Guardrail systems are part of road safety schemes and fall within the category of vehicle restraint or road safety barriers. These restraint barriers act to prevent straying vehicles from leaving the safe drive areas, colliding with unforgiving hazards next to the road or moving into a potentially fatal situation such as over the side of a cliff, over the side of a highway bridge onto the passing vehicles below, or into a water source.
Given the protective functions of the barriers, it is imperative that the systems be able to stop, prevent breakthrough or to redirect colliding vehicles, or a combination of the above. Various types of road barriers are installed, based on factors such as:
- Location of the hazard
- Road surface available
- Surface available next to the road
- Whether for temporary or permanent application
- Average speed of travel on the particular road
- Types of vehicles that use the road
- Whether pedestrians and cyclists use the section next to the road or only motorised vehicles
- Length of the section where it must be installed
- Maintenance requirements of the particular barrier
- Ground clearance of the vehicles that use the road
Guardrails Are Permanent Safety Barrier Systems
The W-beam guardrails, of which Armco Superlite is a leading supplier in South Africa, are permanent barriers, unlike the water-filled barriers often seen at road construction sites.
Semi-Rigid Characteristics
Road safety barriers can be grouped according to the rigid nature of the systems. A concrete median or side highway barrier is extremely rigid. It thus has little to no kinetic energy absorption power and does not distribute the kinetic force along the entire system. This type of barrier has stopping power. However, the concrete barrier still operates as an interlocked system, making this type of road barrier extremely strong.
Concrete barriers are meant to prevent breakthrough and thereby stop vehicles from going over the barriers into oncoming traffic. These types do offer some redirection capacity because the barriers are fitted with a slide slope at the bottom.
If a vehicle collides at an angle from the side, the wheels go onto the slope and the design makes it possible to redirect the vehicle into the original path. The friction caused by the steel of the vehicle’s body against the concrete wall helps to slow the vehicle down.
As opposed to the rigid concrete barriers, W-beam guardrail systems are semi-rigid in the sense that the systems prevent breakthrough, but have considerable kinetic energy absorption capacity.
Upon collision with a guardrail, the entire barrier system works together to absorb and distribute the impact energy. This makes it possible to reduce the force of impact on the vehicle occupants.
The W-beam guardrail systems consist of steel panels attached to wood or steel posts. The posts are planted in the soil. The systems come with end-terminals or, where relevant, the end sections are buried in the soil. Delineators are attached to the W-beam panels to make the panels highly visible in low-light and night-drive conditions. As a supplier of guardrails and road safety products in South Africa, Armco Superlite offers D and V shaped delineators. The D shaped ones are required by the Department of Transport.
The W-beam panels, as the name suggests, have W-shape designs along the entire length of the panels. The panels are stronger than would have been the case if they did not have the corrugated “W” shape. These types of guardrails are more rigid than the wire-rope systems of which Armco Superlite is also a supplier.
The wire-rope barriers absorb more kinetic energy than the W-beam systems, but don’t have the same redirection power.
Redirection Power
Road safety barriers are also grouped according to their redirection capacity. W-beam systems have reasonable redirection capacity as the force of impact is taken across the entire system, but the barrier can give way a bit. If a vehicle hits the barrier at a side angle as opposed to head-on, the vehicle is redirected to its original path (depending on the speed of travel and ground clearance). This characteristic is what makes the guardrail systems suitable for placement on U-bends, at the side of mountain passes, and adjacent to roads.
If there is enough space next to the road to allow for a vehicle to return to the original path after corrective steps have been taken without a high risk of the vehicle hitting a hazard, going down a ditch, over a cliff side, into a water source or into oncoming traffic, it is always better not to install a barrier. However, where leaving the road even by two metres only can cause a potentially fatal incident, then it is better to install a road barrier.
The question is whether to install a rigid, semi-rigid or flexible type? The specific road conditions and hazards must be considered. If there is space for redirection then the W-beam guardrail may be the best option, and if there is space for absorption of the impact energy, the wire-rope system can work well. If the road surface is limited, but protection of pedestrians or cyclists in an adjacent path is needed, then the wire-rope system may be appropriate. However, if there is sufficient space behind the barrier, more protection can be afforded to the pedestrians or cyclists with the W-beam type.
It is imperative for the road engineers to consider the safety aspects of each: redirection capacity, stopping power, and maintenance needs. W-beam guardrail systems are exceptionally durable and require very little maintenance, even after suffering side impact. With heavy impact, one or more panels and posts may need replacement, but these types of guardrail systems can also handle relatively high-speed impact.
The end terminal is important to prevent the panel end from penetrating the body of the vehicle upon head-on collision with the barrier end.
Importance of Quality
Regardless of the types of guardrail systems, quality and durability are essential. Roadside maintenance holds a risk for the road users and the workers. It is essential for the barrier to be sturdy, able to withstand light impact without having to be replaced, and able to withstand rain, wind, and sun for a long time. Galvanisation makes the W-beam panels corrosion resistant. With such, it is not necessary to coat the beams every few years with protective paint. This implies a reduced need for maintenance, which in turn reduces risk to road users.
To ensure superior quality guardrail systems are installed, it is best to purchase them from a local and trusted supplier of road safety products. Armco Superlite has an international and national footprint. With years of experience and a track-record of manufacturing road safety and galvanised products according to strict international and SABS standards, the firm has gained a reputation for superior quality products.