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Types of Road Barriers
Traffic barriers are categorised in two ways: by the function they serve, and by how much they deflect when a vehicle crashes into them.
1) Road barriers are used to protect traffic from roadside obstacles or hazards, such as slopes steep enough to cause rollover crashes, fixed objects like bridge piers, and bodies of water. These barriers can also be used as wide medians to prevent vehicles from colliding with hazards within the medians. Unlike roadside barriers, they must be designed to be struck from either side.
2) Bridge barrier is designed to restrain vehicles from crashing off the side of a bridge and falling onto the roadway, river or railroad below. It is usually higher than roadside barrier, to prevent trucks, buses, pedestrians and cyclists from vaulting or rolling over the barrier and falling over the side of the structure. Bridge rails are usually multi-rail tubular steel barriers or reinforced concrete parapets and barriers.
3) Work zone barriers are used to protect traffic from hazards in work zones. Their distinguishing feature is they can be relocated as conditions change in the road works. Two common types are used: Temporary Concrete barrier and Water-filled barrier. The latter is composed of steel-reinforced plastic boxes that are put in place where needed, linked together to form a longitudinal barrier, then ballasted with water. These have an advantage in that they can be assembled without heavy lifting equipment, but they cannot be used in freezing weather.
Road Barriers are further divided into three groups, based on the amount they deflect when struck by a vehicle and the mechanism the barrier uses to resist the impact forces. Barrier deflections listed below are results from crash tests with a 2,000kg (4,400 lb) pickup truck traveling 100km/h (62 mph), colliding with the rail at a 25 degree angle.
• Flexible barriers that are made from wire ropes supported between frangible posts. It is one of the best options for minimising injuries to vehicle occupants; however they may pose a risk to motorcyclists. These barriers deflect 1.6 to 2.6 m (5.2 to 8.5ft) when struck by a typical passenger car or light truck. Impact energy is dissipated through tension in the rail elements, deformation of the rail elements, posts, soil and vehicle bodywork, and friction between the rail and vehicle. Flexible barriers deflect more than other barrier types and need to be repaired following impact to maintain their re-directive capability.
• Semi-rigid barriers are usually made from steel beams or rails. They deflect 3-6 feet (0.91-1.83m): more than rigid barriers, but less than flexible barriers. Impact energy is dissipated through deformation of the rail elements, posts, soil and vehicle bodywork, and friction between the rail and vehicle. Box beam systems also spread the impact force over a number of posts due to the stiffness of the steel tube. As these deflect less than flexible barriers, they can be located closer to the hazard when space is limited. Depending on the impact these barriers may be able to redirect secondary impacts.
• Rigid barriers are usually made of concrete and do not deflect. It should be used only where there is no room for deflection of a semi-rigid or flexible barrier. A permanent concrete barrier will only deflect a negligible amount when struck by a vehicle. Instead, the shape of a concrete barrier is designed to redirect a vehicle into a path parallel to the barrier. This means they can be used to protect traffic from hazards very close behind the barrier, and generally require very little maintenance. Impact energy is dissipated through redirection and deformation of the vehicle itself. Jersey barriers and F-shape barriers also lift the vehicle as the tyres ride up on the angled lower section.
To make sure they are safe and effective, traffic safety barriers have to undergo extensive simulated and full scale crash testing before they are approved for general use. While crash testing cannot replicate every potential manner of impact, testing programmes are designed to determine the performance limits of traffic barriers and provide an adequate level of protection to road users.
In the past, traffic barrier designs often paid little attention to the ends of the barriers. Vehicles that struck blunt ends could stop abruptly or have steel rail sections penetrate into the passenger compartment, resulting in severe injuries or fatalities. As a result, barrier terminals were developed that brought the end of the terminal down to ground level. While this prevents the railing from penetrating the vehicle, it could also vault a vehicle into the air or cause it to roll over, since the barrier end formed a ramp. To address the vaulting and rollover crashes, energy absorbing terminals are also developed in some places. These have a large steel impact head that engages the frame or bumper of the vehicle. The impact head is driven back along the guide rail, dissipating the vehicle’s kinetic energy by bending or tearing the steel in the guide rail sections. A guide rail may also be terminated by curving it back to the point that the terminal is unlikely to be hit end-on, or, if possible, by embedding the end in a hillside or cut slope.
Implementations Issues
Road Safety Barriers are designed to redirect the vehicle and have a lower severity than the roadside hazard they protect. Much of the benefit from the use of barriers comes from a reduction in crash severity. Although a crash may still occur, it is likely to have a safer consequence than colliding with the object that the barrier is protecting.
“In our experience the current standards governing the use of road barriers are highly inadequate. If a substantial change is not brought about in our outlook towards the use of safety items such as barriers, little can be done to improve the situation. This change needs to flow from the ministry level downwards to the executing departments. A lot has been discussed in the past over these issues but no conclusion has been reached. This has caused the entire industry to have a laid back attitude towards this lingering issue. Statistics say over two million people lose their lives on Indian roads every year. It is an unacceptable figure and clearly the lack for safety implementation is evident”, explained, Rahul Saini, Director, BD Industries.
Unfortunately the engineers, contractors and state agencies are still not updated about the international practices prevailing for road safety. They normally are either ignorant or does not understand the need for Road safety products. There is a dire need for enforcement authorities to implement safety in a strict manner. If the government body does not take up the matter seriously, safety can only be an implausible dream. Until and unless the basic framework is not implemented nothing can be assured about safety on Indian roads.
Sudhir Kumar, Director, Alexis Enterprises Pvt Ltd, said, “In my opinion, Indian Government must make a standard for all road safety devices and make a uniform code with tough penalties. It should be made mandatory for all road construction/maintenance activities to follow that code. Highway engineers and law enforcing agencies should be taught these standards and proper training on regular basis should be given. A provision of heavy fine should be made and we must learn to value human life and the culture of compromising with quality, ignorance/lack of knowledge should not be tolerated. All the engineering institutes should equip themselves for imparting periodical training on road safety and related subjects.”
Accidents are a serious problem on highways and will rise with increasing rates of car ownership and the speed of vehicles on roads. There is a need for protective equipment to be installed on the roads, such as road safety fences and road safety barriers. Purely from the perspective of cost-benefit analysis and low incidence of hazards, it might be difficult to justify the need to install road safety barriers or fences along some sections of a highway.
Preeti Swaminathan