GB2590445A - A cattle guard - Google Patents

Abstract

A cattle guard 1 comprising a frame having two opposed frame members 2, 3 and a plurality of parallel bars 6a-I extending between the two opposed frame members, wherein: each end of each bar 4, 5 is rotatably supported by a respective frame member so that each bar may rotate about a respective longitudinal axis of rotation of that bar; each bar has a substantially planer surface which may be located uppermost by rotation of the bar; and wherein the cattle guard further comprises a linkage mechanism (12, 14 figure 3) connected to each of the bars and arranged to rotate the bars together between a position where the planar surfaces of each bar are uppermost and substantially coplanar, making it easier to walk over the cattle guard, and a position where the nonplanar surfaces are uppermost, making it more difficult to walk over the cattle guard, the cattle guard further comprising a locking means 8, (9, figure 2) for locking the bars in a position where the nonplanar surfaces are uppermost (figure 2).

Description

A Cattle Guard The present invention relates a cattle guard and particularly, but not exclusively, to a cattle guard suitable for use on a railway.

One particular application of a cattle guard is for use on railways, to prevent cattle (or pedestrians) straying on to the railway off a crossing, for example off a road (level crossing). Such cattle guards are commonly used on the UK rail network and these normally comprise an array of parallel equally spaced pieces of wood, which are laid inside the rails and possibly to either side outside of the rails.

Each piece of wood is triangular in cross section with an apex of the triangle uppermost. The guard may typically be between one and three meters long and thus prevents cattle and most other large animals walking or jumping over and these also present an awkward obstacle for pedestrians to negotiate.

A significant advantage of the above type of cattle guard is that it is very simple to install and maintain and may last many tens of years without attention. One disadvantage however is that it may impede access to authorised rail workers, for whom a road crossing may otherwise provide easy access onto the railway to perform maintenance work or other necessary tasks.

It is an object of the present invention to provide an improved cattle guard.

According to the present invention there is provided a cattle guard comprising a frame having two opposed frame members and a plurality of parallel bars extending between the two opposed frame members, wherein: each end of each bar is rotatably supported by a respective frame member so that each bar may rotate about a respective longitudinal axis of rotation of that bar; each bar has a substantially planner surface which may be located uppermost by rotation of the bar and a nonplanar surface which may be located uppermost by rotation of the bar; and wherein the cattle guard further comprises a linkage mechanism connected to each of the bars and arranged to rotate the bars together between a position where the planar surfaces of each bar are uppermost and substantially coplanar, making it easier to walk over the cattle guard, and a position where the nonplanar surfaces are uppermost, making it more difficult to walk over the cattle guard, the cattle guard further comprising a locking means for locking the bars in a position where the nonplanar surfaces are uppermost.

The provision of a cattle guard employing rotatable bars, such that a non-planar surface may be rotated uppermost, permits such a cattle guard to be switched to a "walk" state where it may provide a walkway permitting temporary access onto a railway line, for example, when access is required by an authorised user. The same cattle guard may however then to be reset to a "guard" position, by using locking means to lock the bars in the guard position, where the non-planar surfaces are uppermost.

A cattle guard in accordance with the present invention permits a temporary access to be provided across the cattle guard without the need to carry any planks or similar items to bridge the cattle guard.

Preferably each bar is arranged to rotate about its axis of rotation between a first position, a second position and a third position intermediate the first and second positions, wherein: each bar has first and second planar surfaces joined at an apex, the apex defining the non-planar surface; in the first position the first planar surface of each bar is uppermost and substantially coplanar with the other first planar surfaces; in the second position the second planar surface of each bar is uppermost and substantially coplanar with the other second planar surface; and wherein in the third position an apex of each bar is uppermost.

The above arrangement may permit each bar to be square in section and rotated from a guard position, where an apex of the square section is uppermost, to a position where the bar has been rotated through 45°, either clockwise or anti-clockwise, to a position where a planar surface of each bar is uppermost to provide a substantially flat walkway.

The above arrangement is particularly advantageous where: the linkage mechanism comprises a first link member pivotally connected to each bar at a point above or below the axis of rotation of each bar and a second link member pivotally connected to each bar at a point above or below the axis of rotation of each bar; each link member is arranged to move substantially transversely relative to the axes of rotation of the bars, such as to cause the bars to rotate between their first, second and third positions; the link members have a first position, where the bars are in their first positions, a second position, where the bars are in their second positions and a third position, intermediate the first and second positions, where the bars are in their third positions; the locking means being arranged to lock the link members in their third positions.

In one embodiment, the locking means may comprise a first locking member arranged to move between first and second positions and located at or toward a first end or a first side of the cattle guard; and a second locking member arranged to move between first and second positions and located at or toward a second end or a second side of the cattle guard remote from the first end or first side of the cattle guard, and wherein: when in its first position the first locking member prevents the first link member moving to its first position but permits the second link member to move to its second position; when in its second position the first locking member prevents the second link member moving to its second position but permits the first link member to move to its first position; when in its first position the second locking member prevents the second link member moving to its first position but permits the first link member to move to its second position; and wherein when in its second position the second locking member prevents the first link member moving to its second position but permits the second link member to move to its first position, thus when the first and second locking members are both in their first positions, or are both in their second positions, the first and second link members and the bars are all held in their third positions.

More preferably, the two opposed frame members comprise a first frame member located to a first side of the cattle guard and a second frame member located to a second side of the cattle guard, wherein: the first link member is an upper link member located on the first side of the cattle guard and pivotally connected to each bar at a point above the axis of rotation of each bar; the second link member is a lower link member located on the first side of the cattle guard and pivotally connected to each bar at a point below the axis of rotation of each bar; the first and second locking members are both located on the first side of the cattle guard, but at or towards opposite ends of the cattle guard.

A major advantage of the above arrangement is that it may permit the cattle guard to be approached from either end, or exited from either end, and the appropriate one of the first and second locking members operated to either release the bars from the guard position, or to lock the bars in the guard position, regardless of the position of the other locking member.

The cattle guard may alternatively comprise a first frame member located to a first side of the cattle guard and a second frame member located to a second side of the cattle guard, wherein: the first link member is an upper link member located on the first side of the cattle guard and pivotally connected to each bar at a point above the axis of rotation of each bar; the second link member is a lower link member located on the first side of the cattle guard and pivotally connected to each bar at a point below the axis of rotation of each bar; the first locking member is located on the first side of the cattle guard, the cattle guard further comprising: a third link member which is an upper link member located on the second side of the cattle guard and pivotally connected to each bar at a point above the axis of rotation of each bar; and a forth link member which is a lower link member located on the second side of the cattle guard and pivotally connected to each bar at a point below the axis of rotation of each bar, wherein: the second locking member is located on the second side of the cattle guard; when in its first position the second locking member prevents the second link member moving to its first position but permits the first link member to move to its second position by preventing the fourth link member moving to a first position while permitting the third first link member to move to a second position; and wherein when in its second position the second locking member prevents the first link member moving to its second position but permits the second link member to move to its first position by preventing the third link member moving to a second position while permitting the fourth link member to move to a first position.

The above arrangement may permit the first and second locking members to be arranged on diagonally opposed corners of the cattle guard, thus at two opposite sides and two opposition ends of the cattle guard, permitting the cattle guard to be installed with the bars either across or running along the intended direction of the walkway, while still permitting access to each locking member from either end of the walkway passing across the cattle guard.

Each locking member may be arranged to be raised or lowered, or to pivot, to block the path of a selected one of the two link members with which it is associated, providing a very simple and reliable mechanism for both locking and releasing the bars from either side or either end of the cattle guard.

Preferably, the cattle guard further comprises means for preventing access to the first and second locking members, or for locking the first and second locking members in one position. This may for example comprise a padlock or a locked housing, preventing unauthorised movement or access to the locking member or members.

Preferably, each bar has at least one stop on at least one end arranged to limit rotation of the bar and to partially bear any weight placed on the bar. In this manner, any forces placed on the bars by persons walking across it which may act to rotate the bar past its intended walk position, may enable the forces created to be supported locally rather than these being placed entirely on the linkage mechanism.

Preferably, the axis of rotation of each bar is offset below a longitudinal centreline of each bar, when each bar has its non-planar surface uppermost, such that when the bar is rotated so that a planar surface is uppermost, downward pressure applied to the upper planar surface prevents the bar rotating to a position where the non-planar surface is uppermost. In this manner, downward pressure applied on the upper surface effectively acts to urge the bar to a position in which it is retained, preventing the bar from rotating and thus providing a stable walkway to walk across.

Advantageously, the locking means may comprise first and second locking members at respective opposite sides, or respective opposite ends of the cattle guard, each locking member having a first position and a second position, wherein when the bars have their non-planner surfaces uppermost and are locked in position, moving either locking member from one of its positions to the other causes the bars to be released from the locked position, irrespective of the position of the other locking member and wherein, when the bars have their non-planner surfaces uppermost and are not locked in position, moving either locking member from one of its positions to the other causes the bars to be locked in position, irrespective of the position of the other locking member.

In any of the above embodiments it is preferable that the bars are arranged to be rotated by hand, avoiding the provision of any lever to rotate the bars, which may otherwise provide a potential obstacle to a passing train. This may also discourage attempted interference with the cattle guard by unauthorised users, by removing any obvious means of operating or tampering with the cattle guard.

In one embodiment, each bar may formed from glass reinforced plastic so that it may be maintenance free for its intended life.

Where the cattle guard is to be employed on a railway line it is advantageous if it is dimensioned to fit between the rails of a railway line, with the two opposed frame members aligned perpendicular to the rails, for then the bars will run in the direction of the rails, in which direction they are more difficult to walk along when set in the guard position.

One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like numerals are used to indicate like parts and of which: Figure 1 is a perspective view of a cattle guard in accordance with the present invention in a "guard" position; Figure 2 is a perspective view of the cattle guard of Figure 1 but shown in a "walk" position; Figure 3 corresponds to Figure 1 but with frame members and a cover box removed to show the internal components when in the guard position of Figure 1; Figure 4 correspond to Figure 3 but shows the components in the walk position of Figure 2; Figure 5 is a perspective sectional view taken along the line V-V of Figure 3.

Figures 6A to 6C are end views of a bar of the cattle guard of Figures 1 to 4, shown rotated to different angles; Figure 7A is a side elevation of the first locking member; Figure 7B is a side elevation of the second locking member; and Figures 8A to 8B, 9A to 9B, 10A to 10B and 11A to 11B show the locking members of Figures 7A and 7B in respective different positions during use of the cattle guard of Figure 1.

Referring to Figure 1, this shows a cattle guard, indicated generally as 1, in accordance with the present invention. This comprises a first frame member 2 and a second frame member 3 both connected to first and second fixed end bars 4, 5, to form a square perimeter frame of the cattle guard 1. The fixed end bars 4 and 5 are both square section glass reinforced plastic (GRP) tube. Between the two fixed end bars 4 and 5 there are located, in this example, nine rotatable bars 6a to 6i, also formed of square section glass reinforced plastic tube. Each end of each rotatable bar 6a to 6i is supported by a respective one of the first and second frame members 2, 3 via a bearing mounted to a respective hole 7 in one of the first or second frame members 2, 3.

In Figure 1, the rotatable bars 6a to 6i are shown in a first guard position to enable the cattle guard to guard against cattle or other large animals walking across and to deter pedestrians from walking across it. In Figure 2, the cattle guard 1 of Figure 1 is shown with the rotatable bars 6a to 6i rotated through 45° so that a planar surface, or side, of each of the rotatable bars 6a to 6i is uppermost, placing the cattle guard 1 in a walk configuration, where it is relatively safe and easy for a pedestrian to walk over.

The cattle guard of Figures 1 and 2 comprise a number of link members connecting the rotatable bars 6a to 6i, so that they may all be rotated together, and two locking members which engage with the link members to enable the rotatable bars 6a to 6i to be either locked in the guard position of Figure 1, or to be released from the guard position of Figure 1. These are all described in detail later, but Figures 1 and 2 show secure housings 8 and 9 in which the locking members are located, each housing 8, 9 having a respective lockable cover 10 to prevent tampering with the locking mechanism and thus the rotatable bars 6a to 6i of the cattle guard 1.

Referring now to Figures 3, 4, these correspond to Figures 1 and 2 respectively, but omit the first and second frame members 2 and 3 and the secure housings 8 and 9. Figures 3, 4 reveal how the rotatable bars 6a to 6i of the cattle guard 1 of Figure 1 are each connected at a first end to a first upper link member 11 and to a first lower link member 12, and at a second end to a second upper link member 13 and to a second lower link member 14.

Each of the rotatable bars 6a to 6i is pivotally connected to the upper link members 11 and 13 and the lower link members 12 and 14 at vertically separated points, such that rotation of one of the rotatable bars 6a to 6i clockwise, as shown in Figure 3, about a respective axes of rotation 17, causes rotation of all of the rotatable bars 6a to 61, by displacing the upper link members 11 and 13 in the direction of the arrows 15, with the lower link members 12 and 14, being displaced in the directions of arrows 16, so that the rotatable bars 6a to 6i all adopt the position shown in Figure 4, placing the cattle guard in the walk configuration of Figure 2.

It will be appreciated that instead of one of the rotatable bars 6a to 6i of Figure 3 being rotated clockwise, it could equally have been rotated anti-clockwise, which would have again placed all the rotatable bars 6a to 6i in a second walk configuration, as will be described below with reference to Figures 6A to 6C.

Referring again to Figure 3, a first locking member 18 is provided at a first end and on a first side of the cattle guard 1. A second locking member 19 (just visible in Figure 4) is provided at a second end and on a second side of the cattle guard 1. The first locking member 18 is rotatable and may be moved to limit movement at any one time of one only of the first upper link member 11 and first lower link member 12. Similarly, the second locking members 19 is rotatable and may be moved to limit movement at any one time of one only of the second upper link member 13 and second lower link member 14. This is described in greater detail below with reference to Figures 7A to 11B.

Referring now to Figure 5, a perspective sectional view along the line V-V of Figure 3, (but including the first frame member 2 omitted from Figure 3), this shows that the first frame member 2 is a square C-shape in cross section, effectively providing a housing for the first upper link member 11 and the first lower link member 12. The upper link member 11 is seen to be supported by being pivotally connected by a pivot pin (not shown) to an end plate 20 of each of the rotatable bars 6a to 6i, at a point 21. Similarly, the lower link member 12 is supported by being pivotally connected to each end plate 20 of each of the rotatable bars 6a to 6i, at a second point 22, as can perhaps be more clearly seen with reference to Figures 6A.

With continued reference to Figures 5 and 6A, from these it can be seen how the rotatable bar 6a (and all the other rotatable bars 6b to 6i), is rotatably mounted by a bearing 23, in a bearing housing 24 secured to the end plate 20 of the rotatable bar 6a, to a spindle 25 mounted in a hole 7 in the first frame member 2.

With the exception of the rotating bars 6a and Si, each of the other rotating bars 6b to 6h will have associated spindles 25 which are shorter and terminate substantially flush with an outer face of the respective first and second frame members 2, 3. However, in the case of rotating bars 6a and 6i, one of their respective spindles 25 will have an extension portion on which the first locking member 18, or second locking member 19, are respectively mounted and free to rotate thereon, as shown in Figure 5.

With reference now to Figure 6A, this shows the two vertically separated connection points 21 and 22, in the end plate 20 of rotatable bar 6a, for pivotally engaging with respective upper and lower link members 11 and 12. A bearing 23 (one at each end of the rotatable bar 6a) mounted in bearing holder 24 fixed to the end plate 20, permits the rotatable bar 6a (and all the other rotatable bars 6b to 6i) to be rotated either clockwise, from the guard position shown in Figure 6A, to the walk position shown in Figure 6B, or rotated anti-clockwise to the walk position shown in Figure 6C. This rotation will occur around the axis of rotation 17 passing through the centre of the bearings 23, such that each of the rotatable bars 6a to 6i will either "fall" to the right as shown in Figure 6B and as represented by arrow 27, or fall to the left, as shown in Figure 6C and as represented by arrow 28. Thus when unlocked from the guard position of Figure 6A, each bar 6a to Si may rotate clockwise as shown in Figure 6B, or anti-clockwise as shown in Figure 6C, where each of the rotatable bars 6a to Si will then be retained in place by gravity acting upon them and by the weight of a person walking across them.

The cattle guard 1 of Figures 1 and 2 may be arranged to be positioned between the two rails of a railway line with additional cattle guards having fixed bars, being placed outside of either rail, to effectively extend the cattle guard to beyond the width of a train, to a point where a fence or other vertical barrier may extend. Thus in the guard configuration shown in Figure 1, the cattle guard 1 will prevent cattle walking across it along the railway line and deter pedestrians walking across the cattle guard 1.

When an authorised user with a key for unlocking the secure housings 8 or 9 approaches the cattle guard, from either end/side of the cattle guard 1, they may operate the appropriate locking means 18 or 19 to release the cattle guard 1 from the guard position shown in Figure 1 and rotate the rotatable bars 6a to Si to the walk position shown in Figure 2, prior to crossing the cattle guard 1. Similarly, the cattle guard 1 permits the rotatable bars 6a to 6i to then be rotated to the position shown in Figure 1 and locked in place in the guard configuration of Figure 1, using either the first locking member 18 or second locking member 19, depending whether the user is at the opposite end/side of the cattle guard 1, or whether they have returned to the end/side they set out from. This dual end/side operation is made possible by the interaction between the first upper link 11, first lower link 12, second upper link 13, second lower link 14, first locking member 18, second locking member 19 and the rotatable bars 6a to Si. This will now be described with reference to Figures; 7A and 7B; 8A and 8B; 9A and 9B; 10A and 10B; and 11A and 11B, where each pair of Figures is a snapshot in time showing the relative positions of all the above mentioned components, with Figures 7A, 8A, 9A, 10A and 11A showing the first locking member 18, bearing the letter A, and Figures 7B, 8B, 9B, 10B and 11B indicating the position of the second locking member 19, bearing the letter B. Referring first to Figures 7A to 7B, these show rotatable bars 6a to Si (represented by rotatable bars 6b and 6h) in the guard position, with an apex between two flat sides uppermost. In this position, the points 21 and 22, at which the end plate 20 is connected to the first upper link member 11 and the first lower link member 12, are aligned vertically, with the first upper link member 11 and first lower link member 12 arranged one above the other and with their respective ends aligned vertically, as shown in Figure 7A. Because those same rotatable bars 6a to 6b are also connected at their opposite ends to the second upper link member 13 and second lower link member 14, the second upper link member 13 and second lower link member 14 are also positioned as shown, with their respective ends aligned vertically, as shown in Figure 7B.

With the first locking member 18, raised as shown in Figure 7A, and the second locking member 19 raised, as shown in Figure 7B, the first upper link member 11 and second upper link member 13 are effectively locked in place by the first locking member 18 preventing the first upper link member 11 moving to the left, as shown in Figure 7A and the second locking member 19 preventing the second upper link member 13 moving to the left, as shown in Figure 7B (viewed from the opposite side to Figure 7A), thus preventing the upper points of connection with the rotatable bars 6a to 6i moving laterally and thus, by virtue of the axis of rotation 17 of each of the rotatable bars 6a to 6i being fixed relative to the first and second frame members 2 and 3 (not shown in Figure 7A and 7B), the rotatable bars 6a to 6i are locked in the guard configuration of Figure 1.

On approaching the cattle guard 1 and gaining access to the locking member 18 from a first side or first end of the cattle guard 1, a user may unlock the cattle guard by lowering the first locking member 18 from the position shown in Figure 7A, to the position shown in Figure 8A, while the second locking member 19, to which the user hasn't access due to it being at the opposite side/end of the cattle guard 1, remains in the raised position, as shown in Figure 8B. The user can then rotate one of the rotatable bars 6a to 6i, and thus rotate all the rotatable bars 6a to 6i, moving the first upper link member to the left in the direction of the arrow 29 shown in Figure 9A and thus causing the first lower link member 12 to move to the right, in the direction of arrow 30, as shown in Figure 9A. Thus, the second upper link member 13 and the second lower link member 14 on the opposite side 30 move to the position shown in Figure 9B, as again represented by arrows 29 and respectively. If the user should now cross the cattle guard 1, which will now resemble the cattle guard as shown in Figure 2, where the rotatable bars 6a to 6i are held in the position shown by gravity, as previously discussed, and then return to the same side/ end they may then lock the rotatable bars 6a to Si in the "guard" position, shown in Figure 1, by rotating the rotatable bars 6a to 6i to the position shown in Figures 8A and 8B and then raising the first locking member 18 to the position shown in Figure 7A, returning the cattle guard 1 back to its original locked guard configuration of Figures 7A and 7B.

If instead of returning to the first end or first side, the user alternatively proceeds across the cattle guard 1, while it is in the walk configuration shown in Figure 2, the user may then rotate the rotatable bars 6a to 6i, from the second end/side of the cattle guard 1, from the walk configuration of Figures 9A and 9B back to the guard position, as shown in Figure 10A. Here the user will have previously lowered the first locking member 18 to the position shown in Figure 10A (compare this with Figure 9A) and thus by lowering the second locking member 19 at the second end or second side, where the user is now located, to the position shown in Figure 10B, the first locking member 18 and the second locking member 19 will now lock the first lower link member 12 and second lower link member 14 in the positions shown in Figures 10A and 10B, by virtue of these two link members effectively being connected together via points 22 connecting them to common rotatable bars 6a to Si and thus again lock the rotatable bars 6a to Si in the guard position.

Once locked in the guard position shown in Figures 10A and 10B, if the user should again approach from the second side or second end they may then rotate the second locking member 19, to which they have access, from the position shown in Figure 10B to the position shown in Figure 7B, permitting the rotatable bars 6a to Si to be rotated to the walk position shown in Figures 9A and 9B. The user may then again subsequently rotate the rotatable bars 6a to Si back to the guard position of Figure 1 and lock them in that position by either raising the first locking member 18 from the position shown in Figure 10A to the position shown in Figure 7A or lowering the second locking member from the position shown in Figure 8B to the position shown in Figure 10B, depending which end or side they are at.

Referring backs to Figures 10A and 10B, this shows the position of the first locking member 18 and second locking member 19 when a user has exited the cattle guard 1 from the second end or second side, having locked it in place by operation of the second locking member 19 at the second end/side. If a second user should now approach the cattle guard 1 from the first end or first side, thus travelling in the same direction as the first user, they may raise the first locking member 18 from the position shown in Figure 10A to the position shown in Figure 7A and then rotate the rotatable bars 6a to 6i to the "walk" position shown in Figures 11A and 11B, for the second locking member 19 at the second end/ side being in the position shown in Figure 11B (compare this with Figure 103) will permit the rotatable bars 6a to 6i to be rotated to the "walk" position shown in Figures 11A and 113. The user may then leave the cattle guard 1 from the second end/side, rotate the bars 6a to 6i to the guard configuration and then lock them in place by raising the second lock member 19 from the position shown in Figure 10B to the position shown in Figure 11B.

It will be observed from Figures 9A, 9B, 11A and 11B that the bearing housing 24, when the rotatable bars 6a to 6i are load bearing (either in the walk configuration of Figure 63 or the walk configuration of Figure 6C) will engage with respective lower and upper profiled edges of upper and lower link members 11 to 14 which will prevent over rotation of the associated rotatable bar 6a to 6i.

The invention, as described above with reference to the illustrated embodiment, permits the cattle guard 1 to be approached from either the first end/first side or the second end/second side and be set either to the locked guard position of Figure 1 or to one of the walk positions as illustrated in Figure 2, by operation of the nearest locking member 18 or 19, irrespective of the position of the locking member 19 or 18 at the opposite end or opposite side, to which the user will not have access.

One embodiment of the present invention has been described by way of example only and it will be appreciated that many alternatives are possible which fall within the scope of the following claims. Particularly it should be noted that the locking members disclosed could be on the same side, but at opposite ends of the cattle guard and both operate on the some pair of upper and lower link members.

Claims (15)

1. Claims 1. A cattle guard comprising a frame having two opposed frame members and a plurality of parallel bars extending between the two opposed frame members, 5 wherein: each end of each bar is rotatably supported by a respective frame member so that each bar may rotate about a respective longitudinal axis of rotation of that bar; each bar has a substantially planner surface which may be located uppermost by rotation of the bar and a nonplanar surface which may be located uppermost by rotation of the bar; and wherein the cattle guard further comprises a linkage mechanism connected to each of the bars and arranged to rotate the bars together between a position where the planar surfaces of each bar are uppermost and substantially coplanar, making it easier to walk over the cattle guard, and a position where the nonplanar surfaces are uppermost, making it more difficult to walk over the cattle guard, the cattle guard further comprising a locking means for locking the bars in a position where the nonplanar surfaces are uppermost.
2. 2. A cattle guard as claimed in Claim 1 wherein: each bar is arranged to rotate about its axis of rotation between a first position, a second position and a third position intermediate the first and second positions; each bar has first and second planar surfaces joined at an apex, the apex defining the non-planar surface; in the first position the first planar surface of each bar is uppermost and substantially coplanar with the other first planar surfaces; in the second position the second planar surface of each bar is uppermost and substantially coplanar with the other first planar surfaces; and wherein in the third position the apex of each bar is uppermost.
3. 3. A cattle guard as claimed in Claim 2 wherein: the linkage mechanism comprises a first link member pivotally connected to each bar at a point above or below the axis of rotation of each bar and a second link member pivotally connected to each bar at a point above or below the axis of rotation of each bar; each link member is arranged to move substantially transversely relative to the axes of rotation of the bars such as to cause the bars to rotate between their first, second and third positions; the link members having a first position, where the bars are in their first positions, a second position, where the bars are in their second positions and a third position, intermediate the first and second positions, where the bars are in their third positions; the locking means being arranged to lock the link members in their third positions.
4. 4. A cattle guard as claimed in Claim 3 wherein the locking means comprises: a first locking member arranged to move between first and second positions and located at or toward a first end or a first side of the cattle guard; and a second locking member arranged to move between first and second positions and located at or toward a second end or second side of the cattle guard, remote from the first end or the first side of the cattle guard, and wherein: when in its first position the first locking member prevents the first link member moving to its first position but permits the second link member to move to its second position; when in its second position the first locking member prevents the second link member moving to its second position but permits the first link member to move to its first position; when in its first position the second locking member prevents the second link member moving to its first position but permits the first link member to move to its second position; and wherein when in its second position the second locking member prevents the first link member moving to its second position but permits the second link member to move to its first position, thus when the first and second locking members are both in their first positions, or are both in their second positions, the first and second link members and the bars are all held in their third positions.
5. 5. A cattle guard as claimed in Claim 4 wherein the two opposed frame members comprise a first frame member located to a first side of the cattle guard 10 and a second frame member located to a second side of the cattle guard, wherein: the first link member is an upper link member located on the first side of the cattle guard and pivotally connected to each bar at a point above the axis of rotation of each bar; the second link member is a lower link member located on the first side of the cattle guard and pivotally connected to each bar at a point below the axis of rotation of each bar; the first and second locking members are both located on the first side of the cattle guard, but at or towards opposite end of the cattle guard.
6. 6. A cattle guard as claimed in Claim 4 wherein the two opposed frame members comprise a first frame member located to a first side of the cattle guard and a second frame member located to a second side of the cattle guard, wherein: the first link member is an upper link member located on the first side of the cattle guard and pivotally connected to each bar at a point above the axis of rotation of each bar; the second link member is a lower link member located on the first side of the cattle guard and pivotally connected to each bar at a point below the axis of rotation of each bar; the first locking member is located on the first side of the cattle guard, the cattle guard further comprising: a third link member which is an upper link member located on the second side of the cattle guard and pivotally connected to each bar at a point above the axis of rotation of each bar; and a forth link member which is a lower link member located on the second side of the cattle guard and pivotally connected to each bar at a point below the axis of rotation of each bar, wherein: the second locking member is located on the second side of the cattle guard: when in its first position the second locking member prevents the second link member moving to its first position but permits the first link member to move to its second position by preventing the fourth link member moving to a first position while permitting the third first link member to move to a second position; and wherein when in its second position the second locking member prevents the first link member moving to its second position but permits the second link member to move to its first position by preventing the third link member moving to a second position while permitting the fourth link member to move to a first position.
7. 7. A cattle guard as claimed in claim 4, 5 or 6 wherein each locking member is arranged to be raised or lowered, or to pivot, to block the path of a selected one of the two link members with which it is associated.
8. 8. A cattle guard as claimed in any one of claims 4 to 7 further comprising means for preventing access to the first and second locking members, or for locking the first and second locking members in one position.
9. 9. A cattle guard as claimed in any preceding claim wherein each bar has at least one stop on at least one end arranged to limit rotation of the bar and to partially bear any weight placed on the bar.
10. 10. A cattle guard as claimed in any preceding claim wherein the axis of rotation of each bar is offset below a longitudinal centreline of each bar, when each bar has its non-planar surface uppermost, such that when the bar is rotated so that a planar surface is uppermost, downward pressure applied to the upper planar surface prevents the bar rotating to a position where the non-planar surface is uppermost.
11. 11. A cattle guard as claimed in any preceding claim wherein the locking means comprises first and second locking members at respective opposite sides, or respective opposite ends of the cattle guard, each locking member having a first position and a second position, wherein when the bars have their non-planner surfaces uppermost and are locked in position, moving either locking member from one of its positions to the other causes the bars to be released from the locked position, irrespective of the position of the other locking member and wherein, when the bars have their non-planner surfaces uppermost and are not locked in position, moving either locking member from one of its positions to the other causes the bars to be locked in position, irrespective of the position of the other locking member.
12. 12. A cattle guard as claimed in any preceding claim wherein the bars are arranged to be rotated by hand.
13. 13. A cattle guard as claimed in any preceding claim wherein each bar is in the form of a square tube, with two adjacent sides of the tube defining two planer surfaces and the intervening apex defining a non-planar surface.
14. 14. A cattle guard as claimed in any preceding claim wherein each bar is formed from glass reinforced plastic.
15. 15. A cattle guard as claimed in any proceeding claim dimensioned to fit between the rails of a railway line with the two opposed frame members aligned with the rails.