at least a couple of weeks worth of sensed vehicle data. More preferably, the device is able to store at least one months worth of sensed vehicle data. More preferably still, the device is able to store a three to six months worth of sensed vehicle data. There is no upper limit on the size of the memory 50 within the scope of the present invention -the largest available memory size at the time of manufacture may be used (so long as it fits within the housing 10, etc.). The power drawn by the device 10 is not particularly dependent on the size of the memory 50, so the memory size is not considered to be a limiting factor in terms of power consumption and battery life.

The temperature sensor 70 is an example of an environmental sensor which may form part of the device 10. Such environmental sensors are used to calibrate the vehicle sensor 60, for example, based on sensed environmental conditions (temperature in this case).

The GPS receiver 80 is operable to receive a time signal so as to o determine a respective data time associated with each sensed vehicle data point. S...

The GPS receiver is a type of radio clock and it is not intended that the present invention be limited to GPS receivers alone for the purpose of determining the S...

* times associated with the sensed vehicle data. Any form of radio clock may be used within the scope of the invention. A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use multiple transmitters, like GPS.

Furthermore, clocks other than radio clocks are also envisaged within the scope of the present invention for determining the associated data times. For example, an internal microcontroller clock and/or a solar clock could be used to determine the times associated with the sensed vehicle data. However, radio -11 -clocks, such as GPS receivers, have the advantage that they do not drift (Cf.

internal microcontroller clocks which may drift over long periods). Furthermore, radio clocks are very accurate (cf. solar clocks which are less so). A high level of accuracy in the clock allows for potential synchronisation of the device 10 with other such traffic counting devices 10 or external communication devices 18.

The power supply 40 is arranged to power the traffic counting device 10.

In particular, the power supply 40 provides power to transmitter/receiver assembly 30, the memory 50, the vehicle sensor 60, the temperature sensor 70, the GPS receiver 80, and the microcontroller 90, as required. The power supply 40 comprises a rechargeable battery 42 arranged to be charged by a charger 44 connected to a solar cell 46. Power control circuitry 48 is also provided as part of the power supply 40. However, it will be appreciated that the power control circuitry 48 may be provided as part of the microcontroller 90 rather than as a separate component as shown in Figure 1. The use of a rechargeable battery 42 acts to extend the lifetime of the device 10. A rechargeable solar power supply, such as that shown in Figure 1, is a reliable well-known technology. For example, such a power supply is used in the SolarLite stud mentioned above.

Similar components may be used in the power supply 40 of the present traffic counting device 10. Such a rechargeable solar power supply 40 enables the o device 10 to function continuously for 6 to 10 years. A further advantage of using a rechargeable solar power supply is that the solar cell 46 may additionally be used as part of a solar clock, as mentioned above. In other words, the time of S...

day is calculated based on the daily cycle of sunlight detected by the solar cell 46. This is a very simple way of determining the approximate time of day without the need for a GPS receiver 80 or other separate clock component. Thus the solar cell 46 may have two purposes: firstly as an energy source for recharging the battery 42, and secondly as a component of a solar clock. The solar cell 46 may have a third purpose as part of a visible light sensor if the vehicle sensor 60 were to be a visible light sensor rather than a magnetometer. In an alternative embodiment, the power supply 40 may be a power storage device such as a supercapacitor or the like. -12-

As shown in Figure 1, the microcontroller 90 is connected to the transmitter/receiver assembly 30, the power supply 40, the memory 50, the vehicle sensor 60 (either directly or indirectly), the temperature sensor 70, and the GPS receiver 80. The microcontroller 90 enables the device 10 to function in the manner described below.

Figure 2 schematically illustrates the traffic counting device 10 in use. An overview of the method of collecting traffic data using the traffic counting device is shown in flowchart form in Figure 3.

The device 10 is disposed in the surface of a road 12. A vehicle 14 is travelling along the road in a direction shown by arrow X. In step Sb in Figure 3 the vehicle sensor 60 of the device 10 senses the passages of vehicles along the road 12. In step S12 the sensed vehicle data is then stored in the memory 50 of the device 10. In step S14 the wireless receiver 34 of the device 10 listens for the presence of an external communication device 18 such as a laptop, handheld computer or PC. If no external communication device 18 is detected (step S16), then the device 10 simply continues to sense, store and listen as in steps Sb, S12 and S14 of Figure 3. However, if an external communication device 18 is detected (step S18), then the wireless transmitter 32 of the device 10 will send an "acknowledgement" signal to the external communication device 18 so that the * .S* ** o external communication device 18 is aware of the presence of the device 10. * .**

. Then in step S20 the wireless transmitter 32 may transmit some or all of the stored vehicle data in response to a data request from the nearby external S...

* communication device 18. In Figure 2, the external communication device is a laptop 18 operated by a user 20 at the roadside. Two-way communication * S between the laptop 18 and the transmitter/receiver assembly 30 of the traffic counting device 10 is illustrated by the dashed line 22. During the data transmission from the device 10 to the laptop 18, the device 10 continues to sense, store and listen as in steps Sb, S12 and S14 of Figure 3. Thus, the device 10 continuously senses for vehicles and logs the collected data.

The vehicle sensor 60 is only able to detect nearby vehicles (i.e. vehicles in the proximity of the device 10). In other words, the vehicle sensor 60 of the device 10 has a limited detection area 16 such that the vehicle sensor 60 is able -13-to detect a vehicle within the detection area 16 but is not able to detect a vehicle outside the detection area 16. Thus the vehicle 14 shown in Figure 2 is will not be detectable by the vehicle sensor 60 of the device 10 until the vehicle 14 has travelled some distance further along the road 12 in the direction of arrow X. In Figure 2, the device 10 is located in the centre of a lane 12a of the road 12 and is intended to count vehicles in that lane 12a only. Thus, a dimension of the detection area 16 is comparable to the width W of the lane 12a. If a dimension of the detection area 16 were increased, or of the device 10 were instead positioned in the centre of the road 12 between the two lanes 12a and 12b, then the device would be used to detect vehicles in both lanes 12a and 12b of the road 12. Preferably, if the device 10 were intended to detect vehicles in both lanes 12a and 12b of a two-lane road 12, then the device 12 would be positioned centrally in the road 12 between the two lanes 12a and 12b, and a dimension of the detection area 16 would be comparable to the width of the road 12.

Let us now consider an embodiment in which the vehicle sensor 60 is a 1-axis magnetometer which continuously monitors the ambient magnetic field at a typical sampling rate of 128Hz. As a vehicle comes within the detection area 16 of the device 10, changes in the measured magnetic field occur. When no a...

... o vehicles are present, the magnetometer may continually or intermittently (e.g. a..

.... periodically) measure the background magnetic field to provide a reference value.

The magnetometer may automatically self-calibrate to the local environment, and 4*SI * to any long-term variations of the local magnetic field, by allowing this reference a'.

value to change over time.

When a vehicle is sensed Sb, the sensed vehicle data is stored S12 in !", the memory 50. The sensed vehicle data may be a simple vehicle count based on the sensed magnetometer data. However, more advanced data processing may also be performed (either by the sensor interface 62 or the microcontroller 90) in order to provide additional vehicle data such as vehicle size, vehicle speed, etc. The data times associated with the sensed vehicle data may also be determined by the microcontroller 90 and stored in the memory 50. This provides -14 -an additional, useful layer of information in the stored vehicle data. As discussed above, the data times may be determined by means of a radio clock, such as the GPS receiver 80, or may be determined some other way. The time of passage of each sensed vehicle over the device 10 may be stored.

In a preferred embodiment, the sensed vehicle data and associated data times are stored in the memory 50 in the form of so-called "interval data" or "interval counts". In other words, each individual sensed vehicle data point is not stored separately in the memory 50. Instead, the memory 50 only stores a summary of the sensed vehicle data over a given time period or "interval". As an example, a 1-minute interval (or sample period) might be used for this purpose such that data is sampled on a minute-by-minute basis. In this case, the vehicle data sensed by the vehicle sensor 60 over a given 1-minute time period might be stored in the memory 50 in the form of (a) a single time stamp identifying the 1-minute period in question, and (b) a number of vehicles sensed by the vehicle sensor 60 during that 1-minute period. For example, if four vehicles are sensed one minute, then six vehicles are sensed the next minute, then five vehicles are sensed the following minute, the data stored might be in the form "1-4, 2-6, 3-5".

Other sensed vehicle data may additionally be stored as required. However, by splitting the sensed vehicle data up into sub-periods of 1-minute each, the o amount of data being stored is considerably reduced without a significant loss in I..

data content or resolution or detail. Alternatively, the above sensed data may be stored in the form "4, 6, 5, t", say, where t is the most recent time stamp, thus t...

* further reducing the amount of data to be stored. Clearly, interval periods other than 1-minute are envisaged within the scope of the invention (e.g. 5-minutes, 10-minutes, etc.).

When the device 10 is arranged such that "interval data" is stored in the memory 50 as described above, the step S12 of storing the sensed vehicle data in the memory 50 occurs at regular predetermined time intervals (e.g. at 1-minute intervals in the example described above). The storing step S12 involves storing the vehicle data sensed since the previous storing step. Thus, the most recent minute of sensed vehicle data is stored in the memory 50 every minute. This is a practical way of doing the data storage. A 1-minute buffer memory is required (possibly as part of the memory 50) to store the detailed vehicle data sensed by the vehicle sensor 60 in the current 1-minute period before the detailed vehicle data is summarised as "interval data" and stored more permanently in the memory 50.

As an alternative to storing "interval data" in the memory 50, the vehicle data may instead be stored in the memory 50 on a vehicle-by-vehicle basis. In this embodiment, the data to be stored in the memory 50 per vehicle may include (a) the time that the vehicle was sensed by the vehicle sensor 60, (b) the vehicle speed, (C) the vehicle length, etc. At some point in time, the memory 50 will become full of sensed vehicle data. As discussed above, it is intended that this point not be reached for about 6-months after the device 10 has been installed. However, when the memory does become full, it is desirable that the oldest stored vehicle data be overwritten with new sensed vehicle data such that the memory 50 always contains the sensed vehicle data for the most recent time period (e.g. the data for the previous 6-months). Hence, the memory 50 is a re-writeable memory. This enables the memory 50 to act as a rolling data storage device which always contains the most up-to-date data. This has the advantage that the device 10 remains useful beyond the capacity of the memory 50.

S... . . . *,** 2o As indicated by step S14 in Figure 3, the wireless receiver 34 is operable *. to listen for the presence of a nearby external communication device 18. In order * o..

to reduce the power requirements of the device 10, and thereby increase the working lifetime of the device 10, the wireless receiver 34 need not listen *..

* continuously for nearby external communication devices 18. Instead, the *:* wireless receiver 34 intermittently listens for nearby external communication devices 18. In one embodiment, the wireless receiver 34 listens at regular time intervals. For example, the wireless receiver 34 may listen every 30 seconds or so. This is an appropriate time intervals since a user 20 need only wait at the roadside with his laptop 18 for a period of up to 30 seconds before establishing communication with any nearby active devices 10. Alternatively, 10-second, 20-second, or 1-minute listening periods are envisaged. -16-

Since data is most likely to be collected from the device 10 by a user 20 during working hours, it is possible to vary the listening time interval depending on the time of day. For example, the wireless receiver 34 may listen every 30 seconds or so during the day, and may listen less frequently (or not at all) overnight. The time of day may be determined from a radio clock such as the GPS receiver 80 for this purpose. Alternatively, since accuracy is not key in this regard, a solar clock comprising the solar cell 46 may be used to distinguish day from night so as to alter the listening interval accordingly. The idea of listening less frequently when there is less likelihood of an external communication device 18 being present reduces the average power consumption of the device.

In the preferred embodiment, the wireless transmitter 32 remains inactive until a nearby external communication device 18 has been detected by the wireless receiver 34. As mentioned above, once an external communication device 18 has been detected S18, the wireless transmitter 32 sends an "acknowledgement" signal to the external communication device 18 so that the external communication device 18 is aware of the presence of the device 10.

Keeping the transmitter inactive for as long as possible has the advantage of reducing the power consumption of the device 10. However, depending on the data collection strategy, it may be desirable for the wireless transmitter 32 to transmit a "beacon" signal (preferably intermittently) in order to notify any nearby . external communication devices 18 of the presence of the active device 10. The wireless receiver 34 would then be arrange to listen for a response to this beacon signal from an external communication device 18. In this case, there is no need S. * for a separate "acknowledgement" signal to be sent by the transmitter 34 to the external communication device 18 to notify the external communication device 18 *:..: of the presence of the device 10.

Once two-way communication 22 has been established between the traffic counting device 10 and a nearby external communication device 18, the wireless transmitter 32 may transmit on demand some or all of the vehicle data stored in the memory 50. In particular, the external communication device 18 may request at least a portion of the vehicle data stored in the memory 50 by means of the two-way communication link 22. This request is received by the wireless receiver -17- 34 and passed to the microcontroller 90. The microcontroller then retrieves the requested data from the memory 50 and passes it to the wireless transmitter 32 for transmission to the external communication device 18 by means of the two-way communication link 22. Typically, one month of vehicle data might be downloaded to the external communication device 18 in one go. Having been downloaded to the external communication device 18, the requested data would not be deleted from the device 10, but would still be retained in the memory 50 in case a further external communication device 18 is detected and wishes to download overlapping vehicle data.

Thus, the device 10 may be left in the road 12 for an extended period and data need only be collected from the device 10 as necessary (6-monthly if appropriate), or less frequently if nothing of relevance has occurred (e.g. no traffic accidents/queues/etc. which require investigation or analysis).

It should be noted that a magnetometer-based device 10 according to the preferred embodiment of the present invention costs about three times less than

the prior art Marksman 500 radar-based device.

It is envisaged that two or more devices 10 may be used in conjunction with one another for accurate determinations of vehicle speed and the like. In this context, it is desirable that the devices 10 be synchronised with one another.

*::2 In a first configuration, it is contemplated that the synchronisation be achieved by inclusion of a radio clock such as the GPS receiver 80 in each device 10. In a second configuration, it is contemplated that the synchronisation be achieved by means of establishing two-way communication between the two-or more devices 10. The transmitter/receiver assembly 30 of each device 10 could additionally be *2 used for this purpose.

Although preferred embodiments of the invention have been described, it is to be understood that these are by way of example only and that various modifications may be contemplated within the scope of the appended claims.

Claims

CLAI MS: 1. A traffic counting device comprising: a housing for disposal in a road surface; a power supply disposed within the housing for powering the traffic counting device; a vehicle sensor disposed within the housing and operable to sense the passage of vehicles along the road surface; a data storage device disposed within the housing and operable to store sensed vehicle data; a wireless receiver operable to listen for the presence of a nearby external communication device; and a wireless transmitter operable to transmit at least a portion of the stored vehicle data in response to a data request from a nearby external communication device.
2. The traffic counting device of claim 1 wherein the data storage device comprises a non-volatile memory.

**o
3. The traffic counting device of claim 1 or claim 2 wherein the data storage *. device has sufficient memory to store vehicle data sensed over a period of about three months or more. a..

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4. The traffic counting device of any preceding claim wherein the data *.25 storage device comprises a memory having a size of 128kB or more. a

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5. The traffic counting device of any preceding claim wherein the vehicle sensor comprises a magnetometer.
6. The traffic counting device of claim 5 further comprising an environmental sensor for calibrating the magnetometer.
7. The traffic counting device of claim 6 wherein the environmental sensor comprises a temperature sensor.
8. The traffic counting device of any preceding claim wherein the power supply comprises a rechargeable battery and a solar cell operable to charge the battery.
9. The traffic counting device of any preceding claim further comprising a radio clock operable to receive a time signal so as to determine times associated with the sensed vehicle data.
10. The traffic counting device of claim 9 wherein the radio clock comprises a GPS receiver.
11. The traffic counting device of any preceding claim wherein the transmitter and the receiver are each arranged to communicate with external devices using a wireless communication technology or protocol comprising one of radio-frequency, infra-red, Bluetooth, ZigBee and Wi-Fi.
12. The traffic counting device of any preceding claim wherein the housing is *. formed to look like a conventional road stud. I...
13. The traffic counting device of any preceding claim in combination with an S..* external communication device. * . * **

*:*.
14. A method of collecting traffic data using a traffic counting device disposed in the road surface, the traffic counting device comprising a vehicle sensor, a data storage device, a wireless transmitter and a wireless receiver, the method comprising the steps of: sensing the passage of vehicles along the road surface using the vehicle sensor; storing the sensed vehicle data in the data storage device; * ,, S -20 -using the wireless receiver to listen for the presence of a nearby external communication device; using the wireless transmitter to transmit at least a portion of the stored vehicle data in response to a data request from a nearby external communication device.
15. The method of claim 14 wherein the wireless receiver intermittently listens for the presence of a nearby external communication device.
16. The method of claim 15 wherein the wireless receiver listens at regular time intervals for the presence of a nearby external communication device.
17. The method of claim 16 wherein the regular time interval is of the order of seconds.
18. The method of claim 15 wherein the wireless receiver listens for the presence of a nearby external communication device at time intervals that vary depend ing on the time of day. S...
19. The method of claim 18 wherein the time of day is determined by a solar ** clock that is provided as part of the traffic counting device, the solar clock comprising a solar cell. S...S *. S

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20. The method of any of claims 14 to 18 further comprising the step of *: determining times associated with the sensed vehicle data. * .

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21. The method of claim 20 wherein the determining step comprises wirelessly receiving an external time signal.
22. The method of claim 20 or claim 21 wherein the storing step further comprises storing the times associated with the sensed vehicle data.I

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23. The method of any of claims 14 to 22 wherein, once the data storage device is full, the oldest stored vehicle data is overwritten with new sensed vehicle data such that the data storage device always contains the sensed vehicle data for the most recent time period.
24. The method of any of claims 14 to 23 wherein: the storing step occurs at regular predetermined time intervals; and the storing step comprises storing the vehicle data sensed since the previous storing step.
25. The method of claim 24 wherein the predetermined time interval is of the order of 1 minute.
26. A traffic counting device substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.
27. A method of collecting traffic data using a traffic counting device, the method being substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings. S... * S * * S *S.. * S * S.. *.*. *. S..S S. * * . S * .* * S S S * *S