1 5 A PARKING MAT This invention relates to a parking mat. This invention has particular, but not exclusive, application to a parking mat for 10 motor vehicles and wherein reference will be made to same. However, it will be appreciated that this invention may be used in conjunction with other types of vehicles, including trailers and such like. It has been noted that some persons have difficulty judging how far the front of a motor vehicle they are attempting to park is spaced from an adjacent wall and, as a 15 consequence of their lack of judgement, may strike the wall with the front of the motor vehicle. In an effort to avoid accidents, such as the one described, various means of indicating to the driver a preferred parking position of the motor vehicle relative to an adjacent wall have been devised by others. These include suspending a heavy object, such 10 as a tennis ball, on a string from a ceiling, said ball being positioned such that it will strike the front windscreen of the motor vehicle when the motor vehicle reaches a predetermined distance away from the wall that is located in front of the vehicle. However, the use of a ball suspended from a piece of string can not be used in certain situations, such as outdoors, where there is no structure situated directly above the vehicle windscreen from 15 which to suspend the ball. It has also been observed that the ball itself will not halt a moving motor vehicle. Accordingly, a distracted driver or a driver who is slow to react may not notice the ball strike the windscreen or will not react quickly enough, and as a consequence the motor vehicle may strike the wall located directly in front thereof. 30 It is therefore an object of the present invention to provide a parking mat for motor vehicles which will alleviate at least some of the disadvantages associated with the prior art. With the foregoing in view, this invention in one aspect relates to a parking mat for a motor vehicle that includes a plurality of wheels, said parking mat including: 35 a base having at least one contact face that in use shall engage a foundation upon which the mat rests when in use, and which also includes a front edge portion; a first obstruction that extends upwardly from said base and which includes a rearwardly inclined front face that extends upwardly from said front edge portion over 2 5 which a vehicle wheel in use may roll, said first obstruction having an upper, rearwardly located, first wheel engaging edge portion; a second obstruction that extends upwardly from said base and which is spaced from said first obstruction, said second obstruction having an upper, forwardly located, second wheel engaging edge portion, and 10 an inclined upper wheel contact surface located intermediate said first and said second obstructions, and whereby said first and said second wheel engaging edge portions are spaced apart a distance that will allow some rolling movement of the motor vehicle wheel there between while the wheel is in contact with said upper wheel contact surface, said movement of the wheel on said mat being limited in the forward direction by contact [5 of the wheel with said second wheel engaging edge portion and in a rearward direction by contact of the wheel with the first wheel engaging edge portion, said upper wheel contact surface sloping upwardly from a base of said first obstruction to a base of said second obstruction. Preferably the contact face is constructed from a material that when placed in !0 contact with a foundation, such as a foundation that is made of concrete or such like, will resist sliding movement of the mat relative to the foundation. The contact surface may also exhibit a rough appearance. For example, the contact face may be constructed from reconstituted motor vehicle tyres. Preferably the second obstruction presents a greater obstacle to overcome than the !5 first obstruction. In other words, preferably more power will need to be applied to the driving wheels of the motor vehicle in order that the wheel which is in contact with the mat may pass over the second obstacle than was necessary in order that said wheel could previously pass over the first obstruction. For example, the height of the second obstruction above the upper wheel contact surface may be substantially higher than the 30 height of the first obstruction above the foundation. The second obstruction may comprise substantially more mass than the first obstruction and may be designed in such a manner so as to resist any significant deformation of the obstruction that would make it easier for the motor vehicle to travel there over. Further, unlike the first obstruction that included an upwardly inclined front face, it is preferred that the second obstruction shall have a front 35 face that does not make contact with the motor vehicle wheel that is supported on the mat. In the preferred embodiment the first and second obstructions extend along substantially the entire width of the mat. However, it will be appreciated that in other 3 5 embodiments the first and/or the second obstruction may be significantly narrower than the width of the mat and/or may comprise a plurality of individual obstructions that are arranged in a row that extends transversely across the mat. It is also preferred that the width of the mat is greater than the width of a motor vehicle tyre. For example, the width of the mat may be equivalent to the width of 0 approximately two and a half motor vehicle tyres. The distance separating the first and second obstructions may permit a motor vehicle wheel that is supported on the mat to roll only a small distance, such as approximately 200 mm. In another embodiment, this invention relates to a parking mat for a motor vehicle 5 that includes a plurality of wheels, said parking mat including: a base having at least one contact face that in use shall engage a foundation upon which the mat rests when in use, and which also includes a front edge portion; a first obstruction that extends upwardly from said base and which includes a rearwardly inclined front face that extends upwardly from said front edge portion over 0 which a vehicle wheel in use may roll, said first obstruction having an upper, rearwardly located, first wheel engaging edge portion; a second obstruction that extends upwardly from said base and which is spaced from said first obstruction, said second obstruction having an upper, forwardly located, second wheel engaging edge portion, and .5 an inclined upper wheel contact surface located intermediate said first and said second obstructions, and whereby said first and said second wheel engaging edge portions are spaced apart a distance that will allow some rolling movement of the motor vehicle wheel there between while the wheel is in contact with said upper wheel contact surface, said movement of the wheel on said mat being limited in the forward direction by contact 30 of the wheel with said second wheel engaging edge portion and in a rearward direction by contact of the wheel with the first wheel engaging edge portion, characterised in that the mat is constructed from recycled motor vehicle tyres. Preferably the upper wheel contact surface slopes upwardly from a base of the first obstruction to a base of the second obstruction. 35 In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: 4 5 Fig. 1 is a pictorial view from above of a parking mat constructed in accordance with the present invention; Fig. 2 is a pictorial view from below of the parking mat illustrated in figure 1; Fig. 3 is a plan view of the parking mat illustrated in figure 1; Fig. 4 is a side view of the parking mat illustrated in figure 1, and 0 Fig. 5 is a pictorial view showing the parking mat in use. Figures I to 4 illustrate a substantially rectangular shaped parking mat 10 that is made entirely from recycled or re-constituted motor vehicle tyres and which includes a base 11, a first obstruction 12, a second obstruction 13 and an inclined upper contact surface 14 located between said first and said second obstructions. 5 The base 11 is substantially rectangular in shape and includes a roughened lower contact face 15 that is adapted to engage a foundation upon which the mat rests in use, and a front edge portion 16 that extends the entire width of said base. The first obstruction 12 extends upwardly from the base 11 and along the entire width of said base. The first obstruction 11 includes a rearwardly inclined front face 17 0 that extends upwardly from the front edge portion 16 over which a vehicle wheel in use may roll. The first obstruction 12 also includes a rear face 18 that slopes down from a substantially flat top surface 19, located between the front and rear inclined faces 17 and 18, to the upper contact surface 14, and whereby the transition between said top surface 19 and the inclined face 18 defines an upper, rearwardly located, first wheel engaging edge 5 portion 20. The second obstruction 13 extends upwardly from the base 11 and along the entire width of said base. The second obstruction 13 includes a rearwardly inclined front face 21, that is separated from a forwardly inclined rear face 22 by a substantially flat top surface 23, and whereby the rear face 22 merges with a rear edge portion 24 of the base 11. The 30 transition between the top surface 23 and the rearwardly inclined front face 21 defines an upper, forwardly located, second wheel engaging edge portion 25. The height of the top surface 19 above the base 11, namely the distance separating the top surface 19 and the contact face 15, is significantly less than the height of the top surface 23 above the upper contact surface 14. 5 The upper contact surface 14 slopes upwardly from a base 26 of the first obstruction 12 to a base 27of the second obstruction 13, as shown in figure 4. Further, the first and second obstructions 12 and 13 are spaced apart a distance that will allow some 5 5 rolling movement of a motor vehicle wheel 51 there between while the wheel is in contact with said contact surface 14, said movement of the wheel on said mat being limited in the forward direction by contact of the wheel with said second wheel engaging edge portion 25, and in a rearward direction by contact of the wheel with the first wheel engaging edge portion 20. 10 The mat 10 is made from recycled or reconstituted motor vehicle tyres. As a consequence the mat 10 typically weighs approximately five kilograms. In use, the mat 10 is placed on a foundation, such as a concrete garage floor, a predetermined distance away from a wall, door, post or piece of furniture, that a driver of a motor vehicle wishes to avoid striking when parking a motor vehicle 50, partially shown in 15 figure 5. As the motor vehicle is driven in the direction of the arrow 40, the most forward located vehicle wheel 51 will first strike the rearwardly inclined front face 17. Preferably the momentum of the motor vehicle at this point in time will be sufficient to permit the wheel 51 to roll over the front face 17 and top surface 19 of the first obstruction 12, and 20 whereby the sensation caused by contact between the wheel 51 and the first obstruction 12 shall be interpreted by the driver of the vehicle that he or she should now apply sufficient force to the vehicle's brake pedal to prevent the wheel rolling over the second obstruction 13 and preferably arrest all movement of the vehicle in the direction of arrow 40 with the wheel 51 supported on the upper contact surface 14. At this point, the vehicle may roll in 25 the direction of arrow 41 till the wheel 51 abuts against the first wheel engaging edge portion 20. Should the wheel 51 strike the second obstruction 13, hopefully the resulting contact between the wheel 51 and the second wheel engaging edge portion 25 shall be sufficient to arrest further movement of the vehicle in the direction of arrow 40. 30 Preferable when the wheel 51 is abutting the second wheel engaging edge portion 25, whatever part of the motor vehicle that extends beyond the mat in the direction of arrow 40 shall be spaced from whatever object the driver was wanting to avoid striking with the motor vehicle when parking said vehicle. As a consequence of the mat's weight and friction between the lower contact face 35 15 and an abutting concrete foundation upon which the mat 10 rests, it is believed that there will be very little, if any, movement of the mat relative to the foundation caused by 6 5 the wheel 51 making contact with the mat. As a consequence, it is believed that no mechanical fasteners will be required to affix the mat to the foundation. It will of course be realised that while the foregoing description has been given by way of example of this invention, all other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and 0 ambit of this invention as herein defined in the appended claims.