This invention relates to vehicle crash barriers which are particularly although not exclusively for use alongside highways.

Vehicle crash barriers are commonly disposed alongside high speed roads. They may serve a variety of purposes including, in particular, keeping on the roadway a vehicle which, when out of control, strikes the barrier at an acute angle. It is desirable that, in performing this function, some element of impact load absorbtion takes place so that the vehicle is not too seriously damaged and its driver has some chance of steering it to a safe stop.

Both for the reason set out above and also because it would create an unacceptable "tunnel-like" road, it is not desirable to line high speed roads with massive walls of concrete or other material. Thus many proposals have been made for metal crash barriers which may be "stand-alone" or disposed above a comparatively low concrete wall.

A particular problem exists where a road bridge crosses another road or the track of a railway. In these circumstances it becomes even more desirable to prevent a vehicle passing through or over a crash barrier.

Usually, vehicle crash barriers of metal construction comprise one or more rails extending parallel with the road surface and supported, on their side away from the road, on vertical posts firmly anchored on top of a wall

or in the ground. It is desirable that the rails do not distort upon impact sufficiently to create a "pocket" between one support post and the next so that the vehicle concerned strikes that next post head on.

It is also desirable, particularly on bridges over railway tracks that a sight barrier is provided to discourage pedestrians from straying on to the bridge. This is frequently a cladding sheet that serves no structural purpose. Any such cladding sheet or other sight barrier structure is preferably designed both to improve the visual appearance of the crash barrier to a driver travelling along the road at high speed in the sense to reduce a "tunnel-like" impression referred to above and to contribute to the effectiveness of the crash barrier.

When the crash barrier is of metal it is well known to construct it of aluminium alloy. There is no problem of rusting; all the constructional elements used can be extruded and an aluminium alloy crash barrier can readily be as strong as a steel one. However aluminium alloy items are light, easy to handle and valuable. It is desirable therefore that such crash barriers should not be capable of easy disassembly.

According to one aspect of the present invention there is provided a vehicle crash barrier of metal construction and comprising at least one rail, extending generally parallel with a road surface, and mounted on spaced-apart generally vertical supports located on the side of the rail remote from the road characterised in that the rail is hollow and is divided into at least two closed compartments by a web extending between the supports and a part of the surface

of the rail remote therefrom so as to transmit an impact load on the surface directly to the supports.

Preferably the mounting between the rail and the supports is so shaped that part of any impact load on the rail having a downward component is transmitted vertically down the supports.

A sight barrier in the form of sheet-like cladding may extend from the rail to a location generally level with the base of the supports. The upper end of the sight barrier is preferably located inwardly of the outermost part of the rail or rails and the lower end of the sight barrier preferably has a part lying sufficiently close to fastenings for the supports as to prevent access thereto and includes a section welded or riveted in place so that disassembly of the crash barrier cannot be carried out quickly and simply.

The crash barrier is conveniently mounted on top of a concrete wall which may be of the order of 900 mm high with the barrier being of the order of 600 mm high.

An embodiment of the present invention will now be described by way of example with reference to the single figure of the accompanying drawing which shows diagrammatically in end elevation and partly in section a vehicle crash barrier of aluminium alloy.

Referring to the drawing an aluminium alloy vehicle crash barrier indicated generally at 1 is mounted on a concrete wall 2. The barrier 'comprises a series of spaced apart supports 3 linked together by a rail 4 and a sight barrier indicated at 5. The wall 2 is precast in inter¬ locking sections with buttresses 6 at intervals on which the supports 3 are mounted.

The supports 3 are formed from an extruded -ϋ- shaped extrusion cut diagonally and welded together to constitute a hollow post having an inclined rear wall 7 extending between a lower end 8 and a smaller upper end 9. The lower end 8 is welded to a base plate 10 and a cap indicated at 11 covers the upper end 9. As shown in the drawing the front face 12 of the support is vertical. The construction of the support 3 is conventional and will not be further described or illustrated.

The base plate 10 extends outwardly of the lower end 8 and is secured to the upper surface 13 of the buttress 6 by bolts, two of which are shown at 14 and 15.

The cap 11 has a top plate 16 downwardly inclined towards the back plate 7 and a generally vertical front wall 17 having an upper part 18 and an outwardly displaced lower part 19 joined by a step 20. The front face 12 of the support is cut away at its upper end to provide a shoulder 21 on which the step 20 is supported. The uppermost end of the top plate 16 and the parts 18 and 19 extend outwardly of the support on each side thereof and the plate 16 and parts 18 and 19 are all welded to the support 3.

The rail 4 is extruded and has a back wall 22 with upper and lower parts 23 and 24 separated by a step 25. The remaining periphery 26 of the rail is externally circular in section but has increased wall thickness approximately between the lines A and B. A web 27 extending approximately diametrally of the rail, and being continuous with the step 25, divides the rail into two discrete and (apart from its ends) closed chambers 28 and

29. The parts 23 and 24 are thickened at 30 and 31 and formed with appropriately spaced threaded apertures so that when the rail is mounted on the front wall 17 bolts 32 pass through holes in the outward extensions of the parts 18 and 19. It will be noticed that the step 25 rests on the step 20 and the outer face of the part 23 is aligned with the front face 12.

The sight barrier 5 has upper, lower and intermediate parts 33, 34 and 35. The part 33 is extruded with a flat base 36 to lie along the front face 12 of each support and has an outwardly turned upper end 37 with a thickened part 38 shaped to be in close contact with the rail 4 and is riveted thereto at intervals along its length. At its lower end the base is turned outwardly at about 30* and has a lip 39.

The lower part 34 is extruded and has a base 40 with an upwardly turned inner end 41 and an inclined outer end 42 the upper part 43 of which is lipped to be aligned with the lips 39 and the lower part 44 of which terminates generally at the level of the surface 13 of the buttress 6. The inner end 41 is bolted at 45 to the upturned arms 46 of brackets such as 47 the other arms 48 of which are engaged by the bolts 15. The end 41 lies in contact with the outer face 12 and the base 40 extends closely over the bolts 15. The intermediate part 35 is of sheet-like material and is riveted to the lips 39 and 43 so that access to the bolts 15 cannot be gained without cutting away part of the sight barrier 5.

Adjoining extruded rails 4 are joined together by identical bridging extrusions 49 indicated in chain lines in the chambers 28 and 29 and are held by bolts (not

shown) passing through the parts 23 and 24. Adjoining parts of the sight barrier 5 are joined by brackets 50 fastened thereto and also shown in chain lines.

In practice the respective heights of the wall 2 and the barrier 1 may be about 900 mm and 600 mm. It has been found that the arrangement described can withstand the impact of a 30 ton tanker striking the rail 4 at a speed of 40 mph and an angle of 20*. In these circumstances the tanker is diverted back into the roadway.

The web 27 is important insofar as, upon impact on the rail 4 the load is transferred to the support. It has also been found that the division of the rail 4 into two separate chambers enhances the resistance of the rail to tearing. If the wall of one of the chambers is torn upon an impact the other chamber resists further collapse of the rail.

If a crashing vehicle tilts and engages the rail 4 above the web 27 the stepped mounting between the rail and the support transmits part of the impact load vertically down the support. If desired the rail could have a further web (not shown) dividing the chamber 28 so as to facilitate transmission of such angled impact load.

The arrangement of the sight barrier 5 increases the difficulty of dismantling and stealing a length of the barrier; makes a small contribution to impact absorption because of its contact with the front face 12 and breaks up the motorists sight line.