The main purpose of a highway guardrail along the highway is to form a safety barrier to help protect a motorist who has drifted off the road.
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If a car is running off the road for one reason or another, the best thing that can happen is for that car to come to rest unimpeded.
Sometimes, however, that is not possible and that is where guardrails come in.
In certain places on any given stretch of road, the roadway might have steep embankments or side-slopes next to it, or even be lined with trees.
Utility poles, bridge piers and retaining walls are other obstacles. In these cases, striking a guardrail would be greatly preferable to striking the obstacles, so guardrails are usually installed.
They lessen the severity of a potential crash and make the roads safer.
The guardrail can act in a myriad of ways from deflecting a vehicle back onto the road, slowing it down or stopping it, or in some cases just slowing it down enough and allowing it to proceed past the guardrail.
Guardrails are not a 100% failsafe, but they do help.
Obviously the size of the vehicle and the speed with which it hits the highway guardrail plays a part in how effective the guardrail is in slowing a vehicle.
Before guardrails are installed, engineers weigh all the potential factors to make sure that the placement works as well as possible in all conditions.
The guardrail itself functions as an entire system rather than just stand-alone pieces. Each piece serves a different purpose as part of the whole. Everything from the posts that are driven into the ground to the way the guardrail connects to the post is important and plays a part.
The end terminal and the anchoring system at the end terminal is just as important. But overall, the highway guardrail basically consists of two key parts; the guardrail face and the end terminal.
A guardrail system is always put through performance tests before it is actually installed along a roadway. The performance of the system is assessed through crash tests that are done in a controlled environment. You can click here to see more about Highway Guardrail Performance direct from the Federal Highway Administration
Safety professionals use certain criteria to determine if the system meets standards.
The guardrail face test is used to determine if a car is directed back onto a roadway when it meets the rail.
The end treatment tests are then conducted by having a vehicle strike the rail dead-on and also at an angle. This will determine if the system is properly absorbing energy from a vehicle.
For head-on impacts, the end treatment should absorb most of the energy so that the guardrail can gate or extrude, and the vehicle can pass through.
This will slow the vehicle down as it passes behind the guardrail, allowing it to come to rest with minimal damage.
The tests used to test a guardrail system are usually conducted at about 60 MPH, so it is important to understand that if a vehicle hits the guardrail at higher speeds, the system may not operate properly.
Very high speeds are especially troubling because guardrail systems are simply not meant to accommodate vehicles traveling far above posted speed limits.
The faster the vehicle is going when it strikes the guardrail, the more damage might occur because the energy demonstrated is so much more.
Even a guardrail system that is working at peak performance can only absorb so much energy.
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A highway guardrail is designed to improve road safety. With this as the main purpose, the barrier must also be designed to be safe. Although it cannot prevent accidents altogether and there is no guarantee that it will save lives in every incident, if installed correctly and at the right location, it can help to prevent accidents, reduce the risk of fatalities and can help reduce the severity of injuries.
But, if a guardrail is installed with the purpose of improving road safety, why is there no guarantee that it would stop a vehicle from going down a ravine or for a vehicle’s occupants not to be severely injured upon a vehicle collision with the guardrail?
As with any other road safety product, it is designed with the purpose of improving the safety of a particular stretch of road. However, also as with any other road safety device, only the performance of the barrier upon impact at a particular speed by a vehicle with a particular height clearance, can be determined. But with numerous factors affecting a specific situation, it is not possible to determine which factors will affect the particular situation. Given the countless possibilities, determining with certainty how the barrier will perform in every given situation is challenging, if not near impossible. A slight change in the angle of impact, speed, vehicle ground clearance and the reaction of the driver or another vehicle involved in the incident can affect the outcome.
The barrier serves several purposes, among which is to keep the vehicle in an upright position upon side-impact with the guardrail. This is possible because of the slight deflection capability of the barrier while it is just high enough to prevent the colliding vehicle from going over or from becoming airborne. This is important to prevent roll-over and limit the risk of fatalities.
In many instances, the risk against which the barrier protects is more dangerous than the obstacle the barrier presents. These types of barriers are installed when there isn’t sufficient space for a straying vehicle to return to its original safe travel path, or to come to a controlled stop before hitting an unforgiving object. The barrier itself is far more forgiving as it gives way a bit, takes the impact energy and distributes it along the entire length of the system, away from the vehicle and its occupants and prevents the vehicle from hitting the object, such as a wall or cliff wall. Every bit of impact energy absorbed and taken from the vehicle means less impact on the vehicle’s occupants.
Also, considering that if a vehicle were to go down a cliff or ravine, it would mean several impact moments, possible rollover, excessive speed acceleration and an uncontrolled stop against a solid object, and stopping the vehicle from going over, makes the guardrail safer than the risk against which it protects.
Should a vehicle stray from the road without a barrier in place and land in a water source, the risk of drowning is imminent. The guardrail, even if it does cause some damage to the vehicle upon impact from the collision, stops a potentially fatal situation from occurring. This makes it safer than not having such a barrier in place.
As mentioned earlier, the barrier is tested for specific performance. This is done according to strict standards. Each component forming part of the barrier meets quality standards. Therefore, the road user has the assurance that the product meets safety, performance and quality standards.
From the fasteners to the panels and even the posts, can be hot-dip galvanised to protect against corrosion. This is not only important for the longevity of the product and the subsequent lower cost of ownership during the lifespan of the barrier, but it is also essential to ensure product integrity. A rusted piece of steel loses its strength and is a hazardous object. Road users have the assurance that the zinc coating used in galvanisation is at a particular thickness and has completely bonded with the underlying steel. If any part of the surface should be scratched, the zinc offers itself, ensuring the steel doesn’t lose its integrity.
If wooden posts are used, then the posts are made from specifically treated timber to protect against rotting, cracking and splitting. The post’s strength, appropriate height and integrity characteristics are important as steel panels are attached to the posts. Should the posts be compromised in any way then the strength and safety of the barrier would be negatively affected.
The steel panels can be curved considerably. With superb structural strength and adequate flexibility, the steel does not easily break upon impact. Also, end terminals are installed to prevent vehicle body or windscreen penetration from a head-on impact with the end of the guardrail. In many instances, the end of the steel from the last beam in the barrier is buried. This also serves to prevent vehicle body penetration from a head-on collision with the end of the barrier.
As one of the leading manufacturers of road safety products in South Africa, Armco Superlite produces premium quality products, which meet strict international standards. A closer look at the Armco W-beam guardrails reveals why these can be considered to be safer than many other types of barriers.
The steel panels have a W-shape across their vertical profile. This type of corrugation gives the beams extra strength to handle impact and maintain integrity. The steel panels are made in lengths of 3,81 m and 4 m, although special lengths are available upon request. Several individual sections make up the entire length of the barrier. Because individual sections are attached to the posts, instead of one solid section, should a section be damaged, then only that particular section needs to be repaired or replaced. Each section can be curved to fit the required radius (from 3 to 45 m). This makes them suitable for installation on extremely curved road sections, as often found on mountain passes, and multi-level parking garages.
The steel panels are manufactured to meet the requirements of SANS 1350 and are available in hot-dip galvanised steel according to the requirements of SANS 121 / ISO 1461. Clients can also order non-coated panels. In the latter case, protective paint should be applied to ensure longevity and protection against corrosion.
The end-wing terminals or protection are available in the bullnose or standard end designs.
Posts
As mentioned earlier, the panels are attached to posts, which can be buried in the soil or attached to the surface with special bolts as would be the case with a multi-level parking garage. The standard wooden posts measure 1800 mm in length with a diameter of 150 mm to 175 mm. The tops are bevelled or domed, according to client requirements. Each post is creosoted to protect the wood and conforms to the requirements of SANS 457.
Deflectors
To make the barrier highly visible in low-light and night driving conditions, deflectors are fitted onto the steel beams. Armco supplies the D-shape types as required by the Department of Transport, as well as the V-shape types. The products have a long lifespan as they are manufactured from Chromadek, which doesn’t rust or develop mould. The retro-reflective material meets the requirements of CKS 191. The client specifies the particular colour for the deflectors. Installation is made easier with the slotted base design.
View and download more information on the Armco W-beam highway barrier.
In Summary
Although any type of barrier is an obstacle, making it a hazard on its own, the many benefits of having a high-integrity guardrail in place outweigh the risks posed by having a barrier next to the road. Urban planners, surveying experts and civil engineers work together in road design and choosing installation locations. The barriers are only installed where essential to protect road users against collisions with hazardous objects, and to prevent vehicles from going down ravines and redirect them back to the safety of their original travel path. The barriers are designed with safety in mind. As such, each component is made according to strict safety, manufacturing, durability and quality requirements.
The structural strength and functionality, ease of installation and the high visibility, as well as the performance of these guardrails, make them essential road safety devices to help reduce incidents and potentially, the severity of accidents and the risk of fatalities.
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