Improved Guard Rail Assembly Field of the invention [001] The present invention relates to posts for guard rails and in particular to improve the posts which assist the guard rail in performing its function during a collision. Background of the invention [002] Prior art posts assist guard rail systems to perform their function of holding a rail in place for as long as possible during a collision by being frangible or being collapsible in a controlled manner. [003] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. Summary of the invention [004] The present invention provides a post and guard rail assembly, the post including an elongated mounting hole for connecting the guard rail directly to the post by means of a bolt passing through the guard rail and the mounting hole, the mounting hole being located below an upper edge of the post, the post including an aperture or slot spaced from the mounting hole and below the upper edge, whereby in the event of a collision by a vehicle with the assembly, a portion of a periphery of the aperture or slot will separate to allow the bolt and the guard rail to move from the post. [005] The aperture or slot can be an elongated closed slot. [006] The guard rail can be bolted to each post by a bolt and a nut. [007] The present invention provides a post for a guard rail system including an elongated mounting hole for the connection of a guard rail to the post by means of a bolt passing through the guard rail and mounting hole, the mounting hole being located at a predetermined distance below an upper edge of the post, the post including an aperture or slot located above the mounting hole below the upper edge, the aperture or slot having a peripheral length longer than the peripheral length of the mounting hole. [008] The aperture or slot can be an elongated closed or open slot. [009] The post can have a portion that will separate from the post during a collision. 1 [010] The present invention also provides a guard rail assembly comprising a plurality of posts as mentioned in the paragraphs above, and a guard rail directly secured to each post by a bolt that passes through the guard rail and post. [011] The rail can be bolted to each post by a bolt and a nut. [012] The present invention provides a post for a guard rail system including an elongated mounting hole for the connection of a guard rail to the post, by means of a bolt passing through the guard rail and mounting hole, the mounting hole being located at a predetermined distance below an upper edge of the post, the post including one or more apertures or slots located above the mounting hole and at or below the upper edge, the one or more apertures or slots being located near to a central longitudinal axis of the mounting hole, wherein one aperture spaced from the mounting hole has a peripheral length longer than the peripheral length of the mounting hole.. [013] The apertures or slots can be elongated closed or open slots. [014] A last slot before or at the upper edge can be an open slot. [015] Land between adjacent slots can be frangible. [016] The land between adjacent slots can include weakened areas or portions. [017] The land between adjacent slots is adapted to be torn or sheared by a bolt which is initially located in the mounting hole as the guard rail moves upwards relatively to the post during a collision. [018] One aperture or slot before or at the upper edge can have a width that is larger than a width of the preceding slot or aperture, to allow a bolt securing the guard rail to the post to pass through the last slot or aperture. [019] The present invention also provides a guard rail assembly comprising a rail and a post as described in the previous paragraphs. [020] The rail can be bolted to the post by a bolt and a nut. [021] The bolt can include a head and a first shank portion which is unthreaded and a second shank portion which is threaded for securing the rail to the post with a nut, the bolt being characterised by the first shank portion being substantially larger in diameter than the second shank portion whereby an external face of the first shank portion will bear against a surface of the post in the vicinity of the mounting hole. 2 [022] The first shank portion can slidably secure the rail to the post so that the rail is free to move between the head and an external surface of the post. [023] The bolt can attached to the post after being threaded through the rail with a nut that is tightened to a torque which has been predetermined. Brief description of the drawings [024] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [025] Figure 1 is a post in perspective view showing an outer surface thereof; [026] Figure 2 illustrates a cross-section through a bolt and rail mounted in a post such that of Figure 1; [027] Figure 3 illustrates a post similar to figure 1 with a single open slot above the mounting hole having like parts to Figure 1 being like numbered; and [028] Figure 4 illustrates a post similar to figure 1 with a single closed slot above the mounting hole having like parts to Figure 1 being like numbered. Detailed description of the embodiment or embodiments [029] Illustrated in Figure 1 is a post 10 which is substantially of a C-shaped cross section 12. The post 10 has in one side an obround mounting hole 14 approximately 60mm in length and of a diameter or width being approximately the diameter of the threaded shank 36 of a bolt 30 as illustrated in Figure 2. [030] Coaxially arranged between the upper end of the mounting hole 14 and the upper edge 12 of the post 10 is a series of four elongated obround slots or apertures 16, 18, 20 and 22 which extend, end to end, between the top of the hole 14 and the edge 12. [031] The slots 16, 18, 20 and 22 are substantially the same width as the obround hole 14 and have their central longitudinal axes collinear with each other and with the central longitudinal axis of the mounting hole 14. [032] Between adjacent hole 14 and slot 16, and slots 16 and 18, and slots 18 and 20, and slots 20 and 22, are lands L which are sized so as to enable a bolt 30 mounted in the mounting hole 14 if acted upon by a substantial upward force, such as may occur in a collision that the lands L will break or fracture, as a rail 40 is forced upward relative to the post 10 and the bolt 30 moves through the slots separating lands L or otherwise deforming them to fracture. 3 [033] If desired the lands L can be weakened by holes drilled or formed at either end of the land L or by weakened areas such as might be formed by V-shaped groove and the like. For example lines of weakness on the land L can be such as those illustrated as 18.1 in Figure 1. [034] Whilst four slots 16 to 22 are illustrated a single slot with a single land between it and the top of the mounting hole 14 can be provided, giving a bolt 30 a clear run from the start of the single land L to the top of the post 12 as is illustrated in figure 3 and 4. [035] Illustrated in Figure 2 is a cross section through a bolt 30, post 10 and rail 40 assembly. The bolt 30 utilised to mount rail 40 to the post 10 has a head 32, a reduced shank 34 and a further reduced diameter threaded shank 36. The shank 34 forms a shoulder which will not pass through the mounting hole 14 whilst the shank 34 allows the rail to slidably move along it between the underside 33 of head 32 and the external surface of the post 10 in the vicinity of the mounting hole 14. [036] Such a bolt rail and post assembly will ensure that the rail is secured to the post 10 but is not clamped to the post 10 thus making it easier for the bolt 30 to slide relative to the post 10 in the mounting hole 14 and up through the lands L and through the adjacent slots towards the top edge 12 in the case of a collision. [037] The last hole 22 can be provided as a much wider hole so that the nut which would secure the bolt 30 to the post 10 can simply pull through and escape from the post 10. Thus a large circular hole 22 can be provided or a square shape hole or slot being much larger than the external periphery of a nut or bolt head used to secure the rail 40 to the post 10. [038] As an alternative the upper edge or land between the top edge of the slot 22 and the top edge of the post 12 can be removed such as shown by the dotted lines 22.1 in Figure 1 or in Figure 3, allowing the bolt 30, once it reaches the hole 22 to simply slide off the end of the post 10 without having to engage another land L. [039] Preferably the nut is torqued onto the bolt 30 so that the rail is secure, yet the rate of movement of the rail or the amount of force to move the rail relative the post will have to exceed a predetermined limit. Such a torque will need to be predetermined so that the rail will only move upwards when subjected to a force of collision of a predetermined amount so as to satisfy Australian and Overseas standards relating to such guard rail systems. [040] As shown in Figure 3 and Figure 4, the aperture or slot 16 is located above and spaced from the mounting hole 14. It is further located at or below the upper edge of the post 10. It can be seen from Figures 3 and 4 that the aperture or slot 16, which is near to the longitudinal 4 axis of the post 10, has a peripheral length or perimeter, that is longer than the peripheral length or perimeter of the adjacent mounting hole 14. As shown in Figure 4, a portion of the periphery of the aperture of slot 16 extends between weakened or frangible regions in the post, as marked by lines 22.1 in Figure 4. In the event of a collision by a vehicle with the guard rail and post assembly, this portion of the periphery will separate from the post 12. The separation allows the guard rail and the bolt which attaches the guard rail to the post, to move away from the post 12. [041] Whilst the above embodiment shows a C-section post 10 other shape posts such as the "0" post known as the Ochoa post or other shape posts can be utilised with the present invention. [042] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [043] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. [044] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein. 5