Ingulstad, Arnulf (Cappelens Vei 12, Oslo, N-1162, NO)
In most countries the public roads authorities have laid down special requirements with respect to the design and mounting of guard rails. In Europe (EEA), standardised requirements with regard to highway guard rails and the testing thereof have been drawn up. These requirements were adopted as Norwegian Standard NS-EN 1318-1 in November 1998.
Guard rails are split into classes. Which classes the public roads authorities choose to use depends upon along which roads they are to be mounted, what type of vehicles use the roads, the permitted speed limits on the roads and the geographical conditions along the roads.
The guard rails are approved by the public roads authorities in the respective countries based on standard full-scale collision tests at approved laboratories in Europe.
Today most of the countries in question throughout the world use a standardised, profiled steel strip or bar secured to a particular type of steel post having a so-called sigma profile, and where the posts are spaced apart at 2 and 4 metres.
In some countries, such as Canada and Norway, the posts used are chiefly wooden posts, which are essentially round in Norway, whilst in Canada they have a rectangular cross-section.
The primary purpose of a highway guard rail is to prevent personal injury by preventing vehicles from driving off the road.
However, there are a number of matters that must be taken into consideration.
In the event of an impact, the guard rail is to bring the car back on to the road with minimum damage to the car and minimum injury to the driver and passengers. This is achieved by the guard rail yielding slightly on collision so that the speed of the car is reduced, and then the car is guided back on to the road.
In the event of an impact, the guard rail must not give way so much that the car drives into the roadside ditch, down a slope or over a drop.
It is essential that the guard rail should not be pulled down towards the ground when the posts are bent, as this would cause the car to drive over the guard rail with catastrophic consequences.
The guard rail must not be so yieldingly elastic that it throws the vehicle too far out into the road after a collision with the danger of meeting traffic oncoming traffic.
Lastly, the guard rail must have a property and mode of action such that it gives a simultaneous speed reduction on buckling, friction with the guard rail bar and moderate bending of the posts so that the load (deceleration) for driver and passenger is not too great.
In the aforementioned CEN standards, limits are set which must be observed with respect to these various areas. Here, it is important to note that tests are not carried out and approval given for individual components of a guard rail, it is the finished, complete guard rail that is tested for collisions on a life-size scale and the result that is approved, if any, is the result of the interaction between all the parts included in the guard rail.
The problems it is endeavoured to obviate with the inventive subject are those outlined above, namely that wooden posts splinter and form extremely dangerous, sharp or pointed broken pieces which in the event of a collision may be flung around in the area of the collision, that bars and posts are not so rigid that they constitute a danger in themselves, that the guard rail is not pulled down to the ground when the posts are knocked down, thereby preventing it from being driven over, or that the guard rail is so elastic that it throws the car into the traffic and possibly against oncoming traffic.
At the same time, economic aspects associated with purchase and maintenance also have a certain importance as, of course, does the fact that the guard rail should be simple to mount and in given cases also simple to repair. An important aspect is service life before replacement must be planned.
The present invention thus relates to a highway guard rail assembly comprising hollow mounting posts of a suitable plastic material and a guard rail bar of metal extending
from post to post and attached to the posts, wherein the bar is fastened to the post by bolts and associated nuts, wherein the bolt runs through only one or both walls of the post, and this assembly is characterised in that the bolt hole in the bar is reinforced with a washer or the like between the nut (the head) and the bar whilst the bolt hole (holes) in the post walls have a diameter greater than the diameter of the bolt, but slightly smaller than the diameter of the bolt head (the nut), the bolt head (the nut) resting directly against the post wall.
The present invention thus describes a fastening system for the fastening between post and guard rail bar which makes it possible to achieve a collision progression which, as has been found in tests at an approved Swedish traffic laboratory, is considerably more favourable as regards most of the aforementioned requirements set in the CEN standards, now Norwegian Standard NS-EN 1319-1, than is achieved with conventional wooden or steel posts.
The present invention will be illustrated in more detail by means of the attached figures, wherein: -Figure 1 shows the fastening of a guard rail bar to a post in a preferred embodiment; and -Figure 2 shows the fastening of a guard rail bar to a post in an alternative embodiment.
In Figure 1 the guard rail bar 2 is secured to the post 1 by means of a bolt 3 which passes through the guard rail bar 2 and the nearest wall 5'of the post 1.
In the illustrated embodiment the bolt head 8 is on the road side of the bar 2 whilst the corresponding nut 4 is inside the hollow post.
Of course, the bolt may be inserted the other way around so that the head 8 is inside the post 1 and the nut 4 is on the outside.
An adjusting washer is placed between the head 8 (or the nut 4), whilst there is no such adjusting washing between the nut 4 (the head 8) and the wall 5'of the post 1.
On the contrary, the wall 1 in the area for the bolt is"weakened"in that the bolt hole 7 has a larger diameter than the bolt 3.
On the other hand, the hole 7 in the wall 5'must not be so great that the bolt 4 (the head 8) does not span across it to ensure that sufficient fastening under normal stresses is obtained.
Of course, other types of weakening are conceivable and a person versed in the art will clearly see such possibilities.
The advantages of this method of fastening will be discussed in more detail below In the embodiment shown in Figure 2, the bolt 3 runs through the whole post 1, that is to say, through the wall 5' (as in Figure 1) and also the wall 5". The same considerations also apply here as regards the dimensioning of the bolt hole 7 in relation to the nut 4 (the head 8). In this case too, an adjusting washer 6 is positioned as reinforcement between the head 8 (the nut 4) and the bar 2 and the mode of action is otherwise as described below.
The fact is that it has been found that plastic posts 1 in the event of a collision give way and are bent down to the ground under the car, but because the fastening as described above has been"weakened"and adjusted, the bar 2, owing to the design of the hole 7 (or a similar weakening) in the post, will be torn loose before the bar 1 is pulled down to the ground.
This means that the post 1 per se does not constitute an obstacle, it will be bent elastically under the car, but the bar 2 will act as a band which intercepts the car and leads it back to the carriageway.
The substantial capacity of the plastic material to absorb energy on deformation, its flexibility, the dimensioning of the plastic post 1 and not least the fastening of the guard rail bar 2 to the post 1, results in a highly favourable collision progression, substantially better than in the case of steel or wooden posts, which has recently been confirmed by full-scale laboratory tests, but which no-one was fully aware of previously.
This fastening system thus represents a considerable contribution to the enhancement of road traffic safety and not least to a reduction in damage and injury in the event of a collision against the guard rail
In addition, plastic posts are a very environmentally friendly product, are easy to maintain, have a very long service life and can be recycled, all of which are considerable advantages over the previously used posts of impregnated wood or galvanised metal.
It has been found that the said advantages are achieved with hollow plastic posts without any form of internal ribbed reinforcements or the like. It has also been found that hollow posts which are"run over"by a car will straighten up and in fact recover a considerable part of their original strength so that immediately after a collision they will, if nothing else, function as an optical obstacle for subsequent cars, can serve as a point of attachment for warning tapes which may be hung up, and serve as a new point of attachment for a preliminary repair in those cases where a more extensive repair must be delayed for various reasons.
Another advantage when using slightly elastic posts of this kind is that they yield a little when snow ploughs, often in bends, are pressed against the guard rail bar when clearing the roads in the winter. Thus, the damage often caused to guard rails when severe weather conditions prevail is avoided.
As mentioned above, plastic posts have a certain degree of flexibility and will return to their original shape after the snow plough has driven past.