Crash barrier

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A crash barrier is a barrier on a road designed to prevent vehicles from leaving the roadway to improve road safety. Common sites for crash barriers are:

median separators on multi-lane highways
bridge supports
mountain roads

In a crash test, a crash barrier is a rigid or deformable obstacle against which a car is impacted, or which impacts a car to be crash tested.

The design of the road barrier is generally such that a vehicle hitting the barrier is steered back onto the road. This may be achieved by designing the supports so that they break off on impact, allowing the barrier to deform and push the vehicle back on track. In some cases cost cutting has led to a failure of this mechanism, with so-called "duck-nesting" (after the shallow nature of a duck nest) of barrier support bases. When this happens the supports tilt over at the base instead of breaking off, allowing the barrier to collapse and the vehicle to go over the barrier.

Large vehicles with a high centre of gravity, such as Sport utility vehicles, are also vulnerable to going over barriers on impact.