GB2372895A

GB2372895A - Boundary protection system

Info

Publication number: GB2372895A
Application number: GB0104895A
Authority: GB
Inventors: Ronald William Barnes
Original assignee: Systems Engineering and Assessment Ltd
Current assignee: Systems Engineering and Assessment Ltd
Priority date: 2001-02-28
Filing date: 2001-02-28
Publication date: 2002-09-04
Also published as: WO2002069301A2; GB0104895D0; AU2002236011A1; WO2002069301A3

Abstract

The invention provides a boundary protection system and a method for monitoring the position of approaching vehicles along an identified path with respect to a boundary along the line of the said path, and comprises: a boundary determining means for determining the position of real or virtual boundaries 15 to 18 along the said identified path; a tracking means for tracking the position of at least one approaching vehicle with respect to one of the said boundaries; and an alerting means responsive to at least part of an approaching vehicle crossing the said boundary, whereby to provide a collision warning indication. In one embodiment the boundary determining and/or the said tracking means comprise a radar transmitter 21 and at least two receiver elements 22a,b spaced apart by one or more wavelengths of the transmitted signal, and a processing means for processing reflected radar signals 24 received by the said receivers to determine the distance and bearing of points on a physical boundary or to track the position of an object (e.g. 46) moving along a line corresponding to or offset from a virtual boundary with respect to the said receivers. The invention also contemplates the use of a GPS receiver for determining the boundary.

Description

BOUNDARY PROTECTION SYSTEM

This invention relates to a boundary protection system and in particular concerns a roadside Safety system for detecting and alerting roadside users of potential collisions with approaching vehicles.

Each year in the United Kingdom around 250 people are killed or injured on motorway hard shoulders. Research has shown that the majority of accidents on the hard shoulder involve stationary vehicles being hit by other vehicles (67%) with 10% of accidents involving pedestrians being hit. Most accidents are caused by vehicles veering off the main carriageway due to lack of driver concentration. The more serious accidents, as indicated by fatalities, occur on downhill bends and there is a particular problem in the UK with right hand bends where vehicles are more likely to wander onto the hard shoulder. In countries where vehicles drive on the right hand side of the road, down hill left hand bends present similar problems.

Vehicle repair and recovery operatives are particularly exposed to the dangers of the roadside and in 1998 six recovery operatives were killed. Four of these people were killed on motorway hard shoulders and two on the main carriageway.

A recent study by The Hard Shoulder and Roadside Safety Group, a UK industry, government and government agency group, identified a number of practical measures which could be taken to reduce the number of roadside accidents. The study identified

the use of technology as one way of improving roadside Safety.

One Safety system under development and disclosed in GB-A-2, 332, 320 uses a laser to detect the presence of objects along the laser's line of sight. In this system a laser is mounted on the rear of a recovery vehicle together with a CCTV camera for aligning the laser. A monitor in the cab of the vehicle linked to the CCTV allows an operator to aim the laser along a line of sight corresponding to the motorway hard shoulder/carriageway boundary or roadside verge/carriageway boundary to the rear of the vehicle. The system comprises a laser range finder which allows the operator to set an operational range for the laser, Say 150m, so that any object detected by the laser in that range will cause an alarm signal to be activated. The alarm is intended to give the vehicle recovery operative and other parties sufficient time to vacate the roadside area when there is an imminent danger of collision.

There are a number of drawbacks associated with the above mentioned Safety system. One drawback is the complexity of the system. Another drawback is the likely cost of the system due its complexity, and a further drawback is the potential danger of the laser to other road users. The above Safety system may also be difficult and time consuming to set up since care must be taken to Safely aim the laser before use.

A further problem associated with the Safety system disclosed in GB-A-2,332, 320 occurs when the section of road approaching the breakdown vehicle is curved. On curved roads the Safety system requires several spaced laser range finders to be positioned along the roadside such that each successive range finder or similar

detection means covers a respective part of the total distance of the curved path. The use of separate laser range finder units adds to the overall cost and complexity of this system and adds significantly to the time and effort required to deploy the system on the roadside or other such location to be protected. Depending on the direction of curvature of the bend the successive laser beams can constitute a serious hazard to other road users due to the beams being directed across the adjacent carriageways in the direction of the approaching vehicles. It may be possible to overcome this problem by providing reflectors at the positions of the successive laser range finder emitters so that no laser light traverses the adjacent carriageways. The provision of such reflectors would however complicate the system and also add significantly to the set up time required to deploy the system since each of the lasers would need to be aimed at a respective reflector before the system could be used.

There is a requirement therefore for a boundary protection system which is both simple in terms of construction and operation that can be deployed on the roadside to protect breakdown service personnel and the like from the danger of potential collisions. There is a particular requirement to provide such a Safety system for use on curved sections of road.

According to an aspect of the invention there is provided a boundary protection system for monitoring the position of approaching vehicles along an identified path with respect to a boundary along the line of the said path; the said system comprising: a boundary determining means for determining the position of a real or virtual boundary along the said identified path;

tracking means for tracking the position of at least one approaching vehicle with respect to the said boundary ; alerting means responsive to at least part of an approaching vehicle crossing the said boundary, whereby to provide a collision warning indication.

The system according to this aspect of the invention overcomes many of the problems associated with known systems in that the boundary, which may be real or virtual, that is to Say a real physical boundary such as a crash barrier or the banks of a road cutting or a virtual barrier such as a carriageway/hard shoulder road marking, is determined by boundary determining means when the system is set up. The system readily enables curved boundaries such as the carriageway/hard shoulder boundary on a curved section of motorway to be determined. By tracking the position of approaching vehicles with respect to the boundary it is possible to determine whether the approaching vehicle constitutes a hazard to the Safety of roadside users such as breakdown service vehicle personnel and the like on a Safe side of the boundary. The above aspect of the invention avoids the use of relatively expensive laser range finder components; the use of successive laser range finder apparatus on curved sections of road; and, also the use of laser light which could present a hazard to road users if used incorrectly. In addition, by tracking the position of approaching vehicles with respect to the boundary it is possible to determine whether the vehicle constitutes a hazard even if it has temporarily strayed into the Safety region defined by the boundary before its course is corrected so that it no longer constitutes a danger, that is to Say by tracking the vehicle its course may be compared with historical data to determine whether there is an imminent danger of collision. In this way it may be possible to

adjust the sensitivity of the Safety system so that false alerts are minimised to maximise the effectiveness of the system.

Preferably, the said boundary determining and/or the said tracking means may comprise a radar transmitter and at least two receiver elements spaced apart by one or more wavelengths of the transmitted signal, and a processing means for processing reflected radar signals received by the said receivers to determine the distance and bearing of points on a physical boundary or to track the position of an object moving along a line corresponding to or offset from a virtual boundary with respect to the said receivers. In this way beam processing may be used first to determine the boundary which is to be protected and then to track the position of approaching vehicles with respect to that boundary. By making use of two or more receive elements it is possible to obtain an accurate bearing of the signal reflected from an object. This may be achieved, for example, by the method of processing the relative phase of the returning signal across the receive elements, or alternatively, by the method of comparing the amplitude of the return signal from two or more receive beams which are aligned at slightly different bearings. Half beam processing of reflected radar signals can provide relatively accurate positional data and it is envisaged that accuracies of 0.1 degrees should be possible with the above system. The use of half beam processing allows the Same equipment to be used in a first mode as a boundary determining means and in a second mode as a tracking means. In this way it is possible to reduce the number of components in the system and provide a relatively inexpensive boundary protection system that is capable of operating with minimum user input to monitor the position of approaching vehicles with respect to a boundary such as a

motorway hard shoulder/carriageway boundary. The radar transmitter receivers can be used initially to track the position of an oncoming vehicle in any one of the lanes of the carriageway to determine the curvature of the carriageway as a whole. This information can be used to determine the line of the boundary since the boundary will be approximately parallel with the course of the vehicle tracked by the radar. In this way the system may be easily set up at any location regardless of the extent of road curvature with minimum or no effort on the part of the system operator. The system can therefore be set up simply by tracking the position of one or more approaching vehicles to determine the line of the boundary and then used subsequently to track the position of other vehicles with respect to the boundary so determined.

In preferred embodiments, the said boundary determining means and/or the said tracking means comprises means for identifying moving objects. In this way it is possible to filter the received radar signal so that only the components of the signal due to moving objects are used to track approaching vehicles.

Preferably, the said identifying means comprises a Doppler filter means. In this way it is possible to filter the received radar signal so that only those reflected components that have a frequency shift due to movements of the vehicle or vehicles from which they are reflected are processed by the system. It is possible therefore to remove components of the received radar signal due to reflection with other structures in the region being monitored. By using the Doppler effect to filter unwanted return signals it is also possible to remove components of the reflected signal due to movements of vehicles in the opposite direction on an adjacent carriageway of the road.

In preferred embodiments, the said boundary determining means further comprises offset determining means for determining the offset distance of a moving object with respect to the said virtual boundary. When the system is initially set up it is possible to track a vehicle to determine the curvature of the road over which it is travelling and also the distance from the receivers of the vehicles when it passes so that an offset value may be determined which represents the distance between the course of the vehicle and the carriageway/hard shoulder boundary. In this way, it is possible to track a vehicle in any lane of a multi-lane carriageway at set up time in order to determine the curvature and relative position of the boundary.

In another embodiment of the invention the said boundary determining means comprises a position determination means for determining the relative position of a number of points along a line corresponding to or offset from a virtual boundary. In this way it is possible to determine the position of the boundary independently of the tracking means by determining the relative position of a plurality of points along a line that corresponds to the boundary or a line parallel to the boundary.

Preferably, the said position determining means comprises a Global Positioning System receiver, and the said boundary determining means further comprises memory means for recording positional data from the said Global Positioning receiver at a plurality of points along the said line corresponding to or offset from the said virtual boundary. The global positioning receiver readily enables global position data to be recorded for a number of points along the line of the boundary or a line offset from

the boundary during initialisation of the system at set-up time. This may be achieved by recording the GPS position of a number of points on the hard shoulder, Say over 200m or so, as the vehicle approaches the position on the hard shoulder where it is to be parked during repair or recovery of the assisted vehicle. This readily enables the curvature of the road to be determined from the recorded positions. The position of the boundary can be determined from this information together with information relating to the position of the receiver on the vehicle and the likely distance of the receiver to the boundary to be monitored, for instance the average distance between a point on the vehicle and the hard shoulder boundary when the vehicle is travelling substantially along the centre of the hard shoulder as it approaches the vehicle to be assisted.

In preferred embodiments, the system further comprises curve fitting means for processing positional data relating to points along the said line corresponding to or offset from the said virtual boundary, thereby to determine a continuous boundary line. In this way it is possible to obtain an accurate indication of the line of the boundary from positional data relating to relatively few points along the line of the boundary when the boundary to be monitored is a relatively smooth curve.

Preferably, the said boundary determining means comprises a learning algorithm which could be a neural network. The establishment of the virtual boundary involving the uses of one or more objects moving on a road such as a motorway requires the system to'learn'the position of the boundary by observation of the moving objects. This can be implemented by an appropriate algorithm to establish

the boundary creasing range and bearing of the moving objects. Any discontinuities from this information can be eliminated by means of a curve smoothing process since it is known that the curve in the road is smooth. The algorithm can be implement by conventional means or by the use of a neural network process. A neural network readily enables the boundary determining means to learn the characteristics of the boundary to be protected at each new location of the system during initialisation and calibration thereof. The use of the neural network can enable the system to be independent of user inputs at set up time. This can greatly improve the effectiveness of the system since all human factors can be removed.

According to another aspect of the invention there is provided a vehicle comprising a boundary protection system as set forth in any one of the appended claims.

According to a further aspect of the invention there is provided a method of monitoring the position of approaching vehicles along an identified path with respect to a boundary along the line of the said path; the said method comprising the steps: determining the position of a real or virtual boundary along the said identified path; tracking the position of at least one approaching vehicle with respect to the said boundary; providing a collision warning indication in response to at least part of an approaching vehicle crossing the said boundary.

Various embodiments of the invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of a multi-lane carriageway with a stationary vehicle having a boundary protection system according to an embodiment of the invention positioned on the near side of the carriageway which may be a road side verge such as a motorway hard shoulder.

Figure 2 is a schematic plan view of a boundary protection system in accordance with an embodiment of the invention; Figure 3 is a schematic view of a phase relationship for half beam processor for determining an angular bearing; and, Figures 4a and 4b show respective amplitude and phase angle relationships for reflective radar signals at the receiver in the time domain, Figure 5 is a schematic representation of the relative amplitude and relative bearing characteristics of two receive beams; Figure 6 is a schematic representation of the relative bearing characteristic determined from the beam pattern of two receivers.

Referring to Figure 1, part of a curved section of one side of a multi-lane highway such as a motorway or main road is indicated at 10. The highway comprises two traffic lanes 11 and 12, for the movement of the vehicles in the direction of travel indicated by arrows 13, and a hard shoulder lane 14 parallel with the lanes 11 and 12 on the nearside of the lane 11 as defined by the direction of travel 13. The lanes 11 and 12 and hard shoulder 14 are defined by a series of parallel road markings 15,16, 17 and 18 which define respective lane and hard shoulder boundaries. As is usually the practice the road markings 15,16, 17 and 18 do not define physical boundaries between the lanes and hard shoulder although a physical boundary may run along the

side of the offside boundary 18 on the side of lane 12 in the form of a central reservation crash barrier or the like and a similar boundary may be provided along the edge of the road along the road marking 15 on the nearside of the hard shoulder 14.

In locations where the highway is formed in a cutting a physical barrier in the form of a wall or bank may run along the side of the road parallel with the nearside hard shoulder boundary 15.

The radius of curvature of the bend in the highway 10 is relatively large so that vehicles may travel Safely at relatively high speeds through the bend. The radius of curvature of the bend shown in Figure 1 is such that the curvatures of the lanes 11 and 12 and hard shoulder 14 are substantially the Same. This is typical of most motorway and main road bends found in the UK road network.

In Figure 1 a service vehicle 19, which may be an emergency services vehicle or a breakdown and/or recovery vehicle, is parked on the hard shoulder behind a vehicle 20, also on the hard shoulder, and which is to be assisted by the service vehicle 19.

The vehicle 19 is provided with a boundary protection system for monitoring the position of approaching vehicles in the lanes 11 and 12 with respect to the lane boundary 16 of the hard shoulder 14.

In one particular embodiment the boundary protection system comprises a radar transmitter 21 and two receiver elements 22a, 22b which are spaced apart horizontally in a plane above the ground plane of the highway 10 with the transmitter 21 to provide a directional radar system which covers the area of the highway the rear of

the vehicle 19 as shown by radar beam arcs 23 and 24. The arcs of the radar beam in Figure 1 are exaggerated for clarity and in preferred embodiments a beam angle of between 12 and 15 degrees should be sufficient to cover the area of interest behind the vehicle (19 as shown to the right of the drawing in Figure 1).

The boundary protection system fitted to the vehicle 19 comprises a boundary determining means for determining the position of a real or virtual boundary such as the dashed line 25 which is parallel to and offset from the road marking 16 representing the traffic lane 11 and hard shoulder boundary. A tracking means is provided for tracking the position of approaching vehicles with respect to the boundary 25 in the area covered by the arcs 23 and 24 to the rear of the vehicle 19.

In the event that the tracking means show that at least part of an approaching vehicle has crossed the boundary 25 a warning signal is generated in the region of the vehicles 19 and 20 so that personnel can quickly evacuate the area by the vehicles so as to be clear of the area if a collision occurs. The warning signal may be provided through the horn of the service vehicle 19 or other audible and/or visible alerting means as may be appropriate.

Referring to Figure 2, in one embodiment the boundary determining means and tracking means are provided by the transmitter 21, the receivers 22a and 22b and a signal processor 23 which comprises a half beam processor for processing the reflected radio signals received at the receivers 22a and 22b. As can be seen in Figure 2, the receivers 22a and 22b are spaced apart by a half wave length or a number of half wave lengths, as determined by the operating frequency of the transmitter and

receiver apparatus. The distance between the transmitter and receiver apparatus and a moving object 27 is determined by the signal processor 23 in the usual way based on the time interval of reflected pulses from the transmitter. The bearing of the object with respect to a notional axis 29 of the receivers, as indicated by angle 28, is determined by the phase relationship of the reflected signal at the respective receivers 22a and 22b.

The relationship between the bearing 28 and the phase difference of the reflecting signal at the respective receivers 22a and 22b is shown in Figure 3. As can be seen in Figure 3, for small angles 28, Say plus or minus 10 degrees there is a linear relationship between the phase difference 24 of the respective receivers and the bearing angle 28. In this way it is possible to determine the bearing of an object providing a radar return to the receivers 22a and 22b in accordance with the phase relationship of the reflected signals at the receivers.

The bearing to phase angle relationship is further illustrated in Figures 4a and 4b which show respectively the amplitude and phase angle of a time domain radar return from a moving object such as a vehicle on the highway 10 moving within the arcs 23 and 24 towards the transmitter and receiver on the vehicle 19. In Figure 4a the peak 40 represents the radar return of a vehicle as it approaches the receivers 22a and 22b on the vehicle 19. The leading edge 41 of the peak rises steeply as the vehicle approaches the receivers where the strength of the radar return increases to a maximum when the approaching vehicle is nearest the receivers. As the vehicle passes through the boundaries of the beam defined by the boundary arcs the signal

diminishes on the trailing edge side 42 of the signal. As can be seen in Figure 4b, the peak 40 corresponds to a linear change 43 in the phase relationship between the two received signals which indicate the change in bearing of the vehicle as it approaches and passes the receivers.

Referring now to Figure 5, in an alternative embodiment the two receivers 22a and 22b are aligned at slightly different angles with respect to one another and the signal processor 23 comprises appropriate circuitry and/or software for comparing the amplitude of the return signal from the receive beams at the receivers 22a and 22b.

In Figure 5, the relative amplitude and relative bearing characteristics of two receive beams 50 and 51 are shown for the respective receivers 22a and 22b. As can be seen in Figure 5, on measuring the relative amplitude, that is the signal strength, of the return signal in each beam 50 and 51, Say the amplitude Sa at point 52 on beam 50 and the amplitude Sb at point 53 in beam 51, it is possible to obtain the bearing of the reflective object from the relative amplitude of the respective return signals. The relative amplitudes Sa and Sb are normalised with respect to the absolute and amplitude by means of the following equation.

P = (Sa-Sb)/ (Sa + Sb) Where P is the normalised parameter.

Once the value of P has been calculated it is possible to determine the relative bearing of the reflecting object using the bearing characteristic shown in Figure 6. The characteristic shown in Figure 6 is determined from the beam pattern of the receivers

22a and 22b.

Referring back to Figure 1, it can be seen that approaching vehicles, such as vehicle 44, travelling in the lanes 11 and 12 will pass through the radar beam as they pass the arc 23 so that the bearing of a vehicle with respect to the receivers as it exits the beam is the Same regardless of the lane it is travelling in. It is possible to determine which lane the approaching vehicle is travelling in by simply determining the distance of the vehicle as it exits the beam from the radar return signal. In this respect it is possible to track one or more vehicles travelling in the lanes 11 and 12 at set up time to calibrate the system, first to determine the curvature of the bend to be monitored and second to determine the radial offset of the return signal generated by the passing vehicle with respect to the virtual Safety boundary 25.

Appropriate circuitry and/or software in the form of a learning algorithm or a neural network incorporated in the signal processor can be used during the initial learning stage to calibrate the system by simply tracking one or more vehicles when the system is set up. Once the system has been set up and the position of the boundary 25 determined the system can then monitor traffic in the region and range of the radar beam so that a warning signal can be generated in the event that an approaching vehicle, or at least part of an approaching vehicle, crosses the boundary 25 or performs a manoeuvre which is recognised by the signal processor as possibly leading to collision with the stationary vehicle 19. In this regard the signal processor may be programmed to recognise vehicle movements which indicate that an approaching vehicle is out of control before the vehicle or at least part of the vehicle crosses the

boundary 25. The warning signal may be provided by alerting means such as the standard horn apparatus fitted to the vehicle 19 and additionally through the light system of the vehicle to provide a visual indication as well as an audible indication of an impending collision so that personnel in the region of the vehicle may evacuate the danger area surrounding the vehicle.

It is envisaged that a typical operating frequency of the radar system may be 10 GHz (X-Band) as the radar signal will penetrate rain and other forms of precipitation in use. However, other frequencies are contemplated including higher frequencies in the range being considered for automatic cruise control and anti-collision protection by the automotive industry.

The signal processor is provided with filter means 25 to extract the Doppler shifted components of the returned radar signal to eliminate radar returns from stationary objects. In addition, the signal processor comprises a means 26 for range and angular gating so that the radar beam only covers the area of interest and thereby reduces the amount of signal processing required. Further, the receive signals are base banded, for example by heterodying, and digitised for processing to extract the signal versus range and relative phase angle between the half beams. In preferred embodiments the system utilises appropriate software and digital signal processing to extract this information.

As is shown schematically in Figure 1, the radar return 44 provided by a vehicle travelling in lane 12 fluctuates considerably as the vehicle travels in the region of the

beam. The radar return indicates that the vehicle follows a very tortuous path as it travels in the lane 12. This is of course not the case and the signal may be smoothed by appropriate curve fitting software incorporated in the signal processor to provide a smoothed curve 45 which represents the curvature of the road being monitored.

In another embodiment the curvature and position of the virtual boundary 25 is determined independently of the tracking means in that the signal processor comprises an input from a global positioning system receiver 27 so that positional data for a plurality of points along the path of the hard shoulder 14 can be recorded as the service vehicle 19 approaches the vehicle 20 along hard shoulder 14. By recording positional data for points spaced apart over Say 200m or 250m, it is possible to apply a curve fitting algorithm to determine the curvature of the section of the hard shoulder over which the service vehicle travels. It is also possible to determine an offset distance corresponding to the position of the virtual boundary 25 with respect to the global position receiver 27 based on the position of the receiver 27 with respect to the offside part of the service vehicle 19. In this embodiment the radar transmitter and receivers operate as before to monitor the movement of vehicles in the lanes 11 and 12 in respect to the boundary 25 so determined.

In both embodiments the signal processor is further adapted to process the return radar signals to determine the speed and distance of approaching vehicles and provide an alarm signal in the event that the speed and distance characteristics of an approaching vehicle constitute a threat to the Safety of personnel in the region of the vehicles 19 and 20.

The embodiments described above are based on a radar system. It is possible to establish such a virtual boundary by means of the use of an optical camera, either singular or in pairs. Use of a single camera whilst allowing the extraction of bearing information does not easily allow extraction of range except by the use of object recognition and relative size. With two or more cameras of the stereoscopic effect can be used to determined range.

The processing with an optical system is very similar to that used for the radar in terms of using the moving objects in the image to allow the system to'learn'the position of the hard shoulder/motorway boundary. This virtual boundary can then be used to determine if an approaching object has crossed over into the area of potential danger.

Although the invention has been described with reference to the embodiments shown in the accompanying drawings it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be affected without the exercise of further inventive skill for example the boundary system may be implemented in embodiments for use other than monitoring the movement of approaching vehicles on a highway. The system can also be used in the context of providing a virtual barrier in addition or as an alternative to a physical barrier along the side of roadworks. The identification of a moving target (MTI) as opposed to stationary background and clutter can also be achieved by identifying objects whose range moves between a series of radar pulses and returns. This can be used instead of or in conjunction with the Doppler shift caused by a moving object.

Claims

1. A boundary protection system for monitoring the position of approaching vehicles along an identified path with respect to a boundary along the line of the said path; the said system comprising: a boundary determining means for determining the position of a real or virtual boundary along the said identified path; tracking means for tracking the position of at least one approaching vehicle with respect to the said boundary; alerting means responsive to at least part of an approaching vehicle crossing the said boundary, whereby to provide a collision warning indication.

2. A system as claimed in Claim 1 wherein the said boundary determining and/or the said tracking means comprise a radar transmitter and at least two receiver elements spaced apart by one or more wavelengths of the transmitted signal, and a means for processing reflected radar signals received by the said receivers to determine the distance and bearing of points on a physical boundary or to track the position of an object moving along a line corresponding to or offset from a virtual boundary with respect to the said receivers.

3. A system according to Claim 2 wherein the said boundary determining means and/or the said tracking means comprises means for identifying moving objects.

4. A system as claimed in Claim 3 wherein the said identifying means comprises a Doppler filter means.

5. A system as claimed in any one of Claims 2 to 4 wherein the said boundary determining means further comprises offset determining means for determining the offset distance of a moving object with respect to the said virtual boundary.

6. A system as claimed in Claim 1 wherein the said boundary determining means comprises a position determination means for determining the relative position of a number of points along a line corresponding to or offset from a virtual boundary.

7. A system as claimed in Claim 6 wherein the said position determining means comprises a Global Positioning System receiver, and the said boundary determining means further comprises memory means for recording positional data from the said Global Positioning receiver at a plurality of points along the said line corresponding to or offset from the said virtual boundary.

8. A system as claimed in any one of Claims 2 to 7 further comprising curve fitting means for processing positional data relating to points along the said line corresponding to or offset from the said virtual boundary, thereby to determine a continuous boundary line.

9. A system as claimed in any preceding Claim wherein the said boundary determining means comprises a processor programmed with a learning algorithm for

determining the line of the said boundary.

10. A system as claimed in any preceding Claim wherein the said means for processing reflected radar signals comprises a half beam processor means.

11. A vehicle comprising a boundary protection system as claimed in any preceding Claim.

12. A method of monitoring the position of approaching vehicles along an identified path with respect to a boundary along the line of the said path; the said method comprising the steps: determining the position of a real or virtual boundary along the said identified path; tracking the position of at least one approaching vehicle with respect to the said boundary; providing a collision warning indication in response to at least part of an approaching vehicle crossing the said boundary.

13. A system substantially as hereinbefore described and with reference to the accompanying drawings.

14. A method substantially as hereinbefore described and with reference to the accompanying drawings.