A crash barrier is a piece of traffic safety equipment which is designed to keep cars on the road and in the appropriate lane of traffic. When a car collides with the crash barrier, the barrier is supposed to gently push the car back into the roadway, ensuring that it does not run off the road or into another lane of traffic. There are a number of crash barrier designs in use around the world, and the basic engineering of these barriers is periodically adjusted to address changing trends in car and road design.
The earliest crash barriers were guardrails, made by mounting a rail on a series of posts. This type is still in use today in many regions of the world, with varying levels of reinforcement from traditional guard rails to the super-rail systems used in Europe to contain heavy trucks. Guardrails were followed by concrete crash barriers molded in a variety of wedge shapes, as well as plastic barriers filled with water or sand. High-tech crash barriers made from memory plastics are capable of deforming on impact, and springing back into their original shape when the car is removed.
In addition to the super-rail, some other common crash barrier designs include the concrete step and constant slope barrier, both of which are made from molded concrete, along with the wedge-shaped Jersey wall. The Jersey wall was actually first invented and deployed in California, not New Jersey, but it is in widespread use across the United States, from the notorious Grapevine where the Jersey wall was first deployed to the streets of New York City.
Crash barriers can be used for tasks beyond keeping cars in the right place. They are often used in urban environments for safety, to keep cars out of restricted areas, and to increase security around vulnerable buildings. Concerns about suicide bombers and car bombers have led some cities to surround government buildings with concrete crash barriers in order to obstruct cars and secure these areas.
Although the goal of a crash barrier is to push cars back into the road, these barriers can fail. Poorly-constructed barriers may collapse, allowing a car to run over the crash barrier and off the road or into traffic. In other cases, a crash barrier designed for basic vehicle traffic may fail when it is hit by a truck which is larger and heavier than the vehicles the barrier was engineered for. Motorcyclists are also vulnerable to accidents with crash barriers, as they can be flipped over them and into oncoming traffic upon impact.