This invention relates to road safety fences and to posts therefor, and in particular but not exclusively to road safety fences of the type that employ wire ropes or cables.

Road safety fences that use wire ropes or cables as a vehicle restraining member comprise a series of spaced apart posts that are secured in or on the ground adjacent the roadway for supporting the wire ropes or cables. The fences typically have one or more wire ropes extending along the fence and may be woven between the posts. Road safety fence posts and fences that are known in the art restrain impacting vehicles with the aim of preventing them traversing the fence and travelling into oncoming traffic. When the vehicle impacts the fence, the wire ropes or cables break free from the fence in the vicinity of the impact and deflect such as to restrain the vehicle and absorb impact energy. A road safety fence of this type is described in EP 0 369 659.

A disadvantage with these known road safety fences is that the ropes can deflect to such as extent that an impacting vehicle can still enter or impinge into an adjacent carriageway of oncoming traffic even if it does not traverse the fence. A further disadvantage is that a long length of fence is destroyed or collapses on account of the impact leading to significant reinstatement costs. It is therefore an aim of the present invention to alleviate these disadvantages.

According to a first aspect of the present invention, there is provided a road safety fence post for supporting at least one wire rope adjacent a roadway, wherein the post has a slot at one end thereof and is provided with a restraint for resisting exit of the wire rope from the slot, when the post is part of a road safety fence and a vehicle impacts the road safety fence. In addition, or as an alternative to the slot being provided at one end of the post, one or more slots may be provided in a different position on the post (e.g. on the side of the post). The "slot" may be any means suitable for receiving the wire rope, e.g. a notch, depression, dimple or aperture and may or may not be integrally formed in or with the post. The "wire rope" may be a rope, cable, strand or similar. Any number (one or more) of ropes may be supported on the post, one or more of which are restrained in this way. In a preferred embodiment, the restraint may be a yieldable restraint that yields to allow release of the rope when the rope exerts thereon a force exceeding a predetermined threshold. The yieldable restraint may comprise one or more of a frangible or breakaway component, a deformable member, a moveable component that is resiliently located and/or biased with respect to the post or other releasable restraining device.

In a preferred embodiment, the restraint may be a yieldable restraint comprising a narrowing of the slot relative to the thickness of the rope, said narrowing being such as to deform or yield to allow escape of the wire rope when an upward force exerted by the rope exceeds a predetermined amount. The narrowing may be positioned in the vicinity of the open end of the slot and may optionally comprise a tab formed integrally with the post on one or both sides thereof. The yieldable restraint may be a frangible member bridging the open end of the slot such as to break when a predetermined upward force exerted by the rope on the frangible pin is exceeded, thereby allowing the rope to exit the slot. The frangible member may be formed of a metallic, plastics, or polymeric material. Alternatively, the yieldable restraint may be a cap in interlocking engagement with the top of the post which yields when a predetermined upward force exerted by the rope on the cap is exceeded, thereby allowing the rope to exit the slot.

The cap is formed of a polymeric material. Alternatively, the restraint may comprise a profiled slot, wires, cable ties, tabs, bolts, pins, hooks or other form of fastening/restraining device.

According to the first aspect of the present invention, there is also provided a method of forming a road safety fence comprising placing a plurality of posts, spaced apart from one another in a row alongside a road, wherein each post has a receiving means for receiving a wire rope or cable, laying a wire rope or cable in the receiving means, and at least partially closing at least some of the receiving means by a yieldable restraint operative to resist exit of the rope or cable therefrom when subjected to a force that is less than a predetermined value.

According to the first aspect of the present invention there is further provided a method of forming a road safety fence comprising placing a plurality of posts, spaced apart from one another in a row alongside a road, wherein each post has an open- ended slot at its end remote from the ground, laying a wire rope or cable in the slots, and at least partially closing at least some of the open-ended slots by a yieldable restraint operative to resist exit of the rope or cable from the slots when subjected to an upward force that is less than a predetermined value. In a preferred method embodying the present invention, the step of closing comprises moving a tab formed in each post from an open position that allows entry of the wire rope or cable into the slot, to a closed position.

According to the first aspect of the present invention, there is yet further provided a road safety fence post comprising a slot formed in and extending from one end thereof for accommodating a wire rope or cable having a thickness, wherein the slot comprises a tab extending from one or both sides thereof to define a slot opening that is narrower than the thickness of the rope whereby the tab(s) serves to restrain the rope in the slot and to yield so as to permit escape of the wire rope or cable from the slot when the wire rope or cable is urged against the tab(s) by a force that exceeds a predetermined value. The tab(s) may be frangible.

According to another aspect of the present invention, a road safety fence comprises posts as defined above with reference to said first aspect.

Embodiments of the first aspect of the present invention are advantageous in that the yieldable restraint delays exit of the rope from the top slot on vehicle impact. The consequent deflection of the rope is reduced thereby helping to reduce the ingress of the vehicle into the adjacent carriageway. A further advantage is that the effective strength of the fence is increased on vehicle impact as more vehicle energy is absorbed by the fence before the rope exits the top slot of the posts. This helps to avoid premature collapse of the fence. A still further advantage is that a shorter length of the fence collapses for a given impact event, relative to prior art fences, resulting in reduced reinstatement costs.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a part elevation of road safety fence in accordance with an embodiment of the first aspect of the present invention; Figure 2 is an end view of the fence of figure 1 ;

Figure 3 is a part-sectional view of the yieldable restraint of figures 1 and 2;

Figure 4 shows a post having an alternative yieldable restraint; and

Figure 5 shows a post with an alternative arrangement of yieldable restraints.

Figures 1 and 2 show a road safety fence post 1 supported on the ground 3 adjacent a roadway (not shown). The post 1 may be of 'S', Z' or another cross- section. The post 1 supports three wire ropes or cables 5, 7, 9 by way of rope location pegs 5a, 7a and 9a. The ropes are woven between successive posts in a similar manner to that described in the aforementioned patent specification EP 0 369 659. A fourth rope 11 is supported in a slot 13 that extends from the top 15 of the post 1. It will, however, be appreciated that any number (one or more) of ropes may be supported by the post 1 in a variety of configurations differing from that shown in Figure 1. One or more ropes may be supported in one or more slots at the top 15 of the post 1 and/or one or more ropes may be supported in one or more slots or by one or more location pegs along one or more of the sides of the post 1.

As can be seen in Figure 3, a polymeric restraining cap 17 is secured to the top end 15 of the post 1 by means of a metallic or polymeric stud 19 which is received through location holes 21a and 21b provided in the post. The stud 19 is fixed in place by nuts 23a, 23b. The polymeric stud 19 may be of a plastics material or a glass reinforced polymer with breaking characteristics that allow the stud to yield under a predetermined upward force exerted by the rope.

The restraining cap 17 and stud 19 serve to restrain exit of the rope 11 from the slot 13 when subjected to an upward force as a vehicle impacts the fence. The stud 19 is configured to break when the upward force exceeds a predetermined amount so that on initial vehicle impact, the rope 11 is retained in the slots of the fence posts for longer. The stud 19 may be provided with a frangible portion 25, in the form of a cut- away or scored surface portion that weakens the stud 19 so that it yields under a lower upward force. The restraining cap 17 may be fitted over the nuts 23a, 23b or eliminated altogether.

In an alternative embodiment illustrated in Figure 4, a narrowing 27 of the slot 13 may be provided at the open end 15 thereof. This narrowing may take the form of a tab 29 formed integrally with the post 1 , being stamped from the same steel sheet as the post itself. The thickness of the rope 11 is greater that the width of the narrowing 27 so that when an upward force on the rope 11 exceeds a predetermined level, the tab 29 deforms to allow exit of the rope 11 from the slot. A line of weakness 31 may be provided at the junction between the tab 29 and the remainder of the post 1 to facilitate breaking off of the tab 29 from the post under the upward force of the rope 11. This post is provided with notches or cut-outs for supporting a wire rope (not shown) along the fence. The yield strength of the restraint is less than the post yield in terms of the force required to pull the post out of the ground. Figure 4 also shows an alternative arrangement for support of the ropes 5, 7, 9 running alongside the posts 1. Here, rope receiving means 33 in the form of a notch or slots are provided in or on the post 1.

In Figure 5, each receiving means 33 is formed integrally in or with the post, or may be a separate component attached to the post. The receiving means 33 may comprise e.g. a slot, notch, groove, depression, dimple or other device for receiving / supporting the rope 5, 7, 9. A yieldable restraint 32 may be provided at one or more of the receiving means 33, and may take the form of any of the yieldable restraints 17, 19, 27, 29 described above. In the event of an impact on the fence, the yieldable restraint 32 will initially resist egress of the rope or ropes 5, 7, 9 from the slots 33, until a predetermined threshold is reached. In this case, the force of the ropes 5, 7, 9 on the restraint 32 could be in any direction against the restraint 32.

In the embodiments of Figures 1 , 2 and 3, the yieldable restraint 17, 19, 27, 29 is provided in a slot provided in the upper end 15 of the post 1. The restraint 17, 19, 27, 29 thus serves to resist vertical forces imparted to the rope 11 in the event of an impact and to yield when the force exceeds a predetermined threshold. In the embodiment of Figure 5, the ropes 5, 7, 9 extending alongside the post are supported in receiving means 33, rather than by post location pegs 5a, 7a, 9a, as shown in Figure 5.

Each of the yieldable restraints utilised in resisting egress of the ropes in the top and/or side slots may take the form of any one or more of the above described embodiments. It will be appreciated that the restraints can be utilised on one, some or all posts in a safety fence, and that the same or different restraints can be used in any combination on each post or along the length of the fence for any or all ropes supported thereby.

The yieldable restraint serves to hold the wire rope or cable in the post slots for longer on vehicle impact. It also helps to reduce rope deflection and prevents the rope jumping out of the post slots too far ahead of the vehicle impact area.