How Crash Cushions Work to Save Lives

 Whether you refer to these road safety products as impact attenuators or crash cushions, their functions are the same. They act to protect maintenance workers, motorists, vehicles, and structures against damage and fatalities associated with collisions.

Read on if you want to know more about the types of crash cushions, which ones to install that suit your requirements, and how these devices save lives. We also discuss two impact cushions available from Armco Superlite in South Africa.

Where are crash cushions installed? crash cushion

Impact cushions are normally installed in front of a structure to protect against impact force. You’ll see these devices at overpass structural support systems, in front of toll-booth terminals, in front of temporary work areas to protect workers and equipment from potential vehicle impact and at the ends of barriers.

What are the two main ways crash cushions work?

Upon side impact, the attenuator deflects the colliding vehicle back to the clear zone or travel path away from danger. Upon head-on collision, it absorbs the impact energy and brings the vehicle to a stop. It can open  space or deflect upon side impact, depending on the type of impact attenuator.

What is the difference between a temporary and permanent type?

Temporary ones, like truck-mounted attenuators, serve to protect structures, equipment and workers against impact from vehicles for a specific period. The permanent types like guardrail end terminals, the crash cushions at toll-booth terminals, and those at highway off-ramps or splits in lanes are installed for ongoing protection. These types are installed at a specific location and not moved around.

What is the difference between gating and non-gating crash cushions?

Gating and non-gating refer to the design and function of the attenuator. The gating option makes it possible for the colliding vehicle, upon side impact, to enter an area where it can reduce speed sufficiently to come to a stop before hitting the hazard. If there is not enough clearance space, there must at least be space to ensure the vehicle can slow down to a safe speed before it hits an object.

The non-gating option deflects the colliding vehicle upon side impact, while it stops the motion of the colliding vehicle upon head-on collision. The attenuator absorbs the impact energy, thereby reducing the impact on the colliding vehicle. It also brings the vehicle to a stop. This type is permanent and usually anchored to prevent it from moving on impact.

A gated attenuator is generally more economical than the non-gated type. However, the gated type needs a large clear zone to work correctly. If there isn’t enough space, the straying vehicle can pass through the gate into another type of danger like that of oncoming traffic. The non-gated type is suited for usage in the road median because it doesn’t allow the erring vehicle through.

What is meant by re-directive and non-redirective crash cushions?

The re-directive crash cushion deflects the colliding vehicle to the clear zone area, thereby directing it away from the hazard. The non-redirective type, as the name suggests, doesn’t deflect the vehicle away from danger. Instead, it slows the vehicle’s motion, bringing it to a stop.

What is the purpose of crash cushions?

The main purpose of the crash cushion is to stop a vehicle before it hits a hazardous object, such as road work equipment, a permanent structure or a person. With this in mind, the permanent attenuator is designed to quickly slow down a vehicle. To achieve the purpose, the design includes mechanisms to reduce speed and handle the force of the impact.

Why are crash cushions needed?

Many severe accidents happen when motorists stray from their intended path and hit a non-forgiving, rigid object. This can occur when a motorist attempts to switch lanes to access a highway offramp at the last minute. It can also happen when a motorist isn’t paying attention, leading them to depart from the intended path right into a hazardous roadside fixture.

A vehicle’s brakes can fail, or it might travel at an extremely high speed, causing the motorist to lose control over the steering. This can lead to a high-speed impact with, for instance, a toll booth. The crash cushion reduces the damage to the vehicle upon impact with the object or redirects it away from the hazardous object.

What is a gore point?

It’s a section of a highway exit where a landscaped area is located in the centre of the v-shaped split between the lanes. Crash cushions are installed at the gore points and overpass sections, as motorists can decide at the last moment to take the off-ramp or change lanes.

How many hits does the average impact attenuator take per year?

Accurate statistics are hard to come by in South Africa regarding the number of impacts the average crash cushion undergoes per year. However, according to a 2018 report by the traffic division in Texas, USA, an average of six such impacts on the average impact attenuator per year.

Which types of temporary crash cushions exist?

The first type is the water-filled or sand-filled option. Several such barriers can be placed in succession to stop a vehicle. The vehicle’s speed is reduced with each one it hits, causing it to slow down significantly in a brief span.

The second type is the truck-mounted option. This is a crash cushion mounted at the back of a truck. It doesn’t need to be fixed to a position and then moved again. The truck is parked at the space where roadside maintenance is performed. The truck with its attenuator forms a barrier between the vehicles coming from the rear and the people or equipment in front of the truck.

What is the crash cushion padding?

Padding refers to the material and design of the attenuator that absorbs the impact energy of the colliding vehicle and helps to reduce the vehicle’s speed. The padding is in front of the bumper or final stop section of the crash cushion.

How does the impact attenuator reduce the severity of injury when a vehicle collides with it?

If a vehicle hits an unforgiving, rigid object at a high speed, the vehicle’s body and its occupants experience the full force of the impact. The occupants collide with the vehicle’s interior at the same speed as that of the vehicle crashing into the hazard.

With a crash cushion in place, some or most of the impact energy is absorbed by it. This significantly reduces the force of the impact on the vehicle’s body and its occupants. As a result, the severity of injuries can be reduced with an impact attenuator in place.

What are the three main ways crash cushions disperse the collision energy?

The impact energy is distributed through material transformation, friction, and transfer of momentum.

The rows of water-filled barriers to reduce vehicle speed act to transfer the momentum of the colliding vehicle, thereby slowing it down.

With friction types, the attenuators have steel cables that are forced through slots upon impact. This causes friction, which slows down the colliding vehicle and helps to disperse the impact energy. The kinetic impact energy of the collision is converted into heat as a result of the friction.

With deformation, granules, foam or other types of crushable materials within a housing absorb the impact energy. The materials are crushed, slowing down the vehicle and absorbing the impact energy.

Another type of material deformation attenuator is a guardrail where the steel deforms to absorb the impact energy.

Which types of crash cushions are available from Armco Superlite?

The Alpha 70K TMA™ is a truck mounted attenuator, available from Armco Superlite. It is designed to meet the NCHRP 350, Test Level 2 requirements. The temporary crash cushion is effective in protecting expensive equipment, roadside workers, and motorists. The attenuator provides effective collision impact protection at 70km per hour. The design prevents vehicles from under-riding the truck onto which it is mounted.

The device is also fitted with a Durashell Nose® to resist nuisance hit damage. It comes with a tapered nose design to reduce corner damage. Because it’s made from aluminium, it’s corrosion resistant and lightweight enough for easy handling.

An example of a permanent attenuator available from Armco Superlite is the Quadguard® System to protect against hazards of 610mm to 2286mm. It contains a system of cartridges with crushable material to absorb the kinetic impact energy. These are housed in a steel panel framework. The system is tested at NCHRP 350 Test Level 3 and is a non-gated, redirective attenuator. It protects against impact at speeds ranging from 40km per hour to 120km per hour. The cartridges are staged, much like sandbags in a row. This allows for speed reduction from impacting vehicles and stopping them before they hit the unforgiving object.

Get more information on the Armco Superlite range of crash cushions

Visit the road safety product page for more information on the available crash cushions or reach out to discuss your specific attenuator needs.