Guardrail: The Highway Barrier that Improves Road Safety
The W-beam highway guardrail is a road safety device that improves the overall safety profile of a stretch of road. As the name suggests, it is a barrier. As such, it is intended to prevent breakthroughs and to safeguard motorists from leaving the safe travel path or venturing into a hazardous situation.
As a semi-rigid system, it can give way to a certain extent to absorb the kinetic impact energy from a colliding vehicle whereas a rigid system doesn’t give way and is intended to prevent breakthrough rather than protect against impact force.
Where can you expect to see guardrail installations?
The W-beam steel guardrail system’s design allows for the curving of steel panels or beams. This design feature ensures flexibility when it comes to installation applications. You can expect to see the W-beam guardrails at the following locations:
- On the grass median island between two opposite flowing highways.
- At the on- and off-ramp sections of highways.
- On bridges crossing highways, cliffs, and other water sources.
- Curved sections on a road.
- At overpasses and over culverts.
- On mountain passes.
- Urban areas – separating a walk area from the road.
- Ramps between a parking lot’s levels.
- Next to roads at sections passing extreme slopes and cliffs.
- Next to roads between the road and unforgiving rigid objects including trees, streetlights and buildings.
- Next to roads between motorways and cycle paths.
What are the main components of W-beam steel guardrails?
These road safety barriers consist of several components that work together to create a safe barrier. The components include the W-beams, timber or steel posts to which the steel beams attach, the attachment components, delineators and end terminals.
These are made to meet SANS 1350 requirements, with the beams available as uncoated or hot dip galvanised according to SANS 121 / ISO 1461. The hot-dip galvanisation ensures that all parts of the steel are covered for optimal corrosion protection. The beams are available in lengths of 3,81 metres and 4 metres while special lengths can be manufactured upon request.
The beam ends can be buried or fitted with end treatments to prevent the end section from penetrating a vehicle’s body upon head-on impact. End protection is available in both bullnose and standard end-wing designs.
To add maximum visibility to the guardrails, delineators are fitted. These are coated with reflective paint to show motorists the exact location of the barrier at night and during low-light conditions. The delineators are available in V- and D-shapes. The units come with a slotted base design for easy installation.
The beams are attached to the posts. These posts are attached to the drive surface with special bolts in the instance of parking lots or buried in the soil in the instance of timber posts. Specific installation requirements must be met and is best discussed with the manufacturing company. The timber posts are available in bevel and domed top finishes. Each timber post is creosoted to ensure optimal protection and durability. The posts meet the requirements of SANS 457. These are also pre-drilled for faster installation. Each one measures 1800 mm in height with a diameter of 150 – 175 mm.
See more information on the W-beam barrier here.
How does the guardrail work?
The entire system works as a unit to absorb the kinetic impact energy from a colliding vehicle. This impact energy is then distributed through the system, thereby spreading it out, effectively reducing the impact of the collision force on the vehicle and its occupants. This characteristic also helps to reduce the risk of breaking through the barrier.
The system is also designed to reduce the risk of roll-over and for a vehicle to become airborne upon impact. However, it is not possible to guarantee that a vehicle with high ground clearance driving at a fast speed will not be able to pass through or over the barrier.
How does the W-beam guardrail improve road safety?
It is a barrier, which means it protects against vehicles leaving the safe travel path to venture into a hazardous object like a tree. As a barrier, it also prevents vehicles from going down steep slopes, mountainsides or cliffs.
Where placed in the median between two opposite flowing highway lanes, it acts to prevent motorists from making U-turns into the oncoming traffic of the opposite direction lanes. It also prevents accidents from one lane spilling over to another opposite direction lane.
With the beams highly visible at night, motorists can clearly see the edge of the road. This helps to show them how the road curves, enabling them to slow down or take corrective action on steep curves to stay in the safe drive path. With the edge clearly visible at night, motorists can have more confidence to stay on the left side of the road rather than keeping to the median white line in an effort to ensure they stay on the drive path. Median clustering increases the risk of head-on collisions. By reducing the instances of median clustering, the barrier helps to reduce drive risk and thereby improves road safety conditions.
As a barrier between unforgiving objects and the drive path, it also serves to redirect straying vehicles into their original drive paths. A vehicle that hits the barrier panel on a side angle, will also reduce speed because of the friction between the beam and the vehicle’s body.
In urban areas, the barriers serve to prevent vehicles from driving onto walkways or into the cycle paths. In these instances, the guardrail serves to protect people or road users behind the beams from straying vehicles.
Where these barriers are installed in the median section of highways or the on- and off-ramp slopes of freeways, panels are attached to both sides of the posts.
Installation factors to keep in mind
Enough clearance space must be created behind the barrier and the object or hazard against which it protects. If there is sufficient clearance space without the barrier to allow for a vehicle to come to a controlled stop or return to the safety of the path without hitting an object or moving into a hazard like a water source, then it is better to not have a barrier in place.
Where to get more information about the W-beam guardrail in South Africa?
View the road safety product portfolio of Armco Superlite for more information about the W-beam guardrail and related road safety products. Reach out for expert help and a quote on any of the Armco Superlite products.