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Transport planners consider KarabloK for bridge safety

Question: When is a hostile vehicle mitigation system not a hostile vehicle mitigation system? Answer: when the vehicles it is designed to stop are not hostile. And in this case, when it’s intended to improve bridge safety.

Whether a vehicle is driven with menace by terrorists intent on crashing or simply heading for danger with a hapless driver at the wheel, the principle is the same: we put a barrier in place to stop that vehicle.

This has formed the basis of an enquiry by a road bridge builder in the UK who is looking for a way of improving bridge safety – especially around the sides of bridges already built – and is very interested in KarabloK.


Accidents of this kind have happened all too frequently, such as the Great Heck rail crash in the UK in 2001.

Obviously the structure needs to be able to withstand the impact of the sort of vehicles crossing that bridge. This could include large vehicles travelling at speed, similar to those used in truck attacks in continental Europe and in the Middle East.

And although primarily functional, bridge design often involves an aesthetic element. While some bridges may not be considered a thing of beauty, they cannot be an eyesore and neither can any components added to them after their construction.

These points make KarabloK a suitable option. It is the only surface mounted precast concrete barrier system in the world that is certified for an impact load of 7.2 tonnes (16,000lb) at 50mph.

The KarabloK barrier is made of interlocking precast concrete blocks which measure nearly four feet tall, seven feet long and more than four-and-a-half feet wide (120 x 210 x 140cm) with a central rectangular space which is filled with local ballast material, such as gravel or sand. They weigh 7,720lb (3.5 tonnes) before filling.

Units are positioned by crane and joined by unique system in which steel pins lock through each block’s internal reinforcement cage. This not only locks the units together but also provides vital flexibility which enables the barrier to withstand such large impact forces. You can find out more about the unique way KarabloK units are joined together to form a highly effective barrier here.

The barrier can also be built several units high, the same system that locks individual units together horizontally also locks them vertically. And adaptations to the basic KarabloK unit have been made for end-of-wall units, gateways, right angles and junctions allowing up to four walls to meet at a single point.

The barrier needs no foundations or ground fixing which makes it quick and cheap to install. Typically, around 110 yards (or 100m) can be laid in a day. This also makes it appropriate for use as a temporary barrier as it can also be taken apart and stored just as easily as it is assembled.

Finally, when it comes to keeping up appearances, the KarabloK units are made to look good and can be cast in a variety of finishes to match materials already used in the bridge or the surrounding area.

And if that is not enough, the top of the central cavity can also be planted up with the sorts of trailing plants and shrubs widely used by local authorities, to soften their visual impact even further.

You can see why civil engineers are now interested in using the KarabloK system to improve bridge safety; barriers save lives.