Barrels are very rarely used in Australia or NZ as a crash attenuator, but they are far more common in places like the USA and Canada, particularly on high-speed freeways and at gore areas.
People often call them “water filled barrels” and assume that in winter they must just turn into giant blocks of ice waiting to be hit. It is a fair question, but that is not actually how these impact attenuators work.
They are designed to absorb energy and slow a vehicle down gradually, not act like a solid obstacle. They are often filled with either a liquid mix or a sand-based material. Where liquid is used, it is not just water. It is commonly mixed with something like magnesium chloride so it does not freeze in cold conditions.
Even more interesting, if you see a whole row of them protecting a hazard, they are usually not all filled the same. The first barrels may contain only a small amount of liquid or sand, and each barrel further along contains progressively more (and they will have elevated floors in them so they don’t create a launching ramp).
The reason is simple. We do not want a vehicle to go from motorway speed to zero instantly. We want controlled deceleration and a gradual transfer of energy. Less violent force transfer means less occupant trauma and a much better chance of survival.
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