A 1800 kg placebo? the limitations and risks of using concrete barriers
Walk through any major city in the world or attend any major event and you will find one ubiquitous object: large concrete blocks or barriers arranged to protect pedestrian areas from potential attack. Though they vary in shape, size and weight, the typical concrete barrier weighs 1,800 kilograms and is typically placed via a forklift, sitting unsecured and unanchored to the road. Many of these concrete barriers and blocks were installed over the past 24 months following a series of deadly attacks where vehicles were used to ram into crowds to cause mass casualties. The deadliest incident occurred in Nice, France in July 2016 when a lone perpetrator drove a large truck into a crowded pedestrian area during holiday celebrations. The result was 86 people killed and 434 injured. This was followed by similar attacks in Germany, the UK, Sweden, Spain, the United States, and Japan.
Many of these barriers are being deployed without an understanding of their limitations. It may seem like common sense that an 1,800-kilogram concrete block will stop a vehicle, but the human brain was not designed with an intuitive understanding of physics. When actually tested, the results can be quite shocking as demonstrated by the video below.
A false sense of security is no security at all
Concrete barriers are being deployed and used without appropriate testing and modelling. For example, how these concrete barriers have been angled has not been considered in many cases despite the fact that the angle of impact can significantly impact how these barriers perform. The type of ground that concrete barriers are placed on can affect its performance, as can environmental factors like weather (for example, rain can decrease the friction coefficient between the barrier and the surface of the road).
Perhaps most concerning is that many of these barriers have been placed in a manner that does not account for potential debris or displacement of the barrier if a vehicle were to impact it. As demonstrated in the video above, when a vehicle of sufficient mass and speed hits one of these barriers, they effectively transform into 1,800-kilogram projectile. Alongside the fact the the vehicle will continue into the crowds behind the barrier, it is also likely that the barrier itself will severely injure and harm pedestrians as well.
When provided the results of the tests, those who manufacture these concrete barriers were unsurprised. As one manufacturer put it, deploying concrete barriers to protect crowds against hostile vehicle attacks “…is a pure placebo effect.”
It is arguable that the barriers do impart a deterrent effect on an area, and certainly a barrier is better than no barrier at all. But this is deterrence based purely on perception and not physics, and it is ultimately physics which will determine whether an attacker will be stopped or whether they will simply go straight through. Who will be liable for when such a situation arises? It may only be a matter of time until we find out.
 Read more about the tests carried out by the German Motor Vehicle Inspection Association (DEKRA) here: https://www.dw.com/en/do-bollards-offer-protection-against-vehicle-attacks/a-43300057