What Are Road-Safety Barriers and How Do They Work?

As the name suggests, road-safety barriers are temporary or permanent devices installed on the side or median of a road to improve safety for road users. These safety barriers must protect the motorists, motorcyclists, cyclists, and pedestrians that use the path on both sides of the devices. With such an important role, the correct installation, type of barrier, and place of installation are essential to ensure effective protection. To fully understand such safety systems, we first have to look at the main functions that these traffic rails have:

• Preventing straying vehicles from leaving the safety of their drive lanes.
• Redirecting straying vehicles back into their drive paths.
• Preventing errant vehicles from colliding with hazardous objects next to the road.
• Preventing errant vehicles from colliding with pedestrians, cyclists, or motorcyclists using paths dedicated to them next to the road.
• Preventing pedestrians and cyclists from crossing the road or getting in the way of vehicle traffic.
• Preventing animals from getting into the drive lanes.
• Reducing the accident rate on a particular stretch of road.
• Reducing the risk of serious injuries or fatalities associated with vehicles leaving the safe drive lane and moving over the edge of a mountainside, down a slope, or into a body of water.
• Guiding road users at night to show where the driving surface ends.
• Improving driver confidence in low-light conditions and at night, as adequate protection is available to prevent vehicles from straying from the safe path night.
• Reducing median clustering because drivers have more confidence to keep to the left side of the lane, thus helping to reduce the risk of head-on collisions due to median clustering.
• Indicating specifically allocated paths such as pedestrian, cyclist, bus, emergency or motorcyclist paths.
• Preventing motorists from making U-turns on a highway where the rails divide the two carriageways of the highway and thereby reducing the risk of serious fast-lane accidents.
• Preventing these fast-lane accidents on one side of a dual-carriageway highway from spilling over to the fast lane of the opposite carriageway.
• Preventing motorists from getting onto highways at unauthorised places.
• Sufficiently reducing the speed of a vehicle upon an angled impact to ensure its safe return to the drive lane.

The safety barriers are installed:

• On bridges to prevent vehicles from going over the edge;
• At dangerous curves in the road;
• At sections where the risk of colliding with hazards upon straying from the safe drive path is high;
• Where there is not enough open space next to the drive lane to ensure safe correction of the mistake and return to the road;
• In urban areas to prevent vehicles from moving onto pedestrian zones; and
• On the median between the opposing carriageways of highways.

How The Safety Barriers Work

The force of impact on the vehicle and its occupants in an accident where the vehicle hits, for instance, a tree or another vehicle can be immense and many people lose their lives every year because of such collisions. A hazard such as a wall or post does not yield sufficiently upon impact and the result is that the entire impact force is exerted on the vehicle and its occupants. With modern vehicles made to deform upon impact, the vehicles already absorb a lot of the impact force to reduce the effect on the occupants. However, when vehicles collide with unforgiving objects such as trees, vehicles absorb the full impact force and the object virtually none, which can result in serious injuries for the occupants.

Barriers such as W-beam guardrails are designed to absorb a large part of the impact force and disperse it through the entire system. This reduces the force of the impact on the colliding vehicle and its occupants. Some safety barriers are also designed to prevent vehicles from breaking through whilst also preventing colliding vehicles from vaulting over the guardrails. With the high speeds that can be reached by modern vehicles, the force exerted on the vehicle upon impact with a stationary object can be massive. As such, the guardrails must also serve to reduce the kinetic energy exerted on the vehicle upon impact and thereby reduce damage to the vehicle and the severity of injuries to its occupants. The safety barriers are designed to replicate the crumpling effect designed into the vehicle body and this makes it possible for the systems to act as impact buffers. The type of barrier determines how much of the kinetic energy can be dissipated when struck by a colliding vehicle.

A rigid system, such as a concrete barrier, does not allow a vehicle to break through at all. Because it doesn’t yield, most of the impact force is transferred to the colliding vehicle. Such rigid systems are usually installed on the median between two carriageways of a highway where it is essential to prevent a straying vehicle from breaking through. Instead, the design is made to deflect angled impacts. At the bottom part of the system is sloped in a slide angle. When the errant vehicle hits the barrier from the side, the wheels ride up the slight slope and this helps to prevent it from breaking through and guides it back into the travel path. The friction caused by the impact helps to reduce the speed of the vehicle.

With a semi-rigid system, such as the W-beam guardrail, the metal panel attached to the steel or wooden posts acts as a unit to absorb the kinetic energy of the impact and disperse it throughout the system. The guardrail is designed to cater to the speeds and vehicle heights as relevant to road the where it is installed. It can partially deform, as well as redirect and deflect. Where the guardrail is installed on the median of two opposing lanes, it has a panel on both sides of the posts. With this type of guardrail, it is essential to have enough clearance space behind the system to allow for some movement of the guardrail upon impact.

The wire-rope system consists of posts to which cables are attached. These barriers have tension-cable systems in place. Upon impact, the vehicle is redirected back to its safe path but it could break through at high speed. The main benefit is that these systems take up very little space. This makes it possible to install these barriers on sections where little road space is available for a W-beam guardrail or concrete barrier. The impact energy of the vehicle is dispersed throughout the cable system to reduce impact forces on the vehicle and its occupants.

Water-filled road-safety barriers cannot prevent vehicles from breaking through but rather serve as temporary safety barriers to prevent straying vehicles from entering roadworks or hazardous areas next to the road. The system consists of interlocking units to form a wall. The units are filled with water or sand to weigh them down and keep them from being blown over by winds, moved, or removed. They are placed to create a separation between the road area used by traffic and the equipment or workers busy with construction or emergency operations.

It is best to buy all these types of road-safety barriers from reputable suppliers in South Africa as the systems manufactured and supplied by market-leading local suppliers are made according to strict safety standards relevant to South Africa. Such suppliers are also able to provide installation guidance and help in the selection of the relevant barrier types and their end-terminals for the specific areas where the systems must be installed.

Factors that are taken into consideration for installation include, but are not limited to:

• The types of vehicles using the particular section of road.
• The average speed of travel.
• Clearance heights of the vehicles.
• The risk of vehicles breaking through.
• The space available for installation.
• The traffic flow on the section of road.
• The type of risk against which protection must be provided.
• The maintenance requirements of the particular safety system.
• The cost of the materials.
• The durability of the materials.
• The lifespan of the system.

Suppliers in South Africa are familiar with the legislative and regulatory requirements for road-safety barriers in the country. They can advise regarding the choice of system such as a flexible barrier that deforms upon impact to take the full kinetic force, a semi-rigid system that absorbs a part of the force and prevent a vehicle from breaking through, and a rigid system that prevents breaking through but does not yield and disperse impact forces away from the impacting vehicle at all. Careful consideration should be given to installation instructions. All such systems must be installed by trained personnel under the supervision of qualified engineers.