The F-shape barrier is a concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 crash barrier, originally designed to divide lanes of traffic on a highway

Highway

A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

. It is a modification of the widely-used Jersey barrier

Jersey barrier

A Jersey barrier or Jersey wall is a modular concrete barrier employed to separate lanes of traffic. It is designed to both minimize vehicle damage in cases of incidental contact while still preventing crossover in the case of head-on accidents....

 design, and is generally considered safer.

A parametric study, one that systematically varies the parameters, was done through computer simulations of barrier profiles labeled A through F. The result showed that the one labeled F performed better than even the shape of the Jersey barrier. A series of full-scale crash tests later confirmed these computer-based results. What is known today as the F-shape barrier takes its name from these tests and not from any part of the shape of the barrier, unlike, for example, T-walls.

In spite of these tests, the F-shape barrier has not supplanted the Jersey-shape. The Jersey-shape barrier was already in wide use, and it also met the crash-test criteria. The states' contractors already had a significant investment in the Jersey-shape casting forms and it would cost them money to change the profiles of the forms.

The F-shape and the Jersey-shape have the same slopes, but the distance from the ground to the slope break point of the F-shape is 255 millimetres (10 in), which is 75 millimetres (3 in) lower than the Jersey-shape. This lower slope break point reduces vehicle lift, improving the barrier's performance.

Because the Jersey-shape design requires very little modification to become an F-shape design, asphalt resurfacing can convert the Jersey-shape barrier into a more F-shape-like barrier that is safer for lighter cars. However, these increased layers of asphalt also reduce the working height of the barrier which reduces its effectiveness for heavier vehicles.

The UK equivalent is the concrete step barrier

Concrete step barrier

A concrete step barrier is a safety barrier used on the central reservation of motorways and dual carriageways as an alternative to the standard steel crash barrier.The barrier has contained all vehicles up to 13.5 tonnes.-United Kingdom:...

.